X-ray Electron Microprobe Research Articles

The Gd-Al-Si Isothermal Section at 500 °C

Phase relations in the Gd-Al-Si system have been established and experimentally studied at 500 °C. The system has been experimentally investigated by mean of scanning electron microscopy (SEM), electron microprobe analysis (EDXS) and x-ray powder diffraction (XRPD). The existence of four ternary compounds has been confirmed: τ1 GdAl2Si2 (hP5-CaAl2Si2 type), τ2 GdAlSi (tI12-αThSi2 type), τ3 Gd4AlSi3 (oC8-CrB type) and τ4 Gd6Al3Si (tI80-Tb6Al3Si type). Three ternary compounds show a composition homogeneity range: τ2 dissolves Si up to about 37 at.%, τ3 shows an homogeneity range (towards the GdSi compound) to 45 at.% Si concentration value, finally the τ4 phase dissolves 5 at.% of Si. All binary compounds dissolve the third element, except for GdAl The ternary system is characterized by 16 three-phase fields, and 16 two-phase fields.

Inhibition Performance of Cetyltrimethylammonium Bromide against Reinforcing Steel Corrosion in Simulated Concrete Pore Solutions

Cetyltrimethylammonium bromide (CTMAB) surfactant was employed as a corrosion inhibitor for reinforcing steel in this work. The corrosion behavior of the steel in the simulated polluted concrete pore (SPCP) solution with 0.1 M NaCl and pH11.00 and the corrosion inhibition effect of CTMAB were investigated by electrochemical impedance spectroscopy and polarization curve measurements. The morphologies and compositions of the steel surface were characterized by Electron Micro-Probe Analyzer and X-ray photoelectron spectroscopy. The results showed that severe pitting corrosion of the steel in the SPCP solution took place. CTMAB with an appropriate concentration could effectively control the steel corrosion. The inhibition efficiency of CTMAB reached 87.6% at the optimum concentration of 0.005 M. CTMAB acted as an adsorption type inhibitor and improved the corrosion resistance of the steel by forming an adsorption film on the steel surface.

The discreditation of girdite

AbstractGirdite, a mineral described byWilliams in 1979 from the Grand Central mine, Tombstone, Cochise County, Arizona, USA, has been re-examined by powder X-ray diffraction, single-crystal X-ray diffraction and electron microprobe. Type material from The Natural History Museum, London and the United States National Museum of Natural History (Smithsonian Institution) was examined. The original description of girdite is shown to have been based upon data obtained from at least two and possibly three different phases, one corresponding to ottoite and another probably corresponding to oboyerite, although the latter itself appears to be a mixture. The discreditation of girdite as a valid mineral species has been approved by the IMA-CNMNC, Proposal 16-G.

Textural and compositional evolution of Au-hosting Fe-S-As minerals at the Axi epithermal gold deposit, Western Tianshan, NW China

