Particulate contamination analysis was carried out on samples taken from the Verification Engineering Test Article (VETA) x-ray detection system. A total of eighteen tape lift samples were taken from the VETA optical surfaces. Initially, the samples were tested using a scanning electron microscope. Additionally, particle composition was determined by energy dispersive x-ray spectrometry. Results are presented in terms of particle loading per sample

Germani, Mark S.

English

NASA Technical Reports Server

p Report to:
National Aeronautics and Space Administration
George C. Marshall Space Flight Center
Marshall Space Flight Center, Alabama 35812
Order No. H-11942D
ANALYSIS OF PARTICULATE CONTAMINATION
ON TAPE LIFT SAMPLES FROM THE
VETA OPTICAL SURFACES
Submitted by:
McCrone Associates, Inc.
Mark S. Gejarrani, Ph.D.
Principalinvestigator
Date: 21 February 1992
MA Number: MA-21600
Copy 16 of 16
(NASA-CR-189918) ANALYSIS OF PARTICIPATE N92-19694
CONTAMINATION ON TAPE LIFT SAMPLES FROM THE
VETA OPTICAL SURFACES (McCrone Associates)
26 p CSCL 070 Unclas
G3/25 0072171
mccrone associates, inc.
850 PASQUINELLI DRIVE • WESTMONT, ILLINOIS 60559
https://ntrs.nasa.gov/search.jsp?R=19920010452 2020-03-17T12:42:26+00:00Z
ANALYSIS OF PARTICULATE CONTAMINATION ON TAPE LIFT
SAMPLES FROM THE VETA OPTICAL SURFACES
INTRODUCTION
We received two plastic boxes, each containing nine tape
lift samples. The boxes were labeled Parabola and Hyperbola
and they had been sealed with tape. The samples in each box
were labeled 1 through 9. You indicated in your letter dated
17 November 1991 that Sample 9 in each box was a control.
You requested that we analyze Parabola samples 1, 4, 8 and 9
and Hyperbola samples 1, 5, 8 and 9.
The plastic boxes were opened in our Class 100
cleanroom. The tape lift samples consisted of a loop of tape
stuck to the bottom of the plastic container. We cut out an
approximately 1" long section of tape from the top of the
tape loop. Each section of tape was mounted onto an adhesive
covered 1" diameter aluminum block. The four Parabola and
Hyperbola samples were placed into pre-cleaned plastic boxes
and kept inside of zip-lock plastic bags. The remaining tape
lift samples were kept in their plastic containers. The
containers were resealed and placed back inside their plastic
bags. The four Parabola samples are designated PI, P4, P8
and P9; the four Hyperbola samples are designated HI, H5, H8
and H9.
SAMPLE ANALYSIS
The samples were coated with a thin film of evaporated
carbon. This is done to render the surface conductive so
- 1 -
that the samples can be examined in the scanning electron
microscope. The samples were analyzed using our automated
scanning electron microscope. Using this instrument, it is
possible to perform unattended analysis of the particle
contamination on the tape lift surfaces. Particles are
detected by an increase in their backscattered electron
signal above a preset video threshold. The video threshold
is set at a fixed level above the average video signal from
the tape lift surface at each field of view. The samples are
analyzed at a magnification of 600X and each field of view is
approximately 150 x 150 jum. We believe that under these
conditions we are able to detect inorganic particles as small
as 0.5 /urn in diameter. For each particle, we determine its
shape and size, location, and elemental composition as
determined by energy-dispersive x-ray spectrometry. Particle
data from each sample is transferred to a Dec Microvax II
minicomputer.
Particles with less than 200 net x-ray counts are
deleted from the data set. These are particles that do not
exhibit any characteristic x-ray peaks in their energy-
dispersive x-ray spectra. These may be organic or polymeric
particles, or artifacts from features on the tape lift
surface itself. For example, folds or cracks in the surface
of the adhesive may be detected and "analyzed" by the
automated scanning electron microscope, cracks occur in the
tape lift surface when it is carbon coated. These cracks can
appear bright in the image due to electron beam charging.
- 2 -
Cluster analysis is used to determine the particle types for
the remaining inorganic particles in the samples.
