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Abstract Chemical and mineralogical investigations of the FEBEX repository demonstration experiment after 18 years confirmed those reactions which were identified in previous large scale tests: Fe-corrosion, Mg-accumulation, cation exchange, and mineral dissolution/precipitation. These reactions were mostly restricted to the bentonite-heater contact. However, other processes were detected. Fe oxidation of carbon-containing steel was dominated by oxic corrosion and hydrolysis possibly through a similar Fischer-Tropsch synthesis reaction, leading to the monitored generation of H 2 , CO 2 and both reduced (alkanes, alkenes) and oxidized non-volatile (carboxylic acids) hydrocarbons, which are in partial equilibrium with CO 2 /carbonate under oxidation states highly reduced. Therefore, temperature, water, oxygen (due to no gas-tight conditions), and other oxidizing agents regulated the redox state and activities of all species involved in the bentonite barrier, being sulfates reduced to H 2 S and pyrite, Fe-oxides (hematite/goethite) to magnetite and siderite, and Fe(III)-bearing smectite to saponite and chlorite. These mineral phases were detected as main corrosion products. The dissolved Fe2+ ions generated by reduction of Fe-oxides diffused away forming surrounding greenish halos in the bentonite. Because air was not excluded, most of the corrosion was oxic but locally reducing conditions were established. Significant Mg accumulation was observed at the heater contact, which is related with the highest salinity values of the porewater (Na Mg Ca Cl water-type, 0.41 M ionic strength), the presence of saponite (trioctahedral Mg-smectite), brucite and Fe-rich chlorite; and a modification in the dehydroxylation temperature of the dioctahedral smectite clay mineral particles, together with the precipitation of carbonates and an increase in Ca/Mg at interlayer sites, Na being depleted. The mechanism for the structural clay mineral alteration seems to be Fe(III) structural reduction, rather than the C-steel heater/liner corrosion. Because Fe2+ cations are more stable in trans octahedral sites, rearrangements in crystal lattice seem to have formed cis-trans interstratifications favouring the migration of Mg to octahedral sites and the segregation of Mg2+ trioctahedral domains. Thus, both a solid-state transformation, producing high-charge/low charge layers similar to vermiculite ones; as well as dissolution-precipitation transformation, with the crystallization of a trioctahedral Mg-smectite (saponite), brucite and chlorite in localized zones of the bentonite barrier, seem to be inferred, depending probably on f (O 2), temperature, the amount of structural Fe(II) and Mg concentration in the pore water. The observed clay mineral transformations induced changes in some of the physico-chemical properties of the bentonite, decreasing the total cation exchange capacity and BET surface area. However, these modifications were restricted to the bentonite at close contact with the heater. The rest of bentonite from the FEBEX in situ test maintained its performance as an engineered barrier. Highlights • Iron and Mg-bentonite interactions at real conditions of a HLW repository system after 18 years of experiment. • Mg-accumulation at bentonite/heater interface with precipitation of brucite, saponite and Fe-rich chlorite. • Both solid-state and dissolution/precipitation transformations of smectite are observed. • High-charge interstratified clay minerals with a cis-trans vacant configuration were formed. • Fe reduction due to oxidation of reduced saturated hydrocarbons produced by C-steel heater corrosion and hydrolysis. [ABSTRACT FROM AUTHOR]

This paper presents results on the composition of Portland clinkers produced with non-conventional raw-materials and fuels, focusing on the distribution of selected trace elements. Clinkers produced with three different fuel compositions were sampled in an industrial plant, where all other parameters were kept unchanged. The fuels have chemical fingerprints, which are sulfur for petroleum coke and zinc for TDF (tire-derived fuel). Presence of carbonatite in the raw materials is indicated by high amounts of strontium and phosphorous. Electron microprobe data was used to determine occupation of structural site of both C3S and C2S, and the distribution of trace elements among clinker phases. Phosphorous occurs in similar proportions in C3S and C2S; while considering its modal abundance, C3S is its main reservoir in the clinker. Sulfur is preferentially partitioned toward C2S compared to C3S. Strontium substitutes for Ca2+ mainly in C2S and in non-silicatic phases, compared to C3S.

