Preparation And Performance Investigation Of Inorganic Thermal Insulation Foams Based On Sodium Silicate Solution

Energy crisis is gradually got the attention of the people, and energy conservation and emissions reduction becomes an important development strategy in our country. The building energy saving is a significant role in the energy conservation and emissions reduction work. With the continuous development of city in our country, a large number of thermal insulation materials are used in the urban construction. The organic heat preservation materials have caused a serious fire accidents and thus the fire hazard of them causes the attention of related departments. Relevant laws have strengthen the restrictions on insulation materials, and the inorganic heat preservation material gradually receives the attention of people. But the inorganic heat preservation material has a complex classification, and the thermal insulation performance is relatively lower than that of the organic insulation material, resulting in the confined application and the low-level market share. Therefore, development of new high efficient inorganic heat preservation material has a strong practical significance. In view of the present situation of inorganic heat preservation material in our country, this article is to prepare an inorganic thermal insulation foam with low thermal conductivity, low density and high compressive strength, using sodium silicate as the main material with fly ash, glass fiber, or inorganic acid/salt as additives. The main research work includes the following aspects:1. Research the foaming and solidification process of the inorganic thermal insulation foam based on the sodium silicate and its performance. It is found that sodium silicate solution releases a large amount of water vapor in the process of foaming, and the solidification process of sodium silicate solution starts after 118℃ and the Si-O tetrahedron reacts with each other to form layered and reticular three-dimensional structure. This process is stable after 300℃. In the end, the inorganic thermal insulation foam has excellent thermal insulation properties (thermal conductivity below 0.042W/m·K) and low density (below 60kg/m3), but the compressive strength is too low (0.3MPa).2. Fabricate the inorganic thermal insulation foam by sodium silicate with fly ash as the additive. The Al-O and Si-O structures in fly ash can combine with the Si-O structure in the sodium silicate solution to form part of the S-O-Al structure.Through the research of the sintering temperature, holding time, heating rate, modulus of sodium silicate and solid content, the final process parameters and preparation recipe can be obtained. Based on above results, the product has the thermail conductivity of 0.049W/m·K, density of 97kg/m3 and compression strength of 0.44MPa. In addition, it is found that the samples fabricated by the presintering treated fly ash have a higher thermal conductivity. And vitrified beads, gasification of slag and diatomite are the promising candidate as the additive.3. Fabricate the inorganic thermal insulation foam by sodium silicate with glass fiber as a support. In the sintering process, some SiO2 in the glass fiber can integrate into the sodium silicate solution and react with the original Si-O group to generate Si-O-Si structure, and then gradually form a three-dimensional network structure. Through the research of the sintering temperature, modulus of sodium silicate and solid content, the final process parameters and preparation recipe can be obtained. Based on above results, the product has the thermail conductivity of 0.046W/m·K, density of 80kg/m3 and compression strength of 0.46MPa.4. Facbricate the inorganic thermal insulation foam using sodium silicate modified by inorganic acid and salt. For boric acid, through changing the sintering temperature, the modulus sodium silicate and the content of boric acid, the final samples can obtain the thermal conductivity from 0.042 to 0.044W/m·K and density between 80 and 100kg/m3, respectively. The performance of the samples sintered by sodium silicate with liquid phosphoric acid, hydrochloric acid and sulfuric acid is more sensitive to acid concentration, and the capacity that acid can ionize hydrogen ion also has apparent effect. Potassium dihydrogen phosphate and disodium hydrogen phosphate are suitable as additive to fabricate inorganic thermal insulation foam. But the physical properties of the sintered samples is more sensitive to the content, and the density and thermal conductivity of the samples are a little high. Borate can effectively improve the compression strength of the sintered samples, and meet the needs of exterior wall thermal insulation material.5. Reasearch the water absorption and water resistance of the inorganic thermal insulation foams. By comparison, it is found that the samples fabricated by sodium silicate modified by boric acid and borate have the lower water absorption and the softening coefficient of them are above 0.85, showing high water resistant ability. Therefore, boric acid and borate is currently the most suitable additives. In addition, for the inorganic thermal insulation foam prepared by sodium silicate modified by boric acid and sodium tetraborate, the thermal conductivity, density and compressive strength are generally superior to those of the existing inorganic exterior wall thermal insulation material.