Reply To: Site availability is poor

[Andrew Palfreyman]

Latest report
http://us8.campaign-archive1.com/?u=87935f5eb37481cdcd48cf498&id=52e1f80838&e=a62ed3a024
highlights important impurity issues.
“An alternative source might be a very thin layer of tungsten oxide—too thin to be seen or removed during the electrodes’ cleaning. Tungsten oxide dissociates at 1970 C, far below tungsten’s vaporization point of 5500 C, so an oxide layer will be far more fragile. The oxide layer might well give rise to the tungsten in the plasma as well. If this is the case, repeated firing will burn the oxide layer off and impurities will fall.”

Looking here (assuming this is the correct oxide – there are several)
https://en.wikipedia.org/wiki/Tungsten_trioxide
it seems that a hydrogen gas treatment at moderate temperature might be a shortcut to getting rid of this surface layer, if indeed this be the problem.

WO3 + 3 H2 → W + 3 H2O (550 – 850 °C)

But repeated firing to get a feel for the asymptote seems the most reasonable short-term course of action.
It might be enough.