Extensive Solid Solution Research Articles

Analysis of the Solid Solution Microstructure of (HF) Al-Zn Alloys

Rapidly solidified Al-Zn alloys with Zn contents ranging up to 50 wt.% were made under vacuum, by high-frequency (HF) induction melting, from compacted mixture targets of Al and Zn of fine (99.99 % purity) elemental powders. The microstructural characteristics and strengthening mechanisms were investigated. The crystallographic microstructures were characterized by means of X-ray diffraction (XRD) analyses and optical microscopy observations as well as Vickers microhardness testing. Detailed overviews of alloying solubility of zinc in aluminium were given. Extensive solid solutions of CFC Al were found in the (HF) Al-Zn alloys, and a higher Vickers microhardnesses compared to that of pure (HF) aluminium.

Phase equilibria and crystal structures in the system Eu–Pd–B

Phase equilibria in the ternary system Eu–Pd–B have been determined from X-ray powder diffraction for the isothermal section at 850 °C in the concentration range up to 34 at.% Eu. Phase relations at 850 °C are governed by one ternary phase, Eu 2 Pd 14.9 B 4.9 , which crystallizes with the Nd 2 Pd 14+ x B 5− y -type structure. Rietveld refinement of X-ray powder intensity data confirmed space group I4 1 /amd, a = 0.85653(3) nm, c = 1.66124(6) nm, x = 0.9, y = 0.1 ( R F 2 = Σ| F 0 2 − F c 2 |/Σ F 0 2 = 0.054). At 850 °C Eu 2 Pd 14.9 B 4.9 appears without any significant homogeneity region. At temperatures below 730 ± 10 °C the tetragonal phase decomposes and a new monoclinic phase was found to form: Eu 3 Pd 25− x B 8− y . Rietveld refinement of X-ray powder data proved isotypism with the La 3 Pd 25− x B 8− y -type structure (space group P2 1 / c , a = 1.17103(3) nm, b = 1.05623(2) nm, c = 1.60102(4), β = 102.199(1), x = 1.7, y = 0.07; R F 2 = 0.054). At 850 °C, the solubilities of third component in europium borides and palladium borides are generally insignificant, but binary Eu 1− x Pd 3+ x is an exception (AuCu 3 -type structure, 0.01 < x < 0.10) as it exhibits an extended solid solution for boron extending into the ternary at 850 °C up to EuPd 3 B y ( y = 0.55). Furthermore, a rather large homogeneity region of fcc-Pd(Eu,B) extends into the ternary system.

Synthesis of copper alloys with extended solid solubility and nano Al2O3 dispersion by mechanical alloying and equal channel angular pressing

Cu–4.5 wt % Cr and Cu–4.5 wt % Cr–3 wt % Ag alloys, with and without nanocrystalline Al2O3 dispersions (particle size <10 nm), were synthesized by mechanical alloying/milling and consolidated by equal-channel angular pressing (ECAP) at ambient temperature. Microstructural characterization and phase analysis by X-ray diffraction, as well as scanning and transmission electron microscopy, provided evidence for the formation of a Cu-rich extended solid solution with nanometric (<30 nm) crystallite size after 25 h of milling, with uniformly dispersed alumina nanoparticles embedded in it. Consolidation of Cu–4.5 wt % Cr–3 wt % Ag alloy with 10 wt % nanocrystalline Al2O3 by eight ECAP passes was shown to result in a composite with an exceptionally large hardness of 390 VHN and enhanced wear resistance. The electrical conductivity of the pellets of the latter alloy without Al2O3 is about 30% IACS (international annealing copper standard), whereas pellets with 5 or 10 wt % Al2O3 dispersion exhibit a conductivity of about 20–25% IACS. Thus, the present room temperature synthesis and consolidation route appear to offer a promising avenue for developing high-strength, wear/erosion-resistant Cu-based electrical contacts with nano-ceramic dispersion.

