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Boron carbide

The black diamond

Because of its properties, boron carbide (B₄C) is considered an extremely hard and wear-resistant technical ceramic material. That’s why it’s ideally suited for processing extremely hard materials – whether in powder or paste form as an abrasive or lapping agent or sintered as a blasting nozzle. Boron carbide products are characterised by minimal wear and an exceptionally long service life at low costs. In addition, lightweight boron carbide composite structures are used for ballistic protection in modern military equipment. This all-round material also serves as a filler, e.g. to increase wear resistance in metals or plastics, as high-temperature semiconductors and as neutron absorbers in nuclear facilities.

Boron carbide as abrasive and lapping agent

Industry today requires efficient, heavy-duty processing materials for surface treatment – for example of carbide metals or solid ceramics – which combine several requirements such as service life, quality and cost efficiency.

Capabilities of the material boron carbide

Boron carbide is one of the hardest engineering materials known to man (hardness around 30,000 N/mm²) – only diamond and cubic boron nitride are harder. Boron carbide in the form of powder and pastes are therefore ideally suited as an abrasive and lapping agent with a high material removal rate for processing super-hard materials.

Fields of application of boron carbide as abrasive and lapping agent

  • Boron carbide powders and pastes enable problem-free surface processing of wear-resistant carbide metals, non-ferrous metals, titanium as well as minerals, ceramics and hard plastics such as PTFE. Due to its extreme hardness, this material is also ideal for trimming wire saws that are used to slice oxide or non-oxide ceramics and even sapphires.
  • In addition, boron carbide is suitable as a cutting material in tool machining, e.g. for drilling brittle and hard materials.
  • Boron carbide pastes are commercially available and are used in a variety of ways:
    • For lapping of machine components
    • For machining of tools, drawing dies, wire guides and dies of all kinds
    • For surface treatment of cylinder liners and running surfaces, valves, valve seats and injection pumps
    • For processing of cutting and punching tools, milling cutters, reamers, gages, optical lenses, ceramics, synthetic and natural gemstones

Water-soluble boron carbide pastes with polyalcohols can be used in temperatures of up to max. 200 °C/392 °F. Oil-based boron carbide pastes (rust protection) are even suitable for application temperatures of up to a maximum of 350 °C/665.6 °F.

Tip: If necessary, petroleum and oil can be used as thinners. The use of petroleum or benzine is recommended for cleaning machined components.Tip: If necessary, petroleum and oil can be used as thinners. The use of petroleum or benzine is recommended for cleaning machined components.

Advantages of boron carbide pastes

  • A high surface quality is achieved through the narrow grain gathering
  • High removal rates ensure a short processing time
  • Even grinding, including at high temperatures

Boron carbide for ceramic blasting nozzles

Blasting with abrasive, exceptionally hard blasting media requires extremely resistant blasting nozzles: for deburring, removing impurities or for surface treatment. Of crucial importance is a long service life with low material costs.

Capabilities of the material boron carbide

Boron carbide is one of the hardest engineering materials with exceptional abrasion resistance. In sintered form, this makes the material ideal for blasting nozzles with uniform blasting power, minimal wear and an exceptionally long service life even when extremely hard, abrasive blasting agents such as sand, corundum and silicon carbide are used.

Material comparison based on the relative costs per blasting time

Blasting nozzles made of:

Boron carbide

0.9

Carbide metal / KO3

1.8

Silicon carbide

2.1

Silicon nitride

2.2

Aluminum oxide

2.8

Typical fields of application of boron carbide blasting nozzles

  • Deburring of moulded parts
  • Shot peening (cleaning in construction, engraving in the glass industry, modeling in the dental industry)
  • Preparing surfaces for coatings or bonding
  • Removing contaminants
  • Finishing matt surfaces
  • Dental and fine jet nozzles for cleaning and modeling of e.g. dentures, or matting or engraving of glass

Boron carbide ceramic as ballistic protective material

Modern military equipment with good hard armour protective material depends on a high degree of hardness and compressive strength, and a high modulus of elasticity coupled with low weight. Boron carbide is superior to all alternative materials in this area. Because compared to armoured steel or aluminium oxide, the same ballistic protection is achieved but at a significantly lower weight. Particularly high degrees of protection are achieved when boron carbide is combined with a high-quality composite carrier structure made of polyethylene-based fibres such as Spectra Shield or Dyneema, as well as aramid fibres such as Kevlar and Twaron.

