EPA-650/2-73-008



October 1973
Environmental  Protection Technology Series
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                                      EPA-650/2-73-008
DEVELOPMENT  OF  A  SUPPLEMENTARY
        EMISSION  MEASUREMENTS
           MONITORING  SYSTEM
                        by

                   Paul F. Bennewitz

              Thunder Scientific Corporation
                   623 Wyoming S. E.
              Albuquerque, New Mexico  87123


                Contract No. 68-02-0588
                Program Element No. 1A1010


             EPA Project Officer: Fredric C. Jaye
              Chemistry and Physics Laboratory
           National Environmental Research Center
         Research Triangle Park, North Carolina  27711
                     Prepared for

             OFFICE OF RESEARCH AND DEVELOPMENT
            U. S. ENVIRONMENTAL PROTECTION AGENCY
                  WASHINGTON, D.C. 20460

                     October 1973

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This report has been reviewed by the Environmental Protection Agency and



approved for publication.  Approval does not signify that the contents



necessarily reflect the views and policies of the Agency, nor does



mention of trade names or commercial products constitute endorsement




or recommendation for use.
                                11

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          TABLE OF CONTENTS
Abstract  	    i
Objective	ii
Scope   	    1
Introduction  	    2
Interstitial sensing  	    3
Technical discussion  	    4
Fig. 1, Density states three        5
        dimensional lattice
Fig. 2, Cutaway ILS Array ....    6
Fig. 3, Frequency Vs wave vector    7
Defect Structure  	    8
Fig. 4, Replacement lattice ...    9
Ligand Field Theory 	   11
Fig. 5, Standing wave, defects  .   12
Fig. 6, H20 Molecule	13
Fig. 7, Far infrared stretching    14
        frequencies
CO, C02, 02, H20	15
Material Selection  	   16
Material Analysis 	   17
Group Selection, Sensor firing     18
        and construction  ....
Test System Configuration ....   19
Fig. 8, Block Diagram EMMS  ...   20
Fig. 9, C02 Gas Sensor	21
Fig.10, Steam test	21
Fig. 11, Test Unit #7	23
Fig.12, Test Unit #5	24
Fig.13, Signal conditioning ...   25
02, H20 Sensor	26
Fig.14, Test Unit #6,  calibration  27
Fig.15, Test Unit #6	28
Fig.16, Test Unit #5,  steam ...   29
Fig.17, Test Unit #5,  steam ...   30
Life Tests	31
System Components 	   32
Fig.18, WSIS-1000, BR-101R  ...   33
Fig.19, Gas Sampling System ...   34
        Bottom, top view
Fig.20, System, front panel and .   35
        Control panel
Fig.21, Atmospheric system and  .   36
        Test chamber
Conclusion	38
Fig. 22,Flow Chart    	39
Fig. 23, System Gas Flow	40
References	41

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                        ABSTRACT
A prototype Supplementary Emission Measurements System
was designed and developed to provide measurement of
C02, CO, H20, and C^in stack gases of stationary
emission sources.

Sensors were developed or obtained from other sources
to meet the criteria set forth in the requirement.

The system was designed to facilitate direct readout
of all channels via individual analog metering.  In
addition, outputs of 0 to 1 VDC were provided for on-
line computer feed.

The system was equipped with a stack sampling probe,
filters and pump to provide full and complete stack
sampling and measurement capability.

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              OBJECTIVES AND/OR BACKGROUND
The project for development of a Supplementary Emission
Measurements Monitoring System was organized with the
following design goals and objectives:
1)  Design a prototype subsidiary emissions measurements
    system to measure C02,  CO, 1^0 and 02 in stack
    emission gases.

    Ranges Requested:
    C02  0 - 20%        - 0.5% minimum sensitivity
    CO   0-5%        - 0.1%    "
    H20  0 - 20%        - 0.5%    "
    02   0 - 7%, 0 - 22%

2)  To procure or  develop sensor with  the  specified
    typical minimum  ranges and sensitivities.

3)  To supply flow velocity of 20 to  120 feet per second.

4)  To supply temperature measurement  in the range of
    50° to 700°F.

5)  To equip the system as required with sampling probes,
    filters, pump, etc.

6)  To supply analog meter readouts and  simultaneous
    analog 0-1 volt outputs  for all  parameters.

7)  To equip the system with  suitable  zero  and  calibra-
    tion circuitry as required.
                          ii

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               Report of Development of a
           Supplementary Emission Measurements

                    Monitoring System
SCOPE

This report describes sensors and systems developed to
provide precise measurements and readout of subsidiary
emissions consisting of C02, CO, H20 and 02 as required
by the Environmental Protection Agency.

Unique methods were  implemented which, due
to past developmental experience at Thunder Scientific
Corporation, were considered to be an advance of the
state-of-theart and highly applicable to the requirement,
Sensing Elements (Solid-State)

This report describes the use of various types of semi-
conductor materials for discriminatory sensing of various
pollutant gases;  a superior and unique semiconductor
method was used, based upon prior experience gained in
the recent development by Thunder Scientific of the ad-
vanced state-of-the-art Brady Array bulk-effect humidity
sensor.  It has been determined that the Brady Array is
most effective, accurate and reliable because of its
interstitial lattice method of sensing.

