Tungsten carbide powder is commonly used for hardfacing metals. Hardfacing is the process in which a tougher, harder material is applied to a softer base metal. Tungsten carbide improves the wear-resistant properties of a base metal. It is applied to mining equipment parts (shovel teeth, heel plates, bucket wheel excavator teeth, wear parts, crushing hammers, cutter drums and longwall miners), mineral processing equipment (hammers, chutes, pulverizing and grinding parts), earth-moving and construction equipment (grader blades, cutting edges, augers, trencher teeth, ground engaging tools and tunneling equipment), drilling tools, processing equipment and agriculture equipment (subsoilers, discs and injectors).

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Tungsten carbide is used in common consumer goods, including razor blades. Tungsten carbide powder is used in men's wedding bands to give them a dark hue and to improve their scratch-resistance. Tungsten carbide powder is used to make sporting equipment and devices, such as trekking poles, cross-country skis, bicycle studs and drive tracks for snowmobiles. Hikers and trekkers use tungsten carbide-tipped poles and walking sticks to reduce pressure on leg joints and for balance. They are effective in providing traction on rock surfaces.

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Solid carbide is more expensive than steel tools or carbide-tipped drills. In addition, solid carbide is brittle and must be used in a rigid, stable setup that minimizes vibration and movement. Solid carbide also requires a steady temperature or the tools may fracture. Flood coolant can keep carbide cool.

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By drying, calcination tungstate and ammonium paratungstate can be prepared from tungsten trioxide. Drying temperatures around 100℃, the main material is physically adsorbed water vapor but only at higher temperatures the material is calcined to remove ammonium paratungstate and tungstic acid molecule of water and ammonia compounds.

Acid usually calcination in air, 180 ℃ starts dehydration at 500 ℃ for complete dehydration, tungsten oxide formation: H2WO4 = WO3 + H2O ↑

Ammonium paratungstate calcined by heating in air at different temperatures will produce different phase, when the temperature is raised to about 500 ℃, can be completely converted to tungsten trioxide.

Shao-Yi, who used differential thermal analysis and X-ray diffraction observation during calcination of APT and analysis, that the heating APT in the air phase change its course as follows: at a temperature of not less than 240 ℃, APT converted to ammonium metatungstate (AMT), continue heating to 300 ~ 350C, the conversion of the amorphous material (ammonium tungsten bronze ATB), temperature was raised to 400C, into a hexagonal type W03, temperature reached 500 ℃, to obtain a three triclinic crystal tungsten oxide. The purity determined APT purity tungsten trioxide, APT crystal form of the crystal tungsten trioxide hereditary, calcination temperature and the rate of thermal decomposition of the product physical properties of tungsten trioxide has a significant impact.

Calcined at different temperatures with a number of APT, WO3 products vary greatly surface area and particle size, the higher the calcination temperature, the more coarse particle size of the obtained WO3.


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Blue tungsten oxide (TBO) is an important raw material manufacturing of tungsten powder , tungsten oxide reduction due from tungsten powder blue easier to control the particle size and particle size composition , is conducive to the reduction process in the tungsten powder and mixed with other elements, so the TBO is gradually replace the tungsten trioxide production of special tungsten material as tungsten powder materials.

Blue tungsten oxide is an industrial product name , its composition mainly by WO2.9, WO3 and WO2.72 composed of several tungsten oxide , the proportion of each component depending on APT or restore the temperature calcination atmosphere and speed.

Preparation of blue tungsten oxide there are three main methods : APT sealed calcination , APT hydrogen reduction and inherent mild reduction . At present in China more industrial application is the first two methods .