Temperature dependence, 0 to 40 °C, of the mineralogy of Portland cement paste in the presence of calcium carbonate

Thermodynamic calculations disclose that significant changes of the AFm and AFt phases and amount of Ca(OH)2 occur between 0 and 40 °C; the changes are affected by added calcite. Hydrogarnet, C3AH6, is destabilised at low carbonate contents and/or low temperatures < 8 °C and is unlikely to form in calcite-saturated Portland cement compositions cured at < 40 °C. The AFm phase actually consists of several structurally-related compositions which form incomplete solid solutions. The AFt phase is close to its ideal stoichiometry at 25 °C but at low temperatures, < 20 °C, extensive solid solutions occur with CO3-ettringite. A nomenclature scheme is proposed and AFm–AFt phase relations are presented in isothermal sections at 5, 25 and 40 °C. The AFt and AFm phase relations are depicted in terms of competition between OH, CO3 and SO4 for anion sites. Diagrams are presented showing how changing temperatures affect the volume of the solid phases with implications for space filling by the paste. Specimen calculations are related to regimes likely to occur in commercial cements and suggestions are made for testing thermal impacts on cement properties by defining four regimes. It is concluded that calculation provides a rapid and effective tool for exploring the response of cement systems to changing composition and temperature and to optimise cement performance.

Phase transition boundary between B1 and B8 structures of FeO up to 210 GPa

We have determined the phase transition boundary between NaCl-type (B1) and NiAs-type (B8) structures of FeO up to 208 GPa and 3800 K on the basis of synchrotron X-ray diffraction (XRD) measurements in situ at high pressure and temperature using a laser-heated diamond-anvil cell (DAC). The boundary is located at 200 GPa and 3200 K with positive Clapeyron slope. These results show that B1 phase of FeO is stable along the whole mantle geotherm, whereas B8 phase is stabilized at the inner core condition. Additionally, FeO coexisted with metallic Fe in the present experiments. We found that hexagonal close-packed (hcp) iron is stable over the entire present experimental conditions. Moreover, the direct chemical analyses of the recovered sample demonstrated that solid iron did not contain any detectable oxygen. While extensive solid solution between Fe and FeO has been speculated above 60–80 GPa, the present results strongly suggest that the system Fe–FeO is simple eutectic at least to 200 GPa pressure range.

Synthetic amphiboles and triple-chain silicates in the system Na2O-MgO-SiO2-H2O: phase characterization, compositional relations and excess H

AbstractThe presence of structural OH in amphiboles in excess of the usual two OH per formula has been debated for over 40 years (Gier et ah,1964; Leake et ah,1968). However, the reality of the excess-OH phenomenon is still an open question, because accurate water analyses of amphiboles are rarely available. In this study, we review the data available on the chemically simple synthetic system Na2O—MgO-SiO2-H2O (NMSH) and present new results from NMR, infrared spectroscopy, and X-ray-diffraction that allow re-interpretation of previous studies of NMSH amphiboles along the pseudobinary join between the two end-member compositions Na2Mg6Si8O22(OH)2 and Na3Mg5Si8O21(OH)3.We show that there is extensive solid solution involving excess H at 650—750°C, but also document the presence of a wide miscibility gap below 600°C. This miscibility gap is defined by amphiboles very close to the end-member composition Na3Mg5Si8O22(OH)3 coexisting with amphiboles with compositions near the ‘normal’ Na2Mg6Si8O22(OH)2 end member.We also report the characterization of triple-chain silicates (TCS) in the NMSH system and their phase relations with NMSH amphiboles. The upper thermal stability field of the key TCS Na2Mg4Si6O16(OH)2relative to its decomposition to two NMSH amphiboles with a combined equivalent composition has been determined and a pronounced backbend of the transformation boundary documented. Phase relations observed in synthesis experiments suggest that at 550—650°C all TCSs have compositions close to Na2Mg4Si6Oi6(OH)2. Infrared spectroscopy indicates that the TCS synthesized on this composition, studied in detail here, vary from end-member Na2Mg4Si6Oi6(OH)2 to binary solid solutions with less than ∼6 mol.% clinojimthompsonite component. No clear spectroscopic evidence for a ‘Drits’ component NaMg4Si6Oi5(OH)3 (Drits et al.,1975) has been found. Analysis of H2O by vacuum extraction and Karl-Fischer titration indicates large excesses of H2O in all the TCSs studied here that clearly exceed the amounts expected from (OH) groups alone. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) indicate that this excess H2O is structural. We propose that the excess H2O is likely to be molecular H2O located in the ^4-site channels. The observed backbend of the triple-chain decomposition curve is in agreement with a reaction involving dehydration and loss of this molecular H2O. However, the absolute amount of analysed molecular H2O exceeds that expected from the change in Clapeyron slope alone.While demonstrating the reality of excess OH in amphiboles, the evidence presented in this paper also points to interesting avenues for future research on both amphiboles and TCSs, such as understanding the dynamics and enhanced crystal chemistry of excess OH and molecular H2O in pyriboles.

