BorON in Industrial Fluids and Lubricants


Borates are well established and widely used in the manufacture of industrial and automotive fluids, such as lubricants, hydraulic fluids, water-treatment chemicals, closed system heat exchanger fluids, antifreezes, brake fluids, fuel additives, and metalworking fluids. In these fluids, borates impart numerous benefits:
  • Lubrication
  • Corrosion inhibition
  • Buffering action
  • Freezing-point reduction
  • Boiling-point elevation
  • Stabilization of thermal oxidation
  • Prevention of sludge formation
  • Reduction in moisture sensitivity

Boron in industrial fluids

Many boron-containing lubricating oils are consumed in automotive (eg, motor oil, transmission fluids) and aviation applications. Others are used in industrial applications (eg, greases, gearbox and metal-forming lubricants) or in non-lubricating uses, such as working fluid in hydraulic pumps.

Lubrication with borates

Lubricants are made by blending additives, viscosity modifiers, ashless dispersants, detergents, inhibitors, antiwear agents, friction modifiers, and flow enhancers into a base oil stock to meet certain performance characteristics or specifications. Ideal lubricants should have the following properties:

  • Excellent thermal oxidative stability
  • Reduced friction
  • High-temperature anticorrosion
  • Low sludge pumpability at low temperatures
  • Good elastomer compatibility
  • Good storage stability
  • No sulfur odor
Borates are widely used in the manufacture of additives for lubricating oils. Extreme-pressure additives have been developed based on the stable dispersion of alkali borate microspheres. Hydrated potassium and lithium borates have received much attention in this area. These inorganic borate spheres interact with metal load-bearing surfaces to form a film of extraordinary resilience. This tenacious film provides outstanding load-carrying capacity and wear protection. The small size and low density of dispersed borates make the lubricant very stable. Additives containing nitrogen and boron—prepared by reacting polyamines, carboxylate esters, or amine/ester mixtures with boric acid or boric oxide at elevated temperatures—have also been proposed for lubricating oil compositions.

Boron for lubricants

Borate Compounds in Liquid Lubricants
Boron-containing lubricants can be used in the form of oxides, esters, or boric acid. Liquid lubricants typically use organoboron compounds dissolved in oil or insoluble, inorganic boron salts dispersed in oil in nanoparticulate form. The latter is particularly useful in lubricants that must meet the needs of both high temperatures and high loads.

Anticorrosion with borates from U.S. Borax

Corrosion—the destructive interaction between a metallic surface and a nonmetallic environment—is generally accepted to be an electrochemical phenomenon. The metal in a corrosive medium has many anodic and cathodic sites on its surface. As in any electrochemical cell, oxidation takes place at the anode, where the reaction product is metal ions that are released into the surrounding medium. Conversely, at the cathode, oxygen or hydrogen ions are reduced. The equal rate of anodic and cathodic reactions means that inhibiting either of these half-reactions can decrease the overall corrosion rate.

Anodic inhibition is accomplished by growing an oxide film on the surface of the metal—a form of controlled general corrosion called passivation. If film breaks are not repaired, however, rapid pitting can occur. Borates can act as a nonoxidizing anodic inhibitor in aqueous solution, where it can affect passivation in the presence of oxygen.

Borates have been shown to inhibit corrosion in several applications, including in nuclear power plants. Optibor® boric acid has been shown to inhibit stress-corrosion cracking and intergranular attack in steam generators in nuclear power plants. Potassium borates (such as 20 Mule Team® Borax potassium pentaborate and 20 Mule Team Borax potassium tetraborate) are recommended for corrosion inhibition of closed cooling water auxiliary systems, as the potassium-based inhibitor prevents corrosion without producing secondary radiation in any significant amount.

Borates anticorrosion benefits

Borates in automotive uses

Borates’ anticorrosive properties are also prized in the automotive industry. Most passenger automobiles use a mixture of water and antifreeze to remove approximately 50% of the heat generated by internal combustion engines. The antifreeze solutions used in these radiator systems must feature:

  • A low freezing point
  • A high boiling point
  • An efficient heat-transfer medium
  • Corrosion inhibition
  • Chemical stability
  • Low toxicity
An aqueous solution of ethylene glycol or propylene glycol meets most of these requirements. But glycol-based antifreezes can oxidize to produce corrosive organic acids in automotive coolant systems. In antifreezes, the buffering action of borates keeps the pH of these fluids above 7, preventing acid formation and inhibiting corrosion. 20 Mule Team Borax borax decahydrate or Neobor®, together with other components, serves this purpose. These products are readily soluble in glycols, are non-toxic, and can be handled safely.

In moisture-sensitive brake fluids (generally made from triethylene glycol monoalkyl ethers), borates act to prevent vapor-lock. The borate ester of the glycol ethers is a good partial replacement for glycol ethers. Borate esters are made by reacting triethylene monoalkyl ethers and Optibor boric acid under proper conditions. The absorption of moisture into the brake fluid converts the borate esters back to boric acid and glycol ethers. The released boric acid remains dissolved in the fluid and so has a minimum effect on the boiling point. Brake fluids with a borate ester content of 63% (or 4.4% boric oxide—B2O3) can meet U.S. Department of Transportation (DOT) specifications and the needs of higher-performance vehicles.

In fuel additives, borate esters have been used to help prevent pre-ignition and keep carburetors clean. In aviation fuel, borates have been used to help prevent bacterial and fungal growth in storage or use tanks, yielding a clean-burning fuel.

