Preparation of metal powder


According to the principle functional changing, usually divided into two categories: mechanical and physico-chemical method. The metal powder can also be obtained directly from the refining solid, liquid metal, gas. Furthermore, reduction, pyrolysis and electrolysis of the metal compounds in various states by changing the system. When the performance of the refractory metal carbides, nitrides, borides and silicides and approach combining restoration can be directly used to obtain the metal powder. Since preparation methods are different, a powder of shape, structure and size and other characteristics are often very variable. In preparation for powder, the most widely used methods are the reduction, atomization and electrolysis.

The use of reducing agents for use oxygen in the metal oxide powder may reduce the metal powder. Reluctant includes hydrogen gas, ammonia, gas, natural gas, etc.. There are reluctant solid carbon and sodium, calcium, magnesium and other metals. Reduction of commonly used hydrogen or ammonia to produce tungsten, molybdenum, iron, copper, nickel, cobalt and other metal powders. Reduction of carbon is often used to produce iron. Metal with strong reducing agent sodium, magnesium, calcium, can produce tantalum, niobium, titanium, vanadium, zirconium, beryllium, thorium, uranium and other metal powder (see thermal metal reduction). High pressure reduction of metal salts with aqueous hydrogen can be obtained by nickel, copper, cobalt and their alloys or with powder coating (see hydrometallurgy). The restoration of the rule of law in the dust particles are mostly irregular shape of the spongy structure. Reduction of particle size powder depends on temperature, time, and the granularity of raw materials and other factors. The reduction may be made of metal powder from the bulk metal. It is a widely used method.

The atomization of the molten metal into small droplets and solidifying the powder of the cooling medium). Second rate (melt index and high fluid medium) method is to use high pressure atomization air, nitrogen, argon (gas atomization) and high pressure water (water spray) liquid medium of the jet stream to crush the metal . Also the use of rotary grinding disc and merge into each other (from the post filter and power) of rotation of the centrifugal atomization method, and other methods such as vacuum atomization spray dissolved hydrogen, ultrasonic atomization, etc. As droplets and heat exchange conditions are good, the overall rate of condensation droplets can reach 100 ~ 10000K / s, higher by several orders of magnitude when the ingot. Therefore, the uniformity of the alloy composition, a small organization, which is made of alloy without macro-segregation, and excellent performance. Overall nearly spherical powder spray, water spray system can shape Debu standards. Features such as the powder particle size and organization of the crystalline form depends on the melting properties (viscosity, surface tension, reheating) and atomization of the process parameters (such as the melt flow diameter, structure of the nozzle, the pressure of stream flow rate of media, etc.) are available for almost all the atomizing method of producing molten metal, particularly suited for the production of alloy powder. The method is very efficient, and easy to expand the industrial scale. Currently, only used for industrial mass production of iron, copper, and aluminum powder of different alloys, but also is used to produce high purity (O2 <100 ppm) High temperature alloys, high-speed steel, stainless steel and titanium alloy powder. Furthermore, the cooling system technology for rapid cooling dust (rate of condensation> 100,000 K / s) and more attention. It can be produced with a material of high performance ceramics.

The use of continuous current through the aqueous solution of metal salt, metal ions of the cathode discharge is precipitation, which is easily broken into powder. The metal ions of the same overall dissolution of metal anode, and the anode to cathode current under the effect of migration. The main factors that affect the size of the powder is the electrolyte composition and the conditions of the electrolysis (see electrolyte solution). Mostly dendritic powder of high purity electrolyte overall, but this method consumes a high cost, high. The application of electrolysis is also very wide, which is used to produce copper, nickel, iron, silver, tin, lead, chromium, manganese and other metal powders, in certain conditions, also be prepared from alloy powders. For tantalum, niobium, titanium, zirconium, beryllium, thorium, uranium and rare earth metals and refractory, often used as a composite molten salt electrolyte (see the electrolysis of molten salts) so that the system has powder.

As the grain homogeneous fine and highly active, fine dust which is less than 10μm has a special status in manufacturing materials (for example, alloys, ultra-dispersion strengthened metal into the hole, a metal tape) and direct applications (such as solid rocket fuel and magnetic fluid seal, magnetic ink, etc.) In addition to the carbonyl and electrolytic extraction, vacuum arc evaporation condensation method, spraying, total decomposition of the double salt precipitation, gas and Other methods of reduction can also be used.

The thermal spray powder plays an important role in the engineering of atomic energy coating material and other specialized applications. Using the two methods of chemical deposition of the milling gas and the liquid phase, such as the thermal dissociation of hydrogen reduction with hydrogen in the high pressure reduction, substitution, electro-deposition and other coating methods can produce metal and the metal powder, a mixture of various metals and non-metals.