New Process for Forming Potassium Tungsten Aluminum Bars

The tungsten bar containing potassium is a material for manufacturing high-temperature heating devices such as electric light sources, electronic devices, vacuum sputtering. The manufacturing process is as follows: in the blue tungsten oxide powder, an excess of silicon, aluminum, and potassium are added to make the doping blue tungsten is then reduced to doped tungsten powder under high temperature hydrogen.

The doped tungsten powder is acid-washed with hydrochloric acid and hydrofluoric acid and powdered, and then pressed into a billet by a die, and then sintered into a potassium-containing metal tungsten bar. The purpose of this process is to retain a certain amount of potassium in the formed tungsten bar, so that the tungsten bar forms a potassium foam band in the subsequently processed tungsten material to prevent the grain growth and grain boundary sliding of the tungsten crystal grain. Move to ensure high temperature and sag resistance of tungsten materials.

Studies have shown that during the reduction process of doped blue tungsten, only a small amount of potassium can be incorporated into the tungsten crystal lattice, and only in the presence of a large amount of potassium, silicon, and aluminum, and eventually remain in the tungsten strip. Most of the added dopants, potassium, silicon, and aluminum, adhere to the surface of the tungsten powder particles after the reduction process. This results in poor billet formation, non-uniform crystals, and a low density of tungsten. Deteriorating subsequent pressure processing conditions is a harmful component.

The content of a potassium doped tungsten powder and tungsten bar production process is as follows:

(1) Preparation of doped blue tungsten powder: In a doping pan, add 400Kg of pure water and turn on the stirrer. The proportion of each substance in the ratio of blue to tungsten is: SiO2 0.30 wt%, K2O 0.35 wt%, Al2O3 0.05 wt%, add blue tungsten 300Kg the doping machine was heated by steam heating and the temperature was stirred at 70° C for 3 hours. Then, the temperature was increased to evaporate water and kept for 3 hours. After cooling for 2 hours, it was discharged through a 80 mesh sieve.

(2) Powder reduction: The doped blue tungsten is loaded into a high-temperature alloy boat and continuously pushed into an eleven-tube and five-temperature zone reduction furnace. The volume of blue-tungsten is 500g, the boat speed is 2 boats/h, and the hydrogen is reversed in the furnace. The hydrogen dew point is -50°C, the hydrogen flow rate is 1.5 cubic meters/h, the reaction zone temperature is 550-920°C, and the reduction reaction time is 10 hours. After the furnace powder is discharged, it is sieved by 120 mesh to obtain 238Kg of doped tungsten powder.

(3) Alkali washing and pickling: In a reaction vessel with a volume of 1 cubic meter, add 0.5 Kg/L sodium hydroxide solution 500Kg, add K-doped tungsten powder, heat to 70°C, keep for 1 hour, remove the upper alkali solution, and react after adding pure water to the pot, stir it for 10 minutes and let stand for 20 minutes. 500Kg 0.6 mol/L hydrochloric acid solution was added, and the mixture was stirred for 1 hour and allowed to stand for 20 minutes. Remove the upper layer of hydrochloric acid solution from the next pickling supplement and then use the reaction pot plus pure water to the middle, stirring for 10 minutes and then set aside for 20 minutes. The upper aqueous phase is siphoned out and washed with pure water. After the pH value of the aqueous phase is 4 or more, the material is discharged from the reaction pot to suction filtration, sucked dry, then sent to the oven, vacuum dried at 100° C for 8 hours, cooled and filtered by 160 mesh. After the mixture of potassium-doped tungsten powder was analyzed and analyzed, the powder had a particle size of 3.20μm, a potassium content of 92ppm, a silicon content of 210ppm, and an aluminum content of 20ppm. The washing water is mixed and neutralized with sodium hydroxide until the neutral precipitate is discharged.

(4) Press molding: The above tungsten powder is loaded into a molding rubber tube, the head is sealed, the isostatic press is placed in a pressing chamber, and the pressurization is performed under a pressure of 220MPa for 5 minutes, and pressed into a doped tungsten billet.

(5) Low-temperature sintering: The  tungsten billet is loaded into a molybdenum boat and pushed into a heating zone of a sintering furnace, and heated at a temperature of 1150° C for 1 hour. Push it to the cooling zone to cool it for 1 hour.

(6) Vertical melting sintering: Place the pre-fired tungsten billet in a special fixture in a vertical melting furnace and heat up according to the program under hydrogen protection conditions. The holding current is 4260amps and the holding time is 30 minutes. Power down, cut off the power supply, and cool the material. For the tungsten-doped tungsten bar, the density of the tungsten bar was 17.6-17.8 g/cm3, and the potassium content was 85 ppm. The cross section of the tungsten bar was uniform.

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