Thermal behaviour of ceramics obtained from the kaolinitic clays of Terra Alta, Catalonia, Spain

The thermal properties and evolution of mineralogy and colour of kaolinitic clay from the Terra Alta region were studied. The mineralogy of these materials consists mainly of kaolinite (13–27 mass%) and quartz (48–86 mass%). Minor illite, hematite, K-feldspar and calcite also occur. The linear expansion and absorption curves were used to predict the optimal firing temperature of the raw clays. During firing, from 1100 °C the water absorption decreases steeply, due to an increase in liquid phase, which penetrates into the pores and close the porosity. At this temperature, the firing shrinkage increases progressively. The fired clays are mainly composed of quartz, cristobalite and mullite, with minor hematite and rutile. Mullite starts to appear at 1050–1100 °C. SEM observations show that porosity decreases with the firing temperature. The colour properties were measured in the raw clays and in the fired bricks at different temperatures. The lightness, L*, is lower in the fired test pieces respect to the natural clays. This colour varies according to the hematite content, being from white to reddish in the fired samples.

INCORPORAÇÃO DO RESÍDUO DE VIDRO PLANO EM CERÂMICA VERMELHA

The present work aims to evaluate the influence of different residue incorporations on the physical and mechanical properties of a typical red ceramic composition, replacing the sand, by using the residue from the first stage of tempered glass manufacturing. Ceramic specimens were prepared with incorporations of 0 and 20% of flat glass waste. The samples were obtained by extrusion, dried and fired at 800, 900, 1000 ° C in a laboratory oven. Analyzes of the raw materials were performed, among which the thermal, morphological, physical and chemical can be highlighted. Tests on the fired ceramic specimens were also performed. The firing properties obtained were the dry bulk density, relative density, water absorption, dry linear shrinkage, linear firing shrinkage and flexural strength. The results showed that both the increase of the glass content and the increase of temperature had a positive influence on the studied properties. Furthermore, it confirmed that the glass waste acted in order to lower the proper firing temperature. Flat glass waste is therefore a highly recommended fluxing element for the red ceramic industry, as it can be incorporated in quantities as significant as 20% without major negative effects on the properties, therefore optimizing the amount of waste used and acting positively on the properties studied, reducing energy and raw material costs.

Influence of Mong Duong fly ash on the physical properties of dry pressed ceramic tiles

Although fly ash is a solid waste of coal-fired power plants, it is also a potential raw material for the building materials industry. In the present work, the fly ash collected from Mong Duong I power plant was characterized and used as a substitute for kaolin and feldspar at sixteen percent of a ceramic tile raw mix. The results show that fly ash promotes sintering and helps upgrade wall tiles from unsatisfactory to grade BIIa and floor tiles from grade BIII to grade BIb. These changes have significant economic and environmental implications. However, due to a relatively high firing shrinkage, it is necessary to have appropriate adjustments if applied in industrial production.

Production of ceramic construction materials as an environmental management solution for sulfidic mine tailings

Mine tailings (MT) waste valorization in construction materials can be one possible solution because they may allow an alternative for some applications as an important contribution for a more circular economy. The aim of this work was to study the feasibility of using a sulfidic mine tailing in the production of building materials such as ceramic roof tiles. The introduction of 5, 10 and 20% MT in ceramic roof tiles promoted an improvement on the final properties of these materials. The use of 20%MT has decreased the firing temperature from 1150º to 1050 ºC, hence promoting energy savings and lower costs. Properties as density and water absorption were improved. Firing shrinkage, many times responsible for cracking, also decrease with the use of MT and, in this way, improve the production rate. The 20% MT ceramic formulation achieved the highest value of strength with lowest firing temperature. For the effects of sulphates' emission (SO2 and SO3 gases) upon firing, a solution was proposed involving their reaction with water and, through condensation, providing afterwards sulphuric acid as a process by-product. The use of high sulphide MT in ceramic roof tiles processing could be viewed as a potential safe waste management solution for these particular mine tailings.

