Zirconium Hydroxide, Zirconic Acid

Hydrated zirconia, precipitated from an acid solution by ammonia or caustic alkali, contains an indefinite amount of water; it is slightly soluble in water, and appears to be feebly alkaline, since it colours yellow turmeric paper brown. Its solubility in acids depends on the conditions of its precipitation. When precipitated cold it is easily soluble in dilute acids; when precipitated hot, or washed with hot water, it can be dissolved only in concentrated acid. In these properties hydrated zirconia resembles hydrated alumina. When precipitated zirconia is heated to 100° C. it attains to the composition ZrO₂.H₂O. This product is called zirconic acid. A less hydrated form of zirconia, known as metazirconic acid, is obtained by boiling zirconium oxychloride with water as long as chloride is abstracted and drying the product at 100° C.; it has the composition 3ZrO₂.2H₂O. Metazirconic and zirconic acids are supposed to be related to -one another as stannic and metastannic acids are related. According to van Bemmelen, however, zirconia forms no true hydroxide, these products being the colloidal oxide, containing accidental amounts of water.