Zou Jianxin

1. Introduction to Titanium Nitride



TiN has a typical NaCI type structure, belonging to a face centered cubic lattice, with a lattice constant of 0.4241nm, where titanium atoms are located at the corner apex of the face centered cubic. TiN is a non stoichiometric compound with a stable composition range of TiN0.37-TiN1.16. The nitrogen content can vary within a certain range without causing changes in the TiN structure. TiN powder is generally yellow brown, ultrafine TiN powder is black, and TiN crystals are golden yellow. The melting point of TiN is 2950 ℃, the density is 5.43-5.44g/cm3, the Mohs hardness is 8-9, and the thermal shock resistance is good. TiN has a higher melting point than most transition metal nitrides, but a lower density than most metal nitrides, making it a distinctive heat-resistant material. The crystal structure of TiN is similar to that of TiC, except that the C atoms are replaced with N atoms. TiN is a relatively stable compound that does not react with metals such as iron, chromium, calcium, and magnesium at high temperatures. TiN crucibles also do not react with acidic or alkaline slag in CO and N2 atmospheres. Therefore, TiN crucibles are excellent containers for studying the interaction between molten steel and some elements. When TiN is heated in vacuum, it loses nitrogen and generates titanium nitride with lower nitrogen content. TiN is an attractive structural material with golden yellow color, high melting point, high hardness, good chemical stability, small wetting with metal, and high conductivity and superconductivity, which can be applied to high-temperature structural materials and superconducting materials.



Preparation method of titanium nitride powder



2.2.1 Direct Nitridation Method of Titanium Powder or TiH2



Direct nitridation method is one of the traditional preparation methods of TiN, which uses Ti powder or titanium hydride powder as raw material, reacts with N2 or NH3 to generate TiN powder, and the synthesis temperature is 1000-1400 ℃. Luoxishan synthesized TiN by directly reacting TiH2 powder in nitrogen gas; The advantages of this method are that there is no need for hydrogenation treatment during the reaction process, reducing hydrogen purification, and producing TiN powder with uniform particle size and composition, as well as low impurity content. Zhao Yang et al. crushed sponge titanium to a certain size, and then nitrogen nitrided it under a certain pressure and temperature to obtain the required particle size of titanium nitride after crushing. A. S. Bolokang uses a diameter of 45 μ M pure titanium powder was ball milled at a speed of 250rpm in a charged argon atmosphere for 12, 16, and 20 hours. The crystal structure and microscopic analysis of the small samples showed that the initial spherical titanium powder transformed into flat thin sheets after ball milling. Although ball milling at different times did not change the crystal structure of the product, prolonging the reaction time can increase the absorption and conversion of nitrogen by Ti powder at lower temperatures; The longer the reaction time, the higher the conversion rate. However, when synthesizing TiN from Ti powder, the material temperature often rises too high, resulting in the sintering or melting of the generated TiN, making it difficult to prepare TiN powder with smaller particle size. In addition, Liping Zhu et al. prepared TiN powder using NH4Cl as raw material in a mixture of N2 and H2 gas at 500-800 ℃. Analysis found that the generated TiN particles have a particle size between 20-33nm and a surface area of 30-60m2/g. An increase in temperature is not conducive to the synthesis of TiN powder with small particle sizes.



2.2.2 In situ nitriding method



In situ nitriding method, also known as ammonia nitriding method, is a method of directly nitriding nano TiO2 into TiN under ammonia atmosphere. Li Jingguo et al. used nano TiO2 as raw material and used ammonia gas nitridation method to place nano TiO2 powder in a quartz boat in a tubular atmosphere furnace. Ammonia gas was used as a reducing agent and nitrided at different temperatures for 2-5 hours. After cooling to room temperature, the minimum particle size of about 2 was obtained



TiN powder at 20nm. The reaction requires a low temperature and can start converting to TiN at 700 ℃. After nitriding at 800 ℃ for 5 hours, nano TiO2 can be fully converted to TiN. Zhang Bing et al. used the nano TiO2 powder synthesized by the sol-gel method as raw material, and carried out in-situ nitridation in ammonia to synthesize the TiN nano powder with the particle size of about 40nm and 80nm. The reaction conditions such as synthesis temperature and time were compared and analyzed. The results showed that the nitridation rate of the TiN powder prepared by the in-situ nitridation method increased with the increase of temperature and reaction time.



