Low Firing Temperature Research Articles

Analysis of Kushan Coins (1st–3rd Centuries C.E.) by Multi-Spectroscopic Techniques

Seven Indian copper coins of the Kushan Period (1st–3rd centuries C.E.) were studied by multi-analytical techniques like WD-XRF, XRD, and FESEM-EDX to understand coin composition and the metallurgical process of fabrication. Analytical results reveal a compositional gradient in the distribution of elements between the external surface and the inner core of the coins, and the coins show isolated patches of surface mineralization leading to the formation of copper oxides, magnesium silicate, and silica. The analysis also showed the probable use of sulfide ore of copper for smelting and poor workmanship for this hoard. The impurities like sulfur, iron, silica, etc. could not be removed due to low firing temperature and improper poling during smelting. Striations have formed in the coin interior, with grain boundaries showing micro-cracks due to stress like punching or hammering with the die. The coins under study are a single-phase copper with associated impurities of Si, Al, P, and Mg in all coins and black spots of copper sulfide in coin inner core.

LIME-GYPSUM BINDERS IN THE TECHNOLOGY OF HEAT INSULATING MATERIALS SYSTEMS CaO - Al2O3 - SiO2

In Ukraine, at present, insulating materials whose phase composition is represented by pseudo-wollastonite (CaO·SiO2) and anorthite (CaO·Al2O3·2SiO2) are not industrially produced. At the same time, such materials are more effective in heat-insulating ability compared to chamotte lightweight with comparable characteristics of porosity and apparent density. Moreover, these materials do not wet and do not react with aluminum melts and its alloys with other non-ferrous metals, which in recent years has led to the large-scale import of such products for lining electrolytic cells, induction furnaces and the manufacture of injection equipment. An additional motivation in the development of such materials is the modern and progressively growing tendency to obtain, on the basis of synthetic wollastonite, anhydrous and specially granulated in the form of microspheres powder mixtures of a new generation – slag-forming and heat-insulating steels for casting steel and molds of continuous casting machines. The above circumstances stimulated the development of such materials for reasons of availability of raw materials in Ukraine, the possibility of using a simple method of forming products – casting self-hardening masses into calcareous forms on lime-gypsum binders, as well as relatively low firing temperatures. The report discusses the issues of technology of heat-insulating materials based on pseudo-wollastonite and anorthite using examples of a number of experimental compositions of injection molding materials with varying amounts of binder, lime / gypsum ratio, and the addition of alumina. The technological parameters are analyzed: the moisture content of the casting mass, the setting end time and the firing temperature of the samples, as well as the physical and mechanical properties achieved by the samples of the materials: apparent density, compressive strength and general shrinkage. The results of x-ray phase analysis of samples of materials and the features of the formation of microporosity according to the results of petrographic analysis of powder samples in immersion preparations are presented. Variants of technology modification are proposed to expand the functional applicability of research materials and increase their physical and mechanical properties.

Mineral binding material with the use of paper manufacturing wastes

The possibility of making of mineral astringent material of the low temperature burning at utilization of wastes of production of paper – scope is shown. The analysis of compositions of raw material mixtures on the basis of the system chalk -clay-scope is conducted with varying of concentration of scope at the set descriptions of product of burning. The compositions of mixtures with introduction of 25 - 51 % scope is determinated. The features of phase composition and indexes of properties for mineral astringent with the use of scope as technogenic raw material are shown at the maximal temperature 1100 0С of burning.
 Industrial use of multi-tonnage waste of various industries, including scopes from paper production, allows to solve complex issues of technology of production of silicate materials, resource conservation and ecology.
 The feasibility of using scopes as man-made raw materials in the technology of mineral binders is determined by the peculiarities of the chemical and mineralogical composition - the presence of a complete complex of oxides necessary for the formation of a given phase composition during firing and the possibility of intensification of the sintering increase in the reactivity of the silicate system at.
 The efficiency of practical use of an osprey on the basis of the above developments is defined as the prospect of increasing the volume of utilization of industrial waste, as well as obtaining a new kind of mineral binder material in the low-temperature firing, which differs from romance with improved strength indicators.

