United States
Environmental Protection
Agency
Environmental Sciences Research
Laboratory "^PT^
Research Triangle Park NC 27711 *V»*
Research and Development
EPA-600/S3-83-107 Jan. 1984
Project Summary
Identification of Compounds in
Particulate Pollution by
X-Ray Diffraction
J. V. Gilfrich and L S. Birks
The ability of x-ray diffraction tech-
niques (Seeman-Bohlin and Bragg-
Brentano) to identify small amounts of
material deposited on low-mass
substrates was examined. The Seeman-
Bohlin focusing camera had somewhat
better resolution than the Bragg-
Brentano diffractometer, but the
Bragg-Brentano diffractometer was
commercially available and was
equipped with sophisticated computer
programs for identifying the crystalline
compounds.
Four commercial diffractometers
with automated "search-match"
capabilities were used to measure
simulated and actual pollution
paniculate samples deposited on filter
substrates and in bulk. These
instruments are shown to be moder-
ately efficient for identifying mixtures
of reasonably-well-crystallized
compounds in the simulated samples
(average of 60% successful identifica-
tion). While the actual samples pro-
duced poor results, the software that
might improve the results is still being
developed. X-ray diffraction shows
potential as a method to characterize
pollution partinulate samples.
This Project Summary was developed
by EPA's Environmental Sciences
Research Laboratory, Research
Triangle Park, NC, to announce key
findings of the research project that is
fully documented in a separate report of
the same title (see Project Report order-
ing information at back).
Introduction
The identification of chemical species
in air pollution particles is important to
health studies, air chemistry research,
emission control strategies, and source
apportionment modeling. Techniques are
needed for the identification and
measurement of these chemical species.
X-ray diffraction (XRD) has been used
routinely for many years in qualitative
and, in some cases, quantitative analysis.
Recently, XRD has been used to measure
free silica in the work environment.
However, XRD has not been used as a tool
in routinely measure compounds in
source emissions.
The purpose of the present study was to
evaluate several XRD methods for use in
source emissions measurements. In the
first phase, we conducted laboratory
experiments to compare two types of x-
ray optics, Seeman-Bohlin (S-B) and
Bragg-Brentano (B-B), used for determin-
ing the compounds present in particulate
pollution samples collected on thin
substrates. In the second phase, we
evaluated commercial automated B-B
XRD instruments equipped with "search-
match" facilities to provide computer
identification of the compounds present.
To test the success of identification in
both phases of this work, we used
simulated samples in which mixtures of
known compounds were deposited on
thin substrates. In the second phase, we
also examined bulk samples and actual
pollution samples collected from source
emissions
Results
Samples of (NKUfoSO*, CaC03 and a
mixture of the two were run on both the
B-B diffractometer and the S-B camera.
The S-B film was traced with a
densitometer. In all cases, the
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compounds were easily identified.
However, the loadings were 1 mg/cm2
higher than most actual collected
samples. The XRD patterns matched the
Joint Committee for Powder Diffraction
Standards (JCPDS) cards, but line
intensity differences were noted. For
example, reversal of the strongest and
second strongest lines occurred with
some samples, which may be due to
preferred orientation developed in the
sample grinding. This problem may not
exist in "real world" aerosol samples.
The samples used in Phase II were first
x-rayed at the Naval Research Labora-
tory, then sent to four companies who
make XRD equipment. The single
compound samples with loading of about
200 //g/cm2 caused no problems.
However, low loaded samples and
redeposited bulk fly ash samples
produced poor patterns and, therefore,
poor results. Simulated bulk samples
made up from reagent chemicals pro-
duced fairly good patterns, and the four
components were identified. None of the
actual samples collected in the field
produced patterns which could be
identified satisfactorily.
Recommendations
Use of Automated
Diffractometers
The modern automated diffractometer
shows promise as a method to character-
ize particulate pollutants. The "search-
match" program used with the
diffractometer was only moderately
successful in identifying crystallized
compounds. An off-line computer
program through which the data might
be run for redundancy (assuming that the
raw data can be retrieved from the
automated instrument) might be
desirable. One such program is available
from Interactive Sciences Corporation,
which implements the NIH/EPA Chemical
Information System (CIS). When the
"search-match" software is further de-
veloped, these off-line programs will not
be necessary.
Sample Holder
The sample holders on the commercial
instruments were adaptations of the
standard bulk sample holder, which had
the filter mounted on the surface of the
flat plate and the cavity containing the
bulk powder behind the filter. The
adopted sample holders were not ideally
suited for filler samples. The most
appropriate sample holder was used at
Siemens, where a United States Steel
Corporation design was available. This
holder was designed: 1) to contain a 25
mm silver filter for the determination of
free silica in airborne dust and 2) to be
handled by an automatic sample changer.
J. V. Gilfrich and L S. Birksare with the Naval Research Laboratory, Washington,
DC 20375.
Kenneth T. Knapp is the EPA Project Officer (see below).
The complete report, entitled "Identification of Compounds in Particulate Pollution
by X-Ray Diffraction," (Order No. PB 84-122 829; Cost: $8.50, subject to
change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Sciences Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
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