Cr2O3 Content Research Articles

Feasibility of using Cr-containing vitrification product as cement admixture: Structural evolution and chromium immobilization

With China already committing to bring carbon dioxide emissions to a peak before 2030, reducing the amount of used cement is an economical and effective measure. In this study, chromium-containing vitrification products were used as a cement admixture to achieve chromium reduction and immobilization. This study presents the effect of MgO/B2O3/Cr2O3 on the relationship between the network structure and chemical resistance of a Cr-containing glass matrix. The acid/alkali resistance of the glass specimens improved with an increase in Cr2O3 content under the same matrix composition. With the replacement of CaO by MgO, the chemical resistance of boron-free glass specimens improved, while that of Mg/B-containing glass specimens significantly decreased. The behaviors of the glass matrix in chemical environments affected the hydration and chromium immobilization of cement clinkers. In paste specimens, the pozzolanic reaction of the glass powder enhanced the densification of specimens. The mechanical strength was attributed to the filling effect of pozzolanic gels and undissolved glass powder in the mortar samples. B-containing glass powder negatively affected the mechanical strength and chromium immobilization of cement samples, while an appropriate amount of MgO and Cr2O3 was beneficial to the physical and chemical properties of the material. Therefore, chromium-containing waste glass can be effectively used to produce eco-friendly building materials.

Influence of Cr2O3 on the Viscous Flow Behavior and Structure of Cr‐Containing Molten Titanium Slag

Herein, the influence of Cr2O3 on the viscous flow behavior and structure of Cr‐containing molten titanium slag is investigated in this work. The melting and viscosity properties are studied by hemisphere method and rotating cylinder method, respectively. In addition, the structure of Cr‐containing molten titanium slag is investigated by Raman spectroscopy. It is shown in the results that the melting temperature and viscosity both increase with the increase of Cr2O3 content. The activation energy for viscous flow increases with increasing Cr2O3 content, which is in the same trend as viscosity. When the Cr2O3 content increases from 0% to 3%, the simpler 6‐coordinated Ti4+ and TiO44− monomer unit transformed into more complex O–Ti–O deformation and Ti2O64− chain unit. Furthermore, the fraction of relatively complex silicate structural units shows an increasing trend. Cr2O3 behaves as a network former and enhances the degree of polymerization of network structure, and the variation of Cr‐containing molten titanium slag structure is consistent with the increasing trend of viscosity.

Effects of Mo Particles Addition on the Microstructure and Properties of 316 L Stainless Steels Fabricated by Laser Powder Bed Fusion.

Application of the 316 L stainless steel (SS) is limited by its relatively low wear resistance, insufficient strength, and poor corrosion resistance in special environments. To this end, effects of Mo particles addition on the microstructure, mechanical properties, and corrosion resistance of the laser powder bed fusion (LPBF) 316 L SS are investigated in this study. The results show that the addition of Mo particles from 0 wt.% to 10 wt.% can modify the crystal orientation and improve the strength, wear resistance, and corrosion resistance of LPBF 316 L SSs. Particularly, the LPBF 316 L SS forms a biphasic structure with a similar ratio of α-Fe to γ-Fe with 5 wt.% Mo addition. As a result, the corresponding samples possess both the excellent toughness of austenitic SSs and the high strength and corrosion resistance of ferrite SSs, which reaches a high tensile strength of about 830 MPa, together with a low friction coefficient of 0.421 μ. Since the Mo particles addition is beneficial to increase the content of Cr2O3 on the samples surface from 13.48% to 22.68%, the corrosion current density of 316 L SS decreases by two orders of magnitude from 569 nA to 6 nA, while the mechanical properties remain favorable. This study is expected to serve as a reference for the preparation of LPBF SSs with excellent integrated performance.

