Cr2O3 Content Research Articles

Dielectric and energy storage characteristics of 0.2, 0.4, 0.6, 0.8 wt% Cr2O3 doped PbZr0.52Ti0.48O3 ceramics synthesized by spark plasma sintering

The microstructure, phase analysis, impedance and modulus spectroscopies, dielectric and energy storage characteristics have been carried out on Cr2O3 doped PbZr0.52Ti0.48O3 (PZT) ceramics. The PbZr0.52Ti0.48O3 + x Cr2O3 (x = 0.2, 0.4, 0.6 and 0.8 wt%) ceramics were synthesized by solid state reaction method following spark plasma sintering technique. The particle size of calcined powders lies between 200 nm and 500 nm, and the particles have largely faceted morphology. The analysis of X-rays diffraction patterns of the ceramics reveals perovskite structure with tetragonal lattice having P4mm space group. No additional peak related to Cr- based compound has been detected, which indicates Cr solubility in the PZT solid solution. The Cr2O3 doped PZT samples exhibit ≥ 99.3 % relative density with average grain size lower than that of undoped PZT samples reported. The peak value of dielectric permittivity (εm) was found to decrease when the Cr2O3 content is above 0.2 wt%; however, it increases for 0.8 wt% Cr2O3 doped sample. Such behavior is explained based on the multivalent nature of chromium ions. The impedance and modulus spectroscopic analyses reveal the contributions of grain relaxation and confirm the non-debye type of relaxation. The modulus studies reveal the presence of hopping mechanism in the material. The DC conductivity curves show a typical Arrhenius type behavior of electrical conductivity. The energy storage studies reveal an increase in remnant polarization and coercive field for samples containing up to 0.6 wt% Cr2O3 and the results are in agreement with the XPS observations. The highest energy storage density (∼0.1 J/cm3) and efficiency (∼64%) under an electric field of 25 kV/cm were observed for 0.2 wt% and 0.8 wt% Cr2O3 doped PZT samples, which are attributed to the dominant presence of donor Cr5+ ion.

Reclamation of post-tin mining areas using forages: A strategy based on soil mineralogy, chemical properties and particle size of the refused materials

The physical and chemical properties of refused materials in post-mining areas have received in-depth attention, while the mineralogy as a driver of the potential nutrient reserve has been ignored in reclamation practices. The objective of the study was to evaluate mineralogical, chemical, and physical properties and heavy metals of refused materials (spoil and tailings) as the basis for reclamation. Seven representative soil profiles were described and sampled to a depth of 130 cm for various soil analyses and to assess soil limiting factors for crop growth. Eleven forage species were tested in a field plot trial and their adaptability and biomass production against extreme limiting soil properties were evaluated for two consecutive growing seasons. Results showed that tin mining has drastically altered the soil texture from sandy clay loam under native conditions to loamy sand and sand under post-tin mining, resulting in serious unfavourable conditions for crop growth. Potential nutrient reserves have been depleted as revealed by the dominance of quartz minerals with small amounts of tourmaline, opaque minerals, zircon and garnet. Total elemental analysis using X-ray fluorescence (XRF) showed extreme high SiO2 content (92–96%) associated mainly with the dominance of quartz in the mineral constituents, and extremely low contents of Ca, Mg, P, K and S expressed as oxides (<0.2% altogether). This suggests that all nutrients are a severe constraint for crop growth. Among the analyzed total heavy metals, Cr2O3 contents were high (204–286 mg kg−1), while SnO contents were low (0–153 mg kg−1). However, the health risk is negligible because they were preserved in the structure of host minerals. Rehabilitation of post-tin mining was successfully performed using various forage types by implementing “a pot planting point system” accompanied by animal manure and complete fertilizer applications. Six out of the eleven forages tested, namely Cynodon dactylon, Pennisetum purpureum cv Mott, Brachiaria decumbens cv Humidicola, Pennisetum purpureum cv Taiwan, Brachiaria decumbens cv Mulato, and Paspalum atratum were recommended based on their high adaptability and significantly higher fresh biomass production (varying from 16.5 to 24.7 ton ha−1 season-1). Findings from this study provide alternatives for forage production systems to support livestock establishment. Soil mineralogy provides important information on nutrient reserves and should be considered part of an integral soil characterization including physical and chemical properties, and heavy metal contents of post-tin mining sites to ensure successful reclamation.

