Preparation of alkali metal hydrides by mechanical alloying

Abstract Rubidium and cesium hydrides are not commercialized and we have set up, a few years ago, a method of synthesis at the laboratory scale. It is based on the reaction of alkali metal with hydrogen obtained by thermal decomposition of uranium hydride UH3 at a temperature of 450°C, which gives a pressure of hydrogen close to 3 bars. This synthesis leads to a very pure alkali metal hydride MH, but the rate of the reaction remains quite small: a few hundreds of milligrams in 24 h. A new method, based on mechanical alloying, consists in milling the alkali metal, at room temperature, under a pressure of hydrogen close to 5 bars. The reaction proceeds in 16 h and gives 3–15 g of very pure MH (from sodium to cesium, respectively) at once.