Ammonium Pentaborate

Ammonium Pentaborate

Stabilization and protection

Whether inhibiting heat, flame, or corrosion, the purity of this alkaline salt makes it an excellent choice.

Electrolytic capacitors containing ammonium pentaborate

Multifaceted Ammonium Borate for the Way We Live

From fire protection to electric capacitors, 20 Mule Team® Borax ammonium pentaborate is a workhorse. This versatile product dissolves easily, stores well, and is ideal for scenarios in which alkali metals cannot be used.


Electrolytic capacitors

Special quality-grade ammonium pentaborate is used in the preparation of both wet and dry electrolytic capacitors. It is a component of electrolytes for developing a thin oxide film on aluminum foil when an electric current is applied, as well as for inserting into an aluminum container during the final assembly of capacitors. The purity of the boron-containing components (boric acid, borax, and ammonium pentaborate) is essential to the production of high-quality capacitors, so our refinement process makes this product ideal.

Metallic oxide solvent

Ammonium pentaborate is also an excellent solvent for metallic oxides at high temperatures. This capability makes it useful in the preparation of special welding, soldering, and brazing fluxes for stainless steel or non-ferrous metals, where alkali borates cannot be used. And, its stabilizing effect makes it a good choice for use in gunning and patching compounds, to extend the life of basic refractories in steel furnaces.

Flame retardant

One of this product’s most important uses is in the protection of cellulosic materials such as cotton, paper, rayon, and wood composites. By inhibiting oxidation, borates divert decomposition products from flaming and smoldering combustion toward the development of char. Spray ammonium pentaborate borate solutions on paper (or dip the paper into the solutions) to create a fire-retarded product or add ammonium pentaborate to other fire-retardant formulations.

In polymer applications, ammonium pentaborate can be used as an effective flame retardant in:

  • Epoxy
  • Thermoplastic polyurethane (TPU)
  • Urethane foam

Other applications

The product is also used in intumescent coatings for steel. In certain proprietary water treatment chemicals, ammonium pentaborate helps to inhibit corrosion, protecting ferrous metals against oxidation.

Use this readily soluble non-alkali borate when alkali metals are not an option.


Ammonium Pentaborate APPLICATIONS
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Whether inhibiting heat or building electrolytic capacitors, the purity of U.S. Borax ammonium pentaborate makes it an excellent choice.


Available Grades

Ammonium pentaborate results from the controlled reaction of ammonia, water, and boric acid. It is an alkaline salt and consists of white crystalline granules.

The product is stable to about 230°F (110°C), at which point it loses all but two moles of water. If heated sufficiently, it releases the balance of its hydration water and decomposes to boric oxide and ammonia.

In aqueous borate solutions at room temperature, pH decreases slightly as the concentration of ammonium pentaborate increases. Details about the product’s hydrogen ion concentration and solubility in water is located in the product data sheet.
Chemical and Physical Properties

Molecular weight: 272.15

Specific gravity: 1.58

Appearance: White crystalline granules

Solubility: About 10.9% by weight at room temperature

Stability: Ammonium pentaborate shows little tendency to cake except after prolonged storage or if it becomes severely wetted by rain or substantial water penetration. It is also capable of absorbing moisture if exposed to a humid environment.

Chemical Composition (Theoretical)

Boric oxide, B2O363.95%

Ammonium oxide, (NH4)2O: 9.57%

Water of crystallization, H2O: 26.48%

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

Ammonium Pentaborate in Action

Borates Are the Multi-Tool for Fire Safety in Plastics and Polymers
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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 500 customers with more than 1,700 delivery locations globally. We supply 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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