The hydration reaction of the following substances were examined from the quantitative viewpoint : P-CSA (free lime-C4AF-anhydrite type expansive additive), combination of P-CSA, C3A and gypsum, combination of P-CSA and alite. In the hydration reaction of P-CSA, free lime reacts abruptly with water in the initial stage to form calcium hydroxide, and later C4AF and anhydrite react gradually to form ettringite. In the hydration reaction of C3A-gypsum-P-CSA system, the reaction ratio of C3A was relatively small in the initial stage of hydration but rapidly increased during 3 to 7 days of reaction period. The reaction ratio of gypsum and anhydrite showed a high value i the initial stage. As a result, although the mole ratio of SO3/Al2O3 in the starting composition of the system showed a similar value to the theoretical value of monosulfate, the mole ratio of SO3/Al2O3 increased in the initial stage of reaction, and ettringite was formed. It is inferred that P-CSA realizes expansion by generating a large quantity of ettringite utilizing the reaction of C3A in cement, in combination with the reaction to generate calcium hydroxide from free lime in the expansive additive.
For the purpose of effective HCl gas removal from municipal solid waste incineration, a comparison was made for CaO and Na2CO3 sorbent for HCl sorption, in terms of HCl sorption capacity as well as HCl sorption rate. HCl gas sorption tests of CaO and Na2CO3 were conducted by using a flowtype tube reactor packed with fine particles under the particle diameters of 5 μm in the temperature range of 473-1073 K, at a total flow rate of 3×10-4 m3·min-1, of which the inlet gas mixture were HCl (1000 ppm) -N2. As the results, a maximum conversion value of 0.92 for HCl removal by CaO was obtained at 873 K. On the other hand a maximum conversion value of 0.87 was obtained for Na2 CO3 at 673 K. The rates of HCl sorption by CaO and Na2CO3 were explained by chemical reaction rate control under the present conditions. The pore of CaO was confirmed to disappear by sintering above the temperature of 973 K, which led to the reduction of HCl sorption capacity. A maximum HCl sorption capacity of Na2CO3 was obtained at 673 K, in which the crystal structure of Na2CO3 started to transform to Natrite. The reduction of HCl sorption capacity was attributable to the reduction of pore volume caused by the change in crystal structure.
Calcium phosphate films were deposited on stainless steel plate under various pH conditions of electrolytic solution of CaHPO4·2H2O by electrochemical procedure at room temperature. The pH at electrolyte dissolution was adjusted by nitric acid and the subsequent pH was adjusted by ammonium hydroxide. Calcium-deficient hydroxyapatite film a-DAp was deposited with pH 0.96 at the electrolyte dissolution and with pH 5.82 at the electrolysis initiation. The pH of the electrolytic solution was nearly constant from start to about 200 min and gradually decreased to about 3 after 400 min. The a-DAp had a feature of broccoli-like mass of which crystallinity was very low and the molar ratio Ca/P of 0.98. The low molar ratio was explained by substitution of H+ for Ca2+ during long time electrolysis in the bath of pH about 3.