Study On Design And Preparation Technology Of Ultra-low Thermal Conductivity Foamed Ceramics

The key to promote building energy conservation lies in the development and production of intrinsically safe,functional,modern livable,excellent quality of high-quality green new insulation wall materials.The research of foamed ceramic thermal insulation material is of great significance to promote the implementation of green building standards.However,poor insulation performance,low output,high energy consumption and high cost are the major bottlenecks restricting the benign development and technological upgrading of foaming ceramic insulation board industry.High entropy ceramics have good thermal stability,high hardness,low thermal conductivity and good corrosion resistance.Compared with traditional ceramic materials,high entropy ceramics show obvious differences in composition,structure or properties,breaking through the limitation of simple component design,and providing a broader idea and guidance for the development of new material systems and optimization of key properties.In this paper,based on the high entropy design concept and Ca O-Al₂O₃-Si O₂ternary system,the high entropy ceramic Mg_0.5Ca_0.3Ba_0.2Al₂Si₂O₈ with ultra-low thermal conductivity was optimized by uniform design methods with upper and lower limit constraints,and the front-end foaming process was further studied to solve the technical bottleneck in the current foaming ceramic production process.The research conclusions are as follows:（1）Based on the concept of high-entropy design,Ba²⁺was introduced into Ca Al₂Si₂O₈ to transform the material from the Ca O–Al₂O₃–Si O₂ ternary system to the Ba O–Ca O–Al₂O₃–Si O₂quaternary system to reduce the thermal conductivity of the ternary system and improve its stability.For the experiment,Ba O–Ca O–Al₂O₃–Si O₂ multicomponent ceramics with ultra-low thermal conductivity were designed using uniform design methods by controlling the mass ratio of the raw materials.The results show that when a sample with Ca O:Ba O:Al₂O₃:Si O₂ molar ratio of 0.459:0.156:0.061:0.324 was sintered at 1400℃ for 300 min,the sample exhibited ultra-low thermal conductivity(0.4783 W·m^-1·K^-1,70℃).This value was much lower than the commonly observed low thermal conductivity of other materials,such as Zr O₂ and 3YSZ.In addition,the developed material exhibits a compressive strength of 57 MPa,good thermal stability at high temperatures and low cost.（2）Furthermore,Mg²⁺was introduced into the Bao-Ca O-Al₂O₃-Si O₂ quaternary system to further optimize the properties of ultra-low thermal conductivity ceramics.Results show that the(Mg_0.5Ca_0.3Ba_0.2)（Al Si）₂O₈ high entropy ceramics exhibit good high temperature stability,high Young’s modulus（64.56 GPa）and low thermal conductivity(thermal conductivity measured via heat flow method at 70℃ is only 0.3676 W·m^-1·K^-1),which is far lower than3YSZ(2.9 W·m^-1·K^-1)widely used at present.It has important application value for developing thermal insulation materials with low cost and excellent thermal insulation performance.（3）The four front-end foaming processes of polyurethane foaming,H₂O₂ foaming,gelating material foaming and gypsum curing foaming were studied and compared.Compared with the other three methods,gypsum curing foaming method has the advantages of high porosity,uniform distribution of pores,high curing efficiency and accurate control of product size.The results show that when the water-cement ratio of slurry is 0.6,the foam ceramic insulation board made by injection molding and sintering at 1180℃for 2 h has the advantages of low density（0.2836 g/cm³）,low thermal conductivity(0.15 W·m^-1·K^-1)and low cost,so the product has strong competitiveness.