The present communication describes the synthesis of anti-slip enamel exhibiting glass-ceramic nature using new matte frits and raw materials. The glass-ceramic glazes obtained are characterized by various instrumental techniques (X-ray fluorescence (XRF), scanning electron microscopy (SEM), X-ray diffraction (XRD), mechanical profilometry and microhardness measurements) to elucidate the nature of the crystallized phases, their morphology, surface roughness and the finished tile microhardness. The quality of the glazed piece is evaluated by the regulations of chemical resistance, stain-resistance and slipperiness. The enamel obtained devitrifies in crystals of calcium and barium silicoaluminates. It complies with anti-slip and stain-resistance standards, because its surface roughness is similar to that of non-slip enamel. [ABSTRACT FROM AUTHOR]

The need of a concerted multi-disciplinary approach in the investigation of intermetallic systems and the role of thermochemistry are underlined. The activity carried out in the Author’s laboratory in the alloy thermodynamics is summarized. The different instruments (calorimeters) built in laboratory are briefly presented and their performance discussed. The results obtained in the measurement of the enthalpy of formation mainly of several rare earth alloys are described. The characteristics of the Eu and Yb thermochemistry and crystallochemistry are finally underlined.

The objective was to identify and characterize the mineral phases containing nickel in the San Felipe ore body located in Camaguey, Cuba. X-ray diffraction techniques, optical microscopy, scanning electron microscopy with energy dispersive analyzer and transmission electron microscopy with coupled EDX analyzer were used. It was determined that the main nickel bearing mineral phases in San Felipe were smectite, lizardite, chlorite, asbolite, goethite and maghemite. Within the group of smectites, the nontronite (ferric-magnesium smectite) accounts for approximately 65% in weight of the horizon ore bodies and it is the main mineralogical species containing nickel mineralization; it was also characterized from the crystal chemistry point of view. These results can be used to measure the industrial efficiency grade in the San Felipe future plant. [ABSTRACT FROM AUTHOR]

A ternary hexaerbium triacontacobalt enneakaidecasilicide, ErCo5Si3.17, crystallizes as a combination of disordered variants of the hexagonal UCo5Si3 ( P63/ m) and Yb6Co30P19 ( P) structure types and is closely related to the Sc6Co30Si19 and Ce6Rh30Si19 types. The Er, Co and three of the Si atoms occupy sites of m.. symmetry and a fourth Si atom occupies a site of .. symmetry. The environment of the Er atom is a 21-vertex pseudo-Frank-Kasper polyhedron. Trigonal prismatic coordination is observed for the Si atoms. The Co atoms are enclosed in heavily deformed cuboctahedra and 11-vertex polyhedra. Crystallochemistry analysis and the data from electronic structure calculations (TB-LMTO-ASA) suggest that the Er atoms form positively charged cations which compensate the negative charge of the [Co12Si9] m− polyanions. [ABSTRACT FROM AUTHOR]

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Light harvesting chalcogenide materials have strong potential applications for photovoltaic due, in part, to the ability of their structures to accommodate shift from the ideal stoichiometry. This study is devoted to the chemical and structural investigations of two specific series of materials, Cu(In, Ga)Se2 (CIGSe) and Cu2ZnSnS4 (CZTS). Both of them receive currently a strong incentive in the domain of thin film solar cells. On the basis of accurate chemical analyses, conventional powder and single-crystal X-ray diffraction, resonant X-ray scattering with synchrotron radiation the capacity of the chalcopyrite and kesterite structures of CIGSe and CZTS to accommodate deviations from the stoichiometry is discussed. Formally, the former is found to be more flexible than the latter even if this one can self adapt to copper-poor and copper-rich compositions without any structural change except in terms of the cation distributions. [ABSTRACT FROM AUTHOR]

