On carbon and oxygen impurities content in tungsten

In order to determine the carbon and oxygen impurities in ingots and single crystals of tungsten, obtained by various methods, spark mass-spectroscopy, activation with He-3 particles and oxidation melting in vacuum are used. The standard methods give practically identical data (0.005-0.01% for each element) in all specimen which underwent electronic, crucible-free zone melting (ECZ) and flame arc melting according to the method advanced by the IMET AN USSR, no matter what the system used or whatever the purity of the original metal was. At the same time the results of analysis using more sensitive new methods confirm that tungsten is more thoroughly refined free of oxygen and carbon with ECZ and flame-arc melting. Event in less purer crystals of tungsten obtained by flame-arc melting the content of carbon impurities is 3.10-4% and of oxygen impurities if 10-4%. Depending on the initial carbon content in tungsten this carbon can be eliminated either by carbon oxide formation or by direct evaporation