Oxide reduction:
Reduction of compounds particularly oxides by the use of reducing agent in the form of either solid or gas according to the reaction:
Fe2O3 + 2C --> 2CO2 + 3Fe
This is a convenient, economical and extremely flexible method for controlling the properties of the product regarding size, shape and porosity over a wide range. The production of iron, copper, tungsten, and molybdenum powders from their respective oxides are well-established commercial processes. On a smaller scale, oxide reduction is also used for production of cobalt and nickel powders. This process yields extremely fine powders with irregularly shape particles, good compactibility (high green strength) and sinterability, low final porosity of such powders and relatively low cost.
Electrolytic method:
Metal powders can be produced by electro deposition from aqueous solutions and fused salts. This method is reversed adaption of electroplating. A hard and brittle mass is deposited which is subsequently ground to powder having a dendritic shape . This technique is mainly employed for commercial production of iron and copper powders.
Special Methods:
Prealloyed powders:
It is a common practice to use either blended elemental powder mixtures or prealloyed powders. In general, premixes are easy to compact and effect less tool wear but they need longer sintering times than prealloyed powders. Recently great interest has aroused in the production of prealloyed steel powders; the addition of alloying elements being made to permit the production of a strong material. This technique is mainly employed for production of stainless steel and other alloys with high alloying element content that cannot be produced by mixing or blending of powders. Products of prealloyed powders have a remarkable properties like corrosion resistance, high tensile strength and resistance of high temperatures.
Precoated powders:
Metals can be coated with a film of a certain element by passing metal powder through an element carrier gas. In this method each powder particle can be coated homogenously and obtaining a powder having some properties of the coating material after sintering. This technique allow the use of cheap powder as a carrier of the effective coating material. This method produce a more homogeneous products after sintering than that produced from mixed or blended powders.
