Boron Nitride (BN) Introductions

Boron Nitride [10043-11-5], exists as three different poly-morphs:
Alpha-boron nitride (α-BN), a soft and ductile polymorph with a hexagonal crystal lattice similar to that of graphite, also called hexagonal boron nitride(HBN) or white graphite;
Beta-boron nitride (β-BN), the hardest manmade material and densest polymorph, with a cubic crystal lattice similar to that of diamond, also called cubic boron nitride (CBN) or borazon;
Pyrolitic boron nitride (PBN), from a chemical point of view, boron nitride oxidizes readily in the air at temperatures above 1100°C, forming a thing protective layer of boric acid(H3BO3) on its surface that prevents further oxidation as long as it coats the material. Boron nitride is stable in reducing atmospheres up to 1500°C.

INNOVACERA Material Grades

HPBN
High purity hot pressed boron nitrides
Diffusion bonded (no binder)
Low dielectric constant & loss tangent
Minimal moisture pick-up
Chemically purified
Thermally purified

ZRBN
Boric oxide binder
Highest density
Highest strength

CABN
Calcium borate binder
High density
Best moisture resistance

Thermal Management

The unique combination of excellent electrical insulation and thermal conductivity makes BN very useful as a heat sink in high power electronic applications. Its properties compare favorably with aluminum oxide and other electronic packaging materials, yet is easier to form and finish.

High Temperature Environments

Temperature stability and excellent resistance to thermal shock make BN the material of choice in the toughest high temperature environments such as equipment for plasma arc welding, diffusion source wafers, and semiconductor crystal growth equipment & processing.

Molten Metal Handling

BN is inorganic, inert, nonreactive with halide salts and reagents, and is not wet by most molten metals and slags. These characteristics, combined with low thermal expansion, make it ideal for interface materials used in various molten metal processes.

Industrial Preparation

Cubic BN or Borazon, is produced by subjecting hexagonal BN to extreme pressure and heat in a process similar to that used to produce synthetic diamonds. Melting of either phase is possible only with high nitrogen overpressure. The alpha-phase decomposes above 2700°C. at atmospheric pressure and at ca.1980°C in a vacuum.
Hexagonal BN is manufactured using hot pressing or pyrolytic deposition techniques. These processes cause the orientation of the hexagonal crystals, resulting in varying degrees of anisotropy. There is one pyrolytic technique that forms a random crystal orientation and anisotropic body; however, the density reaches only 50 to 60% of the theoretical density. Both manufacturing processes yield high purity, usually greater than 99wt.% BN. The major impurity in the hot-pressed materials is boric oxide, which tends to hydrolyze in the presence of water, degrading the dielectric and thermal-shock properties of the material. The addition of calcium reduces water absorption. Hexagonal hot-pressed BN is available in a variety of sizes and shapes, while the pyrolytic hexagonal materials are currently available in thin layers only.

Sourcing: Francois Cardarelli 2008 Springer London [Materials Handbook, A Concise Desktop Reference] 2nd Edition ISBN 978-7-5603-4451-5

氮化硼介绍：
氮化硼[10043-11-5]存在三种不同的多形体：
1. α-氮化硼(α-BN)，这是一种柔软而延展的多形体，其六角晶格类似于石墨，也称为六角氮化硼（HBN）或白色石墨；
2. β-氮化硼(β-BN)，这是最坚硬的人造材料，也是密度最高的多形体，其立方晶格类似于钻石，也称为立方氮化硼（CBN）或硼氮石；
3. 热裂解氮化硼(PBN)，从化学角度来看，氮化硼在1100°C以上的空气中容易氧化，形成一层薄薄的硼酸（H3BO3）保护层，这层保护层防止了进一步氧化，只要它覆盖了材料表面。氮化硼在还原性气氛下稳定，可达1500°C。

INNOVACERA材料等级：
1. HPBN
– 高纯度热压氮化硼
– 扩散结合（无粘合剂）
– 低介电常数和损耗切线
– 最小吸湿
– 化学纯化
– 热纯化

2. ZRBN
– 硼酸盐粘合剂
– 最高密度
– 最高强度

3. CABN
– 钙硼酸盐粘合剂
– 高密度
– 最佳防潮性

热管理：
氮化硼具有出色的电绝缘性和热导率的独特组合，使其在高功率电子应用中作为散热器非常有用。其性能与氧化铝和其他电子封装材料相比具有优势，同时更容易成型和加工。

高温环境：
氮化硼具有温度稳定性和优异的耐热震性，因此在最苛刻的高温环境中，如等离子弧焊设备、扩散源晶片和半导体晶体生长设备及处理设备等方面成为首选材料。

熔融金属处理：
氮化硼是一种无机、惰性、不与卤化盐和试剂反应的材料，大多数熔融金属和渣浆不会沾附其表面。这些特性与低热膨胀相结合，使其成为各种熔融金属过程中使用的界面材料的理想选择。

工业制备：
立方氮化硼或硼氮石是通过将六角氮化硼置于极高的压力和温度下制成的，这个过程类似于制造合成钻石的过程。在高氮过压的情况下，才可能熔化任何一相。α-相在大气压下在2700°C以上分解，在真空中约在1980°C分解。
六角氮化硼是通过热压和热裂解沉积技术制造的。这些过程会导致六角晶体的定向排列，从而产生不同程度的各向异性。有一种热裂解技术可以形成随机晶体定向排列和各向同性体；然而，密度仅达到理论密度的50%至60%。这两种制造过程都可以获得高纯度的氮化硼，通常大于99wt.% BN。在热压材料中的主要杂质是硼氧化物，它在水存在的情况下容易水解，降低了材料的介电性能和耐热震性。添加氧化钙可以减少吸湿。六角热压氮化硼可以制成各种尺寸和形状，而六角热裂解材料目前仅以薄层形式提供。