Tungsten powder is used as a filler material in plastic composites, which are used as a nontoxic substitute for lead in bullets, shot, and radiation shields. Since this element's thermal expansion is similar to borosilicate glass, it is used for making glass-to-metal seals.
Current uses are as electrodes, heating elements and field emitters, and as filaments in light bulbs and cathode ray tubes. Tungsten is commonly used in heavy metal alloys such as high speed steel, from which cutting tools are manufactured. It is also used in the so-called 'superalloys' to form wear-resistant coatings.
The technological process of preparing metal tungsten powder with metallurgical tungsten material includes the following steps: concentrating coarse Na2WO4 solution to crystallize and recovering excessive alkali, dissolving Na2WO4 crystal to obtain solution with WO3 concentration of 180-250 g/l and pH value of 7.5-8.5, adding alkali metal salt and evaporating to crystallize, treating the crystallized product in hydrogen atmosphere at 350-450 deg.c for 2 hr to obtain 'bluish tungsten' or calcining the crystallized product at 600-700 deg.c to obtain 'yellowish tungsten', and final reduction with hydrogen at 750-850 deg.c to obtain metal tungsten.