Sol–gel preparation of yttria-stabilized zirconia thin films and transfer to polycarbonate substrates

Yttria-stabilized zirconia (YSZ) precursor gel films with or without acetylacetone (AcAc) were prepared on polyimide-polyvinylpyrrolidone layers that were deposited beforehand on Si(100) substrates. The gel-film deposition and firing were cycled, and the resulting YSZ films were transferred to polycarbonate (PC) substrates by heating the film and pressing the PC substrates on it. The fractions of the area of the film that was successfully transferred and that failed to be transferred were evaluated by image analysis. Higher firing temperatures were effective in decreasing the porosity, while they increased the fraction of the area of the film that failed to be transferred, which may be caused by an increase in adhesion at the YSZ/Si(100) interface. AcAc in solutions was also effective in decreasing the porosity, but reduced the successful transfer area fraction, which may result from the reduced film/PC adhesion due to the lower surface roughness of the film. However, the transfer area fraction could be increased from 5 to 74% when the uniaxial pressure on transfer was increased from 0.16 to 8.66 MPa for the film of 8% porosity prepared from the AcAc-containing solution via final heat-treatment at 900 °C. Such a high pressure was ineffective, on the other hand, for the film of a lower porosity of 4% fired at 1000 °C, suggesting that the optimization of preparation conditions that allows low porosity at low firing temperatures would be one of the keys for realizing the transfer of dense films.

Development of Zrconia Powder for Low Temperature Firing

Development of Zrconia Powder for Low Temperature Firing

Synthesis and characterization of nanocrystalline hydroxyapatite and its catalytic behavior towards synthesis of 3,4‐disubstituted isoxazole‐5(4H)‐ones in water

In the present work, the nanocrystalline particles of hydroxyapatite (HAp) using an easy alkoxide‐based sol–gel technique including triethyl phosphate [PO (OC2H5)3] and Ca (NO3)2·4H2O as P and Ca precursors have been synthesized. The sample characterization was performed by X‐ray diffraction, Fourier transform‐infrared analysis, scanning electron microscopy, thermal analysis (thermogravimetric analysis/differential thermal analysis), and elemental analysis of energy‐dispersive X‐ray analysis. It is interesting that single phase of HAp was obtained at a low firing temperature of 500°C. Modified Scherrer equation as the Williamson−Hall method was applied for the measurement of crystallite size distributions and micro‐strain of the sample. The determined crystallite size by complementary technique of transmission electron microscopy has good consistency with those obtained from the Scherrer formula. Moreover, we reported the one‐pot synthesis of 3,4‐disubstituted isoxazole‐5(4H)‐ones through the aqueous solution reaction of three components of ethyl acetoacetate, hydroxylamine hydrochloride and various aromatic aldehydes at room temperature. This protocol offers several advantages, including a simple work‐up procedure, very short reaction times (under 25 min), in accordance with the principles of green chemistry, recyclability, excellent yields (87–98%) and environmentally friendly.

Raman spectroscopy for firing condition characterization: Case study of Karelian medieval pottery

AbstractRaman spectroscopy together with the scanning electron microscopy and X‐ray diffraction were applied to study the firing parameters (temperature and atmosphere) of medieval pottery from Karelian hill forts in the North‐Western Ladoga region (Russia). Because the evidences of pottery manufacture including firing facilities were not discovered during the excavations of medieval Karelian fortresses, the application of Raman spectroscopy combined with the other techniques appeared to be an effective approach to reconstruct the technology of ceramic production in medieval Karelia. Scanning electron microscopy ‐energy‐dispersive X‐ray spectroscopy and X‐ray diffraction analysis showed that the Karelian pottery refers to noncalcareous and low‐temperature fired ceramics. Using the thermometer based on the thermal evolution of Raman spectral parameters of the charcoal identified in the ceramic paste of some specimens, the firing temperature for those was estimated to be close to 800 °C. These data are in accordance with the more frequent occurrence of anatase rather than rutile in the studied ceramic sherds that also corresponds to low firing temperature. The presence of hematite suggests firing in oxidizing atmosphere, in rare case the detected magnetite indicated the incomplete oxidizing atmosphere. The reconstruction of Karelian pottery firing procedure based on the obtained data supposes that the firing was carried out in bonfires. The present study contributes to the deciphering the firing conditions for noncalcareous and low‐temperature burnt ceramics, for which no significant modifications of starting minerals during heating are usually observed.

