A Means of Increasing the Oxidation Resistance of Diamond

Abstract

IN the search for techniques by which to determine small amounts (0.01–1 per cent) of light-atom impurities in laboratory-prepared diamond¹, we have attempted to use strongly oxidizing melts and combustion in oxygen to destroy the host. Useful results for the carbon-13 distribution in undoped diamonds² have already been obtained by the direct combustion technique. However, straightforward combustion in oxygen did not produce complete oxidation of boron-doped diamonds. Microscopic examination of the incompletely burned diamonds and their behaviour toward alkali suggested that the residue was covered with a layer of boric oxide, which, being continuous and of low vapour pressure, inhibited further attack of oxygen on the diamond. Complete oxidation of the sample could be achieved only by alternately heating the sample at 800° C in oxygen and washing the residue in the platinum boat with successive portions of 1 N sodium hydroxide and water. The boric oxide that was removed from the diamond surface by these washing steps was determined by potentiometric alkalimetric titration of the borate in the combined wash solutions.