The chemical properties of nitrogen element are very stable, but under some special conditions, it can form nitrides with many elements. Among these nitrides, the transition metal nitrides — Titanium nitride (TiN) has become the focus of research at home and abroad. Titanium nitride is a small wet structural material with attractive gold color, high melting point, high hardness, good chemical stability, and metal, and has high conductivity and superconductivity. It can be used in high temperature structural materials and superconducting materials.
1. Structure and properties TiN has a typical NaCl structure, belonging to a face-centered cubic lattice. The top of face-centered cubic is nitrogen atoms, and titanium atoms are located in the (1/2,0,0) space of face-centered cubic. TiN is a non-stoichiometric compound, and its stable composition range is TiN0.6~TiN1.16. Nitrogen content can change within a certain range without causing changes in TiN structure. TiN powders are generally yellowish-brown, ultrafine TiN powders are black, and TiN crystals are golden yellow. TiN the lattice constant of a = 4.23 nm, TiC of lattice constant is a = 4.238 nm, TiO the lattice constant of a = 4.15 nm, the lattice parameters of three kinds of material is very close, so the TiN nitrogen atom in the molecule can be oxygen, carbon atom in an arbitrary than replace solid solution formation, physical and chemical properties of titanium nitride determined by the content of nitrogen, when the nitrogen content is reduced, the lattice parameters of titanium nitride instead increases, the increase of hardness have microscopic, but titanium nitride earthquake resistance decreases.
Physical properties: melting point of 2950.6 ~ 3205.8℃, linear expansion coefficient of 5.712 ~ 7.053×106(1/K)(25℃), density of 5.435 ~ 5.447g/cm3, thermal conductivity of 25.081(W· M-1 ·K-1)(300 ~ 2000℃), Mohrwell hardness of 8 ~ 9. In general, the color of ti nitride powder is tan, the color of black is ultrafine TI nitride powder, the color of yellow is TI nitride crystal, a large number of aggregation of TI nitride crystal has golden metallic luster. Chemical properties of titanium nitride: relatively stable, with water and acid (hydrochloric acid and sulfuric acid) do not react, but it can be incorporated into hydrofluoric acid, if hydrofluoric acid contains oxidant, titanium nitride will be completely dissolved in hydrofluoric acid. Titanium nitride dissolved in a strong base solution breaks down and releases ammonia gas.
2. Application of Titanium nitride Titanium nitride has good physical and chemical properties, such as high melting point, good chemical stability, high hardness, good conductivity, heat conduction and light performance, etc., making it very important in various fields, especially in the field of new ceram and gold decoration. The industry demands more and more titanium nitride powder. As a coating, titanium nitride has low price, abrasion resistance and corrosion resistance, and its many properties are better than vacuum coating. The application prospect of titanium nitride is very broad. It is mainly used in the following aspects: (1) Ti is highly biocompatible and can be used in clinical medicine and stomatology.
(2) Titanium nitride has a low friction coefficient and can be used as a high-temperature lubricant. (3) Titanium nitride, with metallic luster, can be used as a simulated gold decoration material, and has a good application prospect in the surrogate gold decoration industry; Titanium nitride can also be used as gold coating in jewelry industry. It can be used as a potential material to replace WC, so that the application cost of the material can be greatly reduced.
(4) Super hardness and wear resistance, can be used for the development of new tools, this new type of tools than ordinary cemented carbide tool durability and service life are significantly improved.
(5) Titanium nitride is a new multi-functional ceramic material. The addition of a certain amount of titanium nitrite to TiC-Mo-Ni series cermet can significantly refine the hard phase grains, so that the physical properties of cermet have been greatly improved at room temperature and high temperature, and the high temperature corrosion resistance and oxidation resistance of cermet have been greatly improved. The strength, toughness and hardness of ceramics can be enhanced by adding TiN powder to ceramics in a certain proportion. Titanium nitride nanometer is added to TiN/Al2O3 multiphase nanometer ceramics, which is evenly mixed by various methods (such as mechanical mixing method), and the obtained ceramic materials containing titanium nitride nanoparticles form a conductive network inside. This material can be used as an electronic component in the semiconductor industry. (6) Adding a certain amount of TiN to magnesium-carbon bricks can greatly improve the slag erosion resistance of magnesium-carbon bricks. (7) Titanium nitride is an excellent structural material, which can be used for steam injection thrusters and rockets. Titanium nitride is also widely used in bearings and sealing rings, which highlights the excellent application effect of titanium nitride.
(8) Based on the excellent electrical conductivity of titanium nitride, it can be made into a variety of electrodes and contact first-class materials. (9) Titanium nitride has a high critical superconducting temperature and can be used as an excellent superconducting material. Titanium nitride has a melting point higher than most transition metal nitrides and a density lower than most metal nitrides, making it a unique refractory.
