Here’s Everything about Boron Nitride

November 14, 2024

What is Boron nitride

Boron nitride is a new type of ceramic material based on the synthesis of boron and nitrogen elements. The advanced ceramic material is super hard and resistant to high temperatures and chemical corrosion. It is a covalent compound with the chemical formula BN; its composition is 43.6% boron and 56.4% nitrogen.

Boron Nitride Crystal Structure

Boron nitride exists mainly in the form of four isomers, namely hexagonal boron nitride (HBN), rib-square boron nitride (RBN), cubic boron nitride (CBN), wurtzite boron nitride (WBN) respectively.

Hexagonal Boron Nitride (h-BN) Crystal Structure

Hexagonal boron nitride (HBN) is a white powder composite material. The crystal structure of HBN boron nitride is similar to that of graphite, and their physical and chemical properties are also very similar; therefore, hexagonal Boron Nitride Ceramic is also called "white graphite". From the perspective of hexagonal boron nitride molecule and structure, it is a stacked layered hexagonal crystal system, which is the same as the crystal structure of graphene, Refer to figure 1, and it is the most stable crystal phase in boron nitride.

Figure 1: hBN and rBN Crystal Structure

Rhombohedral Boron Nitride(r-BN) Crystal Structure

Rhombohedral boron nitride is known for its unique molecular geometric arrangement order. Its crystal structure belongs to the rhombohedral system, Refer to Figure 1, Rhombohedral boron nitride has unparalleled chemical and physical properties and performs outstandingly in specific high-tech fields.

Cubic Boron Nitride (c-BN) Crystal Structure

The crystal structure of cubic boron nitride is similar to that of diamond, Refer to figure 2. It has extremely high hardness, wear resistance, and chemical stability. Compared with the Vickers hardness of synthetic diamond of 100GPa, the value of cubic boron nitride is as high as 108GPA.

Figure 2: cBN and wBN Crystal Structure

Wurtzite Boron Nitride(w-BN) Crystal Structure

The crystal structure of wurtzite boron nitride is also hexagonal but slightly different from hexagonal boron nitride, Refer to Figure 2. It is a very rare substance and is 18% harder than diamond.

How is Boron Nitride Made

The following content will outline several mainstream preparation methods for boron nitride materials:

1. Chemical vapor synthesis

This method uses thermal chemical vapor deposition or pulse plasma technology to decompose and deposit boron nitride film or powder on the substrate surface using reaction gases containing boron and nitrogen, such as BCl3, B2H4, NH3, etc., under low temperature and low-pressure conditions. Chemical vapor synthesis has simple equipment and is suitable for large-scale production.

2.‌Borax-ammonium chloride method

This method uses anhydrous borax and ammonium chloride as the primary raw materials to react and synthesize boron nitride in an ammonia atmosphere. The chemical reaction formula is Na2B4O7+2NH4CI+2NH3→4BN+2NaCl+7H2O.

3.Boric anhydride method

This method uses boric anhydride (B2O3) as the primary raw material and tricalcium phosphate as the filler. The two are mixed in a mass ratio of 5:3 and then subjected to a nitridation reaction. The reaction product is treated with hydrochloric acid and alcohol to obtain crude boron nitride.

4. Borax-urea method

This method pre-purifies borax and urea by recrystallization, then mixes and nitrides them at 900-1100°C for 1-2 hours to obtain coarse-crystalline boron nitride.

Na2B4O7+2CO(NH2)2→4BN+Na2O+4H2O+2CO2↑

Strengths of Boron Nitride

※ High insulation resistance

※ Low dielectric constant, k=4

※ High dielectric strength: High insulation breakdown strength, up to 40 KV/mm

※ Low friction coefficient: Within 0.1~0.3, the friction heat is minimal

※ High hardness: Cubic boron nitride and wurtzite are even harder than diamonds.

※ Lightweight: Boron nitride is low-density and lightweight compared to other Advanced Ceramics.

※ Small thermal expansion coefficient

※ Excellent thermal conductivity: Boron nitride ceramic material has high thermal conductivity

※ Excellent thermal shock resistance: No cracks will occur in the rapid cooling and heating environment up to 1500℃:

※ High-temperature resistance: Boron nitride melting point is 3000℃. Structural stability and mechanical properties can be maintained.

