In 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.

A kaolin deposit from Mankon (northwest Cameroon) was prospected and studied for potential applications in ceramics. Six samples were investigated with X-ray diffraction (XRD), infrared (IR) spectroscopy and scanning electron microscopy (SEM) to determine the mineralogical composition and with X-ray fluorescence (XRF) to determine the chemical composition and properties for ceramic applications. The main minerals in the clays are kaolinite/halloysite and anatase associated with alunite, illite, gibbsite and maghemite. The kaolin samples have abundant organic matter (4–10%) and low absorption of methylene blue (0.2–2.5 meq/100 g), while SiO2 (33.28–56.31%) and Al2O3 (19.26–35.87%) are major oxides. The particle-size distribution derived from sieving and the hydrometer method indicates that 12–38% of the samples are in the <2 μm clay fraction. The clays have low to moderate plasticity (7–21%). One sample with K-feldspar and plagioclase displays the necessary properties for red ceramic products. SEM confirmed the occurence of halloysite in sample M9. The high kaolinite/halloysite content (64–97%), associated with low Fe2O3 content (0.5–1.4%) demonstrates that five samples are suitable raw materials for white firing industrial kaolin.

Clay minerals and organic matter occur frequently in fault zones. Their structural characteristics and their textural evolution are driven by several formation processes: (1) reaction by metasomatism from circulating fluids; (2) in situ evolution by diagenesis; and (3) neoformation due to deformation catalysis. Clay-mineral chemistry and precipitated solid organic matter may be used as indicators of fluid circulation in fault zones and to determine the maximum temperatures in these zones. In the present study, clay-mineral and organic-matter analyses of two major fault zones – the Adams-Tinui and Whakataki faults, Wairarapa, North Island, New Zealand – were investigated. The two faults analysed correspond to the soles of large imbricated thrust sheets formed during the onset of subduction beneath the North Island of New Zealand. The mineralogy of both fault zones is composed mainly of quartz, feldspars, calcite, chabazite and clay minerals such as illite-muscovite, kaolinite, chlorite and mixed-layer minerals such as chlorite-smectite and illite-smectite. The diagenesis and very-low-grade metamorphism of the sedimentary rock is determined by gradual changes of clay mineral ‘crystallinity’ (illite, chlorite, kaolinite), the use of a chlorite geothermometer and the reflectance of organic matter. It is concluded here that: (1) the established thermal grade is diagenesis; (2) tectonic strains affect the clay mineral ‘crystallinity’ in the fault zone; (3) there is a strong correlation between temperature determined by chlorite geothermometry and organic-matter reflectance; and (4) the duration and depth of burial as well as the pore-fluid chemistry are important factors affecting clay-mineral formation.

Iranian montmorillonite (MMT) was modified with hexadecyltrimethylammonium bromide (HDTB) and used as a nano-additive for the enhancement of the mechanical and anticorrosion properties of an epoxy coating. Infrared (IR) spectroscopy, thermo-gravimetric analysis (TGA), transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis indicated that HDTB reacted with MMT (with 97% yield) and increased the d001 spacing of MMT from 1.27 to 3.92 nm. Some 1, 3 and 5 wt.% of organically modified montmorillonite (OMMT) were added to the epoxy coating formulation. XRD and TEM/image processing analysis showed that the extent of intercalation/exfoliation of OMMT was substantially greater than that of MMT. Dynamic mechanical analysis showed that the glass transition temperature and storage modulus increased significantly with the addition of OMMT. Electrochemical impedance spectroscopy (EIS) and salt spray/image processing results revealed that addition of OMMT to the epoxy coating significantly increased the corrosion resistance of the coating compared to neat and MMT-containing epoxy coatings. The optimum concentration of OMMT was 3 wt.%. At this concentration, the mechanical and anticorrosion properties were greatly superior to those of neat and MMT-containing epoxy coatings.

Second-century CE (common era) household pottery sherds found in the city of Napoca (present day Cluj-Napoca, Romania) in Roman Dacia were investigated by polarized light optical microscopy, X-ray powder diffraction, Fourier-transform infrared spectroscopy and cold field emission scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy to obtain information on technology, raw materials and site of production. Compositionally, all samples are similar with comparable fine and semi-fine microstructures and oriented microtextures. Optically, there is a gradual transition from microcrystalline to an amorphous illitic-muscovitic matrix. The small aplastic inclusions are mostly quartz and feldspar. Fine-grained carbonate aggregates are distributed inhomogeneously in the ceramic body. Well-preserved Middle Miocene foraminifera tests are characteristic of the ceramics. The gradual thermal changes of the matrix and the newly formed phases upon firing, such as ‘ceramic melilite’, Fe-gehlenite, clinopyroxene, glass, hematite and some maghemite support inferences regarding the technological constraints in producing the pottery. The firing took place in a mostly oxidizing atmosphere and the temperature extended from at least 850°C to >900°C. The Middle Miocene marly clay from the area surrounding the site shows similar mineralogical and micropalaeontological contents to those of the ceramic specimens and is the best candidate for the raw material used for local production of the Roman pottery.

