Cr2O3 Concentrations Research Articles

Performance and properties evolution of near-term accident tolerant fuel: Cr-doped UO2

Chromium-doped UO2 fuel has received significant interest due to the ability for chromium to produce pellets with large average grain size (>30 μm), which has shown to increase fission gas retention during operation. Sintering of chromium-doped UO2 pellets was pursued with oxygen potential and sintering atmosphere controlled to tailor the final microstructure of the material. Chromium additions in this study ranged from 750 to 7800 ppm. Cr concentrations were studied pre and post sintering using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). Effects of chromium content on lattice parameter and microstructure were examined with X-ray diffraction (XRD) and scanning electron microscopy (SEM). Contraction of the UO2 lattice parameter was observed, as well as enlargement of grain size with increasing chromium content up to 4900 ppm Cr2O3. SEM indicated Cr incorporation within the matrix and the formation of chromium oxide precipitates throughout the microstructure at high Cr concentrations. Evaluation of thermophysical properties of Cr-doped UO2 pellets were conducted up to 1200 °C to illustrate their evolution with increased dopant concentration and microstructural changes. The results show that grain size is maximized at 52 μm with Cr2O3 concentration equal to 4900 ppm; however, grain size decreases at higher Cr2O3 concentrations. No significant changes were observed in specific heat capacity, linear thermal expansion, and coefficient of thermal expansion compared to undoped UO2. The thermal conductivity also decreased through the incorporation of Cr2O3 dopants above 750 ppm and is shown to be ∼15 % lower than reported UO2 values.

Oxidation of accident tolerant fuels models based on Cr-doped UO2 for the safety of nuclear storage facilities

Oxidation of Accident-Tolerant Fuels (ATF) is important from the nuclear safety point of view because it could provoke the release of radioactive material. Despite of the use of ATFs in current nuclear reactors, no studies regarding their oxidation are available. Thus, we propose here an experimental study on Cr2O3-doped UO2 samples, which were subjected to a thermal treatment ranging from room temperature up to 973 K in oxidant conditions. The aim is to assess the potential oxidation resistance of Cr-doped UO2 based model systems. Next, the effect of oxygen partial pressure and the influence of Cr2O3 dopant concentration concentrations on fresh UO2 fuel oxidation were evaluated. Two oxygen compositions (1% and 21%O2) were used to further evaluate the impact of Cr2O3 concentrations on UO2 oxidation. The results show that, despite no effect of the dopant is found in air (21% O2), there is a clear decrease in the oxidation degree at 1%O2. These results are intended to provide a fundamental reference for future investigations of Cr2O3-doped UO2 corrosion behavior and performance to be accounted in new designs of storage facilities.

Post‐collisional alkaline lamprophyre magmatism in northern Iran: Implications from whole‐rock geochemistry and mineral compositions

AbstractThe Shanderman lamprophyre dykes crop out in the western part of the Alborz Mountains (Talesh). These rocks are classified as camptonites, composed of primary olivine, Ti‐rich diopside, kaersutite, biotite, plagioclase, K–feldspar, and minor Ti–rich spinels, magnetite, pentlandite–pyrrhotite/chalcopyrite, and powellite–scheelite. Secondary analcime–wairakite, serpentines, and prehnite are common minor minerals within the studied rocks. Olivine, Ti‐rich diopside, spinel, and amphibole show distinct chemical zoning. Spinels display a core‐to‐rim decrease in Cr2O3, MgO, and Al2O3 concentrations and an increase in TiO2 and FeOT (total Fe as FeO), reflecting the oxidation state increase due to hydrothermal fluid influx. Low SiO2 contents (<42 wt%), high MgO (12.44 to 13.98 wt%), and Fe2O3T (12.76 to 13.43 wt%), Cr (318–537 μg/g) and Ni (231–327 μg/g) contents indicate the ultrabasic nature of the rocks. The samples show potassic character (2.1–2.8 wt% K2O), along with elevated LREE and LILE, and also exhibit minor positive Eu anomalies (Eu/Eu* = 1.09 to 1.20). Olivine–spinel geothermometry indicates a maximum crystallization temperature of 1227 °C (ave. 988 °C ± 65 °C). Exsolution of pentlandite–pyrrhotite/chalcopyrite solid solutions occurred during magma cooling and crystallization. At lower temperatures, analcime–wairakite and prehnite partially replaced plagioclases. The geochemical modeling of the rocks indicates the Shanderman lamprophyre magmas were derived from low‐grade melting (<5%) of amphibole–bearing garnet lherzolite source without or with very few phlogopites. The primary magma of Shanderman lamprophyres was derived from a depth of ~135 km by partial melting of a metasomatized mantle source in a post‐collisional environment.

