Sintering Of Clay Research Articles

Colour Transformation and Textural Change in Biotite: Some Remarks for the Interpretation of Firing Technology in Greyware Pottery Thin-Sections

Firing is a crucial step in the production of pottery, as it irreversibly transforms the clay into ceramic. Clay sintering and subsequent vitrification occur during firing, together with other transformations undergone by specific minerals and rock inclusions according to their optical and physical properties, including their colour. Some of these are visible in thin-sections and might be interpreted as technological markers or contribute to the estimation of firing temperatures, although most of them are poorly documented. In this paper, we approach the transformations in colour, texture and optical properties that occurred in biotite inclusions from medieval greyware pottery. Our study considers a batch of 40 pottery samples from medieval Catalonia analysed by XRD. According to the estimated firing temperature ranges and atmospheres, we examined the behaviour of biotite at different temperature ranges from 700 °C to 1000 °C by means of optical microscopy, considering its size, shape and abundance, and compared these features to a wider assemblage of thin-sections from medieval earthenware. The results obtained are interesting, as they offer a valuable reference for petrographic studies on pottery. We discuss the potential of ceramic petrography as a way to perform more precise and refined sample selection for further analysis on archaeothermometry.

Amorphous silica wastes for reusing in highly porous ceramics

AbstractThe paper analyzes a solution in green manufacturing of foamed or cellular ceramics. The objective of this study was to determine the technical solution for rice husk ash and “tales” of mixed glass cullet reusing based on the specific properties of these materials for creation of spherical holes inside ceramic using the process of coalescence of cellular glass. The paper reports on experimental results obtained from the production of lightweight cellular glass granules produced using glass cullet and rice husk ash. Lightweight cellular glass granules were mixed with clay, pressed and fired in air at 920°C. Clay sintering and the formation of ceramic were followed with the coalescence of cellular structure of glass granules and with the formation of spherical hollows inside the matrix. Density and strength of the fired ceramic bodies were determined. It is observed that the lightweight ceramics with density 900 ÷ 920 kg/m3 possess a compressive strength of about 5 MPa that is acceptable for bricks or tiles manufacture. The utilization of amorphous silica waste for lightweight ceramics manufacture helps in reducing waste disposal concerns and costs associated, and also transforms the waste into an alternative raw material with added value, moreover making the final product cheap.

Effect of temperature and clay addition on the thermal behavior of phosphate sludge

The aim of the present work is to characterize the phosphate sludge from the area of Youssoufia (rich in CaO∼31%) and to study its thermal behavior alone and when mixed with clay from Safi (Morocco). This may contribute to its valorization as an alternative raw material for ceramic industries. The evolution of phases during the thermal treatment of phosphate sludge, clay and sludge–clay mixtures at different mass ratios (25wt%, 50wt%, and 75wt%) was performed at different levels of temperatures from 600 to 1120°C. Mineralogical analysis by X-ray diffraction (XRD) showed that the sludge mainly consisted of quartz, calcite, dolomite, and francolite. Dolomite and calcite vanished after sludge heating and two new phases were formed, namely akermanite and monticellite. For clay, it mainly consisted of illite, kaolinite, quartz, calcite, and dolomite. After clay sintering at high temperature, a new phase was formed, i.e. anorthite. The effects of the MO/SiO2 ratio (MO=CaO+MgO) in mixtures (clay+sludge) on the crystallization behavior of diopside and fluorapatite, and the disappearance of the akermanite were investigated. The results showed that the crystallization of diopside–fluorapatite increased when the MO/SiO2 ratio increased.

INFLUENCE OF CHROMIUM ELECTROPLATING WASTEWATER SLUDGE ADDITIVE ON THE PROPERTIES OF CAY BODY

This study focuses on estimating the possibility to use chromium electroplating wastewater sludge (GPN) as an additive to ceramic products. The influence of electroplating sludge addition on the properties of clay body from easily fusible clay was investigated. It was determined that clay sintering with a 5 % GPN sludge additive fired at 900–1025 °C was similar to that of the Girininkai clay. The total shrinkage of this ceramic body, depending on a sample firing temperature and time, is by 1.49–8.72 % less than that of clay body without additives. Water absorption is higher by 0.28–6.63 % than that of the Girininkai clay ceramic body. With increasing the additive concentration, the sintering of clay is getting worse. After firing at 1050 °C for 1 h, a ceramic body with the 10 % GP addition absorbs by 16.30 % more water than the Girininkai clay body does. Chromium ion concentration in the leachate from a ceramic body with 5 % the sludge additive fired at 1000−1050 °C for 4 h is less than the concentration limit to the natural environment. According to the results of clay body sintering and the chromium concentration in the leachate from this ceramic body, galvanic electroplating sludge could be used as an additive to building ceramic manufacturing.DOI: http://dx.doi.org/10.5755/j01.ct.65.1.8714

