Marilena Valadares Folgueras

Effect of quartz sand replacement by agate rejects in triaxial porcelain

The ceramics industry, given the high volume of materials processed, stands as one of the largest consumers of natural raw materials but has also the capacity and potential to make significant contributions to solving environmental problems associated with other industries rejects. This work investigates the effects of quartz sand replacement by agate rejects (scrap) in a traditional triaxial porcelain composition. The study was carried out using the design of experiments (DoE) method. Characterization results were used to calculate statistically significant and valid regression equations, relating dried and fired body properties with clay, feldspar and agate scrap contents in the unfired mixture. The regression models were then discussed against X-ray diffraction and scanning electron microscopy results and used simultaneously to delimit the combinations of those three raw materials most adequate to produce a porcelainized stoneware floor tile with specified properties. Thus, an alternative use of an otherwise waste material is proposed, which can be translated into economic benefits and an important and welcome relief on environmental and waste disposal concerns.

Synthesis and characterization of hematite pigment obtained from a steel waste industry.

Pigments that meet environmental and technology requirements are the focus of the research in the ceramic sector. This study focuses on the synthesis of ceramic pigment by encapsulation of hematite in crystalline and amorphous silica matrix. Iron oxide from a metal sheet rolling process was used as chromophore. A different content of hematite and silica was homogenized by conventional and high energy milling. The powders obtained after calcinations between 1050 and 1200 °C for 2h were characterized by X-ray diffraction and SEM analysis. The pigments were applied to ceramic enamel and porcelain body. The effect of pigment was measured by comparing L*a*b* values of the heated samples. Results showed that the color developed is influenced by variables such as oxide content employed, conditions of milling and processing temperature. The results showed that the use of pigment developed does not interfere in microstructural characteristics of pigmented material. The best hue was obtained from samples with 15 wt% of chromophore, heated at 1200 °C in amorphous silica matrix.

Microstructural characterization of ceramic floor tiles with the incorporation of wastes from ceramic tile industries

Ceramic floor tiles are widely used in buildings. In places where people are bare feet, the thermal sensation of cold or hot depends on the environmental conditions and material properties including its microstructure and crustiness surface. The introduction of the crustiness surface on the ceramic floor tiles interfere in the contact temperature and also it can be an strategy to obtain ceramic tiles more comfortable. In this work, porous ceramic tiles were obtained by pressing an industrial atomized ceramic powder incorporated with refractory raw material (residue from porcelainized stoneware tile polishing) and changing firing temperature. Raw materials and obtained compacted samples were evaluated by chemical analysis, scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), thermogravimetric analysis (TGA), and differential thermal analysis (DTA). Thermal (thermal conductivity and effusivity) and physical (porosity) measurements were also evaluated.

Effects of Raw Materials on the Technological Properties of Brick Compositions Using a Statistical Design Approach

The simultaneous effect of raw materials (A, B and C) on physical and technological properties of brick compositions was studied. This investigation was carried out using the statistical design of mixture experiments. Ten mixtures of three raw materials were selected and used in the experiments design. Those mixtures were processed under conditions similar to those found in the ceramics industry. Fired body characterisation results were then used to iteratively calculate statistically significant and valid regression equations (trace plots), relating linear firing shrinkage, open porosity, fired bending strength and water absorption with the proportions of raw materials. The microstructures of some selected samples were studied using scanning electron microscopy. Mixtures with high clay B contents were most adequate to produce, under constant processing conditions, a brick with specified properties. The microstructures are characterized by a low closed porosity and absence of vitreous phase.

An Optimisation of Scrap Agate Powder Contents in Triaxial Ceramic Bodies Using Mathematical and Statistical Strategies

In the present study, the waste scrap agate, obtained as a by-product of rock agate beneficiation as decorating ends and media for wet grinding was used as inert filler in a traditional triaxial red stoneware tiles composition. The effects on the technological properties have been investigated. The study has been carried out using the mixtures experiments method for the experimental design. Characterization results were used to calculate statistically significant and valid regression equations, relating dried and fired body properties with clay, feldspar and scrap agate contents in the unfired mixture. The regression models were then used simultaneously to delimit the combinations of those three raw materials most adequate to produce a ceramic body with specified properties. The use of mathematical optimisation shown that, for the particular raw materials under consideration, there is a rather forgiving composition range of clay (20-68 wt.%), feldspar (17-50 wt.%) and scrap agate (15-45 wt.%) contents within which it is possible to simultaneously specify the technological requirements for triaxial red stoneware tiles bodies, not only of the fired products but also of the intermediate materials at important stages of the processing.