Beneficiation of fluxed titaniferous slag to a marketable titania product using the modified upgraded slag process

ABSTRACT Smelting production of a limestone-fluxed titaniferous slag with low MgO content for subsequent beneficiation using the modified Upgraded Slag (UGS) process was investigated, with the aim of producing a marketable titania product. Smelting of titaniferous magnetite (titanomagnetite) with a carbon reductant and limestone flux was conducted in a water-cooled copper crucible in an iron-suscepting induction furnace under argon. The resulting titaniferous slag contained high residual iron (from the susceptor and incomplete iron reduction in the titanomagnetite), which caused crystallization of an ulvospinel. The slag was beneficiated using the modified UGS process, an industrial roast–leach process used for beneficiation of low-titania slag to a feedstock suitable for production of titania pigment. The upgraded product contained 90.5 mass% TiO2, with a recovery of 83%. Although the TiO2 grade met the feedstock specification for pigment production via the chloride route, SiO2, Al2O3, CaO, and Cr2O3 concentrations exceeded the specification and the particle size distribution was too fine.

The Loongana (CL) group of carbonaceous chondrites

A coordinated study of the petrology, mineral chemistry, and bulk chemical and isotopic composition of the five ungrouped carbonaceous chondrites Coolidge, Loongana 001, Los Vientos (LoV) 051, Northwest Africa (NWA) 033, and NWA 13400 reveals that these meteorites have a similar set of properties that distinguishes them from the other carbonaceous chondrite groups and allows definition of the new Loongana (CL) group of carbonaceous chondrites. The basic characteristics of the investigated samples are: (1) Lithophile element ratios (e.g., Al/Mg, Si/Mg) are within the typical range of other carbonaceous chondrite groups. (2) Fe-Ni metal abundances are considerably higher than for CV, but similar to CR chondrites. (3) Chondrule size-frequency distributions are similar to CV, but dissimilar to CR chondrites. (4) The mean CAI abundance is ∼1.4 vol%, i.e., lower than in CV but much higher than in CR chondrites. (5) Very low amounts of matrix (17–21 vol%), the lowest among the main carbonaceous chondrite groups (CI, CM, CO, CV, CR, CK). (6) Olivine is nearly equilibrated, with mean fayalite (Fa) values between 12.5 mol% (Loongana 001) and 14.7 mol% (NWA 13400) as a metamorphic effect. (7) Lower Al2O3 and higher MgO and Cr2O3 concentrations in matrix, compared to matrix in CV, CK, and CR chondrites. (8) Volatile elements (Mn, Na, K, Rb, Cs, Zn, Se, Te, Pb, Tl) are considerably depleted compared to all other main carbonaceous chondrite groups, reflecting the low matrix abundance. (9) Bulk O isotope compositions plot along the CCAM line (Δ17O −3.96 to −5.47‰), partly overlapping with the CV and CK chondrite fields but including samples that are more 16O-rich. (10) Unique positions of CL values in the є54Cr-є50Ti isotope plot, with є54Cr values similar to CV, CK, and CO, but є50Ti values similar to CR chondrites. All CL chondrites studied here are of petrologic type 3.9 to 4, indicating that they have been thermally metamorphosed on the parent body. The diagnostic features of CL chondrites detailed here provide a basis for identifying CL members of lower petrologic types. Such samples will be important for determining the pristine state of these meteorites and their components.

Geochemical and geochronological dataset of rutile from a Variscan metabasite in Sardinia, Italy.

