Development of methods for the characterization of melting batches

摘要

Glass batch melting has been studied by many researchers on various scales and under various conditions but no comprehensive understanding has been reached. In view of this situation, a major part of this work was devoted to the improvement of five new experimental methods suitable for the investigation of batch melting. These are: conductometry, thermal diffusivity, heating microsopy, batch free time (BFT) and weight loss measurement. Firstly, as for the development of conductometry, three meaningful ways to present batch reactions in terms of "DTA", "voltage drop", and "electrical conductivity" were concluded. It was also possible to determine the duration of stages characterized by foaming. Secondly, for thermal diffusivity, an optimized output signals at a frequency of 50 Hz with time interval of 150 s was applied. It showed good measurment results. As a conclusion, the grain-to-grain contact in model calculations should be taken into account by a dimensionless shape factor of 2.5 to 3.5. Local conductometry combined with temperature measurement allowed to measure simultaueously the electrical conductivity and the local temperature in a melting batch. The measurement of the local thermal diffusivity was performed by an evaluation of the runtime of a periodically generated heat pulse. Thirdly, for the heating microscope, a new way to present the effect of gas release from glass batches prior to refining was developed. It was found that minor batch additions additions have a large influence. Fourthly, the BFT results show that the reaction behavior of container flint and green glass batches was more sluggish than that of crystal glass batches. By observation through a silica tube furnace, the beginning of batch reactions with cullets at the surface deep into the glass melt were observed. After 2 minutes foam was formed and decreaed within 10 minutes. Finally, weight loss determination for samples up 200 g was developed. It was found that the mass loss of soda ash detected in a vertical tube furnace started at a lower temperature and was completed at a higher temperature than suggested by the results measured by thermogravimetric analysis (TGA). These new characterization methods not only open concepts for the presentation and interpretation of batch reactions, but also close the experimental gap between conventional lab scale characterization and the behavior actually observed in industrial production.