Characterization of ceramic tiles prepared from two clays from Sergipe — Brazil

We report an investigation of stain formation after use of clay–ceramic floor tiles produced by an industry from Sergipe, Brazil. Two types of raw materials have been used (C1 and C2) and test specimens were prepared at firing temperatures of 1000, 1120 and 1140 °C, being afterwards immersed in muriatic acid, evidencing stain formation for C1 tiles. After ICP chemical analysis, the original clays and tiles were characterized by powder X-ray diffraction (XRD) and TGA measurements, evidencing that C1 contained a higher carbonate percent than C2. Tile specimens were evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM), flexural strength, apparent density, linear shrinkage, and water absorption. In contrast to tiles prepared from C2, those prepared from C1 presented higher interparticle porosity and both linear shrinkages and water absorption variations with temperature were very incipient, suggesting that the high porosity and the low sintering caused the low staining resistance.     

Mineralogical transformations of calcareous rich clays with firing: A comparative study between calcite and dolomite rich clays from Algarve, Portugal

Mineralogical transformations during firing of two extremely calcareous clays, one calcite and other dolomite rich, and relatively poor in silica were studied. Original clays were mineralogical and chemically characterized with X-ray diffraction (XRD) and X-ray fluorescence (XRF). Firing of both clays was carried out in the temperature range 300–1100 °C under oxidizing conditions and the mineralogical transformations were investigated with XRD, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and scanning electron microscopy associated with energy dispersive X-ray spectroscopy (SEM-EDS).Important compositional differences in the neoformed phases were observed between calcite and dolomite rich clays. In the Ca-rich clay the assemblage gehlenite + wollastonite + larnite was observed. In the Mg(Ca)-rich clay the reaction products included akermanite, diopside, monticellite, forsterite, periclase and spinel.XRD and SEM-EDS showed the presence, in both clays, of a potassium–calcium sulfate in samples fired between 900 and 1100 °C.     

Mineralogy of clay raw material from Burkina Faso and Niger used for ceramic wares

Some clay deposits in West Africa provide raw materials for the local and traditional manufacture of ceramic products. We selected three clays in Burkina Faso, with the references ROG, GRI and POT and a fourth one, AKN1 in Niger. These clays have been mined for many years. There is growing demand for such materials and the reserves are sufficient to meet this demand. The ROG and GRI clays are used as construction materials in both fired and unfired bricks. The POT and AKN1 clays are used for producing the porous ware of fired pottery. A study was carried out to look at some of the physico–chemical characteristics of these raw materials in order to enhance their use. This is a preliminary study which will be followed by further investigations into the production of different ceramic wares. An analysis of the chemical and mineralogical composition of the materials and some investigations of their fired properties during a firing cycle up to 1000°C has demonstrated that, taken as a whole, they possess satisfactory characteristics for the described applications.     

Evolution of fluorine emissions during the fast firing of ceramic tile

The present paper examines the emission–adsorption phenomena of fluorine compounds in various ceramic tile body compositions with different fluorine and calcium contents, processed by fast firing cycles in an electric laboratory batch kiln and in continuous fast-cycle industrial combustion kilns (roller kilns). In the roller kilns, fluorine emission was monitored by analysing the fluorine content in both solid and gas samples throughout the kilns.It was found that fluorine emission during firing in air atmosphere in the laboratory batch kiln began at temperatures above 800 °C and increased progressively up to peak firing temperature. In the roller kilns, however, the emissions started at lower temperatures and decreased in certain kiln zones. This decrease indicates that there are regions in these kilns in which fluorine is adsorbed rather than emitted by the material being processed.A fluorine adsorption process is thus shown to occur in the preheating stage in the roller kilns, despite the rapid heating rate. However, encouraging this adsorption process in order to foster the formation of crystalline phases is ineffective in abating fluorine emissions when ceramic tiles are fired at peak temperatures exceeding 1100 °C.     

