Calcite and aragonite are formed by homogeneous precipitation method utilized hydrolysis of urea. Calcite is formed by agitating the reaction solution, aragonite is formed by without agitating the reaction solution. But, the yield of them were about 40%. Then, the formation area with addition of hydrogen peroxide and glutamic acid were investigated. As a result, calcite and aragonite were obtained with more than 90% yield by adding a hydrogen peroxide. Vaterite was obtained with more than 90% yield by adding hydrogen peroxide and gultamate.
For materials design of the accelerator, it is important to analyze the hydration reaction of the accelerator. Accordingly, the effect of sodium aluminate, which is a typical component substance of the accelerator, on the initial hydration was investigated. The hydration reaction of amorphous calcium aluminate, which is a kind of calcium aluminate compounds, significantly depends on the addition of sodium aluminate. Sodium aluminate inhibited the hydration of amorphous calcium aluminate. This phenomenon was supposed that the sodium aluminate provide on the surface of amorphous calcium aluminate particles with aluminum hydroxide ion, which create gel hydration products. In addition, it was proven that increasing the calcium ion concentration could prevent hydration inhibition.
This paper discussed that influences of interstitial phase content or C3A content on the autogenous shrinkage of the cement paste of which interstitial phase content was more than of ordinary Portland cement. Cement clinkers were prepared by using industrial raw materials and chemical regents in the laboratory. Interstitial phase content of clinkers was changed in the range of about 18 to 30 mass %, and C3A content was changed in the range of about 4 to 15 mass%. Autogenous shrinkage, chemical shrinkage and hydration products were investigated. The autogenous shrinkage strain increased with increasing C3A content. When C3A content was more than 9 mass%, however, the autogenous shrinkage decreased with increasing C3A content. This phenomenon was corresponded to the change of autogenous shrinkage strain within 10 hours hydration. This shrinkage could not be explained only the amount of ettringite formation or the change of the microstructure. It seems that the clarification of this autogenous shrinkage needs the investigation including the effect of C-S-H.
Characteristics of alumina cement mortar containing colemanite or calcined colemanite are studied. Colemanite and calcined colemanite delay hardening of alumina cement mortar containing blast furnace slag powder (ACBB mortar). Calcined colemanite has stronger delaying effect because it elutes a significantly greater amount of boron as it contains a greater amount of boron and has a greater specific surface area than colemanite. ACBB exhibits practical strength at 1 day of age even though colemanite or calcined colemanite having the delaying effect is added in an amount of up to 10% of mass because alumina cement seems to have a higher hydration activity than portland cement. Furthermore, in the case of adding calcined colemanite, the compressive strength at 28 days age is increased to a higher value by adding the colemanite, and the compressive strength becomes a similar level to that to which no additive is added. Acid resistance of the alumina cement mortar is maintained, even when colemanite or calcined colemanite is added. They exhibit much higher acid resistance compared with mortar hardened bodies prepared using ordinary portland cement or blastfurnace slag cement class B. Colemanite functions as an inhibitor of conversion of alumina cement because Ca6Al2 [B (OH) 6] 9.8 (OH) 14.2·20H2O seems to form as a stable phase. From measurement results by XRD, the presence of colemanite could not be observed at 1 day of age, in other words it reacted.
The conversion of waste cast iron powder exhausted from a foundry into pyroaurite-like compounds has been investigated by coprecipitation and hydrothermal methods, aiming at resource recovery. An acid pretreatment of waste cast iron powder and an addition of a magnesium source were necessary processes to convert into pyroaurite-like compounds. The hydrothermal method brought pyroaurite-like compounds with good crystallinity, while the coprecipitation method did ones with poor crystallinity. The resulting materials exhibited removal properties for nitrate and phosphate ions. The products, therefore, seem usable as removal agents for toxic anions in waste water.
Calcium-deficient hydroxyapatite (DAp) crystals were deposited on a stainless steel from mixed solutions of calcium nitrate and ammonium hydrogen phosphate by electrochemical method. The electrolyte solution pH was adjusted to 5.0. Various morphologies of DAp were observed depending on bath temperature and current density. At room temperature and at low current densities, high crystalline calcium hydrogen phosphate, and at the same time, low crystalline hydroxyapatite-like product were obtained. At 50-80°C and at low current densities, narrow and long crystals oriented perpendicularly to the substrate in the deposits. At 80°C and at high current densities, c-axis-oriented plate-like crystals were deposited. The Ca/P molar ratios of the crystals obtained from solutions with Ca/P = 1.67 and 2.0 were nearly equal to 1.60 at higher current densities.