In-situ O-isotope analysis of relict spinel and forsterite in small (

We report high-precision secondary ion mass spectrometer triple oxygen isotope systematics (95 individual analyses) from 37 micrometeorites (MMs) collected from South Pole Water Well (SPWW), Antarctica. The study population focuses on unmelted coarse-grained (Cg) MMs (n = 23) with both multiple (n = 14) and single-mineral (n = 9) varieties investigated. We also analysed relict minerals in porphyritic cosmic spherules (n = 13) and the relict matrix in a single scoriaceous fine-grained (Fg) MM. The target minerals investigated are primarily olivine (Fo ∼ 43–99%) and spinel. Textural, chemical and isotopic data confirm that both olivine and spinel grains have retained their pre-atmospheric O-isotope compositions, allowing inferences to be drawn about their formation and parent body affinities. We separate the study population into three groups: spinel-free particles (consisting of the CgMMs and PO cosmic spherules), spinel-bearing MMs and the single FgMM.Olivine grains in spinel-free MMs vary between δ17O: −12.6‰ and +3.5‰, δ18O: −9.6‰ and +7.5‰, and Δ17O: −9.5‰ and +1.3‰ and define a slope-1 profile in δ18O–δ17O isotope space. They are most likely fragmented chondrules, with both type I and type II varieties represented. Their observed Mg#-Δ17O distribution is best explained by a mixture of CM chondrules and either CR chondrules, Tagish Lake chondrules or WILD2 cometary silicates. One of these chondrule-like MMs has an isotopically heterogeneous composition, characterised by a single olivine grain with a markedly 16O-rich composition (Δ17O: −16.3‰), suggesting it is a relict silicate fragment of AOA material that was incorporated into the chondrule precursor.We analysed 11 spinel grains in five spinel-bearing MMs. In all instances spinels are nearly pure MgAl2O4 with isotopically light (16O-rich) compositions (ranging from δ17O: −34.4‰ to −0.9‰, δ18O: −30.8‰ to +11.0‰, and Δ17O: −18.3‰ to −4.4‰). They are therefore 16O-poor relative to spinel found in unaltered CAIs, indicating a different origin. Grains with high Cr2O3 contents (>0.5 wt.%) are interpreted originating from Al-rich chondrule precursors, while low Cr2O3 spinels (<0.5 wt.%) are interpreted as CAI-derived material affected by parent body aqueous alteration.Finally, we report a single FgMM with a 16O-poor composition (Δ17O > 0‰ and δ18O > +15.0‰). This particle adds to our growing inventory of water-rich C-type asteroid samples united by their formation history which is characterised by accretion of abundant heavy water.Our work strongly supports findings from earlier in-situ O-isotope studies, concluding that small MMs overwhelmingly sample material from CC parent bodies and that CgMMs largely sample chondrules and, to a lesser extent, CAI material. The analysis of CgMMs therefore provides insights into the primitive O-isotope reservoirs that were present in the early solar system and how they interacted.

Effect of Phase Composition on Leaching Behavior and Mechanical Properties of Ceramics from Ferrochrome Slag and Tundish Slag.