Yb-Sn-Te ternary system

Phase equilibria in the Yb-Sn-Te ternary system were studied for the first time by physicochemical methods. Phase diagrams were constructed for the Yb-Sn binary subsystem and YbTe-SnTe, YbSn-SnTe, Yb5Sn3-YbTe, YbSn-YbSnTe2, YbSnTe2-Te, Yb5Sn3-YbSnTe2, Yb-SnTe, and YbSnTe2-Sn inner sections. A liquidus surface projection for the title system was constructed. The system was found to have the following features: one ternary compound of composition YbSnTe2, which melts congruently at 1335 K, and extensive solid solutions based on SnTe and YbSnTe2.

Crystal structure and superconductivity in the Th-doped LaPtSi compounds

Abstract As observed with X-ray powder diffraction, the tetragonal structure of the parent compound LaPtSi, which crystallizes in the LaPtSi-type structure with space group I 4 1 md , is retained in (La 1− x Th x )PtSi up to the solubility limit near x = 0.5. By considering the size factor of Hume–Rothery theory of alloy phase formation, it is not marvelous that the extensive solid solutions cannot be fully completed in (La 1− x Th x )PtSi. We present the room temperature powder X-ray diffraction patterns, the room temperature lattice parameters and the dc magnetic susceptibility between 1.8 and 4.0 K for three single phase polycrystalline samples in (La 1− x Th x )PtSi with x = 0, 0.25 and 0.50. The refined lattice parameters show that both the a -axis and the volume of the unit cell v contract clearly, though the c -axis gives a less percentage expansion due to doping with thorium. It is found that the change in T c with x is similar to the change in the lattice parameter a or v , which indicates that the stiffening of the lattice under pressure has a dominant effect on the decrease in T c in this system.

Crystal structures, site occupations and phase equilibria in the system V–Zr–Ge

Abstract The V–Zr–Ge system was studied for two isothermal sections at 900 and 1200 °C. Three ternary compounds VZrGe (tI12, I4/mmm, CeScSi-type), VxZr5−xGe4 (oP36, Pnma, Sm5Ge4-type) and V4+xZr2−xGe5 (oI44, Ibam, Si5V6-type) were structurally characterized. Optical microscopy and powder X-ray diffraction (XRD) were used for initial sample characterization and electron probe microanalysis (EPMA) of the annealed samples was used to determine the exact phase compositions. The variation of the cell parameters of the various ternary solid solutions with the composition was determined. The three ternary phases were structurally characterized by means of single crystal and powder XRD. While VZrGe is almost a line compound, VxZr5−xGe4 (0.2 ≤ x ≤ 3.0) and V4+xZr2−xGe5 (0.06 ≤ x ≤ 1.2) are forming extended solid solution ranges stabilized by differential fractional site occupancy of V and Zr on the metal sites.

Interface Excess and Polymorphic Stability of Nanosized Zirconia-Magnesia

Controlling the phase stability of ZrO2 nanoparticles is of major importance in the development of new ZrO2-based nanotechnologies. Because of the fact that in nanoparticles the surface accounts for a larger fraction of the total atoms, the relative phase stability can be controlled throughout the surface composition, which can be tuned by surface excess of one of the components of the system. The objective of this work is to delineate a relationship between surface excess (or solid solution) of MgO relative to ZrO2 and the polymorphic stability of (ZrO2)1−x−(MgO)x nanopowders, where 0.0 ≤ x ≤ 0.6. The nanopowders were prepared by a liquid precursor method at 500 °C and characterized by N2 adsorption (BET), X-ray diffraction (XRD), X-Ray photoelectron spectroscopy (XPS), and Raman spectroscopy. For pure ZrO2 samples, both tetragonal and monoclinic polymorphs were detected, as expected considering the literature. For MgO molar fractions varying from 0.05 to 0.10, extensive solid solution could not be detected, and a ZrO2 surface energy reduction, caused by Mg surface excess detected by XPS, promoted tetragonal polymorph thermodynamic stabilization with relation to monoclinic. For MgO molar fractions higher than 0.10 and up to 0.40, Mg solid solution could be detected and induced cubic phase stabilization. MgO periclase was observed only at x = 0.6. A discussion based on the relationship between the surface excess, surface energy, and polymorph stability is presented.

