Toyohiko Sugiyama

Maintenance of large surface area of alumina heated at elevated temperatures above 1300 °C by preparing silica-containing pseudoboehmite aerogel

Abstract Silica-containing pseudoboehmite aerogel was prepared so that the surface area of alumina was maintained large after heating at elevated temperatures. Below 1300 °C, depending on the amount of silica added, the prepared samples transformed to γ-, δ-, and θ-alumina with columnar shaped particles, but not to α-alumina. As a result of the suppression of the phase transformation, heated samples had large pore volume (0.6–1.8 cm 3 / g ) and large surface area (70–300 m 2 / g ) . After heating at 1400 °C, while complete transformation to α-alumina occurred for 2.5 and 10 wt% silica with the additional formation of mullite for the latter, θ-alumina still remained present up to 5 wt% silica. When there was no formation of mullite, the surface area was quite large (23–37 m 2 / g ) . The cause for the maintenance of large surface area of alumina was discussed from the structure of the starting alumina source and the effect of the added silica.

Environmental Friendly Ceramic Building Materials

The global warming is one of the most serious problems. The decrease of CO2 emissions in our daily life is an important subject today. Recently, an application of water retentive materials as a paving material has attracted a great deal of attention in Japan. This material is effective for reducing heat island phenomenon, which is also a recent problem in many cities in Japan. Water retained in the material during rainfall evaporates when heated by sunshine. The latent heat absorbed by evaporating water works to cool the surroundings. The water retentive ceramic products are expected to be useful for building materials as well as pavements. Several performances are required on the water retentive ceramics when it is used as building materials. Its cost and quality are the important factors. Porous ceramic materials formed by pressing without firing is one of ideal low cost and eco-friendly candidates. The porous ceramics is also expected to be produced from recycled ceramic materials. By optimizing its composition and forming method, a water retentive material with high performance was developed. The trial product had the properties as follows; fracture toughness: 1300N, bending strength: 175N/cm, water absorption: larger than 30%, and precision in size (length): +-0.5mm for 150mm. The product showed also enough frost resistance. In this paper, the fundamental properties of the porous ceramics prepared without firing are discussed with referring to the results of the field experiments.Another subject recently studied by several tile manufactures in Japan is the glazed tile with high solar reflectance. The exterior walls covered with such a high solar reflectance tile keeps the surface temperature of the wall lower under the strong sunshine of summer. It is effective against heat-island phenomenon. In this paper, the outline of the research results on visible and infrared reflectance of many kinds of glazes is also discussed.

Construction of a Glaze Database

In the research of ceramic glazes, the process of preparing the glaze test pieces and improving the recipe is repeated. Our institute, AIST Japan, has more than 300,000 glaze test pieces from over 80 years of ceramic studies. These pieces are the physical evidence of the processes and the results of glaze test experiments. As such, they provide valuable information for glaze and ceramic research. The Ceramic Color Database has been constructed to make this fundamentally important information widely accessible in support of R&D in the ceramics industry. The database includes: glaze name, firing temperature, firing atmosphere, coloring, chemical composition, recipe, physical state, and other information, as well as images of the glaze pieces. The database has been used in recent ceramics research, and its effectiveness has been verified. It was also recognized that the vast amount of data provided by the database is useful in the material development and basic research of fields other than ceramics. The database has been improved based on such usage status. In this paper, the structure and usage of the database are described and the future development of the database is discussed.

Solar Reflectance of Glazed Tiles

Exterior wall tiles with high solar reflectance are effective in mitigating heat-island phenomenon. Such walls have also the potential to decrease the warming up of building interiors in mid-summer. For the purpose of increasing the solar reflectance of wall tiles, several kinds of glazes were prepared to measure their visible and infra-red spectral reflectance by the spectrophotometer. The incident angle of sunlight on vertical exterior wall is larger than 70 degrees at midday of the summer season in Japan. The reflectance theoretically increases with the increase of incident angle. It is important to examine the reflectance against the sunlight with varied incident angles. The practical solar reflectance of glazed tiles is calculated by measuring the hemi-spherical integrated spectral reflectance with an oblique incident light. The glazed tiles having layered structure were also prepared and their spectral reflectance was investigated.

