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Inorganic solidified foam (ISF) is a novel material for preventing coal fires. This paper presents the preparation process and working principle of main installations. Besides, aqueous foam with expansion ratio of 28 and 30 min drainage rate of 13% was prepared. Stability of foam fluid was studied in terms of stability coefficient, by varying water-slurry ratio, fly ash replacement ratio of cement, and aqueous foam volume alternatively. Light microscope was utilized to analyze the dynamic change of bubble wall of foam fluid and stability principle was proposed. In order to further enhance the stability of ISF, different dosage of calcium fluoroaluminate was added to ISF specimens whose stability coefficient was tested and change of hydration products was detected by scanning electron microscope (SEM). The outcomes indicated that calcium fluoroaluminate could enhance the stability coefficient of ISF and compact hydration products formed in cell wall of ISF; naturally, the stability principle of ISF was proved right. Based on above-mentioned experimental contents, ISF with stability coefficient of 95% and foam expansion ratio of 5 was prepared, which could sufficiently satisfy field process requirements on plugging air leakage and thermal insulation.

Thermal insulation and setting properties are considered to be two significant parameters when inorganic solidified foam (ISF) is applied to control and extinguish coal fires. Based on studies concerning the thermal properties of porous media and experimental research on the relationship between porosity and the addition of aqueous foam, an equation describing the change in thermal conductivity with aqueous foam volume is deduced and then amended.Microscopic analysis of the process of setting is conducted by scanning electron microscopy. The results show that the coagulation of a single bubble wall and bubbles connecting with each other lead the ISF to lose fluidity gradually. A loss of fluidity time (LFT) index is then proposed on the basis of field process requirements and the aforementioned microscopic analysis, and a home-made instrument to test LFT is developed. Effects of aqueous foam volume and accelerator type, along with its addition quantity, on the LFT of ISF are investigated. The relationship equation provides a theoretical foundation for steerable adjustment of the LFT. Furthermore, under the restriction of cost, thermal conductivity threshold and LFT, the parameters of the feasible construction state areas of four different accelerators were compared; in this study AC3 was found to be the most appropriate accelerator. NotationA accelerator amount (wt%) a, b, c coefficients F aqueous foam volume (ml) K e effective thermal conductivity (W/m K) k g thermal conductivity of gaseous phase (W/m K) k s thermal conductivity of solid phase (W/m K) V f aqueous foam volume (ml) å porosity (%) r true density (kg/m 3 ) r 0 dry density (kg/m 3 )

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