Determination of O content in metal powders: results of round robin tests on Co and Ni

In the powder metallurgical production of materials, the analytical characterisation of the starting powders, especially the determination of the O content, is of the utmost importance. Depending on the conditions of storage in the time between production of the powders and their processing, the very large and active surface area can cause drastic changes in the properties of the materials because chemical reactions of the adsorbed surface gases and moisture with the powders take place. In an attempt to define an analytical procedure for the accurate determination of the O content under these complex circumstances, round robin tests were organised by the Sonderwerkstoffe Working Group of the Chemists' Committee of the Gesellschaft fur Bergbau, Metallurgie, Rohstoff- und Umwelttechnik (GDMB). Furthermore, the possibilities of identifying the various O species and their distribution between surface and bulk of the powder particles (e.g. adsorbed/chemisorbed H2O, CO2, dissolved/bound oxide) by means of different heat extraction procedures were studied. The results of the investigations of Co, Ni, and WC powders are presented.