Development of Low-Temperature Sintering Stoneware Bodies

We studied on development of stoneware bodies, which sintered at low-temperature in ball clay-quartz-Indian feldspar system and ball clay-quartz-Indian feldspar-nepheline syenite system. It was found that the ceramics around 30wt% ball clay, 44wt% quartz, 26wt% Indian feldspar composition showed high shrinkage rate (9.4%) by sintering at 1200°C in ball clay-quartz-Indian feldspar system. Dense stoneware with low water absorption rate (0.1%) was fabricated by sintering mixtures composed of 30wt% ball clay, 44wt% quartz, 10wt% Indian feldspar, 16wt% nepheline syenite at 1100°C 2h in ball clay-quartz-Indian feldspar-nepheline syenite system.

Long-Term Optical and Thermal Examinations of Ceramic Wall System with Solar-Altitude Dependent Reflectance

Many ceramic tiles are used as outer skins of office and residential buildings and they prevent severe weathers of solar ray, temperature, wetness and wind. The solar irradiance to the outer walls is a significant factor to influence the heat flow into room and consequently the energy load due to air conditioning. Particularly in the region where clear seasonal change is experienced, optical and thermal properties of the wall surfaces are desired to be controlled as a function of season; solar reflective in hot days in summer; solar absorptive in chilly days in winter. The ceramic walls with solar-altitude dependent reflectance are expected to be a simple and efficient method for autonomous control of heat flow into the room and in this study they were investigated from the viewpoints of optical property and shape of the tiles. The correlation between solar absorption and luminous reflectance revealed that there are some ceramic tiles whose solar absorption slightly depends on solar altitude. The triangular-shaped ceramic tiles that have reflective-upward and absorptive-downward surfaces were investigated in optical and thermal properties, based on one-year exposure of the tiles to solar radiation and ray-tracing simulation. These measurement and simulation found that the triangular-shaped tiles are an effective approach to the control of solar absorption and suggested the effective shape and surface property of the tiles such as optical reflectance, surface specularity and triangular angle.

Visible and Infra-Red Reflectance of Several Typical Japanese Glazes for Roof Tiles and Wall Tiles

. Tile coating with a higher reflectance of sun light are effective in mitigating heat-island phenomenon. Covering the surface of the ground or the exterior of buildings with such high reflectance coatings has attracted attention because of its high cost effectiveness. Recently, companies producing Japanese roofing tiles or wall tiles have been trying to develop high reflectance glaze for their products. However, while we have enormous amounts of data on visible reflectance measured through the study of glaze coloration, there are comparatively less data pertaining to infrared reflectance on pottery glazes. Though optical properties of simple glass and ceramics have been extensively studied, pottery glazes are complex glass-crystalline micro-composites. The pottery glazes sometimes have heterogeneous structures caused by phase separation, crystallization in the base glass, oriented crystallization on the surface, and so on, which are considered to affect infrared reflection. In this paper, several kinds of typical Japanese glazes are characterized from the point of view of the visible and infra-red spectral reflectance, and the improvement of these characteristics is discussed.

Ceramic Brick with High Water Retentivity Prepared from Ceramic Waste and by Products

Many kinds of industrial waste were examined as potential constituents of ceramic bricks or tiles. The basic physical properties of these materials were measured, such as sintering temperature, water absorption, porosity, density, color, chemical stability and bending strength. Several kinds of sintered ceramics containing large amounts of waste materials were obtained by adjusting the amount of the waste materials added to the ceramics. These were fired at temperatures lower than 1000°C. A lowering of firing temperature results in a reduction of discharge of CO2 on the production process. Ceramic brick with high water retention is expected to mitigate the heatisland phenomenon by the latent heat of evaporation. Porous ceramics were prepared using industrial waste, burned ash and recycled roofing tile as raw materials. The permeability, water retentivity, water absorption, and other properties of the porous recycled ceramics were investigated. The pF value of the ceramics was measured as an indicator of water retentivity. An appropriate method of characterizing water retentive ceramic materials was also discussed based on results of fundamental examination of the ceramics under practical conditions.