Energetics of nanoparticle oxides: interplay between surface energy and polymorphism†

Many oxides tend to form different structures (polymorphs) for small particles. High temperature oxide melt solution calorimetry has been used to measure the enthalpy as a function of polymorphism and surface area for oxides of Al, Ti, and Zr. The results confirm crossovers in polymorph stability at the nanoscale. The energies of internal and external surfaces of zeolitic silicas with open framework structures are an order of magnitude smaller than those of oxides of normal density

Mechanical activation on phosphogypsum: hydrosodalite system

The application of phosphogypsum in the production of binding materials is problematic because of phosphate, fluorine and other soluble impurities. These impurities influence the strength development of binding materials and during operating time can be released (efflorescence) from binding materials’ products. For these reasons, it is important to neutralize the above-mentioned impurities. The objective of the work was to investigate the neutralization process of the acid impurities of hemihydrate phosphogypsum (obtained from Kovdor apatite mine) with zeolite hydrosodalite. Mechanical activation together with the neutralizing zeolite additive was used in this research. Mechanical activation was carried out in a ball mill. Two types of samples were formed: one type with non-milled mixtures and the second type with milled mixtures. The additive of 0, 3, 5, and 10% of hydrosodalite was chosen. This paper describes the process of adsorbing of hazardous phosphate impurities by hydrosodalite. The compressive strength of phosphogypsum specimens with hydrosodalite additives subjected to mechanical treatment was higher as compared to the specimens without mechanical activation and additive of hydrosodalite. In this case pH values of milled mixture with hydrosodalite become neutral for these samples. It was determined that the mixture of phosphogypsum with hydrosodalite under mechanical treatment is an effective additive for neutralizing the acidic phosphogypsum mediumKauno technologijos universitetasVandens ūkio ir žemėtvarkos fakultetasVytauto Didžiojo universiteta