Densification processes of the bodies consisting of kaolin and feldspar were investigated kinematically by means of isothermal shrinkage measurement, and microstructurally by X-ray diffraction method and observation with polarization microscope and scanning electron microscope.
Results of thermal shrinkage measurement of the specimens showed three distinct shrinkages occurred at about 500°, 900° and 1100°C or higher temperatures. The shrinkage occurred at about 500°C seemed to be caused by the decomposition of kaolin minerals, so that the shrinkage decreased with the increase of feldspar content of the bodies. The shrinkage observed at about 900°C seemed to occur with diffusion sntering process of metakaolin grain boundary. Apparent activation energy of the shrinkage process was increased with the increase of the feldspar content. The increase might be caused by interruption of the grain boundary diffusion with the presence of feldspar particles incorporated into the bodies. The rate constant of the shrinkage process at 900°C decreased with the increase of the feldspar content. The decrese seemed to be interpreted by the decrease of metakaolin content in the bodies.
The shrinkage observed at about 1100°C might be associated with densification processes occurred by viscous flow of spinel type intermediate phase grains with small amount of the melt formed from a little impurities contained in the kaolin and feldspar fine particles. Apparent activation energy for the shrinkage process increased appreciably with the increase of feldspar content. The increase seemed to be caused by the increase of fusion products of the feldspar with rising temperature. The rate constant of the shrinkage process at 1060°C was increased with the increase of feldspar content. The increase seemed to be caused by the same reason mentioned just above.
It was inferred that the shrinkage occurred at higher temperatures than 1100°C was also caused by the viscous flow mechanism. The shrinkage diminished when most pores in the body were closed in the glassy matrix. When the bodies were fired at 1500°C, all bodies showed bloating, that is, the bodies became an over firing stage. Further, changes of the constituent minerals and microstructure of the bodies with the densification process were described.

抄録全体を表示

Inclusion free platy single crystals of α-SiC, 5-20mm in diameter are obtained by an improved sublimation method. Growth experiments are performed by transporting silicon vapour from molten silicon to the growth cavity at 2500°C for 10 to 15 hours. Results relating to the growth feature, crystal shape and polytype composition of those crystals are nearly the same as those by ordinal sublimation method.
Quality of those crystals, especially the electron mobility is not satisfactory yet. This is considered to be based upon the lack of purification of highly dense graphite used to construct the reaction system, and also upon the difficulty to evacuate inner atmosphere of the tightly closed system at elevated temperatures. Some proposal for further improvements of the new method are discussed.

抄録全体を表示

Hot-pressing experiments were carried out with high purity alumina in graphite dies at 1300°-1600°C under an applied pressure of 200kg/cm². Densification behaviors of the compacts were measured by a dilatometric method during the hot-pressing runs.
A new rate equation for hot-pressing was proposed based on a consideration of effective stress relating to porosity. The equation is expressed as follows:
d ρ/dt=ασ(1-ρ)e^4(1-ρ), and the integrated form f(ρ)=ασt+C
where α includes viscosity coefficient for the plastic flow mechanism or diffusion coefficient for the diffusion mechanism. ρ-f(ρ) relations were given in this paper.
The densification data were analyzed with Murray's, Rossi's, Fryer's, Shimohira's and the new rate equations. Fryer's and the new rate equations seemed to be more satisfactory to express the densification behaviors of the compacts. Several activation energies for the processes were obtained with these rate equations.

抄録全体を表示

The rate of cristobalite formation from a kaolinite saturated with some monovalent cations was studied comparing with the crystallization nature of some amorphous silica, i.e. precipitated-, thermally decomposed-silica gels, and powdered silica glass, to which 1-2 mol% of alkali carbonates had previously been added.
The results obtained are summarized as follows.
1) The adsorbed cations controlled the nucleation period of cristobalite formation and the Li ion was the most powerful accelerator for the nucleation.
2) The nature of crystallization from the silica gels resembled closely to that of the cristobalite formation from the kaolinite except that quartz phase appeared from Li containing-silica gels.
3) The crystallization from the kaolinite and the silica gels could be considered as homogeneous nucleation process by reason of the linear growth rate and of that the alkali ions would had been intimately distributed throughout the very fine amorphous silica particles.
4) The aspect of crystallization from the coarsely powdered silica glass differed quitely from those of the kaolinite and the silica gels, i.e. Li ion retarded the crystallization and the process could be considered as heterogeneous nucleation.

抄録全体を表示

In order to clarify the distribution of titania in the phases of the portland cement clinker, 0, 5, 10 and 15% of 3CaO⋅2TiO₂ were added to the model clinker which was composed of 35% of 3CaO⋅SiO₂, 35% of 3CaO⋅SiO₂, 15% of 3CaO⋅Al₂O₃ and 15% of 4CaO⋅Al₂O₃⋅Fe₂O₃ in weight, and the samples were heated between 1350° and 1500°C. They were then examined by means of X-ray diffraction analysis, microscopic observation and electoron probe microanalysis.
The following results were obtained;
1) Titania replaces a part of silica in 3CaO⋅SiO₂ and 2CaO⋅SiO₂ phases and also the liquid phase during heating, and the degree of replacement is independent of the concetration of Al₂O₃ and Fe₂O₃ in each phase.
2) The solubility limits of Al₂O₃, Fe₂O₃ and TiO₂ are approximately 1, 1 and 3% respectively in 3CaO⋅SiO₂ phase, and 2, 2 and 6% or more in 2CaO⋅SiO₂ phase.
3) As a result of replacement of SiO₂ by TiO₂, 3CaO⋅SiO₂ phase decreases while 2CaO⋅SiO₂ phase increases, due to insufficient CaO content when TiO₂ is added in the form of 3CaO⋅2TiO₂ to the clinker.
4) The grain size of 3CaO⋅SiO₂ phase increases by the addition of 3CaO⋅2TiO₂.
5) Especially in the liquid phase most of SiO₂ can be replaced by TiO₂.
6) Titania in the liquid phase concentrates on cooling in the light interstitial or ferrite phase rather than in the dark interstitial or aluminate phase.

抄録全体を表示

Powders of alumina ceramics and aluminagraphite composite were sinter-joined to graphite using a vibratory hot-press technique. This technique is essentially based on the conventional hot-press technique except the addition of vibration. Vibration was generated by the out-of-balanced motor and transmitted to powders through the bottom graphite punch. A sample assembly was heated by resistance heating of graphite mold. Strong bonding was achieved by adding vibration to the plastic and/or viscous powders at high temperature. 4 figs., 1 table 1 ref.

抄録全体を表示