Geometrical Properties of Tungsten Powder

Tungsten powder is one of most important raw material for production of tungsten carbide, tungsten alloy, pure tungsten and the properties of it strongly affect performance of subsequent products .The geometrical properties of tungsten powder includes grain size, specific surface area, morphology of tungsten powder, etc.
tungsten powder photo
Grain size
The grain size of tungsten powder heavily influence the process of powder forming, sintering, machining and the performances of Final products. For instance grain size of tungsten carbide is mostly determined by the grain size of tungsten powder which is an raw material of tungsten carbide . Dry sieving method and Fisher method are commonly used in measuring tungsten powder’ grain size which often dived into 5 levels:
Ultracoarse particle: Average grain size>30μm;
Coarse particle: Average grain size 10-30μm;
Medium particle: Average grain size 3-10μm;
Fine particle: Average grain size 0.5-3μm;
Ultrafine particle: Average grain size <0.5μm.
 
Specific surface area
Specific surface area of tungsten powder directly determines the powder’s surface activation energy, which often used for evaluate powder’s average grain size. Commonly BET method for measuring specific surface area are applied for tungsten powder.
 

Blue Tungsten Oxide (BTO)

Blue tungsten oxide (BTO) is also called tungsten blue oxide (TBO),from which reduction reaction of ATP by hydrogen come, is an common raw material for tungsten powder,it have certain advantage in high specific surface area,easy reduction.
BTO'S PHOTO
The tungsten-oxygen system is rather complex which could be stable stoichiometric binary oxides(WO3, WO2.9, WO2.72 and WO2).TBO is an mixture of different compounds, mainly WO2.90 and ammonium tungsten bronze(ATB).TBO have been used to produced tungsten powder from 1970s, and now is the most important precursor in the line from oxide to W and WC powder. 
 
The main blue tungsten oxide preparation methods are pyrometallurgical process and hydrometallurgical process.The former is widely applied in industry,commonly using reduction reaction of ATP by hydrogen in rotary furnace.The chemical equations of TBO's preparation as shown follows:
 
5(NH4)2•O•12WO3•5H2O→5(NH4)2•O•12WO3+ 5H2O
5(NH4)2•O•12WO3→12 WO3+10NH3+5H2O
2NH3→N2+3H2
WO3+H2→WO2.9+H2O
 
The factors affecting  properties of TBO in preparation process are temperature,heating rate and heating time, etc.
 

Carbon Distribution of Tungsten Carbide Powder

Tungsten carbide powder is the most important raw material for cemented carbide production, carbonized by tungsten powder and carbon black with an appropriate proportion by carbon distribution calculation. The carbon distribution strongly affected the properties of tungsten carbide powder.

Tungsten atom and carbon atom can synthesize two kinds of compounds, WC and W2C.The former’s Molecular is the main and right ingredient of tungsten carbide powder, which carbon element mass accounted for 6.12%, the principle of carbon distribution. The formula is as follows:

Qc=(Xc/(100-Xc)+(0.75*Xo2)/100)*Qw

Qc­-the carbon black mass;

Xc-the carbon mass ratio;

Xo2-the Oxygen content;

Qw-the tungsten powder mass.

Because of uneven composition or inaccurate condition controlling, carbon mass ratio of tungsten carbide powder often deviate from 6.12%; therefore the extra carbon amount or tungsten powder should be added. The formula is as follows:
Qe=Q((100-Qa)/(100-Qt))

Qe­-the extra carbon black mass needs;

Qa-the Practical carbon black mass;

Q-the WC powder mass;

Qt-the total carbon black mass needs.

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