Sinterability of CaO prepared from Al2O3 coated CaCO3-Ca (OH) 2 powder was investigated in order to clarify effect of Ca (OH) 2 and small amount of Al2O3 content.The CaCO3-Ca (OH) 2 mixed powders were coated with a chelate compound of aluminum corresponding to 0-0.1mass%Al2O3. The CIP'ed compacts of the powders were sintered at a rate of 300°C·h-1 up to 1500°C in air and held at 1500°C for 2h to prepare CaO ceramics. The bulk density and fine structure for the CaO ceramics were measured in process of sintering. The bulk density for the CaO ceramics prepared from CaCO3-Ca (OH) 2 mixed powder was higher than that from CaCO3 powder at the temperature above 800°C. The bulk density of the CaO ceramics was slightly increased with increase of Al2O3 content, while the CaO grain size was greatly increased with Al2O3 content.
Glass fiber reinforcing material for GFRC has problems such as degradation of strength by reaction with alkaline materials. Most of all research in this problem had been oriented to modify the glass composition or to coat the surface with polymer. Here we focussed to modify the hardened matrix to have low pH. The matrix was made by carbonation instead of hydration, and the durability of glass dispersed in the matrix was discussed. The degradation speed of soda-lime glass in carbonated matrix was ca. five times smaller than that of hydrated matrix. So glass fiber which has a composition in wider range can be used for GFRC, and we can obtaine these materials with low cost.
Hydroxyapatites (HAp) samples of various compositions (Ca/P molar ratio) and with or without trace metallic elements were synthesized by a precipitation method in Ca (OH) 2-H3PO4 system at various temperatures. Their morphologies and thermal stabilities have been investigated by using various analytical techniques, for example, XRD, TG-GC-MS, FT-IR, TEM. The precipitates were carbonate-containing HAp with small particle size. Thus a new index, Ca/ (P + C) was introduced instead of Ca/P. The HAp samples were from 1.62 to 1.73 for the Ca/ (P + C). Synthesized HAp decomposed to HAp and TCP for Ca/ (P + C) < 1.67 or to HAp and CaO for Ca/ (P + C) > 1.67 with heating above 630-850°C. Further, specific surface area of standard HAp samples with trace metallic elements were larger than those of high purity HAp ones. This phenomenon was found to be due to the difference in pore volumes between the high purity and the standard HAp. When the Ca/ (P + C) molar ratios increase, the unit cells become smaller. Thus it was suggested that vacancies at PO43- sites arise as the Ca/ (P + C) molar ratios become larger. It waas also suggested that a lattice water is substituted for OH- site for Ca/ (P + C) < 1.67 or PO43- site for Ca/ (P +C) > 1.67.
The hydroxyapatite (Caio (PO4) 6 (OH) 2; HAp) and chlorapatite (Caio (PO4) 6C12; CAp) powders with addition of tetragonal zirconia (ZrO2) polycrystals (TZP; 3 mol% of yttria (Y2O3) solid solution) were prepared by two kinds of ultrasonic spray freeze drying (USFD) techniques : single-nozzle (SN) and double-nozzle (DN) USFDs. The SN-USFD was performed (i) using a solution containing 0.50 mol·dm-3 Ca (CH3COO) 2 and 0.30 mol·dm-3 PO (OCH3) 3 with the Ca/P ratio of 1.67 and (ii) using a solution containing 1.00 mol·dm-3 ZrOCl2 and 0.0619 mol·dm-3 YCl3. In this case, each solution was sprayed into a chamber chilled with liquid nitrogen, using an ultrasonic vibrator. The materials were freeze-dried and then calcined to form carbonate-containing HAp and TZP, respectively. The composite powder was prepared by mixing these two kinds of powders mechanically. In the case of DN-USFD, two kinds of solutions described above were simultaneously sprayed into the chamber chilled with liquid nitrogen, using two ultrasonic vibrators.The freeze-dried materials were calcined at 950°C for 1 h to form CAp and TZP. When these SN- and DN-USFD-derived composite compacts containing 2 to 80 mol% of TZP addition were hot pressed at 1100°C for 1 h, the relative densities attained -95%. These hot-pressed composite compacts contained HAp, TZP and their reaction products. Although the grains with sizes of -0.5μm were homogeneously packed in the case of SN-USFD-derived composite compact, the grains with sizes below 0.5μm were dispersed on boundaries of grains with sizes of 1 to 2μm in the case of DN-USFD-derived composite compact.
Carbonation of ZnO thin film was investigated in order to understand degradation of ZnO-based transparent conductive films, gas sensors and other electronic devices. The ZnO thin film (thickness : 400 nm) sputter-deposited on a glass substrate was exposed to the atmosphere of carbon dioxide (1.0×105 Pa) and saturated water vapor (2.3×103 Pa) at 20°C until 8 weeks when an exfoliation of the film occurred remarkably. The X-ray diffraction analysis showed a degradation of ZnO and formation of ZnCO3 and the basic carbonates. The crystal growth of ZnCO3 occurred independent of the orientation of the original ZnO crystal. Zn3CO3 (OH) 4·2H2O was detected in the early stage (1-2 weeks) and disappeared quickly. Zn3CO3 (OH) 4·2H2O was estimated to exist mainly at the surface of the film. Zn5 (CO3) 2 (OH) 6 and Zn2CO3 (OH) 2 increased during the present experiment. Zn2CO3 (OH) 2 was expected to exist mainly at the inner part of the film.
It has been suggested by authors that the series of treatment; chlorination at 500°C followed by heat-treatment at 1000°C and dechlorination at 700°C, significantly improve the adsorption capacity of carbonaceous materials. An effect of heat treatment before chlorination on adsorption capacity and the influence of chlorination on carbonization reaction of porous carbonaceous materials were investigated using phenol-formaldehyde resin. When the phenol-formaldehyde resin were heated at 500-600°C, the maximum nitrogen adsorption capacity of 0.67 mmol·g-1 was obtained. However, the adsorption capacity decreased with an increasing of the heat treatment temperature before chlorination. From the measurements of weight change on chlorination and heat-treatment, FTIR, electrical conductivity, HRTEM and XRD, it can be concluded that carbonization reaction is promoted by the chlorine treatment at relatively low temperature and leads to the formation of smaller crystallite than those produced without chlorination.