2.2.3 Aluminum thermal reduction method



Jiang Tao and his team weighed Al powder and TiO2 powder at a ratio of 4:3 and ground them evenly before loading them into stainless steel pipes of a tubular resistance furnace. The mixture of Ar-N2 gas was filled, and the tubular furnace was heated to the required temperature to produce titanium powder. Subsequently, the prepared titanium powder was evenly distributed on the porcelain boat and placed in the tubular resistance furnace. The tubular furnace was vacuumed and filled with depressurized NH3. After heating to the reaction temperature, TiN powder was prepared. Gan Mingliang et al. synthesized titanium nitride by aluminothermic reduction and nitridation of TiO2 in a planetary ball mill with aluminum powder and titanium dioxide as raw materials, and anhydrous ethanol as the medium under flowing nitrogen atmosphere and sagger carbon burying conditions. However, because aluminum participates in the aluminothermic reduction reaction under carbon burying conditions, it also reacts with oxygen in the carbon powder bed, so that the aluminum involved in the aluminothermic reaction is insufficient, resulting in the presence of rutile in the product. The titanium nitride powder prepared by reducing rutile by aluminothermic reduction method contains aluminum oxide, a by-product.



2.2.4 Magnesium thermal reduction method



The preparation of TiN by magnesium thermal reduction of TiO2 involves two steps, namely the reduction and nitridation of metallic titanium. Lin Li synthesized TiN powder with low oxygen content using the method of Mg+C combined reduction under a certain nitrogen pressure and temperature. Jianhua Ma et al. used metal Mg powder, 3



The average particle size of nano TiN particles prepared by titanium dioxide and ammonium chloride under high pressure at 650 ℃ is 30nm, and they have good thermal stability and oxidation resistance in air at 350 ℃. In the Ti Mg O system, when the reaction reaches equilibrium, the oxygen content in the system is 1.5%~2.8%, which means that the oxygen content of Ti prepared by magnesium thermal reduction of TiO2 must be greater than 2.8%. However, the high price of high-purity titanium makes large-scale production costs too high, so it is necessary to find new reduction methods.



2.2.5 TiO2 carbon reduction nitridation method



The carbon thermal reduction nitridation method for preparing titanium nitride is the most convenient and efficient method among the preparation methods, and it requires a wide range of raw materials with low prices, which is easy to promote in industrial production, thus having great research value.



Therefore, many scholars have studied the effects of changes in reaction conditions on the quality and synthesis rate of synthesized TiN powder in the laboratory. Wu Yiquan synthesized TiN from TiO2 as raw material by reacting with N2 at 1380-1800 ℃ for about 15 hours in the presence of graphite or TiC. The research of Wu Feng et al. in the carbothermal reduction nitridation synthesis of TiN shows that the conversion efficiency of anatase is higher than that of rutile, and the synthesis efficiency of carbon black is higher than that of flake graphite. Yu Renhong et al. used anatase, rutile, analytical pure activated carbon and carbon black as raw materials to prepare titanium nitride powder in a full isothermal thermogravimetric nitriding furnace under high-purity nitrogen; The forming pressure and mixing method have almost no effect on the synthesis of TiN, while the carbon content has a significant impact on the reaction. When the carbon content is insufficient, the oxygen content in the product is higher, and when the carbon content is large, secondary decarburization is more difficult. The optimal titanium carbon ratio is 1:



2.1。



2.2.6 Self propagating high-temperature synthesis method



The principle is to ignite the pressed titanium powder in N2 at a certain pressure, and after reaction, TiN powder can be prepared. The characteristic of this synthesis method is to use the heat released by the reaction itself to maintain the required energy for the reaction, thus saving energy. As for the combustion synthesis between Ti and N2, which is a gas-solid phase, it can be carried out at lower nitrogen pressure (0.1-1MPa). Wang Weimin et al. synthesized titanium nitride powder using this method and studied the effects of process factors such as N2 partial pressure, sample compression parameters, and diluents during the preparation of TiN; The results indicate that adding diluents and increasing nitrogen partial pressure are beneficial for synthesizing high-purity TiN. The preparation of TiN using this method has been widely studied and commercialized in many countries such as Russia.