Known monocrystalline semiconductors in chip form, when
connected to appropriate circuitry via applied electrodes,
exhibit various characteristics relative to sensitivity
to the environment and various gases, particularly to H20
in various concentrations;  however, not without degrada-
tion and irreversible effects to be discussed later.  The
consensus of opinion in both the past and present has been
to assume that when designing a new sensor, for example a
humidity sensor, or other types, one should rely upon
various effects of different types of materials to achieve
the end result, with little thought given to designing
specifically to the requirement.  Previous sensors, such
as those designed for measurement of moisture or relative
humidity, relied upon surface phenomenon to achieve a
measurement.  Desiccants or hygroscopic materials have
been heavily relied upon as attractants for moisture for

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measurement.  If observed under high magnification, all
the above configurations may be seen to be agglomerating
water or forming islands of moisture during the process
of measurement.  This means loss of response time and
other characteristics leading to undesirable results.
Also, because the surfaces of these devices are limited
in area, dynamic range is very narrow.

In the case of the Brady Array, humidity sensor, a semi-
conductor bulk-effect device was constructed which could
be proven mathematically to be electrically neutral.  A
method was discovered in the process of development which
allows the construction of microminiature lattice arrays
made up of many crystal semiconductor junctions, separated
by interstitial spaces.  These junctions, estimated to
number a million or more, present a very large geometric
area, if all crystal faces were spread out side by side.
Because the water molecule is extremely small, and the
structure is electrically neutral, the molecules may
drift randomly and freely into and out of the structure,
causing interation within the semiconductor
structure which stresses bonds and changes the volumetric
resistance when percent relative humidity or molecular
density is changed.  Because of the semiconductor nature
and the array effect of the structure, the sensor exhibits
a near one-to-one ratio in output voltage vs. input exci-
tation as the surrounding moisture or molecular density
is changed.

It is this method of approach, the interstitial lattice
sensing method (ILS) , which was used extensively through-
out the requirement.
Introduction

In the following technical discussion, reference will be
made periodically to the interstitial lattice method of
sensing as applied to a semiconductor-type bulk-effect
sensor.  This method and the processes involved are pro-
prietary, with patents obtained or in process, having been
solely developed by Thunder Scientific during in-house
funded R&D programs recently completed, to conceive,
develop and construct an advanced state-of-the-art humidity^
        which is a solid-state bulk-effect semiconductor
device.  This sensor, designated the Brady Array, is pre-
sently being marketed along with signal conditioning
modules also developed at Thunder Scientific, with excel-
lent results .

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Interstitial Sensing

Interstitial lattice sensing (ILS) is a method wherein
an extremely complex crystal array is processed and con-
structed within a diffusion type furnace.  Contrary to
normally known configurations of semiconductors where
the semiconductor is a monocrystalline structure or die
consisting of a single slice cut and diced from a single
zone-grown crystal, the interstitial lattice array,
measuring only 10 mils in diameter and 100 mils in length,
consists of thousands of semiconductor junctions preformed
and processed so as to provide interstitial bulk access
to all faces of the crystal lattices and junctions within
the structure.  Thus, single molecules of various gases
and constituents may easily drift into and out of the
array, creating Fermi-related energy exchanges, causing
the bonds within the lattices to be stessed.  Because they
are vibrating at a descrete and synonymous stretching fre-
quency with the impressed molecular field, energy is
released within the structure to the free electrons therein,
which causes a shift of the Fermi level, thus causing a
change in the volumetric resistance of the structure (see
Figure 2) .


Appropriate signal conditioning, generating an excitation
voltage in a simple bridge arrangement and a demodulator for
conversion of the signal to direct current, thus supplies
an output signal across an output termination proportional
to the phenomena, for analysis by direct reading end in-
struments or computer manipulation.
Greater Sensing Area vs. Size

The crystal lattice array, sensing by interstitial means,
provides a sensor area, when viewed at a molecular level,
hundreds of magnitudes greater than that provided by a
monocrystalline semiconductor.  Rather than presenting one
or a few semiconductor junctions to the medium, which sub-
sequently will greatly limit the dynamic range of readout,
the ILS presents a large geometric area if all crystal
faces and junctions were laid out side by side.
Therefore, dynamic ranges of many orders of magnitude
become available.  This is a major asset when dealing
with units of measurement such as those related to
pollution and contaminant levels, i.e., PPHM, PPM, %,
mass , etc.
                             — 3 —

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Technical Discussion

In a monocrystalllne semiconductor, great care is taken
to prevent the influx of, or contamination by, impurities,
both in the processing environment and following packaging.
For example, the use of Si02 in the field electrode of MOS
transistors has caused difficulties, since this glass
easily absorbs foreign ions that can move under field in-
fluence through the glass.  Thus sodium ions can easily
move within the glass if outside fields are applied, and
therefore, a change in conductivity and dielectric constant
causes a change in impedance and capacity values.  Other
impurity atoms such as CO, HCL and HF can possibly move
through the glass, causing permanent changes in impedance
and capacity.

At first glance, one would tend to assume that because of
these phenomena, monocrystalline semiconductors could be
used directly to detect these impurities;  however, this  is
not entirely ture.  The prime reason in this instance,
whether the monocrystalline semiconductor is Si02 or Ge or
combinations or with various dopants, is that  the principal
of operation must be based upon a  theory of absorption or
adsorption. such as in the previously mentioned surface-
type humidity sensors, thus narrowing the dynamic range
and creating major problems of repeatability and reproduci-
bility.

