Low-temperature Foaming Mechanism of Silica-based Solidified Products Prepared by Alkaline Activation

The glassy volcanic sand produced mainly in the Kyushu region of Japan is called “Shirasu” and is composed of fine particles of silica-based compounds. Rapid heating to about 1000 ℃ makes the Shiras particles to expand and foam. The particles form a balloonlike hollow structure called a “Shiras balloons”. In this study, solidified bodies of shirasu particles were prepared by alkali activation and foamed at low temperatures. The effects of sample preparation conditions, such as the concentration of added NaOH, treatment temperature, and time, on the foaming properties were investigated. The mechanism of low-temperature foaming of silica-based solidified bodies was discussed.