![<?echo $_SERVER['SERVER_NAME'];?>](/template/twentyseventeen/skin/images/header.jpg)
Metal powder refers to a group of metal particles having a size of less than 1 mm. Including single metal powder, alloy powder and certain refractory compound powders with metallic properties are the main raw materials for powder metallurgy.
Powder properties
The metal powder is a loose material whose properties reflect the nature of the metal itself and the properties of the individual particles and the characteristics of the particle group. The properties of metal powders are generally classified into chemical properties, physical properties, and process properties. Chemical properties refer to metal content and impurity content. Physical properties include the average particle size and particle size distribution of the powder, the specific surface and true density of the powder, the shape of the particles, the surface topography and the internal microstructure. Process performance is a combination of properties including powder flow, bulk density, tap density, compressibility, formability and sintering dimensional changes. In addition, powders are required to have other chemical and physical properties, such as catalytic properties, electrochemical activity, corrosion resistance, electromagnetic properties, and internal friction coefficients, for certain special applications. The properties of the metal powder depend to a large extent on the method of production of the powder and its preparation process. The basic properties of the powder can be determined by specific standard test methods. There are many methods for measuring the particle size and distribution of the powder, and generally, sieve analysis (>44 μm), sedimentation analysis (0.5 to 100 μm), gas permeation, microscopy, and the like are used. Ultrafine powder (<0.5 μm) was measured by electron microscopy and X-ray small angle scattering. Metal powder is customarily divided into five grades of coarse powder, medium powder, fine powder, fine powder and ultrafine powder.
Preparation method
Generally, it is divided into mechanical method and physical chemical method according to the principle of transformation. It can be obtained by direct refinement of solid, liquid and gaseous metals, and can also be transformed from metal compounds in different states by reduction, pyrolysis and electrolysis. Made. Carbides, nitrides, borides, and silicides of refractory metals can generally be obtained directly by compounding or reduction-combination methods. The shape, structure and particle size of the same powder often vary widely depending on the method of preparation (Figure 2). The preparation methods of the powder are listed below, and the most widely used ones are reduction method, atomization method, and electrolysis method.
Reduction method
The reducing agent is used to capture oxygen in the metal oxide powder, and the metal is reduced to a powder. The gas reducing agent includes hydrogen, ammonia, gas, natural gas, and the like. The solid reducing agent is carbon and a metal such as sodium, calcium or magnesium. Hydrogen or ammonia reduction, commonly used to produce metal powders such as tungsten, molybdenum, iron, copper, nickel, cobalt. Carbon reduction is commonly used to produce iron powder. Metal powders such as barium, strontium, titanium, zirconium, vanadium, niobium, tantalum, uranium, etc. can be produced by using metal strong reducing agents such as sodium, magnesium, calcium, etc. (see metal thermal reduction). Nickel, copper, cobalt and its alloys or coated powders can be obtained by reducing the aqueous metal salt solution with high pressure hydrogen (see hydrometallurgy). The powder particles produced by the reduction method are mostly irregular shapes of a sponge structure. The particle size of the powder depends mainly on factors such as the reduction temperature, the time, and the particle size of the raw material. The reduction method produces a powder of most metals and is a widely used method.
Atomization method
The molten metal is atomized into fine droplets and solidified into a powder in a cooling medium (Fig. 3). Figure 4 widely used two-stream (melt flow and high-speed fluid medium) atomization method is to use high-pressure air, nitrogen, argon gas (gas atomization) and high-pressure water (water atomization) as a spray medium to crush the metal liquid flow . There are also centrifugal atomization methods using rotary disk pulverization and spinning of the melt itself (consumable electrode and crucible), and other atomization methods such as hydrogen atomization vacuum atomization, ultrasonic atomization, and the like. Due to the fine droplets and good heat exchange conditions, the condensation rate of the droplets can generally reach 100~10000K/s, which is several orders of magnitude higher than that of the ingot. Therefore, the composition of the alloy is uniform and the structure is fine. The alloy material prepared by the alloy has no macrosegregation and excellent performance. The gas atomized powder is generally nearly spherical, and water atomization can produce an irregular shape. The characteristics of the powder such as particle size, shape and crystal structure depend mainly on the properties of the melt (viscosity, surface tension, superheat) and atomization process parameters (such as melt flow diameter, nozzle structure, pressure of the spray medium, flow rate, etc.). . Almost all metals that can be melted can be produced by atomization, and are particularly suitable for the production of alloy powders. This method is highly efficient and easy to expand on an industrial scale. It is currently used not only for the mass production of industrial iron, copper, aluminum powder and various alloy powders, but also for the production of high-purity (O2 <100ppm) high-temperature alloys, high-speed steel, stainless steel and titanium alloy powders. In addition, the use of chilling technology to produce fast condensing powders (condensation rate >100,000 K/s) is receiving increasing attention. It can be used to produce high performance microcrystalline materials (see fast cold microcrystalline alloys).
