Research On The Properties Of Silica Nanoporous Thermal Insulating Materials

SiO2 nanoporous thermal insulating materials consist of fumed silica fibers,opacifiers and inhibition of sintering.It has many good personalities,such as light weight,high temperature resistance,high porosity,low thermal conductivity and so on.It can be applied to the field of heat insulation and heat preservation in metallurgy,chemical industry,aeronautics and astronautics,etc.It has become a research hotspot presently in the field of high-performance thermal insulating materials.In this paper,the thermal conductivity and volume stability of nanoporous insulating materials compounded with HL200 series fumed silica have been investigated.When the samples were calcined at 1000?,the thermal conductivity and microstructures of samples at certain temperatures were tested.In order to reduce the manufacturing cost of the thermal insulating material,we also investigated the thermal conductivity and volume stability of nanoporous insulating materials compounded with cheap silica fume.In addition,we investigated the thermal conductivity and volume stability of nanoporous insulating materials compounded with Al2O3 to improve the high temperature volume stability of thermal insulating material.The obtained results were as follows:(1)The thermal conductivity of nanoporous insulating materials compounded with fumed silica in a certain range,the thermal conductivity of the sample ranges from 0.021 to 0.025W/(m·K)and the thermal conductivity of samples adding silica fume ranges from 0.021 to 0.031W/(m·K)when the temperature is at 700-1000?.When the samples were calcined at 1000? for 24 hours,the volume shrunk sharply.Through XRD analysis,we found the fumed silica in the insulating material changed from amorphous state to crystalline SiO2.The nanoporous in the samples were destroyed.So the samples were unsuitable to be used at 1000?.(2)The thermal conductivity of nanoporous insulating materials compounded with silica fume increases with the increasing of temperature,and the higher the mass fraction of silica fume in the sample,the higher the thermal conductivity of the sample at the same temperature.The thermal conductivity of the samples ranges from 0.031 to 0.052W/(m·K).When the temperature is 900? or below,the thermal conductivity and volume stability of nanoporous insulating materials are all good.When the temperature rises to 1000 ?,the volume shrinkage is more serious.From the point of view of cost reduction,it is feasible to prepare nanoporous insulating materials with silica fume.It is necessary to improve the volume stability of the material at high temperature.(3)The thermal conductivity of nanoporous insulating materials compounded with Al2O3 increases with the increase of temperature,the thermal conductivity of the samples ranges from 0.021 to 0.030W/(m·K).The volume shrinkage of Al2O3 samples decreases with the increase of the mass fraction of Al2O3.The internal pore of the sample is basically maintained,the porosity is high,and the sintering condition is not obvious.Al2O3 has very good inhibition effect on nanoporous insulating material,and the more Al2O3 is added,the more obvious the inhibition and sintering effect on nanoporous insulating material is.(4)Al2O3 is added to nanoporous insulating materials to improve the volume stability of the material at high temperature.When the mass fraction of silica fume is 45%,the thermal conductivity of nanoporous insulating materials compounded with Al2O3 increases with the increase of temperature,the thermal conductivity of the samples ranges from 0.031 to 0.039W/(m·K).In 1000?,Al2O3 is very good for the high temperature volume shrinkage inhibitory effect of nanoporous insulating material,and the Al2O3 content is more,its inhibitory effect on sintering of nanoporous insulating material is more obvious.