Nickel zinc ferrite thick film with linseed oil as organic vehicle for microwave device applications

The properties of nickel zinc ferrite (Ni0·5Zn0·5Fe2O4) thick film with Ni0·5Zn0·5Fe2O4 nanopowders as active powders and linseed oil as the organic vehicle is studied and investigated in this work. Ni0.5Zn0.5Fe2O4 thick film paste samples have been prepared with various weight ratios to study the rheology properties of the pastes. Rheology results show that paste with 30% wt. Ni0.5Zn0.5Fe2O4 has suitable rheological shear-thinning behavior, which is required for formulating screen printing pastes. Dielectric and magnetic properties of the thick film show values lower than bulk Ni0·5Zn0·5Fe2O4, which is relatable to the weight ratio of the ferrite in thick film and thickness of approximately 20 μm. With a low firing temperature of 200 °C, a screen printed microstrip patch antenna with a Ni0·5Zn0·5Fe2O4 thick film layer as substrate overlay has an increase in return loss by 64.22% and also increase in bandwidth by 84.61%, which has shown great potential for microwave devices applications.

Investigation of concurrent emissions in visible, UV and NIR region in Gd2O2S: Er, Yb nanophosphor by diverse excitation wavelengths as a function of firing temperature

Herein, we report the concurrent emissions in Visible, Ultraviolet (UV) and Near-Infrared (NIR) range by a single Gadolinium Oxysulphide (Gd2O2S) nanophosphor doped with Erbium (Er3+) – Ytterbium (Yb3+) and the optimization of its multiplexed photoluminescence (PL) profile as a function of firing temperature. The multimode emissions sensitized by an assortment of excitation wavelengths – 285 nm, 450 nm, 808 nm, and 1064 nm, revealed the roles of complex energy transition processes between several Er3+ excited states and single Yb3+ excited state. Stoke's shift of excitation by 285 nm in the visible region giving dominant violet emission along with green and red emissions portrayed the downconversion (DC) characteristics of the synthesized nanophosphor. The excitation by 450 nm produced emissions with anti-Stoke's shift to UV region; and, Stoke's shift to visible and NIR bands; disclosing the presence of simultaneous upconversion (UC), DC and NIR Quantum cutting (NIR-QC). Apart from usual UC of 808 nm excitation in the visible region, a vast anti-Stoke's shift to UV region displaying high-energy UC along with DC to NIR band displayed the multifarious excitation conversion by Gd2O2S nanophosphor. Incidence of 1064 nm also leads to large anti-Stoke's shift to UV, visible and NIR region strengthening the upconverting profile of the fabricated nanophosphor. The emission intensity of multiplexed PL investigated as a function of firing temperature (1000°C–1250 °C) divulged the optimization cycle of the synthesized nanophosphor for each excitation wavelength. The nanophosphors fabricated at lower firing temperature were found to be more efficient in absorbing and converting higher frequency photons whereas for upper firing temperatures the lower frequency photons were more favored. The obtained broad spectral conversion by a single Gd2O2S nanophosphor can be exploited to give a tailormade phosphor for the desired application such as sunlight harvesting, NIR detectors, biomedical imaging, and others.

Zakarpatskiy perlit as component of mineral woven fabric material

Thanks to the peculiarities of the chemical composition and structure, perlite has received application for manufacturing building materials - thermal insulation and ceramic
 Results over of research of the silicate systems with transcarpathian perlite as raw material for making of mineral astringent material are driven. The features of the chemical-mineralogical composition, phase transformations during burning and astringent properties of material at the use of perlite from Beregovsky deposit in composition initial raw material mixtures are shown.
 To determine and optimize raw material stock at the production of mineral binder material of low-temperature roasting type of natural or romanticum, a computer program "RomanCem" was used.
 After burning with a maximum temperature of 1100°C, the test of the binder material from the investigated 3-component mixtures with Transcarpathian perlite is characterized by differences in phase composition and properties.
 When using for the manufacture of mineral binder material of low-temperature firing of a gypsum natural or romantic cement 3-component mixtures based on the limestone system - perlit - clay, the content of Transcarpathian perlite is possible from 4 to 22 mass. %.

