Barium Oxide, BaO

Barium Oxide, BaO, may be formed by the direct combination of its elements. It is obtained by calcination of the hydroxide or nitrate. A high temperature is required to prevent contamination with the peroxide. Barium carbonate cannot be decomposed under the conditions prevailing in the limekiln. For production from witherite on the commercial scale it is necessary to heat with carbon, when the following reaction takes place: -

BaCO₃ + C = BaO + 2CO.

According to a patent of Frank's, barium oxide may be obtained by heating together barium carbonate and carbide.

3BaCO₃ + BaC₂ = 4BaO + 5CO.

Barytes may be used instead of witherite, and is generally a purer mineral. By heating with coal or coke in the reverberatory furnace, or preferably by using a gaseous reducing agent at 600°-650° C., barytes may be reduced to the sulphide, which can be readily converted into the hydroxide and thence into the oxide.

The United Barium Company at Niagara Falls patented a process for preparing barium oxide directly from barium sulphate. The sulphate is mixed with sufficient carbon to reduce a quarter of the sulphate to sulphide, and the whole is heated in the electric furnace. The following reactions take place: -

BaSO₄ + 4C = BaS + 4CO BaS + 3BaSO₄ = 4BaO + 4SO₂.

By heating barium chloride with zinc oxide at white heat, zinc chloride is made to volatilise and barium oxide is left.

Barium hydroxide may be prepared electrolytically and then converted into the oxide.

As ordinarily produced, it is a white (or often greyish) amorphous powder, the density of which varies considerably, from 4.78 – 5.76, with the method of production. It may be obtained in a crystalline form by slow calcination of the nitrate, but, owing probably to the fact that, unlike calcium and strontium oxides, barium oxide does not dissolve in the nitrate, the crystals are only microscopic. There are apparently two forms, cubic, of density 5.74, and hexagonal, of density 5.32. By fusing in the electric furnace at a lower temperature than is possible in the case of calcium or strontium oxides, and allowing to cool, a crystalline mass is obtained. Barium oxide also crystallises out when a mixture of barium and lithium carbonates is heated to 1150°-1250° C. The heat of formation of barium oxide is 125.86 Cal. Hydrochloric acid reacts with barium oxide even at ordinary temperatures, probably owing to the difficulty of making it completely anhydrous. Sulphuretted hydrogen and sulphur dioxide only react when heated. By heating with carbon dioxide the reaction is so vigorous that the product becomes incandescent and may reach a temperature of 1200° C. A basic carbonate of indefinite composition results.

Investigations of the temperature of dehydration of hydrated barium hydroxide have led de Forcrand to the conclusion that barium oxide should be represented as a condensed product, (BaO)_n.

In the presence of small quantities of phosphorogens, barium oxide is phosphorescent.

Barium oxide dissolves in fused barium chloride to the extent of one molecule of oxide to one of chloride. Mixed crystals containing 17.7 per cent, of oxide separate out.

Owing to its tendency to form barium peroxide, the oxide may be used as a reducing agent for organic compounds.