1.2.7 Ammonia hydrolysis



Ammoniolysis is a method of producing the required products through chemical reactions in an ammonia system using liquid ammonia as a solvent.



In the liquid ammonia system, liquid ammonia can undergo self ionization and achieve dynamic equilibrium, producing two opposite charged NH4+and NH2-2 ions dispersed in the solvent; The covalent compounds can dissolve in this system and dissociate into positive and negative electric properties at the covalent bond; Finally, in the liquid ammonia system, ions with different electrical properties recombine to form new compounds. The preparation of TiN powder using this method involves two processes: precursor generation and ammonolysis. He Jing et al. used oxalic acid C2H2O4 • 2H2O (analytically pure) and TiCl4 (analytically pure) as raw materials to obtain H2 [TiO2 (C2O4) 2] precursor crystals. Then, the precursor of H2 [TiO2 (C2O4) 2] was ammoniated at 1050 ℃ for 2 hours to obtain TiN particles with a size of about 70nm and a relatively uniform particle size.



The reaction temperature required for liquid-phase chemical reactions is relatively low, but the high cost of raw materials and the use of organic solvents limit industrial production. NH3 pollutes the environment and has a significant irritating effect on the human body, requiring exhaust gas treatment, increasing equipment costs and process complexity



The complexity level and the generated TiN products are prone to agglomeration, which affects the quality of TiN.



2.2.8 Microwave carbothermal reduction method



Liu Yang et al. used nano TiO2 powder and carbon black as raw materials to synthesize titanium nitride nano powder by microwave heating; And the effects of microwave synthesis temperature and holding time on the generation rate were explored. The results indicate that the method of microwave heating can synthesize nanoscale titanium nitride powder at lower temperatures (1200 ℃). Using the microwave carbothermal reduction method, Liu Binghai et al. heated at 1200 ℃ for 1 hour to obtain a particle size of 1-2 μ Uniform and high-purity titanium nitride powder between m; Unlike the widely used carbon thermal reduction method, this method reduces the synthesis temperature of TiN by 100-200 ℃ and shortens the synthesis cycle to 1/15 of the conventional method. When Zeng Lingke et al. studied the microwave carbothermal synthesis of carbonitride compounds, they used self-made nano anatase TiO2 ultrafine powder and market purchased nano carbon black as carbon sources, synthesized by microwave heating, and introduced nitrogen at the synthesis temperature of 1000~2000 ℃ to prepare titanium nitride. The synthesis rate reached 100%, the particle size distribution was 20~85nm, the particle size was small, and the synthesis rate was high. Ramesh et al. prepared TiN powder using microwave technology for carbon thermal reduction of TiO2. This method is combined with combustion synthesis, utilizing microwave induced reactions to form fewer intermediate products and shorten the synthesis time throughout the entire reaction process.



In addition, there are mechanical grinding method, sol gel method, plasma method, molten salt method, solvothermal method, etc



Application of 3 TiN



The application of titanium nitride mainly functions in two aspects: firstly, it is added as an additive or bonding material to cermets to improve the strength, hardness, and toughness of the body; 2、 Apply wear-resistant and corrosion-resistant coatings on the surface of the workpiece.



3.1 Application of titanium nitride powder



Domestic and foreign hard alloy researchers have optimized the performance of WC by adding TiN to it, and demonstrated the performance of TiN. The prepared alloy products are both wear-resistant and ductile. Cobalt plays an important role in national defense and space industry. It is understood that one tenth of the world's cobalt is used as bonding material for WC components, which can enhance the wear resistance and corrosion resistance of the prepared materials. Therefore, it is widely used to manufacture cutting tools; TiN has many advantages similar to WC, such as high hardness, melting point, and good wear resistance, so it can also be used as a cutting tool. When using TiN as a component, the bonding material can be replaced by nickel, reducing cobalt consumption and greatly reducing production costs. These properties may make TiN-Ni an excellent substitute for WC Co. TiN powder can also be used as an abrasive for polishing precision instruments. When processing steel, the addition of TiN and Ti (C, N) powder can increase the grinding performance of the steel, which can even surpass Al2O3 and SiC, and improve the surface accuracy of the produced steel.