Bleaching of kaolins and clays by chlorination of iron and titanium

The quality of the clays and over all kaolin is measured in function of iron content, since this element gives an undesirable reddish color to this type of minerals. The use of chlorination for iron and titanium removal from different clay and kaolin minerals, used in Argentinian ceramic industry, has been investigated to establish reaction mechanisms, precautions and optimal conditions to bleach the clays. The method consists of the calcinations of the pellets in a flow of chlorine gas at temperatures between 700 and 950 °C, to remove the iron and the titanium by volatilization of the respective chlorides. Isothermal and non-isothermal chlorination assays were made and the effects of the temperature, reaction time, and carbon content in the sample over the bleach of the minerals and the phase transformations suffered by these minerals during the chlorination step were investigated. The removed amounts of iron and titanium were determined by X-ray fluorescence, the phase transformations were followed by X-ray diffraction and the samples' bleaching was established making an analysis of the space of the color by the spectrophofotometric method CIELAB. Also, a thermodynamic analysis of the system using HSC Chemistry for Windows software was made. The experimental results show that for red clay with high colloidal iron content, the optimum working temperature for the iron quantitative removal, without aluminium loss, is close to 850 °C, in controlled atmosphere free of O₂ and H₂O; lower temperatures require long reaction times. The extraction of titanium is not quantitatively achieved, as that of iron, even for long reaction times, because this element is present in different structures, with the consequent variation of its reactivity. The content of carbon and organic matter in the clays, in the case of the San Luis red clay, is enough for extraction improvement. However, the optimum concentration of carbon can vary depending on the type of clay and the amount of Fe₂O₃ in the mineral. The formation of phases such as α-Al₂O₃, a product of chlorination, increases the piece hardness. The methodology used in this work allows for obtaining a great improvement in the color of the final product of the firing, achieving ceramic materials with notable whiteness, even with red clays.     

Economy analysis of the implementation of extruded tiles fabrication in a ceramic industry containing ornamental rock waste

As a result of the economic crisis faced in Brazil, industries in the red ceramic sector have economic problems. The objective of this work was to evaluate, technologically and economically, through analysis of economy, the implementation of the production of ceramic tiles, a material with higher added value than bricks and ceramic blocks, in a ceramic industry located in the state of Rio de Janeiro, Brazil. The ceramic tiles were produced containing the incorporation of ornamental rock waste (ORW). The state has a region that has a red ceramic pole, but produces only products with lower added value. For this, specimens were produced with four different ceramic masses burned at temperatures in the range of 800 to 1050°C. Three masses were produced with different clays from the region (ceramic mass 1, 2 and 3) and a ceramic mass 4 was evaluated containing the clay that presented the best results and with the inclusion of sand and ORW, aiming at the analysis of economy. It was found that the masses containing only clays showed satisfactory parameters of resistance, but showed deficiencies in water absorption. The fourth mass, however, presented acceptable values in all the evaluated properties and was chosen to carry out a full-scale industrial test, which enabled the development of economic analysis and an economic analysis using the theory of real options. The results obtained in this last stage were also positive, providing an internal rate of return of 16.82%, above the minimum practiced rate of 15%, proving the efficiency of the economy applied to the manufacture of extruded tiles in the industries of the study region.     

Influence of firing temperature on the ceramic properties of clays from Campos dos Goytacazes, Brazil

The characteristics of two clays used for red ceramic production in Campos dos Goytacazes, southeast of Brazil, were investigated. Characterization was performed by X-ray diffraction, chemical analysis, as well as granulometric and plasticity measurements. Technological properties related to water absorption, linear shrinkage and flexural strength were obtained from specific tests. Samples were prepared by pressing clay bodies at 20 MPa, which were then fired at temperatures from 850 to 1200 °C. The results showed that both clays from three deposits are highly plastic due to the elevated percentage of kaolinitic clay minerals. The samples richer in clay minerals present higher linear shrinkage as well as a decrease in water absorption in comparison to the others. The effectiveness of these clays for red ceramic production has been discussed in terms of the Winkler diagram.     

Behavior of kaolinite and illite-based clays as landfill barriers

The technical requirements for the landfill of municipal wastes in the European Union (EU) are given in the Council Directive 1999/31/EC. A geological barrier of at least 1 m thickness with a hydraulic conductivity (HC) of 1 · 10^− 9 m/s is required. Where the geological barrier does not naturally meet the above conditions, a geological barrier of at least 0.5 m thick must be artificially established. We studied at controlled conditions, the ability of some clays (kaolinite or illite based) to act as landfill barriers. Several Spanish ceramic clays were compacted in columns (0.5 m length) and characterized for mineralogical, physical–chemical and heavy metal ions adsorption properties after 10 months leaching experiments. Zn, Cd, Pb and Cr salts were dosed in the synthetic leachates in order to test their in-depth retention. The specific surface area decreased in the material located near the clay–leachate interface region (< 6 cm) due to biofilm formation around clay particles, but bulk mineralogical properties were not affected. Although all the clays fulfilled the HC requirements, the diffusion of anions (chloride) reached more than 30 cm in kaolinite–illite or pure illite clays. The presence of significant traces of smectite (< 5%) was critical in anion transport retardation. Heavy metal ions were generally retained in the first 10 cm but in high surface-area illitic clays, the anions and heavy metal ions transport was stopped at < 6 cm. The clay mineralogy and the presence of carbonates and soluble salts greatly influenced the behavior of the barrier materials. Carbonate dissolution and precipitation affected < 6 cm depth. Divalent cations of carbonates selectively occupied the exchangeable positions and inhibited the retention of Na⁺, NH₄⁺ and K⁺, in the leachates. Sulphate was reduced at a depth of 20–30 cm. This biogeochemical process contributed to cadmium retention, presumably precipitated as sulphide.     

