The granularity and uniformity of tungsten and copper powder has an effect on tungsten copper electrode sintering, and the decreasing granularity will improve the comprehensive properties of materials, such as the density, the hardness, the electric and thermal conductivity. Theoretically, powder metallurgy (PM) uses metal powder (or metallic oxide powder) as raw materials, after compacting and sintering, the granularity of powder is coarser. Compared with PM, nano tungsten copper has higher surface energy, which atoms move by higher interfacial energy, shrink the small pores in sintering process and in case of the diffusion of pores. Therefore, nano tungsten copper research is beneficial for the densification at lower temperature.
Although the process of nano tungsten copper is similar to the traditional PM, which can be divided into preparation, compacting and sintering, due to the characteristic of nano particle, there are some differences between them. Overall, the most widely used process of nano tungsten copper main are Sol-Gel method, Metal Alloying (MA), Mechano-Thermo-chemical Process, spray drying and so on.
Metal Alloying (MA), uses high energy ball milling for tungsten copper mixed powder grinding, achieves the nano powder (the granularity is about 20nm-30nm). Then compacts the blank by the nano powder and sintering in hydrogen atmosphere at 1000℃, nano tungsten copper with high related density can be achieved.
The so-called sol - gel (Sol-Gel) is the use of compounds with high chemical composition as the precursor in the liquid phase under these uniformly mixed materials, hydrolysis and condensation reactions to form a stable transparent sol in solution sol particles by aging between slow polymerization to form a three-dimensional network structure of the gel, the gel network between full solvent loses fluidity to form a gel. After drying, sintering and solidifying, sol can be produced with molecular or nano substructure. At the academic front, some researchers succeed in preparing MoW and CuW high-performance powder. However, this kind of process has some shortcomings, such as the content of water vapor and impurities is difficult to control in the process of hydrogen reduction, which these problems will influence the later sintering process.
Mechano-Thermo-Chemical process, uses ammonium paratungstate and copper nitrate as raw materials to prepare a mixed solution, and then spray drying the mixed solution to obtain a metal powder mixture through a rotary atomizer and the subsequent drying process of the precursor, the precursor of combustion, the formation of tungsten copper W-Cu composite oxide powder, then milled oxide powder and two-step hydrogen reduction, thereby preparing nano-tungsten-copper composite powder.
