Preparation and application of magnesium nitride

Chemical formula of magnesium nitride Mg3N2, greenish yellow powder or lump, relative density of 2.712, decomposition at 800℃, sublimation at 700℃ in vacuum, magnesium nitride as ionic compound, rapid hydrolysis in water. Soluble in acid, insoluble in ethanol: magnesium nitride is widely used. Magnesium nitride is an indispensable sintering agent in the solid state reaction of boron nitride and silicon nitride, which are new ceramic materials with high hardness, high thermal conductivity, wear resistance, corrosion resistance and high temperature resistance. Magnesium nitride plays an important role in the recovery of nuclear fuel, purification of magnesium alloy melt and catalysis in the formation of hBN reaction. In addition, Mg3N2 as an additive can effectively desulphurize and add alum, thus improving the density, strength, tension and bearing capacity of steel.

At present, the main preparation methods of magnesium nitride include direct reaction method of magnesium powder with nitrogen, reaction method of magnesium with nitrogen in nitrogen plasma flow, magnesium coil explosion method in nitrogen atmosphere, low pressure chemical gas complementary product method, self-propagating high temperature synthesis method, nano magnesium nitride synthesis method, etc. Recently, G. Soto et al. prepared amorphous magnesium nitride films with different Mg∶N ratios on Si substrates in a molecular nitrogen environment by pulse laser deposition. These methods limit their industrial production due to high cost, long process, complex equipment operation, or low yield of magnesium nitride.

Although the direct reaction of magnesium powder with nitrogen has industrial value, the production of magnesium nitride powder needs higher reaction temperature and longer reaction time, and the shape of particles is incomplete and easy to agglomerate, which can not meet the requirements of industrial quality. NH3 can be decomposed into N- with broken bonds more easily than N2, and the decomposed H2 can inhibit the formation of MgO, so ammonia gas can be used as the nitrogen source. Chen Faqin et al. used liquid ammonia as nitrogen source to prepare magnesium nitride powder by direct nitriding of magnesium powder. The following conclusions could be drawn: Through thermodynamic analysis, liquid ammonia could react with magnesium powder more easily than nitrogen to prepare magnesium nitride; High quality magnesium nitride powder with high purity and uniform powder particles can be prepared at 600℃ and ammonia atmosphere for 1h, then heated to 800℃, ammonia flow rate of 500ml/min and nitriding time of 1h.

Magnesium and its alloys are the lightest metal structure materials in engineering applications. In recent years, the plastic forming technology of deformed magnesium alloys has become an important research field in the world magnesium industry. Magnesium base alloys will play a more important role in the future of energy shortage. At present, magnesium-based alloys are indispensable and important materials in aerospace, automotive, electronics, construction industry and daily life. However, magnesium-based alloys are widely used but also have their own weaknesses, such as low hardness, low strength, and low melting point than steel and other commonly used metals. How to improve the plastic forming ability of magnesium alloy has become a hot topic in the research of magnesium alloy. Therefore, it is of great academic and industrial application value to seek for high specific strength and specific stiffness as well as good hardness and strength.

In recent years, with the development of high-end production, mechanical and electrical products, the mechanical properties of magnesium alloy need to be further improved, the use of granular reinforced magnesium alloy material can play a magnesium base alloy matrix and enhanced phase, significantly improve the strength of magnesium base alloy, elastic modulus, hardness and wear resistance. At the same time, because of its low cost, high strength and stiffness, particle reinforced magnesium alloy material has a wide application prospect in advanced manufacturing and other modern industrial production fields.

Based on the above purposes, non-toxic and pollution-free magnesium nitride nanotube particles were added into the magnesium base alloy to enhance the strength of the magnesium base alloy material, obtain good toughness and hardness, and effectively improve the electrical and thermal conductivity. The chemical composition and mass fraction of mg-base alloy are as follows: Mg-90-98, and the remaining component is Al. For the patent of magnesium base alloy performance improvement, China’s existing magnesium base alloy in patent 200880017616.2, by adding indium, scandium, yttrium and other precious metals and 2-3% rare earth metals, the sample grain size is less than or equal to 3 microns after melting, the invention added more precious metal elements = high, high manufacturing cost. In patent 201210324168.9, Er,Cu,Ag, which have the ability to improve the formation of Mg alloy amorphous, are selected as alloying elements, and the alloy material is prepared by ordinary casting and hot extrusion methods, and then the magnesium base alloy is obtained by casting and extrusion. Although the addition of rare metals can improve the toughness, hardness and wear resistance of mg-base alloy materials, it increases the smelting cost of mg-base alloy. At the same time, further research is needed to achieve higher strength and wear resistance.

CN201610474622.7 proposed a preparation method of magnesium nitride carbon nanotube particles reinforced magnesium base alloy material with stable processing technology, low production cost, no pollution and emissions, which can be produced under conventional melting conditions. Compared with the traditional magnesium base alloy material, the strength, toughness, hardness and wear resistance are greatly improved. Therefore, the aim is to enhance the mechanical properties of magnesium base alloy materials by adding magnesium nitride – carbon nanotube particles reaction.

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