Effect of Both the Phase Composition and Modification Methods on Structural-Adsorption Parameters of Dispersed Silicas

Tripoli from two Ukrainian deposits was studied in its natural and modified forms. The investigation of natural and modified tripoli involves the identification of their phase compositions through X-ray diffraction and the analysis of their water vapor adsorption-desorption isotherms. The obtained results are evidence of changes in the structural-adsorption parameters of tripoli as a result of modification. Their treatment in boiling water or acid causes apparent alterations of contents of the main phases and sizes of their crystallites, whereas their calcination causes not only the dehydroxylation of surfaces and the agglomeration of phases, but even phase transformation in the case of carbonate tripoli. After analyzing water vapor adsorption-desorption isotherms of natural and modified tripolis, some correlations between their adsorption parameters, phase compositions, main phase contents and crystallite sizes have been found.

Water Vapor Adsorption by Some Manganese Oxide Forms

Manganese oxide forms prepared by different methods differ by their compositions, phase ratios in polyphase samples, and crystallite sizes (XRD and TEM characterization). Among the phases, tunnel-structured β-MnO2 (pyrolusite), α-MnO2 (cryptomelane), ε-MnO2 (akhtenskite), and β-Mn2O3 (bixbyite) have been identified. Water vapor sorption isotherms showed substantial differences in the affinities of water molecules to oxide surfaces of the manganese oxide forms under study. The parameters of the BET equation and pore size distribution curves have been calculated. The manganese oxide forms have mesoporous structures characterized by uniform and non-uniform pore sizes as well as by moderate hydrophilic behavior.