Preparation of alkali metal hydrides by mechanical alloying

Rubidium and cesium hydrides are not commercialized and we have set up, a f ew years ago, a method of synthesis at the laboratory scale. It is based on the reaction of alkali metal with hydrogen obtained by thermal decompositi on of uranium hydride UH, at a temperature of 450 degreesC, which gives a p ressure of hydrogen close to 3 bars. This synthesis leads to a very pure al kali 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 alloy ing, consists in milling the alkali metal, at room temperature, under a pre ssure 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. (C) 2 001 Elsevier Science BY All rights reserved.