| Energy saving and Emission reduction is an important research topic in the world, and the use of efficient thermal insulation material is one of the key measures. Super insulation materials represented by amorphous Si O2 exhibite an excellent heat insulation performance, and are hopeful to be widely used in the filed of industrial insulation. But high cost and low intensity are the main restriction factors, therefore, the research on reducing cost and increasing intensity of Si O2 super insulation materials is of great practical value and social significance.In this paper, fumed nano-Si O2 as the main raw material, Si O2 insulation materials were prepared by the dry processing, in order to reduce the cost. Porous characterisitic, insulation performance and mechanical properties have been systematically studied. High humidity-reinforcement and the addition of radiation shieldings to improve the insulation performance were put forword, which has realized the improvement of intensity and the decrease of thermal conductivity at high temperature, and has important significance in promoting the market oriented application of Si O2 insulation materials.The main research contents in this paper are as follows:1. Pore scals and distribution characteristics of nano-Si O2 powder in the dry processing under different pressure conditions have been systematically studied. Pores inside of hard aggregates(the first stage pores) are the intrinsic pores in Si O2 powder, size and distribution of which are independent of pressure. Pores between hard aggregates(the secend stage pores) and between soft aggregates(the third stage pores) gradually decreased and even disappeard with the increases of pressure. Density of the sample increases and porosity decreases with the decrease of the secend and the third stage pores. When the forming pressure is over 4MPa, size of the main pores in insulation materials is in nanometer range.2. Insulation performance of nano-Si O2 insulation materials has been systematically studied. In dry processing method, thermal conductivity of insulation materials at room temperature decrease initially and then increase with the increase of pressure.When the forming pressure is 4MPa, thermal conductivities of insulation materials are the lowest and 0.019 W/ m·K at room temperature. Thermal conductivity is positively correlated with temperature and is 0.2 W/m·K at 800℃. Adding radiation shieldings is a effective method to reduce thermal conductivity at high temperature, and the kind and addition of radiation shieldings have significant influence. Si C with the diameter of 3.8μm is the best one. With 25% of Si C mass fraction, thermal conductivity of insulation material reachs 0.018 W/m·K at 800℃.3. Research on enhancement technology of nano-Si O2 insulation materials has been carried out, and fiber-enhancement and high humidity-reinforcement method are the effective measures. By adding 5% silica fiber, compressive strength of insulation materials has been increased to 0.91 MPa from 0.5MPa. In addition, high humidity-reinforcement method has been put forward and analyzed. When the hygroscopicity of sample is up to 25% under 40℃ and 95% relative humidity, compressive strength of sample can be up to 1.7MPa, while the thermal conductivities are almost the same. In humidity-reinforcement method, as vapor enters, silicasol is formed in the gap between one aggregate particle and another, and various condensation polymerization occurre in the drying process, which leads to aggregates connection and compressive strength improvement. Lower temperature and airtight space are the key conditions of humidity-reinforcement method, and cracking of materials is always caused by high temperature and pressure.4. High temperature stability of insulation mateials is evaluted in the last part of the paper. Refire linear shrinkage of nano-Si O2 insulation materials is less than 2% as temperature lower than 800℃. When over 800℃, refire linear shrinkage increase and cracking of materials will be caused when over 1000℃. |
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