A c. 500 m wide and 1.5 km long body consisting of basic to ultrabasic rocks, metamorphosed up to granulite-facies and retrogressed to amphibolite-facies conditions during the Variscan orogeny, crops out near Olbia (NE Sardinia, Italy). Among abundant samples, one, collected from a garnet-rich centimetric layer, was chosen for a detailed analysis of rutile; chemical analyses of rutile were performed with the electron microprobe on petrographic thin sections, whereas U/Pb ages were determined by LA-ICP-MS on rutile mounted in epoxy resin. Chemical analyses show that rutile included in other minerals (Rtinc) commonly show higher SiO2 and FeO contents and lower Nb2O3 and ZrO2 contents if compared with rutile in the matrix of the garnet-rich layer (Rtmat). Cr2O3 concentrations are quite similar in both types of rutile. Rtmat commonly shows a greater variability in minor elements, especially Nb2O3 (0.049–0.284 wt.%) and SiO2 (0.019 - 0.193 wt.%) whereas Rtinc compositions are more homogeneous except for FeO (0.251–0.562 wt.%). The U-Pb isotopic data provided discordant ages and defined a lower intercept in the Tera-Wasserburg diagram of 273 ± 13 Ma. Few compilations of geochemical and geochronological data on rutile in Variscan metabasites can be found in literature, thus these data represent a new insight on a mineral phase the significance and scientific interest of which are rising in the last years. Future studies on the origin and ages of emplacement and metamorphism (either prograde or retrograde) of this kind of rock, widespread in the Variscan chain, will benefit from these data as a term of comparison.

Structural and optical absorption studies on Cr2O3 doped SrO-P2O5 glasses.

Cr2O3 doped glasses in the system xCr2O3-(60-x) P2O5-40SrO, where x=0.0, 0.025, 0.05, 0.1, 0.2, 0.4 & 0.6mol% were prepared and investigated by X-ray, UV-Vis, and FT infrared spectroscopy. According to the X-ray data, no sharp peaks can be observed, but only abroad halo which points the amorphous nature of the glass samples. Optical absorptions have shown that Cr ions are present in two possible oxidation states (trivalent & hexavalent). Increasing Cr2O3 concentrations in the glass network cause a reduction in the indirect and direct optical energy gap of prepared samples from 3.94-3.5eV and 4.92-4.4eV, respectively. This behavior is related to the network forming ability of Cr2O3. FTIR spectra of Cr2O3 containing glass showed some differences compared to base glass samples. In addition, calculated physical and optical parameters reveals a close similarity to base glass that can be correlated to the minor addition of Cr2O3.

Luminescence and EPR properties of high quality ruby crystals prepared by the optical floating zone method

Rubies (Cr: Al2O3 single crystals) with 0.025–0.4 mol% Cr2O3 were prepared by the optical floating zone method, and characterized by X-ray diffraction (XRD), electron paramagnetic resonance (EPR) spectroscopy, optical transmission and photoluminescence (PL). Crystals were free of inclusions and cracks, and had high transmittance in the visible region. In addition to the well-known signals from Cr3+ in the α-Al2O3 structure, the EPR spectra indicated the presence of very weak signals, which may correspond to paramagnetic centres associated with an oxygen vacancy, and an electron-loss oxygen centre, O−. The concentration of these paramagnetic centres was at a minimum for Cr2O3 concentration of 0.15 mol%, and additional Cr3+-derived peaks were also observed with Cr2O3 concentrations >0.15 mol%. The PL spectra also varied with Cr2O3 concentrations; the emission intensities of the PL spectra increased with Cr2O3 concentration for concentrations ≤0.15 mol%, then decreased with the further increases in Cr2O3. Thus the maximum luminescence emission intensity and the minimum concentration of paramagnetic structural defects were observed with 0.15 mol % Cr2O3, and the presence of additional interactions involving Cr3+ ions may contribute to the partial quenching of the luminescence at higher Cr3+ concentrations. Overall, the optical floating zone method represents an effective and economic approach to the preparation of high quality rubies, and their optimum optical properties were observed with Cr2O3 concentrations of 0.15 mol%.