Ferrochrome slag (FS) and tundish slag (TS) are two typical slags containing high contents of Cr2O3 (3.88 wt.%) and MnO (18.69 wt.%), respectively. In this study, batches of ceramics were prepared from FS and TS, and their Cr/Mn leaching behaviors, mechanical properties and microstructures were investigated. Results showed that ceramics with 80 wt.% FS or 85 wt.% TS had acceptable properties. By controlling its composition and sintering temperature, pyroxene or spinel phases could become the main crystalline phases of the fired ceramics containing either of the two slags. For both slag series, pyroxene phases contributed to higher bending strengths, whereas spinel phases led to lower Cr/Mn leaching rates. Both ceramic containing 20 wt.% FS and ceramic containing 85 wt.% TS had the main crystals of pyroxene phases and possessed the highest bending strengths (FS20: 114.52 MPa and TS85: 124.61 MPa). However, both ceramic containing 80 wt.% FS and ceramic containing 25 wt.% TS with main crystals from the spinel phases had the lowest Cr/Mn leaching rates (FS80: Cr 0.05% and TS25: Mn 0.43%). Therefore, optimum designs for the compositions of ceramics from different slags were achieved by changing the proportions of pyroxene and spinel phases to obtain a balance between the high strengths of materials and the stable retention of heavy metal ions. This study provides an important basis for long-term research on the large-scale reuse of heavy metal-containing slags in the ceramic industry.

Metasomatic Modification of the Mesoarchaean Ulamertoq Ultramafic Body, Southern West Greenland

AbstractNumerous ultramafic rocks occur as lens-shaped bodies in the Archaean continental crust exposed in southern West Greenland. As some of the oldest exposed ultramafic bodies, determining their origin, as mantle segments or magmatic cumulates, is an important yet controversial issue. The origin of these Archaean ultramafic rocks remains unclear, in-part because these rocks have undergone metasomatic modification since their formation, yet the effects of this metasomatism have so far not been assessed in detail, despite being crucial for understanding their geochemical evolution. Here, we examined the petrology, mineral and whole-rock chemistry of the largest ultramafic body located within the Mesoarchaean Akia terrane, known as the Ulamertoq ultramafic body, to elucidate the poly-metamorphic and metasomatic events that overprinted the protolith. Pronounced lithologic zoning from hydrous mineral-rich layers to orthopyroxene-rich ultramafic rocks at the boundaries between ultramafic rocks and the granitoid country rocks was formed locally by metasomatic reactions related to the granitoids. The main body of ultramafic rocks, far from the contacts, can be classified into four types based on mineral assemblage and chemistry. The fine-grained orthopyroxene aggregates and large poikilitic orthopyroxenes have low Cr2O3 and CaO contents, suggesting a secondary origin. Trace element compositions of orthopyroxene and/or amphibole in the main ultramafic rocks indicate that at least three types of metasomatic agents were required to form these minerals and the associated whole-rock chemical variations within the ultramafic body. Variations represent differences in the proportions of metasomatic orthopyroxene and/or amphibole and phlogopite added to a dunitic protolith. The main body of Ulamertoq ultramafics experienced metasomatism under granulite-facies. Retrograde cooling occurred, to 650°C–850°C and &amp;lt;1.8 GPa prior to local metasomatism via country-rock reaction. The presence of titanian clinohumite and its associated mineral assemblage in the least-metasomatised dunites suggest the possibility that the main ultramafic rocks went through a hydration/dehydration process at ~800°C–900°C and &amp;lt;2 GPa prior to metasomatic modification. This study demonstrates that it is important to consider the effects of multi-stage metasomatism and metamorphism in order to elucidate the origin of the Archaean ultramafic rocks in Greenland and elsewhere.

Chrome-diopside Xenocrysts Entrained in a Neoproterozoic Lamprophyre Dyke from the Mysuru Area: Their Origin and Implications for Lithospheric Thickness Beneath the Western Dharwar Craton, Southern India

