Barium oxide (BaO) structure, properties, uses, risks

Sherman Hoover
Barium oxide (BaO) structure, properties, uses, risks

The barium oxide It is an inorganic solid formed by a barium atom (Ba) and an oxygen atom (O). Its chemical formula is BaO. It is a white crystalline solid and is hygroscopic, that is, it absorbs moisture from the air, but when doing so it reacts with it..

The rapid reaction of barium oxide with water makes it used in chemical analysis laboratories to dry out, that is, eliminate water from organic solvents, which are liquid compounds that serve to dissolve other substances..

Barium oxide BaO solid. Leiem [CC BY-SA 4.0 (]. Source: Wikimedia Commons.

BaO behaves like a strong base, therefore it reacts with many types of acids. For example reacts easily with carbon dioxide COtwo from the air to form barium carbonate BaCO3.

It is used in the manufacture of polymers for power cables and as an ingredient for resins to seal holes in teeth that have been cured.

Barium oxide (BaO) is also used in the ceramic industry, both for coating it with glaze and for manufacturing it. It is also used in cement mixtures to increase the compressive strength of the final product..

Article index

  • 1 Structure
  • 2 Nomenclature
  • 3 Physical properties
    • 3.1 Physical state
    • 3.2 Molecular weight
    • 3.3 Melting point
    • 3.4 Boiling point
    • 3.5 Density
    • 3.6 Solubility
  • 4 Chemical properties
  • 5 Risks
  • 6 Obtaining
  • 7 Uses
    • 7.1 As a desiccant for organic solvents
    • 7.2 In discharge lamps
    • 7.3 In the manufacture of ceramics
    • 7.4 In the preparation of cement mixtures
    • 7.5 In various applications
  • 8 References


Barium oxide BaO is made up of a Ba cationtwo+ and an oxygen anion Otwo-.

Barium oxide BaO ions. Author: Marilú Stea.

In its crystals, BaO forms cubic ionic networks (cube-shaped) of the sodium chloride type.

Cube-shaped crystalline structure of barium oxide BaO similar to sodium chloride. Green: barium. Blue: oxygen. Benjah-bmm27 (talk · contribs) [Public domain]. Source: Wikimedia Commons.

The electron configuration of the barium ion is: [Xe] 6s0 as it has lost the two electrons of the 6s shell. This configuration is very stable.


-Barium oxide

-Barium monoxide

Physical properties

Physical state

Yellowish-white crystalline solid.

Molecular weight

153.33 g / mol

Melting point

1923 ºC

Boiling point

Approximately 2000 ºC.


5.72 g / cm3


Slightly soluble in water: 3.8 g / 100 mL at 20 ºC.

Chemical properties

Barium oxide BaO reacts rapidly with water, giving off heat and forming a corrosive solution of barium hydroxide Ba (OH)two, which is the most soluble hydroxide among the alkaline earth metal hydroxides.

BaO + HtwoO → Ba (OH)two

BaO is a strong base. Reacts exothermically (i.e. with evolution of heat) with all types of acids.

With COtwo BaO reacts to form barium carbonate BaCO3.

BaO + COtwo → BaCO3

BaO is hygroscopic, so if it is left exposed to the environment, it gradually joins the humidity of the air, forming Ba (OH)two which combines with carbon dioxide COtwo from the air to give barium carbonate BaCO3.

When barium monoxide BaO is heated in the presence of air it combines with oxygen to form barium peroxide BaOtwo. The reaction is reversible.

2 BaO + Otwo ⇔ 2 BaOtwo

In the presence of water, it can react with aluminum Al or zinc Zn, forming the oxides or hydroxides of said metals and generating hydrogen gas Htwo.

May initiate polymerization of polymerizable organic compounds, such as epoxides.


May be toxic if swallowed. It should not come into contact with the skin. It is irritating to the eyes, skin and respiratory tract. It can be harmful to the nervous system. It is capable of causing low potassium levels, resulting in heart and muscle disorders.


Barium oxide BaO can be obtained by heating barium carbonate BaCO3 with charcoal. BaO is formed and carbon monoxide gas CO is released.

