What are metal boride nanoparticles?

Metal boride nanoparticles explained

Metal borides are compounds of a metal and boron. At the nanoscale, they take on properties that bulk materials do not have: stronger infrared absorption, higher surface reactivity and the ability to be formulated into stable inks and coatings. This makes metal boride nanoparticles useful in a range of industrial and optical applications where hardness, infrared shielding or thermal stability are needed.

What makes metal borides different from other hard materials?

Most hard materials, such as metal oxides or carbides, offer hardness and little else. Metal borides combine hardness with useful electronic and optical properties. The boron-metal bond in the crystal structure creates a rigid lattice that gives metal borides their mechanical strength, while the free electrons in the structure interact with light, particularly in the infrared range.

This combination of properties, hardness plus optical activity, is what makes metal boride nanoparticles interesting for coating applications. A single coating layer can function as both a wear-resistant surface and an infrared shielding layer at the same time. Metal borides are also classified as refractory borides, meaning they retain their properties at high temperatures. Most metal borides have melting points above 2000°C, which makes them stable under the kind of thermal stress that would quickly degrade other coating materials.

The main types of metal boride nanoparticles

Lanthanum hexaboride (LaB₆)

LaB₆ is the most widely studied metal boride nanomaterial for coating applications. It absorbs strongly in the 800 – 1400 nm near-infrared range and has a Vickers hardness of ca., 2000 HV (19.6 – 22 GPa). LaB₆ nanoparticles work as an infrared absorber at very low doses, between 10 and 100 mg per square metre, which keeps coatings thin and transparent. The combination of infrared absorption and extreme hardness in a single material is what sets LaB₆ apart from other metal borides.

For more on LaB₆ specifically, visit our LaB₆ nanoparticles page.

Cerium hexaboride (CeB₆)

Cerium hexaboride has similar properties to LaB₆, but with higher electrical conductivity. CeB₆ has a low work function and is used as a cathode material in electron microscopes and other electron-emitting applications. Compared to LaB₆, CeB₆ cathodes have lower evaporation rates and higher electron emissivities, which means they last longer and produce a more stable electron beam. CeB₆ cathodes also show lower carbon contamination in the electron column, which makes them a preferred choice in high-precision electron microscopy. Its infrared absorption properties are less pronounced than those of LaB₆, but its high conductivity makes it useful in applications where electrical performance matters alongside optical properties.

Calcium hexaboride (CaB₆)

Calcium hexaboride is one of the hardest metal borides, with a Vickers hardness of around 2700 HV. It has semiconducting properties and is used in research and development applications. CaB₆ is also being studied for its potential as a thermoelectric material.

Strontium hexaboride (SrB₆)

Strontium hexaboride belongs to the same hexaboride family as LaB₆ and CeB₆. Unlike LaB₆, SrB₆ absorbs primarily in the visible light range and is transparent in the near-infrared range. It is studied for its magnetic and thermoelectric properties rather than for infrared absorbing coating applications.

Titanium diboride (TiB₂)

Titanium diboride is one of the hardest metal borides available, with a Vickers hardness of up to 3400 HV. It has high electrical conductivity and excellent wear resistance. TiB₂ is used in hard coatings for cutting tools, wear-resistant industrial applications and as an additive in metal matrix composites. Unlike the hexaboride compounds, TiB₂ does not have the same infrared absorption properties, but its hardness and conductivity make it useful in applications where mechanical performance is the primary requirement.

Metal boride nanoparticles in coating applications

The properties of metal boride nanoparticles make them useful in several coating applications:

Infrared shielding coatings

LaB₆ nanoparticles are used in solar control coatings for automotive glass, architectural glazing and optical films. They block near-infrared radiation while keeping visible light transmittance intact, reducing heat build-up in buildings and vehicles.

Hard and wear-resistant coatings

TiB₂ and LaB₆ nanoparticles are used in wear-resistant coatings where high surface hardness is needed. Their refractory boride structure gives them thermal stability alongside mechanical strength.

Cathode materials

LaB₆ and CeB₆ single crystals are used as hot cathode materials in electron microscopes, electron beam welding equipment and X-ray tubes, where a stable, high-intensity electron beam is needed at high temperatures.

Functional ink coatings

Partners in Chemicals offers LaB₆ as part of a patented ink platform (WO2025063847) that uses metal boride nanocrystals formulated into a stable ink. This ink can be applied through spray coating, dip coating or inkjet printing and dries below 90°C, making it possible to coat flexible and heat-sensitive substrates that cannot be processed by conventional high-temperature methods.

For more on the ink platform and how it compares to CVD and PVD, read our article on CVD, PVD and ink-based coating.

Metal boride nanoparticles and the Partners in Green Chemicals portfolio

Partners in Chemicals supplies metal boride nanoparticles, including LaB₆, as part of a broader portfolio of functional materials. For an overview of the metal borides available and their applications in green chemistry, visit the metal borides page on Partners in Green Chemicals.

Summary

Metal boride nanoparticles combine hardness, infrared absorption and thermal stability in a single material. The main types used in coating applications are LaB₆, CeB₆, CaB₆, SrB₆ and TiB₂, each with different properties and applications. LaB₆ is the most widely used for infrared shielding coatings, while TiB₂ offers the highest hardness for wear-resistant applications. A new ink platform makes it possible to apply metal boride nanoparticles as functional coatings at low temperatures, on substrates that conventional methods cannot reach.