Application of thermal analysis to mineral synthesis

Abstract

Differential thermal analysis (DTA) and thermogravimetry (TG) are applied to various fields of mineral science. The present work illustrates the importance of the application of thermal analysis to mineral synthesis, to the determination of the mechanism and optimum temperature of synthesis and the thermal behaviour of minerals and starting materials. Selected examples of applications in this field are given. These include DTA studies of the synthesis of topaz, cryptohalite, wulfenite, perovskite, scheelite and the refractory materials, baddeleyite and corundum.Thermal analysis is proved to be an important and valuable tool in mineral synthesis.

Thermoluminescent characterization of Al2O3-derived synthetic topaz

“…The presence of the topaz in the samples is attributed to two possible reactions (3 and 4); reaction (3) occurs between aluminum oxide, water vapor and silicon tetrafluoride, whilst reaction 4 takes place between the products of reaction 2 with water vapor. The thermodynamic feasibility of the reactions was determined using the FactSage ® program and databases and from the literature [34]. Using the XPowder ® program e which is based in the nonlinear least squares method e, a semi-quantitative phase analysis of the amount of topaz formed (Table 2) was conducted.…”

Topaz synthesis using Al2O3, Al(OH)3 or Al2Si2O5(OH)4 and color centers promoting its radioluminescence response

“…Traces between 5 and 10 ppm H 2 O are usually present in high purity nitrogen. In the case of reaction (4), formation of intermediate reaction products (AlF 3 and SiO 2 ) via reaction (3) is necessary, after which, topaz synthesis occurs by the reaction of such intermediate products with water [29].…”

Formation pathway, structural characterization and optimum processing parameters of synthetic topaz – Al2SiO4(OH,F)2 – by CVD

“…However, from the technological and economic standpoints, as well as drawbacks associated to the use of high processing pressures, long processing times (up to 3 months), high reactiveness and difficulty to handle the chemicals involved, some of the above mentioned fabrication routes have been unappealing [6,[8][9][10][11][12]. The chemical vapor deposition (CVD) route is an alternative for topaz synthesis due to the relatively low processing temperatures, pressures, and times.…”