Abstract In comparison to the eastern Dharwar Craton, the mantle-derived xenocrysts/xenoliths are extremely rare or even unreported from the western Dharwar Craton, southern India. A Neoproterozoic (ca. 800-900 Ma) lamprophyre cropping out in the Mysuru area of southern India contains chrome-diopside xenocrysts (Cr2O3 content varying from 0.2 – 1.23 wt%) which provide important evidence about the pressure-temperature conditions and lithospheric thickness beneath the western Dharwar Craton. Studied chrome-diopsides show compositional zoning which is lacking in the liquidus phases (amphiboles and feldspars) of the lamprophyre which additionally favors a non-cognate origin of the former. Based on the compositional zoning, all the chrome-diopside xenocrysts can be divided into three groups: (i) Group I- which are euhedral and show reverse zoning with increasing Cr-content from core to rim; (ii) Group II- which are characterized by fractures and resorption textures, show complex reverse zoning and display up to three distinct compositional layers, and (iii) Group III- which evidence the reaction of chrome-diopsides with lamprophyric melt and are marked by alteration phases, such as actinolite and chlorite, together with relicts of some unaltered xenocrysts. High Cr2O3, moderate MgO and low Al2O3 content of all the three varieties of chrome-diopside suggest them to represent disaggregated xenocrysts of mantle-derived garnet peridotite. Temperature-pressure estimates for chrome-diopside xenocrysts ranges from 895 - 1026 °C (± 30 °C) and 32 – 38 kbar respectively and correspond to depth range of 106 – 127 km. The study reveals that lithospheric thickness during the Neoproterozoic beneath the western Dharwar craton was at least ~115 km and is similar in composition to that of the cratonic lithosphere found in the other cratonic domains.

Effect of Cr content of Fe-10Mn-xCr (x = 0.5, 1, 2, 3 and 4 masspct) on slag/steel reaction and as-cast microstructure

With the development of medium/high manganese steel which has excellent mechanical properties, research on its corrosion resistance is attracting more attention. In this study, the effect of anti-corrosion element Cr on the reaction between Fe-10Mn-xCr alloy and CaO-SiO2-Al2O3-MgO refining slag, as well as the as-cast microstructure of steel were investigated by adding different Cr content (0.5, 1, 2, 3, 4 mass pct). The results showed that Mn content in steel was significantly reduced, and Cr content changed little after slag/steel reaction. The Cr2O3 content in slag increased a little with the increase of initial Cr content, while MnO content presented the opposite trend. The inclusion types in steel remained the same with different Cr content, including MnO and MnO-SiO2 type, of which MnO-SiO2 inclusions was the main type. Most inclusions were spherical-shaped with size less than 3 μm. Thermodynamic analysis indicated that the reaction between Mn in steel and SiO2 in slag was the mechanism of steel and slag composition change and inclusion types. The above results indicate that adding Cr has little effect on the reaction between Fe-10Mn and CaO-SiO2-Al2O3-MgO top slag. After slag/steel reaction, the as-cast microstructure of steel specimens were lath martensite with BCC structure. With Cr content increasing, the microhardness increased gradually.

Study of complex processing of 10-160 mm grade chromium tailings by encapsulation in GreenCrete™ composite sulfur concrete

In recent years, methods of utilization of lumpy mineral raw materials of chromium production by encapsulation with modified sulfur from substandard grades of oil to obtain sulfur concrete have become increasingly popular. A significant amount of lumpy waste with a low content of Cr2O3 (~ 5-7% w/w) is formed when Kazakhstani chrome raw materials are processed by gravitation methods, and they can only be used as backfill in mine construction or as a component in building and road-building mixtures. Wastes from chromium deposits in Kazakhstan are located in close proximity to oil deposits in the Aktobe region, which are characterized by a high content of sulfur-containing heavy oils, which can be jointly disposed of in the form of sulfur concrete. Composite material - sulfur concrete is produced based on sulfur polymer binder - GreenCrete™ modified sulfur under GOST R 56249-2014. The possibilities of the sulfur-concrete composite formation process for the use of beneficiation tails of 10-160 mm class chromium raw material as inert materials have been studied. The characteristics of the samples obtained during the tests allow us to draw conclusions about the relatively successful encapsulation of chromium production waste in an amount of 15% by weight of the sample with the formation of sulfur concrete of the M400 class, while with a 10% content of materials for enrichment of chromium raw materials, the M500 indicator was achieved.

