Key Engineering Materials Vol. 608

Abstract: Lime mud from a pulp mill was used as an additive in brick clay from the southern part of Thailand. It was mixed with the clay from Cha-Aud district, Nakorn Sithammarat province. The chemical composition of lime mud and the clay was characterised by X-ray fluorescence (XRF), and the mineralogical composition was measured by X-ray diffraction (XRD). The particle size distribution was also measured. The main composition of lime mud is CaO, and Cha-Aud clay consists of SiO₂ and Al₂O₃ as major oxides. The lime mud contains calcite as a major phase when Cha-Aud clay is constituted by quartz, kaolinite, illite and goethite. Particle size distribution of lime mud is in the range of 1-50 μm. After the lime mud was neutralized using hydrochloric acid, it was mixed with Cha-Aud clay at 10 wt%. Samples with and without lime mud were sintered at 700, 800, 900 and 1000°C for 1 hour. The results showed that lime mud can be used as an additive in brick clay. Both types of samples were similar in terms of physical properties when their linear firing shrinkage, water absorption and flexural strength were in the same range.

Abstract: The mill scale (MS) waste is produced in steel industry during the milling process from the rapid oxidization of the hot iron products, and is mainly consisted of iron oxides (>95%). The aim of this work is to evaluate the utilization of MS (known in Greece as “kalamina”) as an admixture in clay bricks manufacturing by applying extrusion and sintering processes. For that purpose, specimens were formed from various clay/MS mixtures (up to 9 wt% MS) and then fired at different temperatures (up to 1100°C). Shrinkage and weight loss upon firing as well as density, porosity, bending strength and thermal conductivity of sintered specimens were determined and studied as a function of the % MS content and the firing temperature for optimization. The experimental results show that the incorporation of MS in clay bricks production is feasible, as an efficient secondary resource, thus turning waste from one industry into useful feedstock for another one. Specifically, the mechanical performance and thermal conductivity are not significantly affected with increasing the mineral admixture percentage and the sintering temperature.

Abstract: Residual stresses in traditional ceramics may have different origin and nature. In glazed tiles (both porous and sintered), they can be due to the thermal expansion mismatch of glaze and body. Another type of residual stresses in glazed and unglazed porcelain tiles is due to temperature gradients during cooling, which give rise to volume variations in different areas of the same ceramic ware. Thermal gradients may originate not only between the surface and the core of the tile, but also between the upper and the lower face of the tile. The common practice in the porcelain tile industry to use differential cooling to control the planarity of the finished product induces permanent changes of volume in different areas of the ceramic ware, which give rise to permanent states of stress. At room temperature there are two main stress relaxation mechanisms, depending on the nature of the tiles: cracks growth in porcelain tiles and post-expansion in porous tiles. Generally, residual stresses relaxation cause delayed curvature according to these different mechanisms. Optical dilatometry and optical fleximetry techniques allow to investigate the volume changes induced by the cooling rate and the glaze-body coupling, factors responsible for residual stresses.

Abstract: Our objective was to make transparent glaze using oak ash which has a high content of CaO and contains P₂O₅. However, the melting point of oak ash is above 1340^°C, making it difficult to make transparent glaze using only oak ash. In order to lower the melting point of oak ash, flux materials were mixed to oak ash and melting characterization was carried out. Feldspar, which is largely composed of Na₂O and K₂O andlimestone largely composed of CaO were used as the flux materials. The materials were added 10, 20 and 30wt%, respectively, in order to produce the glaze. Depending on the type and amount of flux materials added, the samples were fired at temperatures between 1280~1320^°C in the reducing atmosphere. As the amount of feldspar added was increased, the melting point decreased substantially. Samples with limestone added did not melt completely even at temperatures 1300^°C and wollastonite phase was observed in the glaze layer.

Abstract: One method of improving the strength of porous ceramics is to add Al₂O₃ in ceramic raw materials and then they must be sintered at high temperature for densification. However, the non-plastic property of Al₂O₃ leads to a decline in plasticity of clay body, thus severely interfering with forming process. Besides porous ceramics have fine cracks and pores distributed within porous ceramics, these fine cracks on the surface also result in weakening of the sintered body. In this study, we attempted to improve the strength while compensating for the weakness of porous ceramics by the surface infiltration of strengthening materials after the first sintering step at 900^°C. MgCl₂, Al (NO₃)₃, and KNO₃ were used as surface strengthening materials. The effect of Infiltration factors, solution concentrations (1-3 moles) and infiltration time (1-5 seconds) on the mechanical properties of the sintered body are investigated. When the strength was assessed after the second sintering step at 1250^°C, an 30% increase in strength was obtained with Al (NO₃)₃ infiltrated in a 3 mole solution for 5 seconds. An analysis of the crystal phase of the strengthened body revealed a higher intensity of the mullite phase arising from the infusion of surface strengthening materials. Consequently, the mullite phase led to a higher strength value.

Abstract: Lightweight ceramics have a low density, which leads to a decrease in strength and toughness. In the development of lightweight ceramics, high-strengthening technology is necessary. Alumina fiber was mixed with raw materials for the purpose of producing high-strength lightweight ceramics. After adding alumina fiber at 1, 3, and 5wt% and sintering at 1300^°C, we found that strength and toughness increased in proportion to the amount. Instead of the high melting temperature of alumina fiber, it is reacted with matrix and generated mullite phase. And lots of alumina fiber remains in the matrix, thereby allowing improvements in strength and toughness. When alumina fiber was not added, we found a low density of 1.35~1.80 g/m³, along with low values for strength and toughness at 30~60MPa and 0.7~1.2 MPa m^1/2 respectively. With 1wt% addition of alumina fiber, we obtained a higher strength of 92MPa at 1300^°C, which is close to the strength of general white porcelains at 112MPa.

Abstract: 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.

Abstract: The objective of this study is to investigate the effect of red clay, grog and cement content (5,10,15,20%) on unfired clay brick’s properties. The comparative properties of construction bricks produced by the community fulfilled the requirements of Thai industrial standard (TIS 77-2545) for brick processing in Small and Micro Community Enterprise of Clay Brick Making Group in Son Bun Reung village. The physical and mechanical properties were tested consisting of the volume shrinkage, bulk density, appearance porosity, moisture expansion, slaking, compressive and fractural strength. The result showed that physical-mechanical properties were improved by the addition of cement. The unfired clay brick consisting of 100% grog and 20% cement had 4.5% shrinkage value. The bulk density and appearance porosity were 1.77 g/cm² and 3.5%, respectively. The fractural strength of unfired clay bricks was 41.2 kg/cm². The compressive strength of unfired clay bricks was 282.4 kg/cm². The clay bricks were not slaking.

Abstract: Dan Kwian, Sukhothai and Ratchaburi pottery clays are economically important pottery clays. They are well known in the Thai ceramic society for making Dan Kwian pottery, Sawankhalok pottery and Dragon jars, respectively. There have been several studies of these pottery clays. However, few of them used statistics to analyze their results. This work is a comparative study of the compositions and properties of these three pottery clays using statistical software to analyze the results. Results show that the major components of these pottery clays are SiO₂ and Al₂O₃. The Modulus of Rupture (MOR) of each pottery clay fired at 700°C are not significantly different. Sukhothai pottery clay fired at 900°C has a higher MOR and bulk density while its porosity, water absorption and apparent specific gravity are less than those of the Dan Kwian and Ratchaburi pottery clays fired at the same temperature. Additionally, the current study developed regression equations for estimating the properties of all pottery clays under study. Finally, it was found that the L*, a*, b* and reflectance spectra of all pottery clays increased when firing temperature was increased from 700 to 900°C.