-------
    3r—
                                                                   15 ppm
                                                                  Hardness
          0.06 weight  percent detergent  concentration    A
          0.12 weight  percent detergent  concentration    o
          0.18 weight  percent detergent  concentration    a
 a>
 "5
 a:
 c
 o
 .
 o
o
STPP and  NTA  Concentration,  weight  percent

                    (a)
                                                                   50 STPP
                                                                    0 NTA
          0.06 weight  percent detergent  concentration
          0.12 weight  percent detergent  concentration
          0.18 weight  percent detergent  concentration
                                                  150 ppm
                                                  Hardness
                STPP and  NTA Concentration,  weight  percent

                                    (b)
                                                                   50 STPP
                                                                    0 NTA
FIGURE 13.  CORROSION  RATE OF  ELECTROLYTIC  COPPER  AS A  FUNCTION
           OF STPP AND  NTA CONCENTRATION  AT (a) 15-PPM   AND
           (b) 150'PPM  WATER  HARDNESS  AND  130 F
                               37

-------
    2.01—
 o
 0)
 v.
 
-------
                   2
relationship 1 |j,A/cm  = 0.46 mpy.   Since  drastic changes in b.  and bp values
could not account for such differences between weight loss and electrochemical
data, it appeared that poorly  conducting  tarnishing films developed on the
copper electrodes caused a low assessment of linear polarization corrosion
rates.
Die-Cast Zinc

Tables 14 and 15 summarize the  coupon-weight-loss  data  for die-cast zinc in
the STPP and NTA detergent solutions  at  130 and 160 F.   Weight losses were
between 4.5 and 102 mg per coupon  over the  2-day exposure periods to give
both low and high corrosion rates  between 2.1 and  44.3  mils per year.  As
shown by surface photographs  of exposed  coupons in Figures 15 to 18, a
variety of features were obtained.  In this material,  general corrosion
usually resulted in a continuous corrosion-product film on coupons (Figure 15)
that sometimes was semivoluminous.  Pitting corrosion of the order of 1 to
1-1/2 mils depth was usually  associated  with a moderate density of pitting
corrosion deposits on the surface  which  were reasonably large and also
slightly voluminous product  (Figure 16).  An example of such pitting corrosion
is shown in the photomicrograph of Figure 19.   It  was evident from metallo-
graphic studies (Figure 19) that the  pitting corrosion extended deeper (a
factor of two) than surface optical measurements would  reveal.  A higher
density of pitting corrosion  deposits but of smaller size (Figure 17)
generally indicated less aggressive pitting as evidenced in the photomicro-
graph of Figure 20.  Corrosion  of  the die-cast zinc occurred in all
solutions, but, as shown in Figure 18, the  corrosion could be limited to
mild  low density pitting.

Figure 21, in which the weight-loss data are summarized, allows the effects
of detergent concentration and  water  hardness to be more readily evaluated.
In terms of overall weight loss, with the exception of the point at 0.18
weight percent NTA with 150-ppm water hardness, it is evident that the
soft-water conditions of both NTA  and STPP  detergents were the most corrosive.
Of these solutions, the most  corrosive appeared to be the NTA-based solutions.
The least overall corrosive  solution  appeared to be the STPP-based solutions
with 150-ppm water hardness.  Again with the exception of the point of 0.18
weight percent NTA and  150-ppm  hardness, corrosion was maximum in 0.12 weight
percent detergent concentrations.  This  behavior was contrary to results on
aluminum, copper, brass, and  lead  in  which  corrosivity increased with increase
of detergent concentration.   It appears, therefore, that the slightly deeper
but less dense pitting  in 0.12  weight percent solutions was sufficient to
cause greater weight loss than  the less  deep but sometimes more dense
pitting in 0.06 and 0.18 weight percent  solutions.  As seen from Figure
21, however, at very large corrosion  rates  above 30 mils per year, the corrosion
was general.  Although  severe pitting of 1  to 3 mils depth in 2 days in 0.12
percent solutions represents  localized attack at a rate of 180 to 540 mils
per year, it is doubtful that this rate  would be sustained but rather would
become stifled by its own corrosion product.
                                 39
-------
Table 14.  Coupon-Weight-Loss Data for Die-Cast Zinc in 50 Weight Percent STPP-based Detergent
Detergent Concentration, Hardness,
weight percent ppm
0.06 15


150

0.12 15




150





0. 18 15


150

(a)
mdd = milligram/ (decimeter)2/day
mpy = mils penetration/year
"^•"•"•••^••••••S
Coupon
D44
D45

D46
D47
Dll
D12
D13
D14

D21
D22

D23.
D24

D25
D26

D27
D28


=====
130
130

130
130
160
160
130
130

160
160

130
130

130
130

130
130


Exposure,
days
2
2

2
2
2
2
2
2

2
2

2
2

2
2

2
2


Corrosion
94.8
76.1

10.5
16.9
38.4
52.7
104.4
103.7

77.8
86.9

49.2
63.7

73.5
92.4

40.3
31.6


Rate(a)
19.1
15.4

2.12
3.41
7.76
10.7
21.1
21.0

15.7
17.6

9.94
12.9

14.8
18.7

8.14
6.38


Remarks
Very mild shallow pitting of
high density plus low density
pitting up to 0.4 mil deep.
Very mild shallow pitting of
low density.
General corrosion with patches
of pitting (Imtl deep).
Mostly pitting corrosion of
high density but small
depth (0.4 mil).
Mostly pitting corrosion of
high density and small
depth (0.4 mil)
Mostly pitting corrosion of
high density and moderate
depth (0.7 mil).
Patches of light pitting
corrosion (up to 0.5 mil
deep).
Patches of very light pitting
corrosion (up to 0.5 mil deep)


-------
    Table 15.  Coupon-Weight-Loss Data for Die-Cast Zinc In 50 Weight Percent NTA-Based Detergents
Detergent Concentration, Hardness,
weight percent ppm Coupon
0.06 15 D40
D41
150 D42
D43

0.12 15 D9
D10
D16
D17
150 D15
D18

D19
D20

0.18 15 D29
D30

150 D31
D34
Exposure,
Temp F days
130
130
130
130

160
160
130
130
160
160

130
130

130
130

130
130
2
2
2
2

2
2
2
2
2
2

2
2

2
2

2
2
, Corrosion Rate^a'
mdd
158
163
22.9
17.6

234
222
183
173
135
115

77.1
116

92.2
115

154
195.2
mpy
31.9
33.0
4.6
3.6

44.3
44.8
37.0
35.0
27.3
23.2

15.6
23.5

18.6
23.2

31.0
39.4
Remarks
White voluminous deposit.
Uneven general corrosion.
Very low density pitting
corrosion up to 0.8 mil
deep.
White corrosion product.
General corrosion.
White corrosion product.
General Corrosion.
Mostly pitting corrosion of
low density and moderate
width and depth (1.5 mil).
Slightly less pitting of
about same depth (1.5 mil).
Small general corrosion.
Mostly pitting corrosion of
medium density and low depth
(up to 0.5 mil).
General corrosion.

(a)                             2
  mdd = milligram/(decimenter) /day

  mpy = mils  penetration/year
-------
     P417
 FIGURE 15.  DIE-CAST ZING COUPON D34
            AFTER EXPOSURE
            Note continuous deposit
            associated with general
            corrosion
                                        P418
                                 FIGURE 16.  DIE-CAST ZINC COUPON  D29
                                            AFTER EXPOSURE
                                            Note the moderate density
                                            and reasonably  large  size
                                            of pitting corrosion
                                            deposit.
     P636
FIGURE 17.
DIE-CAST ZINC COUPON D45
AFTER EXPOSURE
Note the very high density
but smaller size of pitting
corrosion deposits.

                 42
         P638
FIGURE 18.   DIE-CAST  ZINC  COUPON  D43
            AFTER EXPOSURE
            Note  the  extremely  low
            density of  pitting  corrosion
            deposits  and low  general
            corrosion.
-------


          C-3922                                                250X
FIGURE 19.  CROSS SECTION OF PITTED AREA IN COUPON D18
            Note extended fine corrosion paths beneath main pits.

          C-3923

FIGURE 20.  CROSS  SECTION OF  PITTED  AREA  IN  COUPON  D14
            Note smaller  pit  size  than  in Figure  18.

                                 43
250X
-------
    501—
    40
 o
 0)
 0>
 o.

 in
 "5
 c
 o
 o
 O
      ).06
                                  15 ppm   150 ppm

                                 Hardness  Hardness
          50 weight percent STPP based  detergent

          50 weight percent NTA  based  detergent
                p---denotes pitting  corrosion
                    0.12

    Detergent Concentration, weight percent
0.18
FIGURE   21.
CORROSION RATE  OF DIE-CAST ZINC  AS A  FUNCTION

OF  DETERGENT  CONCENTRATION IN  15 PPM AND 150

PPM WATER HARDNESS  AT 130 F
                              44
-------
    50
    40
 o
 CD
 O
 CL
 CO
QC


O

O
k.
l_
o
    20
    10
      O
      50
                                                           15 ppm
                                                          Hardness
                 0.06 weight percent detergent concentration
                 0.12 weight percent detergent concentration
                 0.18 weight percent detergent concentration
                            P---denotes  pitting  corrosion
                                                             A
                                                             o
                                                             a
                                                                  50 STPP
                                                                   0 NTA
                STPP and  NTA  Concentration,  weight percent
FIGURE  22 (a).  CORROSION  RATE OF DIE-CAST ZINC AS A FUNCTION  OF
                STPP AND NTA CONCENTRATION   AT  15 PPM WATER
                HARDNESS AND  130 F
                               45
-------
                                                          150 ppm
                                                          Hardness
                0.06 weight  percent detergent  concentration
                0.12 weight  percent detergent  concentration
                0.18 weight  percent detergent concentration
                            P---denotes  pitting  corrosion
 o:

 c
 o
 'in
 o
                                                                  50 STPP
                                                                   0 NTA
                STPP and  NTA  Concentration,  weight percent
FIGURE  22 (b).  CORROSION  RATE OF DIE-CAST  ZINC AS  A  FUNCTION OF
                STPP AND NTA  CONCENTRATION  AT  150  PPM  WATER
                HARDNESS  AND  130  F
                               46
-------
Figures 22(a) and 22(b) present the weight-loss data to indicate the increased
corrosivity of NTA-based solutions over corresponding STPP-based solutions.
As shown in Table 16, the corrosivity factor varied between 1.5 and 4.7.


    Table 16.  Increased Corrosivity Factors for NTA Solutions Over
               STPP Solutions with Die-Cast Zinc


    Detergent Concentration,
        weight percent	15-ppm Hardness	150-ppm Hardness
0.06
0.12
0.18
1.9
1.7
1.3
1.5
1.7
4.7
In soft-water solutions, the corrosivity factor increased from 1.3 to 1.9
with decrease of concentration.  However, in hard-water solutions, the
corrosivity factor increased with increase of concentration to a maximum
of 4.7.