The Axi deposit is the largest low-sulfidation epithermal gold deposit in Chinese Western Tianshan, Central Asian Orogenic Belt. In this contribution, combined petrological observations, electron microprobe analysis (EMPA) and X-ray backscattered electron images (BSE) have been conducted on Fe-S-As minerals to reveal their textural and compositional evolution. Pyrite and arsenopyrite are ubiquitous. Their texture and composition show gradual changes with time. Four generations of pyrite can be identified, named Py1, Py2, Py3 and Py4 from early to late. The coarse-grained, euhedral to subhedral Py1 (mostly 100–300μm) from the quartz-chalcedony stage is the earliest, and predates gold mineralization. Sometimes they contain silicate and arsenopyrite (Apy1) inclusions. Compositionally, they are enriched in Pb (up to 0.60wt%), but depleted in As (0.06–7.61wt%, mostly <0.30wt%) and Au (0.01wt%–0.25wt%, mostly <0.10wt%). Subhedral to anhedral Py2 grains (50–1000μm) coexist with other sulfides such as chalcopyrite, sphalerite, galena and tetrahedrite in the quartz-polymetallic sulfides stage. They are unusually rich in Au (with a mean value of 0.06wt%), Ag (with a mean value of 0.04wt%), Cu (with a mean value of 0.21wt%) and As (with a mean value of 3.06wt%), implying a syn-mineralization feature. Subsequent Py3 occurs as very fine-grained disseminations of euhedral crystals (10–50μm) in quartz-polymetallic sulfides stage and carbonate-quartz stage. They display clear oscillatory zoning and contain arsenopyrite (Apy3), sphalerite and Sb-Te mineral inclusions. Their Au content vary greatly from 0.02wt% to 1.02wt%, with corresponding As content varying from 0.07wt% to 8.28wt%. The post-mineralization Py4 crystals (30–5000μm) mainly occur as foliated, sheaf, or radiaxial aggregates in carbonate-quartz stage. They have the lowest Au (with a mean value of 0.04wt%), As (with a mean value of 0.32wt%), Co (with a mean value of 0.04wt%) and Ni (with a mean value of 0.04wt%) concentrations, although dramatically high S contents (with a mean value of 52.72wt%). Correspondingly, there are three generations of arsenopyrite: Apy1 (20–50μm) and Apy3 (3–15μm) mainly occur as inclusions in Py1 and Py3, respectively, whereas the latest Apy4 (<5–60μm) can occur either as serrated grains surrounding Py4 or overgrowth Py1 and Py3, or as individual euhedral to sub-euhedral grains. They also contain considerable, but much higher Au contents than pyrite, with the values of 0.6wt%–1.1wt% for Apy1, 0.18wt%–1.32wt% for Apy3 and 0.50wt%–1.75wt% for Apy4, respectively. Besides, they also contain considerable amounts of trace elements such as Co, Zn, Pb, Sb and Se. Arsenopyrite geothermometer constrains the ore-forming temperature responsible for Apy3 formation to 325–385°C. Our result reveals that significant invisible gold accommodated by sulfides is the main cause of refractory ores at the Axi deposit.

Synthesis, structure formation, and thermal expansion of A+M2+MgE4+(PO4)3

The compounds AMMgE(PO4)3 (A = Na, K, Rb, Cs; M = Sr, Pb, Ba; E = Ti, Zr) were synthesized by the sol–gel procedure followed by heat treatment and studied by X-ray diffraction, differential thermal and electron microprobe analysis, and IR spectroscopy. The phosphates crystallize in the kosnarite (KZr2(PO4)3, space group $$R\bar 3$$ ) and langbeinite (K2Mg2(SO4)3, space group P213) structural types. The structure of KPbMgTi(PO4)3 was refined by full-profile analysis (space group P213, Z = 4, a = 9.8540(3) A, V = 956.83(4) A3). The structure is formed by a framework of vertex-sharing MgO6 and TiO6 octahedra and PO4 tetrahedra. The K and Pb atoms fully occupy the extra-framework cavities and are coordinated to nine oxygen atoms. A variable-temperature X-ray diffraction study of KPbMgTi(PO4)3 showed that the compound expands isotropically and refer to medium-expansion class (linear thermal expansion coefficients α a = α b = α c = 8 × 10–6°C–1). The number of stretching and bending modes of the PO4 tetrahedron observed in the IR spectra is in agreement with that predicted by the factor group analysis of vibrations for space groups $$R\bar 3$$ and P213. A structural transition from the cubic langbeinite to the rhombohedral kosnarite was found for CsSrMgZr(PO4)3. In the morphotropic series of ASrMgZr(PO4)3 (A = Na, K, Rb, Cs) the kosnarite–langbeinite transition occurs upon the Na → K replacement. The effect of the sizes and electronegativities of cations combined in AMMgE(PO4)3 on the change of the structural type was analyzed.

