The classification and application of non-ferrous metal powders

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Non-ferrous metals refer to the metals other than the ferrous metals (iron, chrome and manganese) and the alloys that use the ferrous metals as the base. Or it can refer to the metals other than iron and the alloys that use iron as the base according to the iron and non-ferrous classification method that used by America and Western Europe. The different allocation of chrome and manganese may be the only difference between these two kinds of classification methods. Among nearly 70 kinds of nonferrous metal elements, those have powder products and important application occupy about 1/3. According to the classification of metals, the main non-ferrous metals are as follows: heavy metals include copper powder, lead powder, zinc powder, tin powder, antimony powder, nickel powder, cobalt powder, chromium powder and manganese powder; light metals include aluminum powder and magnesium powder; refractory and rare metals include tungsten powder, molybdenum powder, tantalum powder, niobium powder, vanadium powder, titanium powder and zirconium powder; precious metals include gold powder, silver powder, platinum powder and palladium powder; metalloids include silicon powder, boron powder and so on.

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Copper powder is one of important raw materials in the powder metallurgy industry, its consumption ranks second after iron powder. Except for being used as the raw materials in the powder metallurgy materials and products, copper powder also has very wide direct application and the consumption is only less than aluminum powder. There are 3 kinds of leading industrial process that can be used in producing aluminum powder: a. electrolytic process. As the powders that produced by this method have high purity and wide application range, it has become a main production method that is still used today by most countries, but it has big power consumption as well as can cause environment pollution and other shortcomings; b. oxide reduction method. Represented by atomization granulation-oxidation-reduction process that carried out by America, the performance and variety of powders are both better than electrolytic copper powder and can meet the application requirements, besides, this method has overcome the shortcoming of electrolytic process; c. hydro-metallurgical method. It includes leaching-high pressure hydrogen reduction, leaching-replacement or electrolysis and other processes, which is mostly used in the comprehensive utilization of low grade copper mineral material. In the industrial application, the consumption of pure copper powder occupies the most proportion, for example, it can be used in the Cu-10Sn tin-bronze powder that used for making the oil bearing and so on. This is because the powder metallurgy copper-base parts are still produced by the premixed powders (the mechanical mixture of pure copper powder and the added element powders, such as tin powder, lead powder and zinc powder) that are suitable for cold pressing-sintering process or partial pre-alloy powders (the mechanical mixture is treated by the diffusion alloying process before being heated). (Pre) copper base-alloy powder that is produced by atomization method include lead-bronze powder ((Cu-Pb-Sn series), which is used in making bimetal bearing pad, tin-bronze powder (Cu-6Sn-6Zn-3Pb), which is used in making oil bearing, spherical tin-bronze powder (Cu-8Sn-3Zn), which is used in making filter element, brass powder (Cu-10-30Zn series), which is used in making structural parts and argentan powder (Cu-18Ni-17Zn). The usages of copper powder are as follows: a. it can be used as the raw material of powder metallurgy material and product, for example, it can be used as the leading material of copper base oil bearing, friction material, brush, bimetal bearing pad, structural part, electrical part and filter element and so on as well as the raw material components of other powder metallurgy materials and products, the infiltration agent that used in connecting the product components; b. its direct applications are as follows: it can be used in the colored coating, printing ink, metallic paint, conductive coating, marine antifouling coating, agricultural fungicide as well as copper brazing material, chemical catalysts and so on.

Tin powder, lead powder and zinc powder are mainly produced by atomization method. Tin, lead and zinc are the main alloying elements of copper base alloy. Therefore, tin powder, lead powder and zinc powder that are used as the raw material components should also be added in the process when copper powder is used in producing copper base powder metallurgy material and product. In addition, they can be directly used in producing fluxes, rubber as well as the additive of plastic, firework and metallic pigment, etc.

