Preparation of surface-vitrified micron sphere using perlite from Xinyang, China

Micron porous spheres with vitrified surface were prepared by expanding the perlite from Shangtianti in Xinyang, China. The samples were extensively characterized by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). In addition, the types of water in raw particles were determined by infrared spectroscopy (FT-IR). Expansion was simulated in a pilot-plant furnace allowing the careful control of temperature and time. The study of several perlites with different grain sizes showed that water content, preheating temperature, expanding temperature, calcination time and size of raw particles had considerable effect on the glassy structure and expansion volume. Perlite expansion process was optimized for preheating temperature 250–350 °C, expansion temperature 1150–1200 °C and expansion time of 10–15 s. Infrared spectroscopy provided evidence for the states of water in the particle, which expanded. The expansion ratio was strongly influenced by the raw grain size. Using electric furnace, micron perlite spheres with grain size of 50–800 μm and bulk density of 200–500 g/cm3were efficiently produced. Horizontal electric furnace was a good candidate to be considered in engineering applications.