3.2 Application of titanium nitride thin film



TiN film has the advantages of high hardness, good wear resistance, and good corrosion resistance, and is widely used in various tool molds and friction corrosion resistant parts. TiN coating has a perfect golden color, known as titanium gold, and is widely used in watch cases, watch chains, decorations, and other handicrafts. It not only makes handicrafts beautiful and decorative, but also has a strong decorative effect; It has good corrosion resistance and can extend the service life of handicrafts. The color of TiN thin films is closely related to the nitrogen content. As the nitrogen content decreases, the films will appear in colors such as gold, ancient copper, purple copper, and pink, giving them unique optical functions.



Titanium nitride thin film has a high reflectivity (thermal insulation effect) in the near-infrared region, and is suitable for medium to far 7



The infrared region has a high reflectivity (with low radiation), while the visible region has a high transmittance (ensuring the requirements of light extraction) and a low reflectivity (no light pollution). Compared with other films, these special properties determine that it can be widely used as an energy-saving thin film with excellent performance. The TiN coating on the surface of glass has become a new "thermal mirror material". When the coating on the glass exceeds 90nm, it can increase the infrared reflectance by over 75%, improving the insulation performance of the glass. Fu Shuying analyzed the film structure, film thickness, absorption rate, and reflectivity, and found that the prepared TiN film has good spectral selective absorption characteristics, which can be used as a heat absorbing surface for solar collectors and directly as a building material for photothermal conversion. Due to the high temperature resistance of (Ti, Al) N coatings, they have also been applied in solar selective absorption layers and solar control windows in recent years.



The titanium nitride coating on the surface of the workpiece can effectively reduce the adhesion of the cutting edge workpiece, maintain the geometric stability of cutting, optimize the surface quality of the tool, increase the cutting force and feed amount, significantly improve the machining accuracy of the produced product, and also multiply the service life and durability of the tool. Therefore, it is widely used on the surface of cutting tools and drill bits. Wei Xiaoyun et al. confirmed through electrochemical corrosion experiments that in a 1mol/L H2SO4 solution, the corrosion resistance of TiN infiltrated coatings is 1.4 and 4.2 times higher than that of individual stainless steel and Q235 steel substrates, respectively. TiN coating acts on the surface of wear-resistant materials and is an ideal wear-resistant layer. Due to its adhesion and good wear resistance, it is widely used in wear-resistant devices, such as piston sealing rings, bearings, and gears in automotive engines; In addition, TiN coatings are also widely used for tool surfaces in forming technology, such as the surface of sheet metal forming tools in the automotive industry.



TiN film has good biocompatibility, non-toxic, low density, light weight, and high strength. It is an ideal medical material and can be used as surgical instruments and implants for human body implantation. Qi Feng et al. at TiHe8



The surface of the gold artificial heart valve is covered with a layer of TiN coating, which enhances the wear resistance of the valve frame and increases the lifespan of the artificial heart valve. In the application of artificial joints, titanium and titanium alloys are light in weight, low in elastic modulus, and strong in shock absorption. Artificial joints are not easy to cause prosthesis loosening, and have high ultimate tensile strength, yield strength, and fatigue strength, as well as high Corrosion fatigue and corrosion resistance. TiN thin films can also be used on the surface of some medical thin film materials as reinforcing films. Some scholars have improved the mechanical properties and adhesion of hydroxyapatite (HA) to a large extent by plating TiN films on its surface.



Coating TiN thin film on IF-MS2 can improve the wear resistance of molybdenum disulfide lubricant. Not only does it greatly improve the lubrication performance of aviation material components such as engines in aerospace devices, but it also enhances the resistance of aviation materials to high temperatures and friction.