In order to improve the dispersibility of halloysite nanotubes (HNTs) in polytetrafluoroethylene (PTFE), the modification of HNT surfaces was studied with three types of modifiers (polymethyl methacrylate [PMMA], sodium dodecyl sulfate [SDS] and carboxylic acid). The modified HNTs were characterized by Fourier-transform infrared (FTIR) spectrometry, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and contact angle measurements. The HNTs were used to reinforce the mechanical properties of PTFE. The mechanical results indicated that the tensile strength of the modified HNT-filled PTFE nanocomposites (F-HNT/PTFE) improved to an acceptable degree and Young's modulus increased significantly. The tribological results showed that the wear rate of F-HNT/PTFE decreased by 21–82 and 9–40 times compared to pure PTFE and the pristine F-HNT/PTFE, respectively.

The aim of this research was to determine the temperature of kaolin calcination in order to obtain an intermediate product (metakaolin) for the synthesis of geopolymers with potential application as self-supporting zeolitic membranes. The products obtained were analysed with X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The structural analysis of the metakaolins obtained suggested that the optimal temperature for the proposed application is 700°C. After alkali activation of metakaolin, it is possible to obtain zeolite A and hydroxysodalite. The factors analysed, determining the type and quantity of crystalline phases, were activation temperature and concentration of sodium hydroxide solution (activator). The largest amounts of zeolites were obtained by alkali activation with 9 mol/dm3 NaOH solution at 70°C.

Kaolin and diatomite are abundant and widely available geological materials that may immobilize or stabilize functional chemical species on their surfaces for various applications. Acid-treated kaolin and diatomite were intercalated with photocatalyst Ag-TiO2 nanoparticles using the sol–gel technique to prepare nanocomposite ceramic materials. The nanocomposites were sintered between 900°C and 1000°C to induce thermal reactions and to enhance nanoparticle–substrate attachment. Chemical and thermal characterizations of the acid-treated materials and intercalated nanocomposites were performed with energy-dispersive X-ray (EDX) analysis and differential scanning calorimetry (DSC), respectively. The Brunauer–Emmett–Teller (BET)-specific surface area and scanning electron microscopy (SEM) were employed for physical and microstructural characterization of the nanocomposites, respectively. Morphological studies revealed a uniform distribution of Ag-TiO2 nanocrystallites in pores and on mineral particle surfaces. The BET analysis showed remarkable surface and grain modification by sintering. Decreases in the BET-specific surface area were observed for the sintered ceramic nanocomposite, Ag-TiO2-kaolin (20.244 to 5.446 m2/g) and Ag-TiO2-diatomite (19.582 to 10.148 m2/g).

This paper describes a detailed petrographic and isotopic study of hypabyssal sheets of quartz-syenite that represent the ultimate differentiation product of the oceanite alkaline magmatic reservoir of the Piton des Neiges stratovolcano (Réunion Island). Clay minerals of the corrensite to chlorite series crystallized during the late-magmatic activity, with quartz, carbonates and accessory minerals from juvenile fluids filling the primary porosity of the quartz-syenite. It is proposed that a double chemical transfer occurred at the end of the crystallization process: degassing of the exsolved CO2-rich and SiO2-rich fluid from the magmatic chamber through the porous quartz-syenite and diffusion of Al, Fe and Mg from the intruded basalts affected by the juvenile fluids towards the primary porosity of the quartz-syenite, feeding the crystallization of late-magmatic clays in the residual primary pores after quartz and carbonate deposition. This process may be generalized to alkaline plutonism, as well as to the primitive crusts of terrestrial planets, and may be the first source of clays in early planets.