Microstructural evaluation of a clay ceramic incorporated with petroleum waste

In this work an extensive SEM/EDS microstructural investigation associated with technological properties was carried out on kaolinitic clay bodies incorporating different amounts, up to 20 wt.%, of a bentonite-treated petroleum waste. The clay bodies were fired at temperatures from 850 to 1100 °C and then bend tested until rupture. Fracture surface observation revealed the existence of relatively small BaSO₄ particles that do not significantly contribute to the rupture process. By contrast, larger clay matrix embedded particles and voids exert more influence on the ceramic rupture. Since these particles are also normal features in waste-free clay bodies, the incorporation of bentonite-treated petroleum waste cannot be directly related to the rupture process. Exception occurred above 10 wt.% added waste and temperatures higher than 1000 °C, at which the comparatively higher amount of non-plastic quartz particles plays a role in the decrease of strength.     

Effect of firing temperature and atmosphere on ceramics made of NW Peloponnese clay sediments. Part I: Reaction paths,crystalline phases,microstructure and colour

Archaeometric investigation on ancient ceramic collected from excavations in NW Peloponnese demonstrated that the ancient potters used the local Plio-Pleistocene clay sedimentary deposits for a large historical period. Three representative raw materials of these local sediments were chosen for experimental work aiming to evaluate their firing behaviour in a propane-fired kiln, with a different atmosphere and temperature. The determination of mineralogy and microstructure was carried out by XRD and SEM-EDS analysis. For ceramics fired at 850 and 950 °C, no significant mineralogical and microstructural differences were observed between the oxidising and reducing atmosphere. The main pyrometamorphic phases are fassaite, gehlenite, anorthite and wollastonite. On the contrary, at 1050 °C in reducing atmosphere, gehlenite and wollastonite are diminished whereas the content of anorthite, fassaite and amorphous phase is higher. The higher vitrification is attributed to Fe²⁺ that participates either in the formation of eutectic phases or in low melting crystalline phases.     

Influence of mineralogical composition of applied ball clays on properties of porcelain tiles

Relations between quality of ball clays applied in raw materials batches for manufacture of porcelain tiles, and physical properties and microstructure of obtained tiles, were investigated. Studied clays constituted 35% of the batch, while the other components were unchangeable. Stoch index, new IR 3620/3700 index and XRIR index (Stoch index multiplied by IR 3620/3700 index), were proposed to take into account crystallinity of kaolinite and contents of illite and smectites in studied clays. Relationship between XRIR index value of clay, and water absorption and abrasion resistance of the obtained ceramic material, was found. Water absorption of the tile is also correlated with grain size distribution and bending strength of used clay. Optimal ball clay for porcelain tile production should exhibit: Stoch index - min. 4.3; IR 3620/3700 index - min. 1.2; XRIR index - min. 4.8; grain size median - max. 0.27 μm; bending strength after drying - min. 8.0 MPa.     

Granite as flux in stoneware tile manufacturing

Natural granite was used to completely replace both feldspathic and inert components of a traditional ceramic body. Raw material from Sinai (Egypt) was added (in the range 20-35 wt%) to a commercial Egyptian ball clays (from Aswan, Egypt) in order to obtain laboratory tiles sintered at 1220 °C.Densification was studied according to ISO rules, while sinterability was estimated by optical dilatometry. Chemical, physical and microstructural analyses were accomplished to find the relationship between both the phase composition and microstructure of the fired bodies properties. The fired samples show moderate thermal expansion as well as reasonable bending strength. Therefore, as a nonconventional raw material in the modern ceramic production, the studied batches are recommended for the production of industrial fast firing tiles showing properties similar to commercial ceramic floor and/or wall tiles.     