A limited number of X-ray diffraction studies conducted on corrosion
products indicate that ZnSO^, Zn(OH)2> and ZnO were the major components
of these products.  From coupons D25/D26 in an STPP-based solution, the
compounds ZnSO^ • 3Zn(OH)2  • ^H^O, and ZnO were identified.  Similar com-
pounds ZnS04 • 6Zn(OH)2 • 4H20, and ZnO were identified on coupons D31/D34
from an NTA-based solution.

The electrochemical linear  polarization corrosion rates for die-cast zinc
are summarized in Figure 23.  These results were calculated using Equation 5
with values of bA = 0.070 volt and bg = °°determined from polarization curves.
As seen from Figure 23, determined corrosion rates generally decreased from
early values of about  15 mils per year to steady values after 1 to 3 days
of 1 to 5 mils per year.  It was apparent that the mixed solutions of 37.5
STPP-12.5 SNTA showed  no marked differences in corrosion behavior  from those
of the pure STPP or SNTA solutions.  It was evident that the linear polari-
zation method gave corrosion rates of the order of 6 times smaller than
rates determined by weight  loss.  As for 1100 Aluminum, brass, and copper,
the data indicated that the presence of a poorly conducting film  on die-
cast zinc in these detergent solutions interferred with the evaluation of
corrosion rate by this method.  In many measurements with die-cast zinc,
the measurements were  similar to those in Figure 4(a); i.e., an unsymmetrical
current response, indicating localized corrosion.  This localized corrosion
was evidenced as pitting of the electrodes.

201 Nickel
This metal was exposed  to  0.12 weight  solutions  of both  STPP-and NTA-based
detergents with  15- and 150-ppm water  hardness at 130 F  for  periods of  14
days.  No weight loss was  obtained  on  coupons, thus  indicating  corrosion
rates  of the  order of 0.01 mil per  year  or  less.
                                 47
-------
                                                                       15 ppm
                                                                      Hardness
                     0.12 weight percent of 50 STPP detergent
                     0.12 weight percent of 50 NTA detergent
                     0.12 weight percent of 37.5 STPP-12.5 NTA detergent
  o
  0>
  Q)
  Q.
  (ft
  a>
  a
  a:

  I  30
  o
                           I                        2
                              Exposure  Time,  days

                                      (a)
  o
  o
20
     10
      8

      6
                                                                 150 ppm
                                                                 Hardness
                 0.12  weight percent of 50 STPP detergent
                 0.12  weight percent of 50 NTA detergent
                 0.12  weight percent of 37.5 STPP-12.5 NTA detergent
                                I                         2
                                    Exposure Time, days

                                           (b)
FIGURE  23.  CORROSION  RATE OF DIE-CAST ZINC AS  A FUNCTION  OF  EXPOSURE
             TIME  IN (a) 15 PPM  AND  (b) 150 PPM  HARDNESS  SOLUTIONS  AT
             130 F  AND  USE OF  THE  LINEAR  POLARIZATION  METHOD
                                    48
-------
     0.6
     0.4
     0.2
Q.

w
-------
The electrochemical linear polarization measurements on this material are
summarized in Figure 24.  These results indicated for 0.12 weight solutions
at 130 F that corrosion rates decreased appreciably from 0.2 to between 0.06
and 0.07 mil per year within a day's exposure.  The decrease in corrosion
rate paralleled a change in corrosion potential from about -0.27 to -0.21
volt versus SCE.  It was evident that there was no marked difference in
corrosion behavior in mixed solutions containing 37.5 STPP-12.5 NTA and the
pure STPP and NTA-based solutions.  Corrosion rates were not significantly
different to indicate any marked differences in the corrosivity of the
solutions.  The corrosion rates of 0.06 to 0.07 mil per year indicated a
very corrosion-resistant material that could be used safely in either the
STPP- or NTA-based detergents.


Type 304 Stainless Steel

This metal was  exposed  to 0.12 weight percent solutions of both STPP and
NTA-based detergents containing 15- and 150-ppm hardness at 130 F for
periods of  14 days.  As for 201 Nickel, this metal showed no weight loss,
thus  corrosion  rates of the order of 0.1 mil per year or less were
 indicated.

The  linear  polarization corrosion rate measurements for this metal are
 summarized  in Figure 25.  The data in Figure 25 showed that initial corrosion
rates of about  0.15 mil per year decreased to between 0.02 and 0.06 mil
per year after  1 day's  exposure.  The decrease in corrosion rate paralleled
changes in  corrosion potential from about -0.26 to -0.21 volt versus SCE.
Analysis of the data in Figure 25 indicated that detergent solutions in hard-
water conditions; i.e., with more Cl~ were more corrosive than those in
 soft-water  conditions.   It was evident that mixed solutions of 37.5 STPP-
 12.5  NTA showed no marked corrosion differences to pure STPP or NTA solutions.
Type  304 stainless steel which was slightly more corrosion resistant than 201
Nickel was  the  most corrosion-resistant material as measured in this study.


Type 420 Stainless Steel

This alloy was  similarly exposed  to 0.12 weight percent solutions of both
STPP and NTA-based detergents with 15- and 150-ppm water hardness at 130 F
for periods  of  14 days.  No weight loss was observed for this metal, thus
indicating  corrosion rates of the order of 0.01 mil per year or less.

Figure 26 shows the linear polarization corrosion rates determined for this
alloy.  It was  apparent from Figure 26 that some changes occurred in corrosion
rates in NTA and  STPP solution in the soft-water condition but that, generally,
corrosion rates were small (values between 0.06 and 0.15 mil per year). As
for Type 304 stainless  steel, the hard water conditions were the slightly
more corrosive  solutions.  The corrosion rates of this material were slightly
higher than those  for Type 304 stainless steel and 201 Nickel, but they are
representative  of a good corrosion-resistant material.
                                 50
-------
     0.4
     0.2
                  0.12 weight percent of 50 STPP detergent
                  0.12 weight percent of 50 NTA detergent
                  0.12 weight percent of 37.5 STPP-12.5 NTA detergent
 15 ppm
Hardness
   o
   A
   a
a>
"o
CC
c:
O
v>
2
i_
o
                             I                         2
                                Exposure Time, days

                                        (a)
 0.4



 0.2



 O.I
Q08

0.06

0.04


Q02
                      0.12 weight percent of 50 STPP detergent
                      0.12 weight percent of 50 NTA detergent
                      0.12 weight percent of 37.5 STPP-12.5 NTA detergent
150 ppm
Hardness
                                     Exposure Time, days

                                             (b)
FIGURE  25.
         CORROSION  RATE  OF TYPE 304 STAINLESS  STEEL AS  A FUNCTION  OF
         EXPOSURE TIME  IN  (a)  15 PPM AND (b) 150 PPM  HARDNESS  SOLUTIONS
         AT 130 F AND USE OF THE  LINEAR  POLARIZATION METHOD
                                      51
-------
o
o>
tO
o
DC
in
o
     0.4 i—
 0.2



 0.1

0.08

Q06


O04



0.02
                     0.12 weight  percent  of  50 STPP detergent
                     0.12 weight  percent  of  50 NTA detergent
                     0.12 weight  percent  of  37.5 STPP-12.5 NTA  detergent
 15 ppm
Hardness
   o
   A
   D
                                                                                   u
                                 I                         2
                                     Exposure  Time, days

                                            (a)
 0.4



 0.2



 O.I

0.08

0.06


0.04



0.02
150 ppm
Hardness
                     0.12 weight  percent  of 50 STPP detergent
                     0.12 weight  percent  of 50 NTA detergent
                     0.12 weight  percent  of 37.5 STPP-12.5 NTA detergent
                                 I                         2
                                     Exposure Time, days

                                             (b)
 FIGURE  26.
           CORROSION  RATE  OF  TYPE 420 STAINLESS STEEL  AS A  FUNCTION
           OF EXPOSURE  TIME IN  (a)  15 PPM  AND (b) 150 PPM HARDNESS SO-
           LUTIONS AT  130 F AND USE OF  THE LINEAR POLARIZATION METHOD
                                     52
-------
1020 Carbon Steel

Weight loss data for 1020 carbon steel are summarized in Tables 17 and 18
for STPP and NTA solutions respectively.  Weight losses for this material
varied between 9.5 and 125 mg over the 2-day exposure periods to give
corrosion rates between 4.4 and 57 mils per year.  The corrosion rates
varied, therefore, between low and very high.  In general, four types of
corrosion behavior were obtained as typified by Figures 27 to 30.  Figure
27 shows the appearance of general, even corrosion; Figure 28 shows general
corrosion with heavier localized corrosion.  This material also evidenced
localized etching corrosion which would occur with no evidence of an adherent
deposit as shown by Figure 29 or under a reasonably adherent deposit as
shown by Figure 30.  The etched areas generally revealed a faceted structure
in surface microscopy but metallography indicated that this corrosion
did not penetrate beyond a surface layer, e.g., as grain-boundary corrosion.

The weight-loss data are summarized in Figure 31.  Although trends are not
evident in Figure 31 (due to localized corrosion producing misleading low
overall corrosion rates), this materials action is probably similar to the
others.  Thus, considering that the localized corrosion results represented
by 'L' in Figure 31 are probably much higher rates, it appears that the
corrosion rates probably increase with increase in detergent concentration.
The NTA-based solutions in the soft water condition appear to be the most
corrosive of all.  It does appear also that an increase in detergent
concentration favors localized corrosion for both STPP and NTA solutions.

The weight-loss data shown in Figures 32(a) and 32(b) allow determination
of the increased corrosivity factor for NTA solutions over STPP solutions.
These results summarized in Table  19, show that the increased corrosivity

        Table 19.  Increased Corrosivity Factors for NTA Solutions
                   Over STPP Solutions with 1020 Carbon Steel
   Detergent Concentration,
      weight percent           15-ppm Hardness	150-ppm Hardness
0.06
0.12
0.18
2.9
7.1
-3.0
-------
           Table 17.   Coupon-Weight-Loss Data for 1020 Carbon Steel in 50 Weight Percent STPP-Based Detergents
Detergent Concentration, Hardness,
weight percent ppm Coupon
0.06 15 H45
H46