The oxygen-rich nanoparticles optimized by heat treatment enhance the corrosion resistance in selective laser melted 304L stainless steel

The effect of heat treatment on the corrosion property of selective laser melted (SLM) 304L stainless steel (SS304L) was investigated by adjusting the oxygen-rich nanoparticles and the microstructure. A significant improvement in the pitting resistance of SLM SS304L was found after the 1100 °C heat treatment. The heat treatment eliminated the melt pool boundaries, reduced the defect density and promoted the formation of uniform and dispersed oxygen-rich nanoparticles. In addition, the Cr2O3 content in the passive film increased after the heat treatment. These factors enhanced the stability of the passive film and improved the corrosion resistance of SLM SS304L.

Circadian feeding characteristics of different abalone species and construction of a gastrointestinal evacuation model

Abalone are of significant economic importance in the marine shellfish market in China. In order to examine feeding characteristics and formulate a model of gastrointestinal evacuation for Haliotis discus hannai, H. gigantea, and H. discus hannai ♀ × H. fulgens ♂, fecal output after intake of feed labelled with chromium sesquioxide (Cr2O3) was subjected to uninterrupted monitoring for 72 h. Feed consumption levels of H. discus hannai, H. gigantea, and H. discus hannai ♀ × H. fulgens ♂ were seen to harbor a circadian rhythm. Over 90% of the feed intake occurred between 20:00 and 04:00, and fecal output of H. discus hannai, H. gigantea, and H. discus hannai ♀ × H. fulgens ♂ was continuous over the experimental period. The cosine fitting peak phases of fecal output of H. discus hannai, H. gigantea, and H. discus hannai ♀ × H. fulgens ♂ appeared at 09:07, 08:46, and 08:24, respectively, all about 9 h after the appearance of each feeding peak. Based on the measured Cr2O3 content in feces, about 70% of the gastrointestinal evacuation of the labelled feed occurred 12–24 h after consumption. The time-dependent variation of the percentage evacuated of three abalone species agrees well with the logistic model (R2 > 0.99); H. discus hannai, H. gigantea, and H. discus hannai ♀ × H. fulgens ♂ evacuated 50% of the feed within about 19 h, and 95% was evacuated at 32.99, 30.09, and 29.96 h, respectively. In this work, a non-destructive method was used to accurately measure the time required for the gastrointestinal evacuation of abalone, provided that abalone could ingest feed without fasting. This work not only enriched the basic knowledge of abalone’ digestive physiology, but also provided a theoretical reference for developing reasonable feeding strategies.

Mineral Associations of Concentrates from Gold-Bearing Placers of the Miass Placer Zone (South Urals) and Possible Primary Sources of Gold

Abstract —The placer deposits of the Miass valley in the Southern Urals have been known since the beginning of the 19th century. Over two centuries of mining more than 120 tons of gold have been extracted from alluvial and alluvial–deluvial placers. Despite the industrial significance of this territory, native gold of alluvial deposits is practically unstudied and there is no data on the mineral composition of concentrates. Native gold and heavy fraction minerals from seven placers of the Miass placer zone of deluvial–alluvial and alluvial types were researched. The study of the typomorphic features of native gold and distribution of heavy fraction minerals in loose deposits makes it possible to determine the genetic types of primary sources of placer formation. Chrome-spinel and ilmenite prevail in the concentrates, magnetite, epidote, rutile, titanite, clinopyroxene, hematite, zircon, garnets, and monazite are less common. Chromespinelides of various placers are represented by chromite and subferrichromite, they are characterized by a high average content of Cr2O3 (50.9 wt.%). Chromespinelide chemical composition features show evidence of its penetration into placer sediments from rocks of the ophiolitic association. The composition and morphological features of phosphates of rare earth elements (monazite and xenotime) indicate their metamorphogenic nature and penetration into placers from the Riphean strata. Native gold is characterized by a low degree of roundness. Mineral inclusions in native gold are represented by sulfides, arsenides, bismuthides, cuprous gold, platinoids. Composition of native gold from the Miass River valley placers varies over a wide range. The main admixtures are silver (4.5–23.4 wt.%) and mercury (up to 5.14 wt.%), copper (up to 2.03 wt.%) was noted in several grains. The EBSD study of native gold internal structure showed predominance of primary crystallization structures, a low degree of deformation and growth of gold-rich rims with a fine-grained mosaic structure. Formation of gold-rich rims in gold grains in placers is explained by recrystallization of the most deformed parts of gold during transportation. Placers occurred due to the destruction of primary sources located in the upper reaches of streams or near them, which is confirmed by a low degree of grains’ roundness. The composition of native gold in combination with a set of micro-inclusions indicate the gold–sulfide-quartz type of mineralization of most primary sources.

