Hydroxyapatite (HAp) was prepared by the oxidative decomposition of calcium chelate (EDTA-Ca) using H₂O₂, and its morphology was investigated.
Morphological changes of HAp particles depended primarily on the amount of decomposition of EDTA-Ca. The morphology of HAp particles varied from a platy form to a japanese bladder cherry-like form (polyhedron crystal based on hexagon) and then to a chestnut-like form. When the additive rate of H₂O₂ was reduced, the morphology of HAp particles varied from a chestnut-like form to a japanese bladder cherry-like form and then to a platy form.
The composition of HAp with a japanese bladder cherry-like crystal form was calcium-deficient and carbonate-containing (Ca/P atomic ratio=1.52-1.56, CO₃ content = approximately 5.5%). The HAp decomposed into a mixture of HAp and β-Ca₃ (PO₄) ₂ by heating over 800°C.

View full abstract

The quantitative analysis technique of dihydrate and hemihydrate gypsum in cement was studied by thermogravimetry. DTG peaks attributed to the dehydration of dihydrate and hemihydrate gypsum were sufficiently separated by using the lidded sample cell with a micro-hole less than about 30μm in diameter. So the quantitative analysis became easily possible. The reasons of these phenomena were that the water pressure in the cell became higher caused by the dehydration of calcium sulfates and so the equilibrium of the dehydration shifted to higher temperature zone. The minimum limit of quantitative analysis of this technique was about 0.2% for dihydrate gypsum. The precision of this technique was not influenced by the type and fineness of calcium sulfates.

View full abstract

The carbonation mechanism of calcium hydroxide and calcium silicate hydrates with CaO/SiO₂ mole ratio 1.23 and 0.40, was studied by real-time measurements of the absorption of carbon dioxide gas (concentration 10%) and the weight change under 30, 60 and 80% relative humidity.
The rates of carbonation were remarkably changed with relative humidity. the carbonation of calcium silicate hydrates is proceeded ed gradually with carbonation time, but the carbonation of calcium hydroxide is developed rapidly at early stage, except carbonated under 30% relative hu-midity, and the carbonation of calcium hydroxide does not occurred at late stage.
Generally, the carbonation reaction is slower at 30% R. H. as compared to the carbonation at 60 and 80% R. H. It is necessary that the surfaces of hydrates are saturated with water in order to occur the carbonation reaction. But, the carbonation of calcium silicate hydrate with CaO/SiO₂ ratio 0.40 is rapidly proceeded. Because it's carbonation products, which is calcium carbonate and silica gel, were absorbed with a large amounts of water and the surface was easily saturated with water.
The polymorphism of calcium cabonates is formed by the differents of relative humidity and CaO/ SiO₂ ratio of calcium silicate hydrates.

View full abstract

Eight kinds of Na₂O-TiO₂-P₂O₅ glasses with P₂O₅ content, of 30 to 40 mol% were prepared. In the series of glasses with the same P₂O₅ content, the density and the glass tran-sition temperature increased linearly with an increase of TiO₂ content, whereas the ther-mal expansion coefficient decreased. The same behavior in properties was also recognized in the series with Na₂O/P₂O₅= 1. These results indicated that TiO₂ is very effective for strengthening of glass structure. From the glasses with TiO₂ content of 30 mol% or more, NaTi (PO₄) ₃ (NTP) was produced as the main phase by crystallization. The crystallized samples prepared from 40Na₂0 30TiO2 30P₂O₅ and 30Na₂O 40TiO₂ 30P₂O₅ glasses at various temperatures showed thermal expansion coefficients of - 0.2 to 4.0 × 10^-6°C^-1. The low thermal expansion values of these crystallized glasses are due to the formation of NTP.

View full abstract

The hydration process and the hydration rate of 12CaO·7Al₂O₃ solid solution (C₁₂A₇ss, 11CaO·7Al₂O₃·Ca (OH) ₂, 11CaO·7Al₂O₃·CaF₂ and 11CaO·7Al₂O₃·CaCl₂) with and without various chlorides (CaCl₂, MgCl₂, NaCl, NH₄Cl and AlCl₃) has been determined at 25°C. Various Cl₂A7ss were prepared in burning method. The hydration rate of Cl₂A7 ss with nearly the same specific surface area are found to be in the order : 11CaO·7 Al₂O₃·Ca (OH) ₂ < 11CaO·7Al₂O₃·CaCl₂ < 11CaO·7Al₂O₃·CaF₂. When Cl₂A7 ss with various chlorides are hydrated, 3CaO·Al₂O₃·CaCl₂·10H₂O (Friedel's salt) is formed as the primary hydrate. The hydration rate of Cl₂A7ss is decreased by the coexistence of CaCl₂, MgCl₂, NaCl or NH₄Cl except AlCl₃. Hence, the setting time of Cl₂A7ss is extended and the unhydrate exists for a long time comparatively. After a certain period of time, the rehydration starts with heat evolution. When 11CaO·7Al₂O₃·Ca (OH) ₂is immersed in CaCl₂ solution, the surface of the unhydrate is covered with the microcrystals of Friedel's salt. Therefore, the retardation mechanism of Cl₂A7ss in the presence of chlorides is probably explained by covering the surface of unhydrate with Friedel's salt.

View full abstract

For the purpose of expanding applications of zeolite rocks occurred in Tochigi Prefecture (Oya, Utsnomiyashi, and Takashio, Yaitashi), their mineralogical properties and adsorptive properties for ammonium ion and methylene blue (M.B.) solutions were examined.
Three zeolite rocks containing 59%, 50% and 28% clinoptilolite, were used in this experiment. Samples of Oya and Takashio origin were found to contain a small amount mordenite. Chemical analyses showed that the samples of Tochigi origin had high Fe₂O₃ contents, and that there was difference between origins in the composition of exchangeable cations, i.e, alkali metals and alkaline earth metals. Cation exchange capacity (CEC) values were 155, 138 and 69 meq/100 g, respectively. Adsorption rates for ammonium ion tended to conform with increment of zeolite contents. The high adsorption amounts of Ammonium ion and methylene blue with samples of Oya origin were thought to be caused by their content of montmorillonite.

View full abstract

As-recived samples of limestones (from Kuzuu, Tochigi Prefecure) and shells (clams from Ariake) were calcined at 1010°C, crushed and screened, followed by hydrothermal treatment at 110°C in an autoclave. The resultant ashes were analyzed by various methods.
Results obtained are summerized as follows :
(1) Na⁺ ion concentrations were found to be 0.386 ppm in limestones and 67.004 ppm in shells.
(2) The H⁺ ions (proton) were detected in shells by the Ion Micro-analyzer, indicating the presence of organic substances in shells.
(3) Intensity ratios of the powder X-ray diffraction patterns were different, (001) diffraction intensity of the shell ash was extremely larger than that of the lime.
(4) Electron Microscope observations revealed that the lime ash consisted of spindle and irregular-shape particles, while particles in the shell ash mostly had hexagonal plate-shape, and the average particle size of the shell ash was about 10-20 times as large as that of the lime.

View full abstract