150 H47
H48
0.12 15 Hll
H12
H13
£ H14
150 H21
H22
H23
H24
0.18 15 H25
H26
150 H27
H28
=====
Temp,
F
130
130

130
130
160
160
130
130
160
160
130
130
130
130
130
130
Exposure,
days
2
2

2
2
2
2
2
2
2
2
2
2
2
2
2
2
Corrosion E
mdd
60.7
56.0

26.4
23.8
43.9
70.2
41.4
40.1
167.9
213.3
109.5
138.3
273.8
271.6
68.8
58.0
ropy Remarks
11.1 Dark brown deposit. General
10.2 corrosion plus heavier localized
corrosion.
4.83 Bright appearance. General
4.35 corrosion.
8.03 Local etching corrosion.
12.9
7.58 Local etching corrosion.
7.34
30.7 Mostly heavy general etching
39.0 plus some localized.
20.0 Mostly general mild etching.
25.3
50.1 General even corrosion
49.7
12.6 Local etching corrosion.
10.6
                                f\
(a)   mdd = milligram/(decimeter)  /day
     mpy = mils penetration/year
-------
          Table 18.   Coupon-Weight-Loss Data for 1020 Carbon Steel in 50 Weight Percent NTA-Based Detergents
Detergent Concentration, Hardness,
weight percent ppm Coupon
0.06 15 H41
H42
150 H43
H44
0.12 15 H9
H10
HIS
H19
150 H15
H16
H17
H20
0.18 15 H29
H30
150 H31
H32
Temp,
F
130
130
130
130
160
160
130
130
160
160
130
130
130
130
130
130
Exposure,
days
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
Corrosion
mdd
161
157
116
85.8
152
140
277
311
180
207
130.1
110.0
97.9
81.6
185
137
Rate(a)
mpy
29.5
28.7
21.2
15.7
27.8
25.6
50.6
56.9
32.9
37.8
23.8
20.1
17.9
14.9
33.9
25.1
Remarks
General and some heavier
localized corrosion.
Reddish-brown film. Even
general corrosion.
Localized shallow etching
(2-mil deep) under corrosion
product.
General corrosion.
Intense local etching corrosion.
Local etching corrosion.
Local etching corrosion.
Localized and general corrosion.
(a)   mdd = milligram/(decimeter)  /day
     mpy = mils penetration/year
-------
     P416
FIGURE 27.
1020 CARBON STEEL COUPON H26
AFTER EXPOSURE
Note general corrosion.
    P639
FIGURE 28. 1020 CARBON STEEL COUPON H41
           AFTER EXPOSURE
           Note general corrosion and
           heavier localized corrosion.
    P419
FIGURE 29. 1020 CARBON STEEL COUPON H27
           AFTER EXPOSURE
           Note corrosion-deposit-free
           localized corrosion.
                                      P638
                                 FIGURE  30.  1020  CARBON STEEL COUPON H46
                                             AFTER EXPOSURE
                                             Note  corrosion-deposit-covered
                                             localized  corrosion.
                                 56
-------
    70
    60
    50
                                                 15 ppm   150 ppm
                                                Hardness  Hardness
           50 weight' percent  STPP based detergent
           50 weight  percent  NTA based detergent
                                 o
                                 A
     0.06
                                denotes  localized corrosion
                0.12
Detergent  Concentration,  weight percent
0.18
FIGURE  31.  CORROSION  RATE  OF 1020 CARBON  STEEL AS A FUNCTION
            OF  DETERGENT  CONCENTRATION  IN 15 PPM  AND  150 PPM
            WATER  HARDNESS  AT 130 F
                              57
-------
   60
    10
 15 ppm
Hardness
          0.06 weight percent detergent concentration
          0.12 weight percent detergent concentration
          0.18 weight percent detergent concentration
                             denotes  localized corrosion
      0
     50
          _J
           50 STPP
            0 NTA
               STPP and  NTA Concentration,   weight  percent
FIGURE  32 (a).  CORROSION RATE OF 1020 CARBON  STEEL AS  A FUNCTION
               OF STPP AND NTA CONCENTRATION AT 15 PPM  WATER
               HARDNESS AND  130 F
                             58
-------
    60
    50
o
O)
o>
Q.
tf)
40
 -  30
o:

c
g
'to
o
i_
o
O
    10
       0.06 weight percent  detergent  concentration

       0.12 weight percent  detergent  concentration

       0.18 weight percent  detergent  concentration



                      L---denotes  localized  corrosion
                                                  150 ppm

                                                  Hardness
      0
      50
                                                             _J

                                                             50  STPP

                                                              0  NTA
                STPP  and  NTA Concentration,  weight percent
FIGURE 32 (b).
            CORROSION  RATE OF !020 CARBON  STEEL  AS A  FUNCTION

            OF STPP AND NTA CONCENTRATION  AT  150 PPM  WATER

            HARDNESS  AND  130 F
                              59
-------
0)
CL
   100 -
    80

    60


    40
20




 10

 8

 6
 o
cc
 c

I  I0°
 t   80
 o
°   60
     4O




     20




     10

     8

     6
       0.12 weight percent  of 50 STPP detergent
       0.12 weight percent  of 50 NTA detergent
       0.12 weight percent  of 37.5 STPP-12.5 NTA detergent
 15 ppm
Hardness
   o
   A
   a
                           I                         2
                               Exposure Time,  days

                                       (a)
                   3
                                                          150 ppm
                                                          Hardness
       0.12  weight percent of 50 STPP detergent
       0.12  weight percent of 50 NTA detergent
       0.12  weight percent of 37.5 STPP-12.5 NTA detergent
                                   Exposure Time, days

                                           (b)
FIGURE  33.  CORROSION RATE OF  1020 CARBON STEEL AS  A  FUNCTION  OF  EXPOSURE
            TIME  IN  (a) 15 PPM  AND  (b) 150 PPM  HARDNESS SOLUTIONS AT  130  F
            AND USE  OF THE  LINEAR POLARIZATION  METHOD
                                     60
-------
 the  corrosion rate increased over the first day's exposure to steady state.
      >ehavior paralleleda  change in corrosion potential from about -0.6 to
     • volt  versus  SCE.  The  linear polarization results  which were evaluated
       :he  determined values  of bA = 0.14 volt and bc = ooand Equation 5  Rave
 corrosion  rates between about 15 and 40 mils per year  which were in good
           with weight  loss data.   The linear polarization results appeared
 to indicate  that  STPP  solutions were more corrosive  than NTA solutions  with
 the  mixed  STPP-NTA solutions of intermediate behavior.   The STPP solution
 •n the   .ft-water condition  appeared to be  the most  corrosive.   In several
      ons, the linear  polarization method gave responses similar to that
 ihown in Figure 4(a)  indicating a  localized form of  corrosion,  as evidenced
 on the electrode  after experiments.

 A limited  number  of studies  were  made of corrosion products by  X-ray diffraction
 Coupons H27/H28 and H45/H46  from STPP solutions  were found  to contain a
     1)3 product as  did  coupons  H29/H30 from an NTA solutions.   Coupons  H43/
         from a NTA  solution showed  the  presence  of a 6  -FeOOH  product  with a
               for NaFe02 and a  very  faint pattern for Fe304.  It  appears that
   OH)3 which  was  sharper from  samples  off  coupons H45/H46  was  aided by  the
 soft-water condition of the  low-STPP  concentration.  This solution  corresponded to
 the  lowest PH  value of  10.0  of  these  solutions  producing this corrosion  product.

 Chemica1 Lead

Tables 20 and  21  summarize the weight-loss  data  for chemical lead in  STPP
    NTA  solutions, respectively.  Weight  losses varied between  11 and 223 mg
 per coupon over the 5-day exposure periods.  Corrosion rates between  1.3 and
29 mils  per year were moderately low and very high, respectively. The corrosion
      J material appeared to be general and a dull white  or  gray deposit
typi::ied in Figure 34 was observed on the specimens.
        P415
     FIGURE  34.
  (a)
(b)
CHEMICAL LEAD COUPON L26  (a) BEFORE AND
Note fine white deposit.
                                                          (b) AFTER EXPOSURE
                                 61
-------
               Table 20.  Coupon-Weight-Loss Data for Chemical Lead in 50 Weight Percent STPP-Based Detergents
Detergent Concentration, Hardness,
weight percent ppm Coupon
0.06 15 L45
L46
150 L47
L48
0.12 , 15 Lll
L12
L13
L1A
c* 150 L21
L22

L23
L24
0.18 15 L25
L26
L27
L28
Temp,
F
130
130
130
130
160
160
130
130
160
160

130
130
130
130
130
130
Exposure,
days
5
5
5
. 5
5
5
5
5
5
5

5
5
5
5
5
5
Corrosion
mmd
34.4
32.8
10.1
13.4
25.1
25.4
54.3
62.3
72.1
78.9

65.3
57.3
177.2
150.8
95.0
100.2
Rate(a)
mpy
4.37
4.17
1.28
1.70
3.19
3.23
6.90
7.91
9.16
10.0

8.29
7.28
22.5
19.2
12.1
12.7
Remarks
Dull greenish-gray film. General
corrosion.
Dull light gray film. General
corrosion.
Dull gray. General corrosion.

Dull gray with yellow spotted
areas. General corrosion.
Dull gray and traces of white
and brown deposits. General
corrosion.
Dull gray with traces of white
deposit. General corrosion.
Fine dull white deposit. General
corrosion.
Dull gray with trace of white.
General corrosion.
(a)   mdd = milligram/(decimeter)  /day
     mpy = mils penetration/year
-------
              Table 21.   Coupon-Weight-Loss Data for Chemical Lead in 50 Weight Percent NTA-Based Detergents
Detergent Concentration, Hardness,
weight percent ppm Coupon
. 0.06 15 L41
L42
150 L43
L44
0.12 15 L9
L10
L16
^ L17
W 150 L15
LI 8
L19
L20
0.18 15 L29
L30
150 L31
L32

Temp,
F
130
130
130
130
160
160
130
130
160
160
130
130
130
130
130
130

Exposure,
days
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5

(a)
Corrosion Rate
mdd
104
119
43.8
28.3
219
226
112
137
169
155
109
101
146
174
131
127

mpy
13.2
15.2
5.56
3.59
27.8
28.7
14.2
17.4
21.4
19.7
13.8
12.8
18.5
22.0
16.6
16.1

Remarks
Fine white deposit. General
corrosion.
Dull light gray film. General
corrosion.
Fine crystalline deposit. General
corrosion.
Fine crystalline deposit. General
corrosion.
Coarse crystalline white deposit.
General corrosion.
White crystalline deposit.
General corrosion.
Fine white deposit. General
corrosion.
Dull gray with traces of
yellowish-green white
deposit. General corrosion.
(a)   mdd = milligram/(decimeter)  /day
     mpy = mils penetration/year
-------
    50
    40
0>
ex
(A
0)
"5
o:
g
'in
o
*_
o
o
30
    20
    10
       50 weight percent  STPP based  detergent
       50 weight percent  NTA  based  detergent
 15 ppm   150 ppm
Hardness  Hardness
   o        •
   A        A
     0.06
                              0.12
              Detergent Concentration, weight  percent
                0.18
FIGURE  35.
          CORROSION  RATE  OF  CHEMICAL  LEAD  AS A FUNCTION
          OF  DETERGENT  CONCENTRATION  IN 15 PPM  AND  150
          PPM WATER  HARDNESS  AT  130 F
                             64
-------
     30 i—
     20 9=
                      0.06 weight percent  detergent concentration
                      0.12 weight percent  detergent concentration
                      0.18 weight percent  detergent concentration
                                                           15 ppm
                                                          Hardness
                                                             A
                                                             o
                                                             D
 a>
 o.
a>
"a
a:
c
o
o
o
                 STPP and NTA Concentration, weight percent

                                     (a)
                                                                   50 STPP
                                                                    0 NTA
30
     20
                                                          150 ppm
                                                          Hqrdness
                 0.06 weight  percent  detergent concentration     A
                 0.12 weight  percent  detergent concentration     •
                 0.18 weight  percent  detergent concentration     •
                 STPP and  NTA  Concentration,   weight percent

