ИСТИНА

The magnesium and alkaline-earth metal fluorides can be used for different applications some of which require samples that possess large surface area. But it is not easy to produce metal fluorides in highly-dispersive form. Here we propose a new method for the preparation of MF2 (M = Mg, Ca, Sr, Ba) having large surface area with the use of beta-cyclodextrin as a structure forming agent. The samples were obtained by the decomposition of the metal trifluoroacetate hydrates with the addition of beta-cyclodextrin and subsequent annealing at the 420 °C. It was determined by the X-ray diffraction analysis that the products of the decomposition are metal fluorides. But the impurity of metal carbonate begins to form at some content of beta-cyclodextrin in the mixture. However the content of the beta-cyclodextrin that leads to the formation of the metal carbonate depends on the corresponding metal (65, 45 and 30 wt. % of beta-cyclodextrin for M = Ca, Sr, Ba). The formation of the metal carbonates is possible because of the beta-cyclodextrin decompose with large evolution of CO2. The relative stability of MF2 and MCO3 can be compared on the data based on their solubility. The solubility of MF2 increases from M = Ca to M = Ba; on the contrary the solubility of MCO3 decreases from M = Ca to M = Ba. So, at the certain content of beta-cyclodextrin the formation of the metal carbonate becomes more preferred. It is interesting to mention that these data are in good agreement with the values of specific surface areas of the metal fluorides. So Figure 1 show that surface area of metal fluorides increase with the increasing of beta-cyclodextrin content in the reaction mixture but after some content of beta-cyclodextrin surface area decrease. Perhaps it can be explain by the appearance of the metal carbonate impurity in the final product.