Study On The Preparation And Doping Sm₂O₃of Zno Varistor Ceramics

The purpose of the paper is to prepare high-voltage ZnO vairous ceramics. Firstly thedevelopment, application theory, fundamental characteristics and conduction mechanism ofZnO vairstor were stated. Then The inlfuence of ball-mixture medium, ball-mixture time,adhesive dosage, forming pressure, pressure-holding time and sinteirng temperature onproperties of ZnO vairstor ceramics were researched. And the doped process of ZnOVairstors were optimized, and the influence of doping Sm2〇3on the electrical properties andmicrostructure of ZnO vairstor ceramics were emphasized on. The microstructure of ZnOsample was analyzed by scanning electron microscopy and X-ray diffraction. Based on theArchimedes theorem, we could calculate the density of varistor ceramic and the electricalparameters of varistor ceramic could be measured by I-V characteristics test.l he expeirment results of ZnO vairstors ceramics indicate that the mixture of ethanoland polyvinyl alcohol should be used for milling medium duirng the ZnO vairstor millingprocess，but distilled water or ethanol should not be chosen. With the ball-mixture timeincreasing, the dispersion effect of Slurry becomes better and better. Adding agglomerantdosages can be beneficial for sample molding, the ultimate addition amount is10.02wt%.the density of sample will be accrescent with the increase of pressure，The limited pressureof sample is lOMPa; The length of pressing time make no different to the sample. Theoptimum sinteirng temperature of ZnO vairstor ceramics is1350。C，and the density ofsample is high.Meanwhile, the oxide of elements Pr,Co,Cr have an elfeet on electrical properties ofZnO vairstor ceramics. Finally, the optimum composition of ZnO vairstor ceramics whichsintered at1350°C for1hour is:95ZnO-lPr60"-2Co203-2Cr203(mol%)，whosecharacteirstic is the best, Vi1200V/mm, a=34; However, The varistor voltage is closeto the range limits, so that the95.5ZnO-1Pr60ii-2C02O3-1.5Cr203vairstor ceramics isthe best recommended value for the next expeirment, whose vairstor voltage and nonlinearcoeiffcient are is308V/mm and is21respectively. Doping contents of Srr^Cb impact microstructure and electrical properties of95.5ZnO-1Pr60j i-2C02O3-1.5Cr203varistor ceramics greatly. The result show that dopingS1TI2O3can promote liquid phase sinteirng of ZnO vairstor ceramics; and increases thevairstor voltage, the non-linear coefifcient and the density, the vairstor voltage andnonlinear coeiffcient increases and then decreases with the increasing of S1112O3contents，while the density become higher; when the amount of Sm2〇3increased to0.3mol%, theZnO vairstor achieved the best optimum electrical characteristics, the varistor voltagereach435V/mm and the nonlinear coeiffcient is35.