The evaporation of potassium during sintering of doped tungsten

An experimental set-up is presented which allows the in situ measurement of potassium release during sintering by self-resistance heating in an UHV chamber. Potassium release is detected by a quadrupole mass spectrometer, which also allows the measurement of silicon and aluminium evaporation. In addition, several other data are collected during sintering: the specimen's temperature (measured by a pyrometer), total pressure, heating current and voltage. Standard sintering programmes consisting of dwell times at three different temperatures have been performed. In addition interrupted programmes or programmes with modified heating rates or dwell time have been made. A potassium-release model has been developed based on an image force driven potassium bubble migration within the tungsten particles. The potassium release during the sintering experiments was in good agreement with the release predicted by the model. (C) 1998 Elsevier Science Ltd. All rights reserved.