(11) Titanium nitride can be coated on glass as a film. In the case of infrared reflectance greater than 75%, when the thickness of titanium nitride film is greater than 90nm, it can effectively improve the insulation performance of glass. In addition, by adjusting the percentage of nitrogen elements in ti nitride, the color of ti nitride film can be changed to achieve the ideal aesthetic effect.
3. 3.1 the preparation of titanium nitride titanium powder or TiH2 direct method with titanium nitride powder under the nitrogen or hydrogen atmosphere, in 1273 ~ 1673 k under 1 ~ 4 h, nitride product after repeating several times, can get the stoichiometric nitride titanium powder, its formula is: 2 ti + N2 = 2 tin can also use metal hydride TiH2 nitride, can response under 1273 k, and its formula is: 2 TiH2 tin + 2 h2 + N2 = 2
The advantage of this method is that it is easy to operate and high quality titanium nitride powder can be obtained, but the disadvantage is that the raw material price is too high for mass production, and this process is easy to produce powder sintering phenomenon, resulting in losses. 3.2 Thermal reduction nitrification of TiO2 The thermal reduction nitrification of TiO2 takes TiO2 as raw material, carbonized graphite as reducing agent, and N2 to generate TiN. The synthesis temperature is 1380~1800℃, and the reaction time is about 15h. In this reaction environment, carbon not only reacts with oxygen, but also reacts with titanium to form TiC. Because the lattices of titanium carbide, titanium nitrite and titanium oxide are very close, the three are easy to form a solid solution. TiN obtained by this method is generally of low purity and high O and C contents. In order to obtain TiN with low O and C contents, a higher reaction temperature and a longer reaction time are required.
In addition, experts also use another method, namely magnesium powder and titanium oxide reaction at a low temperature in a certain proportion of the reaction to prepare titanium nitride. 3.3 Microwave carbon reduction Microwave carbon reduction is a REDOX reaction at a high temperature with inorganic carbon as a reducing agent. Liu Binghai et al. in China used this method to prepare titanium nitride powder. The specific operation is as follows: taking titanium oxide as raw material, heating carbon with microwave until the temperature reaches 1200℃, and maintaining the reduction reaction at this temperature for 1h, the titanium nitride powder is obtained. Compared with the conventional method, the titanium nitride powder obtained by this method has higher purity, lower synthesis temperature (100 ~ 200℃ lower than the original), shorter cycle (1/15 of the conventional method) and other advantages.
3.4 Chemical Vapor deposition (CVD) Chemical vapor deposition (CVD) takes gaseous TiCl4 as raw material, H2 as reductant and N2 to produce TiN, and the synthesis temperature is 1100~1500℃. This process is used to enhance the hardness and wear resistance of metals and ceramics. This synthesis of TiN has high purity, but low production efficiency and high cost. This process is a common method for metal, ceramic and other articles to coat TiN film to make it beautiful. 3.5 Self-propagating high-temperature synthesis method self-propagating high-temperature synthesis method is also called combustion synthesis method. In this method, the titanium powder (billet) is ignited directly in nitrogen (limiting certain pressure), and TiN product is obtained after the titanium powder is burned in nitrogen. The process has been extensively researched and commercialized in Russia, the United States, and Japan. According to domestic research reports in this field, Wang Weimin et al. prepared TiN ceramic powder by this process, and studied the influence of such technological parameters as billet density, diluent and nitrogen partial pressure on the synthesis. Liu Suying and others studied the process. 3.6 Mechanical alloying Method Mechanical alloying method is a new synthesis method in which titanium powder is placed in a system of ammonia or nitrogen gas, and high-energy ball mill is used to make them interact with each other under the strong collision and agitation of grinding balls to obtain nano-titanium nitride. In China, Liu Zhijian et al. used TiH1.924 powder instead of Ti powder to react with nitrogen and adopted this high-energy ball milling process. After 100h of high-energy ball milling in flowing ammonia gas, almost all TiH1.924 powder was converted into TiN, and the conversion rate was greatly improved. Moreover, Zhou Li et al. subsequently prepared titanium nitride nanometer powder by the same method, and the reaction time was only 9h. 3.7 Molten salt Synthesis There has been no report on the preparation of titanium nitride by molten salt synthesis, but the study on the preparation of titanium nitride by this method is a good research direction. This method USES the molten salt with low melting point as the reaction medium. The reactants can be dissolved in the molten salt. The whole reaction is completed at the atomic level. The product obtained by this method is of high purity, simple operation, short reaction time, no harsh requirements on reaction temperature, easy to control the morphology and particle size of the product, and no agglomeration. 3.8 Sol-gel method Sol-gel method is to mix the reactants evenly in the liquid phase condition, and then conduct hydrolysis and condensation process, the reactants will form transparent sol in the solution, the sol after aging and slow polymerization process will form gel, gel after drying, curing will get the materials we need. This method is used in the operation of some organic solvents toxic side effects, to the human body has a certain harm.
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