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Transport properties of Ca2NaMg2V3O12 garnet
Get PDFThe results from dc conductivity and thermopower measurements on Ca2NaMg2V3012 single crystals are reported. The charge transport is shown to occur via tnermally activated hopping of electrons situated at V4+ tetrahedral sites. The importance of correlation effects at higher concentrations is emphasized
Sol gel synthesis for preparation of yttrium aluminium garnet
No full textSol-gel—synthesis for preparation of pure yttrium aluminium garnet powder with small grain size is subject of this ongoing study. Starting materials were sulfates and chlorides of yttrium and aluminium. To obtain pure YAG (Y3A1SO1Z) pH during hydrolysis as well as temperature during calcination and conversion into YAG must be carefully chosen. Presence of water has an adverse effect on the degree of agglomeration. To avoid this the influence of dispersion liquids was studied and this led to optimized conditions for precipitation. Sintering behaviour is discussed
Reaction engineering parameters of the carbothermal production of beta'-sialon from kaolin
No full textThe grain model has shown to be an appropriate reaction engineering model for the carbothermal production of beta-sialon from kaolin when pelletized mixtures of kaolin and coal are used as starting materials. When pellet size is below 1 mm in diameter (spherical pellets) pore diffusion can be
neglected and the overall rate is controlled by the chemical reaction rate. Above this size, pore diffusion shows a significant influence. This holds for reaction temperatures of 1400°C. The apparent activation energy is about 400 kJ/mole.
When the CO partial pressure is kept below 0.05 atm., at 1400°C relatively simple reactor design calculations can be used. Under these conditions the formation of beta-sialon can be treated as an elementary reaction. In general at least two steps of the complex reaction scheme are rate determining. This means that in order to achieve a reliable model, these steps should be distinguished. Experimental procedures should be developed to enable elucidation and separate modelling of these steps
Gas pressure sintering of alpha'-sialon ceramics
No full textAlfa-sialon ceramic densified via a gas pressure sintering process is an attractive subject at present. A gas pressure sintering process with three steps specially for the information and densification of alfa-sialon ceramics has been optimized. This investigation indicates the improvement of the characteristics of alfa-sialon (also including alfa + beta-sialon composite) ceramics by use of a gas pressure sintering process involving the formation of a transient liquid phase
Gas pressure sintering of alpha'-sialon ceramics
No full textAlfa-sialon ceramic densified via a gas pressure sintering process is an attractive subject at present. A gas pressure sintering process with three steps specially for the information and densification of alfa-sialon ceramics has been optimized. This investigation indicates the improvement of the characteristics of alfa-sialon (also including alfa + beta-sialon composite) ceramics by use of a gas pressure sintering process involving the formation of a transient liquid phase
Sol gel synthesis for preparation of yttrium aluminium garnet
No full textSol-gel—synthesis for preparation of pure yttrium aluminium garnet powder with small grain size is subject of this ongoing study. Starting materials were sulfates and chlorides of yttrium and aluminium. To obtain pure YAG (Y3A1SO1Z) pH during hydrolysis as well as temperature during calcination and conversion into YAG must be carefully chosen. Presence of water has an adverse effect on the degree of agglomeration. To avoid this the influence of dispersion liquids was studied and this led to optimized conditions for precipitation. Sintering behaviour is discussed
The alteration of the grain boundary structure in YAG ceramics due to annealing
No full textAnnealing conventionally sintered YAG for a long time at high temperature (350 K below Tsinser) results in a marked increase of the grain boundary thickness. Impedance measurements showed that the grain boundary conductivity in annealed samples is a function of the oxygen pressure
The alteration of the grain boundary structure in YAG ceramics due to annealing
No full textAnnealing conventionally sintered YAG for a long time at high temperature (350 K below Tsinser) results in a marked increase of the grain boundary thickness. Impedance measurements showed that the grain boundary conductivity in annealed samples is a function of the oxygen pressure
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