RESULTS
Table I is a summary of the particle analysis results
from the tape lift samples for the VETA optical surfaces.
This table contains the area analyzed, the number of
inorganic particles >0.5 /xm in diameter in the analysis area,
particle loading, the average particle diameter, and the area
fraction obscured by particles. The area fraction is
determined based upon the average particle diameter for each
sample and is not integrated over all particle sizes for the
sample. The individual particle data can be obtained from
the data files on the enclosed floppy disk.
The control samples, P9 and H9, had particle loadings of
2.07 x 10 and 4.94 x 10 particles per square micrometer,
respectively. Samples P4, P8 and H5 had similar particle
loadings to control sample P9, although they were somewhat
higher than the value for control sample H9. Samples H8, PI
and HI had significantly higher particle loadings than on
either of the two control samples. Sample H8 had the highest
particle loading at 1.41 x 10 particles per square
micrometer, followed by sample PI with a particle loading of
9.44 x 10 particles per square micrometer and sample HI
with a particle loading of 8.72 x 10 particles per square
micrometer.
- 3 -
The samples had average particle diameters in the range
of 1.5 to 4.8 jum. The area fraction obscured by particles in
the two control samples were 3.7 x 10 and 2.1 x 10 for
samples P9 and H9, respectively. All of the other samples
had a higher area fraction obscured by particles than either
of the control samples. These values ranged from a low of
5.5 x 10 for sample P8 to a high of 7.6 x 10 for sample
PI.
Figures 1 through 8 are average particle size
distributions for the samples. The particle size
distributions are for average diameters from 0 to 20 /urn with
each bin representing 1 /urn. The size data for the individual
particles in each sample can be found in the data files on
the floppy disk. Particles have irregular shapes. Shape
factors are typically 1-3. Shape factor (SF) is defined as:
P2
SF = *
where P and A are projected particle perimeter and area,
respectively.
The cluster analysis results for the samples are given
in Tables II through VII. The particle data sets from
control samples P9 and H9 were combined for cluster analysis.
This was done to provide a larger number of particles for
cluster analysis. Together, the two sample data sets contain
a total of 60 particles. Table II is the results of the
cluster analysis for the combined control samples. This
- 4 -
table lists the cluster code, the percent number of particles
in each cluster, the elemental composition for each cluster,
and the possible materials represented by each cluster. The
cluster codes listed in Tables II through VII correspond with
the cluster codes that can be found in the data files on the
floppy disk. In Tables II through VII, I have only listed
those clusters that represent more than 5% of the total
number of particles in a sample or a combined set of samples.
For the most part, the samples contained a variety of
particle types. Table III lists the cluster analysis results
for sample H5. Table IV lists the cluster analysis results
for the combined data sets from samples P4 and P8. Table V
lists the cluster analysis results for sample HI. Table VI
lists the cluster analysis results for sample PI. Table VII
lists the cluster analysis results for sample H8.
The particle types in control samples P9 and H9 and
samples H5, P4, P8 and HI are very similar. These samples
contain major amounts of magnesium silicate (talc), calcium
carbonate, potassium chloride salt, and iron rich particles
(iron oxide, iron metal, steel). The identification of the
material for each particle type is based solely on the
energy-dispersive x-ray analysis results. Energy-dispersive
x-ray analysis provides data on elements with atomic number
greater than 11 (sodium). We do not have any data on
elements lighter than sodium such as carbon, oxygen,
nitrogen. Therefore, these are not unambiguous material
identifications. For example, in the case of particles that
- 5 -
contain major amounts of iron, we cannot distinguish whether
these are iron oxide, iron metal or steel. The difference
between iron metal and steel is only a small amount of
manganese which we may not detect in very small particles.
Therefore, the material identification should be used with
caution. The major particle types in samples PI and P8 are,
however, somewhat different from the other samples and the
controls. For example, the major particle types in sample PI
are aluminosilicate minerals and what we believe to be a
calcium sulfate. These two particle types are not present in
major amounts in the other samples or the controls. In the
case of sample H8, the predominant particle type is sodium
chloride salt. This particle type was also not present as a
major particle type in the other samples and the controls.