An efficient strategy for enhancing the corrosion resistance of S31254 super austenitic stainless steel through slight Mo segregation

Super austenitic stainless steel (SASS) is one kind of high Mo-alloy steel with excellent corrosion resistance when applied in an extremely corrosive environment. However, high contents of Cr and Mo tend to form precipitates along the grain boundary at high temperatures, leading to a great deterioration of corrosion resistance. Herein, a method of short-time aging treatment at 500 °C and 550 °C was explored, which was intended to regulate the distribution of elements at grain boundaries to improve corrosion resistance. The results indicate that before the precipitates nucleation, as the temperature rises from 500 °C to 550 °C, the Mo element has obvious diffusion behavior towards the grain boundary. Also, the uniform distribution of a small amount of Mo at the grain boundary can be conducive to improving the corrosion resistance. In addition, B inhibits the separation of Mo to grain boundary and delays the formation of the precipitated phase. The addition of B improves the intergranular corrosion resistance of SASS, especially after aging at 500 °C, which is attributed to the passivated film's Cr2O3 and Mo(VI) content. However, when the aging temperature reaches 550 °C, more Mo segregates to the grain boundaries, resulting in Mo-depleted zones, which decreases corrosion resistance.

Recycling of Chrome-Containing Waste from a Mining and Processing Plant to Produce Industrial Products

Prolonged development of ore deposits, ore beneficiation and metallurgical smelting of concentrates result in the accumulation of wastes, forming large-scale dumps and sludge ponds negatively affecting the environment and human health. The creation and introduction of industrial waste treatment technologies will make it possible to dispose of them with the production of valuable commercial products and improve the environmental situation. In a research article on chemical beneficiation with the subsequent gravitational beneficiation of chrome-containing slurry tailings of Donskoy Ore-Mining and Beneficiation Plant (DOMBP), which processes chrome ore of the Kempirsay deposit in the Republic of Kazakhstan, Aktobe region, having considerable stocks of such waste is presented. The chromium-containing slurry tailings were heat-treated at 1100 °C, sintered with ammonium sulfate, water and sulfuric acid in a defined ratio at 300 °C, and then the resulting sinter was leached with water at 90 °C. The cake was washed to separate the liquid part from the solid part. The solid precipitate is the chromium-containing cake, which is upgraded by gravity concentration to a grade concentrate for ferroalloy production. When the solution is evaporated, magnesium sulfate with ammonium sulfate forms the Tutton’s salt ammoshenite. High-throughput chromium oxide extraction of 93.9% was achieved as a result of the research, and three products were obtained: (1) standard chromium concentrate with 49.48% Cr2O3 content, (2) ammoshenite used as a nitrogen–magnesium fertilizer and (3) forsterite, which is concentrated in gravity concentration tailings and can be used in the production of refractory minerals.

Influence of Cr2O3 Concentration on the Green Color of Flux Synthesized Emeralds Using the CIE1976 Color System

AbstractThe color of emeralds is predominantly influenced by the concentration of Cr3+. However, the evaluation of the trend of green color depth of emeralds, based on the practical single crystal synthesis with several instrumental analysis is not investigated in previous researches. Specifically, if the Cr2O3 content is controlled to be in the range of 0.2–0.4 wt%, then emeralds can be synthesized with the most esthetically pleasing color. Therefore, the effect of Cr2O3 concentration within the aforementioned range on the color of emeralds is studied using powder X‐ray diffractometry, digital microscopy, electron probe microanalysis, and micro‐spectrophotometry to understand how to achieve the most esthetically pleasing color. As a result, detailed behaviors relating to the absorbances, L*, a*, and b* values, and the relationship between the emerald crystal color changes and increases in Cr2O3 concentration are elucidated. Notably, the absorbance, L* and a* values change significantly when the Cr2O3 concentration is low (0.00–0.236 wt%). However, the changes in these values are moderate when the Cr2O3 concentration is higher (0.236–0.504 wt%).

