A method for preparing molybdenum boride powder

Boride molybdenum compounds with high melting point, high hardness, wear resistance, high temperature resistant, corrosion candle and low coefficient of friction etc., plays a very important role in modern industry, are widely used in metal materials, coating materials, high temperature structural materials, the cathode material, corrosion resistant, wear resistant materials and other fields, and with the progress of science and technology, The application field of molybdenum-boride compounds will be further expanded, and this material will show more excellent application value and huge market prospect.

According to the binary phase diagram of MO-B, molybdenum-boride compounds can exist in the form of six phases: Mo2B, α-Mob, β-Mob, MoB2, Mo2B5, MoB4. At present, there are few research reports on B-Mo compounds at home and abroad. Gao Yang from the Institute of Metal Materials of Dalian Maritime University published an academic paper titled “Formation Process of Explosive Sprayed Molybdenum-boride cermet Coating” in the “Papers of the Sixth International Thermal Spraying Symposium”. In this paper, the author prepared two kinds of MoB powder of 5-10μm and 10-30μm by sintering process, but X-ray diffraction showed that the synthesized powder contained α-Mob, β-Mob, MoB2 and Mo2B5 phases, and no single MoB phase powder was obtained. This to some extent limits the practical application of this material in production technology. Wang Yadong et al. of Wuhan University of Technology published an academic paper entitled “Preparation and Capacity Output Performance of metal borides as Aqueous Anode Materials” in Chinese Science Bulletin, Vol. 57, No. 27, 2012. In this paper, Mo powder and B powder with molar ratio of 1:0.5 were synthesized by mechanical ball milling method into the mixture of amorphous MoB0.5 and elemental Mo. However, molybdenum boride of single phase was not obtained, and MoB0.5 still existed in amorphous form. The central south university’s wang in his doctoral thesis “molybdenum alloy research on preparation and properties of high temperature oxidation resistance coating by means of in situ chemical vapor deposition method in the first activity on molybdenum substrate deposition of high boron element, and then by molybdenum boron element and matrix element diffusion reaction in situ, in the substrate surface to form a layer of molybdenum molybdenum boride layer (MoB), This method has great limitations, molybdenum boride can only be formed on molybdenum matrix, and the synthesized molybdenum boride can only be used as a coating on molybdenum matrix.

Therefore, it is necessary to prepare a kind of molybdenum boride powder with complete crystal and single phase to improve the application value of molybdenum boride material in industry.

A new preparation method of molybdenum boride powder material, this preparation method is the first time to synthesize molybdenum boride powder by high temperature and high pressure, and no similar synthesis method has been found in the current patents, reports and papers. The specific preparation method includes the following steps:

Step 1. Firstly, B powder and Mo powder are placed in graphite crucible and molybdenum crucible coated with BN powder, respectively. The reduction temperature of boron powder is 1000-1500℃, and the reduction temperature of molybdenum powder is 600-1200℃.

Step 2. The reduced B powder and Mo powder are added to the ball mill mixing tank with the molar ratio of 0.5 or 1 or 2 or 2.5 or 4, and the ball mill is mixed for 2-96h. The ball mill medium is edible alcohol, and the ball mill can and ball mill ball are made of polytetrafluoron.

Step 3. Pour the ball milled mixture into a stainless steel tray, and then place it in a vacuum drying oven for drying at a temperature of 60-120℃.

Step 4. Transfer the dried material in Step 3 to the graphite crucible coated with BN powder on the inner wall, and then place the graphite crucible in the high temperature and high pressure vessel. Under the condition that the pressure in the vessel is 0.5-30 GPa, the temperature rise rate of 0.5-30℃/min is raised to 1200-2400℃, and sintering is carried out for 1-8 h. Molybdenum boride particles, reserve;

Step 5. Put the molybdenum boride particles obtained in Step 4 into a pulverizer and pulverize them into powder. After that, according to the particle size distribution requirements of the product, select a suitable mesh screen for screening, and obtain molybdenum boride powder with molar ratio of B and Mo of 0.5 or 1 or 2 or 2.5 or 4.

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