NASA / TM-2003-212345 

Dwell Time and Surface Parameter Effects 

on Removal of Silicone Oil From D6ac 

Steel Using TCA 

R.E. Boothe 

Marshall Space Flight Center, Marshall Space Flight Center, Alabama 

I 

I 

April 2003 

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NASA / TM-2003-212345 

Dwell Time and Surface Parameter Effects 

on Removal of Silicone Oil From D6ac 

Steel Using TCA 

R.E. Boothe 

Marshall Space Flight Center, Marshall Space Flight Center, Alabama 

National Aeronautics and 

Space Administration 

Marshall Space Flight Center MSFC, Alabama 35812 

I 

I 

April 2003 
Acknowledgments 

NASA Center for Aerospace Information 

7 12 1 Standard Drive 

Hanover, MD 2 1076-1 320 

(301) 621-0390 

The author gratefully acknowledges the contributions of DeWitt Bums, Environmental Effects Group, Materials 

and Processes Department, Marshall Space Flight Center. The author also wishes to thank Ode11 Huddleston 

and Russell Hamlin of ATWThiokol, Huntsville Division, for preparation of the test articles. 

Available from: 

National Technical Information Service 

5285 Port Royal Road 

Springfield, VA 22 16 1 

(703) 4874650 

.. 

11 
TABLE OF CONTENTS 

1 . INTRODUCTION .......................................................................................................................... 1 

2 . TEST DESCRIPTION .................................................................................................................... 2 

3 . TEST RESULTS ............................................................................................................................. 5 

4 . CONCLUSIONS ............................................................................................................................ 17 

... 

111 
LIST OF FIGURES 

1. 

~ 2- 

3. 

Process flow for grit-blasted substrate ................................................................................ 3 

Process flow for polished substrate ............ ...... .. ...... ... .. .. .. ..... ...... .. .. ............... ..... ......... .. .. .. 4 

Analysis results of cleanliness verification of polished coupons prior 

to silicone application ...... .............. .. .......... ........ .. ... . .. ... .... .. ..... .. ........ ..... .......... .. .. .. .. .. .. .. .... 5 

4. Analysis results of cleanliness verification of grit-blasted coupons immediately 

after blasting prior to silicone application .. ... .......... ... ..... .... .......... .......... .............. ... ..... .. .... 6 

5. Analysis results of grit-blasted coupons Nos. 1 and 2 immediately following 

silicone application . .. ...... ... .. .. .. .. ....... ... .. . .. ... ... .. ... .. .... .... .. .. ..... .. .... ...... .... . ......... .. ........ ....... . 7 

6. Analysis results of polished coupons Nos. 1 and 2 immediately following 

silicone application ..... . . . . . . . . . . . . . . . . . . . .. . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 

7. Analysis results of complete silicone removal from polished coupon No. 1 

after 24-hr staging ............................................................................................................... 9 

8. Analysis results of incomplete silicone removal from grit-blasted coupon 

No. 1 after 24-hr staging ..................................................................................................... 10 

9. Analysis results of grit-blasted coupon No. 1 following additional processing .. . .. . .. ..... .... 11 

10. Analysis results of complete silicone removal from polished coupon No. 2 

after 1-wk staging ................................................................................................................ 12 

11. Analysis results of incomplete silicone removal from grit-blasted coupon 

No. 2 after 1-wk staging ...................................................................................................... 13 

12. Analysis results of grit-blasted coupons Nos. 3 and 4 immediately following 

silicone application .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 

Analysis results of incomplete silicone removal from grit-blasted coupon 

No. 3 after 24-hr staging ..................................................................................................... 13. 

15 

Analysis results of incomplete silicone removal from grit-blasted coupon 

No. 4 after 1-wk staging ...................................................................................................... 14. 

16 

iv 
1. 

2. 