Boralsilite, Al16B6Si2O37, and "boron-mullite:" Compositional variations and associated phases in experiment and nature

Boralsilite, the only natural anhydrous ternary B 2 O 3 -Al 2 O 3 -SiO 2 (BAS) phase, has been synthesized from BASH gels with Al/Si ratios of 8:1 and 4:1 but variable B 2 O 3 and H 2 O contents at 700-800 °C, 1-4 kbar, close to the conditions estimated for natural boralsilite (600-700 °C, 3-4 kbar). Rietveld refinement gives monoclinic symmetry, C2/m, a = 14.797(1), b = 5.5800(3), c = 15.095(2) Å, β = 91.750(4)°, and V = 1245.8(2) Å 3 . Boron replaces 14% of the Si at the Si site, and Si or Al replaces ca. 12% of the B at the tetrahedral B2 site. A relatively well-ordered boralsilite was also synthesized at 450 °C, 10 kbar with dumortierite and the OH analogue of jeremejevite. An orthorhombic phase (“boron-mullite”) synthesized at 750 °C, 2 kbar has mullite-like cell parameters a = 7.505(1), b = 7.640(2), c = 2.8330(4) Å, and V = 162.44(6) Å 3 . “Boron-mullite” also accompanied disordered boralsilite at 750-800 °C, 1-2 kbar. A possible natural analogue of “boron-mullite” is replacing the Fe-dominant analogue of werdingite in B-rich metapelites at Mount Stafford, central Australia; its composition extends from close to stoichiometric Al 2 SiO 5 to Al 2.06 B 0.26 Si 0.76 O 5 , i.e., almost halfway to Al 5 BO 9 . Boralsilite is a minor constituent of pegmatites cutting granulite-facies rocks in the Larsemann Hills, Prydz Bay, East Antarctica, and at Almgotheii, Rogaland, Norway. Electron-microprobe analyses (including B) gave two distinct types: (1) a limited solid solution in which Si varies inversely with B over a narrow range, and (2) a more extensive solid solution containing up to 30% (Mg,Fe) 2 Al 14 B 4 Si 4 O 37 (werdingite). Boralsilite in the Larsemann Hills is commonly associated with graphic tourmaline-quartz intergrowths, which could be the products of rapid growth due to oversaturation, leaving a residual melt thoroughly depleted in Fe and Mg, but not in Al and B. The combination of a B-rich source and relatively low water content, together with limited fractionation, resulted in an unusual buildup of B, but not of Li, Be, and other elements normally concentrated in pegmatites. The resulting conditions are favorable in the late stages of pegmatite crystallization for precipitation of boralsilite, werdingite, and grandidierite instead of elbaite and B minerals characteristic of the later stages in more fractionated pegmatites.

Magmatic unmixing in spinel from late Precambrian concentrically-zoned mafic–ultramafic intrusions, Eastern Desert, Egypt

