Preparation, Characterization And Thermal Shock Resistance Of Spodumene Ceramics

The mechanical property and thermal property are the embodiments ofthermal shock resistance of ceramic materials which is the first criteria of hightechnology ceramic materials. Because of the special spiral-chain structure,stable structure and extremely low expansion coefficient, spodumeneceramics among ceramics materials with thermal shock resistance are widelyused in many areas such as kiln furniture, induction heating parts,microcrystalline ceramic panel with thermal resistance, high temperatureclamp, components of internal combustion engine and other electronic fieldwhich require stable size and high precision. Therefore, spodumene ceramicshave great potential in ceramics with thermal shock resistance.Using Al₂O₃,SiO₂and Li₂CO₃as raw materials as well as adding variousZrO₂, a series of spodumene ceramics were prepared with the sinteringtemperature scope for1325℃¹400℃by pressureless sintering method,which density, crystal phases and microstructure were characterized. Theresults show that both ZrO₂content and sintering temperature have importantimpact on the density of spodumene ceramics. Adding0-6wt%ZrO₂, densespodumene ceramics can be obtained at the sintering temperature for1325-1375℃, and porous spodumene ceramics with relative density of41.11%can be obtained at the sintering temperature for1400℃when adding4-6wt%ZrO₂. Therefore, the density or porosity in a wide range can becontrolled by the adjustment of the content of ZrO₂and sintering temperature.From the SEM images of sample’s microstructure, it is obvious that thesize of grains and porous is uniform, and the porous shape is round and all gasholes are interconnected. At the same sintering temperature, the more ZrO₂added, the higher the porosity, and the bending strength tends to reduce（except S2formulation）. For the same formulation, the porosity tends toincrease with increasing sintering temperature and the bending strength reduces greatly. The maximum of bending strength is up to6.38MPa and theminimum is45.16MPa. Compared to the larger change of relative density,bending strength change is not notable which is thought closely to be relatedto the reinforcement of ZrO₂.Using quenching-strength method as evaluating thermal shock resistanceof samples, the results shows that the microstructure change of samples afterthermal shock is not obvious and the phase composition of samples is stable,and any crack is not observed among grains, porous walls. The analysis ofresidual strength after thermal shock indicates that bending strength firstlyreduce and then rise as increasing thermal shock times for the samplessintered at1325℃, in which the maximum of residual bending strength is33.72MPa and the minimum is14.08MPa after10thermal shock times. Forsamples sintered at1350℃, bending strength of sample S1tends to rise withincreasing thermal shock times, which bending strength is even more than50Mpa after15thermal shock times, while that one of sample S4with a lesschange tend to reduce firstly and rises later, which residual bending strengthis up to16.62Mpa when the times of thermal shock reach15. For samplessintered at1375℃,residual bending strength of sample S2declines dramaticlywith increasing thermal shock times, and residual bending strength of sampleS4is close to initial strength after25thermal shock times. For the samples S3and S4with high porosity sintered at1400℃, the residual bending strength is16.72MPa and1.7MPa after25thermal cycles times, respectively.The formation mechanism of the high porosity is also investigated in thisstudy. It is believed that the increase of ZrO₂content and sinteringtemperature would lead to the great increase of the viscosity of the liquidphase produced during sintering process. The gas of CO₂obtained from thethermal decomposition of Li2CO3was restrained in the sample body and gasconstant expansion with the increase of sintering temperature caused theformation of a large number of round holes in samples. The discovery offers a new effective route for preparation of porous ceramics.