Ji Wei Fan

The Effects of Sintering Temperature on the Properties of Mg-Mn-Zn Ferrites

The present work shows the results of investigation on the effects of sintering temperatures of (Mg0.25Mn0.1Zn0.65)Fe2O4 ferrite on its sintered density, initial permeabilty, resistivity and microstructure. To achieve better sintered density and initial permeabilty, the sintering temperature should be ≥1200oC. However, the higher sintering temperature results in larger the grain size, which causes the reduction of the resistivities of Mg-Mn-Zn ferrites. Furthermore, the resistivities of samples are environmental temperature sensitive, and possibly possess the similar function of NTC thermistor over the testing range 25-225oC.

The Effects of SnO2 Doping on the Electrical Properties of ZnO Varistors

The SnO2 doping can increase the nonlinear coefficients of ZnO varistors, the highest α value is achieved at the 0.75 wt% doping level samples sintered at 1150oC. The improved I-V nonlinearity may be attributed to the donor behavior of Sn4+ ions. The SnO2 doping can enhance the ZnO grain growth that lower the breakdown field of doped samples.

The Electrical Properties and Impedance Analysis of ZnO Varistors Doped with Different Cu2O Contents

The Cu2O addition deteriorates the electrical properties of ZnO varistors, which is a good agreement with similar findings on Ag2O additions. The best fitted impedance analysis reveals that the Cu2O addition increases grain resistance and lowers the grain boundary resistance, results in low nonlinearity and higher leakage current of ZnO varistors.

Laser Glazed Color Surface on Whiteware

Traditional procedure of firing glaze is usually time consuming, energy costly and not environmental friendly. This paper reports the result of laser glazing on whiteware, and compares the glossiness and chromaticity of the glazed color surfaces by using a spectrophotometer. The cobalt blue and cobalt black color glaze surfaces are prepared by either traditional firing or laser glazing. Study shows that laser glazing is practicable, the resultant color glaze surface has better glossiness but the chromaticity is slightly weaker than that processed by traditional firing. The method of laser glazing is simple, can save energy, and worth to study further.

The Thermally Stimulated Current (TSC) Technique on Evaluating Degradation of ZnO Varistors

Thermally stimulated current (TSC) is a simple and effective test technique to study the thermal activated charge, electron trap and activation energy of dielectric and semiconducting materials. It is well known that the addition of glass frits can improve the degradation property of ZnO varistors. An activation energy of 0.45 eV has been found on the ZnO varistors with/without glass frits after the DC degradation by using TSC method. The tested quantity of thermal activated charges, QTSC, may represent the numbers of migrated zinc interstitials. ZnO visitors doped with glass frits have less QTSC. Experiment indicates that TSC test is a convenient method to evaluate the degradation behavior of ZnO varistors.

Laser Glazing of Peacock Blue Glaze on Porcelain

This paper presents the study of making peacock blue glaze surface by laser processing. The factors that may affect the quality of the glazed surface, especially the main laser processing parameters, were discussed. The structures and phase transitions of the glaze clad by laser were studied by X-ray diffraction, scanning electron microscopy and metallographic microscope. The color change and thermal stability of the glaze were tested. The results showed that the glazed surface clad by laser with a laser power of 25 W presented good visual characteristics. The color change of these glazed surfaces was inconspicuous with the increase in scanning speed. Several types of microcrystalline were also found in the glazed surface clad with a laser power of 25 W when the scanning speed was 10 mm/min. The glazed surface and the clay body were bonded tightly. The thermal stability of the glazed surfaces with good visual characteristics was also good.

Laser Processing Speed vs Morphology of Glazing Ceramics

Laser processing glazing ceramics is a new application of laser technique. This article presents the study of laser processing speed of glaze cladding. It found that the laser processing speed affected the morphology of glaze cladding significantly. Within the experimental conditions, rise of processing speed can decrease the depth of melted zone and the width of glaze cladding, vice versa.

The Effects of B2O3 Addition and Sintering Temperature on the Electrical Properties of SnO2 Based Varistors

SnO2 based varistor ceramics, as new type of varistor materials, have attracted increasing interest around the world. However, the effect of B2O3 addition on novel SnO2 based varistors is still unclear. In this paper the effects of B2O3 addition on the electrical properties and sintering temperature of the SnO2-Co2O3-Ta2O5 system were investigated. The experiments revealed that addition of trivalent boron can improve the densification of SnO2 based ceramics. The samples doped with 0.025mol% B2O3 had the highest sintering density. However between 0mol% to 0.1mol% B2O3 addition region there was little effect on non-linearity and breakdown field of SnO2-Co2O3-Ta2O5 system. Obviously, the sintering temperature had a predominant influence on the SnO2-Co2O3-Ta2O5 system; the samples sintered at 1400°C were superior to those sintered at 1350°C.

The Effect of Parameters of Laser Processing on the Morphology of Glaze Cladding

Laser processing ceramic materials is a new application of laser technique. This paper presents the study of laser processing parameters of glaze cladding. It found out that the parameters of laser processing affected the morphology of glaze cladding significantly. Within the experimental conditions, rise of output power or drop of processing speed can increase the depth of melted zone and the width of glaze cladding, vice versa.

The Effects of Cu Dopant on the Microstructure and Non-Ohmic Electrical Properties of ZnO Varistors

The doping effects of Cu on the microstructure and non-ohmic electrical properties of ZnO varistors were studied. Addition of Cu2O can enhance the ZnO grain growth during sintering. The SEM and EDS results revealed that the added Cu mainly distributed in the grain boundary and spinel phases of ZnO varistors. The Cu2O addition increased the both of grain and grain boundary resistances. However it decreased the non-ohmic electrical characteristics of ZnO varistors, which is a good agreement with similar findings on Ag2O additions, but contrasts to the reports of good non-ohmic electrical property which found on binary Cu doped ZnO varistors.