Abstract Spinel is widespread in the ultramafic core rocks of zoned late Precambrian mafic–ultramafic complexes from the Eastern Desert of Egypt. These complexes; Gabbro Akarem, Genina Gharbia and Abu Hamamid are Precambrian analogues of Alaskan-type complexes, they are not metamorphosed although weakly altered. Each intrusion is composed of a predotite core enveloped by pyroxenites and gabbros at the margin. Silicate mineralogy and chemistry suggest formation by crystal fractionation from a hydrous magma. Relatively high Cr 2 O 3 contents are recorded in pyroxenes (up to 1.1 wt.%) and amphiboles (up to 1.4 wt.%) from the three plutons. The chrome spinel crystallized at different stages of melt evolution; as early cumulus inclusions in olivine, inclusions in pyroxenes and amphiboles and late-magmatic intercumulus phase. The intercumulus chrome spinel is homogenous with narrow-range of chemical composition, mainly Fe 3+ -rich spinel. Spinel inclusions in clinopyroxene and amphibole reveal a wide range of Al (27–44 wt.% Al 2 O 3 ) and Mg (6–13 wt.% MgO) contents and are commonly zoned. The different chemistries of those spinels reflect various stages of melt evolution and re-equilibration with the host minerals. The early cumulus chrome spinel reveals a complex unmixing structures and compositions. Three types of unmixed spinels are recognized; crystallographically oriented, irregular and complete separation. Unmixing products are Al-rich (Type I) and Fe 3+ -rich (Type II) spinels with an extensive solid solution between the two end members. The compositions of the unmixed spinels define a miscibility gap with respect to Cr–Al–Fe 3+ , extending from the Fe 3+ –Al join towards the Cr corner. Spinel unmixing occurs in response to cooling and the increase in oxidation state. The chemistry and grain size of the initial spinel and the cooling rate control the type of unmixing and the chemistry of the final products. Causes of spinel unmixing during late-magmatic stage are analogous to those in metamorphosed complexes. The chemistry of the unmixed spinels is completely different from the initial spinel composition and is not useful in petrogenetic interpretations. Spinels from oxidized magmas are likely to re-equilibrate during cooling and are not good tools for genetic considerations.

Application of In Situ Techniques for Investigations in Lithium-Ion Battery Materials

Some examples for the application of various in situ techniques in the investigation of lithium-ion battery materials are given. The effect of crystallite size on lithium insertion behavior of anatase TiO2 is shown by in situ Raman microscopy. In TiO2 with a crystallite size of 10-20 nm, an extended solid solution domain is found compared to samples with ca. 80 nm crystallite size. Graphite exfoliation is investigated by in situ Raman mapping and differential electrochemical mass spectrometry (DEMS). Inhomogeneities within single graphite particles are found with Raman mapping. CO2 formation at Li(Ni,Co,Al)O2 electrodes is monitored with DEMS and in situ ATR-SNIFTIRS. CO2 evolution is measured at elevated temperatures by DEMS, but formation of CO2, dissolved in the electrolyte, is also detected at room temperature by ATR-SNIFTIRS.

On the ternary Laves phases Ti(Mn 1− xAl x) 2 with MgZn 2-type

Abstract Alloys with composition Ti(Mn1−xAlx)2 (xAl = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.55, 0.6, and 0.67) were studied by X-ray powder diffraction (XPD), optical microscopy, electron probe microanalysis (EPMA) and electronic density functional theory. EPMA and XPD defined an extensive solid solution of up to xAl = 0.64 at 900 °C. Structure determination from Rietveld refinements of X-ray powder diffraction data for Ti(Mn1−xAlx)2 (0 ≤ xAl ≤ 0.60) and from single crystal X-ray counter data for xAl = 0.2 revealed a C14-MgZn2-type Laves phase, where Ti atoms fully occupy the 4f sites, whereas Mn and Al atoms share the 6h and 2a sites in various ratios. By means of density functional theory, the structural stabilities and site preferences of nine ternary compositions, Ti(Mn1−xAlx)2 (xAl = 0, 0.125, 0.25, 0.375, 0.500, 0.625, 0.750, 0.875, 1.00), were further calculated for a large number of structural models. The derived Al content dependent structural stabilities, lattice parameters, and site occupations as well as enthalpies of formations are in nice agreement with experimental results. Based on the calculated data, we analyzed the occupation behaviour of Al atoms substituting for Mn atoms at the 2a and 6h sites: up to concentrations xAl

Hydriding characteristics of [formula omitted] prepared by mechanical milling of the product of hydriding combustion synthesis

Abstract Hydriding combustion synthesis (HCS) and mechanical milling (MM) are both well-known methods for production of magnesium-based hydrogen storage alloys. The former can produce high active hydride by a simple process, and the latter can synthesis various metastable hydrogen storage materials such as nanocrystalline, amorphous and extended solid solutions phases with excellent hydrogen sorption properties. In the present study, HCS and MM were combined, aiming to decrease sorption temperature for Mg 2 Ni . The high active Mg 2 NiH 4 , synthesized by HCS, was mechanically milled for 0.5, 6, 40 and 80 h with 5 wt% of graphite under argon atmosphere. The effect of the milling process on the morphology and crystal structural of Mg 2 NiH 4 were investigated by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). The hydrogen storage properties were examined by a Sieverts type apparatus. The nanocrystalline Mg 2 NiH 4 milled for 40 h has the best sorption kinetics, which can absorb 2.4 wt% hydrogen at 303 K within 100 s in the first cycle. Several reasons are considered to explain the improvement in hydriding kinetics.

