Study On Exfoliation Of Expanded Vermiculite And Its Dispersion In Organic Solvent

With the development improvement of industry in our country and equipment in high working temperature,the requirement of temperature resistance of sealing material in industrial devices become more and more strict.As a kind of layered silicate mineral,vermiculite can be used to prepare high temperature sealing gasket with excellent expansion performance and oxidation resistance.In order to obtain vermiculite based spiral wound gasket tape with smooth surface and soft texture,the tape casting method was introduced.The preparation of vermiculite slurry with suitable particle size and stable dispersion performance is the key for tape casting.Therefore,the preparation of expanded vermiculite and its peeling process is investigated using Xinjiang Yuli vermiculite with particle size of 1.4-4mm.In addition,the dispersion property of exfoliated vermiculite powder in alcohol system has been studied,and the method and theory of dealing raw vermiculite has obtained for the casting of vermiculite based sealing materials.The conclusions are as follows:(1)The expansion experiments of vermiculite were carried out by high temperature method,chemical method and composite method.The results show that the expansion ratio of vermiculite is 9 at 800?for 2 minutes.When the temperature of water bath is 80?,the time is 40 minutes,the concentration of hydrogen peroxide is 30%,and the liquid-solid ratio is 2:1,expansion ratio of vermiculite is 14.3 The vermiculite treated by hydrogen peroxide water bath was treated at high temperature.The expansion ratio of vermiculite was 37 at 500?for 3 minutes.The thickness and edge coking of TEV and HEV were observed under optical microscope,which showed that the thermal treatment was a heating process from the outside to the inside,and the distance between HEV sheets was large and well expanded.The thin and light color of CEV sheets showed that the structure of vermiculite was not obvious Change.(2)The expanded vermiculite was peeled by ball milling and high-speed shearing.The particle size D₅₀ of TEV,CEV and HEV samples were decreased with the increase of ball milling time and grinding speed.When the milling time is 4h,the rotating speed is 200r/min,and the concentration is 30%,the particle size D50 of the TEV,CEV and HEV is 8.746?m,7.632?m and 10.84?m,respectively.When the shearing time is 2h,the rotating speed is 2500r/min,and the concentration was 20%,the particle size D50 of the TEV,CEV and HEV is 72.07?m,116.4?m and 50.08?m respectively.XRD analysis shows that the diffraction peak of Vermiculite-phlogopite in the high-temperature expanded powder was disappeared and changed into phlogopite component.The structure of chemical expanded vermiculite is basically unchanged,and the interlayer of vermiculite was partly changes into phlogopite component in the composite expanded vermiculite.SEM analysis shows that the surface of chemical expanded vermiculite flake is flat and clean,and the surface of TEV and HEV flake is flat with small peeling particles.(3)The surface of vermiculite powder was modified by stearic acid(SA)and silane coupling agent(A151).The results show that the contact angle of CEV powder is lower than that of TEV and HEV powder with no modifer.The modification effect of SA is better than that of A151.The SA was adsorbed on the TEV and HEV powder by physical coating,while adsorbed on the surface of CEV powder by forming ester bond coating with the reaction of-COOH in the SA structure and-OH on the surface of vermiculite.The results of sedimentation analysis show that the surface modification can improve the dispersion stability of the powder.The RSH of TEV and HEV powder with the 2%SA can reach to 91.8%and 91.29%respectively,and the CEV powder RSH is 90.14%with 1.5%SA.(4)The dispersion behavior of peeled vermiculite powder was studied by using castor oil(CTO),Tributyl phosphate(TBP)and glycerol trioleate(GTO)as dispersants.The results of sedimentation test show that TBP can improve the dispersion performance of TEV,CEV and HEV powder.The dispersion of the powder was achieved by the adsorption of TBP in the ethanol solvent system by forming a weak electrostatic repulsion between particles.The excessive dispersant will reduce the dispersion performance of the powder.The best dispersant dosage of TEV,CEV and HEV powder is 1%,1.5%and 0.5%with the RSH of slurry is 79.3%,78.8%and90%respectively.