Aluminium Arsenide, Al₃As₂

When a mixture of powdered aluminium and arsenic is heated, no reaction occurs up to 600° C., but above 750° C., if the pressure of the arsenic vapour is kept low, combination takes place with incandescence and results in the formation of a brown microcrystalline powder of composition Al₃As₂. The product is stable at high temperatures and Mansuri stated that it is infusible up to 1600° C. Natta and Passerini, however, found the melting point of the pure arsenide to be 1200° C. It is less stable at ordinary temperatures, a little arsenic being slowly liberated. When freshly prepared it is completely soluble in acid, but after keeping, a slight residue of arsenic remains after dissolution in hydrochloric acid. X-ray analysis by the powder method suggests that the crystals belong to the cubic system and resemble the blendes. The density calculated from the crystallographic data is 3.81; the observed density is 3.60. The compound reacts readily with water, evolving arsine, and is consequently unstable in moist air. With alcohols it reacts to yield alkyl arsines. When heated in air it is oxidised to alumina and arsenious oxide.