Classification of nitride powder
Nitrogen has high electronegativity and can form a series of nitrides with many elements with lower electronegativity, including three types of ionic nitrides, covalent nitrides and metal nitrides.
Ionic Nitride
The nitrides formed by alkali metals and alkaline earth metal elements belong to ionic nitrides, whose crystals are mainly ionic bonds, and the nitrogen elements exist in the form of N3-, also known as salt-like nitrides. The chemical properties of ionic nitrides are more active, and they are easily hydrolyzed to form corresponding hydroxides and ammonia. At present, only Li3N is used in ionic nitrides. Li3N is a deep red solid, belonging to the hexagonal crystal system, with a density of 1.27g/cm3 and a melting point of 813°C. It is easy to synthesize and has high ionic conductivity. It can be combined with solid or liquid The coexistence of lithium is one of the best solid lithium electrolytes currently available.
Covalent nitride
The nitrides formed by group IIIA~VIIA elements are covalent nitrides, and their crystals are mainly covalent bonds. Among them, the compounds formed by oxygen, group VIIA elements and nitrogen elements should be accurately called nitrogen oxides and nitrogen halides. The most widely used covalent nitrides are mainly nitrides of group IIIA and IVA elements (such as BN, AlN, GaN, InN, C3N4 and Si3N4, etc.). The structural unit is similar to the tetrahedron of diamond, so it is also called class Diamond nitride. They have high hardness, high melting point, and good chemical stability. Most of them are insulators or semiconductors. They are widely used in cutting tools, high-temperature ceramics, microelectronic devices, and luminescent materials.
The properties and structures of common covalent nitrides
Metal nitride
The nitrides formed by transition metal elements belong to metallic nitrides, and the nitrogen atoms are located in the cubic or hexagonal close-packed metal lattice gaps, which are also called infill nitrides. The chemical formula of this type of nitride does not follow a strict stoichiometric ratio, and its composition can vary within a certain range. Most metal-type nitrides are of NaCl type structure, and the chemical formula is MN type. Generally it has metal-like properties, such as metallic luster, good conductivity, high hardness, high melting point, wear resistance and corrosion resistance, etc., and has good application prospects in cutting materials, electrode materials and catalytic materials.
Application of nitride powder
Cutting materials
TiN has high hardness (Mohs hardness: 8-9), high melting point (2950°C) and high wear resistance. It is often used as a coating for cutting tools in industry, which can effectively reduce tool wear and increase cutting rate. , But its hardness is still difficult to meet the requirements of high-hardness products.
The hardness of cubic boron nitride (c-BN) is second only to diamond. As an isoelectronic body of C, it not only has many excellent characteristics of diamond, but also has higher thermal stability and chemical inertness, which is a kind of promising development prospect. Tool material.
β-C3N4 is considered to be the hardest material at present and has attracted widespread attention, but its synthesis and characterization are the difficulties of current research.
High temperature structural materials
Silicon nitride (Si3N4) ceramics have high strength, high hardness, low density, corrosion resistance, good thermal shock resistance and excellent high temperature mechanical properties. They are widely used in the reinforcement phase of ceramic matrix composites and are considered to be the most promising. One of the most engineering ceramics.
Hexagonal boron nitride (h-BN) is a covalent bond compound. Because of its outstanding properties such as high thermal conductivity, good chemical stability, excellent thermal stability and better electrical insulation, it is widely used Used in refractory materials and ceramic matrix composite materials.
Luminescent material
Group IIIA~VA nitrides are a hot spot in the field of semiconductor light-emitting device research in recent years. Nitride has the advantages of high physical and chemical stability, continuously adjustable band gap, high saturation speed of wide band gap electron drift, low dielectric constant and good thermal conductivity, and Eu2+ and Ce3+ plasma are easy to be incorporated into the nitride structure to form shorter The Eu-N/Ce-N covalent bond reduces the 5d energy level of the activator ion and redshifts the excitation and emission wavelengths. Therefore, compared with other traditional phosphors, nitride phosphors have obvious advantages in terms of stability, color rendering, excitation wavelength and quantum efficiency, and are of great significance to the preparation of high-efficiency white LEDs.
Electrode material
Li3N has high ionic conductivity, but its decomposition voltage is too low (0.44V) to be directly used as an electrode. Transition metal nitrides have the advantages of good stability, high decomposition voltage and good conductivity, and they have received considerable attention as lithium ion anode materials. At present, the reported metal nitride anode materials include lithium cobalt nitride, chromium nitride, lithium manganese nitride, and vanadium nitride.
Catalytic material
Since Volpe et al. first reacted MoO3 and NH3 to produce γ-Mo2N with a large specific surface area (220m2/g) under temperature programmed conditions in 1985, transition metal nitrides have attracted great research interest as new catalytic materials. Because of its catalytic properties like precious metals, it is used in hydrogenation, hydrogenolysis, Fischer-Tropsch (FT) synthesis, NH3 synthesis and decomposition, hydrodesulfurization (HDS), hydrodenitrogenation (HDN) and electrocatalytic hydrogen evolution (HER), etc. It has good catalytic activity in the reaction.
Superconducting material
MN (M=Nb, Zr, Ti, V, Hf, Ta, Mo) is a NaCl-type face-centered cubic structure, which is a traditional superconductor. Their superconducting temperatures are: NbN, 17.3K; ZrN, 9.0K; TiN, 5.5K; VN, 8.5K; HfN, 8.83K; TaN and MoN, 12K. This type of superconductor has high hardness and stability, and is expected to become a superconductor material with excellent performance.
Absorbing material
Iron (nickel) nitride has high resistivity, high oxidation resistance, corrosion resistance and high ferromagnetism, and has a good application prospect in the field of absorbing materials.
Adsorption material
Porous boron nitride is composed of light elements, has a high specific surface area, high chemical stability and thermal stability, and is an ideal adsorption material.