Of key and significant importance  and one of the most major
disadvantages which should not be  overlooked in evaluation
of devices suggesting monocrystalline structures, is that
these structures, solely by the fact that they are mono-
crystalline, are highly susceptible to doping, even in
limited amounts.  All the various  gases concerning in this
report and most others indicated in the references are
"dopants".  These dopants cause irreversible  changes of
impedance,  capacitance and resistance within monocrystaline
structures.  These  changes are  a major source  of  inaccurate,
unreliable  devices  for the purpose intended.


Interstitial lattice sensing  (ILS)  and the crystal lattice
array represent an  advancement  in  the "state-of-the-art",
based upon  the past two years of research carried on at
Thunder Scientific  Corporation.  This array is a  semiconduct-
ing device  that does lend itself directly to sensing of  the
various parameters  required.  The  ILS device can  be thought
of, in one  sense, as a cross between an amorphous semicon-
ductor and  a monocrystalline semiconductor, i.e., the
                            - 4 -

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                      N(E)
i
Ul
                                          Valonce bond
Conduction band
                                                           FIGURE ONE

                                                           DENSITY STATES THREE  DIMENSIONAL
                                                           LATTICE

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                  GAS CONSTITUENT
                                                   TUNNEL   ELECTRODE
                                                                            DISLOCATION
                                                                            JUNCTIONS
                                   TUNNEL  ELECTRODE
DISLOCATION  SEMICONDUCTING JUNCTIONS
                                                   FIGURE  TWO

                                                   CUTAWAY ILS  ARRAY

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                           n\
FIGURE THREE
FREQUENCY Vs WAVE VECTOR

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electronic properties of defects of the dislocation type
play a somewhat important part, yet the structure is poly-
crystalline while at the same time being deliberately
highly disordered.

This disordering accounts for the large interstitial areas,
most important when sensing gas constituents such as 1^0,
CO, C02 ,  etc.  In effect, the gas tends to behave like and
may be treated as electron gas.  Therefore, in analysis,
one may derive from measurements of temperature dependance,
resistance, thermo-electric power and reflectivity, that
this type of structure if far less sensitive to doping than
either amorphous or monocrystalline structures.

In any crystal, monocrystal, or the individual disordered
mode crystals of the ILS structure, two different vibra-
tional modes exist, which can be related by:


                  -   -_-_   __     4 sin2Kd
               mi
These two vibrational modes are of great importance in real
lattices giving the value for CO at the limits (see figure
3).  Since the lower function corresponds to in-phase move-
ment of nearest neighbors (off and even numbered atoms), it
is called the "acoustical" branch, because the lower fre-
quencies generated in this kind of excitation correspond
to the acoustical range for most crystals.  The upper branch,
shown in figure 3, is called the optical branch, because
these frequencies belong in the electromagnetic infrared
frequency range.  It is these phenomena and characteristics,
among others to be explained, which account for the prime
theory of the ILS array.  The frequency vs. wave-number
functions in figure 3 can have different bands if more than
two different particle masses or more than two force con-
stants are involved.  The main difference between their
frequency range remains the cophase or contraphase movement
of nearest neighbors.
Defect Structure

Contrary to the case of monocrystalline semiconductors where
it is desired to hold point defects to a bare minimum, in
the ILS structure, the opposite is the case.  Defects within
the structure are of absolute necessity in conjunction with
the disordered array for operation of the system.  For
example, in loo.king at the periodic structure in the simple
                            - 8 -

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VO
I
                     2C7
                                   FIGURE FOUR
                                   REPLACEMENT OF Cl~- ION BY H~- ION IN
                                           K+C1~ -LATTICE

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model shown in figure 4, one may begin to understand the
effect of primitive lattice disturbances caused by vacan-
cies or interstitials as applied later to the ILS array.

Consider a displacement of one atom by either a heavier
or lighter one, or, for purposes of ease of description, a
displacement of an ion in an ionic lattice, such as KC1 by
hydrogen.  In this case, the light ion (R-) within the
positive K+ cloud has its own frequency of vibration
(stretching frequency), with an optically active electric
dipole moment.  Because of the very localized nature of
this defect, the additional vibrational modes decrease
rapidly with distance from the defect (actually exponenti-
ally).  However, if these defects are not localized but
comprise many atomic sites as in ILS, the lattice motions
for such a lattice substructure lead to standing wave
modes, literally generating a strain field as electrons
are moved into shared positions, depending upon the density
of the molecular constituent and field applied.  The
lattice motions for such a lattice substructure lead to
multiple standing wave modes  because of the bonds on
either side of the sub-lattice or multiple disturbance.

By representing the substructure by a single dimensional
line leading to a standing wave of: An =A(0)e~iwt sin nkd
(figure 5), because of the limitation L of the size of the
sub-lattice, K is restricted to:
     K
The solution for (A) vanishes for n-0 and n-N  (fixed points),
and for points in between, yields a number K -Vr/Nd independ-
ent modes.

This analogy between defect or sub-lattice excitation and
bound lattice modes may help explain a number  of the effects
to be discussed connected with infrared vibration spectra
of the ILS and the disordered system array.