Phase formation, crystal chemistry, and properties in the system Bi 2O 3–Fe 2O 3–Nb 2O 5

Abstract Subsolidus phase relations have been determined for the Bi2O3–Fe2O3–Nb2O5 system in air (900–1075 °C). Three new ternary phases were observed—Bi3Fe0.5Nb1.5O9 with an Aurivillius-type structure, and two phases with approximate stoichiometries Bi17Fe2Nb31O106 and Bi17Fe3Nb30O105 that appear to be structurally related to Bi8Nb18O57. The fourth ternary phase found in this system is pyrochlore (A2B2O6O′), which forms an extensive solid solution region at Bi-deficient stoichiometries (relative to Bi2FeNbO7) suggesting that ≈4–15% of the A-sites are occupied by Fe3+. X-ray powder diffraction data confirmed that all Bi–Fe–Nb–O pyrochlores form with positional displacements, as found for analogous pyrochlores with Zn, Mn, or Co instead of Fe. A structural refinement of the pyrochlore 0.4400:0.2700:0.2900 Bi2O3:Fe2O3:Nb2O5 using neutron powder diffraction data is reported with the A cations displaced (0.43 A) to 96g sites and O′ displaced (0.29 A) to 32e sites (Bi1.721Fe0.190(Fe0.866Nb1.134)O7, Fd3¯m (#227), a = 10.508 ( 1 ) A ). This displacive model is somewhat different from that reported for Bi1.5Zn0.92Nb1.5O6.92, which exhibits twice the concentration of small B-type cations on the A-sites as the Fe system. Bi–Fe–Nb–O pyrochlores exhibited overall paramagnetic behavior with large negative Curie–Weiss temperature intercepts, slight superparamagnetic effects, and depressed observed moments compared to high-spin, spin-only values. The single-phase pyrochlore with composition Bi1.657Fe1.092Nb1.150O7 exhibited low-temperature dielectric relaxation similar to that observed for Bi1.5Zn0.92Nb1.5O6.92; at 1 MHz and 200 K the relative permittivity was 125, and above 350 K conductive effects were observed.

Microstructure and Dielectric Properties of Heat-Treated SiC-AlN Multiphase Ceramics

Silicon carbide is widely used as an important structural material. It is known for its extreme hardness, high temperature antioxygenic properties and good tribological properties. Moreover, SiC is also an intrinsic semiconductor. SiC can react with AlN and form an extensive solid solution at temperatures between 1800 to 21000C, and has excellent mechanical properties. However, in this article, we study the influence of the microstructure and the dielectric properties of SiC ceramics. SiC-AlN solid-solution ceramics were prepared by hot-pressed sintering using Y2O3 as the sintering additive. The size of SiC and AlN powders were 0.6μm and 1.06µm respectively. The content of AlN starting powders was 14vol%. The hot-processing sintered SiC-AlN multiphase ceramics have reached high density at 1950oC in Ar atmosphere under 30MPa.The hot-processed ceramics were subjected to thermal treatments in a range of temperatures between 11000C and 16000C for 3hr. The grain size increased with the annealing temperature. X-ray diffraction profiles show that phase relationships. Scanning electron microscopy (SEM)) was used to determine fracture surface and the local compositions. Dielectric permittivities and dissipation factor of SiC-AlN composites were investigated with the varieties of annealing temperature and the content of AlN particles. Dielectric constants (ε) and Dielectric loss tangents (tanδ) were measured within the microwave frequency range from 40Hz to10MHz.