Investigation of mechanical properties and stored elastic energy-fragmentation of Al2O3-Cr2O3 ceramic system with increasing Cr2O3 content

In the present study, densification, mechanical properties (elastic modulus, hardness, flexural strength) and stored elastic energy-fragmentation of the pure Al2O3 and Al2O3-Cr2O3 ceramics with different Cr2O3 volume content (0.5, 1, 3, 5, 10 and 20 vol.%) were investigated. The fragmentation behaviour was interpreted from the point of armour application as larger fragments are required for higher penetration resistance. The equibiaxial flexural strength test method was used to measure the fracture strength values. A similar densification behaviour was obtained for the pure Al2O3 and the Al2O3-Cr2O3 ceramic specimens with 0.5, 10 and 20 vol.% Cr2O3 with the obtained relative densities of around 97%TD. The elastic modulus of the pure Al2O3 and Al2O3-Cr2O3 ceramic specimens showed consistent values with the densification except for the Al2O3-Cr2O3 ceramics containing 20 vol.% Cr2O3. All Al2O3-Cr2O3 ceramics have lower flexural strength values than the pure Al2O3. The pure Al2O3 had the smallest crack surface area accompanying the largest fragment size for given fracture energy. This indicates that the pure Al2O3 will break into larger pieces in case of a possible impact.

Effect of Cr2o3 Content on the Phase Composition, Micromorphology and Vanadium Extraction Process of Vanadiumslag

Effect of Cr2o3 Content on the Phase Composition, Micromorphology and Vanadium Extraction Process of Vanadiumslag

Electrospinning technology to prepare in-situ Cr2O3 modified carbon nanofibers as dual-function electrode material for vanadium redox battery

Electrospinning is a special fiber manufacturing process, which has the advantages of simple equipment, low cost, and controllable process conditions. Cr2O3 is grown in situ on carbon nanofibers by electrospinning technology. The effects of different contents of Cr2O3 on the morphology and physicochemical properties of carbon nanofibers are systematically studied. The in-situ Cr2O3 nanoparticles were distributed evenly on the carbon nanofibers, which increase the defect degree of the carbon nanofibers. The carbon fiber electrode modified by Cr2O3 has good electrochemical reversibility and activity for vanadium ion redox reaction. At 150 mA·cm−2, compared with pristine cell, the discharge capacity and energy efficiency of modified battery are increased by 77.2% and 6%, respectively. The energy storage performance of modified battery has been significantly improved. The synergistic effect of carbon nanofibers and second phase catalyst Cr2O3 with high catalytic performance can effectively enhance the performance of VRFB.

Groundmass Chromospinellides from Kimberlites of Khompu-May Kimberlite Field

The current paper presents the results of studying chromites of kimberlite mesostasis forming the Manchary, Aprelskaya, Erel, Turakhskaya, and Artemova pipes within the Khompu-May kimberlite field (central Yakutia). Despite shared texture and structural characteristics and mineral composition of the kimberlites, chromospinellide composition is distinctive in each pipe. Groundmass chromium spinel of the Aprelskaya and Erel kimberlite pipes is characterized by the highest aluminum oxide content (>10 wt. %). Chromites from the Erel and Turakhskaya pipes as well as a fraction of grains from the Manchary pipe with titanium oxide (<4 wt. %) form a field of common composition by Cr2O3 and TiO2 content. The Aprelskaya and Artemova pipes show up to 17 wt. % TiO2 in chromites. Such a difference in titanium content correlates with perovskite content in kimberlite groundmass of the Khompu-May field. The results of the study revealed two trends in evolution of chromospinellide microcrystals (R. Mitchell, 1986) – ulvöspinel associated with typical kimberlites and titanomagnetite characteristic of micaceous kimberlites. Chromospinellides of the Aprelskaya pipe demonstrate the ulvöspinel trend only, suggesting earlier spinel crystallization relative to groundmass mica. Spinellides from the Erel and Artemova pipes follow the titanomagnetite trend only, being crystallized after formation of mesostasis mica. Spinellides from the Manchary and Turakhskaya pipes meet the ulvöspinel and titanomagnetite trend, indicating two stages of mineral crystallization relative to phlogopite.

