This paper was made to investigate synthesis of hexagonal plate like calcium hydroxide by suspending gypsum dihydrate in potassium hydroxide solution. The calcium hydroxide was synthesized easily by suspending gypsum dihydrate in potassium hydroxide solution. The product was characterized by means of X-ray diffraction, thermal analysis (TG-DTA) and scanning electron microscopy. The single phase of calcium hydroxide was obtained above OH/Ca molar ratio of 2.6. The reaction time which was obtained single phase of calcium hydroxide from gypsum dihydrate was approximately 15 minutes. The shape of calcium hydroxide was hexagonal plate. This particle size of calcium hydroxide was controllable by OH/Ca molar ratio in the range of 0.5-5μm. The formation of calcium hydroxide was hardly influenced by suspension concentration.
ZrW208/NiWO4 composite ceramics with controlled coefficient of thermal expansion were fabricated by a spark plasma sintering (SPS) method combined with a solgel process. The NiWO4 powder having positive thermal expansion was prepared by using a sol-gel process with tungsten (VI) chloride and nickel nitrate 6-hydrate as raw materials and ethanol and 2-butyl alcohol as solvents. A ZrW2O8 powder having negative thermal expansion was also prepared by using a sol-gel process with tungsten (VI) chloride and zirconium chloride oxide 8-hydrate as raw materials and ethanol and 2-butyl alcohol as solvents. ZrW2O8/NiWO4 composite ceramics without impurity phases were synthesized at 600t in Ar atmosphere. The thermal expansion coefficient of the ceramics could be controlled in the range from 8.95 × 10-6 to-9.15 × 10-6 [K -1] by changing the compositional ratio of ZrW2O8 and NiWO4.
The metastability of CaSO4·2H2O in 24.63-49.93 (P2O5%) H3PO4 solutions was studied by a wet DTA method. On the basis of the measured values of reaction temperature and induction period for dehydration of CaSO4·2H2O, the relation between H3PO4 concentration Z (P2O5%) and upper limit temperature Y (°C) for metastability of CaSO4· 2H2O in the case of 1 minute induction period for dehydration was given as follows : Y=-4.314e0.04601Z+112.4 From above results, it was confirmed that the metastable zone for CaSO4·2H2O in H3PO4 aqueous solution existed in the wide range of higher temperature than those reported by Nordengren, Zdanovskii and Murakami on metastable equilibrium for CaSO4·2H2O = α-CaSO4·1/2H2O in H3PO4 aqueous solution.
To develop highly efficient hydrated lime for the treatment of flue gas from the municipal waste incineration plants, the authors employed the hydrated lime production process in which water was used for slaking quicklime. Then, we prepared the hydrated lime by slaking quicklime with water of 0.65 to 10 times the mass of quicklime and investigated the relation between pore structure characteristics and dry SO2 adsorption capacity. The mass ratio of water to quicklime was termed SWR (slaking water ratio). From the results, the hydrated lime obtained by slaking with SWR = 0.9 possessed the highest pore volume and SO2 adsorptivity. The hydrated lime prepared by slaking with SWR lesser or larger than 0.9 showed lower pore volume and SO2 adsorptivity. Based on the average crystallite size of the hydrated lime calculated from the half-width of characteristic XRD peak, it was found that the crystallite size increased with SWR and that the pore volume increased with the crystallite size and reached a maximum at 35 nm and then decreased with the increase in crystallite size. To explain this finding, the pore volume was estimated by a simple model using the crystallite size obtained. As the result, it was found that the calculated pore volume was in good agreement with the pore volume measured by N2 adsorption/desorption method.