Industrial optimization power house

From reducing melting temperatures in fiberglass production to inhibiting corrosion in fuel additives, Optibor® has a multitude of uses in numerous industries.
Optibor’s borates are essential to the safety and control of nuclear power stations

Efficient Energy Use

Optibor boric acids (H3BO3) are pure, multi-functional sources of 20 Mule Team® Borax boric oxide (B2O3). Apart from Neobor® (borax pentahydrate), Optibor is our most widely used industrial borate.

Optibor is theoretically composed of boric oxide and water. It can be purchased as granules or as a powder, both of which are stable under normal conditions, free-flowing, and easily handled by means of air or mechanical conveying. In solution, the product is mildly acidic.


Boric oxide and glasses

The boric oxide in Optibor is both a flux and a network former, assisting in the melt and influencing the final product properties of fiberglass and borosilicate glass. Optibor, in combination with a sodium borate (such as Neobor or Dehybor® anhydrous borax), can be used to adjust the sodium-to-boron ratio in glasses which require low sodium levels. This is important in borosilicate glass where boric oxide provides essential fluxing properties at low sodium and high alumina levels.

Ceramic frits

For the glassy surfaces of ceramics and enamels, boric oxide acts as both network former and flux. In this capacity, it can be used to:
  • Initiate glass formation (at low temperatures)
  • Ensure a thermal fit between glaze and body 
  • Reduce viscosity and surface tension
  • Increase the refractive index
  • Enhance strength, durability, and scratch resistance
  • Facilitate lead-free formulations

High-boron frits mature rapidly; improve the speed at which smooth, even glaze surfaces develop; and provide good bases for coloring oxides. Optibor is used as the boric oxide source in the formulation of fast fire frits for tiles because of their requirement for low sodium levels.

Flame retardancy

In cellulose materials, borates change the oxidation reactions and promote the formation of char, thereby inhibiting combustion. Optibor, alone or in combination with Neobor or borax decahydrate, is particularly effective in reducing the flammability of cellulose insulation, wood composites, and the cotton batting used in mattresses.

Nuclear safety

Being a highly effective absorber of thermal neutrons, the boron-10 (10B) isotope is essential to the safety and control systems of nuclear power stations. Optibor SQ is made for the nuclear industry and can be used as a precursor for making isotopically enriched boron-10 materials.


Optibor prevents the oxidation of metal surfaces in welding, brazing, or soldering. It is used as a source of boron for:

  • Strengthening metal alloys and steel
  • Magnesium sand-casting
  • Electroplating


As part of the starch adhesive formulation for corrugated paper and paperboard, and as a cross-linking agent in the manufacture of casein- and dextrin-based adhesives, Optibor greatly improves the tack and green strength of the adhesive by cross-linking conjugated hydroxyl groups.

And more

Optibor can be incorporated in aqueous and non-aqueous systems for corrosion inhibition, lubrication, or thermal oxidative stabilization. It is also used in the manufacture of lubricants, brake fluids, metalworking fluids, water-treatment chemicals, and fuel additives. The product is also used in a variety of other applications:

  • Personal care products (in conjunction with sodium borates), for pH buffering and as a cross-linking agent to emulsify waxes and other paraffins
  • In the manufacturing of nylon intermediates, to catalyze the oxidation of hydrocarbons and increase the yield of alcohols by forming esters that prevent further oxidation of hydroxyl groups to ketones and carboxylic acids
  • In the preparation of industrial products such as boron halides, borohydride, fluoborates, metallic borates, borate esters, and boron-containing ceramics, dye stabilization, and textile finishing paints
  • Electrolytic capacitors
  • Leather processing and finishing
Optibor Applications
Optibor boric acids can be used in combination with a sodium borate (borax pentahydrate or anhydrous borax) to adjust the sodium-to-boron ratio in glasses that require low sodium levels.


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Available Grades  Optibor reduces the linear coefficient of expansion in glass when silica is replaced proportionately with boric acid, facilitating a thermal fit in ceramic glazes and heat resistance in borosilicate glass.  

When heated above 212°F (100°C) in the open, Optibor gradually loses water, first changing to metaboric acid (HBO2), of which three monotropic forms exist. These metaboric acid forms can volatilize at >600°C during heating, leading to potential losses of boron emissions. Dehydration stops at the composition HBO2 unless the heating time is extended or the temperature raised above 302°F (150°C). On continued heating and at higher temperatures, all water is removed, leaving the anhydrous oxide B2O3—an amorphous glass that begins to flow at 842°F (450°C). The amorphous form of Optibor TG has no definite melting point, softening at about 617°F (325°C) and becoming fully fluid at about 932°F (500°C). 

Aqueous solutions of Optibor are mildly acidic, the pH decreasing with increasing concentration. Optibor’s sieve specification is U.S. sieve No. 20, with a mesh size of 0.850 mm and a retained guarantee of ≤ 2.0%. Optibor forms boric oxide above ~300°C, which softens and begins to flow between 350°C and 500°C.

Chemical and Physical Properties

Molecular weight: 61.83 g/mol

Specific gravity: 1.50

Appearance: Free-flowing, white, crystal line granules or powder

Solubility: 5.46% boric acid by weight in saturated solution (water) at room temperature

Stability: Optibor is a stable crystalline product that does not change chemically under normal storage conditions. Wide fluctuations in temperature and humidity can cause recrystallization at particle contact points, resulting in caking. Care should be taken to avoid such fluctuations during product storage and to maintain the integrity of the packaging.

Bulk density: 55 lb/ft3 (881 kg/m3)

Angle of repose: 33°

Chemical Composition (Theoretical)

Boric oxide, B2O3: 56.30%

Water of crystallization, H2O: 43.70%

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

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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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