Research And Preparation Of Nano-Sized SiO₂ Composite Insulation Materials

The thermal insulation materials prepared with the one-component nano-sized SiO2 have some advantages,including low density,high porosity,low thermal conductivity at room temperature,meanwhile they have some defects,such as high thermal conductivity at high temperature,brittleness,poor stability at high temperature.In this paper,the nano-sized SiO2 composite insulation materials are prepared by dry pressing method with the nano-sized fumed SiO2 as raw materials,and infrared opacifiers,high silica glass fibers,xonotlite powders and ZrO2 fibers as functional additives.The key technology parameters are studied for preparing the nano-sized SiO2 composite insulation materials.The effects of the functional additives on the performances of the nano-sized SiO2 composite insulation materials are described.Some research on the hydrophobic property of the nano-sized SiO2 composite insulation materials is done at the same time.The results show that:(1)Mixing process and molding process have a certain impact on the performances of the nano-sized SiO2 composite insulation materials.The comprehensive performance of the nano-sized SiO2 composite insulation materials is the best when the technology parameters are stirring speed of 1200r/min,stirring time of 10min,molding pressure of 6MPa and dwell time of 3min.(2)The addition of the infrared opacifiers with the special type,number and particle size can reduce the thermal conductivity of the one-component SiO2 insulation materials effectively at high temperature;The comparison research on zircon(ZrSiO4),six potassium titanate whisker(K2Ti6O13),SiC has been done.The result shows that SiC has the best infrared shielding effect.When 25%SiC whose average diameter is 2.08?m is added,the thermal conductivity of the samples that have the best insulating performance is 0.032W/(m·K).(3)The mechanism of the effects of reinforcing materials on the mechanical property of the nano-sized SiO2 composite insulation materials has been studied by scanning electron microscope and other devices.The high silica glass fibers can play a skeleton role in enhancing the composite materials.Xonotlite is usually fibrous.The secondary particles with a hollow ball structure can enhance the samples' mechanical performance further.The compressive strength can be improved from 0.12MPa to 0.46MPa when 8%high silica glass fibers and 4%xonotlite powders are added.(4)The stability of the nano-sized SiO2 composite insulation materials at high temperature has been studied with the help of the high-temperature refiring experimental furnace.And the effect of the ZrO2 fibers on other performances of the composite materials is studied further.The study shows that the heating linear shrinkage of the composite materials without ZrO2 fibers is 2.5%at 900?.The shrinkage dues to the water volatilization inside the samples and the dehydration condensation reaction happening on the surface of the fumed SiO2 powders.The samples heated to 1000? whose heating linear shrinkage is 13.3%occur severe deformation because of the sintering phenomenon.When heat resisting ZrO2 fibers is added into the composite materials,the linear shrinkage of the samples decreases to 5.3%under 1000? for 24h.The stability of the samples in the high temperature environment is improved significantly.(5)The effects of the heat treatment temperature and the addition of hydrophobic fumed SiO2 on the nano-sized SiO2 composite insulation materials has been studied by the MoSi2 box resistance furnace and the hydrophobic tester.When the heat treatment temperature is 900?,the hydrophobic rate of the samples is increased from 40%to 58%under the premise of ensuring its insulating performance.When 61%hydrophobic fumed SiO2 is added,the hydrophobic rate of the samples is increased from 40%to 88%.