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28th April 2021 at 19:15 #41384chongbalesGuest
Tungsten concentrates decomposition method has fire method and wet
Purification of tungsten compound
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.
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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
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.