The Formation and Evolution of Uvarovite in UHP Serpentinite and Rodingite and its Constraints on Chromium Mobility in the Oceanic Subduction Zone

AbstractThe uvarovite‐andradite and uvarovite‐andradite‐grossular solid‐solution series are rare in nature. The discovery of uvarovite‐andradite in serpentinite and rodingite from the ultra‐high pressure (UHP) metamorphic belt in southwestern Tianshan provided an opportunity to investigate its behavior in the subduction zone. Uvarovite (defined as chromium‐garnet) from serpentinite is homogeneous in a single grain, covering compositions in the uvarovite‐andradite solid solution series of Adr58–66Uv33–41, with few grossular components. Uvarovite from rodingites contain various Cr2O3 contents (1.7–17.9 wt%) and mineral compositions being in the range of Adr21–31Uv41–50Grs22–37, Adr52–90Uv5–25Grs0–21 and Adr19–67Uv3–63Grs13–42. Discontinuous chemical variation of uvarovite from core to rim indicates that uvarovite formed by consuming andradite and chromite, which could provide Ca, Cr, Al and Fe. Raman signals of water were identified for uvarovite from both serpentinite and rodingite, with high water content in uvarovite from serpentinite. The high pressure mineral assemblage, as well as the association with perovskite, indicated that the studied uvarovite from serpentinite and rodingite was formed through high pressure metamorphism, during the subduction zone serpentinization and rodingitization. High alkaline and highly reduced fluids released from serpentinization or rodingitization in the oceanic subduction zone promote the mobility of chromium and enable its long‐distance migration.

Thermal behavior, crystal structure and electrical conductivity of {(ZrO2)0.92(Y2O3)0.08}1-x(Cr2O3)x (x = 0, 0.05, 0.10, 0.15) solid solution

{(ZrO2)0.92(Y2O3)0.08}1-x(Cr2O3)x solid solution is composed by co-precipitation method and the effects of Cr2O3 content on thermal analysis, crystal structure, microstructure and electrical conductivity are researched. The results discuss the potential for application as a diffusion barrier material at temperatures between 600 and 850 °C to the limiting current oxygen sensors. TG and DSC results show that the main weight loss and heat absorption processes occur below 600 °C and the {(ZrO2)0.92(Y2O3)0.08}1-x(Cr2O3)x solid solution is obtained above 600 °C. XRD analysis shows that the solid solution is fluorite type cubic phase and the solubility of Cr2O3 in (ZrO2)0.92(Y2O3)0.08 is less than 0.10. The SEM-EDS results show that the grain size of the sintered body decreases with increasing Cr2O3 content and distribution of each element is uniform. The conductivity of solid solution decreases first and then increases as Cr2O3 doping content, reaches the maximum value of 4.33 × 10−3 S cm−1 at 850 °C. The doping of Cr2O3 is beneficial to improve the conductivity of the solid solution at low temperature.

Petrogenesis of amphibole-rich ultramafic rocks in the Hida metamorphic complex, Japan: Its role in arc crust differentiation

Amphibole controls major and trace element chemistry of arc magma via fractionation, therefore its formation process is the key to understand arc crustal evolution. Amphibole-rich cumulates, occasionally found associated with felsic plutons or metamorphic rocks, provide complementary insights into the arc magma differentiation. In this study, we conducted a petrological examination of amphibole-rich ultramafic rocks from the Hida metamorphic complex in Japan to better understand its role in arc crust evolution. The studied samples are characterized by large poikilitic amphibole and orthopyroxene enclosing olivine grains with corroded margins. Amphibole showed high Cr2O3 and TiO2 contents (up to 0.9 and 1.2 wt%) and light rare earth element enrichment relative to heavy rare earth elements. Microscopic and geochemical features of amphibole and olivine suggest that the amphibole formed at the expense of early crystalized olivine (± clinopyroxene) from hydrous juvenile magma at a deep crustal level, which is consistent with the estimated crystallization pressure of 0.7–1.0 GPa based on an empirical Al-in-hornblende geobarometer. Considering the arc affinity of parental magma and the amphibole-fractionation trend in bulk chemistry of the Mesozoic plutonic rocks from the Hida Belt, it is implied the formation of amphibole-rich plutonic rocks contributed to arc crustal evolution as amphibole-rich residue complementary to differentiated magma.

