Study On Preparation Of Zirconia Heating Element By Gel-casting

Yttria-stabilized zirconia?YSZ?ceramics are widely used in the field of high-temperature conductive ceramics by virtue of ionic conductivity at high temperatures.The zirconia?ZrO₂?heating element with excellent properties was prepared by the gel-casting process.ZrO₂ power dispersion mechanism in the water was discussed by sedimentation test,Zeta potential analysis and slurry rheology.The influence of dispersant,pH value and volume content of solid pHase on slurry rheology were studied with ZrO₂powder as the main raw material.The acrylamide,N-N-methylenebisacrylamide,ammoniumpersulfate and N-N-N'-N'-tetramethylethylenediamine were used as monomer,crosslinker,initiator and catalysis separately,and the influence of their contents,temperature and time of curing on the gel-casting forming process of ZrO₂ceramic wereexplored.The effect of sintering temperature on the properties and microstructure of ZrO₂ ceramic wereinvestigated.The conductivity of ZrO₂ heating element was measured and compared with that of ZrO₂ heating element prepared by hot die-casting process.The main results areshownas follows:The dispersion of ammonium polyacrylate is the best in the dispersants of ammonium polyacrylate,sodium hexametapHospHate,polypropylene glycol and ammonium citrate.Zeta potential analysis shows that absolute potential value of the ZrO₂ solution can reach 40m V after adding dispersant ammonium polyacrylate,which is 10mV higherthan that of pure ZrO₂solution indicating that the dispersant can make the powder dispersed more evenly and stably.The ammonium polyacrylate is an anionic dispersant and its dispersion mechanism in water is an electrostatic steric stabilization mechanism.The rheological analysis of the slurry shows that when the amount of dispersant is 0.55wt%and pH=12,the volume fraction of ZrO₂ solid pHase can reach 54vol%and the slurry viscosity is 344mPa·s,which still can satisfy the requirement of casting.The solidification time of the slurry is controlled by varying the amount of catalyst,initiator,and temperature.When the temperature is 50?,the initiator is 0.7vol%,and the catalyst is 0.5vol%,the curing time is the most appropriate?within 30 min?.When the evacuation time is 15min,the density of the green body casted from 54vol%slurry is 4.01g/cm^-3,and the strength can reach 29.2MPa.By spraying PVP solution on the mold and the surface of the sample,the peeling pHenomenon is improved obviously.The green bodies of different solid content were dried and sintered and then their shrinkage,bulk density and bending strength were measured.The test results show that the higher the sintering temperature is,the greater the shrinkage rate of body is,the higher the density of the ZrO₂ ceramics is and the greater the strength of the ZrO₂ceramics is.When the content of solid pHase increased,the shrinkage rate decreased,the density become higher and the bending strength rise up.When the volume fraction of solid pHase is up to 54vol%and the sintering temperature is 1900°C,the ZrO₂body has a shrinkage rate of 18.1%,a density of 5.79g/cm^-3,and a bending strength of 898MPa.The conductivity of the ZrO₂ heating tube prepared by gel-casting process is 7.23s/m,which is 36.4%higher than that prepared by hot die-casting.