Despite many reviews and original articles, the actual crystal structure of tubular halloysites remains unclear. Analysis of the structural features of defect-free kaolinite, refined by Bish & von Dreele (1989), shows that the ordered 1Tc kaolinite structure can be described equally well by the orthogonal layer cell {a0, b0, γ0} (γ0 = 90°) or by two enantiomorphic oblique layer cells {a1, b1, γ1} and {a2, b2, γ2}, related to each other by a mirror plane. To simulate diffraction effects for tubular halloysite, the parameters and atomic coordinates of the orthogonal layer unit cell and the layer-displacement vectors t1 and t2 responsible for formation of the kaolinite enantiomorphs were deduced by transformation of the parameters of the defect-free kaolinite refined by Bish & von Dreele (1989). Modelling X-ray diffraction patterns show that the samples consist of either single, two or three phases, with the number and their structural features depending on the morphology of the particles. Samples formed of prismatic particles consist of halloysite-like structure (HLS), kaolinite-like structure (KLS) and halloysite cylindrical structure (HCS) phases occurring in various proportions. Samples of proper cylindrical tubes consist of a single HCS phase, whilst samples formed by particles having morphologies intermediate between proper cylindrical and well-developed prismatic forms consist of the KLS and HCS phases. The KLS phase is comparable to low-ordered platy kaolinite with identical unit-cell parameters, layer-displacement vectors and arbitrary stacking faults, except that the layer displacements are not random as in kaolinite, but are distributed at R = 1 such that t1 and t2 displacements have a strong tendency to be segregated. Structural parameters describing the HLS and KLS phases are identical, but in the HLS phase there is a strong tendency to the regular alternation of the t1 and t2 displacements, and the HLS phases do not contain arbitrary stacking faults. A characteristic feature of the three-phase prismatic samples is that the stacking of the layers along the c* axis is periodic and the layer thicknesses are similar to those of platy kaolinite. In contrast, in the KLS phase formed in samples with particles of intermediate morphologies, the hydrated 10 and 7.25 Å layers are interstratified. The relationship between the structural and morphological features of the coexisting phases suggests a sequence of phase formation from the centre to the surface of halloysite tubes that progresses from the HCS to the HLS via the KLS phase. The results of this study demonstrate that all kaolinite and halloysite (7 Å) varieties are built by the same fundamental structural units.

Clay-mineral type and content, bulk mineralogical composition and alteration of bentonite are very important factors for the ultra-long-term stabilization of barriers and backfills in radioactive waste disposal. This study investigates the effects of clay-mineral type and content on the swelling characteristics and permeability of bentonite–sand mixtures with clay minerals using one-dimensional swelling-pressure and constant-pressure permeability tests. The hydraulic conductivity of bentonite–sand–clay mineral mixtures increased with increasing content of non-swelling alteration products of montmorillonite. Furthermore, hydraulic conductivity was comparable to that determined with the Kozeny–Carman equation for a specific surface area, suggesting that hydraulic conductivity may be estimated based on the abundance of expected alteration products of montmorillonite. This study provides a basis for evaluation of the hydraulic conductivity of bentonite–sand mixtures with known quantities of expected alteration products of montmorillonite.

In deep geological repositories, compacted bentonites have been proposed for use as barrier materials for isolating nuclear waste. The prevailing thermo-hydro-mechanical boundary conditions in the repositories may affect the swelling capacity and permeability of the compacted bentonites. In this study, the effect of preliminary desiccation on the subsequent hydro-mechanical behaviour (swelling pressure and hydraulic conductivity) of compacted Calcigel bentonite was investigated experimentally at 22°C and 80°C. In the first stage of the test, the compacted specimens were subjected to suction-controlled desiccation at 22°C and 80°C using the vapour-equilibrium technique. After the water content reached equilibrium at a given suction, the axial, radial and volumetric shrinkage strains were measured. Afterwards, constant-volume swelling-pressure tests were performed on the desiccated specimens (second test stage) by saturating the dried specimens with deionized water at 22°C and 80°C. At the end of the swelling-pressure test, the hydraulic conductivities of four saturated specimens were measured at each temperature. The volumetric shrinkage strain of the compacted bentonite during desiccation is controlled by suction instead of temperature. In addition, the preliminary desiccation increases both the swelling pressure and hydraulic conductivity of compacted bentonite, particularly if compacted bentonite undergoes extreme desiccation at an applied suction of >700 MPa.

The FEBEX experiment, a full-scale, high-level radioactive waste repository test, ran for ~18 years and hence is the longest-running disposal test to date. The test consisted of a heater emplaced in an envelope of compacted bentonite at the Grimsel test site, Switzerland. The water content of the bentonite was somewhat lower near the heater and increased towards the granite. This phenomenon probably led to gradients in the exchangeable cation population at various locations within the bentonite buffer. The cement (shotcrete) bentonite interface of one block was characterized by a thin (0.1–1.0 mm) reaction zone in which bentonite constituents, carbonates and sulfates occurred. Cation exchange and a slight decrease of the cation exchange capacity were observed near the heater. Oxic corrosion was observed predominantly at the bentonite/steel liner interfaces, pointing towards a role of air entrapped between the liner and heater during emplacement. At the liner surface, intimate intergrowth of bentonite constituents, metal and corrosion products was observed. At the face of the heater, the bentonite blocks were in direct contact with the heater surface without any signs of metal corrosion. Instead, a significant increase in the Mg content was recorded, which is in agreement with previous large-scale disposal tests. The FEBEX experiment proved that the Mg increase and corrosion were independent processes. The increase in Mg may be explained by the formation of trioctahedral domains or the precipitation of neoformed silicates. For the first time, however, brucite was identified as an additional phase that formed at the metal/bentonite interface, pointing towards a special role for Mg mobility in the bentonite barrier.