This paper investigated about synthesis and control of secondary particle size on hollow calcium carbonate, which was spherical aggregate of primary particle. The hollow calcium carbonate was synthesized by adsorbing calcium carbonate onto the octane droplet surface dispersed in calcium chloride solution. The sample was characterized by means of X-ray diffraction, scanning electron microscopy and infrared spectrometer. The calcium carbonate was adsorbed onto the octane droplet surface including palmitic acid. This adsorption was based on-COOCa bonding formed by reaction of calcium ion of calcium carbonate and carboxylato ion of palmitic acid, which existed to the octane droplet surface. The modification of calcium carbonate adsorbed on the octane droplet surface was calcite and the primary particle size was approximate 0.1-0.3 μm. Also, hollow calcium carbonate has cavity inside. Repeating number controlled the wall thickness of hollow calcium carbonate. In the case of repeating number of 5, its wall thickness was about 1.3 μm. The average particle size of hollow calcium carbonate was adjusted from 7 to 18 μm by changing concentration of octane. The pore volume was increased with increase of wall thickness of hollow calcium carbonate with spherical.
Synthesis of CaCN2 from CaO with NH3 and CO was investigated. CaCO3 was formed below 700°C but CaCO3 was not formed above 750°C. The optimum temperature for synthesis of CaCN2 was 700-730°C and the maximum yield was about 38 mol%. Reaction (1) was estimated from materials balance for CaCN2 synthesis at CO concentration lower than 50 mol% : CaO + 2NH3 + CO→ CaCN2 + 2H2O + H2 (1). Similarly, reaction (2) was estimated at higher CO concentrations : 5CaO + 10NH3 + 7CO →5CaCN2 + 2CO2 + 8H2O + 7H2 (2). Increasing the CO concentration, CO would react with formed H2O to form CO2 and H2, which result in eq. (2). NH3/CO ratio of the feed not so much affected the CaCN2 yield and the optimum ratio is about 1.0. The changes in W/F less affected the conversion of NH3 and CO. The CaCN2 yield increased below 40g·h· mol-1 and the yield extraporated to zero W/F reached to 70 mol%. The CaCN2 yield was independent of the average diameter of the CaO granules at 600°C.
Synthetic gyrolite and Z-phase were subjected to treatment with different amount of 0.1N-HCl at 25°C. The removal of interlayer calcium ions and shrinkage of basal spacing occur at the early stage of acid treatment, the basal spacing decreasing to 2.06 nm for synthetic gyrolite and 1.34 nm for Z-phase. For acid-treated products subjected to soak in water at 60°C for 20 h, recovery of basal spacing took place and it may be considered that calcium ions move from octahedral sheets, O and O into interlayer space through the network of tetrahedral sheets, S2 and S2 by the aids of water. Z-phase is slightly superior to synthetic gyrolite as for the stability against acid.
The quality of ceramics product is greatly affected by the mixed and dispersed state of materials. Mixture of hemihydrate gypsum and copper oxide was prepared by dry and wet process, and the cross section of its sintered body was observed to quantitatively evaluate the mixed state by using image analysis. The values of standard deviation of the area occupation ratio of dispersed particles (copper oxide) were measured from 10 independent observation of the four different size of area, which was expressed as (1/2) N·A, where N is the divided dimension and A is the area whose size was about 1000 times of primary particle diameter. The values of standard deviation for different size of areas were constant below the critical dimension (Nc), but those were significantly deviated at the range of N greater than the Nc. The definition of the degree of mixing is proposed in terms of this Nc, whose values are in the range of 0 to 10. Mixing speed can be evaluated quantitatively by using with this degree of mixing. The rate of wet process was 5.4 times faster than that of dry process.
In this paper, the increment of specific surface area of calcium hydroxide powder was experimentally discussed in case of applying carboxylic acid added 1-butanol (0.2 mol) to calcium hydroxide reaction. And the following results are obtained, (1) the specific surface area of calcium hydroxide powder increases by the interaction between alcohol and carboxylic acid, (2) it takes maximum at 0.01 of the amount of carboxylic acid.
A continuous hydrothermal reactor was designed to prepare Xonotlite. It consisted of two pumps, a long thin tube to decrease pressure, and 5 autoclaves for dissolution of silica and calcium hydroxide, formation of Xonotlite, separation of solid from solution, and sampling. Xonotlite fibers up to 7μm were continuously prepared from the starting solutions of silica and calcium hydroxide by hydrothermal reaction at 250°C. The formation time was estimated to be 25 minutes. Xonotltite was crystallized without formation of any solid intermediate compounds.