Читать книгу Encyclopedia of Glass Science, Technology, History, and Culture - Группа авторов - Страница 64

Even when all chemical, physical, and mineralogical specifications are respected, some raw materials may pose special difficulties upon heating. Decrepitation is such a special case affecting mainly dolomite [14] and, albeit to a lesser extent, limestone. It occurs at 300–400 °C, hence well before the onset of decarbonation and decomposition of the (Ca, Mg) carbonate. Although it is still poorly understood [14], decrepitation appears to result from a sudden change in the overall PSD of dolomite, and an overall increase of fines, when dolomite grains locally burst into smaller grains. The decrepitation factor is defined as the increment in the fraction of grains smaller than 60 μm after heating at 1000 °C. It can range from a few to several 10% depending on geological history and, in particular, on the thermal pathway followed by the dolomite after its formation. High‐decrepitation dolomites are detrimental to the glass process because they contribute to further increase in dust and carryover in the furnace atmosphere. The latter in turn contribute to clogging phenomena at the level of regenerator chambers, drastically decreasing their energy‐recovery efficiency. Furthermore, dolomite dusts may increase the overall wear of the furnace‐superstructure refractories through the formation of new Mg‐bearing phases that decrease their overall durability. When a local supply of good‐quality dolomite is lacking, glassmakers may thus find safer to produce Mg‐free glass.