The preparation method of nanometer material

Nanometer powder preparation can generally be divided into physical method ( evaporation condensation method, mechanical containing heavy ) and chemical methods ( chemical gas phase method, chemical precipitation method, hydrothermal method, sol gel method, solvent evaporation method, electrolytic method, high temperature synthesizing method). Preparation is the key to control the particle size and narrow and uniform particle size distribution ( i.e. no reunion or a reunion of light ) and how to ensure the powder chemical purity. As for the actual production in the choice of what kind of preparation method, it should consider the production conditions, the powder quality, yield and cost factors.

Electrolytic process comprising water solution and molten salt electrolysis. The method can be made high purity nanometer metal powder which general methods cannot be prepared or difficult to prepare, especially the electronegativity of metal powder. Such as use electrolytic deposition to make nanometer copper powder.

In ignition conditions, the reaction heat is utilized to form a self-propagating combustion process to produce compound powder method called high-temperature self-propagating synthesis. However, this method is difficult to obtain the nanometer powder, and the product of many performance is difficult to control, the SHS method can be divided into the synthesis of elements and compounds synthesized by two methods. The synthesis of elements is the reactant materials are simple substance, for example titanium powder and amorphous boron powder as raw material, uses the SHS technology can synthesize a thinner two iron boride ( TiB2 ) powder, TiB2 powder purity depends mainly on the purity of raw materials. However, due to the high purity amorphous boron powder is expensive, so that the prepared TiB2 powder has no practical value. The compound is made of metal or metal oxide as reactant, reactive metal as a reducing agent. In addition, the SHS method can also be used for sintering, thermal densification, metallurgical casting, coating etc.

In general, fine and uniform microstructure and fully densified is a nanometer material to achieve the best performance needs. Molding and isostatic molding is the most commonly used in powder metallurgy molding method can also be used for nanometer powder molding. In addition, extrusion molding, injection molding, slip casting, explosive forming special molding method, but also can be used for nanometer powder molding. Compact without appearance defects and pressed density as high as possible, is the pursuit of the goal of molding process. Sintered powder metallurgy production process is the last main procedures, on the properties of the final product plays a decisive role, because the waste caused by sintered could not save through subsequent steps. In addition, sintering high temperature operation, generally require insulation for a long period of time and need appropriate protective atmosphere sintering process, therefore the consumption is an important part of product cost. Pressureless sintering is the most commonly used, the most economical method for sintering. Hot pressing or hot isostatic pressing to sintered material, can obtain complete densification. Microwave sintering, spark plasma sintering and sintering, developed in recent years is a new method for sintering.

Source:http://www.mhcmp.com