Potassium Tetraborate

Potassium Tetraborate

Excellent buffering capabilities

A superb buffering agent, 20 Mule Team® potassium tetraborate can lower the pH of strong alkalis and is also used in welding, soldering, and brazing fluxes.

Potassium Tetraborate in nuclear powered ships

Alkali Borate without Sodium Salts

Potassium tetraborate results from the controlled reaction of potassium hydroxide, water, and boric acid. This alkaline salt has excellent buffering capacity and replaces borax where an alkali borate is needed but sodium salts cannot be used. Potassium tetraborate is also more soluble in water than borax.


Analytical procedures

When dissolved in water, potassium tetraborate hydrolyzes to produce a mildly alkaline solution that can neutralize acids. For example, the pH of a 2% (wt.) solution of potassium tetraborate is 9.2. This value increases slightly with increasing concentrations and diminishes slightly with increasing temperatures. The relatively constant pH of potassium tetraborate solutions makes them excellent buffering agents, often recommended as primary standards in analytical procedures and used in detergents, eye drops, and other applications.

Metallic oxide solvent

Potassium tetraborate is also an excellent solvent for metallic oxides at high temperatures.


The product is used to prepare special welding, soldering, and brazing fluxes of stainless steel or other non-ferrous metals, where it helps prevent the glare that is associated with sodium borate.

Gear lubrication

Dispersed in a very finely divided state, potassium tetraborate improves the load-carrying, inhibits corrosion, and antiwear properties of industrial and automotive gear lubricants. Under extreme conditions, it interacts with metal load-bearing surfaces to form a film of extraordinary resilience. This tenacious film provides outstanding load-carrying capacity and wear protection.

Nuclear safety

As a highly pure form that can generate higher concentrations of boron—a good absorber of thermal neutrons—than other refined borates can, potassium tetraborate is used for emergency shutdowns in nuclear-powered ships.

And, more

Like 20 Mule Team potassium pentaborate, potassium tetraborate can be used to create alight-sensitive composition (diazotype developer).


Buffering capacity of potassium tetraborate

Potassium tetraborate is an excellent buffering agent, able to lower the pH of strong alkalis.


Potassium Tetraborate APPLICATIONS
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Available Grades

Potassium tetraborate shows little tendency to cake except after prolonged storage or when severely wetted by rain or substantial water penetration. The product can also absorb moisture if exposed to a humid environment.

Heated in a vacuum, the crystal line salt begins to melt in its own water at about 100°C (212°F), losing two molecules of water. The anhydrous salt is formed at about 500°C (932°F) and fuses to a clear glass at 815°C (1500°F).

Aqueous solutions of potassium tetraborate show a slight decrease in pH, followed by a moderate increase in pH with increasing concentrations.


Chemical and Physical Properties

Molecular weight: 305.5

Specific gravity: 1.92

Melting point: 815°C; begins to lose water at 212°F (100°C)

Appearance: White crystal line granules or powder

Solubility: 17.8% (as K2B4O7·4H2O) by weight in water at room temperature

Stability: When stored under normal conditions of temperature and humidity, potassium tetraborate is unlikely to change chemically or to cake.

Chemical Composition (Theoretical)

Boric oxide, B2O3: 45.58%

Potassium oxide, K2O: 30.83%

Water of crystallization, H2O: 23.59%

Anhydrous equivalent, K2B4O7: 76.41%

Containers: Products may be available in bulk, IBCs, or small bags

U.S. Borax, part of Rio Tinto, is a global leader in the supply and science of borates—naturally-occurring minerals containing boron and other elements. We are 1,000 people serving 650 customers with more than 1,800 delivery locations globally. We supply around 30% of the world’s need for refined borates from our world-class mine in Boron, California, about 100 miles northeast of Los Angeles.  Learn more about Rio Tinto.

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