DERIVATOGRAPHIC INVESTIGATION OF LOW-TEMPERATURE OXIDATION OF POWDERED METALS

摘要

The process of oxidation upon heating in open air of powders of copper and iron with mean particle diameter 23.0 and 4.5 mu m, respectively, is investigated by means of derivatography. Samples in the form of briquettes with porosity 25-51 vol.- percent were heated to temperatures up to 0.32T_(melt) of the particular metal, 250 or 300 deg C for copper and 300 or 500 deg C for iron. The oxidation kinetics in isothermal holding as well in low continuous heating to a given temperature was studied. A parabolic dependence of the thickness of the layer of scale on the length of the isothermal holding period was established. A growth in the rate of oxidation with increasing porosity of the briquettes was found in several independent experiments. The parameters of the temperature dependence of the oxidation rate constant were established by means of dynamic thermogravimetry. From the results of a measurement of the specific electric resistance the proportion of the contact surface in a cross section of the iron briquettes before and after oxidation was calculated and found to be at most 2 percent, demonstrating the presence in these briquettes of open porosity and that calculations carried out by assuming that a layer of oxides forms on each particle are correct.