                                     (b)
                                                                   50 STPP
                                                                    0 NTA
FIGURE 36.  CORROSION  RATE  OF CHEMICAL  LEAD  AS  A FUNCTION OF
             STPP AND  NTA  CONCENTRATION AT (a) 15 PPM  AND (b)
             150 PPM  WATER  HARDNESS  AND  130 F
                                65
-------
     0.2
     O.I
    0.08

    0.06

    0.04
    0.02
 s
 Q,  0.01

 j« 0.008
      0.12  weight  percent  ot  50 STPP detergent
      0.12  weight  percent  of  50 NTA  detergent
      0.12  weight  percent  of  37.5 STPP- 12.5 NTA detergent
                                                             15 ppm
                                                            Hardness
                                                               o
                                                          a
 a
 cc.
 c
 o
 "8
 o
 o
0.2
     0.1
    0.08

    Q06

    0.04
    0.02
    0.01
   0.008
                                    Exposure  Time,  days

                                            (a)
       0.12 weight percent of 50 STPP detergent
       0.12 weight percent of 50  NTA detergent
       0.12 weight percent of 37.5 STPP-12.5 NTA  detergent
                                                        150 ppm
                                                        Hardness
                                 I                         2
                                    Exposure  Time,  days

                                            (b)
FIGURE 37.  CORROSION RATE OF CHEMICAL LEAD AS A  FUNCTION  OF  EXPOSURE
             TIME  IN  (a)  15  PPM  AND  (b)  150 PPM   HARDNESS SOLUTIONS  AT 130 F
             AND USE  OF THE  LINEAR  POLARIZATION  METHOD
                                     66
-------
Figure 35 summarizes the weight-loss data in Tables 20 and 21.   The data
indicated that the corrosion rate of chemical lead increased with increase
of detergent concentration and that NTA solutions appeared to be more
corrosive than the corresponding STPP solutions.  The most corrosive
solutions were those based upon NTA in the soft-water condition.

Figure 36 shows the weight-loss data from which the increased corrosivity
of the NTA solutions could be determined.  These results are summarized in
Table 22 which shows that the corrosivity factor varied between 1.0 and 3.1.
Values for both soft- and hard-water conditions are similar and increased
with decreased detergent concentration.


        Table 22.  Increased Corrosivity Factors for NTA Solutions
                   Over STPP Solution with Chemical Lead
      Detergent Concentration,
          weight percent	15-ppm Hardness	150-ppm Hardness
                0.06                   3.1      "           3.0
                0.12                   2.1                  1.6
                0.18                   1.0                  1.3
The linear polarization measurements on chemical lead are summarized in
Figure 37.  As seen from Figure 37, large changes in corrosion rates were
measured over the first-day exposure period.  Generally the corrosion
potentials varied between -0.5 and -0.6 volt versus SCE but did not parallel
the marked changes in corrosion rate.  The corrosion rates were calculated
using Equation 5 and the determined values of b^ = 0.30 volt and b^ = °°
from polarization curves.  It was apparent that the corrosion rates measured
by the linear polarization method were very much smaller than those determined
by weight loss.  Again, it would appear that poorly, conducting films produced
on the material in these solutions gave a low assessment of corrosion rate.
X-ray diffraction identified  corrosion products of
and N32S04 on coupons L25/L26 from a STPP solution.  Coupons L29/L30 from a
NTA solution indicated products  of Pb3(C03)2(OH)2 and PbO(red).  The product
PbO (red) was also identified on the coupons L31/L32 from another NTA solution.
Lead was the only material  in which phosphate deposits were identified on
materials exposed to STPP-based  detergents.


Cast-iron Soil-Pipe Material

The weight- loss data for  this material are  shown in Tables 23 and 24 for as-
prepared and soil STPP and  NTA solutions respectively.  Soil-pipe studies
were conducted at 130 F since this temperature related to studies of other
materials and was only slightly  higher than the usual temperature (115 to
120 F)  of detergent solutions goitg to drain.  As shown in Table 23, weight-
loss data on this material  was obtained over exposure periods of 2 and 7
days.   Two exposure periods were used because 2-day corrosion rates were
very high and, therefore, there  was a need  to determine if these corrosion
rates became stiff led on  longer  exposure.   The corrosion rates of this
material were always very high (16 to 120 mils per year) in the fresh
detergent solutions (Table  23).

                                    67
-------
                  Table 23.  Coupon-Weight-Loss Data for Cast Iron Soil Pipe in STPP and NTA-Based Detergents
ON
00
Detergent Concentration, Hardness,

weight percent ppjn Coupon
0.12 of 50 wt. percent 15
NTA-based detergent


150




0.12 of 50 wt. percent 15
STPP-based Detergent




150





(a) mdd « milligran/ (decimeter) 2/day
mpy - mils penetration/year.
Ml
M2
M9
M10
M3
M4

Mil
M12
M5
M6

M13
M14

M7
M8
M15
M16


*


Temp, F
130
130
130
130
130
130

130
130
130
130

130
130

130
130
130
130




Exposure,
days
2
2
7
7
2
2

7
7
2
2

7
7

2
2
7
7




Corrosion
mdd
602
595
391
416
144
150

513 .
325
80.9
100

175
267

246
180
233
230




Rate(a)
mpy Remarks
120 Mottled brown color. General
119 corrosion.
78.2 Light and dark brown. General
83.1 corrosion.
28.8 Mottled brown color. Mostly
30.0 general corrosion with some
pitting. (<0.5 mil depth).
103 Light reddish-brown. General
65.0 corrosion.
16.2 Mottled brown color. Mostly
20.0 general corrosion with trace
of pitting (<0.5 mil depth).
34.9 Light-brown and black deposit.
53.3 Mostly general corrosion
with a little localized.
49.0 Localized and general corrosion.
35.9
46.5 Encrusted brown, gray, and black
45.9 deposit. Mostly general
corrosion with more intense
localized.


-------
      Table 24.   Coupon-Weight-Loss  Data for Cast Iron Soil Pipe in Soiled STPP  and NTA-Based Detergents
Detergent Concentration, Hardness,
weight percent ppm Coupon
0.12 of 50 wt. percent 15 M17
NTA-based detergent M18


150 M19
M20

0.12 of 50 wt. percent 15 M21
STPP-based detergent M22


150 M23
M24

Temp, F
130
130


130
130

130
130


130
130

Exposure,
days
2
2


2
2

2
2


2
2

(a)
Corrosion Rate
mdd
383
354


227
147

175
280


74.8
45.2

mpy
76.6
70.8


45.4
29.4

35.1
56.0


15.0
9.0

Remarks
Light and reddish-brown.
Localized corrosion up to
0.4 mil deep and pits up
to 0.2 mil deep.
Light brown non-adherent
deposit. Large areas of
localized corrosion.
Yellow and light brown de-
posit. Localized corrosion
up to 0.4 mil deep and pits
up to 0.2 mil deep.
Pale yellow, poorly adherent
deposit. Mild general
corrosion.
(a)  mdd = milligram/(decimeter)  /day.
    mpy = mils penetration/year.
-------
 In the 2-day exposure period, the soft-water condition was  more  corrosive
 in NTA solutions at 120 mils per year than STPP solutions with a  rate of
 about 18 mils per year.  In the hard-water condition,  however, the  STPP
 solution was slightly more corrosive at 43 mils per year compared to 30
 mils per year with NTA solution.  Figure 38(a)  shows the typical  appearance
 of coupons M1/M2, M3/M4, M5/M6, and Figure 38 (b),  the appearance  of coupons
 M7/M8 in this series.
               P425        (a)                (b)

   FIGURE  38.   CAST-IRON  COUPONS  (a) M4 and (b) M8 AFTER EXPOSURE.

                Note general corrosion of M4 and mixed corrosion of M8.
From the data  in Table 23, it was apparent that the 7-day exposure in NTA
solutions  showed a  decrease  from 120 to 81 mils per year in soft-water
solution and an increase from 30 to 84 mils per year in hard-water solutions.
It appeared that,  in 7 days, corrosion rates of 81 to 84 mils  per year
obtained were  independent of water hardness.  The decrease in  corrosion
rate from  120  to 81 mils per year in the soft-water solutions  was un-
doubtedly  due  to the formation of a graphitized layer as shown by comparison
of Figures 39  and 40.   The formation of a thin graphitized layer was also
noted on coupons M13/M14 in the STPP solution.
                                  70
-------

              ,     ^      -             •   •
                    *.?
                        •v.  *
                   -

                                      *
                                    -r
         v
                                  •

      *

                           '

                   -
      C-3924


FIGURE 39.   CROSS SECTION OF COUPON Ml
250X
            Note genera 1,  even corrosion and  only  thin  graphitized layer.

      C-3925



FIGURE 40.  CROSS SECTION OF COUPON MlO



            Note the thick graphitized layer.
250X
                             71
-------
In STPP solutions,  the  7-day  exposure  indicated an increase of corrosion
rate from 18 to 44  mils per year in soft-water solutions and from 43 to 46
mils per year  in hard-water solutions.   Thus,  as for NTA solutions, the
7-day  exposure period gave corrosion rates that were independent of water
hardness.   The rates of 44 to 46 mils per year in the STFF solutions were
much lower, however, than the rates of 81 to 84 mils per year in the NTA
 solutions.   The independence  of corrosion rate with water hardness was
 probably due to controlled dissolution through surface films which more
 readily occurred in NTA solutions.  X-ray diffraction of the deposit from
 coupons M7/M8, however, failed to show the presence of crystalline corrosion
 products.

 The weight-loss data in Table 23 is summarized in Figure 41 to allow
 evaluation of the  increased  corrosivity factors of NTA solutions over
 corresponding STPP solutions.  These factors are summarized in Table 25.
 The data in Table  25 indicated, with the exception of the hard-water
 condition  and 2-day exposure period, the NTA solutions were more corrosive

            Table 25.  IncreasedCorrosivity Factors for NTA Solutions
                      Over STPP  Solutions With Cast Iron
Detergent Concentration,
weight percent
0.12
0.12
Exposure,
days
2
7
15-ppm
Hardness
6.7
1.8
150-ppm
Hardness
1.8
       (a)  STPP solution more corrosive than NTA solution
  than corresponding STFP  solutions with increased corrosivity factors between
  1.8 and 6.7.   It appeared  that, with the occurrence of graphitized layers
  within the  7-day exposure  period, the corrosivity factor became equal in
  both hard-water  and soft-water solutions at a value of 1.8.

