Tungsten Carbide Research Paper

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Tungsten Carbide is a compound synthesized by the reaction of tungsten (metal) powder and carbon black (carbon powder) at temperatures of 2600° - 2700° F. Tungsten has a chemical symbol "W" which comes from the name "Wolfram" and that is how it is known in Europe. There are a total of thirteen tungsten containing ores of which four types are the most abundant. These are: Wolframite - FeMn(WO 4 ) 2 Scheelite - CaWO 3 Ferberite - FeWO 4 Hubnerite - MnWO 4 The thirteen tungsten containing ores are in combinations with eight elements which are manganese, calcium, iron, copper, aluminum, lead, sulphur and zinc. The two most abundant and widely used ores are Wolframite and Scheelite. In processing Wolframite the tungsten contained is first converted…show more content…
The sodium tungstate liquid is clear and colorless. The liquid is then filtered from the remainder and collected in large containers where calcium carbonate (Ca 2 CO 4 ) is added precipitating Calcium Tungstate (Ca 2 WO 4 ) which is then filtered out and dropped into a digester containing hydrochloric acid (HCl) where in the prescence of heat tungstic acid (H 2 WO 4 ) is produced. After filtering, the cake is dumped into a slurry tank containing ammonium hydroxide (NH 4 OH). At this point clear colorless ammonium tungstate is formed (NH 4 ) 2 WO 4 . After filtration the rich "W" containing liquid is pumped to a crystallizer. The heat from the steam evaporates the water and a white chemical called Ammonium Paratungstate or APT - (NH 4 ) 2 . (H 2 O) x .WO 4 is precipitated. Application of high heat in a calciner causes the compound to reduce to a blue oxide which is approximately WO 3 O 11 . Pure tungsten oxide is WO 3 and yellow. Further heat under a hydrogen atmosphere in high nickel boats reduces the oxide to tungsten metal powder "W". In the reducing operation the grain size of the tungsten powder is carefully controlled by controlling these…show more content…
High efficiency dust control is a must so that all powder can be recovered and a dust free environment is maintained. Specially designed band saws, slicers and vertical lathes are used as common practice. For special radii and special shapes, either plated wheels are made to the exact form or green silicon carbide wheels are dressed to the required shape. Silicon carbide wheels "load up" readily and require constant dressing. Silicon carbide contamination is always a problem therefore the wheels are "dressed" in other areas far from the preforming departments. 9. Sintering: a) Hydrogen Sintering: A hydrogen atmosphere protects the material from oxidation and reduces some oxides. The hydrogen flow is always in a direction opposite the direction of the material being sintered so as to "sweep" the impurities away. Graphite boats are required and temperatures of between 2500° F and 2750° F are used. All small parts are packed in alundum (Al 2 O 3 ) grain. b) Combination Vacuum Sintering: Pre-sintering is done under inert gas or in vaccum at low temperatures until the paraffin has evolved; the gas is then pumped out and the temperature is continuously increased to the final temperature. Vacuum furnaces
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