A CaCO3 powder was coated with a chelate compound of aluminum and heated at 300°Cto prepare the AL2O3-coated CaCO3 powder. The apparent viscosity of the aqueous slurry with the AL2O3-coated CaCO3 powder was lower than that of the aqueous slurry with the uncoated CaCO3 powder. The hydrophilic property of the CaCO3 powder was improved by means of AL2O3-coating. The AL2O3-coated CaCO3 powder was homogeneously dispersed in water due to the hydrophilic property. The homogeneous dispersion of the AL2O3-coated CaCO3 powder decreased an amount of water restricted on the particle surface and improved the fluidity of the aqueous slurry.
30 mol%CaCO3-70 mol%Ca (OH) 2 mixed powder which is coated with a chelate compound of aluminum corresponding to 0-0.1 mass%AL2O3 was sintered at 1500°C for 2 hours to prepared calcia ceramics of 3-5 mm particle size. The open porosity of the 0.1 mass%AL2O3-containing calcia ceramics was lower than that of fused calcia. Fraction of residual CaO in the 0.1 mass%AL2O3-contained calcia was 90% and 45%. respectively, after dipping in water at room temperature and 85°C for 24 h, while that in the fused calcia was 56% and 3%, respectively. Hydration resistance of calcia ceramics containing small amount of AL2O3 was better than that of fused calcia. It was considered that the higher hydration resistance of the 0.1 mass%AL2O3-containing calcia ceramics was attributed to the lower open porosity.
We have developed phenol resin-alumina cement (PRAC) composite material from the mixture of alumina cement and phenol (resol type) resin precursor, containing small amounts of alcohol soluble polyamide (N-methoxy methyl 6-nylon) and glycerol. The PRAC composite showed high flexural strength (> 200 MPa) and higher heat-and water-resistant properties, compared with MDF (macro-defect-free) cement developed by Birchall in 1981. To clarify the chemical interaction between hydroxyl group and alumina cement in PRAC composite, thermal treatment has been carried out of several model mixtures of alcohols and alumina cement. After the thermal treatment of alumina cement with di-or tri-alcohols under various conditions, considerable amount of acetone insoluble substance was separated from resulting mixtures. Particularly in the case of ethylene glycol, final weight of aceton-insoluble substance attained to 37.6%, based on the weight of starting alumina cement. In present paper, the structure of resulting substance and interaction, which consisted of alumina cement and alcohol, was investigated by FT-IR, XRD, DSC/TG and mass change.
The presented paper investigated the afterglow property and surface modification of Bi3+ doped CaS phosphor showing a blue emission which was prepared by reducing Bi3+ doped CaSO4·2H2O. Especially, the relationship between afterglow intensity and lattice strain, which was formed such as anion vacancy and size of incorporation ion by substitutional incorporation was also noticed. Bi3+ doped CaSO4·2H2O was synthesized by adding 0.2 mol·dm-3 (NH4) 2SO4 solution into 0.2 mol·dm-3 CaCL2 solution including Bi (NO3)3. Bi3+ doped CaS phosphor was obtained by reducing the CaSO4·2H2O in H2S atmosphere at 900°C for 1-5 hours. The sample was characterized by means of X-ray powder diffraction pattern, infrared absorption spectrum and fluorescence spectrum. Formation of CaS phosphor was possible by mixing Bi3+ doped CaSO4·2H2O and Na2SO4 as reduction accelerator. Bi3+ ion in CaS phosphor was incorporated by substitution of Ca2+ ion in the host structure, and the charge compensation was carried out by substitution of Na+ ion. The upper limit of the incorporation of Bi3+ ion was 5 × 10-4 in Bi/Ca atomic ratio. The excitation wavelength was observed at 312 and 419 nm, the emission wavelength of the CaS phosphor excited with 312 nm light was 449 nm and the emission color is blue. The anion vacancy of S2- ion site was formed by substitution of Ca2+ _??_ Na+. The lattice strain rose by increasing number of anion vacancy. The afterglow intensity was enhanced with increase of anion vacancy as trapping center, which could be accumulated the excitation energy. On the other hand, stability of the emission and the afterglow intensity of CaS in the humidity were investigated. As this result, it was confirmed that surface modification was effective.
Antimicrobial activities of colemanite (Ca2B6O11· 5H2O) calcined in the range of 200°C to 500°C for lh were investigated using a calorimeter capable of measuring the heat evolved when soil microbes multiplied by metabolically degrading the glucose in the soil. Antimicrobial activities became evident when colemanite was calcined over about 300°C and maximum over 380°C. Their values of MIC (minimum inhibitory concentration) for the antimicrobial activities were derived using the non-competitive inhibition kinetic model proposed by Takahashi et al.. Major component of colemanite calcined over 380°C was estimated to be CaO · 2B2O3. The CaO · 2B2O3 was synthesized by calcining boric acid with calcium carbonate at 1000°C for 1 h. Also, CaO ·B2O3, 2CaO·B2O3 and 3CaO ·B2O3 were synthesized and these indicated the antimicrobial activities as well as CaO·2B2O3.