  A  number of coupons have been exposed to STPP and NTA solutions which have
  been deliberately  contaminated in order to simulate spent or soiled solutions
  which go to the  drain.   These solutions were made up using metal-salt
  additions of Fe2(804)3 • 6H20, CuSO^ - 5H20, ZnS04 • 7H20, PbS04, and A12(30^)3
  18H20 to 0.12  weight percent  detergent solutions in proportion to the pre-
  determined  corrosion rates of the corresponding metals in these solutions.
  These data  are summarized  in  Table 26.  The soft-water and hard-water NTA
  solutions were adjusted  to pH values of 8.8 and 9.3, respectively, after
  preparation and  the STPP solutions were adjusted to pH 9.3.  The pH values
  corresponded to  mean values of the 1020 steel and die-cast zinc used solutions
  in the corresponding detergents.  These pH values were selected since 1020
  carbon steel and die-cast  zinc suffered the most corrosion and would,
  therefore,  determine the pH conditions of soiled solutions.
                                 72
-------
                                                 15 ppm   150 ppm
                                                Hardness  Hardness
          0.12 weight percent  detergent concentration    o       •
o
a>
a>
CL

in
a>

"b
o:
 c
 o
'vt
 o
 w
 O
o
                                                             50 STPP

                                                              0 NTA
               STPP and NTA  Concentration,  weight percent
FIGURE  41
CORROSION RATE OF CAST IRON  AS A  FUNCTION  OF

STPP  AND NTA  CONCENTRATION  AT 15  PPM  AND

150 PPM  WATER  HARDNESS AND 130 F
                             73
-------
                     Table  26.   Summary  of  Data  for Preparation of Soiled Detergent Solutions
Base Detergent Solution
0.12 wt. percent of
50 wt. percent NTA
and 15-ppm hardness



0.12 wt percent of
50 wt. percent NTA
and 150-ppm hardness



0.12 wt. percent of
50 wt. percent STPP
and 15-ppm hardness



0.12 wt. percent of
50 wt. percent STPP
and 150-ppm hardness



Metal
Fe
Cu
Zn
Pb
Al
Fe
Cu
Zn
Pb
Al
Fe
Cu
Zn
Pb
Al
Fe
Cu
Zn
Pb
Al
Corrosion Rate,
mdd
294 (a)
11.8
178
125
2.87
120 (a)
10.9
96.7
105
1.64
r \

6.0
104
58.3
2.65
124(a)
3.0
56.5
61.3
1.62
Metal Loss /Coupon
In 2 Days, mg
117.3
4.7
76.0
52.9
1.1
47.8
4.4
41.2
44.4
0.6
16.2
2.4
44.4
24.7
1.0
49.4
1.2
24.2
26.0
0.6
Equivalent Weight of Metal Salt Added
To 150 Ml Detergent Solution, mg
537.2 Fe2(S04>3 6H20
18.5 CuS04 5 H20
334.4 ZnS04 7H20
77.2 PbS04
13.6 A10(SO,)0 18H00
2 4 j i
218.9 Fe2(S04)3 6H20
17.3 CuS04 5H20
181.3 ZnS04 7H20
64.8 PbS04
7.4 A1_(SO,)0 18H00
243 2
74.2 Fe2(S04)3 61^0
9.4 CuS04 5H20
195.4 ZnS04 7H20
36.1 PbS04
12.3A12(S04)3 18H20
226.3 Fe_(SO,)~ 6H.O
£, *T "^ *•
4.7 CuSO, 5H 0
4 *£
106.5 ZnSCh 7H 0
38.0 PbS04
7.4 A12(S04>3 18 H_0
(a)  1020 Carbon steel.
-------
The coupon-corrosion data for simulated soiled solutions are given in Table
24.  Comparison of this weight-loss data to the 2-day weight-loss data in
Table 23 for unsoiled solutions showed no consistent trends due to soiling.
Thus, in NTA solutions in the soft-water condition, the corrosion rate
decreased from 120 to 74 mils per year, but in hard water the corrosion rate
increased from 29 to 37 mils per year with soiling.  In STPP solutions and
soft water the corrosion rate increased from 18 to 46 mils per year, but in
hard waters the corrosion rate decreased from 45 to 12 mils per year with
soiling.  In the soiled solutions, it was evident, however, that the NTA
solutions were more corrosive than the corresponding STPP solutions.  In
the soft-water solutions, the increased corrosivity factor was 1.6, and
in hard-water solutions, 3.1.  A greater increase in corrosivity of NTA
solutions was observed in hard-water solutions, i.e., solutions of greater
Cl" content.

Corrosion products on coupons M17/M18 and M21/M22 from the NTA and STPP
solutions, respectively, were found to contain principally 6 -FeOOH.
However, M17/M18 contained Fe-jO^ anda-NaFeC^ in small additions to the
main phase- of 6-FeOOH.
                                 75
-------
                            SECTION IX
                            DISCUSSION
Corrosion studies have been conducted on a variety of materials of construction
associated with laundering:  1100 Aluminum, 260 Brass, electrolytic copper,
die-cast zinc, Type 304 stainless steel,  201 Nickel,  Type 420 stainless steel,
chemical lead, and cast iron in a number of STPP- and NTA-based detergent
solutions.  The solutions were prepared as representative of heavy-duty
granular detergents; i.e., 50-weight percent STPP or NTA at detergent con-
centrations of 0.06, 0.12, and 0.18 weight percent as likely to be employed
by the average housewife in washing machines.  The use of water of hardness
values 15 and 150 ppm to relate to soft and hard water respectively,  and
solution temperatures of 130 and 160 F was also designed to represent con-
ditions most  likely to be met under laundering conditions.  Coupon-weight-
loss data were the main source of corrosion-rate information but was  supple-
mented by limited electrochemical "linear polarization" studies.

It was readily apparent from the corrosion results that the materials in-
vestigated could be classed into four groups with regard to corrosion
behavior in NTA and STPP-based detergents.

Group I included materials having very low corrosion rate in NTA and  STPP
solutions of  the order of 0.01 to 0.15 mil per year.   In this group were
the materials in the following order of decreasing corrosion resistance:
Type 304 stainless steel, 201 Nickel, and Type 420 stainless steel.

Group II included materials of moderate corrosion resistance with pene-
tration of 0.2 to 3 mils per year.  In this group were the materials:
-260 Brass, electrolytic copper, and 1100 Aluminum which were quite similar
with respect  to their corrosion rates.

Group III included materials having poor corrosion resistance on the  order
of 2 to 60 mils per year.  In this group were chemical lead, die-cast zinc,
and 1020 carbon steel.  Of these, chemical lead was slightly more corrosion
resistant.

Group IV was represented by cast-iron soil pipe which had an extremely
poor corrosion resistance material giving corrosion rates between 16 and
120 mils per year in the uncoated condition.

The materials within each of the above groups and the order of the groups
with regard to corrosion behavior are as expected considering the usual
corrosion behavior of the materials studied.  Thus, it has been found that
the usually very inert stainless steel and nickel materials are also  the
most corrosion resistant in the detergent solutions.   On the other hand,
the active base materials such as zinc alloys and carbon steel have been
found to have poor corrosion resistance in the detergents.  Copper, brass,
and aluminum have shown the expected intermediate character for these materials.
                                76
-------
As might be predicted from electrochemical theory, the group classification
of the materials with regard to corrosion rates was closely paralleled by
the corrosion potentials of the various materials.  Thus,  Group I materials
exhibited noble corrosion potentials of about -0.2 to -0.3 volt,  Group III
materials exhibited active corrosion potentials of about -0.6 to -0.9 volt,
and Group II were of intermediate behavior with corrosion potentials of
-0.2 to -0.4 volt.

In almost all experiments, it was found that the soft-water condition of
15-ppm hardness was more corrosive than the corresponding solution with
hard water of 150-ppm hardness at a given detergent concentration.  As
discussed in Appendix B, the greater corrosivity of softer water is well
established; the above results follow the usual trend.  The greater
corrosivity of the softer water was due to the greater concentration of
builder component; i.e., STPP or NTA available from the detergent.  In
harder water, some of the STPP or NTA is used to soften the water by
sequestering the magnesium and calcium ions and, therefore, is no longer
available as a corrosion stimulator.  Also, in softer water, the formation
of protective magnesium and calcium scales is diminished.

In addition to the softer water being more corrosive for the investigated
materials, it was also apparent that for any given water hardness, the
corrosivity of the solutions increased with increase of detergent concen-
tration from 0.06, 0.12 to 0.18 weight percent.  This increase in corrosion
rate was, in part, due to the increased availablility of sequestering
compound for the corrosion process but probably also due to the associated
increase of pH and decrease of specific resistance of the solutions as
shown in Table 27.  The increase of pH with increase of concentration was

          Table 27.  Specific Resistivity and pH Data for Detergent
                     Solutions at Room Temperature
50 Wt. Percent NTA
Detergent Concentration,
weight
percent
0.06

0.12

0.18


Hardness,
ppm
15
150
15
150
15
150


pH
10.3
9.9
10.6
10.4
10.6
10.6
Detergent
Specific Resis-
tivity, ohm cm
1800
1800
1000
950
650
700


PH
10.0
9.8
10.4
10.1
10.3
10.2
50 Wt. Percent
STPP Detergent
Specific Resis-
tivity ohm cm
1600
1500
1000
900
650
600
probably due to the greater amount of OH  formed through the hydrolysis of
the STEP and NTA which are salts of weak acids and strong bases.  It is
apparent from Table 27 that NTA solutions were always slightly more
alkaline by about 0.2 to 0.4 pH units than the corresponding  STPP
                                77
-------
solutions.   This behavior was not due to a higher molar concentration of
NTA at 50 weight percent builder since the molar ratio was 1.34 in favor
of STPP, but was the result of the greater hydrolysis of the NTA detergent.
The slightly smaller specific resistivities of the STPP solutions are
probably associated with the larger ionic mobilities of the electrical
species.  The increased pH of the solutions would, of course, be less
favorable to the amphoteric metals; e.g., aluminum,  die-cast zinc,  lead,
and, tentatively, brass because of its zinc content, since these materials
are strongly corroded in very alkaline solutions.  Increased conductance
favors corrosion processes by more readily allowing ionic transport in the
solutions and the establishment of electrochemical cells on the surface
of the materials.  These data indicate that in either STPP-or NTA-based
detergents, the use of higher-than-average detergent concentration (1 cup
per 17-gallon washing machine) would favor increased corrosion.  Lower-
than-average detergent concentrations would be less corrosive.  In all
cases, however, soft make-up water could be more corrosive.

In addition to the soft water and increase of detergent concentration
giving rise to higher corrosion rates, it was apparent that the NTA
solutions in these conditions were almost always more corrosive than the
corresponding STPP solutions.  As discussed earlier, this behavior may be
due, in part, to the higher pH values of these solutions.  However, the
most plausible explanation is that it is related to the greater sequestering
power of NTA discussed in Appendix B.  The increased corrosivity of the
NTA solutions over STPP solutions was readily shown by the calculated
increased corrosivity factors for the materials.  These factors can be
used to indicate how much more corrosive NTA detergent solutions are than
corresponding STPP detergent solutions.  These factors would thus also
relate to the increased metal-ion pickup of the NTA detergent solutions
or  STPP detergent solutions as seen by a sewer treatment plant.  The
corrosivity factors are summarized in Table 28 for the least corrosion

       Table 28.  Summary of Increased Corrosivity Factors for  NTA
                  Solutions Over Corresponding STPP Solutions


    	Metal	Increased Corrosivity Factor

    1100 Aluminum                            1.0 to 1.3
    260 Brass                                1.3 to 5.0
    Electrolytic Copper                      1.5 to 3.8
    Die-Cast Zinc                            1.3 to 4.7
    1020 Steel                               1.0 to 7.1
    Chemical Lead                            1.0 to 3.1
    Cast Iron                                1.6 to 6.7
resistant metals of the construction materials employed in laundering.  These
factors were determined from weight-loss data for detergent solutions most
likely to be employed by the housewife and at the average hot-water wash
temperature of 130 F.  The data clearly show the increased corrosivity of
the NTA solutions.  The increased corrosivity was particularly marked for
cast iron and 1020 carbon steel and to a lesser extent for die-cast zinc
                                78
-------
and 260 Brass.  Electrolytic copper and chemical lead showed a smaller in-
crease in corrosion rate and 1100 Aluminum was only very slightly effected.
It is apparent, that for conditions corresponding to this work, the NTA
detergent solutions could contain as much as 7 times more metal ions due to
corrosion that would be brought about by similar STPP detergent solutions.