You mentioned in a telephone conversation that the
mirrors had been polished with cerium oxide and you thought
that some of the particulate contamination may be cerium
oxide which had not been cleaned from the mirror. The only
sample in which we found a significant amount of cerium oxide
is sample H8. The cerium oxide particle type represented
only 7% of the total number of particles.
CONCLUSIONS
The results of our analysis of the particulate
contamination on the tape lift samples would seem to conclude
that samples P4, P8 and H5 are not significantly different in
particle loading or particle type from the two control
- 6 -
samples, P9 and H9. Samples PI and H8 are significantly
different from the two control samples, both in particle
loading and in the types of particles found on the tape lift
samples. Sample HI has a higher particle loading than either
of the two control samples, but the particle types are
generally similar to those found in the control samples.
- 7 -
APPENDIX A
Tables
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TABLE II
Cluster Analysis Results for Tape Lift Control
Samples for the Parabola and Hyperbola Mirror Surfaces
SAMPLE: Combined P9 and H9 control samples
NO. OF PARTICLES: 60
CLUSTER CODE
2
9
7
6
3
11
16
PERCENT NUMBER
OF PARTICLES
11
8
7
6
5
3
3
ELEMENTAL
COMPOSITION
Mg, Si
Fe
Ca
Pb
Zn
K, Cl
Mo
POSSIBLE
MATERIAL
talc
iron oxide,
iron metal,
steel
calcium
carbonate
lead metal
zinc metal
salt
molybdenum
disulfide
Ref: MA21600
TABLE III
Cluster Analysis Results for Tape Lift Sample
from Position 5 on Hyperbola Mirror Surface
SAMPLE: H5
NO. OF PARTICLES: 41
CLUSTER CODE
4
1
6,8
2
PERCENT NUMBER
OF PARTICLES
15
12
12
7
ELEMENTAL
COMPOSITION
Mg, Si
Cu, Zn
K, Cl
Ca
POSSIBLE
MATERIAL
talc
brass
salt
calcium
carbonate
Ref: MA21600
TABLE IV
Cluster Analysis Results for Tape Lift Samples
from Positions 4 and 8 on Parabola Mirror Surface
SAMPLE: Combined P4 and P8
NO. OF PARTICLES: 103
CLUSTER CODE
6,15
8
17
1
9
PERCENT NUMBER
OF PARTICLES
21
12
10
9
8
ELEMENTAL
COMPOSITION
Fe
Mg, Si
Pb
Ca
K, Cl
POSSIBLE
MATERIAL
iron oxide,
iron metal,
steel
talc
lead metal
calcium
carbonate
salt
Ref: MA21600
TABLE V
Cluster Analysis Results for Tape Lift Sample
from Position 1 on Hyperbola Mirror Surface
SAMPLE: HI
NO. OF PARTICLES: 109
CLUSTER CODE
1
8
12
10
PERCENT NUMBER
OF PARTICLES
17
9
8
6
ELEMENTAL
COMPOSITION
Fe
Ca
Al
Mg, Si
POSSIBLE
MATERIAL
iron oxide,
iron metal,
steel
calcium
carbonate
aluminum metal,
aluminum oxide
talc
Ref: MA21600
TABLE VI
Cluster Analysis Results for Tape Lift Sample
from Position l on Parabola Mirror Surface
SAMPLE : PI
NO. OF PARTICLES: 221
CLUSTER CODE
3,25
23
2
6
17
22
PERCENT NUMBER
OF PARTICLES
12
9
8
8
8
6
ELEMENTAL
COMPOSITION
Al, Si, Ca
Ca, S
Fe
Mg, Si
Ca
Na, Cl
POSSIBLE
MATERIAL
aluminosilicate
minerals
calcium sulfate
iron oxide,
iron metal,
steel
talc
calcium
carbonate
salt
Ref: MA21600
TABLE VII
Cluster Analysis Results for Tape Lift Sample
from Position 8 on Hyperbola Mirror Surface
SAMPLE : H8
NO. OF PARTICLES: 349
CLUSTER CODE
1
17
6
3
29
PERCENT NUMBER
OF PARTICLES
54
8
7
7
7
ELEMENTAL
COMPOSITION
Na, Cl
Cu, Zn
Mg, Si
Fe
Ce
POSSIBLE
MATERIAL
salt
brass
talc
iron oxide,
iron metal,
