Study on the determination of alumina in aluminium (M. T. Method)

Abstract

It has been reported by Mr. M. Taurnaire on the analytical method of alumina in aluminium by means of separating alumina from aluminium with dilute hydrochloric acid solution.This method is quite simple in operation and can easily applied to the routine analysis work in plants. But, it is considered that the accuracy in this method is not very good because alumina is solved into dilute hydrochloric acid, though slightly.In this connection, the authors have investigated on the solubility of alumina when treated with dilute hydrochloric acid solution by the M. T. method, and on how to opperate the analysis in this method.The findings are summed up as follows:1. The solubility of alumina in dilute hydrochloric acid solution.(1) The solubility of alumina in dilute hydrochloric acid solution decreases with the increase in calcination temperature of alumina.(2) The solubility of alumina increases with the increase in the concentration of hydrochloric acid.(3) The solubility of alumina increases slightly with the increase in standing time after the addition of hydrochloric acid.(4) The temperature of solution is very important. The solubility of alumina increases as the temperature of solution is raised within the range of room temperature. It is especially increased when the temperature of solution is raised to about 40°C. To keep the accuracy of this method, therefore, it must be essential to keep the temperature of solution below room temperature.(5) Amounts of alumina and volume of solution have no effect on the solubility of alumina.2. Others(1) The surface oxide of sample should be removed by use of sodium hydroxide solution and dilute nitric acid solution.(2) For washing out the solution of absorbed aluminium from filter paper, 0.1 N hydrochloric acid and hot water are suitable.(3) In the process of hydrofluoric acid-sulfuric acid treatment, metallic silicon, if present, can be volatized by the addition of few drops of nitric acid.