Bacchus3 + C → BaO + 2 CO ↑


As a desiccant for organic solvents

Due to its ease of reacting with water, BaO has been used since the middle of the last century as a desiccant for gasoline and basic or neutral organic solvents..

BaO is very active drying around it, it takes up moisture very quickly, with evolution of quite a bit of heat, forming barium hydroxide Ba (OH)two which is stable up to about 1000 ºC. For this reason, BaO can be used at high temperatures..

It also has a high water absorption capacity. For each molecule of BaO, one of the water and the Ba (OH) can be absorbed.two resulting can also absorb a certain amount of water.

It is suitable for analytical chemistry laboratories. Not sticky.

It can be used in desiccators, which are large glass containers with a lid where the internal environment is kept dry. BaO keeps the desiccator miniature atmosphere dry.

Desiccators in a laboratory. Solid desiccant such as BaO is placed at the bottom of the base. The original uploader was Rifleman 82 at English Wikipedia. [CC BY-SA 3.0 (]. Source: Wikimedia Commons.

These desiccators are used to place substances or reagents and thus prevent them from absorbing water from the environment.

It also serves to dry basic gases such as NH ammonia3.

In discharge lamps

BaO is placed on the electrodes of discharge lamps as an electron emitting material.

Discharge lamps are made of a tube of glass, quartz or other suitable material, they contain an inert gas and in most cases a metal vapor. Metallic vapor can be sodium or mercury.

Mercury lamp. Dmitry G [CC BY-SA 3.0 (]. Source: Wikimedia Commons.

Electric discharges occur inside the tube because it has a positive and a negative electrode.

The BaO is placed on the electrodes of the lamp. The electrons it emits collide with the atoms of the metal vapor and transmits energy to them..

When an electrical current passes through this gas or vapor, visible light or ultraviolet (UV) radiation is produced..

In the manufacture of ceramics

BaO is used in ceramic glaze coating compositions.

Building facade covered with glazed ceramic. Penny Mayes / Glazed façade. Source: Wikimedia Commons.

However, it has also been tested as an additive in the preparation of glass-ceramic.

BaO effectively improves the mechanical characteristics and chemical resistance of this type of ceramic. It has a strong influence on the thermal properties and the composition of the crystalline phase of the materials obtained..

In the preparation of cement mixtures

BaO has been tested as a component of phosphoaluminate cement.

This type of cement is useful in marine environments, since it does not have the same tendency to hydrate as other types of cement, so it does not suffer from pore formation or expansion..

However, phosphoaluminate cements need to be strengthened in their mechanical performance to be able to withstand marine currents and blows from floating pieces of ice present in the ocean..

The addition of BaO to the phosphoaluminate cement modifies the mineral structure of said material, improves the pore structure and considerably increases the compressive strength of the cement paste..

In other words, BaO improves the compressive strength of this type of cement..

Mix for concrete. Barium oxide BaO is useful for improving certain properties of cement. Thamizhpparithi Maari [CC BY-SA 3.0 (]. Source: Wikimedia Commons.

In various applications

It is used as an ingredient to provide opacity in dental resins for filling holes in teeth, performed by dentists.

It is also used as a nucleating agent for the preparation of polyvinylidene fluoride polymers that are used to insulate power cables..


  1. Partyka, J. et al. (2016). Effect of addition of BaO on sintering of glass-ceramic materials from SiOtwo-To thetwoOR3-NatwoOKAYtwoO-CaO / MgO system. J Therm Anal Calorim (2016) 125: 1095. Recovered from
  2. Zhang, P. et al. (2019). Effect of BaO on mineral structure and hydration behavior of phosphoaluminate cement. J Therm Anal Calorim (2019) 136: 2319. Recovered from
  3. U.S. National Library of Medicine. (2019). Barium oxide. Recovered from
  4. Smith, N.A. (2003). Lighting. Principle. In Electrical Engineer's Reference Book (Sixteenth Edition). Recovered from
  5. Ebnesajjad, S. (2003). Fluoropolymer Foams. Foaming PVDF. In Melt Processible Fluoroplastics. Recovered from
  6. Booth, H.S. and McIntyre, L.H. (1930). Barium Oxide as a Dessicant. Ind. Eng. Chem. Anal. Ed. 1930, 2, 1, 12-15. Recovered from

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