Using Experiments Design to Model the Effect of Raw Materials on the Sintering and Technological Properties of Brick Compositions

Mixtures of clays are often used in the manufacture of bricks. In industrial practice, it is desirable to be able to predict, in an expeditious way, what the effects of a change in raw materials or the proportions thereof might be in the various processing steps towards the final product. When the property of interest is basically determined by the combination of raw materials, an optimisation methodology specific to the design of mixture experiments can be successfully used. In the present study, fired bending strength and linear firing shrinkage were selected as the properties to model. Ten formulations of three different clays were selected and used in the experiments design. Those formulations were wet processed, uniaxially pressed, and then fired at 1000 °C for 2 h.. From the experimental results, regression models were calculated, relating each technological property with the proportions of raw materials. The regression models were then used simultaneously to define which combination of those three raw materials was most adequate to produce, under constant processing conditions, a brick with specified properties.

Rice Husk Ash as a Raw Material to Produce Willemite Pigments

This study focuses in the synthesis of ceramic pigments based on the crystal structure of willemite (Zn2SiO4). The willemite obtained from the combination of commercial zinc oxide and rice husk ash is produced in a conventional ceramic process without the use of mineralizer agent and with the addition of cobalt oxide or nickel oxide as the source of chromophore ions. The synthesis temperature used was 1200°C. The characterization of pigments involves the use of X-ray diffraction and scanning electron microscopy. The pigments applied in matte enamel and sintered at 1100°C or 1200°C developed color between blue and beige. The construction of absorbance curves showed the color development behavior of each pigment. The results showed the possibility of obtaining willemite, from rice husk ash and the color development efficiency of the material, besides showing the interference of chromophore ion (Ni and Co) in color development.

Characterisation of Geopolymer Cements Obtained from Different Sources of Metakaolin

In the present study metakaolin and clay brick waste (CBW) were used as a source of silica and alumina along with precursors aiming to obtain geopolymer cements, which were characterised via scanning electron microscopy (SEM) and X-ray diffraction (XRD). The CBW was obtained from rejected clay brick industrial manufacturing process. The precursors were activated by using of 5.0, 10.0 and 15.0 [mol.L-1] KOH solutions, which was added to K2SiO3 solution at 1:1 weight ratio. To obtain the geopolymer cements the weight ratio of precursor and activators were changed at levels of 0.6, 1.0 and 1.4. The samples were prepared and cured at room temperature for 7 days. The geopolymer cement obtained from metakaolin at 15 mol.L-1 level of KOH concentration and KOH/K2SiO3 ratio of 1:1.4 provided the best cement which can be estimated by the largest reduction and dissolution of crystalline phases in the activation reaction.

Characterization of soil-cement bricks with incorporation of used foundry sand

In order to contribute to the sustainability of the foundry and construction industrial sectors, this work investigated the possibility of employing used foundry sand (UFS) in soil-cement bricks. Modular bricks were prepared with percentages of 10 wt% cement, 0-25 wt% commercial sand, 0-65 wt% used foundry sand, 25-65 wt% clay, and 15-30 wt% gravel dust. A content of 10 wt% Portland cement was adopted to ensure economic feasibility, and gravel was used to improve mechanical strength. The modular bricks were tested to determine their technical properties. The interfaces between the constituent materials were observed by scanning electron microscopy. In durability tests, the bricks showed water absorption and weight loss in accordance with current technical standards. The addition of UFS together with gravel dust reduced water absorption and provided an acceptable level of mechanical resistance, in accordance with established soil-cement standards.

The Use of Dust Emission from Foundry Industry as Raw Material to the Industry of Ceramic Coating

Industrial dust emission is a kind of pollution which might occur due to the green sand mold process in the foundry industry. This material is predominately composed by sand, clay, carbon and metallic oxides. The ceramic industry has already assumed the role of consumer of by-products generated by such industries, mainly by having similarity between the composition of by-products and raw material employed in the ceramic sector. In a preliminary study the dust from exhaustion was define as a thin material with a high content of non-plastic material and the presence of carbon, which can interfere with processing and properties of the final product. This study aims to show the effect of exhaustion powder addition in atomized clay in order to develop ceramic coating. The results of the effect of sintering temperature and the percentage of residue on properties such as apparent density, linear shrinkage, water absorption and open porosity are presented.