CaCO₃ powder was reacted with 2 mol% lactic acid and heated at 300°C to prepare the CaCO₃ particles with porous surface layer. The specific surface area of the CaCO₃ powder thus prepared was 1.8 times higher than that of the untreated powder. The hydrophilic property of the powder of particles with porous surface layer was improved due to its high surface area. The powder was homogeneously dispersed in water because of its hydrophilic property. Then the apparent viscosity of aqueous slurry of the CaCO₃ powder decreased by a factor of 10, compared with that of untreated CaCO₃ powder.

View full abstract

Amorphous calcium phosphate (Ca₃ (PO₄) ₂·nH₂O, ACP) with nanoparticles is known as a metastable precursor of various wet process calcium phosphate salts. It is necessary to take ACP from the liquid phase in a wet process as quickly as possible. However, under present technical conditions, synthesis of ACP is only possible by a wet process that presents difficulties for mass production. On the other hand, mechanochemical treatment is very effective for industrial mass production. Mechanochemical synthesis of ACP was tested by adjusting the mixtures of Ca (OH) ₂ and NH₄H₂PO₄ to Ca/P atomic ratios of 1.00-2.00, and ground for 0-2 h. X-ray intensity of the ground mixture was decreased by grinding at each Ca/P atomic ratio; and it was changed to ACP by grinding for 1 h. The result of TG-DTA analysis showed that the exothermic peak was observed, at an indicated ACP, at about 670°C. Also, the internal structure of the obtained ground substance was an amorphous layer to 35 nm depth from particle surface (75 vol%), Ca (OH) ₂ and CaHPO₄·2H₂O (DCPD) mixture layer to 50 nm depth from particle center (15 vol%), and intercalation was DCPD layer of thickness 10 nm (10 vol%).

View full abstract

Calcium sulfate is often used as a raw material for Autoclaved Aerated Concrete (AAC) to improve several properties. Microstructure and carbonation resistance of gypsum (CaSO4·2H₂O) added AAC were investigated. Anhydrite (CaSO₄) and hemihydrate (CaSO₄·0.5H₂O) recrystallized after autoclaving and filled the finer pores, while the total pore volume was unchanged. Fractal dimension obtained from the water vapor sorption isotherms data increased and Knudsen diffusion coefficient of carbon dioxide gas decreased with the increase of the gypsum content. Carbonation resistance was improved with increase in the gypsum content from 0 to 15 mass%. The mechanism of the increase of the carbonation resistance of the gypsum-added AAC is attributed to the decrease of the Knudsen diffusion coefficient associated with an increase in the fractal dimension of the liquid and gas interface.

View full abstract

The synthesis of the potassium magnesium phosphates was studied by the oxidative decomposition method using EDTA-metal chelate. As a result, three potassium magnesium phosphates were successfully synthesized. These compounds are KMg₇ (PO₄) ₅·12H₂O (described as KM7P5H12), K₉Mg₁₀ (PO₄) ₉ (OH) ₂·8H₂O (K9M10P9H8) and KMg₄ (PO₄) ₃·7H₂O (KM4P3H7).
These potassium magnesium phosphates were prepared under several conditions as follows : concentrations of K⁺ ion, Mg²⁺ ion, phosphate ion and H₂O₂, and initial pH. KM7P5H12 were prepared under the conditions of the Mg²⁺ /P (P : phosphoric oxyacid) molar ratio (described as R value) = 1.0 and low concentration of K⁺ ion and H₂O₂. K9M10P9H8 was prepared under the conditions of R value = 0.1 and the high pH reagion. KM4P3H7 was prepared under the conditions of R value = 0.2 and low concentration of H₂O₂.
Three potassium magnesium phosphates did not change by aging them in KCl solution at 98°C, but KM7P5H12 and KM4P3H7 changed to K9M10P9H8 by aging them in K₂HPO₄ solution at 98°C. The relationship of phases equilibilium between three potassium magnesium phosphates was revealed.

View full abstract