150

Figure 4. Deposition Characteristics of

Figure 4. Deposition Characteristics of

1.55 Percent TCP Vapor in Nitrogen on Quartz

From 600°C to 800°C, the constant deposition rate at each temperature studied indicates that the quarts substrate is noncatalytic for this deposition reaction. The deposition rate as shown in Figure 4 appears to be linear with TCP concentration, indicating the coating formation mechanism is first-order on quartz substrate. The SEM micrographs of a quartz wire and a coated wire surface show the morphology of the coating on quartz to be a smooth granular surface.

100 r

Figure 5. Deposition Characteristics of

1.55 Percent TCP Vapor in Nitrogen on Stainless Steel

Figure 5. Deposition Characteristics of

1.55 Percent TCP Vapor in Nitrogen on Stainless Steel

Deposition studies of TCP vapors on a 316 stainless steel substrate have also been evaluated. The major alloying elements in stainless steel are nickel and chromium. Both of these are corrosion resistant, and have been found to be relatively noncatalytic for the deposition of TCP vapors. Iron appears to be mainly responsible for the catalytic nature of the coating formation. TCP vapor phase deposition data as a function of temperature is shown on Figure 5. The high initial deposit rate, compared with the rate after five minutes, indicates that the stainless steel surface exerts a strong catalytic effect which diminishes rapidly when iron can no longer affect the deposition. The mechanism by which the iron from the stainless steel migrates to the surface coating is currently under study. The effect of temperature on the initial (catalytic) rate and on the final (noncatalytic) rate is significant over the 500 to 800 C temperature range shown. These tests are for a concentration of 1.55 percent TCP in the nitrogen carrier gas. The effects of TCP concentration and iron catalysts at 700 C deposition temperature are shown in Figure 6. The initial catalytic rates based on 2 to 5 second deposit tests are shown on Figure 7. A concentration range of two orders of magnitude are covered in this study. The initial rates appear to be linear, with concentration over the range of 0.016 percent to 0.125 percent TCP in the carrier gas. It appears that the high rate of deposit for the 1.55 percent TCP may already influence the catalytic effect of iron by obscuring the iron from the surface of the coating even at the shortest test feasible with this system. These data do show that after a short catalytic effect from iron the rates of

100 r

Figure 6.

Figure 6.

Deposit Characteristics of TCP Vapor in Nitrogen on Stainless Steel at 700 C as a Function Vapor Concentration

0 0

Post a comment