Tracing the fluid evolution of the Kiruna iron oxide apatite deposits using zircon, monazite, and whole rock trace elements and isotopic studies

The ore genesis of the Paleoproterozoic iron oxide apatite deposits in the vicinity of Kiruna in northern Sweden is poorly understood, despite a century-long mining history and 2500Mt of iron ore with grades of 30 to 70wt% Fe produced in the region to date. Zircon grains from the ore, recently dated at ca. 1874Ma, show very different appearances compared to zircon from surrounding host rocks (ca. 1880Ma) and related intrusions (ca. 1880 and ca. 1874Ma), particularly an inclusion-rich rim. In contrast, zircon from the host rocks, and a proximal granite intrusion, exhibit typical igneous growth zoning. Electron microprobe results show near stoichiometric composition for Zr, Si, and Hf in the host rock zircon grains. The ore zircon crystals have low analytical totals with significant concentrations of Ca, Fe, Y, and P and infrared spectroscopy showed several weight percent of water. These ore zircon grains further show Fe-rich inclusions, zones and/or veins in elemental X-ray maps, and light rare earth elements (LREE) enrichment. Transmission electron microscopy (TEM) shows that the LREE are not due to micro- or nano-inclusions in the zircon, but are likely hosted as LREE oxides in amorphous regions of the grains. Based on these characteristics, the rims on ore zircon grains are interpreted to be of hydrothermal origin. Uranium-Pb in monazite from the ore, measured by SIMS, suggests a secondary event influencing the area at ca. 1624Ma, a period of known geologic activity in Fennoscandia. Electron microprobe X-ray mapping of these monazite grains shows no zoning and relatively low U and Th concentrations.Stark contrasts are visible between the ore (depleted mantle influence) and host rocks (crustal influence) in the whole rock Lu-Hf and Sm-Nd data. The depleted mantle signature of the ore could be related to the Kiruna greenstone group as a potential source region for the iron. The Sm-Nd isotopic composition of monazite from the ore shows a crustal influence, and indicates that the younger event has not disturbed the whole rock Sm-Nd signature of the ore. The hydrothermal nature of the ore zircon grains and the isotopic signatures point to a hydrothermal influence on the ore formation, with a high temperature magmatic fluid related to the intrusions as most likely heat and fluid source.

Deposition of carbon inside gaps of castellated tungsten blocks with intrinsic misalignment

When PFCs have castellated structure, co-deposition of fuel inside gaps between castellated blocks is an important issue. Four different shapes of castellated tungsten blocks were fabricated to study corresponding issues in KSTAR: Conventional “basic” rectangular shape, single chamfer leading edge, double-chamfer and rounded edge, with two different poloidal gap distances of 0.5mm and 1.0mm. These tungsten blocks were exposed plasma of L- and H-mode discharges during a whole campaign in 2014. The blocks were taken out from the vacuum vessel after the campaign. Gap deposition was analyzed by Electron Probe X-ray Micro Analyzer (EPMA) to obtain carbon surface density (atoms/cm2), and by Raman spectroscopy to identify chemical bonding structure of carbon deposits in gaps. The carbon surface density in toroidal and poloidal gaps was in a range from 0.5 × 1015 atom/cm2 up to 6.7 × 1015 atom/cm2. At the gap entrance, contribution of ions is 6.0–6.7 × 1015 atom/cm2, decreased down to 1.0 × 1015 atom/cm2 at a depth of 0.5mm, and remains constant afterwards. The contribution of charge exchange neutral is about 3.0 × 1015atom/cm2 at the gap entrance, and then gradually decreases as a function of distance from the entrance. Deposition in 1.0mm wide gaps show much larger deposition patterns and that particles have reached much deeper inside the gap. Raman spectra show that the intensity ratio I(D)/I(G) decreases from top to the depth of 5mm indicating the increase of hydrogen contents.

Microstructure, mechanical properties and friction behavior of magnetron-sputtered V-C coatings