Xue Kam et al APT decomposed under non-oxidizing atmosphere, blue tungsten oxide process of the study found that the decomposition experienced APT six stages :

First stage: the temperature between 90-180C , APT lose some water :

Second stage: temperature range of 180-260 ℃, ammonia begins to escape from ammonium paratungstate , the higher the temperature , the faster the loss of ammonia . Loss of ammonia product was obtained as ammonium metatungstate (AMT), soluble in water, reconstituted after preparation of high purity ammonium metatungstate products ;

Third stage: temperature range of 260-350 ℃, AMT decomposition, further loss of water and ammonia , ammonium decomposition products appeared tungsten bronze (ATB);

Stage IV : The temperature range 350-450C, at this time begins to decompose ammonia in the gas phase , to produce ammonia tungsten bronze (ATB), and to produce hydrogen and nitrogen from the gas phase can be detected in the product hydrogen. Decomposition of ammonia nitrogen and hydrogen atoms is first generated , the new ecological chemical activity of hydrogen atoms , ammonium tungsten bronze to the oxygen index ( tungsten compound in the x (O) / x (W) molar ratio ) decreases. Formation of ammonium tungsten bronze fixed composition , the ammonia content and oxygen index can vary , generally consisting of (NH4) xWO2.8 ~ 3.0;

Fifth stage: temperature range of 450-550 ℃, decomposition ATB ​​this stage , the hydrogen produced by decomposition of ammonia in the reaction , ATB decomposition products occurs WO3 and WO2.9, ATB under reducing atmosphere in the first section and then converted into the WO2 WO3.9in strong reducing atmosphere conditions , ATB will translate directly into W20O58 (WO2.9).

Stage 6: temperature range 550 N 650 ℃, decomposition products of this phase with the phase composition of systems vary considerably reducing the strength of the hydrogen to further participate in the reaction , so that the low priced tungsten oxide, tungsten oxide, transition , decomposition products , in addition to a small amount of ATB , there WO3, WO2.9 and tungsten oxide WO2.27 etc. , even WO2.


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Metatungstate production methods more, can be divided into solid and liquid phase inversion transformation method two categories. Typical solid phase inversion process is based on the thermal degradation APT method as a raw material, this method is the main industrial production process of the AMT. The phase transformation method of ammonium tungstate solution as raw material, extraction, ion exchange, membrane electrolysis, or a method in the solution and the pH adjusted to the appropriate range, the obtained solution of ammonium metatungstate. Many research phase inversion method, is to develop in the direction of industrial applications.

Production of Thermal Degradation AMT

By controlling the APT and the pyrolysis temperature and the ammonia partial pressure of water vapor, the water-soluble pyrolysis APT metatungstate large amorphous material, and then hydrated into a solution of ammonium metatungstate, the solution was concentrated and cooling crystallization available AMT solid.

APT pyrolysis conversion rate and the temperature, if the pyrolysis temperature is too high, the resulting insoluble tungsten oxide is not, if the temperature is too low, the APT insufficient removal of ammonia and water (by Molecular Formula calculated APT be removed the four NH3 and 4 H2O), insolubles increases. APT suitable temperature to improve the conversion rate of the key.

Preparation of Ion-Exchange AMT

AMT ion exchange process to produce ammonium tungstate solution as raw material, ion exchange method because the process is relatively simple, easy to control, to avoid the formation of APT, not into the new contaminants, the process can be continuous, and thus has potential for development .

Extraction and ion exchange method originally buried in a similar, but in the extraction process is easy to produce solids resulting emulsion, industrial applications, there are certain difficulties. Silicic acid, and the solid is likewise prepared using ammonium tungstate solution, one way to take AMT, but due to the addition of silicic acid may cause contamination of the product AMT, so there is no industrial application. Ion-exchange membrane electrolysis (including ion-exchange membrane electrodialysis) is still in the development stage, to be developed better longer selective membrane, reduce production costs, to be applied to the production.


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Preparation of tungsten metal powder The main methods are: Preparation of tungsten metal powder, the main method

(1) hydrogen reduction of tungsten oxide;
(2) hydrogen reduction of tungsten halides;
(3) tungsten oxide or tungsten acid carbon reduction;
(4) tungsten oxide or metal tungstate thermal reduction method;
(5) molten salt electrolysis.

The most practical industrial method of hydrogen reduction of tungsten oxide. Tungsten halide (WCl6, WF6) can be prepared from hydrogen reduction of tungsten powder with special features, and was gradually extended application of other methods do not apply to the production of plastic tungsten.


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