Boron Nitride Powders

In simple terms, hexagonal boron nitride, hBN, is very similar to graphite. It is the most stable and soft among BN polymorphs, and is therefore used as a filler, lubricant and an additive to cosmetic products. The cubic boron nitride, cBN, has similar crystal structure as diamond, and is the second- hardest known material after diamond. 

Here at Saint-Gobain we do not supply cBN.

Pyrolytic boron nitride, or PBN, is hexagonal boron nitride synthesized and grown on a substrate via chemical vapor deposition.

Here at Saint-Gobain we do not supply PBN. 

The best results occur when there is percolation of the filler particles through the thickness of the composite. This creates a continuous thermal pathway along the filler particles, which will boost the thermal conductivity much more than a system without good particle-to-particle contact. The percolation threshold should be considered when determining the amount of filler to add to the system.

Boron nitride grade selection for thermal conductivity improvement typically depends on 3 key factors –

1. Particle size tolerance of your resin system (or bond line thickness)
2. Desired plane of thermal conductivity improvement (in-plane or through-plane)
3. Mixing/dispersion process employed (high shear or low/medium shear)

You should be sure that the largest particle size does not exceed the intended thickness or cross section of the final product. It isn’t uncommon for formulators to mix more than one size distribution to achieve better packing of the BN particles and optimal percolation in the resin matrix. 

Platelets tend to align in the direction of resin flow, and due to its inherent anisotropy, offer a very good in-plane thermal conductivity.  Platelets also allow for the addition of BN to systems that require a very thin layer or bond line that would be too big to allow agglomerates to be added. 

Agglomerate grades - where small BN platelets are randomly oriented in all directions, like a snowball - overcome this limitation making BN an isotropic filler suitable for in-plane as well as through-plane thermal conductivity improvements.  Spherical Agglomerates (SA grades) are lower density, but have the benefit of high flowability, packing, and tight particle size distribution. High Density Agglomerates (HD grades) are the strongest agglomerates and will resist breakdown during mixing.

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Platelet grades are single-crystal BN particles, that are small but robust, and do not break down under high shear forces. Platelet grades are suitable for high shear operations like twin screw compounding and extrusion.

Spherical and agglomerated grades, on the other hand, are comprised of multiple small boron nitride platelets, held together by interlocking planes without addition of any binder system. This makes these grades particularly susceptible to breaking apart when subjected to high shear. These grades are suitable for low-medium shear mixing operations.

BN is white, non-toxic, stable, and inert. It is oxidation resistant up to about 900°C (unlike graphite, which oxidizes below 500°C). BN keeps its lubricity above 500°C, which is the limiting temperature for graphite as a solid lubricant in air. BN also retains it lubricity in inert or vacuum conditions.

In addition, boron nitride has a low dielectric constant, making it an ideal material for insulation, protection and low dielectric loss.  

Boron nitride powders are the lamellar form of BN, which resembles graphite.  Each powder particle is a platelet made up of many layers. Each layer is a flat plane of covalently bonded boron and nitrogen atoms in a hexagonal pattern. While the bonds within each layer are strong, the forces keeping those layers together, called Van der Waals forces, are very weak, causing the soft and lubricious effect when the platelets are rubbed or sheared, and the layers cleave apart.  

Additionally, the surfaces of high purity Saint-Gobain BN crystals are free of carbon and other impurities, and therefore there is no “drag” or sticky feeling when used in cosmetic formulations.

The key difference is in particle size and crystal morphology. All grades are high purity and pass global regulations for heavy metals.  With grades ranging from 2 to 30 microns in average diameter, the appearance will change as well, going from a matte white appearance to a more translucent or shiny appearance as platelet diameter increases.

Single platelets of high purity hexagonal BN appear transparent when viewed through the platelet face.  This can be seen visually on large platelets, which appear to sparkle when light reflects off the platelet face.  Most fine mesh BN powders form agglomerates that, if not dispersed, appear white and opaque. 

The amount of BN filler in a formulation is completely up to formulator, the application, and desired results. BN is typically added to cosmetic formulations from 3 – 10%.

Standard packaging for boron nitride powders is 25 kg in cardboard boxes or drums. Depending on the grade, our manufacturing lot sizes could be between 250 lbs to 1200 lbs.