Saudi Arabian clays for lead removal in wastewater

Three types of local clays–Tabuk, Baha, and Khaiber–were tested for their abilities to adsorb lead ions from wastewater. The effect of pH on the adsorption of lead ions was also investigated. The clays were treated with hydrochloric acid to activate adsorption sites within clay particles. Untreated Tabuk clay had the largest adsorption capacity, about 30 mg lead/g clay, in comparison with those of Baha and Khaiber clays. The smallest adsorption was observed with Khaiber clay, about 10 mg lead/g clay; this may be attributed to the prior existence of lead within the clay. The adsorption of the acid-activated clays was not enhanced compared to those of untreated clays. The Langmuir model described the experimental data for all untreated clays, while the Freundlich model described the experimental data of untreated Khaiber clay and treated Baha clay. The local clays tested in this study, especially Tabuk clay, may be utilized as cost-effective and efficient adsorbent materials for removing heavy metals from wastewater in Saudi Arabia.     

Ceramic behaviour of five Chilean clays which can be used in the manufacture of ceramic tile bodies

This study is focussed on the behaviour of ceramic clays from Chile which has an important local ceramic industry. Five deposits of clays with industrial application have been studied. The clays come from San Vicente de Tagua-Tagua (SVTT), Litueche (L), Las Compañías – Río Elqui (LC), La Herradura – Coquimbo (LH) and Monte Patria – Coquimbo (MP). The chemical and mineralogical compositions of clays were determined by X-ray fluorescence (XRD) and X-ray diffraction (XRD), respectively. Also, the plasticity index (PI) was measured for each sample. The chemical and mineralogical compositions of samples differ considerably. Test samples have been prepared by pressing and firing in the range of 800–1150 °C. Linear contraction (LC), water absorption capacity (WAC) and thermodilatometric analysis (TDA) were done in order to characterize clays after firing. A considerable decrease in the WAC coinciding with the beginning of vitrification, is observed between 1050 and 1100 °C. At 1150 °C the porosity of the tile bodies decreases significantly and the tile bodies became earthenware. All studied clays seem to be easily adaptable to a correct dry pressing ceramic process. In particular, illite–kaolinite-rich samples show the best behaviour. Samples SVTT are suitable for the production of fast firing vitreous pieces. L samples present the highest refractory behaviour.     

Preparation of decolorizing ceramsites for printing and dyeing wastewater with acid and base treated clay

A new type of decolorizing ceramsites for printing and dyeing wastewater were prepared, by means of acid activation, base neutralization, granulation and heating treatment, by using palygorskite, Hangjin2# clay, bentonite or sepiolite as raw materials. The experimental results show that, the decolorizing ceramsites made of palygorskite have the best performances among different clay minerals in treating printing and dyeing wastewater. Its decolorizing amount is 635 mL g^− 1 and the reduction in COD is 81%, after 5 min static treatment at normal temperature. After calcined at 700 °C for 1 h, the loss ratio of decolorizing ceramsites made of palygorskite is less than 5%. Treated with saturated (NH₄)₂SO₄ solution for 10 min, and then calcined at 300 °C for 10 min, the used decolorizing ceramsites can be reused for more than 15 times. The decolorizing effect of the decolorizing ceramsites is mainly attributed to the combined chemical flocculation reaction of various metal ions in the material, with minor physical adsorption involved.     

Clay content of argillites: Influence on cement based mortars

The pozzolanic activity of four heated powders containing different clays has been tested. Mineral transformations during calcination from 20 to 900 °C have been followed by X-ray diffraction (XRD) and Differential Scanning Calorimetry (DSC). Compressive strength tests were performed at 1, 7 and 28 days on cement–clay mortars using 30% of pozzolanic material as a replacement by mass for cement. Calcination temperatures corresponded to the stages of potentially high reactivity identified by XRD. Results indicated that there exists incompatibility between clay minerals which can not be activated at the same temperatures. Products of recrystallisation of the earlier activated clay were already formed when the second clay type was activated. Concerning the type and the abundance of clay minerals in the raw material, this study evidences that the compressive strength is, at first approximation, correlated with the percentage of activated clay and less with the nature of the clay assemblage.     

Thermal analysis of montmorillonites modified with quaternary phosphonium and ammonium surfactants

