The role of rheology on the shaping technology of ceramic materials has been investigated. It was found that the following classification is adequate to describe the rheological characteristics of relevant systems:
(I) the powder system is described as elastico-plastico-viscous solid,
(II) the slurry system, as elastico-plastico-viscous liquid, and
(III) the mud system, as elastico-plastico-viscous solid and liquid, having intermediate character between plastic solid and plastic liquid.
The extended Ostwald flow pattern was studied over a very wide range of shearing rate, in slurry stage. In order to describe a compaction character in powder stage, relaxation properties were studied. And, in mud stage, de-airing process was analysed on the standpoint of rheological phenomenon.

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Experimental studies by the author and his co?workers on rheological properties of disperse systems were reviewed. These investigations were carried out from the standpoint of comparison with the rheological properties of polymeric liquids such as polymer solutions and melts. Samples investigated are many kinds of disperse systems employing some Newtonian and non-Newtonian liquids as disperse media.
Some rheological peculiarities of the disperse system have been found. In the present review, following problems were discussed. One is a characteristic relaxation mechanism at the time scale longer than the maximum relaxation time of the medium, that is, a long-time relaxation process, and the other is the nonlinear viscoelasticity. They were discussed in relation to the degree of aggregation of dispersing particles and to the diffusional motion of the aggregate. The theoretical relationships by Sadron and Brenner for the rotational diffusion coefficients of the ellipsoid of revolution were applied to low-angle light scattering data for the aggregate particles. Then the characteristic relaxation time of the long-time relaxation process and the rotational relaxation time of an aggregate were related to the degree of aggregation. In the nonlinear region, the characteristic relaxation time was independent of the dynamic strain amplitude. These experimental results strongly suggest that the aggregate of dispersing particles behaves individually as a relaxation or a flow unit having a characteristic relaxation time.

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By using a tensile testing instrument (Shinko Tsushin, TOM 30-J), stress relaxation and stress-strain curves were measured of longitudinal and circumferential strips excised from various portions along the aorta in normal and WHHL rabbits aged from 8 to 30 months. The WHHL rabbit is an inbred strain developed from a mutant with inherited hyperlipidemia. Atherosclerotic changes with gross intimal thickening, sclerosis and atheromatous plaques increased progressively with advancing age.
There existed region and direction-dependent differences in the degree of stress relaxation in the normal aortas. In general, the degree of stress relaxation for longitudinal strips was lower than that for circumferential ones in each aortic portion and did not show any significant regional variation. The degree of stress relaxation of the circumferential strips was similar in the ascending and thoracic aortas but large in the abdominal aorta. In the atherosclerotic aorta, the stress relaxation was large in the thoracic and abdominal aortas compared with the normal aortas, and the difference in the former was larger than that in the latter. This indicates the mechanical effect of atherosclerotic changes which occurred in the intima.
Tension?strain curves were concave toward the tension-axis, indicating a decrease in wall distensibility with increasing strain. The slope of the curve progressively increased with age for all the samples from WHHL rabbits. Furthermore, a positive relationship was obtained between wall thickness and age with the correlation coefficients of 0.66 for the thoracic portion and 0.44 for the abdominal portion. Elastic modulus calculated from the stress?strain curves of the atherosclerotic aortas did not exhibit any distinct age?related changes in the young age group but became higher in the old age group. As a result, the decreased distensibility of the atherosclerotic wall may be attributed mainly to an increase in wall thickness caused by the intimal thickening. In advanced atherosclerotic aortas, wall stiffness explained by an increase in elastic modulus may be an additional factor of the increased wall distensibility.

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