Impact plume‐formed and protoplanetary disk high‐temperature components in CB and CH metal‐rich carbonaceous chondrites

AbstractWe report on the mineralogy, petrology, and oxygen isotopic compositions of ferroan olivine–pyroxene‐normative cryptocrystalline chondrules (Fe‐CCs) in CH chondrites and discuss their origin and the origin of other components in the genetically related CH and CB chondrites. There are two kinds of Fe‐CCs: (1) compositionally uniform (Fe/[Fe+Mg] = 0.17–0.34) chondrules with euhedral Fe, Ni‐metal grains and (2) metal‐free chemically zoned (Fe/[Fe+Mg] = 0.05–0.4) chondrules surrounded by ferroan olivine (Fa44−62) rims; the Fe/(Fe+Mg) ratio increases toward the rims. Both types contain low CaO and Al2O3 (&lt;0.04 wt%), but relatively high contents of MnO and Cr2O3 (up to 1 wt%). Compositionally uniform euhedral Fe, Ni‐metal grains are Ni‐rich (9–20 wt%) and have subsolar Co/Ni ratio. There is a positive correlation between iron content in the metal grains and Fe/(Fe+Mg) ratio in silicate portion of their host chondrules. Some Fe‐CCs experienced postcrystallization solid‐state reduction of ferroan silicates to metallic iron. Ferroan cryptocrystalline chondrules and olivine rims have similar oxygen isotopic compositions (interchondrule Δ17O ranges from ~ −2‰ to 2‰), which are slightly 16O‐depleted relative to those of magnesian olivine–pyroxene‐normative cryptocrystalline chondrules (Mg‐CCs; Δ17O ~ −2‰) commonly observed in CBs and CHs. We suggest that the Fe‐CCs and Mg‐CCs formed in the impact plume under different redox conditions (~IW−1 and ~IW−3, respectively), which may have been controlled by heterogeneous distribution of water‐bearing phases (water ice, hydrated materials) in the collided bodies and/or in the disk. We propose the following impact plume scenario for the origin of Fe‐CCs: (1) condensation of ferromagnesian silicate melt around Fe, Ni‐metal melt droplets from a highly oxidized portion of the plume; (2) crystallization of euhedral metal grains from the supercooled ferromagnesian silicate melt followed by its solidification; (3) condensation of ferroan olivine rims around solidified Fe‐CCs; (4) high‐temperature annealing of Fe‐CCs and their rims in the plume accompanied by Fe‐Mg interdiffusion between ferroan olivine rims and their host chondrules. Subsequently, some Fe‐CC experienced solid‐state reduction to various degrees, possibly in the reduced portions of gaseous plume. The impact plume‐produced or reprocessed components in CBs and CHs include Ca,Al‐poor magnesian and ferroan cryptocrystalline chondrules; Ca,Al‐rich skeletal olivine chondrules; isotopically uniform, 26Al‐poor 16O‐depleted (Δ17O ~ −15 to −5‰) igneous CAIs surrounded by igneous forsterite rims; chemically zoned and unzoned Fe,Ni‐metal grains; and metal‐sulfide nodules. These objects are dominant in CBs and abundant in CHs. The CH chondrites also contain other high‐temperature chondritic components, which avoided processing in the plume and most likely predate the plume event: 26Al‐poor and 26Al‐rich, mostly 16O‐rich CAIs (Δ17O ~ −40 to −10‰) surrounded by Wark–Lovering rims, and porphyritic chondrules (magnesian [type I], ferroan [type II], and Al‐rich) showing a range of Δ17O (from ~ −10 to ~ +5‰). Some of these components appear to have been melted in the plume. We conclude that CH and CB chondrites contain multiple generations of chondrules and refractory inclusions formed by different mechanisms at different times and different regions of the protoplanetary disk, consistent with the hypothesis of Wasson and Kallemeyn (1990).

