Incoloy 800, aluminized coke deposits

A second finding is that the morphology of the coke deposited on aluminized Incoloy 800 and Incoloy 800 surfaces often was quite different. As depicted in Figures 2B, 2D, 2F, 4D, 4F, 5B> 6B, and 8B> the predominant structure of the coke observed on aluminized surfaces tended to be either a film of tar or a globular coke deposit. Filamentous coke was found on numerous Incoloy 800 samples (Figures 2A, 2C> 2E, 3B> 5C-5F, 7A, and 70 whereas filamentous coke was detected at most in only small amounts on the aluminized surfaces of only three runs (Figures 2F, 7B, and 7D). Third, EDAX analyses indicated appreciable metal, generally mainly iron and nickel, in the coke formed on (or brushed off) the Incoloy 800 surfaces analyses of coke deposited on aluminized Incoloy 800 coupons in the same runs indicated trace amounts of aluminum but no detectable iron, nickel, or chromium. 

Surface heterogeneities described earlier often were important relative to coke formed or deposited on aluminized Incoloy 800 surfaces. Figures SB, 6B, and 10B show globular and cylindrical coke which resulted preferentially in the pitted areas of aluminized surfaces in several runs. Filamentous coke formed at 700 C on an aluminized Incoloy 800 coupon subjected to a 0.05 atm. acetylene feed is depicted in Figure 7D every filament observed was in or near a pitted area but interestingly not every pitted area contained filaments. 

In a second recoking run at 800°C, used iDcoloy 800 and aluminized Incoloy 800 surfaces were positioned side by side near the furnace midpoint and subjected to 0.05 atm. acetylene. Two additional coupons were included a second used Incoloy 800 coupon was placed beside a new Incoloy 800 coupon at a position that was 5 cm. upstream of the furnace midpoint. About 27% more coke formed on this second used coupon than on the new coupon beside it as indicated in Table III. Analogously the amount of coke deposited on the aluminized Incoloy 800 coupon in the recoking was 67% greater than the amount deposited in the initial coking run. However the amount of coke formed on the used Incoloy 800 coupon near the midpoint was 17% less than the amount formed in the initial coking run. 

The results of this investigation help clarify why machining is beneficial relative to coke formation rough areas on the surface act as excellent collection sites for coke or tar droplets formed in the gas phase. Such tar droplets eventually become globular coke. Smoother surfaces hence minimize such collection or surface deposits. In addition. smoothing or polishing of both Incoloy 800 and aluminized... 

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