Semiquantitative Analysis of Phase Evolution and Viscosity in Perlite

ABSTRACT Perlite is a noncrystalline volcanic rock with rhyolitic composition that expands four to 20 times its original volume when heated, forming a porous structure widely used in filtration, catalysis, and construction. Raw perlite consists of a noncrystalline aluminosilicate matrix and 10–15 wt.% crystalline phase. Semiquantitative data on perlite crystal species and reliable viscosity measurements of its noncrystalline aluminosilicate component remain scarce. Yet, they are crucial for understanding the morphological evolution of the perlite skeleton during high‐temperature heating. This study developed two methods for measuring the viscosity of the noncrystalline portion of perlite over a temperature range near and above the estimated glass transition temperature using a combined experimental–modeling approach. Both methods integrate semiquantitative X‐ray diffraction (XRD) analysis and simultaneous differential thermal analysis, with viscosity modeled using the Mauro–Yue–Ellison–Gupta–Allan (MYEGA) equation. In the first method, synthesized glass replicating the composition of perlite skeletons is characterized by inductively coupled plasma–atomic emission spectroscopy (ICP‐AES) and semiquantitative XRD, and its viscosity within a temperature range near and above the estimated glass transition temperature of the noncrystalline component is determined by applying the MYEGA equation to heat flow scanning data. In the second method, the crystalline contribution is subtracted from the heat flow curve using temperature‐dependent heat capacity data collected based on crystalline phases characterized by XRD results before applying the MYEGA equation to calculate the viscosity of the noncrystalline perlite skeleton within the temperature range.