steel
cerium oxide
Ref: MA21600
APPENDIX B
Figures
NUMBER OF OBSERVATIONS:
75+
15+
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0.000 20.000
AD
Average Particle Diameter (jura)
FIGURE 1
Tape lift sample PI,
NUMBER OF OBSERVATIONS:
50 +
40 +
30 +
20+**
**
**
* *
* *
**
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0.000
l-l-l-l •I—I—I —I —I--I
20.000
AD
Average Particle Diameter (/zm)
FIGURE 2
Tape lift sample P4
NUMBER OF OBSERVATIONS:
25 +
20+**
**
**
**
**
**
**
**
**
**
15 + **
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0.000
-I—I—I —I--I
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Average Particle Diameter
FIGURE 3
Tape lift sample P8
_
NUMBER OF OBSERVATIONS:
50 +
40+
30 +
**
**
* *
**
**
I **
20+**
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--I--I--I-I--I--I-I-I-I-I-I--I-I--I-I--I-I-
0.000 20.000
AD
Average Particle Diameter (/im)
FIGURE 4
Tape lift sample P9.
NUMBER OF OBSERVATIONS:
50 +
40+
**
**
**
**
**
**
** **
30+** **
** **
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** * *
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** **
I — I — I-
20.0000.000
AD
Average Particle Diameter (/ra)
FIGURE 5
Tape lift sample HI.
NUMBER OF OBSERVATIONS:
10 +
8-
6-
4
2-
* *
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A A
A A
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I 1 1 I 1 1 _ I _ 1 I 1 I 1 ' I
1 1 1 1 1 1 1 1 1 1 1 1 1
0.000 20.000
AD
Average Particle Diameter (;ra)
FIGURE 6
Tape lift sample H5,
NUMBED OF OBSERVATIONS:
200-*-
160-
120
80-
40
(
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— i i i i i i i i i i I I I - I I I I I
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AD
Average Particle Diameter
FIGURE 7
Tape lift sample H8
NUMBER OF OBSERVATIONS:
5 +
4 +
3 +
2+**
**
**
**
**
**
A A
**
**
A A
1 + **
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I I — I —I —I'
AD
0.000 20.000
Average Particle Diameter
FIGURE 8
Tape lift sample H9
N/\SA Report Documentation Page
1, RcQort No 2. snNo. 3. R«cip*m't Cmiog No.
4. TH* Mid Subtrtfc
ANALYSIS OF PARTICULATE CONTAMINATION ON TAPE LIFT
SAMPLES FROM THE VETA OPTICAL SURFACES
S. floport Octt
• February 1992
6. P0rlo«n<ng OtQtnuRJon Code
7. Autho/UI
Mark S. German!, Ph.D.
Principal Investigator
B. pariorfning Oio^ nuation fUport No.
MA21600FR
10. Wort Unit No.
N*n* «nd A&fcvu
McCrone Associates, Inc.
850 Pasquinelli Drive
Westmont, IL 60559
11. Contact or Grtft< No.
"H-11942D
t3, Typa of fUport ttd Ps^od Cov«r«d
12. S Ag«ncv
14, Spoftforing Agency Coov
15.
18.
Automated electron microprobe ana-lyses of particulate contamination on
tape lift samples from the VETA optical surfaces. This 'report details
the individual particle analyses and describes the contaminant particles
on the hyperbola and parabola mirror surfaces .
ORIGINAL PAGE
OF POOR QUALm
17. K«v Woro* ISuggMUd by
VETA
particle contamination
mirror surfaces
18. Distribution SUtamem
Unclassified - Unlimited
I
19. S*rutitV
Unclassified
20. S*cumy CtMti. (oi tfta p«g«|
Unclassified
21. No. at p<ou
25
22. Prica


Analysis of particulate contamination on tape lift samples from the VETA optical surfaces

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