Purpose: The aims of this study were to compare the crystal chemical properties of some commercial mineral trioxide aggregate (MTA) and Portland cements (PC) and to propose a new white MTA product. Methods: The samples (four MTA and two PC types) were analyzed by 1) optical microscopy; 2) laser granulometry; 3) X-ray diffraction and fluorescence; 4) scanning electron microscopy (SEM) and electron probe microanalysis (EPM) (wavelength-dispersive). Results: MTA and PC specimens yielded similar characteristics in their clinker component. The MTA-Angelus specimens displayed a composition overlapping the classical clinker composition (wt%) i.e. 25 silica, nine alumina and 66 lime. However, the bismite, present in large amounts (~15-19 wt%) in all MTA products, contained considerable and diffused heavy (toxic) metals as Pb and Mo, other than Bi. In the MTA clinkers the formation of Portlandite, at water-clinker interface, is favored by the smaller grain size of the MTA particles. However, this may also favor the diffusion of the toxic elements linked to Bi. Significance: In terms of bulk physico-chemical properties, the MTA products can be easily substituted by a fine-grained Portland clinker by adding a non-toxic radio-opaque component, for example, Ba-carbonate. [ABSTRACT FROM AUTHOR]

The crystalline structure of a new compound Rh(III) of (NH4)2[Rh(NO2)3(NH3)(µ-OH)]2 composition has been determined. The crystallographic characteristics are H16N10O14Rh2: a = 6.3963(2) Å, b = 9.3701(4) Å, c = 13.6646(5) Å, β = 102.266(1)°, V = 800.28(5) Å3, Z = 2, d calc = 2.432 g/cm3. The distance Rh...Rh in the dimer is 3.200 Å. [ABSTRACT FROM AUTHOR]

A geochemical study of pegmatitic micas from Minas Gerais State in Brazil was performed with an electron microprobe, in order to examine the variations of Rb, K, Al and F contents. It is observed a linear decreasing relationship between the [Rb/K] ratio of the micas and their contents in AlVI. The interpretation is based on the hypothesis that the partition coefficient CRb/Kmica/fl between fluid and mineral does not vary significantly as a function of temperature and pressure in the narrow conditions of crystallization of pegmatites. It is suggested that the relation: CRb/Kmica/fl=0.55×(5-[AlVI]) is of crystallochemical order. Micas with low contents in Al take higher contents in Rb because the potassic sites where Rb enters are larger. This relation gives another way of calculating the values [Rb/K] of the fluids knowing Rb, K, Al and Si in the micas. This crystallochemistry also allows us to foresee a direct correlation between Rb and F in the pegmatitic micas. To cite this article: J. Quéméneur et al., C. R. Geoscience 336 (2004). [Copyright &y& Elsevier]

A series of polycristalline samples of the type La1−xAxMnO3+δ (A=Na, K), quenched in air at 800 °C, have been analyzed by X-ray, sample density and average valence of Mn ions, in order to determine structure type defectiveness and its evolution vs. atomic fraction of Na and K. It is found that from crystallochemical point of view, both the series are highly similar. They represent solid solutions of rhombohedral symmetry and of the perovskite structure type, both extending slightly over xA∼0.25. Variation of the average valence of Mn ions in the series, confirms initial structure deficiency (2Δ) of the binary matrix to be of cationic type i.e. La(1−Δ)Mn(1−Δ)O3+Δ, partly compensated by the excess oxygen (Δ), the latter as presumably located in vacant positions of the metal sublattices. Within the domain of homogeneity, the solid solutions exhibit some anomalies at xNa∼0.138 and at xK∼0.147, both connected with a substantial change of the structure type defectiveness and clearly seen on xA variations of the (La=Mn)-site deficiency (Δ). The experimental sample densities indicate that the excess oxygen, present in the matrix, quickly disappears vs. lanthanum substituent (at xNa∼0.04 and at xK∼0.05), but the cationic deficiency persists in the series up to the concentrations of the anomalies given above where it vanishes. On further increase of sodium or potassium content, the crystal structure, being free of any defects, starts to exhibit an increasing level of oxygen deficiency Δoxyg=(3+2x−VMn)/2. [Copyright &y& Elsevier]