Strontium Oxide, SrO

Strontium Oxide, SrO, can be obtained by heating strongly the carbonate, hydroxide, or nitrate. The first of these requires a higher temperature for decomposition than calcium carbonate. It may also be formed by the direct combination of strontium and oxygen, the heat evolved being 139.64 Cal. Or 141.2 Cal. Commercially the chief source of the oxide is the sulphate, celestine. Various methods of treatment are possible. The sulphate may be calcined with carbon to form the sulphide and the latter transformed into the hydroxide by the action of a base and again calcined; or the sulphate may be heated in a current of water vapour and carbon monoxide; or, finally, it may be fused with sodium carbonate under pressure, and the resulting carbonate calcined. The oxide has also been prepared by heating the carbonate with the carbide.

As usually obtained, strontium oxide is a white amorphous solid of density varying from 3.93 to 4.61, depending upon the method of preparation. It forms cubical crystals, however, of density 4.75 when prepared by very slow calcination of the nitrate. The transparent liquid, obtained by fusion in the electric arc at about 3000° C., which is more easily accomplished than in the case of calcium oxide, forms on cooling a confused mass of crystals. A crystallised specimen may also be obtained by heating a mixture of strontium carbonate with lithium carbonate.

Sulphuretted hydrogen reacts with strontium oxide in the cold, forming water and sulphur with considerable heat evolution. Sulphur dioxide and carbon dioxide react with strontium oxide when heated, but not in the cold. In the case of carbon dioxide the reaction may become so vigorous that the product is incandescent, and a temperature of 1050° C. may be reached.

Strontium oxide dissolves in fused strontium chloride, one molecule of the former saturating three of the latter.

From a consideration of heat phenomena, de Forcrand concluded that the molecule of strontium oxide should be regarded as a condensed molecule with the formula (SrO)_n.