Fly Ash Utilisation in Mullite Fabrication: Development of Novel Percolated Mullite

Fly ash is an aluminosilicate and the major by-product from coal combustion in power stations; its increasing volumes are major economic and environmental concerns, particularly since it is one of the largest mineral resources based on current estimates. Mullite (3Al2O3·2SiO2) is the only stable phase in the Al2O3-SiO2 system and is used in numerous applications owing to its high-temperature chemical and mechanical stabilities. Hence, fly ash offers a potential economical resource for mullite fabrication, which is confirmed by a review of the current literature. This review details the methodologies to utilise fly ash with different additives to fabricate what are described as porous interconnected mullite skeletons or dense mullite bodies of approximately stoichiometric compositions. However, studies of pure fly ash examined only high-Al2O3 forms and none of these works reported long-term, high-temperature, firing shrinkage data for these mullite bodies. In the present work, high-SiO2 fly ashes were used to fabricate percolated mullite, which is demonstrated by the absence of firing shrinkage upon long-term high-temperature soaking. The major glass component of the fly ash provides viscosities suitably high for shape retention but low enough for ionic diffusion and the minor mullite component provides the nucleating agent to grow mullite needles into a direct-bonded, single-crystal, continuous, needle network that prevents high-temperature deformation and isolates the residual glass in the triple points. These attributes confer outstanding long-term dimensional stability at temperatures exceeding 1500 °C, which is unprecedented for mullite-based compositions.

Coffee Husk as Feldspar Substitute in the Manufacture of Enameled Ceramic Tile

This study researches the effect of adding coffee husk (CH) and coffee husk ash (CHA) as partial feldspar substitutes to the manufacture of enameled ceramic tiles. Clays and other paste additives were characterized using XRD and XRF. The designed prototypes were pressed, dried, and fired at 1,120 °C. The physical (drying and firing shrinkage, apparent density, water absorption) and mechanical (flexion resistance) properties were evaluated and compared with standard fired specimens. Although the physical and mechanical properties of the specimens with 5 and 10 % CH and CHA make them suitable for the manufacture of BIIb ceramic tiles, it was concluded that CH and CHA under the working conditions do not replace feldspar in the preparation of enameled ceramic tiles due to surface quality defects.

A Study on the Utilization of Coal Fly Ash Derived Grog in Clay Ceramics

Grog is an additive material that plays important roles in ceramic making. It improves the fabrication process of green bodies as well as the physical properties of fired bodies. Few low-cost materials and wastes have found their application as grog in recent years, thus encouraging the replacement of commercial grogs with cost-saving materials. Coal fly ash, a combustion waste produced by coal-fired power plant, has the potential to be converted into grog owing to its small particle sizes and high content of silica and alumina. In this study, grog was derived from coal fly ash and mixed with kaolin clay to produce ceramics. Effects of the grog addition on the resultant ceramics were investigated. It was found that, to a certain extent, the grog addition reduced the firing shrinkage and increased the total porosity of the ceramics. The dimensional stability of the ceramics at a firing temperature of 1200 °C was also not noticeably affected by the grog. However, the grog addition in general had negative effects on the biaxial flexural strength and refractoriness of the ceramics.

Limestone Waste Incorporation in Clayey Mass for Rustic Ceramic Tiles Manufacturing

In the south of Ceará (Brazil), Cariri region, there is a production center for roof tiles and bricks. At that same region, there has been an expressive mining of laminated limestone, known as Pedra Cariri (Cariri Stone), which has produced large amounts of CaCO3-rich waste, that causes undesirable impacts to the environment. This work aimed to analyze the feasibility of producing rustic ceramic tiles, made up of clayey masses used in the region with the addition of this waste, aiming at the diversification of red ceramic products in a sustainable way. The mixtures were pressed, fired in maximum firing temperature which varies from 750° to 1150oC and had their physical-mechanical characteristics tested. The results indicated that the clayey mass is composed of kaolinite, feldspar and quartz, while montmorillonite and/or vermiculite is only found in roof tile clayey mass. The waste is mainly made of calcite. In general, the values of water absorption were compatible with porous rustic ceramic tile and the addition of Pedra Cariri waste provided lower values of firing shrinkage as well as the increase of the flexural strength. The samples of roof tile clayey mass (10% of waste at 850°C and at 1150°C) obtained physical-mechanical property values that match Brazilian technical norms to BIII type ceramic tile. Therefore, the mixture formulated with tile clayey mass and limestone waste presents potential to be utilized in the manufacture of ceramic roof tiles.