LIST OF TABLES 

Test matrix ............................................................................................................................. 2 

Test article surface roughness ............................................................................................... 7 

V 
TECHNICAL MEMORANDUM 

DWELL TIME AND SURFACE PARAMETER EFFECTS ON REMOVAL OF SILICONE OIL 

FROM D6AC STEEL USING TCA 

1. INTRODUCTION 

Although silicone oil is considered to be one of the most difficult contaminants to remove from 

a surface, not much is known regarding factors that influence the ability to perform a successful cleaning 

operation. This study was conducted to evaluate the impact of dwell time, surface roughness, and surface 

activation state on l,l, 1-trichloroethane's (TCA's) effectiveness for removing silicone oil from D6ac 

steel. Silicone-contaminated test articles were washed with TCA solvent, and then the surfaces were 

analyzed for residue using Fourier transform infrared (FT-IR) analysis spectroscopy. 
2. TEST DESCRIPTION 

The test matrix is summarized in table 1. Surface roughness extremes from polished to grit 

blasted were evaluated. Silicone dwell times prior to TCA cleaning were 24 hr or 1 wk. The silicone was 

applied either when the surface was activated, meaning the oxidation growth was rapid due to recent grit 

blasting, or passivated, meaning the oxidation growth was minimal. Figures 1 and 2 show the test sample 

process flow. Control samples not contaminated with silicone but stored in a manner consistent with 

silicone-coated coupons were included. 

The dimensions of the D6ac steel test coupons were 2 by 3 by 0.25 in. The polished coupons 

were readied for use by processing through a surface grinder to achieve a smooth finish, and then by 

soaking in chloroform to remove the cutting oil. The rough coupons were prepared by soaking in chloroform and then grit blasting. Activated D6ac coupons were grit blasted =1 hr prior to the silicone application, while passivated coupons were grit blasted 1 wk prior to the silicone application. 

The test articles were contaminated with 1 ,OOO centistokes viscosity Dow Corning 200 silicone 

oil, using a Sono-Tek ultrasonic spray application system. The carrier solvent was TCA, and the coating 

levels ranged from 11 to 13 pg/cm2. The FT-IR analysis was performed using an FT-IR analysis spectrometer manufactured by Surface Optics Corporation, San Diego, CA-the SOC-400 spectrometerfitted with a specular (polished coupons) or diffuse (grit-blasted coupons) reflectance accessory. 

Analysis parameters were 32 scans per spectrum at a resolution of 4 cm-l, noncontact mode, and five 

data points per coupon. The silicone methyl absorbance at ~1,260 cm-l was monitored. The estimated 

detection limits for silicone using these parameters were 0.2-0.3 pg/cm2 for grit-blasted surfaces and 

0.1-0.2 pglcm2 for polished surfaces. 

Table 1. Test matrix. 

6 

*Within 1 

Surtace Roughness 

Silicone Dwell 

Time Prior to 

TCA Wash 

ir after completion of grit blast 

Silicone Application Delay 

Time After Grit Blast 

X 

X 

X 

X 

2 
1 5 coupons 

t 

t I Ra 

t I FT-IR 

b + 

1 

I Grit Blast 1 

I 

+ + 4 

-- Silicone $Ail 

,T,T 

Flush 

Wait 1 Wk 

I I 4 I Silicone 

Silicone Silicone 

Flush 

FT-IR Flush 

FT- I R 

Immediately Apply Silicone (Within 1-2 hr, Target) 

1 Day=24hr+6hr 

1 Wk = 7 Days f 1 Day 

Figure 1. Process flow for grit-blasted substrate. 

3 
Silicone 

Flush 

Ff-IR 

No Silicone I Control- I 

Monitor Via I FT-IR I 

Immediately Apply Silicone (Within 1-2 hr, Target) 

1 Day=24hr+6hr 

1 Wk = 7 Days + 1 Day 

Figure 2. Process flow for polished substrate. 
3. TEST RESULTS 

Figures 3 and 4 summarize FT-IR baseline analysis results for the test coupons. No contamination was detected prior to silicone application. 