Activation Energy for the Sintering of Clay Based Ceramic Powder

Clay based ceramic is one of the most used materials in the form of construction blocks, bricks and tiles. Sintering of clay powders is recommended to be carried out above 900°C to benefit from fluxing phase consolidation. However, solid state consolidation of clay bodies made with mixture of powders may occur bellow this temperature by surface diffusion within the nanopores of the layered silicate particles. The objective of this work was to characterize the activation energy for the sintering of plastic clay at temperatures bellow 900°C. Cylindrical samples of sintered kaolinitic clay powders were tested by diametrical compression at 500, 600, 700 and 800°C in the time interval from 5 minutes to 50 hours. The results showed that the value found for the activation energy could be related to the diffusion of the mineral species that compose the clay. Moreover, this activation value corroborates the efficiency of lower sintering temperature for practical fabrication of clay based ceramics.

The Role of Particle Shape on the Sintering of Clay Based Ceramics

The influence of the clay particle morphology on the structural consolidation process associated with high temperature sintering was studied. By computer modeling, the different degrees of packing related to the distinct shapes naturally assumed by the particle clays as well as the consolidation conditions, based on solid sate reactions and surface diffusion were simulated. The model was compared with experimental data of clays fired at several temperatures. This permitted to explain differences in the behavior of red ceramics that was sintered with clays presenting distinct particle shapes.

Waste Colored Glasses as Sintering Aid in Ceramic Tiles Production

Bentonite, kaolin and Montmorillonite were mixed with 0%, 2%, 5% and 10% by weight additions of mixed color post consumer glass to determine their softening points. And then to determine the effects of glass addition on clay firing, Acustar tinted tempered, Acustar GL-20 and post consumer mixed were used. Six glass samples were produced; 150 micron and 5 micron tinted tempered, 150 micron and 5 micron GL-20 and 150 micron and 5 micron post consumer mix. Bentonite clay was used to mix with these glasses at 0wt%, 2wt%, 5wt%, 10wt%, 25wt% and 50wt% and 5% water was added. The resulting composite blends were then die pressed at 3200 psi to produce rectangular specimens with cross sections of 1.25” x 0.5”. Each specimen weighed approximately 2.5 grams and they were fired at 800℃, 900℃, 1000℃ and 1100℃ in a lindberg box furnace in air. The firing result showed that the addition of only a small percentage of post consumer glass lowers the melting points of clays by 50℃to 150℃. As a result of this the energy consumed to produce the clay products was reduced and the amount of reduction varied from clay to clay. Different size glass particles also resulted in considerably different effects on the clay sintering properties.

Sintering of a clay from Burkina Faso by dilatometry Influence of the applied load and the pre-sintering heating rate

The sintering of a pottery clay from Burkina Faso was studied as a function of the heating rate, at 3 or 10°C/min. The experimental method used was loading dilatometry in isothermal conditions at 1120°C. In these conditions, we found that the densification rate of the material is low, but tend to a limiting value after 2 h at 1120°C, depending on the pre-sintering heating rate and the load used. The relationship between the pre-sintering heating rate and the densification rate indicated the existence of a weakly organised material at higher heating rates. Nevertheless, higher values of shrinkage were observed when the temperature increased continuously. It is, therefore, proposed that the material is subject to a preferential solid state diffusion mechanism at face to face of the remaining kaolinite layers at high temperatures. This mechanism is favoured by higher heating rates, mainly in the temperature range corresponding to the structural reorganisation of the metakaolin phase.

Shrinkage and densification of particulate reinforced ceramic matrix composites

A model is described for the densification of particulate reinforced ceramic matrix composites when the degree of shrinkage is large. A rule of mixtures model can be used to describe the degree of densification in cases where there is no interfacial reaction between the reinforcement and the matrix. The model is illustrated by reaction sintering of sialon with titanium nitride and also by sintering of clay containing silicon carbide. The extent of linear shrinkage and also the rate of densification decreased with increasing volume fraction of reinforcement phase and these effects are explained on the basis of the model. The correspondence between the data and the model allows the prediction of shrinkage in composite systems where there is no interfacial reaction during the densification process.

A rule-of-mixtures model for sintering of particle-reinforced ceramic-matrix composites

A model is described for the densification of ceramics and particle-reinforced ceramic-matrix composites when the degree of shrinkage is large. A rule of mixtures model can be used to describe the degree of densification in cases where there is no interfacial reaction between the reinforcement and the matrix. These models are illustrated by the reaction sintering of sialon and of sialon with titanium nitride, and also by the sintering of clay containing silicon carbide. The extent of linear shrinkage and also the rate of densification decrease with increasing volume fraction of reinforcement and these effects are explained on the basis of the model. The correspondence between the data and the model allow the prediction of shrinkage in particle-reinforced composite systems where there is no interfacial reaction during the densification process.