This study describes reciprocating sliding friction experiments of three types of magnetron-sputtered vanadium carbide/amorphous carbon nanocomposite coatings, VC1−x/a-C, against alumina counterparts under unlubricated conditions. It links micro- to macroscale tribology in order to provide a better understanding of the sliding mechanisms of these nanocomposite coatings with varying constitution and microstructure (i.e. by varying the C/V concentration ratio between 1.2 and 2.9). Correspondingly, the volume fraction of the amorphous carbon phase (a-C) increases with increasing the carbon content as shown by electron microprobe studies, X-ray diffraction and Raman spectroscopy; simultaneously, the volume fraction of nanocrystalline vanadium carbide (VC1−x) decreases, and the crystallite size and crystallinity of the thin films decrease with increasing carbon content. These constitution and microstructure changes have an impact both on the mechanical and the tribological properties of the coatings. Mechanical properties characterization shows that the indentation hardness (H) and the reduced modulus (Er) of the coatings decrease with increasing the carbon concentration (i.e. H ranges between 15 and 33GPa and Er ranges between 239 and 391GPa for the low and high vanadium concentration respectively). A similar behavior was also observed with the results on the critical load of failure obtained from scratch tests, where the coatings with the highest vanadium concentration exhibits higher critical load of failure and thus, better coating adhesion. However, reciprocating micro- and macroscale tribological tests performed at a relative humidity level of 45±5% (i.e. normal load in the microtribological experiments is between 100mN and 1N and for the macroscale tribometry the normal load is 20N) reveal higher friction values and increased wear with the high vanadium content coatings. This sliding behavior is attributed to differences in the third body formation (i.e. carbon based transfer- and tribo-film) and velocity accommodation modes, which are analyzed ex situ by means of X-ray photoelectron spectroscopy (XPS), micro-Raman spectroscopy and atomic force microscopy.

Synthesis, structure and thermal expansion of the phosphates M0.5+x M′ x Zr2−x (PO4)3 (M, M′–metals in oxidation state +2)

Abstract The phosphates M0.5+x M′ x Zr2−x (PO4)3 (M–Ca, Mn, Co, Sr, Cd, Ba, Pb; M′–Mg, Mn, Co) were synthesized by sol-gel method with the following thermal treatment of reaction mixtures. X-ray diffraction, IR spectroscopy and electron microprobe analysis showed that the obtained phosphates crystallized in Sc2(WO4)3 (SW) and NaZr2(PO4)3 (NZP) structural types. Both types of crystal structures are based on a framework comprised of octahedra and tetrahedra, the difference between them is fragments orientation. Thermal expansion of the phosphates was studied in the temperature range 20–800°C. Some compounds were found to belong to low-expanding materials (αav ~2·10−6°C−1).

The 500 °C isothermal section of the Tb–Al–Si system and thermal behavior of selected Al-rich alloys

Phase relationships in the Tb–Al–Si system have been established and experimentally studied at 500 °C. The main experimental techniques used were scanning electron microscopy, electron microprobe analysis and X-ray powder diffraction. Some samples have been analyzed by differential thermal analysis. Six ternary compounds form in the system: the five ternary structures τ1-TbAl2Si2, τ2-Tb2Al3Si2, τ3-TbAlSi, τ5-TbAl0.15Si0.85 and τ6-Tb6Al3Si have been confirmed, while the compound τ4 (Tb2AlSi2, crystal structure oI10-W2CoB2) was not previously known in the literature for the Tb–Al–Si system, but its formation was known in other R–Al–Si (R: Dy,Ho,Er,Tm) systems. The two ternary phases τ4-Tb2AlSi2 and τ5-TbAl0.15Si0.85 show a homogeneity range, at constant Tb content. A number of boundary binary phases dissolve the third element, at 500 °C, forming ternary solid solutions extending into the ternary field: Tb(Al1−xSix)3 (0 ≤ x ≤ 0.13), Tb(Al1−xSix)2 (0 ≤ x ≤ 0.02), Tb5(AlxSi1−x)3 (0 ≤ x ≤ 0.08), Tb5(AlxSi1−x)4 (0 ≤ x ≤ 0.10), Tb(AlxSi1−x) (0 ≤ x ≤ 0.10), Tb(AlxSi1−x)2-b (0 ≤ x ≤ 0.24) and Tb(AlxSi1−x)2−a (0 ≤ x ≤ 0.15). The Al and Si richest part of the system is characterized by the coexistence of three phases (Al), (Si) and TbAl2Si2 (τ1); this behavior is common to all the known R–Al–Si phase diagrams. The phases are involved in the ternary eutectic equilibrium L ⇄ (Al) + (Si) + TbAl2Si2 close to the binary eutectic point of the Al–Si binary system. Experimental measurements confirm the ternary eutectic reaction at a temperature of 565 °C.