0- 

1 . 0.005 - 

0- 

0.005 ’ 

0- 

0.005 - (d) 

0 u-w T1 .- -0.005 1 I 1 I I I I 

4,000 3,500 3,000 2,500 2,000 1,500 1,000 

Wave Numbers (cm-1) 

The absorbance @ 1,230 cm-1 was due to oxide. The oxide was not expected to interfere with detection 

of the 1,260 cm-1 absorbance of Dow 200 silicone. Baselines for the average of five spectra: 

(a) Coupon No. 1 

(b) Coupon No. 2 

(c) Coupon No. 3 

(d) Coupon No. 4 

Figure 3. Analysis results of cleanliness verification of polished coupons 

prior to silicone application. 

5 
. .. 

0 \ 

0 -- 

0 -- 

0 

0.02 - (d) 

0.02 -(e) 

-- I I I I 1 I 

3,500 3,000 2,500 2,000 1,500 1,000 

Wave Numbers (em-1) 

The absorbance @I 900 cm-’ was due to oxide. The oxide was not expected to interfere with detection 

of the 1,260 cm-1 absorbance of Dow 200 silicone. Baselines for average of five spectra: 

(a) Coupon No. 1 

(b) Coupon No. 2 

(c) Coupon No. 3 

(d) Coupon No. 4 

(e) Coupon No. 5 

Figure 4. Analysis results of cleanliness verification of grit-blasted 

coupons immediately after blasting prior to silicone 

application. 

Coupon surface roughness characteristics are summarized in table 2. Average surface roughness 

(Ra) in microinch values for the polished coupons ranged from 22 to 23 pin, while average Ra values for 

the grit-blasted coupons ranged from 91 to 102 pin. 

Grit-blasted coupons Nos. 1 and 2 (activated) and polished coupons Nos. 1 and 2 were processed 

through the Sono-Tek ultrasonic spray application system, concurrently. The silicone coating level 

applied to these coupons was approximately 1&11 pg/cm2 (figs. 5 and 6). The contaminant was visible 

to the unaided eye on the grit-blasted coupons and appeared as tiny “islands” on the surface. The oil was 

not easily observed on the polished test articles. 

6 
Table 2. Test article surface roughness. 

Measurement 1 Measurement 2 

27 23 

19 20 

29 24 

20 21 

97 98 

83 92 

92 105 

101 85 

110 96 

I 1 Ra (pin) 

Measurement 3 

20 

28 

21 

24 

97 

109 

86 

118 

83 

coupon 

Polished No. 1 

Polished No. 2 

Polished No. 3 

Polished No. 4 

Blasted No. 1 

Blasted No. 2 

Blasted No. 3 

Blasted No. 4 

Blasted No. 5 

Measurement 4 Measurement 5 

24 23 

22 22 

21 19 

23 29 

89 112 

78 81 

87 84 

110 98 

98 101 

Average 

23 

22 

23 

23 

99 

93 

91 

102 

98 

0.025 - 

0.020 - 

0.01 5 - 

0.01 0 - 

-0.005 - 0.030- 

0.020 - 

0.01 0 - 

3,500 3,000 2,500 2,000 1,500 1,000 

Wave Numbers (cm-1) 

(b) 

Baselines for the average of five spectra: 

(a) Coupon No. 1, 1,260 Ht = 0.0194 AU 

(b) Coupon No. 2, 1,260 Ht = 0.0197 AU 

Figure 5. Analysis results of grit-blasted coupons Nos. 1 and 2 immediately 

following silicone application. 

7 
0.030 - 

0.020 - 

0.010 - 

Figure 6. Analysis results of polished coupons Nos. 1 and 2 immediately following 

silicone application. 

(b) n I 

8 
Grit-blasted coupon No. 1 and polished coupon No. 1 were reexamined with the FT-IR =24 hr 

after the silicone application and were found to be unchanged. The silicone “islands” on the grit-blasted 

sample had become slightly less distinct, but the average 1,260 cm-l magnitude was identical to zero 

time. Following FT-IR analysis, the two coupons were rinsed with TCA solvent in an attempt to remove 

the silicone. As shown in figure 7, the silicone was completely removed (below the detection limit of the 

FT-IR) from the polished coupon. As shown in figures 8 and 9, the silicone was not completely removed 

from the grit-blasted coupon, even after two flushing operations with TCA, a third operation where the 

coupon was rubbed with TCA-wetted Rymple cloth, and a final process where the TCA-wetted surface 

was scrubbed with a brush. The final silicone level for the grit-blasted coupon was =I pglcm2. 