NEPHRITE FROM ZŁOTY STOK (SUDETES, SW POLAND): PETROLOGICAL, GEOCHEMICAL, AND ISOTOPIC EVIDENCE FOR A DOLOMITE-RELATED ORIGIN

The Zloty Stok Au-As deposit (SW Poland) hosts two distinct nephrite varieties: ‘type 1’ – a grayish green or pale green, translucent, with waxy to greasy luster nephrite composed of actinolite and abundant lollingite; ‘type 2’ – a deep or intense green, less-translucent, with sub-vitreous to dull luster nephrite composed of tremolite and actinolite, with rare lollingite and arsenopyrite. ‘Nephrite type 1’ shows evidence for more intense metasomatism and recrystallization than ‘type 2’, e.g. , more abundant arsenide, sulfosalt, and tungstate minerals, and higher Fe, As, and Co concentrations. The tremolite and actinolite in both types formed at the expense of dolomite—either directly from dolomite or through diopside formation. Calcite is a byproduct of the amphiboles' formation directly from dolomite. Amphiboles have Cr2O3 and NiO concentrations of 0.00–0.04 wt.% and 0.00 wt.%, respectively, typical of dolomite-related nephrites. Diopside composition (up to 51 Wo, 0.00–0.05 wt.% Cr2O3 and 0.00–0.09 wt.% NiO) is similar to other dolomite-related nephrite compositions. Bulk-rock Cr and Ni (<30 ppm and <40 ppm, respectively) and Co, which is less affected by ore mineralization (<10 ppm), are similar to the values in dolomite-related nephrite. Yellow cathodoluminescent diopside is similar to that in other metasomatized dolomitic marbles. Nephrite has δ18O values ranging from +8.3 to +10.4‰ (precision = ±0.1‰), higher than in other typical dolomite-related nephrite. δD values range from –77 to –75‰, similar to the dolomite-related type. Based on these observations, we interpret the Zloty Stok nephrite deposit to have formed as a metasomatic replacement of dolomitic marble. This is the third documented case of a dolomite-related origin (para-nephrite) for nephrite in Europe. Furthermore, the dolomite-related nephrite adds the Lower Silesian Sudetes and its Foreland to rare areas like Wyoming, southern Siberia, China, Korea, and the Alps, where both dolomite-related and serpentinite-related nephrites occur. The Zloty Stok nephrite formed via at least two crystallization events. In the first event, quartz veins and nephrite formed, and the paragenesis included quartz, tremolite, Fe-poor actinolite, Fe-poor diopside and, probably, arsenopyrite. In the second event, Si-depleted actinolite, Fe-enriched diopside, and lollingite formed, and the earlier arsenopyrite was replaced by calcite. The crystallization path reflects progressive metamorphism ( i.e. , temperature rise) or change in the saturation conditions, e.g. , silica and sulfur activity in the fluid. The nephrite formation can be linked with the emplacement and cooling of the neighboring Variscan Klodzko-Zloty Stok granite at ca. 340–298 Ma.

Effect of Cr2O3 addition on the microstructure and electrical properties of SnO2-based varistor

The effect of Cr2O3 addition on the properties of (Co, Nb)-doped SnO2 varistors were investigated. The samples with different Cr2O3 concentrations were fabricated by the conventional ceramic method and sintered at 1,250, 1,300, 1,350 and 1,400 °C for 2 h. It was found that the nonlinear coefficient present a peak value when 0.05 mol % Cr2O3 was added. The leakage current density decreases with increasing Cr2O3 from 0 to 0.05 mol %, but increases when the concentrations increase from 0.05 to 0.07 mol %. The breakdown electrical field increased from 337 to 866 V/mm with increasing Cr2O3 from 0 to 0.07 mol %. The optimal samples obtained by doping Cr2O3 with 0.05 mol % and sintered at 1,300 °C have the highest nonlinear coefficient value of 27 and lowest leakage current density of 9 μA/cm2.

Physical and optical properties of the SLS glass doped with low Cr2O3 concentrations

The aim of this work is to study the physical properties of Cr2O3 -doped soda lime silicate glass in batch of 25Na2O: 10CaO: (65-x)SiO2: xCr2O3 where 0.00 ≤ x ≤ 0.05 mol%. The glass samples were prepared by normal meltquenching technique with 1500°C melting-temperature. The amorphous structure of glass samples were confirmed by X-Ray Diffractrometer (XRD) analysis. The density of glass samples were increased with increasing of Cr2O3 concentration due to the higher molecular weight of Cr2O3 (Mw.=151.9904g/mol) than SiO2 (Mw.=60.0843g/mol). On the other hand, the molar volumes were decreased. It means that network of glasses were compressed because of the substitution of Cr2O3 in the place of SiO2. The refractive index of glass samples was increased. The optical spectra of glass samples were also investigated.