One-step synthesis of heterojunction Cr2O3 nanoparticles decorated Bi2S3 nanorods with enhanced photocatalytic activity for mineralization of organic pollutants

Herein, one-step synthesis of Cr2O3/Bi2S3 nanorods at various Cr2O3 contents (0.01–0.05%) is developed using a hydrothermal approach for degradation of two organic pollutants such as phenol and methylene blue (MB) under visible light irradiation. TEM observation showed that the Cr2O3 NPs around 5 nm at very small content decorated the surface of Bi2S3 nanorods. The photocatalytic performance of synthesized photocatalyst exhibited an effective photocatalytic efficiency of about 90% for Phenol and 80% for MB upon visible light exposure. The photocatalytic performance of 0.04% Cr2O3/Bi2S3 heterostructure was enhanced 2.66 and 2.25 times larger than bare Bi2S3 nanorods for degradation of MB and phenol, respectively. The temperature-programmed desorption ensures that Cr2O3/Bi2S3 heterostructure has more acidic active sites, which increased the OH radical absorption and then increased the photocatalytic efficiency. The electrochemical impedance spectroscopy (EIS), photoelectrochemical behavior and photoluminescence spectra were measured as evidence for the photocatalytic mechanism. The results indicated that the construction Cr2O3/Bi2S3 heterostructure has significantly suppressed the recombination rate of photoinduced carriers and consequently enhanced its photocatalytic efficiency. Additionally, the Cr2O3/Bi2S3 heterostructure revealed high recyclability, durability and stability for five cyclic runs without significant loss of the photocatalytic performance, making the synthesized photocatalyst promising for the remediation of wastewater under sunlight.

Identification and pairing reassessment of unequilibrated ordinary chondrites from four Antarctic dense collection areas

AbstractNew analyses of Cr2O3 contents of olivines from type II chondrules in unequilibrated chondrites (UOC) from four dense collections are reported here. This survey of petrologic type 3 UOCs was undertaken to identify primitive chondrites that may have been overlooked, and to address possible pairing errors. We have identified 23 primitive UOCs (≤3.10) (only five identified previously, for a total of 28 overall), and also recommend other revisions to prior classifications and pairings.

Microstructure and corrosion behavior of FeCrNiCoMnx (x = 1.0, 0.6, 0.3, 0) high entropy alloys in 0.5 M H2SO4

The effect of Mn on the passivation behavior of FeCrNiCoMn high entropy alloy was elucidated in detail via anodic polarization of FeCrNiCoMnx (x = 1.0, 0.6, 0.3, 0) in 0.5 M H2SO4. A decrease in Mn content reduced Mn-related oxide/sulfide inclusions and elevated the Cr2O3 content in the passive film, conferring better corrosion resistance of FeCrNiCoMnx. The XPS results revealed a competitive oxidation of Mn with Cr, which lowered the Cr2O3 content in the passive film. This leads to inferior corrosion resistances of FeCrNiCoMn, FeCrNiCoMn0.6, and an equivalent resistance of FeCrNiCoMn0.3, compared to 304 L stainless steel.

Effect of Cr2O3 on the crystallization, structure, and properties of Ti-bearing blast furnace slag-based glass ceramics

ABSTRACT The effects of Cr2O3 on the crystallization, structure, and properties of Ti-bearing blast furnace slag-based glass ceramics were investigated. The results show that the transition temperature and crystallization temperature decreased with introduction of Cr2O3 as a while. Specifically, the crystallization temperature first decreased, then increased with the increase Cr2O3 concentration from 0.2 wt% to 0.8 wt%, and finally decreased with further increased in Cr2O3 concentration. The crystal phases were identified as anorthite, diopside, and akermanite. As the content of Cr2O3 increased to 0.8 wt%, the dendrites gradually decreased and the granular crystals gradually increased. When the Cr2O3 concentration further increased, the number of granular crystals gradually decreased and the dendrites gradually accumulated. With the increase of Cr2O3 from 0.2 wt% to 0.8 wt%, the structure of the investigated glass gradually depolymerized, while the opposite trend was presented with further increased in Cr2O3 content. With increasing Cr2O3 content from 0.2 wt% to 2 wt%, the flexural strength values and Vickers hardness values of the glass ceramics first increased and then decreased, and the maximum values of flexural strength and Vickers hardness were obtained as 94.371MPa and 974.43MPa, respectively. The prepared Ti-bearing blast furnace slag-based glass ceramics showed good acid and alkali resistance.