Tsang-Tse Fang

Evolution of the formation of barium titanate in the citrate process: the effect of the pH and the molar ratio of barium ion and citric acid

In this investigation, several experiments were conducted to study the effects of the molar ratio of barium ion and citric acid and the pH value on the formation of BaTiO3 by the citrate process. It was found that the molar ratio of barium ion and citric acid and the pH value could affect the chelation of carboxylate groups and Ba/Ti ions at temperatures below 450 °C but they seemed not to influence the formation of BaTiO3. The development of an oxycarbonate intermediate during the thermal decomposition of (Ba,Ti) gel was confirmed, which was suggested to possess a structure of BaTiO3, whereby CO−23 was located inside the layer structure.

The effect of the molar ratio of cations and citric acid on the synthesis of barium ferrite using a citrate process

A model is presented to evaluate the concentration of species in a citric solution for preparing barium ferrite powder. The evaluated concentration of species provides valuable information and help in selecting the optimal condition for preparation of the barium ferrite powder using the citrate process. The influence of the molar ratio of cations and citric acid on the formation of barium ferrite is studied. The formation temperature of barium ferrite decreases as the ratio increases. When the molar ratio of cations and citric acid is 13∶20, the barium ferrite can completely form at 700 °C.

Effects of milling and particle size distribution on the sintering behavior and the evolution of the microstructure in sintering powder compacts

Abstract In this investigation, it was observed that the contamination arising from the milling medium has a great influence on the sintering behavior. The densification rate of the powder milled with ZrO2 balls is largely inhibited, and the activation energy of ZrO2-doped alumina is significantly enhanced. The possible reasons for the enhancement of the activation energy were discussed. The effects of particle size distribution of powder compacts on the microstructural evolution of alumina during sintering were proposed and discussed.

Forming processes of strontium barium niobate ceramics

In forming strontium barium niobate (SBN) ceramics, two methods (pressure filtration and slip casting) were employed to investigate the consolidation behaviour. The zeta potentials were measured to understand the interparticle forces of SBN powders. It was found that the zeta potentials of SBN powders were negative above pH 2.2. Several experiments have been conducted to investigate the effect of pH on the rheological behaviour of SBN slurries with 20 vol% solids loading. The rheological behaviour of the slurries SBN with 20 vol% solids loading at pH 11.5 is shear thinning. It is suggested that the increase of the flow rate of the fluid might have the advantages to enhance the packing density and prevent fine particles from clogging in pressure filtration and slip casting. Two different moulds i.e. plaster and alumina have been used to investigate the effect of pore morphology of the moulds on the cake microstructures. A uniform microstructure of cast cake was formed for using an alumina mould and significant contamination was observed in using a plaster mould.

The role of dopants on the formation and defect structures of the M-type of calcium ferrite

The formation mechanisms of M-type calcium ferrite were further assessed by doping Y2O3, BaCO3 and SrCO3. It was found that the ionic radius, rather than the valence is the predominant factor in the formation of the magnetoplumbite phase of calcium ferrite. The CaO/sd2Fe2O3 phase which played a precursor role in the formation of the M-type calcium ferrite was further verified. The defect structures based on the substitution of Ca2+ by La3+, the charge compensation by Fe2+, and release of oxygen were supported by DTA-TGA and conductivity data. The conductivity was assumed to, occur through a hopping mechanism as it increased with increasing temperature. The estimated values of the activation energy based on the small-polaron conduction were 0.35 to 0.40 eV in the high temperature region and 0.027 to 0.054 eV in the low temperature region. Moreover, the preexponential factor in the conductivity equation is an exponential function of the fraction of the M phase in the specimen.