Influence of Kaolin and Silica on some Refractory Properties of Pingell, Zircon Sand

100kg of zircon sand raw material was obtained from Pingell, Toro Local Area of Bauchi State while silica and kaolin were used as the additive materials in different proportions. The materials as received were wet and in large chunks, and was sun dried prior to crushing with Jaw crusher and sieved with the sieve of size 100 µ to obtain fine powder particles. Samples of various compositions were prepared from the powder particles of Zircon sand (X); Zircon sand and silica (Y); zircon sand, silica and kaolin (Z) and mixed together based on the experiment’s program with a predetermined amount of water in the mixer. Refractory brick test specimens were prepared by standard methods from samples A, B and C and subjected to refractory test such as apparent porosity, bulk density, cold crushing strength, linear shrinkage, thermal shock and refractoriness in order to evaluate the effects of adding silica and gypsum to Pingell zircon sand and investigate its suitability as raw material for refractory brick production and furnace linings. From the result obtained, the average porosity of X, Y and Z is 13.5, 18.3 and 21.6 % respectively while the respective bulk density are 3.2, 2.0 and 1.8 g/cm3. The values of the cold crushing strength for samples X, Y and Z are respectively 25.5, 23.4 and 18.8 MN/m2 but the firing shrinkage is 4.5, 5, and 6.5 %. Thermal shock resistance of 26, 20 and 22 cycles were obtained respectively for X, Y and Z. Refractoriness of 1600, 1580 and 1610 0C were obtained respectively for samples X, Y and Z. The porosity, firing shrinkage and refractoriness increased with increase in the addition of silica and kaolin to zircon sand whereas the bulk density, thermal shock resistance and cold crushing strength of zircon sand decreased with the addition of silica and kaolin but the addition of silica reduced the refractoriness of the zircon sand. The addition of silica and kaolin in the appropriate proportions improved the refractory properties of the zircon sand and hence will find applications in the production of refractory bricks and furnace lining.

Characteristics and firing behaviour of the under-Numidian clay deposits from the Jijel region (northeast Algeria): potential use in the ceramics industry

The Numidian Aquitano-Burdigalian nappe from the Jijel region (northeast Algeria) shows an important clay-rich basal series. In this study, seven representative clay samples were collected from the Djimla and El-Milia areas of this region in order to analyse their mineralogy using X-ray diffraction and Fourier-transform infrared spectroscopy, chemical composition by X-ray fluorescence, particle size, plasticity, morphology by scanning electron microscopy and their ceramic properties. Samples were prepared by pressing the clays and firing them at 800–1100°C, and bulk density, water absorption, linear firing shrinkage, weight loss and bending strength values were determined on the fired samples. The clays are mainly composed of kaolinite and illite, with a small amount of 10–14 Å interstratified clay minerals and chlorite, associated with quartz and feldspars. The main oxides in the samples were SiO2, Al2O3 and Fe2O3. The clays may be classified as moderately plastic according to their Atterberg limits. Ceramic tiles have been produced by dry pressing. At all tested firing temperatures, the clays present the required standard values for linear firing shrinkage, weight loss, bulk density, water absorption and bending strength, and they are defect-free. The main transformations were observed at 1000°C with the appearance of new crystalline phases. The measured technological properties of the investigated deposits confirm that the Numidian clays from the Djimla and El-Milia regions are suitable materials for the production of high-quality structural ceramics.