Exploratory Studies of Substitutions In the Tetrahedrite/Tennantite–Goldfieldite Solid Solution

Abstract Phases on the Fe-tetrahedrite–goldfieldite and Fe-tennantite–goldfieldite joins were synthesized from high purity elements in evacuated silica glass tubes at 450 °C and analyzed using electron microprobe analysis and X-ray powder diffraction. The synthetic studies confirm that the compositions on these joins are determined by a (formal) interplay of the Fe 3+ + Cu + ↔ 2 Fe 2+ , Cu + + Te 4+ ↔ Fe 2+ + (Sb,As) 3+ , Cu + + 2Te 4+ ↔ Fe 3+ + 2(Sb,As) 3+ , and Cu + + Te 4+ ↔ Cu 2+ + (Sb,As) 3+ substitutions, and also for the region close to Te = 2 apfu by □ + Te 4+ ↔ Cu + + Sb 3+ . The latter exchange determines the Te-tennantite/tetrahedrite–goldfieldite join. For the region of goldfieldite just above and below 2 Te atoms pfu , the latter exchange is modified by the Fe n + ↔ n Cu + exchange. The 2Fe 2+ ↔ Fe 3+ + Cu + exchange causes an arc-like retreat of the composition field away from the linear Cu + + Te 4+ ↔ Fe 2+ + (Sb,As) 3+ boundary. Incomplete elimination of Fe, compensated by early onset of Cu vacancies, results in a gradual transition between the region of tellurian td/tn and goldfieldite sensu stricto . This variety of substitution and omission mechanisms determines the proportions of alternative endmembers and intermediate members: Cu 10 Fe 2+ 2 (Sb,As) 4 S 13 , Cu 11 Fe 3+ (Sb,As) 4 S 13 , Cu 12 (Sb,As) 4 S 13 , Cu 12 Te 2 (Sb,As) 2 S 13 , and Cu 10 Te 4 S 13 , plus a measure of the Fe n + ↔ n Cu + exchange. Natural goldfieldite conforms with the synthesis results in its compositional extent. The natural data are mostly not good or complete enough to examine the compositional details suggested here because the calculations described above are very sensitive to the quality of the analyses.

Microstructure Evolution During Stainless Steel-Copper Vacuum Brazing with a Ag/Cu/Pd Filler Alloy: Effect of Nickel Plating

Vacuum brazing of stainless steel and copper plates was done using a silver-based filler alloy. In one set of experiments, around 30-µm-thick nickel coatings were electrochemically applied on stainless steel plates before carrying out the brazing runs and its effect in making changes in the braze-zone microstructure was studied. For brazing temperature of 830 °C, scanning electron microscopy examination of the braze-zone revealed that relatively sound joints were obtained when brazing was done with nickel-coated stainless steel than with uncoated one. However, when brazing of nickel-coated stainless steel and copper plates was done at 860 °C, a wide crack appeared in the braze-zone adjacent to copper side. Energy-dispersive x-ray analysis and electron microprobe analysis confirmed that at higher temperature, the diffusion of Cu atoms from copper plate towards the braze-zone was faster than that of Ni atoms from nickel coating. Helium leak rate of the order 10−11 Pa m3/s was obtained for the crack-free joint, whereas this value was higher than 10−4 Pa m3/s for the joint having crack. The shear strength of the joint was found to decrease considerably due to the presence of crack.

Neutron diffraction of Cu–Zn–Sn ternary alloys: non-invasive assessment of the compositions of historical bronze/brass copper ternary alloys

Neutron diffraction can be used as a tool for the characterization of metal materials in a totally non-invasive mode. In binary alloys with two elements in solid solution, crystallographic structure analysis provides information on the overall element compositions of the metal, based on the linear relationship between elemental fractions and lattice parameters known as Vegard's rule. However, for ternary solid-solution alloys the derivation of the overall metal composition is not straightforward because the problem is mathematically underdetermined. A number of artificially produced samples in the ternary system Cu–Zn–Sn, widely used in antiquity for gunmetal, were investigated by time-of-flight neutron diffraction, inductively coupled plasma mass spectroscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy and electron microprobe analysis. The multi-analysis approach allows definition of the limits and capabilities of neutron diffraction for obtaining the overall composition of a small sample set of ternary alloys, and thus moves the methodical approach a step forward even though it is applicable to the present sample set only. A relation showing an increasing Cu and Sn fraction counterbalanced by decreasing Zn content is presented, which allows the determination of the δ-phase composition from a lattice parameter measurement. Furthermore, the observed Zn loss up to 1.8 wt% for each melting step is of significance for the reconstruction of ancient technologies.

