Carburization of Iron by Ar-CO-H2 at 1523 K.

Abstract

The rate of carburization of iron in Ar-50%CO-10%H 2 gas mixture at 1 523 K have been gravimetrically investigated. It is found that the Ar-CO-H 2 system carburizes faster than Ar-CO, because H 2 combines faster with adsorbed oxygen than does CO. Based on the established results of H 2 O and CO 2 dissociation rate, the rate constant (k 3 ) of the recombination reaction of H 2 and adsorbed oxygen (O ad ) is calculated. It was found that k 3 is about 37.5 times larger than that (k 1 ) of CO and O ad , while the measured k 3 in the present study is only 2.5 times larger than k 1 . With the increase of carbon content, the corresponding equilibrium pH 2 O * at the reacting surface of Fe-C melt becomes sufficiently small. Accordingly the produced H 2 O easily reaches to the equilibrium pressure of pH 2 O * due to the very fast recombination reaction of the H 2 and Oad. This is the reason that the addition of H 2 has small contribution to the overall carburization reaction after liquid phase is formed. Take into account the effect of the produced H 2 O, rate of carburization (v) in CO-H 2 atmospheres is given by the equation: v = k 1 pCOθ 0 +k 3 pH 2 θ 0 (1 -pH 2 O/pH 2 O * ), where θ 0 is the fractional coverage by adsorbed oxygen, pH 2 O is the partial pressure of formed H 2 O at the interface.