As shown in Table 28, cast-iron material, representative of uncoated cast-
iron soil pipe, showed the greatest corrosivity factor.  The high initial
corrosion rates of 16 to 120 mils per year were reduced to 44 to 84 mils
per year on longer exposure periods as graphitization occurred.  It should
be noted, of course, that the sewer pipe is supplied with a thin asphalt
coating which affords some degree of protection for a short period.  The
corrosivity factors and corrosion rates, however, are applicable to the as-
supplied pipe in undiluted detergent solutions.  Corrosion of cast iron was
still high at rates between 12 and 74 mils per year with simulated soiled
detergent solutions thus indicating the inherent high corrosion susceptibility
of this uncoated material.

It should be noted that the NTA and STPP detergent formulations used in these
studies did not contain corrosion inhibitors as might normal detergents.
Thus, the formulations used here would probably be more corrosive than the
corresponding commercial detergents.  However, since neither NTA nor the
STPP detergent formulations used in the studies contained corrosion in-
hibitors, the relative corrosivity of the solutions should be significant
and relate to the behavior of the corresponding commercial detergent
formulations.

With the exception of die-cast zinc and 1020 carbon steel, the corrosion
behavior of the investigated materials was usually in the form of general
even corrosion for both STPP and NTA solutions.  However, die-cast zinc
exhibited pitting corrosion in many experiments.  The pitting was usually
more severe in the solutions representative of the average detergent strength
used by the housewife (i.e., 0.12 weight percent detergent).  Furthermore,
the pitting corrosion extended as fine corrosion paths below the pits.  It
is doubtful that the pitting rates of 180 to 540 mils per year measured
over 2 days' exposure would be sustained at this rate, but the inherent
susceptibility of this material is indicated.  1020 steel exhibited localized
attack in STPP and NTA solutions representative of average and greater than
average detergent concentrations (i.e., 0.12 and 0.18 weight percent).
This corrosion, however, was usually not deep and the associated etched
appearance did not penetrate into the material intergranularly as  the Surface
appearance suggested.  Although 260 Brass corroded in many STPP solutions,
it was apparent that some dezincification occurred.  The dezincification
was confined  to the  surface and did not penetrate into the material.  The
dezincification may  be associated with a limited solution pH range of about
9.9 to 10.4.

Linear polarization measurements to evaluate corrosion rates did not
correlate well with weight-loss data with the exception of results for
1020 carbon steel and probably Type 304 and 420  stainless steel and 201
Nickel.  Because of  good  overall precision of the weight-loss  data using
duplicate samples,  it was concluded that weight-loss data were the most
significant.  The poor correlation with weight-loss data in terms  of
measured corrosion rates was probably due to the formation of  poorly con-
ducting  films  on the materials.  The films gave a low assessment of corrosion
rate in  this method  which effectively depends on measuring the electrical


                                79
-------
resistance of the corrosion process.  Using the results of this method to
compare behavior within a given system, it appeared that the use of mixed
37.5 STPP-1.25 NTA-based detergents did not significantly change corrosion
behavior over that noted for the pure 50 STPP- or 50 SNTA-based detergents.

Since the joint statement  (Appendix A) on December 18, 1970, by the En-
vironmental Protection Agency Administrator and the Surgeon General, con-
cerning the voluntary removal of NIA from detergents, a variety of phosphate
and NTA "free" detergents have appeared on the market.  These products
appear to be based upon  soda ash, silicates, borax, or polyelectrolytes
or mixtures of these with other minor ingredients.^  The corrosivity of
such  detergent formulations to materials used in laundering and sewer systems
was not determined from  a  scan of the open literature, and thus some con-
cern  must be expressed for their use.
                                80
-------
                             SECTION X


                          ACKNOWLEDGMENTS
This work was performed under EPA, WQO Contract No. 14-12-943.  Liaison
was maintained with Mr. Charles E. Myers, Project Officer, of the Division of
Process Research and Development, WQO, EPA.  The support of the project by
the WQO, EPA, under the guidance of Mr. Charles E. Myers, is acknowledged
and appreciated.

The provision of the basic ingredients for preparation of the heavy-duty
granular detergents and useful advice by The Procter & Gamble Company,
Cincinnati, Ohio, is appreciated.
                                 81
-------
                            SECTION XI
                            REFERENCES
1.  "World Soap,  Detergent  Production",  Soap and Chemical Specialities,  46,
    40 (1970).

2.  "More Information on Detergents/Phosphates Issued", Clean Air and Water,
    News, 2,  (38),  9 (1970).

3.  "Preparing,  Cleaning, and Evaluating Corrosion Test Specimens",  ASTM,
    Gl-67 (1967).

4.  Stern, M.,  and Geary, A.  L.,  "Electrochemical Polarization",  J.  Electro-
    chem. Soc.,  104, 56 (1957).

5.  "Standard Reference Method for Making Potentiostatic and Potentiodynamic
    Anodic Polarization Measurements", ASTM, G5-69 (1969).

6.  "Moving in Fast on a Market  that is  Up for Grabs", Chemical Week, 11,
    January 6 (1971).
                                 82
-------
                            SECTION XII
                             GLOSSARY
Builder - A substance added to or used with detergents to increase  their
cleaning action.

Descaling - The removal of corrosion products from a corroded specimen, with
a minimum removal of base metal so that underlying base metal can be  examined
and/or metal weight loss can be determined.

Detergent - Any of numerous synthetic water-soluble or liquid-organic prep-
arations that are chemically different from soaps but resemble them in the
ability to emulsify oils and hold dirt in suspension.

Dezincifica tion - Corrosion of a zinc containing alloy, usually brass,  in-
volving loss of zinc and a residue or deposit in-situ of one or more  less
active constituents, usually copper.

General Corrosion - Corrosion producing uniform penetration of a surface.

Graphitization - Corrosion of gray cast iron in which the metallic  constituents
are converted to corrosion products leaving the graphite intact.

Linear Polarization - A method in which small potential changes AE  of the
order of lOmV applied to an electrode and the resultant current flow AI are
related through the linear relationship AE = RAI where R is a constant.
R, termed the "polarization resistance", is related to the corrosion rate
of the electrode material.  Thus, the linear polarization method enables
corrosion rates to be determined.

Localized Corrosion - Corrosion producing nonuniform penetration of a surface
which ranges from small areas of general corrosion to intense attack at one
or small areas.

pH - A measure of the hydrogen-ion concentration'of a sample which  represents
the logarithm of the reciprocal  (negative  logarithm) of the activity of
hydrogen ions calculated as follows:

                      PH = log 1/(H+) = -  log (H+),
where H  = activity of hydrogen  ions.

Pitting Corrosion - An extreme form of localized corrosion giving rise to
cavities or pits in the surface which have a small width-to-depth ratio
(approximately  less than 6:1).

Potentiodynamic - The technique  of varying the potential of an electrode  in
a continuous manner at a preset  rate.  It  is frequently employed to prepare
polarization plots.
                                83
-------
Sequestration - The formation of a soluble complex chemical from the
reaction of a simple metal ion with a complexing chemical species.

Specific Resistivity - The resistance in ohms measured between two
electrodes which cover opposite faces of a centimeter cube in aqueous
solution at a specific temperature.

Tafel Slope - Application of large potentials to an electrode frequently
yields a current-potential relationship over a region which can be
approximated by

                     E = a + bin/I/,

where E is the electrode potential
      I is the observed current density
      a and b are constants.

The constant b is known as the Tafel slope.
                                84
-------
                           SECTION XIII


                             APPENDIX


          A.  STATEMENT ON NTA, DECEMBER 18, 1970

                                                                   Page

BACKGROUND	         86

RECOMMENDATIONS  	         87



          B.  CORROSION EFFECTS OF NTA WITH SPECIAL REFERENCE        87
              TO ITS USE AS A BUILDER TO REPLACE POLYPHOSPHATES
              IN DETERGENT FORMULATIONS

INTRODUCTION	         88

CHEMISTRY OF AMINO POLYCARBOXYLIC ACIDS	         88

NTA VERSUS POLYPHOSPHATES IN DETERGENTS  	         90

CORROSION REACTIONS OF NTA AND POLYPHOSPHATES  	         91

    Factors Affecting Corrosivity 	         91
    Use of Inhibitors	         91
    Examples of Corrosion Behavior  	         92

DISCUSSION	         93

REFERENCES	         94
                                 85
-------
             A.   STATEMENT  ON NTA,  DECEMBER 18,  1970
Environmental Protection Agency Administrator,  William D.  Ruckelshaus,  and
Surgeon General,  Jesse L. Steinfeld,  said today in a  joint statement:

    "We commend the major detergent manufacturers for their voluntary
    action to discontinue use of NTA  (nitrilotriacetic acid) in the
    manufacturing of detergents,  pending further tests and review of
    recently completed animal studies,  in order to protect the Nation's
    health from any potential hazard.   NTA,  a  chemical being substi-
    tuted for phosphates in some detergents, has been used in gradually
    increasing quantities to reduce the possible contribution of de-
    tergent phosphates to accelerated aging of surface waters in the
    environment.   The aging process,  known technically as  eutrophi-
    cation, results from excessive growth of aquatic plant life;
    overgrowth of algae and nuisance  aquatic weeds has a deleterious
    effect on aquatic life and can have severe impact on water
    quality.  Although the industry was urged  to make the substi-
    tution of NTA for phosphates, and NTA was  subjected to extensive
    testing, recently completed studies of the biological activity
    of NTA combined with heavy metals have raised concern that the
    projected uses of NTA may constitute a hazard to health."
                            BACKGROUND
Early studies, both those conducted by the Federal Water Quality Admin-
istration (FWQA) and the industry,  concentrated on the more conventional
kinds of toxicology studies using NTA alone.   The studies which provide
the basis for today's action were initiated in the National Institute of
Environmental Health Sciences of the National Institutes of Health of the
Department of Health, Education, and Welfare  last spring at the request of
the FWQA, formerly of the Department of the Interior and now an agency of
the Environmental Protection Agency.  The NIEHS was asked to examine the
possibility of adverse reactions (birth abnormalities) secondary to ex-
posure to NTA itself or to NTA administered simultaneously with heavy
metals.  At the dosages employed in the NIEHS studies, which were consid-
erably higher than would ordinarily be encountered by the human population,
the administration of two heavy metals (cadmium and methyl mercury) si-
multaneously with NTA to two species of animals (rats and mice) yielded a
significant increase in embryo toxicity and congenital abnormalities in the
animals studied over the results with the same dosage of the metals alone.