Raman spectroscopy and the inversion degree of natural Cr-bearing spinels

Natural Cr-spinels previously characterized by X-ray single-crystal diffraction and electron microprobe have been analyzed by Raman spectroscopy. The results we report show that there is a strong correlation between the Cr/(Cr+Al) ratio (Cr#) and the A 1g mode for the studied spinels. A strong correlation of this mode with Mg/(Mg+Fe 2+ ) (Mg#) can be seen only for spinels with Mg# higher than 0.60. Other modes can increase, decrease or disappear depending on the Cr#. Among the spinels with low Cr# it is possible to define their order/disorder degree. In fact, spinels with an inversion degree lower than 0.14 show an E g mode at about 400–410 cm −1 , while spinels with Cr# higher than 0.20 register the appearance of a peak in the region 150–200 cm −1 , while other peaks are substituted by smooth curves. The results show that the use of Raman applied to spinel in provenance studies cannot yield a 100% confidence because of the uncertainties in the relation between Mg# and the different modes.

Chromium influence on Mg-Al intracrystalline exchange in spinels and geothermometric implications

Flux-grown spinel crystals belonging to the MgAl 2 O 4 -MgCr 2 O 4 spinel series were investigated to reveal the effects of Cr substituting for Al on cation distribution and their influence on Mg-Al intra-crystalline exchange. Samples were structurally and chemically characterized by single-crystal X-ray diffraction and electron microprobe, and cation distribution was obtained with a tested optimization model for site populations. The results evidenced that the contribution of the tetrahedral bond distance to the unit-cell parameter is smaller than that of the octahedral bond distance, which is driven by the substitution of Cr for Al. Moreover, the influence that Cr exerts on Mg-Al order-disorder intersite exchange is non-linear along the whole series. The comparison between the cation distributions derived from crystal-chemical data and the O’Neill-Navrotsky thermodynamic model (with α Mg-Al = 23 kJ/mol and β Mg-Al = 13 kJ/mol) shows large discrepancies, which can be reconciled assuming α Mg-Al values variable from 23 to 100 kJ/mol as a function of Cr. This suggests that, irrespective of temperature, the Al ordering at the octahedrally coordinated site increases with increasing Cr substitution for Al. The geothermometric implications of the present study point out that closure temperatures, calculated from a well-tested intersite geothermometer, are reliable for spinels with magnesiochromite component smaller than 85%, i.e., Cr/(Cr+Al)

Clay minerals from the Arkitsa fault gouge zone, in Central Greece, and implications for fluid flow

Clay minerals in shallow fault rocks are increasingly recognized as key to the mechanical and seismogenic behavior of faults and fluid flow circulation within the fault core and the surrounding damage zone. We therefore studied faultgouge mineralogy from samples derived from the ENE-trending Arkitsa fault zone, in east-central Greece, in order to testify if the fault is acting as a channel for fluid flow and whether the conditions that characterize the flow can be identified. Clay-gouge samples were collected within the fault core zone, as well as in the broader fault damage area. Consequently, the samples were analyzed by X-Ray Diffraction, SEM and Electron microprobe analyses. The minerals that were identified within the centre of the fault zone are: Montmorillonite, corrensite, illite, micro-calcite, dolomite, quartz, plagioclase and K-feldspars. The absence of corrensite, a clay mineral usually formed in hydrothermal conditions, in the samples from the broader fault damage area indicates that the circulation of hydrothermal fluids is mostly confined within and around the fault core zone. The assemblages within the fault gouge zone and especially the presence of corrensite, combined with the absence of laumontite, indicate hydrothermal alteration at neutral to alkaline conditions and a temperature range at about 100-150 oC.

