Study On Surface Modification And Properties Of Piezoelectric Ceramics

Cement-based piezoelectric composites have excellent integration of good compatibility with concrete,fast response,high sensing precision and integrating sensing and driving.They are very suitable for monitoring damage,deformation and internal stress changes of concrete structures.However,in cement-based piezoelectric composites,the interface can not produce chemical action and relying only on physical adsorption or mechanical biting force when cement is combined with piezoelectric ceramics.the strength is low and its long-term durability can not be guaranteed.This paper is aimed at the difference in structure and performance between cement and piezoelectric ceramics.Therefore,this paper adopts chemical method to prepare silicon-calcium component products with similar cement composition on the surface of piezoelectric ceramics to enhance the compatibility of piezoelectric ceramic functional body and cement matrix.And then use this to prepare cement-based piezoelectric composites with good durability and excellent overall performance.It provides theoretical guidance and technical support for promoting long-term effective monitoring of civil engineering structures.In this paper,PZT-5 piezoelectric ceramics is used as a functional phase,which is cut into thin slices along the polarization direction and formed on the surface to improve the interface of cement-based piezoelectric composites.The silicate cement hydration products are mainly C-S-H gel and calcium hydroxide?mainly silicon and calcium?,thereby preparing SiO₂ film,silicon calcium film,silicon titanium film and silicon titanium calcium film reinforced piezoelectric ceramic functional body.The compatibility with the cement matrix is measured by the contact angle,piezoelectric properties and dielectric properties as the main performance test.The surface of the piezoelectric ceramic sheet is roughened by strong acid.The stronger the strong acid etching,the greater the roughness.Therefore,the roughness Ra is used to reflect the roughening effect.The experimental study was conducted to study the effect of HF concentration C_HF,etching time t,and HNO₃/HF mass ratio on roughness.The results show that the roughness Ra are proportional to C_HF and t,and HNO₃/HF has the greatest influence on Ra.The excessive amount of HNO₃ will seriously corrode the surface of piezoelectric ceramics and affects the properties of piezoelectric ceramics.The SEM images of the surface of the piezoelectric ceramics treated with different factors were analyzed,and the roughening process parameters of roughness Ra of 1.5?m,C_HF=10%,t=60s,and HNO₃/HF=0.5 were selected.The sol-gel method was used to prepare SiO₂ sol.The effects of ethanol,water,pH value,stirring time and stirring temperature on the gelation time,viscosity and refractive index of SiO₂ sol were studied.The design experiment uses different molding methods and drying methods to prepare SiO₂ film.The results show that the optimum conditions for the preparation of SiO₂ sol are:water to silicon ratio n_?H2O/TEOS?=3,alcohol to silicon ratio n_?EtOH/TEOS?=3,pH=2,stirring 2h,the stirring temperature is 45?;the SiO₂ film prepared on the surface of the piezoelectric ceramic by the film pulling machine and the natural drying method is better in hydrophilicity.The SiO₂ sol was modified by calcium nitrate and tetrabutyl titanate as calcium source and titanium source,respectively.The effects of molar ratio,reaction temperature,aging temperature,aging time and pH on the properties of SiO₂ doped sol and its membrane properties were studied.The effects of filming parameters such as layer number,pulling speed and immersion time on membrane properties were investigated.Add low-temperature sintering and silane coupling agent KH-570 to increase the film adhesion,and study the effect of KH-570 dosage and sintering temperature on the performance.The results show:?1?The optimal preparation conditions of calcium-modified SiO₂ sol are:molar ratio of calcium to silicon is 0.2,aging temperature is 30?,aging time is 24h,pH=2,and the adjustable range of calcium to silicon molar ratio is 0.1-0.2,the adjustable range of pH is1.2-2.5.The optimum coating conditions are:the number of layers is three layers,the pulling speed is 10mm/min,the first film immersion time is 5min.The optimum ratio of n_{?KH-570/TEOS?}is 0.02,and the sintering temperature is 160?.?2?The optimum conditions for preparing SiO₂/TiO₂ sol are:titanium to silicon ratio of0.3,reaction temperature of 30?,stirring time of 20 min,aging temperature of 35?,aging time of 24 h.The optimum process film conditions are as follows:the number of layers is three,the pulling speed is 30mm/min,the first film immersion time is 5min.The optimum ratio of n_{?KH-570/TEOS?}is 0.02,and the sintering temperature is 80?.?3?The process conditions of calcium-titanium co-modified SiO₂ sol are:titanium-silicon ratio is 0.3,calcium-silicon molar ratio is 0.2,reaction temperature is 30?,stirring time is 30 min,aging temperature is 30?,and aging time is 24 h.The optimal process film conditions are as follows:the number of layers is three layers,the pulling speed is 10mm/min,the first film immersion time is 5min.the optimum ratio of n_{?KH-570/TEOS?}is 0.02,and the sintering temperature was 160?.Various films were characterized and tested.The XRD test showed that the particle state of all the films was amorphous.The SEM test showed that the silicic calcium film cracked the most,and the addition of TiO₂ could significantly flatten.The EDS test indicates that all the layers have the required elemental materials.The IR tests show that the addition of calcium and titanium affects C-H vibration in the methyl group.The addition of titanium causes Si-O-Ti stretching vibration absorption peak at 950 cm^-1.The Ti-O-Ti stretching vibration absorption peak is generated at 470cm^-1,indicating that TiO₂ and SiO₂ form a separate phase,and some TiO₂-SiO₂ composite film is formed by chemical bonding.The addition of silane coupling agent KH-570 has little effect on the absorption peak.