溶融シアン化ナトリウムの分解反応と窒化能

Abstract

There are many reports on practical problems about the case-hardening of iron and steel by nitriding in fused salts, but there are some unknown points about the mechanism of the reaction of salts and others. In this paper the changes in compositions of pure fused sodium cyanide (NaCN) and cyanate (NaCNO) salts were investigated during heating at 575°C in oxygen or argon atmosphere by means of chemical analysis of the remaining cyanide. Also, the amount of sodium carbonate (Na2CO3) was measured by the gas-chromatographic technique. On the basis of the obtained results, an attempt was made to clarify the behavior of decomposition of the fused salts and also to correlate it with its nitriding effect for steel.The results gained are as follows:(1) NaCNO was decomposed in accordance with the following reaction:(This article is not displayable. Please see full text pdf.) \ oindentIf pieces of iron exist in the salt, the disappearing decomposition rate of NaCNO was accelerated several hundred times. In this case the nitriding of steel can be performed most effectively, because the above reaction (\ efeq1) proceeds on the surface of steel and active nitrogen is much available for that use.(2) With the blow of oxygen gas the following reaction becomes predominant:(This article is not displayable. Please see full text pdf.) \ oindentNevertheless, its nitriding effect is not so strong.(3) The reaction from NaCN to Na2CO3 seems to be a so-called consecutive process producing NaCNO salt as an intermediate product.(4) As the estimation of the nitriding effect is possible from the measurement of CO2 gas evolved during the reaction, the gas-chromatographic technique would be useful to study the reaction in this case.