This study deals with the difference in the initial hydraulic properties of C₁₁A₇· CaF₂ and C₃A₃ CaSO₄ in the presence of Ca (OH) 2 and CaSO₄ at different temperatures. The hydration process of the C₃A₃·CaSO₄-Ca (OH) ₂-CaSO₄ system (C₃A₃·CaSO₄ system) can not distinctly be classified into the dormant period, acceleratory period and decay period like that of the C₁₁A₇·CaF₂-Ca (OH) ₂-CaSO₄ system (C₁₁A₇·CaF₂ system) and the temperature dependence of the C₃A₃·CaSO₄ system by hydration is larger than that of the C₁₁A₇·CaF₂ system. The hydraulic properties of the C₃A₃·CaSO₄ system, in which the dormant period is obscure, are closely concerned with the higher hydraulic activity of C₃A₃·CaSO₄ at least beyond 20°C. These results were explained in terms of the difference in the rate-determining step of their hydration processes. Subsequently, the morphology of ettringite is also dependent on the difference in the hydration process.

View full abstract

This paper presents the influence of fineness and particle size distribution of cement on the fluidity of fresh cement paste and mortar, and discusses it from a view point of compacting-ability of solid (cement and fine aggregate) particles evaluated as a percentage of solid volume in packed state, comparing with the influence of initial hydration.
Under some limited conditions, the fluidity of mortar showed almost the same tendency as that of cement paste corresponding to the difference in the initial hydration of each cement. However, this relationship was not recognized when the Blaine specific surface area and particle size distribution of each cement was different. In such case, the fluidity of cement paste and mortar strongly depended on the compacting-ability of solid particles as well as the initial hydration of cement, and the compacting-ability of cement-fine aggregate mixture was different from that of cement particles alone. High compacting-ability of cement particles without fine aggregate was obtained by lowering the fineness and broadening the particle size distribution. In the case of cement and fine aggregate mixture, the suitable fineness and particle size distribution of cement for high compacting-ability varied with the size and amount of fine aggregate used.

View full abstract

Iron oxide pillared montmorillonite which had been prepared by ion exchange with trinuclea Fe (III) acetato complex ion and subsequent thermal conversion of the complex ions at the temperature ranging from 300 to 500°C was modified by treatment in the aqueous solutions of MC1₂ (M = Ba, Sr and Mn+Zn) and subsequent calcination at 500°C. Uptake amounts of the metal ions by the iron oxide pillared montmorillonite ranged from 0.03 of M/Fe to 0.1, depending on the pillaring temperature and the duration time for the treatment in the solutions.
Specific surface area of the iron oxide pillared montmorillonite decreased on the modification. When the pillaring temperature was low, micropore in the iron oxide pillared montmorillonite deteriorated after the modification. However, microporous structure was kept in the case of the pillaring temperature of 500°C with the specific surface area of 111 m² g^-1 for the Ba-modification. The Ba/Fe ratio of 0.099 for this product is close to that for BaFe₁₂0₁₉. The Ba-modification exhibited a higher selectivity of adsorption for oxygen gas than for nitrogen gas at room temperature.

View full abstract

The effect of yttrium oxide (Y₂O₃) addition on the sintering of magnesium silicon nitride (MgSiN₂) powder has been examined. The sintering conditions examined in this paper were firing temperature (1400 and 1500°C), firing time (1 to 7 h), and the amount of Y₂O₃ (1 to 7 mass%). The phases present, microstructures, flexural strength, and thermal conductivity of the resulting sintered compacts were evaluated using X-ray diffractometry, scanning electron microscopy, flexural testing, and atomic force microscopy. When the MgSiN₂ compact without Y₂O₃ addition was fired at 1500°C for 1 h or more, it partly decomposed to form α- and β-silicon nitride (Si₃N₄). The formation of α- and β-Si₃N₄ upon firing at 1500°C for 3 h could be restricted by the addition of Y₂O₃ as a sintering aid; no α- and β-Si₃N₄ were detected with increasing Y₂O₃ amount up to 3 mass%; further increases in the amount of Y₂O₃ up to 7 mass%, however, produced Y2Si₃O3N₄. Maximum relative density (-90%) was attained when a MgSiN₂ compact with 3 mass% of Y₂O₃ addition was fired at 1500°C for 3 h. The flexural strength of MgSiN₂ compacts with 3 to 7 mass% of Y₂O₃ addition fired at 1500°C for 3 h attained 160 to 200 MPa. Thermal conductivities of the sintered MgSiN₂ compacts with 1 to 7 mass% of Y₂O₃ addition were in the approximate range of 15 to 18 W·m^-1·K^-1.

View full abstract

Phase transition of ammonium polyphosphate form I to II was examined under dry air, humid air, dry ammonia, and wet ammonia at 250 to 300°C. Under these atmospheric conditions, complete phase transition of ammonium polyphosphate form I to II was not done. According to the result, alternate flow of dry air and wet ammonia or wet ammonia and dry air were then examined. Heating form I at 270 to 290°C under alternate exchanging atmospheric condition of a wet ammonia gas and dry air resulted in 100% transformation of form I to II.

View full abstract

Spherical aggregates of hydroxyapatite (HAp) were prepared by the reaction with colloidal calcium carbonate (calcite slurry) and phosphoric acid and/or amonium phosphates (diammonium hydrogenphosphate and ammonium dihydrogenphosphate). Spherical aggregates prepared with calcite slurry and phosphoric acid were composed of low crystalline HAp. On the other hand, the crystallinity of HAp prepared by the phosphoration of calcite slurry with ammonium phosphates was relatively high. The average particle size of HAp aggregates was depended on the reaction temperature. Monodispersive spherical aggregates of HAp with submicron size (0.9μm) were prepared by the reaction with calcite slurry and ammonium phosphates at 85°C.

View full abstract