Dislocations, in conjunction with junction breakdown caused
by the stressed bonds, introduce interband energy levels,
therefore allowing the electrons to move easily through a
lowered field, thus allowing interband transitions to the
conduction band.  It is suspected that many dislocation
space charge pipes or elements of similar nature, perhaps
assisted by the electronic wave functions, account for the
fast response and lack of hysteresis in the ILS array.
                            - 10 -

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In further analysis, in a structure such as the ILS, a
multitude of bonds, known as dangling bonds, are thought
to exist, which are generally commonplace around and in
the space charge pipe sites.  These dangling bonds are in
an excellent position throughout the structure to pick up
shared electrons, thus creating a tremendous amount of
strain or stress upon the inner bonds;  therefore, the
structure will also tend to purge itself of molecules of
the gas constituent of interest when the molecular density
is reduced or removed entirely from the vicinity of the
sensor.  This purging, or flyback as it may be called,
occurs within 150 milliseconds in some cases.
Selection of Semiconductor Materials

Past experience at Thunder Scientific has indicated that
transition metal oxide complexes appear to be the best for
use in the construction of the ILS arrays.  Transition
elements, have partially filled d or f shells.  Before
describing the method to be employed to construct the ILS
array, or configurations and transition complexes analyzed
and employed, further discussion is required to better
understand the semiconducting effects of  transition metal
oxides and their particular applications  to this effort.
Characteristics of the various transition metal oxides are
quite interesting, in that it becomes rapidly apparent that
various  combinations display extremely varied electronic,
ESR and  vibrational spectra and that by very minute variance
of the mix and process times, temperature and diffusion
gases, the stretching frequencies may be  manipulated rather
precisely.  Some of the various coordinate complexes can
be made  to take up an additional odd or even ligand very
readily.  Valence states, relative ionic  radii, associated
bond lengths, and stretching frequencies  are extremely
important in determining the final configuration best fitted
for monitoring each gas constituent.
Ligand Field Theory

To gain  a better understanding  of  the  effects  taking  place
at a molecular  level,  it  is well to  define  and  explore
ligand field theory  as  it  applies  to the  problem  at hand.
Ligand field theory  is  defined,  in this sense,  as  the theory
of (1) the  origin  and  (2)  the  consequences,  of  the splitting
of inner orbitals  of ions  by  their chemical  (gas)  environ-
ments.   The inner  orbitals of  interest  in this  case are  the
partially filled d or  f  orbitals,  primarily  the d.  In  this
discussion, these  splittings  must  be related to the forces
                             -  11  -

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                                                NORMAL LATTICE
n=   0
\3
                                              •	1
   sin nkd
                                           FIGURE FIVE
                                           ONE DIMENSIONAL  STANDING WAVE
                                           OF n DEFECTS  IN  LATTICE

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8
                              FIGURE  SIX



                              H20 MOLECULE

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MOO  21
F-
          CO
   1640 070
     h~f
   ISM  I4»T         1369     I30O    ll«       lift
NO	11—NO,	1I—sort      I—sot—f
                        IMO
                                            FIGURE SEVEN

                                            FAR INFRARED STRETCHING
                                            FREQUENCIES

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involved.  The ILS structure is not purely metal nor is
it purely oxide, but rather a structure achieved by special
processes, consisting of junctions containing both metal
ions and oxide chains that contribute to the over-all spin
and stress effects observed.  (See figure 2).
Carbon Monoxide

Carbon monoxide, CO, is a pi acceptor ligand.  Various pi
carbonyls may also be associated.  CO is a generally inert
molecule and particularly adaptable for detection by the
ILS array.  Dipole moment studies indicate that the moment
of an M-C bond is very low, about 0.5 D, which suggests
that it is close to being electrically neutral as per
Paulings law.  CO has a bond length of approximately 1.128A,
The CO molecule has a stretching frequency of 2145 cm~ .
If the carbonyl molecules are taken into consideration, a
band would then exist of approximately 2125 - 1900 cm~l in
the far-infrared spectrum, providing both medium and strong
spectra for detection resonance.  Many combinations of
carbonyls, and other atmospheric constituents, can be ob-
tained in reactions that take place at normal atmospheric
temperatures and pressures caused by the photochemical
process.
Carbon Dioxide
Carbon Dioxide, C02 , exhibits a stretching frequency from
approximately 1570 to 1640 cm-1.  It shows some tendency
to overlap NO;  therefore, some discrete manipulation of
stretching frequency was necessary to avoid confusion with
NO.  It was suspected that some latitude was available for
this, due to the fact that the NO band is not continuous
across the band of 1580 to 1900.
Oxygen (02)

Oxygen, 02, has an extremely broad band, exhibiting effects
across the entire range.
Water(H20)

The water molecule has a stretching frequency of 3200 to
3600 cm-1 in the far infrared region, which are rated as
strong resonances.  Other minor resonances exist even into
                           -  15 _

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the low infrared;  however, these are weak to very weak
and may be ignored.  To better understand the complete
theory of the ILS array, the water molecule presents an
excellent opportunity in that it is relatively simple and
readily accessible.  The oxygen atom is bonded to two
hydrogens in an arrangement expressed pictorially in
figure 6.  The separation of the hydrogens approximate, by
present conceptual theory, an angle of 105°.  Each hydrogen
precesses at a given rate (A) and in conjunction with this
momental precession, it is believed that a complex preces-
sion exists about 0, as shown by B following through C and
so on.  These perturbations may be attributable to the
anti-symmetric and symmetric 0-H stretching mode at 1600
to 1650 cm""•*••  In addition, quite a good deal of fine
structure is apparent.   Therefore,  as the molecular density
or moisture content of  the atmosphere in the vicinity of
the Brady Array humidity sensor changes, bonds are stressed
as previously explained, thus causing a shift in volumetric
resistance of the Array and subsequent change in readout
voltage.  Further direct explanation of the Brady Array
bulk-effect semiconductor humidity sensor is contained in
a recently published paper (see Appendix).

