Calcium silicate is a porous material as same as diatomaceous used as filter aid. The filter aid property of calcium silicate was investigated.
The results were as follows :
(1) Calcium silicate was composed of large secondary particle above 1 um diameter and the porous cavity was composed of rough surface.
(2) Blain specific surface area related to the shape of primary particle of calcium silicate rather than the particle size distribution by light transmission method. Its value decreased rapidly with the crystal growth of tobermorite from CSH. The porosity also decreased with the crystal growth of tobermolite.
(3) Average specific filtration resistance of cake was strongly influenced by Blain specific surface area rather than the porosity. The filtration resistance of cake decreased with thecrystal growth of calcium silicate as the result of the decrease of Blain specific surface area. It was also important for the low resistance of filtration to increase the porosity of product and to depress the formation of hydrogarnet.

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In order to obtain fundamental data on practical manufacture of alinite rich clinker, the burning conditions and characteristics were investigated. Alinite steadily forms at somewhat higher temperature than that of previous papers, 1200-1300°C. Minor elements influence formation of alinite and burnability of raw meal. Especially, influences of alkali and chlorine are large. Suitable amount of calcium chloride as mineralizer's effect reduces with the increase of burning temperature. The clinker burnt at suitable condition is porous and contains small size belite like football and alinite of 5 to 30, um in size. Contents of Al₂O₃ and Fe₂O₃ in alinite become more and less, respectively, as burning temperature increases.

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The mixture of burnt ashes and asbestos was sintered in the temperature range from 900 to 1200°C in air. The fracture surfaces of sintered bodies obtained were observed with a scanning electron microscope to clarlify the structural features of them. Also, the phases formed during liquid phase sintering were characterized by X-ray diffractometry and EDX analysis. Resultantly, it was shown that gehlenite (2CaO·Al₂O₃·SiO₂), akermanite (2CaO·MgO·SiO₂), and a material consisting of Si, Ca, P, and S were formed by the reaction of burnt ashes with asbestos during sintering. The growth of the gehlenite/akermanite grains was expressed in the equation of Dⁿ-Doⁿ =Kt (n = 4-5) in which the rate determining step was the diffusion of ions in liquid phase. The activation energy of the grain growth was 387 kJ·mol^-1, which was compared with that in diffusion of intermediate and network former ions in glasses.

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Preparation of the porous ceramics from the mixtures of natural zeolite including clinoptilolite and allophane composed mainly of amorphous alumina silica gel has been studied. The mixtures were pressed at 12.25 MPa and fired at a temperature between 1000°C and 1150°C for 40 min. The properties of the obtained porous ceramics are as follows :
They had very few cracks. The shrinkage increased with an increase in the firing temperature, and decreased with an increase in the amount of allophane. The coefficient of water absorption was from 12.8% to 26.9% (1000°C to 1150°C, R =85 (Natural zeolite 85 wt%/Allophane 15 wt%)). The porous ceramic prepared at the temperature of 1150°C had the highest bending strength of 20.97 MPa and the surface hardness of 45 at R =85. In addition, the specific surface area was 0.15 m²g^-1 at R =85, the total cumulative volume was 185 mm₃g^-1 and the average pore radius was 0.473 nm at R=85.
The results indicated that the porous ceramics are expected to use as materials for molds, building such as water permeability plate or water-holding plate, and filters.

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Room temperature grinding of a mixture composed of calcium hydroxide and silica-gel with different water contents was conducted in a planetary ball mill. Afwillite, Ca₃ (SiO₃ (OH)) ₂2H₂O, is synthesized by controlling water content of 23-30% by 2-hour grinding. The 2-hour grinding of the mixture containing more than 38% of water enables us to synthesize mechanochemically other different types of calcium silicate hydrates. Thermal behavior of the ground mixture containing afwillite is quite stable till around 1000 K. The mixture decomposes at around 1100 K, forming wollastonite, Ca₃ (Si₃O₉), while those ground for less than 90 minutes are changed into ε-wollastonite.

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