Influence of Cr2O3 on the Residual Voltage Ratio of SnO2‐Based Varistor

The SnO2‐based varistor is a kind of new varistor ceramic material with high nonlinear electrical properties and high thermal conductivity. To improve the comprehensive performance, we focus on how to lower the residual voltage ratio of SnO2‐based varistor. In this article, the influence of Cr2O3 on the microstructure, nonlinear J–E characteristics and surge current performances have been investigated. By changing mean grain size and bringing oxygen vacancies, different Cr2O3 concentrations make the residual voltage ratio increase or decrease accordingly. The lowest residual voltage ratio we obtained is 1.68, when the content of Cr2O3 is 0.03 mol%, which is comparative to commercial ZnO‐based varistor of the same specifications and close to practical use.

Transparent polycrystalline ruby ceramic by spark plasma sintering

Abstract Fine-grained and transparent polycrystalline ruby ceramics (Cr2O3-doped Al2O3) were successfully prepared by spark plasma sintering (SPS). The effect of Cr2O3 concentration on the grain size, hardness, fracture toughness and thermal conductivity of ruby ceramics was investigated systematically. For 0.05 wt.% Cr2O3, high in-line transmittance of 85% at 2000 nm can be reached, further increase of Cr2O3 concentration leads to the decrease in transmittance. High hardness of 23.95–25.05 GPa can be achieved due to the fine grain size in all ruby ceramics. The fracture toughness of 1.9–2.29 MPa m1/2 indicates that no improvement in fracture toughness over pure Al2O3 can be obtained by Cr2O3 doping in these submicron grained ruby ceramics. High thermal conductivity of 28–29.8 W/(m K) at room temperature, close to that of single crystal sapphire, can be achieved. The change in grain size for different Cr2O3 concentrations is the major reason for the change in mechanical and thermal properties, but not for the change in optical properties.

Chromium mineralization in the Khibiny alkaline massif (Kola Peninsula, Russia)

This paper presents new data on chromium mineralization in a fenitized xenolith in Mt. Kaskasnyunchorr in the Khibiny alkaline massif (Kola Peninsula, Russia) and summarizes data on Cr mineralogy in the Khibiny Mountains. Protolith silicates that contained Cr3+ admixture are believed to be the source of this element in the fenite. Cr-bearing (maximum Cr2O3 concentrations, wt %, are in parentheses) aegirine (5.8), crichtonite-group minerals (2.1), muscovite (1.3), zirconolite (1.1), titanite (1.0), fluorine-magnesioarfvedsonite (0.8), biotite (0.8), ilmenite (0.6), and aenigmatite (0.6) occur in the fenite. The late-stage spinellides of the FeTi-chromite-CrTi-magnetite series, which are very poor in Mg and Al and which formed after Crrich aegirine and ilmenite, are the richest in Cr (up to 42% Ct2O3). Cr concentrations grew with time during the fenitization process. Unlike minerals in the Khibiny ultramafic rocks where Cr is associated with Mg, Al (it is isomorphic with Cr), and with Ca, chromium in the fenites is associated with Fe, Ti, and V (with which Cr3+ is isomorphic) and with Na in silicate minerals. Cr3+ Mobility of Cr3+ and the unique character of chromium mineralization in the examined fenites were caused by high alkalinity of the fluid.

Photoconductivity in LiNbO3 crystals codoped with MgO and Cr2O3

The photoconductivity of LiNbO3 crystals codoped with Cr2O3 and different concentrations of MgO from 0 up to 6 mol % is reported. The spectral excitation of photocurrent presents an intense band corresponding to the Cr3+ induced blue absorption edge, but illuminating at the (4)A(2) -> T-4(1) ionic transition band a weak photocurrent is also excited. The photoconductivity is interpreted in terms of Cr3+ ionization and the formation of Nb-Nb(4+) small polarons as charge carriers. Photoconductivity below about 140 K is suppressed. The analysis of the photocurrent temperature dependence results in a 0.14 +/- 0.02 eV binding energy of the polaron at low temperature. Photoconductivity induced by excitation in the intraionic Cr3+ can be explained by a tunnelling process between the excited Cr3+ and the polaron state at the next-nearest-neighbour Nb-Nb(5+).

