FLUORPHLOGOPITE CERAMIC VIA SINTERING OF GLASS USING INEXPENSIVE NATURAL RAW MATERIALS

Fluorphlopgopite ceramics were prepared from kaolin, feldspar and steatite with the addition of pure chemicals Na2CO3, AlOOH.H2O and MgF2. Glass-ceramics containing the crystal phase fluorphlogopite were prepared using two different routes. The first route was to melt a glass and to crystallise fluorphlogopite by subsequent annealing at 900 to 1050 C for 2 h. Here, fluorphlogopite and cordierite were formed. In the other route, a sintering procedure was applied using the pre-mentioned materials and sintering temperatures in the range 900-1200 C for 2 h. Here, fluorphlogopite [(Na,K)Mg3(AlSi3O10)F2], spinel and norbergite were precipitated. The unit cell parameters of the formed fluorphlogopite phase were larger than those according to JCPDS data. This was due to a partial replacement of Mg by Ca or Ba from the raw materials. The microstructure of the sintered samples showed interlocked fluorphlogopite rods and small spinel crystals. The samples prepared by thermal annealing of the glass showed curved fluorphlogopite and tiny cordierite crystals.