Material Selection

As previously indicated, most, if not all, first transition
series metal oxides will, when processed and doped correct-
ly, exhibit semiconductor phenomena.  With proper process-
ing, the resistance of resultant elements may be controlled
over a broad range of as much as 1014 ohms/cm or more when
using the ILS technique.  Past processing indicates that
the d-block elements with partially filled shells are d
shells, 3d, 4d, or 5.  These d orbitals project well out  to
the periphery of the atoms and ions so that the electrons
occupying them are strongly influenced by the surroundings
(the gas constituent) and in turn are able to influence the
Fermi level and internal environment of the sensor substan-
tially.  The final selection of the precise transition
elements, reactants, doping materials, processing tempera-
tures and diffusion gases were determined during the program
As in the case of  the previously developed bulk-effect Brady
Array, these parameters were developed by a combination,  in
sequence, of mathematical analysis  and emperical. Cut and
try,  X-ray  and spectrum analysis of lattice and crystal
structure had previouly been performed upon the Brady Array
in previous  in-house research  thus  giving some  idea  of
typical structure  to be expected.   The "cut and try" deals
primarily with process  times,  temperature cycling rates  and
diffusion gas content and  flow rates,  following initial
determinations of  sensitivity  to the gas  constituent  of
ineterest.
                             - 16 -

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                   Material Analysis,

                 Studies, and Selection
Initially, studies were instigated to determine proper
bond lengths and radii, ionization potentials, melting
temperatures, transition points, molecular weight, etc.
of various oxides of metals to determine possible compa-
tability and/or sensitivity to the various gases desired
to be monitored.  Far infrared stretching frequencies
were also taken into consideration and listed.  Sources
for these data are listed in the references contained in
this report.

Based upon the above referenced studies, the following
final test groups were selected for initial testing and
analysis .

        EPA Code #1                EPA Code #2
        50% Fe203                  50% F
        30% ZnO                    40% ZnO
        20% Sn02                   10% Sn02

        EPA Code #3                EPA Code M

        50% Fe203                  50% Ti02
        20% ZnO                    50%' V205
        20% Co203
         5% V205
         5% Sn02
        EPA Code #5                EPA Code #6

        50% Co203                  50% Zn
        50% V205                   50% Sn

        EPA Code #16
        Ti02 +
        + Neodymium

Though a total of sixteen  (16) test  groups were  initially
mixed, it was determined that those  listed above were
most applicable based upon the previous  studies.
                            -  17  -

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Group Selection

To determine the applicability of each test group for use
as a sensor, it was necessary to observe the structure of
each when exposed to various firing schedules within the
furnace.  (an Astro Industries Series 1000)  This was done
by placing each raw material mix within ceramic boats and
observing the effects achieved when the material was fired
at 1500°C to 1550°C.  If a disordered polycrystalline
structure or tendency was noted, the material was marked
for prototype sensor construction.  Of the 16 test groups,
those listed previously exhibited this tendency.


Sensor Construction

Each sensor was constructed by hand beneath a microscope upon
glass cover slips.  The material was mixed with a 95% - 6%
mixture of beta terpinal and celulose acetate to form a binder.

The thus mixed material was then placed on a glass cover slip
and formed, using a scalpel until a rectangular form was
achieved measuring approximately 180 mils in length and 25
mils in width, with a depth of approximately six mils.  Four
mil platinum iridium electrodes were then embedded in the
material equally spaced and the overall sensor shaped and
flattened with the scalpel until of such a dried consistency  .
to be picked up off the cover glass with the scalpel.


Sensor Firing

The completed sensors were then placed upon supporting
mandrels within platinum boats and fired for thirty minutes
at 1550°C.  The boats were then removed and the completed
sensor thermally lead bonded to a TO-5 type eight pin header.

Generally, it must be pointed out, at this stage in the devel-
opment that a major portion of the process is one of "cut and
try" including varying of temperature and diffussion gases.

As an example, the final configuration chosen for C02 was EPA
Code #16.  Here several gases were tried looking primarily
for the largest crystal formation.  All gas flows were flowed
at the rate of 100 cc/min.  The final gas chosen was a mix-
ture of air and CO in a 75% air, 25% C02 mixture at atmospheric
pressure.

In the CO sensor, it was determined that it functioned selec-
tively to CO and discriminated against C02 when run at a
current of 300 m.a. driven by a constant current module.

The material mix chosen due to the need for this higher
current was EPA Code #1.  This material when employed within
the sensor showed no deterioration after long term running
at this higher current.
                               - 18 -

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Sensors were constructed of the various selected groups
and designated as follows:
     Test Unit #1
     Test Unit #2
     Test Unit #3
     Test Unit #4
     Test Unit #5
     Test Unit #6
     Test Unit #7
EPA Group //I
1st unit of EPA
2nd unit of EPA
1st unit of EPA
1st unit of EPA
Group #4
Group #4
Group #5
Group #16
2nd unit of EPA Group #1(
2nd unit of EPA Group #5
Tunneling electrodes were used to allow
bonding of the sensor  into a  small TO-5  can
(See photo, Figure 9)
                  thermal lead
                      type enclosure
Electrical Conf iguration

