Applications and properties of nitride powders in modern industry

Nitrides are a class of chemical compounds where nitrogen is combined with elements of similar or lower electronegativity, such as metals. They are known for their high chemical and thermal stability, resistance to corrosion, and mechanical strength, making them valuable in various industrial applications. They are used in structural ceramics, heat conductors, semiconductor technology, and more.

Classification of Nitrides

Nitrogen, with its high electronegativity, can form a range of nitrides with elements that have lower electronegativity. These include ionic nitrides, covalent nitrides, and metallic nitrides. Each type exhibits distinct properties and applications, reflecting the versatility of nitrogen in forming compounds.

Ionic Nitrides

Ionic nitrides, formed by alkali and alkaline earth metals, are known as salt-like nitrides. They are chemically active, easily hydrolyzing to produce hydroxides and ammonia. Lithium nitride (Li₃N) is the most utilized, being a solid electrolyte with high ionic conductivity, a density of 1.27 g/cm³, and a melting point of 813°C. It's essential for solid-state lithium batteries.

Covalent Nitrides

Nitrides formed by elements from groups IIIA to VIIA are known as covalent nitrides, primarily featuring covalent bonds within their crystals. Compounds formed by nitrogen with oxygen and group VIIA elements should be accurately referred to as oxides of nitrogen and halides of nitrogen. The widely used covalent nitrides are those of group IIIA and IVA elements, such as BN, AlN, GaN, InN, C₃N₄, and Si₃N₄, which are also known as diamond-like nitrides due to their tetrahedral structural units similar to diamond. These nitrides are characterized by their high hardness, melting points, and chemical stability. Most are insulators or semiconductors and are extensively used in applications such as cutting tools, high-temperature ceramics, microelectronic devices, and luminescent materials.

Table 1. Properties and Structures of Common Covalent Nitrides

Metallic Nitrides

Metallic nitrides formed by transition metals feature nitrogen atoms situated in the interstices of cubic or hexagonal close-packed metal lattices, also known as interstitial nitrides. Their chemical formulas do not adhere to strict stoichiometric ratios and can vary within a certain range. Most metallic nitrides have an NaCl-type structure, with the general formula MN. They typically exhibit metallic properties such as luster, good electrical conductivity, hardness, high melting points, wear resistance, and corrosion resistance. These properties make them promising for use in cutting materials, electrode materials, and catalytic materials.

Table 2. Properties and Structures of Common Metallic Nitrides

Applications of Nitrides

Cutting Materials

• Titanium Nitride (TiN): It boasts a high hardness (Mohs hardness: 8-9), a high melting point (2950°C), and considerable wear resistance. It is commonly used as a coating for cutting tools in industry, effectively reducing tool wear and enhancing cutting rates. However, its hardness still falls short of the requirements for very hard products.
• Cubic Boron Nitride (c-BN): It is an isoelectronic counterpart to carbon, second only to diamond in hardness. It not only shares many of the diamond's excellent properties but also exhibits higher thermal stability and chemical inertness, making it a cutting material with promising prospects.
• Beta Carbon Nitride (β-C3N4): It is considered to be one of the hardest materials known, garnering widespread attention. However, its synthesis and characterization remain challenging areas of research.

High-temperature Structural Materials

• Silicon Nitride (Si₃N₄): It is renowned for its high strength, hardness, low density, corrosion resistance, thermal shock resistance, and exceptional high-temperature mechanical properties. It is widely used as the reinforcing phase in ceramic matrix composites and is considered one of the most promising engineering ceramics.
• Hexagonal Boron Nitride (h-BN): It is a covalent compound known for its high thermal conductivity, good chemical stability, excellent thermal stability, and decent electrical insulation. These outstanding properties make it extensively used in refractory materials and ceramic matrix composites.

Electrode Materials

Lithium nitride (Li₃N): It has a high ionic conductivity but a low decomposition voltage (0.44V), which precludes its direct use as an electrode. Transition metal nitrides are garnering considerable attention as lithium-ion anode materials due to their good stability, high decomposition voltage, and conductivity. Reported metal nitride anodes include lithium cobalt nitride, chromium nitride, lithium manganese nitride, and vanadium nitride.

Superconducting Materials

• MN (M = Nb, Zr, Ti, V, Hf, Ta, Mo) compounds with a NaCl-type face-centered cubic structure are a class of traditional superconductors. These superconductors are known for their high hardness and stability, and they hold promise as materials for superior-performance superconductors.

Table 3.  MN (M = Nb, Zr, Ti, V, Hf, Ta, Mo) Superconducting Temperature

Wave-absorbing Materials

• Iron (nickel) nitrides, with their high resistivity, strong oxidation resistance, corrosion resistance, and high ferromagnetism, hold promising prospects in the field of wave-absorbing materials.

Absorbent Materials

• Porous boron nitride, composed of light elements, possesses a high specific surface area, chemical stability, and thermal stability, making it an ideal adsorbent material.

As technology advances, nitride powder technology is facing new development opportunities. High-thermal-conductivity silicon nitride ceramics become indispensable components for next-generation high-power electronic devices. In renewable energy, inorganic nitride nanomaterials are attracting widespread attention due to their novel electrochemical activities and high chemical stabilities, especially in applications like electrochemical hydrogen evolution reactions, rechargeable batteries, supercapacitors, solar cells, and fuel cells.

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