Extremely Pb-rich rock-forming silicates including a beryllian scapolite and associated minerals in a skarn from Långban, Värmland, Sweden

AbstractWe report preliminary petrographic and mineral chemical data for a rock hosting an unusual mineral assemblage from Långban, Värmland, Sweden. The rock is a two feldspar-scapolite-spessartine-romeite skarn. The bulk composition and high degree of enrichment in Pb, Sb and As suggest that the rock was formed by reaction between a pre-existing Mn skarn containing the chalcophiles and a potassic granite, with loss of silica, alkalis and CO2. The alkali feldspar is a Pb-rich hyalophane, averaging Or63Ab19Cs15Pb03, the plagioclase feldspar a Pb-rich labradorite, An48Ab48Or02Pb02, and the scapolite a 'mizzonite' (Ca/(Na+Ca) = 0.66—0.70). These minerals show their highest Pb contents recorded in nature to date: up to a maximum of 5.7 wt.% PbO in the hyalophane, 2.1% PbO in the plagioclase, and 5.3% PbO in the scapolite. Laser ablation ICP-MS of a scapolite grain detected substantial Be up to 1.7 wt.% BeO (0.6 Be per 12 tetrahedral cations), as well as Pb up to 7.05 wt.% PbO. The Be is incorporated into scapolite via the coupled exchange [Be(OH)][Al(CO3,SO4)]—1. This is the first documentation of scapolite as the major repository for Be in a rock.The romeite also contains substantial Pb, and shows extensive solid solution towards end-members containing Fe3+, Ti and Sb3+. In some analyses, the dominant end-members areand its Pb analogue rather than (Ca,Pb)2Sb2O7. Complex exsolution textures are displayed in the hyalophane, by hancockite-epidote, romeite-bindheimite and hedyphane-johnbaumite. Ca-rich scapolite and hancockite appear to be new minerals for the Långban deposit.The mineralogy appears consistent with the regional peak conditions ofP= 3 kbar,T&gt; 600°C. Several potential thermobarometers for Mn-rich skarns are identified in this rock.

The phase diagram and crystal chemistry of strontium-doped rare earth cobaltates: Ln 2− xSr xCoO 4+ δ (Ln = La–Dy)

Abstract Single-phase tetragonal K2NiF4-type phases Ln2−xSrxCoO4+δ (Ln = La3+–Dy3+) have been prepared for (x = 0.75–1.50). For the first time, the phase field for these compounds has been defined using a combination of electron microscopy and powder X-ray diffraction. An extensive solid solution was observed for the largest rare earth ions, while only a limited range was found for Ln = Sm3+, Gd3+, and Dy3+. The K2NiF4 structure could not be formed for Y3+ and smaller rare earths ions under atmospheric conditions. Thermogravimetric analysis indicates a range of average cobalt oxidation states increases with Sr-doping and varies from 2.96 to 3.72. Rietveld refinement using X-ray powder diffraction data confirm that Ln3+ and Sr2+ ions are disordered over the same lattice sites.

Phase equilibria in the Fe–Zn–O system at conditions relevant to zinc sintering and smelting

Zincite and spinel phases are present in the complex slag systems encountered in zinc/lead sintering and zinc smelting processes. These phases form extensive solid solutions and are stable over a wide range of compositions, temperatures and oxygen partial pressures. Accurate information on the stability of these phases is required in order to develop thermodynamic models of these slag systems. Phase equilibria in the Fe–Zn–O system have been experimentally studied for a range of conditions, between 900°C and 1580°C and oxygen partial pressures (pO2) between air and metallic iron saturation, using equilibration and quenching techniques. The compositions of the phases were measured using Electron probe X-ray microanalysis (EPMA). The ferrous and ferric bulk iron concentrations were determined using a specially developed wet-chemical analysis procedure based on the use of ammonium metavanadate. XRD was used to confirm phase identification. A procedure was developed to overcome the problems associated with evaporation of zinc at low pO2 values and to ensure the achievement of equilibria. An isothermal section of the system FeO–Fe2O3–ZnO at high ZnO concentrations at 1200°C was constructed. The maximum solubilities of iron and zinc in zincite and spinel phases in equilibrium were determined at pO2 = 1 × 10−6 atm at 1200°C and 1300°C. The morphology of the zincite crystals sharply changes in air between 1200–1300°C from rounded to plate-like. This is shown to be associated with significant increase in total iron concentration, the additional iron being principally in the form of ferric iron. Calculations performed by FactSage with a thermodynamically optimised database have been compared with the experimental results.