We ordered 99.9% pure tungsten for electrodes in a plasma focus device. We found that the density of one electrode was 18.0 g/cc and the other 18.5 g/cc, well below pure tungsten’s 19.25 g/cc. The supplier says that it is in fact 99.9% pure and the sintering process does not allow achieving full density. Is this true? (We doubt it, but would like to know for certain.) Would a melting point test show that it is really an alloy? What other tests can be used?
How about doing EDX on the electrode? I have no idea how large the electrode is, but if it has an appropriate size to put in an SEM-EDX this will be a destruction free way to get elemental analysis on the part.
I should recommend using lantanated one.
Other problem that you could have is that the hardness is not the promised one. I would make a Rockwell or Vickers test and a conductivity test
I think, X-Ray photo electron spectroscopy (XPS) Analyze can help you.
Neutron Activation Analysis (NAA) is the best method for alloy analysis without non-destructive and standard. We have analysed Ti / Al / Ni alloy samples by INAA
Is it possible to determine the lattice parameters by XRD? If the values obtained correspond to literature data for pure W, the density deviations can safely be attributed to porosities due to the sintering process. In a first blind approach I would say the supplier is right as the density deviations can hardly be explained by compositional variations on the basis of zero porosity. It has to be admitted that the supplier reports significant density variations and hence porosity variations.
It may not be a form of analysis, but you can try the following:
if your tungsten is sintered there is the possibility of air (or other gas) bubbles between the sinter grains, which decrease the density - so, I would put your tungsten parts into a good vacuum (if that is possible) and heat them, for example, electrically. The part should be bright glowing. This will cause small defects in your tungsten lattice to "heal out".
If the sintering is the real cause for the smaller density (and it is in fact 99.9 % tungsten) then I would assume that you really have gases between your tungsten grains. Hence after this treatment the density should go up again.
At the values you give above, you would need to have 4% of porosity. You should be able to see this with optical or SEM if you make a metallographic sample.
I know that tungsten for incandescent filaments are usually doped with volatile elements to produce porosity, this increases the creep resistance -- so having some porosity may not be totally bad.
Besides other options ion beam analysis using RBS, glow discharge spectrometry or secondary ion mass spectrometry are suitable. GDS could even be used to measure density when combined with mass loss and crater depth profiling. We have everything on site, so you can send me a sample if you like
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