Chen Shoutian

Influence of Rare Earths on Electric Properties and Microstructure of Barium Titanate Ceramics

Abstract The influence of rare earths on electrical resistivity and microstructure of barium titanate ceramics doped with rare earth ions Y, Dy, Ho, Er and Y at the concentrations of x = 0.001 × 0.01 was investigated by the means of X-ray diffraction, scanning electron microscopy and electric properties testing. The results showed that a dramatic decrease in resistivity occurred at the concentration of 0.3% of La-doped sample. However, the range of concentration for semiconducting samples doped with Dy, Ho, Er and Y was wider, especially for Y-doping. The experimental results indicated that below the critical concentration of Dy, Ho, Er and Y, the substitution took place in the barium sublattice with electronic compensation, above the critical concentration, gradually the rare earth ions began to substitute for titanium. As for Hodoped BaTiO 3 ceramic, the resistivity jump (PTCR effect) near the Curie temperature was the highest in case of lower dopant concentration of 0.3%. Fine-grained structure of sample doped with 0.6% Dy led to the increasing of breakdown electric field strength and dielectric constant of ceramic samples. In contrast, coarsed-grained structure of sample doped with 0.3% Dy showed semiconducting property.

Study on properties of polymers packed by aragonite whisker

Hard PVC and PP were filled by lightweight CaCO/sub 3/ and aragonite whisker respectively. The influences of sort, quantity and surface treatment of fillers on properties of packed polymers were investigated. According to the results, it was found that whisker was much better than calcium carbonate as filler. Firstly, it can improve the manufacturing property of composites. When whisker was selected, the torque in manufacturing procedure was much low. Secondly, whisker can improve the mechanical properties. The tensile strength and impact strength were much high when whisker was chosen as filler. After treating the whisker by suitable coupling agents, the properties of the composites can be improved further more. It was because whisker can arrange in the polymer matrix rapidly and endow excellent strength and toughness to the polymer matrix composites.

Distribution regularity of breakdown field strength of high voltage ceramic capacitor

Electrical breakdown tests on high voltage ceramic capacitors, whose ceramic disks were in two kind of geometry, were carried out under various rates of voltage rise. It was shown that the breakdown field strength of samples in the same form displayed a Weibull distribution for the same rate of voltage rise. With increasing rate, the slope and character strength of the Weibull line improved in the flat samples, but was unchanged in concave samples. In the mean time, the mechanical strength of the ceramic material used in the capacitor was examined and obeyed the Weibull distribution. The Weibull line slope of mechanical strength was nearly same as that of the breakdown strength of concave samples. We concluded that the alternative breakdown of high permittivity ceramic happens when the degree of discharge at weak points exceeds some certain amount. The weak points are the voids and cracks contained in the ceramic, and the discharge at those weak points and electric-mechanical stress seem to be the main sources of electrical breakdown.

Preparation of aragonite by carbonation process

Aragonite calcium carbonate was synthesized by carbonation process, and MgCl/sub 2/ was selected as inhibitor of calcite phase. The effects of concentration of MgCl/sub 2/, pH value of initial suspension, reaction temperature and stirring rate on calcium carbonate polymorphs were investigated. The result indicated that the aragonite phase can be formed at the condition of pH/spl sim/9, above 60/spl deg/C and suitable concentration. The crystal has high aspect ratios ranging from 10 to 40, and can be modified by changing the conditions of reaction.

Different nonlinear conduction mechanism between /spl alpha/-SiC and /spl beta/-SiC

The nonlinear electrical conductivity of /spl beta/-SiC and /spl alpha/-SiC was investigated. /spl beta/-SiC has an excellent nonlinear electrical conductivity when the particle size varies from 14/spl sim/21 /spl mu/m. Compared with /spl alpha/-SiC, the parallel particle size /spl beta/-SiC micro-powder has lower resistance and greater nonlinear electrical conduction coefficient which is marked by /spl beta/. The difference of electrical conductivity between /spl beta/-SiC and /spl alpha/-SiC is interpreted from the crystal structure and shape. It is shown that the cubic crystal structure /spl beta/-SiC has smaller contact area than hexagonal /spl alpha/-SiC with induced higher contact potential barrier. Under high voltage, the electrical conduction mechanism of the tetrahedral parallel configuration /spl beta/-SiC crystal is more complex than the anti-parallel configuration /spl alpha/-SiC crystal.

Charge-discharge breakdown of dielectric ceramic

The breakdown behavior of high-voltage dielectric ceramics experiencing long-time charge and discharge cycles is not the same as its short-time breakdown behavior. In our study, it was found that there are about four types of breakdown and various factors such as test voltage, ceramic Curie temperature, epoxy encapsulation, and interface treatments affect the charge-discharge life. The charge-discharge breakdown of high-voltage ceramics is considered mainly a mechanical fatigue failure due to electrostriction, and a simple mathematical model was deduced from this idea.

The influence of the partial discharge on the electrical aging property of high voltage ceramic capacitor

In this paper, the property of the partial discharge, frequency and temperature dependence of dielectric property are tested in the electrical aging duration. It is shown that there are two kinds of partial discharge in high voltage ceramic capacitor. With the aging time increased, ones initial discharge voltage goes down continuously, and its dielectric spectrums have got changes obviously. The others initial voltage has a rise up to the aging voltage at first, then it goes down to a constant and its dielectric spectrums have few changes. On the base of above, the affection of the partial discharge to the electrical aging property of high voltage ceramic capacitor is concluded.

Dielectric materials based on superimposed effect

Abstract The dielectric properties and phase compositions of two kinds of SrTiO3-PbTiO3-Bi2O3. nTiO2-system ceramics, sintered with different Sr/Pb ratio, are investigated. The result shows that the ceramics, with inhomogeneous distribution of the two different systems, will present two-phase mixed structure. It will result in the superimposing effect in dielectric property as well as the double-hump characteristic in dielectric-temperature curve. Ceramic materials with high dielectric constant, low loss and low temperature variation rate can be obtained through regulating the Sr/Pb ratio within each system and the use level between two systems, and through controlling sintering temperature and the heat preservation time.

New anti-corona material for large-scale electric machine

The non-linear electrical conduction property of /spl beta/-SiC micro-powder/epoxy ester lacquer composite was investigated. The /spl beta/-SiC micro-powder was synthesized under different temperature and has different particle size. Experiment shows that the non-linear electrical conduction becomes greater by increasing the /spl beta/-SiC powder particle size or synthesizing temperature. Under the same particle size conditions, the non-linear electrical conduction coefficient /spl beta/ and corona voltage rising with the /spl beta/-SiC content increased. The /spl beta/-SiC micro-powder is used to regulate the non-linear electrical conduction property of /spl alpha/-SiC, showing that it is possible to replace /spl alpha/-SiC with /spl beta/-SiC for anti-corona material to increase greatly the anti-corona property.

Dielectric loss of BaTiO/sub 3/-based high voltage ceramic capacitor under high field strength

High voltage ceramic capacitors are widely used in high voltage power systems, because they have the merits of small volume, high voltage endurance and low aging. However, high dielectric loss will heat the capacitor under high field strength, and reduce the stability and reliability of capacity. In this paper, results for decreasing dielectric loss under high field strength was reported. It is shown that suitable recipes and technology can decrease dielectric loss and improve the reliability of high voltage ceramic capacitor under high field strength.