Fabrication And Properties Of Thermal Insulating Material Using Hollow Glass Microspheres Bonded By Aluminum-Chrome-phosphate And Tetraethyl Orthosilicate

In this paper,thermal insulating material made by hollow glass microspheres(HGM)with different content of aluminum-chrome-phosphate solution(ACP)and tetraethyl orthosilicate(TEOS)as binders was formed,dried and sintered at 250 oC,450oC or 650 oC for 2 hours.Low density and coefficient of thermal conductivity were achieved by samples made by HGM bonded by silica sol.However,the compressive strength of samples bonded by silica sol was not satisfactory(below 3MPa).The HGM as received was hydrophobic so the binder didn`t concentrate to the contact region and provide bonding force.The HGM was surface modified by NaOH and KH550 to improve the wettability between the binder and the HGM.However,samples made by modified HGM bonded by ACP showed nonuniform distribution of ACP between the inside and outside parts of the samples.After TEOS was added,it formed silica gel quickly in the samples and locked ACP at the surface of the HGM and to the contact region.As a result,the ACP distributed uniformly in the samples and provided wonderful bonding force.Properties such as density,compressive strength,thermal conductivity and microstructure of the specimens were determined.It is found that TEOS improved the distribution of ACP and increased the compressive strength of the specimens.HGM bonded by appropriate amount of ACP and TEOS achieved preferable value of density,compressive strength and thermal conductivity which were significant for thermal insulation materials.The compressive strength of specimens sintered at 450 oC and 650 oC was higher than that of the specimens sintered at 250 oC.Preferable values of compressive strength(9MPa),density(0.44g/cm3)and coefficient of thermal conductivity(0.062W/(m·K))were obtained when specimens with 0.3 weight ratio of ACP and 0.15 weight ratio of TEOS were sintered at 450 oC.