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Abstract: The influences of the chemical composition and the heat-treatment conditions on both the crystallisation behaviour and the high-temperature stability (HTS) of three types of amorphous stone wool fibres of iron-bearing alumino-silicate composition are studied by performing thermal, structural, and compositional analyses. The fibres heat-treated under oxidising conditions exhibit outstanding HTS, i.e., the fibres are able to maintain their original geometric shape in a high-temperature environment. This is attributed to the formation of a nano-crystalline layer on the surface of the fibres as a consequence of the oxidation of Fe2+ to Fe3+. The layer remains after the bulk crystallisation process has been completed. The thickness of the layer increases with increasing initial content of Fe2+ and Mg2+ in the fibres. The nanolayer influences the bulk crystallisation in the manner that it lowers the crystallisation onset temperature, the activation energy, and the Avrami parameter. Such influence benefits the enhancement of the HTS. In contrast, the fibres heat-treated under reducing and inert conditions exhibit poor HTS. This is attributed to the early viscous heating of the fibres because of lack of the nano-crystalline surface layer. The HTS does not depend on the identity of the bulk crystalline phases. [Copyright &y& Elsevier]

Abstract: The thermal expansivities of 10 compositions from within the anorthite–wollastonite–gehlenite (An–Wo–Geh) compatibility triangle have been investigated using a combination of calorimetry and dilatometry on the glassy and liquid samples. The volumes at room temperature were derived from densities measured using the Archimedean buoyancy method. For each sample, density was measured at 298K using glass that had a cooling-heating history of 10–10Kmin−1. The thermal expansion coefficient of the glass from 298K to the glass transition interval was measured by a dilatometer and the heat capacity was measured using a differential scanning calorimeter from 298 to 1135K. The thermal expansion coefficient and the heat flow were determined at a heating rate of 10Kmin−1 on glasses which were previously cooled at 10Kmin−1. Supercooled liquid density, molar volume and molar thermal expansivities were indirectly determined by combining differential scanning calorimetric and dilatometric measurements assuming that the kinetics of enthalpy and shear relaxation are equivalent. The data obtained on supercooled liquids were compared to high-temperature predictions from the models of (Lange, R.A., Carmichael, I.S.E., 1987. Densities of Na2O–K2O–CaO–MgO–FeO–Fe2O3–Al2O3–TiO2–SiO2 liquids: New measurements and derived partial molar properties. Geochim. Cosmochim. Acta 51, 2931–2946; Courtial, P., Dingwell, D.B., 1995. Nonlinear composition dependence of molar volume of melts in the CaO–Al2O3–SiO2 system. Geochim. Cosmochim. Acta 59 (18), 3685–3695; Lange, R.A., 1997. A revised model for the density and thermal expansivity of K2O–Na2O–CaO–MgO–Al2O3–SiO2 liquids from 700 to 1900K: extension to crustal magmatic temperatures. Contrib. Mineral. Petrol. 130, 1–11). The best linear fit combines the supercooled liquid data presented in this study and the high temperature data calculated using the Courtial and Dingwell (1995) model. This dilatometric/calorimetric method of determining supercooled liquid molar thermal expansivity greatly increases the temperature range accessible for thermal expansion. It represents a substantial increase in precision and understanding of the thermodynamics of calcium aluminosilicate melts. This enhanced precision demonstrates clearly the temperature independence of the melt expansions in the An–Wo–Geh system. This contrasts strongly with observations for neighboring system such as anorthite–diopside and raises the question of the compositional/structural origins of temperature dependence of thermal expansivity in multicomponent silicate melts. [Copyright &y& Elsevier]