Chromium Boride, CrB

Chromium Boride, CrB, was extracted from an alloy containing 16 per cent, of boron by the action of hydrochloric acid or chlorine below red heat. It contains 17.4 per cent, of boron, and represents the limit of saturation of chromium by boron. It is non-crystalline, of density 61 at 15° C., and hard enough to scratch glass or quartz. It is attacked by hydrochloric, hydrofluoric, or sulphuric acid, yielding boric acid; nitric acid and alkaline solutions have no action upon it; chlorine decomposes it with incandescence, forming chromous and chromic chlorides; hydrochloric acid acts similarly at red heat, evolving hydrogen; fused alkalies cause oxidation with incandescence. it burns spontaneously in fluorine, and, when heated to a white heat in nitrogen, it yields a greyish-black substance which, with fused potassium hydroxide, gives off ammonia.

A boride of very different properties, but to which the same composition is assigned, has been obtained as a silver-white crystalline powder by the alumino-thermic method, the chromium thermite being caused to react with boron, and excess of chromium being removed from the product by successively washing with dilute hydrochloric acid, nitric acid, and aqua regia. The pure boride had a density of 5.4 at 17° C., and hardness 8. It was unattacked by acids, even hydrofluoric acid, and only slightly attacked by fused sodium hydroxide, potassium nitrate, or potassium chlorate; sodium peroxide oxidised it with incandescence, forming borate and chromate. It possessed weak magnetic properties.