An integrated  circuit  amplifier  was  constructed  as  a  pro-
totype  to achieve  zero offset  and  a  span  of  1  volt  DC
output.  This  amplifier was  inserted  into the  circuit as
shown  in Figure 8.   All sensors  were  initially tested with
this basic breadboard.
 Initial  Test  Results

 Of  all sensors  initially  constructed,  Test Unit
 Unit  #6  and Test  Unit  #7  indicated satisfactory
 ity to C02  and  were  then  further  tested.
                           #5,  Test
                           sensitiv-
 Test  System  Configuration

 Initially  an all  glass test system was constructed as
 shown in  the photograph to allow testing of the sensors
 in  both gas  and  humidity environments.  In addition
 functioning  as  a  mixing manifold for all gases in a
 manner, the  system also provided means of injection
 known amounts of  moisture into the gases if so
                               to
                               precise
                               of
                          desired,
 allowing  the capability of achieving better than
 accuracy  in mixing ratio.
                            + 1%
 Precise accuracies of mixing ratio adjustment and flow
 were controlled by Matheson flowmeters with individual
 calibration curves for the various gas constituents.
 Mathematical computation allowed added precision when
 dealing with the various viscosities and specific gravities
 of the gases.   Precision differential monometers allowed
                            - 19 -

-------
                  CCR
o
I
                              V
MB  GAS ARRAY
  NOTE: CCR= CONSTANT CURRENT REGULATOR
                                                    FIGURE EIGHT
                                                    BLOCK DIAGRAM EMISSIONS MONITOR
                                                    SIGNAL CONDITIONING CHANNEL

-------
COMPLETED SOLID  STATE
   C02 GAS SENSOR
   FIGURE  9
 SENSOR  IN  ONE  HOUR
 STEAM EXPOSURE  TEST
FIGURE 10
           -  21 -

-------
precise balance between the mixed constituents.

In initial testing for gas sensitivity and ranges, the
test system was set up to allow use as a mixing manifold
system only.

A standard Thunder Scientific Brady Array Humidity Sensor
was first installed within the system to detect any
moisture that might be leaking into the system.  First
tests indicated bad leakage, though all gases had been
previously routed through two Ca S04 dessicators columns.
Final source of leakage was traced to the tygon tubing
used in the system.

Following this discovery, all tubing was replaced with a
hard dense walled nylon tubing eliminating the problem.

The test sensor, Test Unit #7 was placed within the system
and tests begun.

Initially dry nitrogen was used as a zero gas to establish
a base.  Gas flows were held to 100 cc/min.  Temperature
of the test chamber was continuously monitored and taken
at each reading.

Test readout equipment consisted of a Fluke 853A Differ-
ential Multimeter, an 8300 DVM and an Esterline Angus
Recorder.

The sensor was first checked for selectivity, the results
obtained are shown in Figure 11.  This recording was obtain-
ed by mixing in two Matheson type flowmeters.  C02 was
first vented into the system at 100% level and the amplifier
adjusted to obtain a 1 volt DC output.  The first recording
shown in Figure 11 displays the response time of the Test
Unit #7 with the chart running at 1.5" per minute.  The
second portion of the recording shown in Figure 1, displays
the response to 100% C02 with the recorder running at  12"
per hour.  CO and 02 were then vented into the system  at
100% concentration, each time clearing the system with
nitrogen.  Selectivity of the sensor to C02 may be noted as
a result.

Test Unit #5 was then installed within the system and  the
recorder run at 6" per minute.  (See Figure 12)  Here, due
to the additional doping and material selection, it will
be noted that the response time is considerably enhanced.

Test unit #5 was then operated in ambient air in live  steam
for one hour.  (See Figure 16)  (See Figure 9)
                           -  22 -

-------
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-------

-------
                                           The SC-1020M signal
                                           conditioning module
                                           shown with the C-3A
                                            environmentalized
                                          cable and Brady Array
The SC-1020M signal  conditioning  module  with Brady Array Model
                     B'R-101  humidity  sensor
                                                       FIGURE  13
                                 - 25 -

-------
Following one hour in live steam, the recording  shown  in
Figure 17 was run to determine any shift  in  calibration
due to this exposure.  It was noted that  a slight  shift
of 44 m.v.  occured.  Considering the stringent environment,
this small amount of deviation was not considered  serious.

A calibration run was made on Test Unit  #6 and the  record-
ing shown in Figure 15 obtained.  It will be  noted  that
the sensor exhibits a near linear response to  CC>2  •   These
data are plotted and the curve obtained  shown  in Figure  14.

Of the test units run and tested, Test Unit  #6 was  selected
for use in the Emission Monitoring System.
Life Tests on The C02 Sensor

The final sensor was  installed  at  ambient  in  an  operational
condition for life  testing.   Prior  to  installation in the
completed system, a  total  of  8000  hours  was  accumulated
with no degradation  in  characteristics  or  output.
The CO Sensor

During tests of  the  various  test  groups,  it was noted that
Test Unit #1 of  EPA  Group  1  exhibited characteristic
sensitivity to CO, i.e.,  response,  etc.   However, sensitiv-
ity to C02 was also  noted.

The CCR, Constant  Current  Regulator,  nominally supplying
20 m.a.  to the CO  sensor  was  changed  to  a variable CCR type
generator and  the  output  current  across  the sensor varied
in steps as the  output  was  evaluated.

It was found that  apparent  "tuning" of the sensor took
place  and as the internal  current thru the sensor was in-
creased, the sensitivity  to  C02  was eliminated, while the
sensitivity to CO  content  was enhanced.