The 181Hf/181Ta Probe in the Li and Nb Sites of Congruent Linbo3 Co-doped with Mg and Cr Ions Studied by γ–γ PAC

The results reported in this work show the relevance of the lithium deficiency for the Li lattice site occupation of dopants in congruent lithium niobate crystals co-doped with 0.1 mol% Cr2O3 and different concentrations of HfO2, up to 3 mol%. The same behavior is observed in a crystal doped with 1 mol% of HfO2 and co-doped with 4 mol% MgO where after annealing most of the Hf/Ta probes occupy the Nb lattice site.

The origin of glasses in hydrous mantle xenoliths from the West Eifel, Germany: incongruent break down of amphibole

Patches of glass with a second generation of small crystals of olivine, clinopyroxene, and spinel are abundant in hydrous peridotite mantle xenoliths with tabular equigranular textures from two maar-type volcanoes, Meerfelder Maar and Dreiser Weiher (West Eifel, Germany). The patches are similar in size to the main phases of the hosting peridotite. Their central part is often occupied by relics of pargasitic amphibole. Mass-balance calculations show that the patches were formed by surface controlled incongruent thermal breakdown of amphibole according to the reaction: amphibole ↔ olivine + clinopyroxene + spinel + melt. Simultaneously with the decomposition of amphibole, small crystals of olivine, clinopyroxene, and spinel grew radially from the patch/peridotite interface toward the centre of the patch. Apart from sector zoning of clinopyroxene, the crystals are virtually homogeneous and are separated from the amphibole by a seam of melt (glass). Secondary olivines reveal higher Mg-numbers, secondary clinopyroxenes higher Cr2O3 concentrations than olivines and clinopyroxenes, respectively, of the host peridotite. The silica contents of melts produced by the above breakdown reaction range from 48 to 52% SiO2 as a function of the composition of the parent amphiboles. Patches surrounded by primary olivines only reveal no reaction with the host peridotite. The variation of SiO2, MgO and CaO in melts from these patches is the result of minor precipitation of olivine and clinopyroxene during fast cooling. If patches are in contact with primary olivine and orthopyroxene, melts are additionally modified by the reaction liquid 1 + orthopyroxene ↔ liquid 2 + olivine + clinopyroxene resulting in more silica-rich compositions between 54 and 58%. For the rare glasses richer in silica, a more complex formation is required. Veinlets along grain boundaries are filled with glasses which are chemically identical to those from nearby patches. This suggests that the veinlets were filled by melts formed by amphibole breakdown during entrainment of the xenoliths to the host magmas.

Efremovka 101.1: a CAI with ultrarefractory REE patterns and enormous enrichments of Sc, Zr, and Y in Fassaite and Perovskite

Inclusion 101.1 from the CV3 carbonaceous chondrite Efremovka is a compact Type A Ca-Al-rich inclusion (CAI) highly enriched in ultrarefractory (UR) oxides. It is the first complete CAI with a UR rare earth element (REE) pattern found in a CV3 chondrite. The inclusion is petrographically complex and was formed in a multistage process. It consists of several lithologically unrelated units.The core contains abundant Y- and Zr-perovskite, Sc- and Zr-rich fassaite, and metallic FeNi enclosed in melilite. All mineral species (except spinel) in all lithological units exhibit the same basic UR REE pattern. Four different populations of perovskites are distinguished by different Y/Zr ratios. A few of the perovskites have Y/Zr ratios similar to those obtained from crystal/liquid fractionation experiments. Perovskites from the other three populations have either chondritic, lower than chondritic Y/Zr ratios or extremely low Zr contents. Ca isotopic ratios differ among three perovskites from different populations, demonstrating a variety of sources and formational processes. Most fassaites crystallized in situ through reaction between the CAI liquid and preexisting perovskites. This process induced redistribution of Zr, Y, Sc, and V between perovskite and fassaite, thus overprinting the original abundances in perovskite. Fassaite reaction rims around FeNi metals are also encountered. They are enriched in V, which was gained from the metal through oxidation of V in metal during fassaite crystallization. The relative abundances of Zr, Y, and Sc in perovskites are complementary to the abundances of these elements in Sc- and Zr-fassaite, indicating subsolidus partitioning of these elements between the two phases. Perovskites are enriched in Y and depleted in Sc and Zr in comparison to fassaites.The core contains two complete captured CAIs, several sinuous fragments, and fine-grained polygonal refractory fragments. An assemblage of andradite-wollastonite-hedenbergite and pure metallic iron is encountered as enclaves in the interior of some sinuous fragments. Metallic Fe and wollastonite formed by reduction of preexisting andradite and hedenbergite nebular alteration products upon inclusion in the highly reduced CAI melt. Numerous spinel clusters and framboids with varying V2O3 and Cr2O3 concentrations are enclosed in individual melilite crystals in the host CAI and captured CAIs. The rim sequence of the host consists of six layers (from the inside outward): (a) FeO-poor spinel, (b) Sc-bearing fassaite, (c) Al-diopside, (d) Al- and Ca-bearing olivine, (e) pure diopside, and (f) Ca-poor olivine. Like the constituents of the CAI core, all mineral layers of the rim sequence, except spinel, have the same UR REE pattern. However, the total REE abundances decrease systematically by 1 order of magnitude from layer 2 to layer 6. This feature strongly suggests formation of the rim sequence by successive condensation from a unique reservoir enriched in UR elements and excludes formation by flash heating. Petrography, mineral chemistry, REE, refractory lithophile element abundances, and Ca isotopic compositions demonstrate the complex multistage formation history of a CAI that on the surface looks like a regular Type A inclusion.

