Sodium Metaborate

Sodium Metaborate

Essential Buffering Agent

Used in the preparation of starch and dextrin adhesives, this product provides increased viscosity, quicker tack, and better fluidity. In textile processing, sodium metaborate helps to stabilize hydrogen peroxide solutions and neutralizes acidic oxidation by-products.

Sodium Metaborate in textiles

High Solubility for Higher Concentrations

20 Mule Team® Borax sodium metaborate, available in 4 mol or 8 mol, is an alkaline salt with excellent buffering capacity. Its high solubility enables sodium metaborate to provide a much higher concentration of borate ions in solution than either Neobor® or 20 Mule Team Borax borax decahydrate at the same temperature. As a result, it is an excellent choice for use in starch and destrin adhesives (among other applications).

Since the development of the Stein Hall process in the 1930s, starch-based adhesives have been a vital component of corrugated paper and paperboard. Sodium metaborate’s high alkalinity helps it break the hydrogen bonding between starch chains—and producing even more extensive chemical changes that create a more highly branched chain polymer of higher molecular weight.

The result? Adhesives with increased viscosity, quicker tack, and better fluid properties than those that don’t use borates. These properties make the adhesive easier to work with. For example, quick tack at reasonably low temperatures is necessary for the proper maintenance of corrugated paperboard machines, which operate at a high speed.


Sodium metaborate’s high alkalinity and the cross-linking reaction of borate anions with polyhydroxy groups makes it an excellent choice for starch- and dextrin-based adhesives. The adhesives it helps to produce are essential for use in corrugated boxes, paper bags, laminated paper boards, carton and case sealing, gummed tape, and tube winding.

Sodium metaborate is also a component of photographic developers and replenishers. Its principal function is as a buffering agent, used to tightly control the pH of the solutions. As such, it produces high-quality fine-grain black-and-white developers and helps to ensurethe correct color balance in color developers.

Textiles such as cotton are bleached with hydrogen peroxide solutions. These solutions can be stabilized by using sodium metaborate. It also neutralizes the acidic oxidation by-products that form during bleaching. And textile manufacturers can control textile sizing by incorporating sodium metaborate-produced starch adhesive material within the thread and binding all the fibers together to increase the thread’s tensile strength.

As an ingredient in hard-surface cleaners, sodium metaborate helps to remove oil, grease, rust, scale, and other particulates from metal or glass surfaces. The borate imparts alkaline conditions that enhance the product’s cleaning action. Sodium metaborate can also be incorporated into liquid laundry detergents for pH control, enzyme stabilization, and its builder properties.

Many proprietary water-treatment chemicals also include sodium metaborate to control pH and inhibit corrosion.

Such chemicals are used on heating systems and cooling towers as protection against corrosion. In automotive and industrial fluids, sodium metaborate can be used for anti-corrosion and reaction with acidic degradation products.

Borates are also being developed as an alkaline agent in several EOR processes, such as alkali-polymer and alkali-surfactant-polymer (ASP) flooding. Tertiary oil recovery from borate-based ASP core floods is comparable to that obtained with similar formulations that contain conventional alkalis and exhibit no injectivity problems in core flood trials.


Boric Acid

Adhesives with increased viscosity, quicker tack, and better fluidity are essential in the manufacture of corrugated boxes, paper bags, gummed tape, and more.



High solubility means that sodium metaborate can release a higher concentration of borate ions in solution.


Available Grades 
  • Anhydrous Boric Acid 4 Mesh – North America 
  • Anhydrous Boric Acid 60 Mesh 
  • 200 Mesh – EMEAI 
  • RG – EMEAI 
Sodium metaborate is stable at ordinary temperatures. However, if exposed to the atmosphere for extended periods, it picks up carbon dioxide from the air and forms sodium carbonate and borax. Sodium metaborate 4 mol will convert to 8 mol when exposed to a humid atmosphere.  

Sodium metaborate 4 mol crystalline salt begins to lose water at about 194°F (90°C). The anhydrous salt fuses to a clear glass at 1770°F (966°C). Some vaporization occurs above 2246°F (1230°C). Sodium metaborate 8 mol crystalline salt begins to lose water at about 128°F (53.5°C). The anhydrous salt fuses to a clear glass at 1770°F (966°C), and some vaporization occurs above 2246°F (1230°C). 

Aqueous solutions of sodium metaborate 4 mol and 8 mol show a moderate increase in pH with increasing concentrations. 
Chemical and Physical Properties (4 Mol)

Molecular weight (NaBO2·2H2O): 101.83

Specific gravity: 1.90

Appearance: White crystal line granules

Solubility: 33.58% (as NaBO2·2H2O) by weight in water at room temperature

Chemical Composition (Theoretical)

Boric oxide, B2O3: 34.18%

Sodium oxide, Na2O: 30.44%

Water of crystallization, H2O: 35.38%

Anhydrous equivalent, NaBO2: 64.62%

Chemical and Physical Properties (8 Mol)

Molecular weight (NaBO2·4H2O): 137.88

Specific gravity: 1.74

Appearance: White crystalline granules

Solubility: 45.46 (as NaBO2·4H2O) by weight in water at room temperature

Chemical Composition (Theoretical)

Boric oxide,B2O3: 25.25%

Sodium oxide, Na2O: 22.48%

Water of crystallization, H2O: 52.27%

Anhydrous equivalent, NaBO2: 47.73%

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

Rio Tinto Borates is a global leader in the supply and science of borates - naturally-occurring minerals containing boron and other elements. Refined borates are essential nutrients for crops. We are 1,000 people serving 500 customers with over 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 east of Los Angeles.  Learn more about Rio Tinto

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