Considerable difficulty was  experienced  in clearing  the CO
sensor with nitrogen,  once exposed  to CO.  It was found that
the sensor would clear  when  a standard air mix was flowed
across it.  Because  of  this,  a special "CO PURGE" valve was
incorporated in  the  system.   Test Unit //I was selected to be
employed in the  final  Emissions  System for sensing of CO.

-------
                                                         EPA  TEST UNIT #6
                                                         GROUP 16
                                                         CALIBRATION  9/13/72
I, .'i !!ij,.! :!.'':  :.:;;::

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                                                                       -  27  -

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-------
The 02 Sensor

Considerable difficulty in the course  of  the  program  was
experienced in obtaining a solid  state  oxygen sensor.   It
was finally determined that, though  it  appeared  possible,
with time, to obtain an oxygen sensor  employing  similar
techniques, that a standard commercially  available  in-
strument would be incorporated for this measurement.  A
Beckman Model 715 Oxygen Analyzer was  chosen  in  the  course
of evaluation.
The H2Q Sensor

The Brady Array Model BR-101  in  conjunction  with  a  stand-
ard signal conditioning module,  Model  SC-1020M-2  manufac-
tured by Thunder Scientific Corporation was  employed  for
measurement of water vapor present within  the  gas  stream.
This system has been employed by many  in  the field  for
measurement of humidity with  a high degree  of  success  over
the past three years.

The Brady Array has a specified  accuracy  of  + 4% RH,  typical
accuracy being better than +2% RH.  The range  covered  is
0% RH to 100% RH.

Due to its specific design, the  sensor can  be  operated  at
elevated temperatures, i.e.,  in  a heated  sampling  enclosure,
ranging up to 160°F. (See Figure 19)
System Flow Transducers

Because it is necessary  to maintain  a  reasonably  consistent
flow across the gas sampling sensors,  a  sensitive  flow
sensor was incorporated.  This  sensor, a  Thunder  Scientific
Corporation Model WSIS-1000 allows measurement  and precise
adjustment of the gas flow within  the  system  to 100 to 200
cc/min.   (See photo in Figure  18)
Stack Temperature

Stack temperature  is monitored  and  displayed  on  an  analog
meter on the front panel.  A  thermocouple  and reference  is
contained within the sampling probe  for  monitor  of  temper-
atures within the  gas  intake.   The  probe is  equipped  with
a back flushable micron  filter  with  the  back  flush  control
located on the front panel of the  switching  module.
                           - 31  -

-------
Stack Flow Rate

Initially the Model WSIS-1000 was investigated for  use
in determining stack velocity, however, it was found  that
the extreme temperatures that could be encountered  within
the stack prevented use of this device.  Though Stack
Flow Rate is displayed on the front panel, no satisfactory
means was discovered in the course of the contract  to
monitor this parameter accurately.
The Em i s s i o n Measurements Moni to ring Sys tern

The Model EMMS-100 Secondary Emissions Monitoring  System
was developed in the course of the contract  to  provide  a
compact, but complete, self contained monitoring system
for monitor and recording of levels of CC>2,  CO  02,  H20  and
temperature in stack gases of power plants or  in other
emissions generating facilities.

The Switching Panel controls all gas switching  and  routing
within the Gas Sampling System and provides  signal  condi-
tioning and control for all transducers in the  system.
System Components

The system is constructed with  1/4"  stainless  steel  tubing,
All dryers, traps, sensor mounting blocks,  etc.  are  con-
structed of stainless steel.  All valves  are  electrically
actuated directly from  the  front switch  panel.   Figure  19

A heated enclosure is contained  in the  top  of  the  gas  sam-
pling system to maintain a  preset temperature  upon all
critical components.  Though  the solid  state  sensors ex-
hibit no sensitivity to water vapor,  it  was desired  to
maintain the system at  a low  level of  relative humidity.
This is accomplished by a proportional  controller  designed
to allow adjustment of  system heat from  ambient to a max-
imum of 160°F.


Switching

All switching is accomplished from the  front  panel of  the
switching module as shown in  the photo.   Figure 20

Switches are of the "push on" "push  off"  variety.   All
switches are labeled and back lighted.
                            -  32  -

-------


WSIS-1QOO FLOW VELOCITY SFNSOR
 LOW PROFILE BRADY ARRAY SENSOR
                                      FIGURE 18
               - 33 -

-------
      GAS  SAMPLING  SYSTEM
    BOTTOM  VIEW
                                   PUMP

                                   SYSTEM VELOCITY
                                   SENSOR WSIS-1000

                                   SYSTEM FLOW VALVE

                                   02 SENSING HEAD
                                   FILTER FLUSH
                                   COMPRESSED  AIR
                                   FILTER
                                   H?0 SIGNAL
                                   CONDITIONING
      TOP VIEW
(  HEAT SHROUD REMOVED  )
                                    SYSTEM CONTROL
                                    VALVES
                                    C02,  CO, & H20
                                    SAMPLING CHAMBERS
                                    GLASS FIBER
                                    INSULATION
                                        TRF.  19
                    - 34  -

-------
       COMPLETE SYSTEM
                                      SWITCHING AND
                                      CONTROL PANEL
                                      GAS SAMPLING
                                      SYSTEM
         SYSTEM SWITCHING
       AND   CONTROL PANEL
                                       ANALOG READOUTS
                                       PROPORTIONAL
                                     /HEAT CONTROLS
                                       RECESSED CONTROL
                                       PANEL
                                       ZERO OFFSET AND
                                       SPAN CONTROLS
 SYSTEM CONTROL
CONTROL SWITCHES
 SINGLE CHANNEL
CAL GAS  CONTROL
    SWITCHES
                                              FIGURE 20
                 - 35 -