Magnetic properties of xCr2O3 · (1 − x)[Bi2O3 · PbO] glasses

EPR and magnetic susceptibility measurements have been performed on xCr2O3 · (1 − x)[Bi2O3 · PbO] glasses with 0 <x ≤ 30 mol%. These data show that the chromium ions are in the Cr3+ valence state. For x ≤ 5 mol% most of these ions are isolated or experience dipole-dipole interactions, but for higher Cr2O3 concentrations the dominant part of them are magnetically coupled by negative superexchange interactions.

Europium silicides and germanides of the Eu M2X2 type crystal structure and the valence states of europium

A coordinated study of the petrology, mineral chemistry, and bulk chemical and isotopic composition of the five ungrouped carbonaceous chondrites Coolidge, Loongana 001, Los Vientos (LoV) 051, Northwest Africa (NWA) 033, and NWA 13400 reveals that these meteorites have a similar set of properties that distinguishes them from the other carbonaceous chondrite groups and allows definition of the new Loongana (CL) group of carbonaceous chondrites. The basic characteristics of the investigated samples are: (1) Lithophile element ratios (e.g., Al/Mg, Si/Mg) are within the typical range of other carbonaceous chondrite groups. (2) Fe-Ni metal abundances are considerably higher than for CV, but similar to CR chondrites. (3) Chondrule size-frequency distributions are similar to CV, but dissimilar to CR chondrites. (4) The mean CAI abundance is ∼1.4 vol%, i.e., lower than in CV but much higher than in CR chondrites. (5) Very low amounts of matrix (17–21 vol%), the lowest among the main carbonaceous chondrite groups (CI, CM, CO, CV, CR, CK). (6) Olivine is nearly equilibrated, with mean fayalite (Fa) values between 12.5 mol% (Loongana 001) and 14.7 mol% (NWA 13400) as a metamorphic effect. (7) Lower Al2O3 and higher MgO and Cr2O3 concentrations in matrix, compared to matrix in CV, CK, and CR chondrites. (8) Volatile elements (Mn, Na, K, Rb, Cs, Zn, Se, Te, Pb, Tl) are considerably depleted compared to all other main carbonaceous chondrite groups, reflecting the low matrix abundance. (9) Bulk O isotope compositions plot along the CCAM line (Δ17O −3.96 to −5.47‰), partly overlapping with the CV and CK chondrite fields but including samples that are more 16O-rich. (10) Unique positions of CL values in the є54Cr-є50Ti isotope plot, with є54Cr values similar to CV, CK, and CO, but є50Ti values similar to CR chondrites. All CL chondrites studied here are of petrologic type 3.9 to 4, indicating that they have been thermally metamorphosed on the parent body. The diagnostic features of CL chondrites detailed here provide a basis for identifying CL members of lower petrologic types. Such samples will be important for determining the pristine state of these meteorites and their components.