Basis weights for ballistic protection by material type

Boron carbide composite systems (German SK4)

< 30 kg/m2

Silicon carbide (German SK4)

36 kg/m2

Aluminium oxide (German SK4)

42 kg/m2

Fields of application of boron carbide ceramics for ballistic protection

  • For ballistic body protection, either: 
    • perfectly fitting monolithic boron carbide plates, or
    • hot-pressed boron carbide plates in combination with high-performance composite carrier structures (backing) are used for front and back body armour.
  • Boron carbide provides excellent ballistic protection and at the same time reduced weight.
  • Ballistic vehicle protection: Military vehicles need protection against a variety of threats in the form of ballistic projectiles and fragmentation – from handguns to medium and large caliber weapons to mines, improvised explosive traps, IEDs (improvised explosive devices), EFPs (explosively formed penetrators) and RPG (rocket propelled grenades). For this purpose, vehicle armour made of light boron carbide composite structures in the form of plates, hexagons or cylinders/pellets are used. They also enhance underbody protection against explosions.
  • Significantly low weight with maximum protection against ballistic projectiles is particularly important for aircraft such as helicopters and airplanes. For example, custom-made ceramic panels made of boron carbide or hot-pressed boron carbide plates are used for pilot seats in helicopters.

Other uses and areas of application of boron carbide

  • Boron carbide powder is a starting material for sintering and hot pressing in the manufacture of boron carbide sintered parts. In this form it can be found, among other things, in dressing and grinding stones and as a lining for ball mills and mortars. Boron carbide powder is also used as a sintering additive for high-performance SiC ceramics. 
  • Due to its extreme hardness (9.6 Mohs), boron carbide is also ideal for coating processes such as thermal spraying (by means of melting, atomising and spraying), for wear protection as well as for welding. 
  • Boron carbide powder normally has a consistently high degree of purity, with the desired boron-carbon ratio of 4:1 achieved almost exactly. The high boron content of 80 percent makes the material an extremely inexpensive boron source. Boron carbide is the starting material for the production of metal borides and boron halides (e.g. boron trichloride BCI3). 
  • Boron carbide is a high-temperature p-type semiconductor. Depending on the doping, the material shows a high degree of electrothermal resistance and in combination with graphite, it’s used as a thermocouple at up to 2,300 °C. That’s why it can also be considered an electricity generator for direct conversion of thermal energy into electrical energy in unmanned space vehicles. 
  • Boron carbide is an extremely effective neutron absorber, which is why it can also be used as a so-called “first wall” in future fusion reactors. 

Production of boron carbide

In its granular crystalline form, boron carbide is produced in an electric arc furnace from boron oxide and carbon at temperatures above 2,400 °C/4,352 °F. In the subsequent processing steps, the resulting shiny black granular crystals are separated from the unreacted material and then crushed, classified and ground to the sub-µ size. Grain size ranges between 0.8 μm and 20 μm (for sinter technology) are customary in the trade. The 3M group is currently one of the largest producers of boron carbide in the western hemisphere.

Form and properties

Boron carbide (B₄C) is also called “black diamond” because of its shiny black crystals (rhombohedral crystal structure). The non-oxide ceramic is characterised by its particular hardness and wear resistance (even at low operating temperatures).

Extreme hardness

9.6 Mohs

Crystal structure

Rhombohedral

Melting point

2.350 °C/4,892 °F

Specific weight

2.50 g/cm³

Boron carbide is chemically inert (resistant to hot nitric acid and hydrogen fluoride) and almost insoluble in water. It’s only significantly attacked by chlorine or oxygen at a temperature above 1,000 °C/1,832 °F. In addition, B₄C is electrically conductive, highly thermally conductive and has excellent heat resistance.

From 3M™ Ceramics Experts: Non-binding advice for your company

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