-------
ATMOSPHERIC GENERATOR  SYSTEM
        TEST CHAMBER
                                 FIGURE  21
             - 36 -

-------
Power
Power is controlled by a back  lighted  switch  on  the
front panel labeled "POWER"
Intake Valve

The "INTAKE VALVE" switch  controls  the  intake  valve at
the input of the gas  system.
Zero Gas

The "ZERO GAS"  input  at  the  rear  of  the  system is con-
trolled by a  front  panel  switch  labeled  "ZERO GAS".
Computer oti Line

The  "COMPUTER ON  LINE"  switch, located on the front of
the  switching panel switches the 0-1 VDC outputs of
all  electronic modules  to a connector available at the
rear  of  the  chassis.
 CO  Purge

 A  switch  is  provided to allow purging of the CO sensor
 with .air  following each reading.
 Filter  Flush

 A  switch  is  also provided for back flush of the sampling
 probe  and filter with compressed air.

 Other  control functions include system heat, pump, Cal
 Gas .
 Sub  Panel  Control Functions

 Control  functions within the sub panel include zero off-
 set  and  span adjustment for all electronic modules for
 calibration adjustment.  In addition, the proportional
 heater  control,  02 analyzer controls and individual channel
 Cal  Gas  switches are included within this panel.
                            - 37 -

-------
Conclus ion

It has been determined  in  the  course  of  the  program that
viable and useful  solid  state  semiconductor  sensors can
be constructed and  tuned to  accurately and selectively
measure CC>2 , CO and 1^0  percentage  ranges within  a  closed
gas sampling system.

That a reasonably  small  compact gas sampling  and  control
system can be constructed  to allow  efficient  use  of the
concept.
                          - 38 -

-------
            EPA SYSTEM GAS  FLOW
                        S02  , NOX
                         ANALYZER
                 FILTER

                 (probe)
u>
VD
WSIS
                       NEEDLE
                        VALVE
                          PUMP
                INTAKE

                VALVE
                                                AIR>
                                                      FILTER
COMPRESSED

AIR VALVE
                                                     GAC
                                  co2

                                  GAC
                                                     CO

                                                     GAC
                                                      2
                                                     GAC
                                         PURGE
                                         VALVE
                                                                               N.
                                                            I
ZERO GAS

VALVE
                                 WATER

                                 TRAP
                 CAL GAS

                 VALVE
                            
-------
H20 SENSOR
CO., SENSOR
CO SENSOR
SC-1020M-2


DRIVER



600 OHM
LINE &
METER



CCR & AMP


DRIVER



600 OHM
LINE &
METER



CCR & AMP


DRIVER


600 OHM
LINE &
METER


°2
SENSOR
SYSTEM FLOW
RATE SENSOR

SYSTEM TEMP
SENSOR

STACK TEMP
SENSOR
ELEC


METER



DRIVER
1
600 OHM
LINE

CCR & AMP


DRIVER



600 OHM
LINE &
METER

PROP

•
CONT

HEATERS





DRIVER
ELEC


DRIVER


i
600 OHM:
LINE &
METER


600 OHM
LINE &
METER

                                                                           STACK FLOW
                                                                           RATE  SENSOR
                                                                                       CCR & AMP
                                                                  FIGURE TWENTY-TWO
                                                                  ELECTRONICS FLOW CHART

-------
                             ft o ;" o r o n c o .T
 i.   Xot:c, N'.  ?. ;  "'.dec crone in Disordered  Structures,"
     Advances  in Phyuics  (British), vol.  16,  pp  49-144,  1967

 2.   Gubanov,  A.:  "Quantum Theory of Amorphous Semiconductors,"
     Consultants  Bureau, New York 1965

 3.   Ovshiaalcy ,  S.  Iv.:  "Reversible Electrical Switching
     Phenomena in  Disorder Structures,"   Pays. ReVt Letters,
     vol  21 #20,  ??  1450-1453,  II Nov 1968

 A.   Xorin I-'.  J.;   "aalidcs,  Oxides and Sulphides oi the
     Transition Metals,"   J.  Appl. Phys.  suppl vol 32 tflO,
     pp 2195-2197, October 1961

 5.   Ferraro,  J. j\. :   "Low Frequency Vibrations of Inorganic
     and  Coordination  Compounds,"  Plenum Press,  New York, 1971

 6.   Szc,  S. X.:  "Physics of Semiconductor Devices," Wiley -
     Interscience, 1969

 7.   i,ei£h;:on, P. A.  (Stanford  Department of Cheraistry):
     "Phouochemiucry of Air Pollution,"   Academic Press,
     New  York, 1961

3.   Sheehy, J. P., Achinger, W.  C.,  Simon,  ?v. A.:   "Handbook
     of Air Pollution,"  Environmental Health Series,  U.  S.
    Sept. of Health,  Education and  Welfare  National Center
    for Air Pollution Control,  Durham,  N. C.

8.  Bennewitz, Paul F'. ;  "The Brady Array  - A New  Bulk-Effect
    Humidity Sensor,"  Society  of Automotive Engineers  #730571
    May,  1973
                                 - 41 -

-------