0.010 

Y 

0.020 

r0.01 0 

0 

0.020 

0.010 

0 

0.004 

0.002 

0 

-0.002 

1,500 1,400 1,300 1,200 1,100 1,000 900 800 700 

Wave Numbers (cm-1) 

Baselines for the average of five spectra: 

(a) Immediately prior to silicone application 

(b) Immediately following silicone application (10 mg/ft2) 

(c) 24-hr following silicone application and immediately prior to TCA flush 

(d) After initial attempt to remove 10 mg of silicone by flushing with TCA; all four silicone 

absorbencies removed 

Figure 7. Analysis results of complete silicone removal from polished 

coupon No. 1 after 24-hr staging. 

9 
0.010 4 J\ /I 

0.01 0 

0.006 

0.004 

0.002 

1,450 1,400 1,350 1,300 1,250 1,200 1,150 

Wave Numbers (cm-1) 

Baselines for the average of five spectra: 

(a) Immediately after blasting and prior to silicone application 

(b) Immediately following silicone application 

(c) 24 hr after silicone application 

(d) Following initial TCA tlush 

Figure 8. Analysis results of incomplete silicone removal from gritblasted coupon No. 1 after 24-hr staging. 

10 
0.004 - (a) 

0.002 -/ 

0- 

0.004 - (b) 

0.002 - 

0 -’ 

0.004 - 

0.002 -- 

0.004 

0.002 - 

0- 

-@- 

I I I I I I I I I I I 

1,360 1,340 1,320 1,300 1,280 1,260 1,240 1,220 1,200 1,180 1,160 

Wave Numbers (em-’) 

Baselines for the average of five spectra: 

(a) Following initial flush with TCA 

(b) Following second flush with TCA 

(c) Following two flushes with TCA and one wiping operation with TCA-wetted Rymple cloth 

(d) Following two flushes with TCA, one wiping operation with TCA-wetted Rymple cloth, and one 

scrubbing operation with TCA and a brush 

Figure 9. Analysis results of grit-blasted coupon No. 1 following 

additional processing. 

11 
One week after silicone had been applied, polished coupon No. 2 and grit-blasted coupon No. 2 

(activated) were reanalyzed using FT-IR to determine if the 1,260 cm-l absorbance intensity had 

changed relative to the initial inspection. Although the average 1,260-cm-' absorbance intensity 

remained unchanged for both test articles, the silicone on the grit-blasted coupon had spread to almost a 

uniform level across the surface. Figure 10 shows that the silicone was completely removed (below the 

detection limit of the FT-IR) from the polished coupon by rinsing with TCA. Figure 11 shows that the 

oil could not be completely removed from the grit-blasted coupon, even when the surface was rubbed 

with TCA-wetted Rymple cloth. The level of silicone remaining on the grit-blasted coupon was estimated at 1.5-2.5 pg/cm2. 

0.035 

0.030 

0.025 

0.020 

0.015 

0.010 

0.005 

0 

0.003 

0.002 

0.001 

0 

-0.001 

-0.002 

1,400 1,300 1,200 1,100 1,000 900 800 

Wave Numbers (em-') 

Baselines for the average of five spectra: 

(a) Immediately prior to TCA flush 

(b) Following flush with TCA; all four silicone absorbencies removed 

Figure 10. Analysis results of complete silicone removal from polished 

coupon No. 2 after 1-wk staging. 
0.020 - 0.010 - 

0.020 - 

0 

0.010 - 

0 

0.020 - (c) 

(a) 

..). 

(b) 

0.010 - 

0 

0.020 - (c) 

0.010 - 

0.020 - 

0 -- 

(d) 

0.01 0 

OY 

3,500 3,000 2,500 2,000 1,500 1,000 

Wave Numbers (em-1) 

Baselines for the average of five spectra: 

(a) Immediately prior to initial TCA rinse 

(b) After initial TCA rinse 

(c) Following second rinse with TCA 

(d) Following second rinse with TCA, then one rubbing with TCA-wetted Rymple cloth 

Figure 1 1. Analysis results of incomplete silicone removal from gritblasted coupon No. 2 after 1-wk staging. 