The thermal stability of seven organically modified montmorillonites (‘organoclays’) has been investigated using differential thermal analysis, differential scanning calorimetry, and thermogravimetry in conjunction with X-ray diffractometry. Six organoclays were synthesised by replacing the interlayer inorganic cations, initially present, with quaternary phosphonium and ammonium surfactant cations. The samples modified with tetrabutylphosphonium (TBP), and butyltriphenylphosphonium (BTPP) ions have an appreciably higher thermal stability than the octadecyltrimethylammonium (ODTMA)-modified clays. Thus, in the case of TBP- and BTPP-modified montmorillonites, the onset temperature of decomposition is close to 300 °C. Samples modified with hexadecyltributylphosphonium (HDTBP) ions have a lower onset temperature of decomposition of 225 °C. In comparison, the onset temperature for ODTMA-montmorillonites (obtained at different concentrations of ODTMA-bromide) ranges from 158 to 222 °C, being highest where the concentration of intercalated surfactant is lowest. The onset temperature for a commercial alkylsilane-treated quaternary ammonium-modified organoclay (S-BEN N-400FP) is 207 °C. The basal spacing of the TBP- and BTPP-modified clays is 1.7–1.8 nm, indicating a monolayer arrangement of quaternary phosphonium ions in the interlayer space, while the value of 2.5 nm for HDTBP-montmorillonite indicates a more open structure. The ODTMA-modified samples have basal spacings ranging from 1.9 to 2.1 nm, indicative of a bilayer to pseudo-trilayer arrangement. The exceptionally high basal spacing of 3.4 nm for the S-BEN N-400FP organoclay might be due to interlayer penetration of organosilane hydrolysis products during synthesis. The thermal properties of organoclays are apparently related to the nature of the surfactants and their arrangement in the interlayer space of montmorillonite.     

The influence of shaping and firing technology on ceramic properties of calcareous and non-calcareous illitic–chloritic clays

Two very different illitic–chloritic clays (calcareous and non-calcareous), both currently used in the Italian brickmaking industry, were used. Technological testing consisted in a simulation of the industrial processing performed at a laboratory scale. The pieces were obtained by three shaping techniques, pressing, extrusion and moulding, and fired at 1000 and 1100 °C, in fast and slow heating cycles. In each case their technological properties were studied. The microstructure and technological parameters of the ceramic pieces vary greatly, depending on the clay composition and the processing techniques. Pressing always produces pieces made from non-calcareous clay with the lowest drying and firing shrinkage, open porosity and water absorption. As it regards the calcareous clay, the lowest values of drying and firing shrinkage and water absorption are obtained by extrusion and moulding, respectively. The mechanical resistance, pore size distribution and critical pore diameter do not reflect clearly the influence of shaping techniques. Independently from the shaping technique adopted, all non-calcareous bodies show higher Maage's indexes than the calcareous ones. In any case, the Maage's durability factor is higher in extruded samples.     

Spectroscopic and porosimetry studies to estimate the firing temperature of some archaeological pottery shreds from India

The present study aims to estimate the firing temperature of archaeological pottery shreds collected from the three archaeological sites namely Maligaimedu, Thiruverkadu and Palur in Tamilnadu state, India. The spectroscopic method Fourier Transform Infrared Spectroscopy (FT-IR) has been employed to find the lower limit of firing temperature of the archaeological pottery shreds by refiring the samples to four different temperatures from 200 °C to 800 °C. From the observation of the hydroxyl band and appearance/disappearance of octahedral sheet structure the firing temperature of the shreds has been estimated. The samples from Maligaimedu site named as MM1, MM3 and MM5, Thiruverkadu and Palur samples were fired to a temperature above 800 °C and the samples of Maligaimedu MM2, MM4 and MM6 were fired below 800 °C. Additionally, porosimetry measurements such as water absorption and mercury intrusion (MIP) were also carried out. The samples MM1, MM3, TK2–TK6, PL3 and PL5 were fired to a temperature less than 900 °C and the other samples to less than 1000 °C.     

An archaeometric study of the Phoenician ceramics found at the São Jorge Castle's hill in Lisbon

A detailed archaeometric study of Phoenician ceramics found in an excavation inside the medieval walls of São Jorge's Castle in Lisbon is described here.Thirty ceramic sherds were studied, grouped into six categories, namely amphorae, containers for domestic use, red slip wares, grey wares, cooking wares and also some indigenous tradition handmade wares.Micro-Raman, X-Ray Fluorescence Emission, X-Ray Diffraction and ground state diffuse reflectance absorption measurements were correlated and used as our main analytical techniques to perform this study. At least three totally different local clay sources were used to produce the here studied pottery, one of alluvial origin using clays collected along the river banks, and another one using clays probably extracted in the oriental part of the Castle's hill. Cooking-ware was made with the use of raw materials with sandy detrital origin. Evidence was also found showing that part of the amphorae, common containers, and grey wares were made with the same raw materials as used in the Phoenician kilns of Almaraz, located in the left margin of the Tagus River, roughly facing Lisbon's Castle hill. The temperatures of the kilns used to fire the amphorae and common containers was in most cases higher than the one used for firing red slip and grey tableware.A detailed laboratorial study of the alluvial clays fired at different temperatures and collected in the Tagus River banks, allowed us, in most cases, to establish the origin of the sources used to produce the Phoenician pottery found in Lisbon.