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This contribution presents the results of structural investigations on the cured and high temperatures of three series of geopolymers. The specimens were synthesized at 80 °C from coal fly ash and three activators of variable composition based on sodium hydroxide and sodium silicate solutions. Structural and microstructural analysis was performed, especially using in-situ measurements of XRD patterns and IR spectra as a function of temperature. The cured compounds' phase content and compressive strength changed slightly depending on the starting chemical composition. All analyzed materials experience a mass loss due to water removal at 300 °C, followed by increased porosity from disintegrating compounds above 300 °C. Higher alkali content improves strength (400–600 °C) possibly due to nepheline formation. The amorphous phase gradually softens during heating, influenced by alkali content. Structural analyses were supported by model calculations of a number of aluminosilicate structures. The cluster analysis using the k-means algorithm was used to divide the PCA space into regions that represent structural similarities, and analyzing specific point positions in the space allowed for several conclusions to be drawn about the studied materials, including that changes in chemical composition and thermal treatment can promote the transformation from sodalite to nepheline and that the glass network has elements that are nepheline-like and may promote its crystallization. [ABSTRACT FROM AUTHOR]

Thermochemistry of crystal phase formation in vitrified municipal and hospital waste combustion ash and Ca, Fe pyroxene crystallization mechanism are presented. Pyroxene structure is capable of accumulate heavy metals and toxicants contained in ash. Due to this vitrification and crystallization is one of most effective method of immobilization dangerous contaminant of waste. [ABSTRACT FROM AUTHOR]

The high-resolution transmission electron microscopy HRTEM study of the atomic scale mechanism of crystal structure organization within the amorphous polymeric structure of the model multicomponent glass TiO2–MgO–Al2O3–SiO2– in the glass transformation temperature range has been undertaken. In the glass transition ( T g) temperature range, glass transforms from the solid of rigid amorphous structure into viscoelastic state of weakened chemical bonds. This is an example of nuclei formation and crystal growth in the polymeric amorphous structure of low atomic scale homogeneity due to middle range ordering. It has been demonstrated that in this case crystal structure formation proceeds by successive displacement and local ordering of atoms in the amorphous structure, like disorder-order transformation in crystalline solid bodies. As the consequence in the crystallization by parent structure reorganization mechanism, traditional model of glass crystallization as well as kinetic models of reactions in solid bodies according Avrami or others, are worthy to be revised. [ABSTRACT FROM AUTHOR]