In addition to their corrosion-inhibitive properties, boron-containing additives have detergent and anti-rust properties, are anti-knocking, and have low sludge formation. Along with ability to provide lubrication, reduction of carbonaceous deposits, these properties make them valuable in automotive oils and lubricants.
Many boron-containing lubricating oils are consumed in automotive (e.g., motor oil, transmission fluids) and aviation applications. Others are used in industrial applications (e.g., greases, gearbox and metal-forming lubricants) or in non-lubricating uses, such as working fluid in hydraulic pumps.

Borates vs. zinc, sulphur, and phosphorous

Synthetic hydrocarbon mixtures are popular lubricants. These synthetic lubricants benefit from a small addition of organic or organometallic compounds that react with a base metal (e.g., iron) in the surface material to form a protective barrier coating. Borates are a popular additive option, offering major advantages such as antiwear efficiency in extreme high-pressure environments, high load-carrying capacity, good film strength, high temperature resistance, and self-lubricating properties. And, unlike zinc, sulphur, and phosphorous additives, borates do not result is sulphur or phosphorous oxides or metallic ash that can reduce the effectiveness of engine exhaust after-treatment filters and catalysts.

Borates in oil and gas

When used in drilling fluids (muds), borates fulfill several functions:

  • Enhanced performance of some polymer-based fluid-loss additives
  • Improved lubricating characteristics of muds
  • Controlled pH of water-based muds
  • Inhibited corrosion in water-based muds (to protect steel tubing, casing, and pipework)
  • Reversible cross-linking of viscosity-modifying polymers in water-based muds, especially when drilling deviated or horizontal wells
  • Stabilization of shale or clay strata in the reservoir formation rock (when used in combination with other components)
  • Inhibition of microbial spoilage of organic additives (e.g., viscosifying gums) in muds.

Boron for drilling fluids

For more information about the use of borates in fluids and lubricants for the oil and gas industry, read Boron in Oil and Gas Production.

Borates in metalworking

Metalworking fluids are primarily used in metal-cutting and metal-grinding applications to remove metal chips, reduce friction, and cool the cutting zone. In these fluids, borates can help to:

  • Inhibit rust
  • Reduce friction and wear
  • Provide efficient cooling
  • Act as bacteriostatic agents

Water-based metalworking fluid formulations generally include a corrosion-inhibitor component. Traditionally, a combination of sodium nitrite and an alkanolamine has been the inhibitor of choice for ferrous metal systems. However, concern over potential health hazards of the nitrite component has reduced or eliminated nitrite in these formulations. One potential replacement is an adduct of Optibor boric acid and alkanolamine plus a triethanolamine (10%), biocide (1%), and water (54%). Another contains 0.4% sodium nitrite, 0.3% sodium molybdate, and 0.1% 20 Mule Team borax decahydrate. (The presence of nitrite in this formulation is not considered hazardous because no amine-containing component is used.)

The major components in cutting fluids are fatty acids, alkanolamines, Optibor, and water. Typically, cutting fluids have approximately 25% of the reaction product between boric acid and alkanolamine. Boric acid alkanolamine esters act as bacteriostatic agents and corrosion inhibitors and have led to the development of high-quality water-miscible cutting fluids, longer emulsion charge life, and better workplace conditions.

Industrial machinery, transportation equipment, and fabricated metal applications account for almost 90% of the demand for metalworking fluids.

Water treatment

In heat-exchange devices that use aqueous solutions, corrosion to metals or alloys can result in deterioration of heat transfer and a shorter service life—particular concerns in central heating systems, cooling towers, and circulating water devices.

In the presence of oxygen, borates can promote the passivating growth of ferric oxide film. In addition, borates have a buffering ability that can make the solutions less aggressive. Borax decahydrate and Neobor are widely used as corrosion inhibitors and pH buffers in heat exchangers (generally similar to the inhibitor compositions used in automotive coolants). The synergism between borates and other inhibitors often decreases the required concentrations of other components in the formulation.

Borates provide protection for ferrous metals under mildly corrosive conditions and act as a buffer and neutralizer of acidic materials. (A minimum concentration of 0.6% borax is necessary to afford protection.) The optimal pH for closed heat-exchange systems is generally in the 9.8 to 10.5 range. This level can be maintained by using borax decahydrate and sodium hydroxide or 20 Mule Team Borax sodium metaborate. (The initial pH of water-treatment chemicals should be about 10-10.5, because the pH decreases in use. The additional alkalinity neutralizes the carbonic acid, due to the carbon dioxide of the air, which is absorbed on standing.) 20 Mule Team Borax ammonium pentaborate is also used in small quantities to protect steel in contact with polyvinyl acetate aqueous emulsions.


Borates in industrial water treatment

For more information about borates’ use in water treatment, read Boron in Other Applications.

20 Mule Team Borax Products

These 20 Mule Team Borax products are developed for use in the manufacture of industrial fluids and lubricants.

Ammonium Pentaborate

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

Borax Decahydrate

From detergents to dyes to adhesives, this mild alkaline salt does it all, particularly excelling as a buffering and fluxing agent. Learn More


With lower transportation, handling, and storage costs, this concentrated sodium borate is used in glass, fiberglass, cleaning products, and flame retardants. Learn More


From reducing melting temperatures in fiberglass production to inhibiting corrosion in fuel additives, Optibor has a multitude of uses in numerous industries. Learn More

Potassium Pentaborate

Unique capabilities make it ideal for the automotive industry, where its addition to gear lubricants improve load-carrying capacity and wear protection. Learn More

Sodium Metaborate

Provides increased viscosity, quicker tack, and better fluidity in starch and dextrin adhesives. Helps stabilize hydrogen peroxide solutions and neutralize acidic oxidation by-products in textile processing. Learn More

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 east of Los Angeles.  Learn more about Rio Tinto

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