The microstructure and properties of ceramic tiles from solid wastes of Bayer red muds

As solid wastes in the alumina production of Bayer method, four kinds of Bayer red muds were successfully added to prepare ceramic tile samples for better waste utilization. The effects of four kinds of red muds on the properties of tile samples were discussed by XRD, SEM and EPMA analyses. Simultaneously, as by-products during the process of alumina production, Fe2O3 impurities were also investigated due to their high level ranging from 24 wt% to 36 wt% in the red muds. According to the radioactive inspection results, the four red muds were radioactive solid wastes which could be used for interior surface of class II civil buildings and exterior surface of buildings (GB6566-2010 China). The main phases of four red muds are boehmite, calcite, quartz and gibbsite. Preferable physical properties were obtained to be 0.12~9.92% in water absorption (belong to stoneware) and 30.57~60.96 MPa in bending strength, when the addition of red muds was 40 wt% (the addition of red muds was designed to be 40 wt% by the Method of Satisfied Chemical Compositions according to our previous experiments) and the firing temperatures were 940~1100 °C, 1080~1140 °C, 1080~1140 °C, 960~1120 °C, respectively. The main mechanism can be explained by the well-crystallized phases below 1100 °C with red muds as raw materials and non-excessive liquid phases at low firing temperatures that prompt the densification of samples. Although the liquid phases could lower the oxygen partial pressure around Fe2O3 and make unfavorable reduction of Fe2O3 into Fe3O4 and gas, they ultimately improved rather than decreased the performance of samples. Excellent properties of the samples make the four red muds appropriate to be used as raw materials for ceramic tiles, in accordance with Chinese National Standard (GB/T4100-2015), European Normalization (EN14411:2012), and American National Standard (ANSIA137.1-08).

Effectiveness of dense Gd-doped ceria barrier layers for (La,Sr)(Co,Fe)O3 cathodes on Yttria-stabilized zirconia electrolytes

This paper presents a detailed study of the effectiveness of Gd-doped Ceria (GDC) barrier layers for preventing reactions between La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) cathodes and Yttria-stabilized Zirconia (YSZ) electrolytes. The GDC barrier layers, which are reasonably dense as produced by a novel process where the GDC and YSZ are co-fired at 1250 °C, were varied in thickness from 1.5 to 6 μm. No measureable Sr transport occurs across the GDC layer of any thickness for a relatively low LSCF firing temperature of 1000 °C, or for thickness ≥ 4.5 μm at any firing temperature. Sr was detected at the GDC/YSZ interface for thinner barriers and higher firing temperatures, in the form of a discontinuous SrZrO3 phase. This zirconate phase forms preferentially at pores and grain boundaries in the GDC layer, probably indicating that these were pathways for relatively fast Sr transport. Atom probe tomography results indicated segregation of impurities to grain boundaries near the GDC/YSZ interface.

Rapid thermal processing of cost‐effective contacts for silicon solar cells

AbstractThis paper reports on the investigation of rapid thermal processing (RTP) of contacting the Al‐BSF solar cell with Ag, Cu, and Ni in conjunction with aerosol printing technique. The study showed a liftoff and delamination, respectively, for the bi and tri stack layers of Ag frit/Ni and Ag frit/Ni/Cu fired above 790°C peak firing temperature. The 770°C peak firing temperature gave excellent electrical performance for both bi and tri stack layer contacts, which is not favorable to forming thick back surface field (BSF) required for high open circuit voltage (VOC). This suggests that the bilayer and trilayer contacts involving Ag frit are limited to low peak firing temperature, but Ni frit, on the other hand, showed a wider firing temperature range. This is supported by low reverse saturation current density (J02) of 1.1 × 10−11 A/cm2 and high shunt resistance (RSH) of 5750 Ω·cm2 for the Ni frit fired at 800°C peak firing temperature. More so, the adhesion of Ni Frit to silicon is better than Ag counterpart as evidenced in the SEM micrograph. Thus, by adopting RTP Ni/Cu contacts, the cost of metallization of solar cell can be dropped from 35% of total processing cost to only 5% to 6%, which is approximately 30% drop in the total cost of processing.

Low-temperature preparation of humidity self-regulating porous ceramics with high strength performance

Nanopores are very important to the moisture adsorption properties of humidity self-regulating ceramics (HSCs). As nanopores disappear easily during high temperature firing processes, it is important to prepare HSCs at low firing temperatures. But such materials generally lack the mechanical strength needed to meet building material standards. Accordingly, this study used fumed silica as a body enhancer added to volcanic mud raw material to prepare an HSC. The effects of fumed silica content, water addition and firing temperature on flexural strength, porosity, and moisture adsorption were investigated in detail. The results show that, by controlling the amounts of fumed silica and water added, the HSC can achieve high moisture adsorption of 302 g/m2. Furthermore, its flexural strength is greater than 12 MPa by only firing at 600 °C, owing to the formation of calcium silicate hydrate in the porcelain green bodies. These results indicate that this proposed method is a very promising and simple approach to the preparation of high strength performance humidity self-regulating porous ceramics.