Crystal chemistry of Al–V–Cr oxy-tourmalines from Sludyanka complex, Lake Baikal, Russia

Twelve Al–V–Cr oxy-tourmalines from the Sludyanka crystalline complex (Russia) were structurally and chemically characterized by single-crystal X-ray diffraction and electron microprobe analysis. Three samples were also optically characterized by optical absorption spectroscopy and refractive index measurements. The data obtained and those of fourteen earlier studied oxy-tourmalines from the same locality show a complete substitution series due to the replacement of Al ↔ V 3+ ↔ Cr 3+ . The cation site distribution results show that Mg has a strong preference for the Z site, whereas the trivalent cations have a preference for Y and Z controlled by their size: Y V 3+ > Y Cr >> Y Al and Z Al >> Z Cr > Z V 3+ . In accordance with the bond-valence theory, the observed increase of F content with increasing Cr content may be interpreted by the occurrence of the local arrangements O1 (F)– Y (CrCrCr) and Z [Cr(Cr,Mg)]– O3 (O 2− )– Y (Cr), while the incorporation of V 3+ into the oxy-tourmaline structure is controlled by the local arrangement O1 (O 2− )– Y (VVV). The unit-cell parameters ( a and c ) are strictly correlated to each other and can be expressed by a quadratic relation dependent on the mean-bond distances 〈 Z –O〉 and 〈 X –O〉. A strong positive correlation between (V + Cr) content and mean refractive index is proposed as a reliable guide to derive the composition of Al–V–Cr oxy-tourmalines from refractive-index measurements.

Concrete alteration due to 55 years of exposure to river water: Chemical and mineralogical characterisation

This article presents a study on concrete alteration mechanisms due to 55years of exposure to river water. Many hydro power structures in cold regions suffer from concrete deterioration at the waterline. Progressive disintegration of the concrete surface leads to exposure of the coarse aggregate and eventually the reinforcing steel. Concrete cylinders drilled out at four vertically different locations on the upstream face of a concrete dam were analysed by electron microprobe analysis, X-ray diffraction, thermogravimetry and scanning electron microscopy. Long-term exposure to the river water, which is regarded as soft water, has led to chemical and mineralogical zonation of the cement paste. Up to five zones with different chemical and mineralogical composition, parallel to the upstream face, were observed in the outermost 8–9mm of the concrete. Decalcification, precipitation of secondary ettringite and the formation of a magnesium-rich silica gel constitute the major changes that define the zones.

Structural incorporation of W6+into hematite and goethite: A combined study of natural and synthetic iron oxides developed from precursor ferrihydrite and the preservation of ancient fluid compositions in hematite

Hematite (a-Fe2O3) and goethite (a-FeOOH) can incorporate considerable amounts of tungsten (W). Although W concentrations up to several wt% in hematite and goethite have been reported in the literature, none of the proposed models for a structural incorporation has been generally accepted yet. Here, the first combination of X-ray absorption fine structure (XAFS) measurements with X-ray diffraction (XRD), Raman spectroscopy (RS), electron microprobe (EMPA) and total reflection X-ray fluorescence (TXRF) provides a general relation between W content and its structural incorporation into hematite and goethite.

Thermodynamics of arsenates, selenites and sulfates in the oxidation zone of sulfide ores: XII. Mineral equilibria in the Cd–Se–H2O system at 25°C

Understanding the mechanisms of cadmium and selenium behavior under near-surface conditions is very important for solving certain environmental problems. The principal aim of this study is physicochemical analysis of the formation conditions of synthetic cadmium selenite CdSeO3 · H2O and experimental investigation of its thermal stability and dehydration and dissociation mechanisms. The synthesis was performed by boiling-dry aqueous solutions of cadmium nitrate and sodium selenite. The obtained samples were identified with electron microprobe and powder X-ray diffraction. Complex thermal analysis (thermogravimetry and differential scanning calorimetry) have shown that CdSeO3 · H2O is dehydrated at 177–241°C in two stages, apparently corresponding to the formation of CdSeO3 · 2/3H2O. The Eh–pH diagrams were calculated using the Geochemist’s Workbench (GWB 9.0) software package. The Eh–pH diagrams have been calculated for the Cd–Se–Н2О and Cd–Se–CO2–H2O systems for the average content of these elements in underground waters. The formation of cadmium selenite, CdSeO3 · H2O in the oxidation medium is quite possible. The existence of CdSeO3 is possible at high temperature.