Aluminum powder and magnesium powder are mainly produced by atomization method. Aluminum powder can also be produced by machining solid magnesium. In the production of aluminum powder and magnesium powder, anti-explosion and flame-proof safety precautions are needed. The direct application of aluminum powder is very wide, of which the consumption is the largest in the non-ferrous metal powders. It is mainly used in the metallic pigment, printing ink, paint coating as well as the aerospace fuel propellant, explosive, firework and so on. Foil shape aluminum powder that is used as pigment and coating can only be produced by specialized wet ball-milling process. Aluminum powder and magnesium powder both can be used as metallothermic reduction agent, explosive and pyrotechnical, such as flare, signal flare and so on. Besides, aluminum powder metallurgy product has been used in office machine and other fields.

Tungsten, molybdenum, tantalum, niobium as well as titanium powder, tungsten powder and molybdenum powder are all produced by oxide reduction method. Bars, boards and wires of metal tungsten and molybdenum are produced by further purifying and processing the raw materials of tungsten powder and molybdenum powder. Besides, tungsten powder and molybdenum powder can also be directly made into tungsten and molybdenum special-shaped parts via powder metallurgy process. Tungsten powder is also an important raw material in producing tungsten carbide powder in the hard carbide industry. Tantalum powder, which is produced by reducing potassium fluotantalate with metal sodium, is mainly used in producing capacitors. After tantalum bar that is made by tantalum powder is smelted and purified by electron beam, it can be made into high purity tantalum powder and tantalum alloy powder by hydrogenation, crashing and dehydrogenation process. Niobium powder can be generated in the process when metal niobium, which is generated by reducing niobium oxide with aluminum in the thermit reaction, is hydrogenated, crashed and dehydrogenated. Titanium powder is generally produced by sodiothermic reduction or magnesiothermic reduction process, in which the sponge shape titanium (titanium sponge) can be further purified and processed into titanium and titanium alloy material, besides, it can be made into titanium powder after being hydrogenated, crashed and dehydrogenated. Titanium powder that has sponge shape is suitable for cold pressure forming, which can be used as the raw material of titanium powder metallurgy products, such as porous titanium filter element, chemical corrosion-resistant titanium parts and so on. Titanium alloy is mainly produced by rotating electrode processing or inert gas atomization, which has been used in producing the parts that used in the aviation and spaceflight industry.

Nickel powder and cobalt powder can be produced by many processes, which have respectively formed main industrial application according to different production methods. Electrolytic process, reduction method and atomization method are the general production methods of nickel powder. Nickel powders that are produced by these three kinds of methods can meet the general application requirements, for example, they can be used in producing porous filter elements, compact nickel material parison, powder metallurgy structural parts as well as the alloying element additives and so on. Carbonyl compound thermal decomposition is mainly used in producing superfine and fine nickel powders that will have high purity and high activity and are mainly used in producing accumulator and fuel cell electrode plate, chemical catalytic material, micropore separation material, electromagnetic shielding material and powder metallurgy material such as magnetic material, alloying element additive and so on. Hydro-metallurgical method is mostly used in the comprehensive treatment of the intermediate product of rich nickel, among which most of them are made into nickel shot that is used in metallurgy industry; by finish machining, a small amount of them are made into nickel powder, which will be made into nickel strip via powder rolling; some of them will be further made into coins. Cobalt powder that is used as the carbide bonding phase is mostly produced by oxide reduction process, while cobalt powder that is produced by hydro-metallurgical method is used in producing cobalt salt and samarium cobalt permanent magnets. Nickel base alloy powder and cobalt base alloy powder, such as the self-fluxing powder (NiCrBSi series) that used in the hardfaced technology as well as the heat resistant, wear resistant and corrosion resistant alloy powders (CoCrW series) and so on, are all produced by the atomization method that uses nitrogen and water as the medium. Nickel base and cobalt base high temperature alloy powders that used in the aerospace industry are mainly produced by vacuum melting-argon atomization method.

Among the precious metal powders, silver powder has most application. Silver powder is used in making battery electrode and silver base electric contact material, conductive ink that used in the electronic industry, ointment, adhesive as well as dental amalgam alloy, water purification, catalysts and so on. Silver powder that has high purity and fine particle as well as used in the electric power and electronic industry is mostly produced by chemical precipitation method, besides, a small amount of them are produced by atomization method. Gold powder, platinum powder and palladium powder have similar production methods with silver powder, which are mainly used as the conductor materials in the electronic industry.