Carburization of Iron by Ar–CO–H2 at 1523 K
Rei Asano, Yasushi Sasaki, Kuniyoshi Ishii
The rate of carburization of iron in Ar–50%CO–10%H2 gas mixture at 1523 K have been gravimetrically investigated. It is found that the Ar–CO–H2 system carburizes faster than Ar–CO, because H2 combines faster with adsorbed oxygen than does CO. Based on the established results of H2O and CO2 dissociation rate, the rate constant (k3) of the recombination reaction of H2 and adsorbed oxygen (Oad) is calculated. It was found that k3 is about 37.5 times larger than that (k1 ) of CO and Oad, while the measured k3 in the presentstudy is only2.5 times larger than k1. With the increase of carbon content, the corresponding equilibrium pH2O* at the reacting surface of Fe–C melt becomes sufficiently small. Accordingly the produced H2O easily reaches to the equilibrium pressure of pH2O* due to the very fast recombination reaction of the H2 and Oad. This is the reason that the addition of H2 has small contribution to the overall carburization reaction after liquid phase is formed. Take into account the effect of the produced H2O, rate of carburization (v) in CO–H2 atmospheres is given by the equation: v=k1pCO q0 + k3pH2q0(1–pH2O/pH2O*), where q<0 is the fractional coverage by adsorbed oxygen, pH2O is the partial pressure of formed H2O at the interface.
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