Papers by Keyword: Anorthite

Abstract: Efforts to reduce the usage of imported raw materials in the ceramic industry have encouraged usage of local calcite minerals for production of refractory ceramic products. Corundum-mullite ceramics as refractory products were prepared by using clay, alumina and calcite mineral (CaO) via powder pressing method. The effect of CaO addition from 2.9 to 6.5 wt.% (R1, R2 & R3) on the mechanical strengths such as bulk density, apparent porosity, firing shrinkage and compressive strength were systematically studied as well as the reheat shrinkage and crystallinity of mullite ceramic bodies. The results indicated that the sintering process was prevented by the formation of anorthite phase at higher CaO content. The bulk density increased continuously as the CaO content was increased from 2.9 to 6.5 wt.%, while the apparent porosity and water absorption decreased with the increment of CaO content especially at temperature 1400 °C. On the other hand, addition of small amount of CaO have improved compressive strength of the ceramic body due to reduction in porosity and increase of crystalline phase. Addition of CaO content higher than 4.8 wt.%, would result in increment of crystallinity of the body due to formation of anorthite phase. It was observed that the R1 body (2.9 wt.% CaO) has the lowest reheat shrinkage percentage compared to other bodies and has complied with the Japanese Industrial Standard of mullite refractory product which is lower than 0.2% shrinkage percentage at 1300°C in the furnace for 8 hours.

Abstract: This paper reports the results of using natural andalusite (Al₂SiO₅) in combination with CaCO₃ and ZrO₂ in order to obtain aluminosilicate product. This work was devoted to the study of the mechanism of new phases creation in the Al₂SiO₅-CaO-ZrO₂ phase system during heating at different temperatures (1000, 1100, 1200, 1300 and 1400°C). Al₂SiO₅, CaCO_3, and ZrO₂ were used in a weight ratio of 45:50:5, respectively. According to the phase composition and chemical analysis in microareas, it was found, that andalusite reacted with CaO giving two calcium aluminosilicates: gehlenite and anorthite at 1400°C. ZrO₂ was presented as the separated phase at this temperature. Other occurring transition phases were: CaZrO₃ at 1000 and 1200°C, Ca₂SiO₄ at 1000, 1100 and 1200°C, Ca₃ZrSi₂O₉ at 1300°C. The synthesis mostly depended on the diffusion of Ca²⁺ ions.

Abstract: Mullite-anorthite as a kind of lightweight refractory combines the low thermal conductivity of anorthite and the excellent thermal properties of mullite. In this work, mullite beads and calcium aluminate cement was used as the main component and bonding agent. The lightweight mullite-anorthite refractory was prepared by difference routes including foaming method, addition of pore-forming agent and sacrificial template method. The phase composition, bulk density, apparent porosity and thermal conductivity of samples were compared. The results showed that anorthite formed as the consequence of the reaction of cement and mullite. Extra addition of foam, cornstarch and polyurethane sponge could decrease the bulk density of samples. The pore size of samples prepared by foaming method was the smallest. The apparent porosity of samples obtained by sacrificial template method was largest, but the thermal conductivity was the highest due to the open pores.

Abstract: Electricity generation at Mae Moh Power Plant in Lampang, Thailand, uses lignite as fuel. The output is 3.0 to 3.5 million tons of fly ash per year and 1.5 to 2.0 million tons of bottom ash per year. Fly ash is widely used in concrete application but for bottom ash, it is not very useful. When considering the phase of bottom ash containing quartz, anorthite and hematite, it was found that there are suitable chemical compositions for replacement of raw materials in ceramic tile. Generally, the stoneware tiles are composed of quartz, mullite, feldspar, and glass phase. Water absorption of stoneware ceramic tiles is below 5%, high strength, fire resistance, and low warpage. Firing or sintering at rather high temperature as 1000-1250 °C is the manufacturing process for this type of tile. The changes in crystal structure and glassy phase formation in tile texture during sintering will be often result the tile to warpage or bent. The more or less lean depends on the viscosity of the glassy phase that occurs at high temperatures in the tile if less viscosity will cause higher warping rate that effect on the shape, and quality of the workpiece. The research has reported that anorthite phase improves the viscosity of a liquid phase or glassy phase when the tile is sintering at high temperatures and lead to high density and low water absorption. This research is interested in studying the effect of using lignite bottom ash as an ingredient in ceramic tile texture to produce low water absorption type by analyzing the effect of percentage of lignite bottom ash to warpage and important properties of ceramic tiles.

Abstract: Influence of limestone sludge (generated during the washing process of limestone crushed aggregates) with high content of CaO in the form of calcite on the properties of brick body made from non-calcareous sludge (from the washing process of quartz sand) as a basic plastic brick clay was determined. Presence of calcite very distinctly influenced the firing process and properties of fired body. Limestone sludge decreases firing shrinkage, bulk density and coefficient of thermal conductivity of the brick body after the firing in the range of 850 – 950 °C. Higher modulus of rupture and water absorption is typical for fired bodies with limestone sludge addition. Most of these improvement are caused by the formation of anorthite only in the bodies based on the limestone sludge.

Abstract: Porous anorthite/mullite composite ceramics with different mullite content were fabricated by foam-gelcasting, using CaCO₃, SiO₂, α-Al₂O₃ as raw material for anorthite phase and mullite powder for mullite phase. Effects of mullite powder content on bulk density, porosity, compressive strength and thermal conductivity of the porous composite ceramics were researched. It has been shown that mullite powder content has great effect on microstructure and properties of the porous anorthite⁄mullite composite ceramics. The open porosity of the prepared porous anorthite⁄mullite composite ceramics is in the range of 58.7 %~77.5 %, the compressive strength is between 4.2 and 30.9 MPa, and the thermal conductivity is in the range of 0.18 ~1.47 W⁄(m·K).

Abstract: As by-product of steeling making, steel slag accounts for 10% to 13% of steel production. Utilization of it as resource has been tried in many fields. For example, it can be used as building materials, most for paving and backfilling. However, utilization level of steel slag is still low, and to find a novel way to utilize steel slag efficiently is urgent. Steel slag includes much calcium and silicon, similar to those of clay, which means that it can be one of the raw materials for ceramic sintering. In this research, the process of steel-slag based ceramics sintering was developed. The ceramic tiles with excellent performance were obtained, with up to 36% steel slag added. By EPMA, the possible crystal phases that exist in the ceramic samples have been discussed. By XRD analysis, the main crystal phases of steel slag ceramics were identified, which are anorthite, α-quartz and magnetite. The clinoenstatite can be obtained through increasing the proportion of steel slag in the formula. The diopside can be obtained if the talc was added. These are key factors to obtain excellent performance ceramic tiles under low sintering temperature.