※ Self-lubricating property: Boron nitride has good self-lubricating properties and can be used as a high-temperature lubricant

※ Non-wetting: Boron nitride ceramics are not soluble in molten glass, metals, acids, alkalis, and salts

※ Chemical stability: BN ceramic material offers chemical inertness and anti-corrosion

※ Excellent machinability: A good machinable ceramic material that achieves any geometries with a tight tolerance

BN Material Grades

According to the purity of boron nitride and the addition of different types of impurities, it can be divided into pure boron nitride and boron nitride composite ceramics.

※ The purity of pure boron nitride includes 99% and 99.5%, two types

※ Boron nitride composite ceramics: SiO2 type, Si3N4 type, AlN type, ZrO2 plus SiC type, TiB2 plus AlN type

Different types of boron nitride can provide individual physical and chemical characteristics to meet the particular requirements of various fields.

Boron Nitride Material Properties

Pure Boron Nitride

Property	Unit	Grade
Property	Unit	BN-1A	BN-2A	BN-1B
Purity of BN	%	99	99.5
Other Ingredients		No	No	No
Density	g/cm³	1.9~2.0	1.55~1.65	2.15
Hardness	HL	300~400	200~300	450
Flexural Strength	MPa	35	33	95
Coefficient of Thermal Expansion(25℃-1200℃）	10^-6/K	-1~2.5	-1~2	1~2
Thermal Conductivity at 20℃	W/m.K	40	60	35
Max Service Temperature	In the air	900℃	900℃	900℃
	Vacuum	1800℃	1800℃	1600℃
	Inert	2200℃	2200℃	1800℃
RT Resistivity	ohm. cm	1*10¹⁴	1*10¹⁴	1*10¹⁴

Composite Boron Nitride

Grade	Unit	BN-T	BN-E1	BN-A	BN-N	BN-S
Main Ingredients		BN+TiB2+AIN	BN+ZrO2+SiC	BN+AIN	BN+Si3N4	BN+SiO2
Density	g/cm3	3.01	2.3~2.35	2.8~2.9	2.5~2.6	2.1~2.5
Hardness	HL		570~620	≧6.5	650~680	700~750
Flexural Strength	MPa	155	160	250~300	280	75
Coefficient of Thermal Expansion(25℃-1200℃）	(10/K)	6.0~7.0	2.0~3.0	4.0~5.0	2.5~3.0	2.5~3.0
Thermal Conductivity @ 20℃	W/m.K	40	15	65	45	20
Max Service Temperature	In the air	950℃	900℃	950℃	950℃	＞1000℃
Max Service Temperature	Inert	2000℃	1700℃	2000℃	1700℃	＞1000℃
RT Resistivity	Ohm. cm	250~1000μ	10¹²	10¹⁴	10¹⁴	10¹⁴

Boron Nitride Applications

Thanks to the versatile characteristics of boron nitride, it has been used in many high-tech industries. You can see the specific uses below:

By Function

※ Boron nitride nozzle

※ Boron nitride bolt carrier

※ Boron nitride thermal paste

※ Cubic boron nitride inserts

※ Wurtzite boron nitride knife

※ Boron nitride barrel coating

※ Wurtzite boron nitride armor

※ Cubic boron nitride cutting tools

※ Combat boron nitride aerosol spray

※Hexagonal boron nitride lubricant

※ Diamond-cutting blade boron nitride

※ Diamond cutting wheel boron nitride

※ Cubic boron nitride CBN grinding wheels

※ Hexagonal boron nitride bullet coating

※ Cubic boron nitride aerosol spray coating

By Structure

※ Boron nitride plate

※ Boron nitride ring

※ Boron nitride rod

※ Boron nitride wafer

※ Boron nitride disk

※ Cubic boron nitride ring

※ Wurtzite boron nitride ring

※ Boron nitride ceramic nanotubes

※ Boron nitride ceramic nanosheet

※ Boron nitride sputtering target disc

Summary

Boron nitride is a ceramic material with high-temperature stability, thermal conductivity, chemical corrosion resistance, and ultra-high hardness. It has played an irreplaceable role in many high-tech fields. Boron nitride can be prepared in various ways, but each method has limitations. With the continuous deepening of the exploration and research of boron nitride, its performance will be further improved and expanded to more application areas.

Author:

Mr. Andy Chen

E-mail:

andy@jinghui0738.com

Phone/WhatsApp:

+86 13760126904