Preparation Process And Performance Optimization Of Foam Ceramics With High Closed Porosity

In recent years,China has accelerated the development of building energy efficiency,green building and assembly-type construction.Foam ceramics have become a highly sought-after green energy-saving wall material due to their light weight and high strength,thermal insulation and water and frost resistance.The preparation of foam ceramic insulation material is beneficial to promote the implementation of green building.However,the overall performance of current foam ceramic products is generally unsatisfactory and the high sintering temperatures lead to high preparation costs.Closed-cell foam ceramics have a unique pore structure and are therefore stronger and better insulated against moisture.In this paper,foam ceramics with high porosity were prepared using quartz sand as the main raw material and CaCO₃,SiC and Fe₃O₄as foaming agents.The influence of raw material components and sintering temperature on the pore structure,density,porosity and compressive strength of closed cell foam ceramics was investigated.The influence of the melt characteristics of the blanks on the foaming properties of foam ceramics is summarised.Contribution to the optimisation of the properties of closed cell foam ceramics.（1）Closed cell foam ceramics are produced at 690～730°C using CaCO₃as the foaming agent and sodium tetraborate as the flux,using the high temperature foaming method.The foaming mechanism of this foam ceramic is revealed.Then the pore structure of the foam ceramics was improved by adding proper SiC.The influence of the melt properties of the blanks on the foaming properties of foam ceramics was explored.The results show that varying the content of sodium tetraborate in the raw material and the sintering temperature have an effect on the foam volume,porosity and compressive strength of the foam ceramics.The addition of SiC improves the high-temperature viscosity and continuity of the blank,resulting in the in-situ sealing of the molten matrix to the foaming gas.Following this,the pore structure of the foam ceramic is effectively regulated.Using high porosity as an evaluation criterion,when the weight ratio of quartz sand,CaCO₃and sodium tetraborate is 6:1:5 and at sintering temperatures of 710°C and720°C.The foam ceramics have a high total porosity of 70%and 78%respectively,at which point the compressive strength is 3.2 MPa and 2.1 MPa respectively.Using high strength and homogeneous pore structure are used as evaluation criteria,when the weight ratio of quartz sand,CaCO₃and sodium tetraborate is 6:1:5 and the sintering temperature is 710°C.Foam ceramics prepared by adding 1wt%of SiC with a particle size of 0.5μm to the blank have a smaller pore size due to the uniform pore structure.The compressive strength of the foam ceramic is up to 10.8 MPa,at which point the total porosity is 51%.（2）High performance closed cell foam ceramics were prepared at 900～1000°C using SiC as the foaming agent and sodium tetraborate as the flux.The influence of the melting characteristics of the blanks on the foaming properties of foam ceramics was investigated.The results show that the melting characteristics of the blank at high temperatures have a strong influence on the foaming properties of the foam ceramic.Poor viscosity or continuity of the blank at high temperatures can lead to foam failure.At high temperatures,a fast melt rate,moderate viscosity and good continuity of the blank are essential to ensure that the foam ceramic has a high expansion rate and a homogeneous pore structure.Evaluated on the basis of high porosity and homogeneous pore structure,when the sodium tetraborate content is 25 to 35 wt%.Best overall performance of foam ceramics sintered at950 to 1000°C for 1h.Relatively dense foam ceramic surface and homogeneous internal pore structure.It has a total porosity of 69～75%and a compressive strength of 8.1～11.2MPa.（3）Closed cell foam ceramics were prepared at 600～700°C based on the Fe₃O₄carbon thermal reduction reaction.The key to the method is a design that can be quickly melted at 600 to 700°C into a blank with the right viscosity and continuity to seal the foaming gas in situ.Using high porosity as an evaluation criterion,the total porosity of the samples sintered at 650°C was 67%when the weight ratio of quartz sand to sodium tetraborate for the blanks was 4:6.At this point the compressive strength is 15 MPa and the pore structure is basically homogeneous.When evaluated on the basis of high strength,when the weight ratio of quartz sand to sodium tetraborate in the blanks was 4:6,the samples sintered at 600°C had a compressive strength of up to 21 MPa due to the uniform pore structure and small pore size.At this point the total porosity is 60%.