Film on the Surface of the Tungsten Contacts

The reason why there is a film on the surface of tungsten contacts is that: during use, particularly have been placing them at high temperatures and high humidity conditions before using for a long time, the surface has generated an oxide film layer, which is tan. After chemical analysis, find that the components of the layer dura is WO₃ (non-conductive), this layer of the dura with high resistance may lead to poor contact or bad contacts conduction, so the equipment will break down.

After metal is oxidized or corroded, if the volume of metal is less than metal oxide’s, the metal surface may form a dense, complete oxide - film; while if the volume of metal is greater than metal oxide’s, the oxide film formed on the surface of the metal is loose, porous and incomplete.

Relational expression as follows:
V_OX=M_OX/D_OX
V=X*M_w/D_w
Then:
V_OX / V= M_OX* D_w/ D_OX* X*M_w＜1, the oxide film is not complete;
V_OX / V= M_OX* D_w/ D_OX* X*M_w＞1, the metal oxide film may be complete and dense;
According to relevant literature, the V_OX / V value of WO₃ is 3.59, more than 1, so that the film on tungsten contacts’ surface is dense and complete. Troubleshooting method: drop a few drops of alcohol on tungsten contacts’ surface, and then the layer of the dura mater will peel off.
Among them,
V_OX → the volume of oxides
M_OX → the molecular weight of oxides
D_OX → the density of oxides
V → the metal volume of generation single oxide molecules
X → the number of metal atom in single oxide molecules
M_w → the atomic weight of the metal
D_w → the density of the metal

 

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