Justyna Sułowska

Comparative study of zinc addition effect on thermal properties of silicate and phosphate glasses

The aim of the study was an analysis of two groups of glasses from the SiO2–P2O5–K2O–CaO–MgO system with various content of network formers in the form of P2O5 and SiO2, modified by the addition of ZnO. Their effect on glass-forming ability, glass transition effect, crystallization process and the kind of crystallizing phases was examined using DSC and XRD methods. It was observed that in both matrixes, the addition of ZnO decreases the glass transition temperature (Tg). The lower Tg values observed in the phosphate matrix glasses and the accompanying higher values of the changes in molar heat capacity (Δcp) in contrast to the silicate matrix glasses may be considered an indicator of the degree of the reconstruction of their amorphous structure, which facilitates the process of their crystallization. It was found that the crystallizing products of the silicate matrix glasses were silicates and phosphates whose structure contained zinc. In the phosphate matrix glasses, it was observed that zinc inhibited the crystallization of silicate phases.

Effect of copper addition on glass transition of silicate–phosphate glasses

Glass transformation effect of mixed SiO2–P2O5–K2O–MgO–CaO–CuO glasses was studied by DSC, XRD, SEM, and Raman spectroscopy methods. The relationship between the parameters characterizing glass transformation effect and an amount of phosphorous and copper forming the glassy structure was discussed. It was shown that an increasing content of phosphorous increased solubility of copper in the structure of the studied glasses which was the result of P–O–Cu bonds formation. Degree of changes of Tg, ∆cp, and time of relaxation values were higher in glasses with higher content of P2O5 and CuO. The observed relations were explained on the basis of the local atomic interactions in the structure of glass.

Characterization of thermally induced of crystalline phases in CuO-containing silicate–phosphate glasses

The DSC, XRD, FTIR, and 31P MAS-NMR methods were applied to study complex crystallization processes occurring during the thermal treatment of multicomponent SiO2–P2O5–K2O–CaO–MgO glasses modified by the addition of variable amount of copper. The crystallization temperatures were found to decrease with the increasing copper content. The products of multistage crystallization identified by XRD and characterized by FTIR and NMR are the Ca9KMg(PO4)7 and Ca19Cu2(PO4)14 phosphates of whitlockite-type, and the CaMgSi2O6 and Cu0.69Mg1.31Si2O6 silicates of diopside type.

Effect of glass composition on the interactions between structural elements in Cu-containing silicate–phosphate glasses

The structure of silicate–phosphate glasses from the SiO2–P2O5–K2O–CaO–MgO–CuO system acting as slow release fertilizers, containing different amounts of copper ions replacing magnesium or calcium ions, was examined by DSC, XRD, 31P, and 29Si MAS–NMR techniques. The chemical activity of the glasses in the 2 mass% citric acid solution was measured by the ICP-AES method. The studies showed that regardless of the kind of replaced components, the Cu ions prefer to associate with the phosphorous Q1 units, forming the domains composed of orthophosphate with P–O–Cu bonds. The formation of domains with chemically stable P–O–Cu bonds resulted in poorer glass solubility under conditions simulating the natural soil environment.