Microwave dielectric properties of low firing temperature stable scheelite structured (Ca,Bi)(Mo,V)O4 solid solution ceramics for LTCC applications

In the present work, a systematic study on microwave properties of Ca1-xBixMo1-xVxO4 (0.2 ≤ x ≤ 0.5) solid solution ceramics synthesized by using the traditional solid-state reaction method was conducted. A scheelite structured solid solution was formed in the composition range 0.2 ≤ x ≤ 0.5. We successfully prepared a microwave dielectric ceramic Ca0.66Bi0.34Mo0.66V0.34O4 with a temperature coefficient of resonant frequency (TCF) near to zero and a low sintering temperature by using (Bi, V) substituted (Ca, Mo) in CaMoO4 to form a solid solution. The Ca0.66Bi0.34Mo0.66V0.34O4 ceramic can be well sintered at only 870 °C and exhibits good microwave dielectric properties with a permittivity (εr) ˜21.9, a Qf ˜18,150 GHz (at 7.2 GHz) (Q = quality factor = 1/dielectric loss; f = resonant frequency), a TCF ˜ + 0.1 ppm/°C. The chemical compatibility with silver indicated that the Ca0.66Bi0.34Mo0.66V0.34O4 ceramic might be a good candidate for the LTCC applications.

Reconstructing past fire temperatures from ancient charcoal material

Charcoal abundance measurements are commonly used to estimate fire activity in palaeoecological studies; however, fire temperature is not directly measured. Reconstructing fire temperature is desirable because the ecological response to fire is, in part, a function of the temperature of the fire, e.g. crown fires >500 °C, slash and burn agriculture <400 °C. Here, we determine whether charcoal chemistry, as inferred from Fourier Transformed Infrared Spectroscopy (FTIR), is a reliable proxy for fire (combustion) temperature. We generated reference charcoal material from a grass species (Panicum capillare) and a woody species (Alnus glutinosa), prepared with three different laboratory treatments (untreated, water, and hydrogen peroxide), and heated to six temperatures (200–700 °C). We picked individual charcoal fragments from lake sediments deposited between ca. 1400 and 450 years ago to compare with the reference charcoal material. FTIR spectra were used to infer the chemical composition of both modern reference and ancient charcoal. The FTIR spectra of the datasets were analysed with model-based clustering.The inferred chemistry of the reference charcoal from the FTIR spectra was in broad agreement with previous studies, and the model-based clustering algorithms were able to distinguish clusters based on the temperature to which the material was heated. The FTIR spectra from the ancient charcoal fragments fell within the range of variability of the modern reference charcoal, allowing for successful classification of the fragments created by fires in the long distant past. We used a probability density function of each statistically significant cluster to infer combustion temperatures for the ancient charcoal fragments. Our results suggest that the use of FTIR analysis of charcoal can differentiate low (200 °C–300 °C), medium (400 °C–600 °C) and high (600 °C–700 °C) temperature fires. Our findings pave the way for generating a better understanding of the role of fire in Earth's system through time.

Ceramic properties of Uşak clay in comparison with Ukrainian clay

ABSTRACTIn this contribution, a new raw material, Uşak clay (Usc), was investigated in order to assess its potential for the ceramic industry by comparing it with a world reference ceramic material, a Ukrainian clay (Ukc). Mineralogical characterization (X-ray diffraction [XRD], scanning electron microscopy [SEM] and Fourier-transform infrared [FTIR] spectroscopy), quantitative chemical analysis (X-ray fluorescence [XRF]) and the thermal properties of Ukc and Usc samples were investigated. Additionally, Atterberg limits, particle-size distribution and cation exchange capacity of both samples were determined. Various technological properties of Ukc and Usc were determined in the temperature range 800–1430°C. The bending and compressive strengths, total linear shrinkage, colour, water absorption and unit-volume mass values were measured. The findings from these analyses show that kaolinite-dominated Ukc and quartz-dominated Usc samples differ from each other not only mineralogically, but also in terms of their chemical, physical and technological properties. The firing colour of Usc was determined as 84% white, and so this can be considered as a light firing clay. In addition, due to its low plasticity, Usc may be utilized to reduce both the plasticity of the ceramic materials and the viscosity in slip-casting applied ceramics. Furthermore, the melting temperature of 1300°C suggests that Usc cannot be classified as refractory. However, this property does suggest an economic value for Usc in terms of developing technological characteristics at lower firing temperatures.

