Preparation And Study On Properties Of Light-weight Porous Silicate Thermal Insulation Materials

With the constant progress of the society,the rapid development of economy,the global demand for energy is increasing.The building energy consumption occupies about 10%of the total global energy consumption,since building energy consumption is so great that it also caused serious impact on the environment.And more than half of the building energy consumption is due to construction glass and wall insulation materials caused by poor adiabatic effect.Therefore,in order to reduce energy consumption and emissions,the invention has low thermal conductivity,low apparent density,not burning,good durability of building thermal insulation materials is the key of the current energy task.In this paper,we use cheap silicate as raw material to prepare some thermal insulation monolith materials by facile methods of hydrothermal redox reaction and microwave foaming.By controlling the pore structure,pore volume,porosity and apparent density to improve the heat-shielding performance by controlling the reaction conditions.The main research contents and results in this study can be summarized as follows:1.Calcium silicate monolith was prepared by the hydrothermal reaction of the slurry of SiO2,calcium hydroxide,and surfactant?OP-10?obtained by high energy ball milling,followed by drying at ambient pressure.Studies show that the kinds of silica to avoid volume shrinkage caused by pore structure collapsed in the drying process plays a very important role.When the molar ratio of silica powder/wet silica gel is 3:1,there is no shrinkage during the stages of both the hydrothermal reaction and drying was observed.OP-10 can improve the pore volume of thermal insulation monolith materials.By this strategy,the shrinkage due to the collapse of pores during the drying of porous materials,which was commonly observed phenomena,was successfully avoided.XRD,SEM,SEM and AFM show that has a unique microstructure of hierarchical macro-/mesoporous ultrathin calcium silicate nanosheets with layered gyrolite crystalline structure.Very interestingly,the calcium silicate nanosheets can be peeled off to be single layer nanosheet?1.23 nm?of gyrolite by the ultrasonication.The nanosheets are mutually interwoven and supported,which results in the formation of macropores among them and the mechanically stable structure of the monolith.Big pore can reduce the capillary pressure and prevent the shrinkage during the stages of both the hydrothermal reaction and drying.The monolith has low apparent density(0.073 g cm^-3)and low thermal conductivity(0.0399 W m^-1 K^-1).There are a lot of big holes between nanosheets,it make calcium silicate thermal insulation monolith get a higher porosity?95.3%?or pore volume(6.84 cm³ g^-1).It is a kind of inorganic thermal insulation material which has good thermal insulation properties.2.Thermal insulation monolith of aluminum tobermorite nanosheets was prepared by a facile method of one-step hydrothermal reaction and molding of a high energy ball milled slurry of fly ash,sodium bentonite,calcium hydroxide,and sodium water glass,followed by drying at ambient pressure.The monolith was characterized by XRD,SEM,TEM and AFM show that,the addition of both sodium bentonite and sodium water glass plays a crucial role in preventing the shrinkage and improving the porosity of the monolith.The monolith has the microstructure of randomly oriented and multually interwoven aluminum tobermorite nanosheets among which there are numerous macropores.Interestingly,the aluminum tobermorite nanosheets can be exfoliated by ultrasonication treatment to provide single-layer ultrathin nanosheets of aluminum tobermorite with a thickness of 1.18 nm and an aspect ratio of¹000.The monolith of aluminum tobermorite nanosheets has low apparent density(0.077 g cm^-3)and very low thermal conductivity(0.03793 W m^-1K^-1).The low thermal conductivity and good thermal insulation performance of the monolith are attributed to its high porosity?93.3%?or pore volume(5.99 cm³ g^-1)due to the presence of numerous macropores among aluminum tobermorite nanosheets.3.Silicon dioxide monolith thermal insulation material was prepared by microwave heating process of the slurry of water glass and ethylene glycol solution.The material has very low apparent density and thermal conductivity,the thermal conductivity is only 0.029 W m^-1 K^-1,apparent density is only 0.0507 g cm^-3.SEM and TEM show that,SDM-A is characterized by the morphology of closely contacted hollow spheres with diameters ranging from 26 to 861?m.The analysis on the diameter distribution of the hollow spheres shows that the diameters of most hollow spheres are mostly distributed in 50¹50?m,and the shell thickness of hollow spheres are 145.9 nm³.65?m.The microwave heating plays a crucial role in the formation of silica foam monolith with high porosity.The microwave heating not only tremendously increases porosity,but also significantly reduces the consolidation time from tens of hours to several minutes.Add a small amount of ethylene glycol can improve total pore volume and closed pore volume of thermal insulation monolith.In the presence of glycol,nSi?OH?₄ can reacts with glycol to form inorganic-organic hybrid network.The formation of the inorganic-organic hybrid bond chains can improve the flexibility of the formed films,thus preventing the breaking of the formed shell of the hollow sphere during the bubble formation by the microwave heating.4.Fly ash thermal insulation monolith was prepared by a method of two-step microwave heating and muffle furnace heating of fly ash and water glass.SEM and TEM show that,FTM-A is characterized by the morphology of closely contacted hollow spheres with diameters ranging from 65.7 to 591.2?m.The analysis on the diameter distribution of the hollow spheres shows that the diameters of most hollow spheres are mostly distributed in 100³00?m,and the shell thickness of hollow spheres are 180 nm³.3?m.Research shows that adding different amount of fly ash has a great influence on the performance of the samples,when not adding fly ash,pore sizes of sample are too large,most of them are connected pores,and thermal conductivity is large.The microwave heating not only tremendously increases porosity,but also significantly reduces the consolidation time from tens of hours to several minutes.Researches show that additive amount of fly ash has a great influence on the thermal insulation performance and compressive strength.To control the additive amount of fly ash,we can get a sample with low thermal conductivity(0.03048 W m^-1 K^-1)and high compressive strength?0.32 MPa?.