13 
I Grit-blasted coupons Nos. 3 and 4, which were allowed to oxidize for 1 wk, were contaminated 

~ 

with =13 pg/cm2 of silicone (fig. 12). 

0.025 - 0.020 - 0.015 - 

(a) 

0.010 

0.005 

0 

0.030 

0.025 

0.020 

0.01 5 

0.010 - 0.005 - 

0- 

-0.005 - I I I I I I 

3,500 3,000 2,500 2,000 1,500 1,000 

Wave Numbers (em-’) 

Baselines for the average of five spectra: 

(a) Coupon No. 3,1,260 cm-1 = 0.024 AU 

(b) Coupon No. 4, 1,260 cm-1 = 0.0237 AU 

Figure 12. Analysis results of grit-blasted coupons Nos. 3 and 4 

immediately following silicone application. 

14 
Coupon No. 3 was reanalyzed with FT-IR after 24 hr and was found to be unchanged with 

respect to the average 1,260 cm-l absorbance intensity. As illustrated in figure 13, attempts to remove 

silicone from this coupon using two TCA flushes were unsuccessful. The quantity of silicone remaining 

on the coupon was estimated to be 0.5-1 pg/cm2. 

0.025 

0.020 - (a) 

1,450 1,400 1,350 1,300 1,250 1,200 

Wave Numbers (cm-1) 

Baselines for the average of five specta: 

(a) 24 hr after silicone application 

(b) Following initial flush with TCA 

(c) Following second flush with TCA 

Figure 13. Analysis results of incomplete silicone removal from gritblasted coupon No. 3 after 24-hr staging. 

15 

I 

I 
Coupon No. 4 was reanalyzed with FT-IR after 1 wk and was found to be unchanged with respect 

to the average 1,260 cm-l absorbance intensity. As illustrated in figure 14, attempts to remove silicone 

from this coupon using two TCA flushes were also unsuccessful. The quantity of silicone remaining on 

the coupon was estimated to be 1 pglcm2. 

0.002 

0 

0.020 

0.01 0 

0 

0.020 

0.01 0 

0 

0.006 

0.004 

0.002 

0 

1,450 1,400 1,350 1,300 1,250 1,200 1,150 

Wave Numbers (cm-1) 

Baselines for the average of five spectra: 

(a) Immediately prior to silicone application 

(b) Immediately after silicone application 

(c) 1 wk after silicone application 

(d) Following two flushing operations with TCA 

Figure 14. Analysis results of incomplete silicone removal from gritblasted coupon No. 4 after 1-wk staging. 

16 
4. CONCLUSIONS 

The predominant factor affecting the ability to remove the silicone oil from D6ac steel by rinsing 

with TCA was surface roughness. Even with scrubbing, the oil could not be completely removed from 

grit-blasted test articles. The silicone was successfully washed from polished test articles after dwell 

times of up to 1 wk. The surface activation state did not appear to be important. 
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April 2003 Technical Memorandum 

t. TITLE AND SUBTITLE 

Dwell Time and Surface Parameter Effects on Removal of Silicone 

Oil From D6ac Steel Using TCA 

5. FUNDING NUMBERS 

5. AUTHORS 

R.E. Boothe 

14. SUBJECT TERMS 

Fourier transform infrared spectroscopy, silicone oil 

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13. ABSTRACT (Maximum 200 words) 

This study was conducted to evaluate the impact of dwell time, surface roughness, and the surface 

activation state on l,l, 1-trichloroethane's (TCA's) effectiveness for removing silicone oil from 

D6ac steel. Silicone-contaminated test articles were washed with TCA solvent, and then the surfaces were analyzed for residue, using Fourier transform infrared spectroscopy. The predominant 

factor affecting the ability to remove the silicone oil was surface roughness.