NTA alters the toxicity of metals by affecting their entry, distribution,
and concentration in the tissues.  Of particular concern is the increased
rate of transmission of metals across the placenta to the fetus which
accounts for the fetal toxicity and congenital abnormalities produced in
animals in the NIEHS studies.  This potentiating effect of NTA with mecals,
together with the projected scale of use of NTA from today's beginning 100-
200 million pounds per year to as much as a billion or more pounds per
year over the next few years, was the basis for today's action.
                                86
-------
There is no evidence at this time to indicate that anyone has been or is
being harmed by the combination of NTA with metals in the environment.
However, prudence dictates not permitting a situation to develop in which
harm may occur to man from the effects of the projected uses of NTA.
                          RECOMMENDATIONS
Representatives of the major detergent manufacturers, though they have not
had an opportunity to analyze fully the NIEHS data, nevertheless have agreed
to discontinue use of NTA in the manufacture of soap and detergent products,
pending further tests and review of these and other studies.  Existing
supplies of NTA-detergent products may be  depleted through normal dis-
tribution.  We want to reemphasize that we have no evidence to indicate
that anyone has been harmed or is being harmed by these products.

However, there are certain areas where prudence would dictate that these
products should not be used.  ¥e recommend that NTA-detergent products
not be used in certain limited areas which have both well water supplies and
septic tanks, and in which these treatment systems are operating under
completely anaerobic conditions and where short-circuiting of septic tank
effluent directly into well supplies is occurring.  The products are:
Amway SA-8, Cheer, Gain, H.L.D., K-50, Laundri-Maid, Liquid All, Loft,
Phos-Free, Roundy's, Sav-us, Ultra, and Valley-Dew. (This list is not
complete).

In responding to one environmental problem, great care must be exercised
to assure that the alternative does not pose equal or greater hazards to
the environment or to human health.  This is certainly the case with de-
tergents in view of the massive quantities produced and ubiquitous nature
of their distribution.  It should be recognized that regulatory efforts by
Federal, State, and local officials must be conducted intelligently with
full awareness of potential secondary effects of those efforts.

As important as the prompt reduction of phosphates in detergents is in
reducing the load of algae nutrients in water, we must reluctantly conclude
that NTA does not appear to be an appropriate alternative at this time.
We continue  to urge that phosphates and other nutrients be removed from
waste waters by the application of proper waste treatment methods across
the country.  Additional studies of NTA are now underway, both by the
industry and within the Government.  Intensive study of other phosphate
substitutes will be necessary to assure, to the extent possible, that they
do not present a similar predicament.


         B.  CORROSION EFFECTS OF NTA WITH SPECIAL REFERENCE TO ITS
             USE AS A BUILDER TO REPLACE POLYPHOSPRATES IN DETERGENT
             FORMULATIONS
                                 87
-------
                           INTRODUCTION
Nitrilotriacetic acid (NTA) originated in Germany during the 30's and was
first marketed under the name "Trilon A".-'-  Its use as a sequestering
agent, particularly in detergent formulations, was not economic until
recently.  During the 60's, more economical methods of manufacture were  ,, _
developed resulting in both a reduction in cost and greater availability. '
In recent years, the use of NTA as a detergent builder has expanded rapidly.
As a detergent builder,  best results are obtained when it is used to re-
place part but not all of the polyphosphate in the detergent mix.   However,
it appears more difficult to process NTA into detergent formulations.-*
              CHEMISTRY OF AMINO POLYCARBOXYLIC ACIDS
Of the amino polycarboxylic acids, EDTA (ethylene diamine tetracetic acid)
is the best known and most widely used. >"~°  The related product NTA
(nitrilotriacetic acid) has only recently become widely known.2  The
chemical structure of the trisodium salt of NTA is shown in Figure 1.

NTA has a capability similar to EDTA to sequester metal ions.  Details of
the chelating chemistry of NTA is rather limited; however, one can obtain
an approximate idea of its chemical performance by studying the behavior
of EDTA.

The sodium salts of EDTA and NTA are highly soluble.  For the trisodium
salt of NTA, saturation in water is reached atabout 40 percent by weight.1
Similarly the solubility of the tetrasodium salt of EDTA is about 51 per-
cent by weight. 10  As might be expected, each of these sodium salts, which
is the salt of a weak acid, has a strong alkaline reaction.

EDTA will sequester almost every polyvalent metal in the periodic table.
Usually the molecular ratio of the metal ion chela ted to EDTA is one
to one.   Similarly NTA will complex or chelate most, polyvalent cations.2
The metal is bound into the chelate structure by both ionic and covalent
bonds forming an extremely stable complex.  This effectively deactivates
the metal and eliminates the detrimental effects often caused by metal
ions in aqueous systems.

The sequestering activity is affected by the pH since there is competition
between hydrogen ions and metal ions.  At high pH, say 10 and above, the
complexing of metal ions is most effective.

In hard waters, NTA (or EDTA) will, in effect, soften the water by the
removal of calcium and magnesium ions from solution. This action prevents
the formation of insoluble soaps and precipitates.  The alkaline earth
complexes are highly stable.  The reaction of NTA and EDTA in sequestering
calcium is shown in Figure 2.2  On a weight basis, NTA will chelate almost
50 percent more calcium ions than will EDTA.  However, the stability con-
stant for any given NTA-sequestered cation is invariably lower than that
for the same EDTA-sequestered cation.  This may require an excess above the
stoichiometric amount of NTA to insure completion of the sequestering
action in some applications.2


                                88
-------
                   CH2—C—ONo
                  /       0
                /       /
               N—CH2—C—ONo
                \         0
                  \      /
                   CH2—C—ONa
                                                               .CH,COONo              ,CH2COOV
                                                      NoOOCCH2-N       +Co**-*NoOOCCH2-N	-/Co + 2Nof
                                                               CH2COONo             ^w.rnn/
                                                     C.V.- 389mg.Co COj/g m.
                                                     or 2-57 parts NTANa3:1 part CaCOz
NoOOCCHZv       ,CH2COONa    NoOOCCH2x
       VNCH2CH2N'      *Co+*      N
NaOOCCHg        "CH2COONa       H2C  \t   ,'  CH2
                                COO-Ca'-OOC
             C.V.=263mgCaC03/gm.
             or 3.80 parts EDTANa^ I port CaCOj
                                                                                 CH2COONa
    FIGURE I.  STRUCTURE OF THE TRISODIUM
              SALT OF NTA (TRISODIUM
              NITRILO TRIACETATE (9)
                                         FIGURE 2.  CHELATING CAPACITY OF THE SODIUM
                                                   SALT OF NTA COMPARED WITH THE
                                                   SODIUM SALT OF EDTA (2)
       400

       350

       300

       250

       200

       150

       100

        50
             SEQUESTRATION OF CALCIUM
                     AT 149 °F
               (O.I%Na2C204 indicator)
mg-CoCOj/gm.
                  NTANoi
                   STPP
                   TSPP
          5  6  7   8   9  10  I!  12
                     pH

FIGURE 3. A COMPARISON OF THE SEQUES-
         TRATION OF CALCIUM BY NTA
         AND BY POLYPHOSPHATES AT
         DIFFERENT pH LEVELS (2)
                © 0.75gm STPP
                © 0.45 gm NTANo3H20
                <3> 0.60 gm NTANa3H20
                  in 100 ml H20
                  water hordness=l50 ppm
                                                     12345
                                                      HCI, milliequivalents
                                           FIGURE 4.  BUFFER CAPACITY OF NTA
                                                     VERSUS TRISODIUM
                                                     POLYPHOSPHATE (STPP) (2)
                                               89
-------
               NTA VERSUS POLYPHOSPHATES IN DETERGENTS


Polyphosphates, as well as NTA, are more effective in sequestering calcium
at the higher pH levels.  At 140 F and at a pH of 10 and above, it can be
seen from Figure 3 that the trisodium salt of NTA is roughly twice as
effective as STPP and three times as effective as the tetrasodium pyro-
phosphate (TSPP) in sequestering calcium. 2  of concern in its effect on
the corrosion environment is NTA's buffering capacity.  As can be seen in
Figure 4, it requires more acid to lower the pH from say 11 to 8, with NTA
in solution than is the case with STPP.2  Thus the sequestering capability
of NTA in alkaline solution is less readily disturbed.

In the typical detergent formula, NTA can be used to replace part or all
of the polyphosphate.  NTA achieves a higher brightness level on fabrics
than does STPP at about one-half the quantity of builder.2  Other benefits
of NTA as a builder in detergent formulation include (a) lower mineralization
of cotton fabric washed in hard water compared to results when using STPP
as a builder, (b) good foam stabilization, (c) improved rinsability of
detergent components from fabrics and hard surfaces because of the greater
solubility of NTA versus STPP, (d) stabilization of minor ingredients such
as bleaches, brightners, and sanitizing a gents. 2>3>5

The important differences between the amino acid chelating agents; e.g.,
NTA and  the polyphosphates,
 (1)  The amino acids can combine with a wider range of polyvalent metal
 ions than the polyphosphates.

 (2)  The polyphosphates tend to revert to the simple phosphate form as
 the result of excessive acid or alkaline conditions.  High temperatures
 also increase this tendency.  For detergents normally packaged in powdered
 form, this instability is usually not a factor but for concentrated liquid
 detergents, formulators often elect to omit the polyphosphate because of
 stability problems.

 (3)  Polyphosphates exhibit a so-called threshold effect, a characteristic
 not present in amino acid compounds.  A few parts per million of poly-
 phosphate will keep much larger molar quantities of chemical compounds,
 which would otherwise tend to precipitate, in solution.

 Because the effects of NTA and STPP, as builders, are not identical, the
 most effective detergent formulations incorporate a combination of both
 products. 2>3  A molar ratio of sodium tripolyphosphate to sodium nitrilo-
 triacetate of 3:1 to 1:3 is found to give good results.^
                                 90
-------
           CORROSION REACTIONS OF NTA AND POLYPHOSPHATES
Polyphosphates have been used in water systems for scale control and for
inhibition of steel corrosion.   Protection appears to be the result of the
deposition of a film at the cathodic sites.12

Under the alkaline conditions and concentrations used in detergent solutions,
polyphosphates are found to be corrosive to alloys of aluminum,  zinc,  and
to copper-nickel-zinc alloys (German silvers).^  When NTA is substituted
for polyphosphate, the same metals are affected.

Factors Affecting Corrosivity

NTA solutions can be expected to be corrosive to metals because of the
following factors:

(1)  NTA ties up the alkali-metal ions, particularly calcium, into soluble
complexes.  This prevents the formation of protective scales, such as
calcium carbonate, in effect, allows corrosion to proceed.

(2)  As metal ions from corrosion reactions enter solution they are se-
questered by the NTA.  This prevents the formation of protective films of
corrosion products.  Existing films may be sequestered by the NTA and
thus removed.  In addition, the low concentration of unsequestered metal
ions in solution stimulates the corrosion reaction by preventing the
attainment of equilibrium.