Electrolysis
A direct current is applied to the aqueous metal salt solution, and metal ions are discharged on the cathode to form a deposited layer which is easily broken into powder. Metal ions are generally derived from the dissolution of the same metal anode and migrate from the anode to the cathode under the action of a current. The factors affecting the particle size of the powder are mainly the composition of the electrolyte and the electrolysis conditions (see aqueous solution electrolysis). Generally, the electrolytic powder is mostly dendritic and has a high purity, but this method consumes a large amount of electricity and has a high cost. Electrolytic applications are also widely used to produce copper, nickel, iron, silver, tin, lead, chromium, manganese and other metal powders; alloy powders can also be produced under certain conditions. For rare refractory metals such as ruthenium, osmium, titanium, zirconium, hafnium, tantalum, and uranium, a composite molten salt is often used as an electrolyte (see molten salt electrolysis) to prepare a powder.
Mechanical pulverization
The solid metal is mainly broken into powder by crushing, crushing and grinding. The equipment is divided into two types: coarse and fine. Crushed equipment such as crushers, roll mills, jaw crushers, etc., which are mainly used for crushing. The main crushing and grinding functions include crushing machines, rod mills, ball mills, vibrating ball mills, and agitating ball mills. The mechanical pulverization method is mainly applied to pulverize brittle and easy-to-work harden metals and alloys, such as tin, manganese, chromium, high carbon iron, iron alloys, etc., and is also used for crushing and reducing the sponge metal prepared by the reduction method, and the cathode deposition prepared by the electrolytic method. It is also used to crush the brittle titanium after hydrogenation, and then dehydrogenate to obtain fine titanium powder. The mechanical pulverization method has low efficiency and high energy consumption, and is often used as a supplement to other milling methods or for mixing powders of different properties. In addition, the mechanical pulverization method also includes a vortex grinder, which causes eddy currents by the two impellers, so that the particles trapped by the airflow collide with each other at high speed and pulverize, and can be used for the pulverization of plastic metal. The cold flow crushing method is to spray a coarse powder onto a metal target with a high-speed high-pressure inert gas stream. Since the gas flow at the nozzle outlet produces adiabatic expansion, the temperature suddenly drops below 0 ° C, and the metal and alloy coarse powder having low-temperature brittleness is pulverized into fine powder. The mechanical alloying method uses a high-energy ball mill to grind different metals and high melting point compounds into a solid solution or a finely dispersed alloy state.
Carbonyl method
Some metals (iron, nickel, etc.) and carbon monoxide are synthesized into metal carbonyl compounds, which are then thermally decomposed into metal powders and carbon monoxide. The powder thus obtained is very fine (having a particle size of several hundred angstroms to several micrometers), and the purity is high, but the cost is also high. Industrially used to produce fine powders and ultrafine powders of nickel and iron, as well as alloy powders such as Fe-Ni, Fe-Co, and Ni-Co.
Direct legalization
The carbon, nitrogen, boron, and silicon are directly combined with the refractory metal at a high temperature. The reduction-chemical process uses carbon, nitrogen, boron carbide, silicon and refractory metal oxides. Both of these methods are commonly used to produce carbide, nitride, boride and silicide powders.
Other methods
Fine powders and ultrafine powders of less than 10 μm are produced in materials (such as dispersion-strengthened alloys, ultra-microporous metals, metal magnetic tapes) and direct applications (such as rocket solid fuels and magnetic fluid seals) due to their uniform composition, fine grain size and high activity. , magnetic ink, etc.) has a special status. In addition to the carbonyl method and the electrolysis method, vacuum powder evaporation and arc spray, coprecipitation double salt decomposition, gas phase reduction and the like are also applied.
The coated powder is increasingly showing superiority in special applications such as thermal spraying and atomic energy engineering materials. Two kinds of chemical powder-making methods, such as hydrogen reduction thermal dissociation, high-pressure hydrogen reduction, displacement, electrodeposition, etc., can be used to prepare various coated powders of metal and metal, metal and non-metal.
Application range
Metal powder can be used as a raw material for powder metallurgy products, and can also be directly applied.
Used as raw material for powder metallurgy products
The metal powder used in this aspect mainly contains iron, tungsten, molybdenum, copper, cobalt, nickel, titanium, bismuth, aluminum, tin, lead and the like, and the consumption amount accounts for about 2/3 of the total output of the metal powder.
The Mesh Pencil Case can be used to hold pens or other small stationery, which is more convenient to carry than pencil case, more comfortable to handle, and easy to clean. It can pack as many things as possible in the smallest space, which is very popular among students and office workers. , can also be used as a Storage Bag, is a multi-purpose storage supplies.
Jilin Y.F. Imp & Exp Co., Ltd is an exporter and manufacturer (Cang nan Y.F. Stationery & Gift Co., Ltd.)in Creative products, such as Backpack ,Shoulder Bag,Pencil Case, Handbag,Multifunctional Bag. Coin Purse .Cosmetic Bag.Storage bags. File Holder .Canvas handbag and Notebook etc. which is a professional stationery company setting research and development, producing, sales and trade into one. Our company always takes quality, service, efficiency and innovation as our management philosophy. Since our brand Y.F. has been put on the market, the products sell well throughout the country consistently, and be exported to Europe and America,, and South America countries as well as regions, where the product enjoys great customer loyalty and good population. Choose Y.F. is not to choose a batch of stationery, but to choose a commitment and responsibility, Thanks for your attention, support, trust an cooperation. Wish to establish long-term business relationship with you in the near future.
Mesh Pencil Case,Mesh Pen Pouch,Mesh Pencil Bag,Nylon Mesh Pencil Case
Jilin Y.F. Import & Export Co.,Ltd , https://www.jlpencilcase.com