Sintering Behavior and Hardness of Tungsten Prepared by Hard Metal Sludge Recycling Process without Ammonium Paratungstate

In this paper, we suggest a novel recycling process for hard metal sludge that does not use ammonium paratungstate. Ammonia, which in the conventional recycling process is essential for removing sodium and crystallized tungstate, was not used in the novel process. Instead of ammonia, acid was used to remove the sodium and crystallized tungstate resulting in the formation of tungstic acid (H2WO4). Tungsten powders were successfully synthesized by hydrogen reduction of the tungstic acid through H2O decomposition, WO3 to WO2 reduction, and tungsten metal formation. The tungsten powders prepared from tungstic acid were spherical in shape and had a higher sintering density than the facet-shaped tungsten powders prepared from tungsten oxide. The spherical shape of the tungsten powders enhanced their sinterability and resulted in an increase in the size of grains. This is a result of the high diffusion rate of the atoms along the particle surfaces. Despite having a higher density, the hardness of the sintered tungsten was lower than that of tungsten from tungsten oxide. High energy milling effectively reduced grain size and improved hardness. The hardness of the tungsten prepared from milled tungstic acid was enhanced to a value (max. 471 HV) higher than the best previously reported value (389 HV). In sum, tungsten can be hardened, thereby improving its sinterability and reducing grain size, with tungstic acid prepared using the proposed recycling process.

Production of tungsten powders with highly developed surface

The process of producing tungsten powders with a highly developed surface by reducing its oxide compounds with magnesium vapor in the temperature range 600—750 °C under dynamic vacuum (0.01 kPa) and with a residual argon pressure in the reactor 0.5—10 kPa has been studied. During the reduction of magnesium and calcium tungstates, tungsten powders were obtained with a specific surface area of 40 m2·g–1, characterized by a mesoporous structure.

Progresses on Development of Manufacturing Methods of High Purity Tungsten Targets

Tungsten has many excellent properties such as high melting point, high electrical conductivity, high electromigration resistance, high electron emission coefficient, high thermal stability and so on. Because of these excellent properties, high purity tungsten targets have wide applications and development prospects in the integrated circuit (IC) industry. In this paper, some manufacturing methods of tungsten targets was summarized and analyzed. The high melting point of tungsten makes powder metallurgy (PM) be the manufacturing methods of tungsten targets. After preforming of the tungsten powders, some sintering and densification processes like atmosphere pressure sintering, Hot Pressing (HP), Hot Isostatic Pressing(HIP) have been carried out. The grain size and the density of the tungsten targets is different by different manufacturing methods.