Barium oxide

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Barium oxide

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UN number	1884
Template:Longitem	Template:Chembox Elements/molecular formula
Molar mass	153.326 g/mol
Appearance	white solid
Density	5.72 g/cm3, solid
Melting point	Template:Chembox CalcTemperatures
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Solubility	soluble in ethanol, dilute mineral acids and alkalies; insoluble in acetone and liquid ammonia
Template:Longitem	−29.1·10−6 cm3/mol
Template:Longitem	cubic, cF8
Template:Longitem	Fm3m, No. 225
Template:Longitem	Octahedral
Template:Longitem	47.7 J/K mol
Template:Longitem	70 J·mol−1·K−1
Template:Longitem	−582 kJ·mol−1
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Barium oxide, also known as baria, is a white hygroscopic non-flammable compound with the formula BaO. It has a cubic structure and is used in cathode-ray tubes, crown glass, and catalysts. It is harmful to human skin and if swallowed in large quantity causes irritation. Excessive quantities of barium oxide may lead to death.

It is prepared by heating barium carbonate with coke, carbon black or tar or by thermal decomposition of barium nitrate.

Uses

Barium oxide is used as a coating for hot cathodes, for example, those in cathode-ray tubes. It replaced lead(II) oxide in the production of certain kinds of glass such as optical crown glass. While lead oxide raised the refractive index, it also raised the dispersive power, which barium oxide does not alter. Barium oxide also has use as an ethoxylation catalyst in the reaction of ethylene oxide and alcohols, which takes place between 150 and 200 °C.

It is most known for its use in the Brin process, named after its inventors, a reaction that was used as a large scale method to produce oxygen before air separation became the dominant method in the beginning of the 20th century, as BaO can be a source of pure oxygen through heat fluctuation.

BaO(s) + ½O₂(g) ⇌ BaO₂(s)

It oxidises to BaO₂ by formation of a peroxide ion (Template:Chem2, or Template:Chem2) — with the same charge of Template:Chem2, and therefore keeping the electrochemical balance with the most stable Template:Chem2. Using the Kröger-Vink notation,

½Template:Chem2(g) + O ⇌ [O]

where J is the species J in the oxygen position within the rock-salt lattice. The complete peroxidation of BaO to BaO₂ occurs at moderate temperatures by oxygen uptake within the BaO rock-salt lattice:

File:Oxygen incorporation into BaO.png

Barium oxide peroxidation from oxygen uptake, adapted from Middleburgh et al, 2012.

Calculations using Density Functional Theory (DFT) suggest that the oxygen incorporation reaction is exothermic, and that the most energetically favoured occupation site is indeed the peroxide ion at the oxide lattice — other than interstitial positions, for instance. However, the increased entropy of the system is what leads BaO₂ to decompose to BaO and release O₂ between 800 and 1100 K (520 and 820 °C). The reaction was used as a large scale method to produce oxygen before air separation became the dominant method in the beginning of the 20th century. The method was named the Brin process, after its inventors.

Preparation

Barium oxide from metallic barium readily forms from its exothermic oxidation with dioxygen in air:

2 Ba(s) + O₂(g) → 2 BaO(s).

It's most commonly made by heating barium carbonate at temperatures of 1000–1450 °C.

BaCO₃(s) → BaO(s) + CO₂(g)

Likewise, it is often formed through the thermal decomposition of other barium salts, like barium nitrate.

Safety issues

Barium oxide is an irritant. If it contacts the skin or the eyes or is inhaled it causes pain and redness. However, it is more dangerous when ingested. It can cause nausea and diarrhea, muscle paralysis, cardiac arrhythmia, and can cause death. If ingested, medical attention should be sought immediately.

Barium oxide should not be released environmentally; it is harmful to aquatic organisms.

See also

• Template:Annotated link

External links

• International Chemical Safety Card 0778