Ammonium Paratungstate as a Raw Material for the Manufacturing of Lamp FilamentTungsten Wire

摘要

The thesis presents a study of the use of tungsten metal for incandescent lampfilaments. Ammonium paratungstate (APT, (NH4)10H2W12O42.4H2O) is an intermediate product in the production of these filaments. APT is also sold as a tungsten precursor on Western World markets. It will be shown that it is an attractive alternative for the traditional tungsten raw materials. A complication, however, is that not only chemically acceptable APT should be purchased, but also that the physical properties seem to have an impact on the final tungsten filament quality. The objective of the research presented in the thesis was to find ways to make the change over to APT possible. Three possible options were considered at the start of the study. In the first option, purchased APT is processed by the standard procedure and physical specifications of intermediate tungsten products are controlled downstream. In the second option, purchased APT is dissolved in aqueous ammonia and recrystallized into APT meeting present physical specifications. APT dissolves, however, slowly in aqueous ammonia. Laboratory experiments showed that the dissolution rate could be improved significantly by calcination under controlled conditions. A third alternative is the conversion of purchased APT into tungstic acid. This acid can be dissolved in aqueous ammonia.