Borax Pentahydrate

Borax pentahydrate is largest volume commercial boron product in the world. More than two million tons of borax pentahydrate are produced annually and shipped to markets around the world.  The largest producers are in Turkey and the United States.  

Although borax pentahydrate occurs in nature as the mineral tincalconite, the commercial product is nearly always made from other borate minerals, mainly tincal and kernite, which are dissolved in water and recrystallized as borax pentahydrate.  For this reason, commercial borax pentahydrate can be regarded as synthetic tincalconite.

The largest uses of borax pentahydrate are in the manufacture of various kinds of glass, most notably insulation fiberglass and borosilicate glass, ceramic glazes and as a boron micronutrient source in agriculture. It also has hundreds of other uses including buffers, anticorrosives, fire retardants, etc.

 

What is borax pentahydrate?

 

Borax pentahydrate is a sodium borate salt.  It is one of the hydrated forms of the sodium salt of tetraborate anion, [B4O5(OH)4]2- (Figure 1).  In aqueous solution this anion exists in equilibrium with other borate anions, including [B5O6(OH)4]-, [B3O3(OH)4]- and [B3O3(OH)5]2-. 

Chemical Formulas.  Several different chemical formulas are commonly used to describe borate compounds, each conveying different information.

Formula weight: 291.29

Common semi-empirical formula: Na2B4O7-5H2O

Resolves oxide formula:

Na2O-2B2O3-5H2O

Structural Formula: Na2[B4O5(OH)4]-3H2O

Figure 1.  The tetraborate anion, [B4O5(OH)4]2-