(3)  NTA penetrates a variety of protective films formed by corrosion
inhibitors.4

Many of these reactions are similar to those of the polyphosphates.  Phos-
phates complex calcium ions (Item 1 above) and also sequester metal ions
from corrosion reactions  (Item 2).13  On the other hand, the presence of
low levels of polyphosphate, unlike NTA, will often increase the effective-
ness of an inhibitor.

Use of Inhibitors

One problem with high levels of polyphosphates  in detergent solutions has•
been the tendency  toward  corrosion of  the  "white metals".  The necessity for
the inhibition of  phosphate-bearing detergents  is well established.4  For
example, aluminum  corrosion can be inhibited by adding silicates.^>14
Without the silicates, the polyphosphates will maintain a fresh surface
for initial attack.  The  proper silicate,  if added, will be chemisorbed on
the metal and prevent further sequestration.  It is found that aluminum
corrosion is effectively  inhibited by  sodium silicate having a ratio of
Si02 : Na20 of about 1.6.^,14  The inhibition of corrosion of copper-
nickel-zinc alloys in phosphate containing detergents can be accomplished
by benzotriazole. 4
                                                                   3
Neither of the above inhibitors is effective toward zinc or "Zamak"  with
either polyphosphate or NTA as builders.   The corrosion rate can be inhibited
to an acceptable range by the addition of  an alkyl phosphonate according
to a British pa tent.4

                                91
-------
      Table  1.  Corrosion of Zamak 3^a) by Detergent(b)  Containing Sodium
               Nitrilotriacetate (NTA) With and Without Inhibitor(c)
               After  6  Hours  in Agitated Solutions at 140 F.4
                                               Loss  in Mg/Sq  Dm/Day
Detergent Concentration
0.27.
0.5%
Type of Water
HardW
Distilled
Inhibited
39
238
Uninhibited
355
688
(a) Nominal composition,  4 Al,  0.04 Mg,  remainder Zn.
(b) See Table 2,  for composition.
(c) Inhibitor is  "0.3 percent  of random octadecyl phosphonic acid prepared
    by adding phosphorous acid to  a random mixture of  octadecenes using
    gamma radiation as a  source of radicals".
(d) Hardness = 8.4 grains per  imperial  gallon or 120 ppm.
See Table 1 for composition of Zamak.


Examples of Corrosion Behavior

The composition of a detergent containing NTA  is  given in Table 2.

    Table 2.  Composition of a Spray-Dried Granular Detergent Containing
              NTA in Percent by Weight^


	Percent

Sodium straight chain alkyl benzene sulphonate having an average        13.3
 chain length of 13 carbon atoms
Sodium tripolyphosphate (STPP)                                          41.4
Sodium nitrilotriacetate (NTA)                                           9.6
Sodium silicate having a SiO£ : Na^O weight ration of 1.6               10.0
Marine oil fatty acids                                                   0.5
Tallow fatty acids                                                       1.5
Sodium carboxymethyIcellulose                                            0.33
Sodium sulfate                                                          11.26
Water                                                                   11.00
Miscellaneous ingredients including perfume,  optical brighteners,         L It
 and pigments
Note that the ratio of STPP to NTA is about 4:1.   The corrosion rates given
in Table 1 are for Zamak 3 in agitated detergent  solutions at 140 F for 6
hours.  The hard water (equivalent to 120 parts per million by weight)
                                92
-------
contained a 0.2 percent concentration of detergent by weight.   The "random
octadecyl phosphonic acid" inhibitor, at 0.3 percent strength,  reduced the
corrosion rate to about 1/9 of that of the uninhibited solution.   The in-
hibition in the distilled water solution with 0.5 percent detergent was
only partially effective.

In another experiment, aluminum and Zamak 3 were found to be corroded
by 0.35 percent detergent solutions, using the same two waters as in the
Zamak 3 tests above.  The detergent composition was:

            Sodium tetrapropylene benzene sulfonate    20%
            Sodium tripolyphosphate                    50%
            Sodium sulfate                             25%
            Inhibitor                                   5%

In this experiment, the exposure was for 3 hours at 140 F at a pH of 9.5.
Adding 5 percent phosphonic corrosion inhibitor, e.g., 10 nonadecyl phos-
phonic acid or pentadecyl benzyl phosphonic acid resulted in inhibition
not only for -aluminum but also for Zamak 3.

When NTA is substituted for the polyphosphate, the corrosion rates also are
unacceptable.  However, the attack on both metals is effectively inhibited
by phosphonic corrosion inhibitors.
                            DISCUSSION
Much of the literature on NTA discusses analytical techniques, problems of
sewerage treatment, efficiency as a detergent builder, and packaging
problems.  Corrosion data are almost nonexistent in the open literature.

One gathers from a study of detergents in general that there is an almost
endless variety on the market. Many of these detergent formulations tend to
be corrosive, and manufacturers of laundry and washing machines have found
it necessary to construct their units of corrosion-resistant materials. >14-1
The introduction of NTA for part of the polyphosphate does not appear to have
altered the situation as far as domestic washing machines are concerned.
A recent suggestion is to replace part of the polyphosphate builder-' by
increasing the amount of surface-active agent to partially compensate for
the change.  It is not easy to predict how these alterations in formulation
will reflect the corrosivity of detergent solutions to white metals such as
zinc and aluminum.  Builders such as sodium carbonate may be required to
maintain alkalinity.

No indication was found in the literature that NTA-bearing, spent-detergent
solutions are more corrosive to sewer lines and to sewerage plants than is
the case for phosphate-based detergents.
                                 93
-------
                             REFERENCES
 1.   Sisley,  J.  P.,  and Wood,  P. J., Encyclopedia of Surface-Active Agents,
     Vol.  _! (1952)  Chemical Pub. Co., N. Y.

 2.   Pollard, R. B., "Amino Acid Chelating Agents in Detergent Applications",
     Soap and Chemical Specialities, 42 (9), 58-62,  130-5 (1966).

 3.   Singer,  J.  J.,  "Chelating Agents in Detergents",  Coap and Chemical
     Specialties, 37 (10),  49-51, 125-6 (1961).

 4.   Zimmerer, R. E., "Detergent Composition", British Patent No. 1,131,738
     (October 23, 1968).

 5.   Kastra,  R.  D.,  "Formulating Detergents With Less Phosphate", Soap and
     Chem. Specialties, 47 (2), 36-42, 54-6, 107 (1971).

 6.   Smith, R. L.,  The Sequestration of Metals, Chapter V, MacMillan Co. (1959),

 7.   Dwyer, F. P.,  and Mellor, D. P., Chelating Agents and Metal Chelates,
     Chapter 7,  Academic Press, New York, N. Y. (1964).

 8.   Martell, A. E., "Complexing Agents", Kirk-Othmer Encyclopedia of Chemical
     Technology, 2nd Edition,  p 1-24 in Vol. 6, John Wiley (1965).

 9.   Shumate, K. S., Thompson, J. E., Brookhart, J.  D., and Dean, C. L.,
     "NTA Removal by Activated Sludge—Field Study", J. Water Poll. Control
     Fed., 42 (4),  631-640, (1970).

10.   The Merck Index, p 428,  Merck & Co. (1960).

11.   McGilvery,  J.  D., "STPP for Modern Detergents", Soap and Chemical
     Specialties, 40 (12),  241-3, 254-7 (1964).

12.   Hatch, G. B.,  "Influence of Inhibitors on the Differential Attack of
     Steel",  Corrosion, .21 (6), 179-87 (1965).

13.   Shen, C. Y., "Properties of Detergent Phosphates and Their Effects on
     Detergent Processing", J.Am. Oil Chem. Soc., 45,  510-16 (1968).

14.   Lange, K. R.,  "Recent Studies in the Roles of Silicate Builders in
     Detergent Formulations",  J. Am. Oil Chem. Soc., 45, 487-92 (1968).

15.   Chandler, R. H., "Corrosion Resistance of Vitreous Enamel", Corrosion
     Prevention and Control,  8 (8),  41-2 (1961).

16.   Stupel,  H., and Koch,  F., "Die Korrosion von Zinc durch Neuzeitliche
     Waschmittel" [The Corrosion of Zinc by Modern Detergents], Werkstoffe
     und Korrosion,  10 (1), 33-39 (I960).

17.   Mosle, H. G.,  Wolf, W.,  and Bode, W., "Untersuchung uber den Einfluss
     von Haushalts  Wasch Mitteln auf Metalle und von Metallen auf Haushalts-
     Waschmittel" [Investigation of the Effect of Domestic Detergents on
     Metals and of Metals on Detergents], Werkstoffe und Korrosion, 15 (2),
     130-4; (3), 221-227 (1964).
                                  94
-------
                               Subject
(1) Accession Number   (2) Field & Group
                 SELECTED WATER RESOURCES ABSTRACTS
                    Input Transaction Form
(5) Organization
             Battelle Memorial Institute, Columbus Laboratories

(6) Title
             Corrosion Potential of NTA in Detergent Formulations
 (10) Author(s)
       Moreland, Peter J.
       Boyd, Walter K.
       Lutz, Garson A.
          (16)  Project Designation
                EPA, WQO  Contract No.  14-12-943
          (21)  Note
 (22) Citation
 (23)  Descriptors  (Starred First)  - corrosion, eutrophication, detergents,
          pollution, phosphates,  plumbing, metals, stainless steels
 (25)   Identifiers  (Starred First)
         NTA, STPP,  laundering equipment, polarization studies

 (27)   Abstract

     Laboratory  studies were conducted  to determine the corrosion potential of
 nitrilotriacetic acid  (NTA) as a  substitute  for  sodium tripolyphosphate (STPP)
 in  detergents.   Coupon-weight loss  and  linear  polarization studies were employed
 to  investigate the corrosion of  typical materials of construction which might
 be  subject  to exposure to NTA in normal use  in laundering.

     Detergent formulations were  used which  were representative of heavy-duty
 granular detergents.   Solutions  of  0.06, 0.12, Snd 0.18 weight percent using
 15- and 150-ppm  water  hardness and  temperatures  of 130 and 160 F represented
 laundering  conditions  used by the average housewife
     NTA-based detergents were more corrosive  by a factor between 1 and 7 to
 the materials 1100 Aluminum, 260 Brass, electrolytic  copper,  die-cast zinc,
 1020 carbon steel  and  chemical  lead.  Corrosion  was generally greatest in NTA
 and STPP solutions with  soft water.  In both soft and hard waters, corrosivity
 increased with increase  of detergent concentration.
     Types  304 and 420 stainless steel  and 201 Nickel were very corrosion re-
 sistant  (0.01 to 0.15  mil per year), 260 Brass,  electrolytic  copper and 1100
-Aluminum were moderately resistant  (0.2 to 3 mils per year) and die-cast zinc,
 1020 carbon steel  and  chemical  lead poorly corrosion  resistant at rates of 2
 to  60  mils  per year.   Cast iron  showed  extreme corrosion  in NTA solutions with
 corrosion rates  between  30 and  120  mils per  year. NTA detergents could increase
 metal  ion pickup at a  sewage plant  by a factor between 1  and  7.
 Abstractor
   Moreland,  Peter J.
Institution
    Battelle Memorial Institute,  Columbus Laboratories
-------