Tungsten smelting

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    calebscholl19
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    Tungsten concentrates decomposition method has fire method and wet
    method.

    Purification of tungsten compound

    The
    silicon, phosphorus and arsenic impurities in sodium tungstate solution are
    presenting in sodium silicate, sodium hydrogen phosphate and sodium hydrogen
    arsenate state. Boiling solution and neutralized with dilute hydrochloric acid,
    when the solution pH is 8-9, the sodium silicate hydrolyze into silicate
    condensation precipitation, add magnesium chloride and ammonium chloride
    solution, make the phosphorus, arsenic generate a very small solubility of
    magnesium ammonium phosphate and arsenate ammonium magnesium precipitation
    removed. Add sodium sulfide to the sodium tungstate solution, molybdenum first
    form the thiosulfate molybdate with tungsten, neutralized with hydrochloric
    acid, make the solution pH from 2.5 to 3.0, molybdenum was formed of insoluble
    precipitates molybdenum trisulfide removed. In the purified sodium tungstate
    solution add calcium chloride solution to obtain calcium tungstate (CaWO)
    precipitation (ie synthetic scheelite), with hydrochloric acid decompose
    calcium tungstate precipitation gets the industrial tungsten acid, at 700 ~ 800
    calcination, get industrial pure tungsten trioxide. If preparing chemically
    pure tungsten trioxide, can be dissolved industrial tungstic acid in aqueous
    ammonia, obtained ammonium tungstate solution, silicon and other impurities
    remain in the slag. The solution through evaporated and crystalline treatment,
    obtains a sheet-like ammonium paratungstate crystal. As the solubility of
    ammonium paramolybdate greater than ammonium paratungstate, after
    crystallization, ammonium paratungstate crystal was reduced molybdenum content.
    After the ammonium paratungstate dried, calcined at 500 ~ 800,
    can be obtained chemically pure tungsten trioxide. In 70s, use tertiary amine
    method to make sodium tungstate solution convert into ammonium tungstate
    solution, simplifying the process and improve the recovery of tungsten.

    Preparation of tungsten powder

    In
    industry, use the method of hydrogen reducing tungsten trioxide or ammonium
    paratungstate to prepare tungsten powder. Reduction process depends on the
    product tungsten powder particle size, particle size composition and oxygen
    requirements. Hydrogen reduces tungsten trioxide preparing tungsten powder is
    generally taken two steps: first in the 550 ~ 800
    reduce tungsten trioxide into tungsten dioxide, and then at 750 ~ 900
    reduce tungsten dioxide into tungsten powder.
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    Also be the first pass into
    hydrogen or not to reduce paratungstate into blue tungsten oxide (blue
    tungsten), and then use hydrogen to reduce into tungsten powder. Tungsten
    powder’s particle size, particle size composition is tungsten powder’s
    important indicator of quality. The reduction reaction was conducted in the
    rotary tube furnace or electric furnace.

    Dense tungsten preparation

    through forming, sintering, melting and other processing obtains
    dense tungsten. The forming is taking tungsten powder into the steel die,
    pressed into the billet or a compact with hydraulic pressure. Large briquettes
    use liquid and other static pressure method molding, can be obtained more
    uniform density compact. Tungsten billet sintered divided into two steps: first
    in the 1100 ~ 1200 temperature sintering, then the current directly through the
    billet for vertical melting (ie, high temperature sintering). The density of
    through vertical melting tungsten was not to17-19
    g/cm. Small shaped, different shaped and large shaped tungsten
    compacts sintered usually use radiant heating or induction heating method to
    achieve the sintering required high temperature, at this time, do not have to
    completely separate operation low-temperature sintering and high-temperature
    sintering. While preparing large tungsten ingots usually use a vacuum or inert
    gas protection arc melting method and an electron beam melting method. Prepare
    high purity dense tungsten is usually use electron beam melting purified.
    Electron beam melting also can be obtained tungsten single crystals, the purity
    was up to 99.99% or more.

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