Comparing ceramic technologies: The production of Terra Sigillata in Puteoli and in the Bay of Naples

Archaeological excavations carried out in the sites of Rione Terra and Via Fascione in Pozzuoli (ancient Puteoli, Italy) unearthed samples of Red Slip Ware attributed to Terra Sigillata from Puteoli and Produzione A della Baia di Napoli, which are among the most important ceramic classes produced in Campania region and circulating in the Roman Empire from the 1st century BCE.Archaeometric analyses performed on twenty-one samples highlighted that stylistic and typological features are connected to technological ones, permitting to clearly distinguish the two different productions. The samples of Terra Sigillata showed fine-grained ceramic bodies, high-CaO content (on average 15.6 wt%), abundant micro-fossils along with quartz, feldspar and micas. The thin red slip, present on both inner and outer surfaces, appears sintered and well preserved. Sintering degree and mineralogical assemblages suggest that the artefacts experienced high firing temperatures (often exceeding 900 °C). On the other hand, the Produzione A samples contain a lower micro-fossils amount and rare volcanic grains. The vessels are covered by a thinner and non-sintered red slip compared to that of Terra Sigillata. Mineralogy and microstructures of the ceramic bodies also suggested lower firing temperatures (850–900 °C). Then, the technology and the exploited clayey raw material were different in the production areas probably highlighting different cultural influences as well as different commercial paths. Finally, the comparison with available data on italic Red Slip Ware allowed us to find some key-parameter for discerning the most important production areas.

Processing of Dolomitic By-Products into Porous Restoration Binder

The goal of this work concerns the synthesis of a binder for restoration purposes that is physically and chemically compatible with dolomitic Roman cement, a historical binder used for the construction of significant architectural heritage objects in the 19thand 20thcenturies. Dolomitic marlstone, the traditional raw material of dolomitic Roman cement, is not being obtained anymore and it is also hard to achieve a constant chemical composition. To address these issues, the experimental synthesis of a low temperature hydraulic binder using locally sourced raw materials, namely dolomite flour and clay, was performed. The developed synthesis technology provides economic and ecological advantages compared to other similar materials, such as lime with pozzolan additive, lime and cement mixtures and magnesium oxychloride cements. The raw material, dolomite flour, is a by–product in the manufacturing process; furthermore, the low firing temperature (800 °C) reduces the power consumption required to obtain the binder.The aim of the work is determination of porosity-related physical characteristics of dolomitic binder that is synthesized by using manufacturing by-product – dolomite flour – as basic raw material to evaluate it’s suitability for restoration purposes.

Mineralogy and geochemical features of Foumban clay deposits (west Cameroon): genesis and potential applications

ABSTRACTFive clay deposits in Foumban, west Cameroon, were studied for their morphological, mineralogical and geochemical properties to determine their suitability for ceramics. The clays were examined with X-ray diffraction, X-ray fluorescence, thermal gravimetric analysis and Fourier-transform infrared spectroscopy. Field studies showed that a homogeneous clayey layer occurs at the upper part of the laterite cover of the interfluves, while the valleys are occupied by a clayey heterogeneous hydromorphic material. The clays are composed of kaolinite, illite, smectite and chlorite, associated with quartz, K-feldspars, plagioclase, goethite, traces of rutile and hematite. Geochemical analyses of these samples show a relatively large amount of SiO2(45–71%), Al2O3(14–31%) and relatively little Fe2O3(up to 11%), suggesting weathering of mainly granitic and rhyolitic parent rocks. The majority of these clays may be used in the production of structural ceramics such as bricks (refractory or not) and tiles. The relatively high proportion of the alkalis (K2O + Na2O; 6–8%) in some samples from Marom and Njindare areas might be responsible for the low firing temperatures. The abundance of smectite limits the application of some Koutaba and Marom clays for structural ceramics, while the high Fe2O3contents (&gt;8%) in some Bangourain clays indicate that some pre-treatment might be necessary prior to use.