Effect of Cr2O3 on the microstructure and wear resistance of coatings prepared from Cr2O3-SiC-Al composite powders

Introducing the in-situ reaction synthesis into the thermal spraying process, the content of each phase in the raw material will directly affect the phase and microstructure of the coating obtained by spraying. Therefore, composite powders with different Cr2O3–SiC–Al mass ratios were used as coating materials, and composite coatings were prepared using an atmospheric plasma spraying process. By analyzing the coatings' phase composition, microstructure, wear resistance, and other properties, the effect of the variation of Cr2O3 content in the composite powders on the performance of the coating was investigated. The results showed that with the decrease of Cr2O3 content in the composite powder, the coatings’ compactness, microstructure uniformity, and wear resistance decreased. The coating prepared by Cr2O3–SiC–Al composite powder with a mass ratio of 65:12:23 had good compactness and microstructure uniformity, the microhardness and toughness were also the best among the three groups of coatings, and it presented higher wear resistance.

Mechanical properties and microstructure of Cr2O3 reinforced 3Al2O3·2SiO2 composite refractories

Chromium-containing refractories have excellent high-temperature corrosion resistance. In this work, Cr2O3 reinforced Al2O3–SiO2 composite refractories were prepared by reaction sintering process. The microstructure, phase composition, mechanical properties and strengthening mechanism of the Cr2O3 reinforced Al2O3–SiO2 composite refractories were investigated. The results show that when the Cr2O3 content is 10–20 wt%, the composites are mainly composed of Cr-mullite (Al3.94Cr0.50Si1.56O10.44), (Al, Cr)2O3, and a small amount of SiO2 phase. When the Cr2O3 content exceeds 20%, the composite refractories mainly consist of (Al, Cr)2O3 and SiO2 phases. The appropriate amount of Cr2O3 can effectively enhance the mechanical properties and compactness of the Cr2O3 reinforced Al2O3–SiO2 composites. This is mainly due to the formation of Cr doped mullite and SiO2 phases, which reduces the sintering temperature of mullite ceramics and improves its density and mechanical properties. The highest hardness (27.03 GPa), flexural strength (213.21 MPa) and compressive strength (528 MPa) values are observed at a Cr2O3 content of 20 wt%. However, excessive addition of Cr2O3 will deteriorate the mechanical properties of the composites. The formation of a large amount of (Al, Cr)2O3 solid solution phase will increase the porosity of the composites, and reduce the compactness and sintering properties of the composites.

Improvement of the corrosion performance of a cold-rolled Co40Cr20Ni30Al5Ti5 high-entropy alloy by adjusting annealing treatments

High-entropy alloys (HEAs) are expected to possess various excellent properties due to their vast composition design space and unique core effects. Annealing treatments after cold rolling are widely discussed as an effective means to improve the overall performance of the alloy. Nevertheless, the effect of annealing treatments on the corrosion resistance of cold-deformed alloys is still somewhat controversial. Therefore, cold rolling and annealing at different temperatures are performed on the Co40Cr20Ni30Al5Ti5 high-entropy alloy to investigate the effect of annealing temperature on its corrosion behavior. The annealing temperature range covers all stages of the HEA recovery-recrystallization-grain growth (in 50 °C gradients). The experimental results show that the HEA recrystallization is fundamentally complete at 850 °C and fully austenitized at 1050 °C. The best corrosion resistance performance is observed at 850 °C, with the lowest corrosion current density (ipass) and the lightest pitting in full immersion experiments. In addition, excellent passivation properties, such as the lowest steady-state current density iss and highest passivation film growth rate, are achieved at 850 °C. Further analyses of the growth films also show that the passivation films formed at 850 °C are thicker and uniform, and additionally have the highest Cr2O3 content. Accordingly, the effects of annealing temperature on HEA corrosion resistance and passivation behavior are discussed. The superior corrosion resistance and passivation behavior at 850 °C are attributed to the coupling of grain size and passivation film composition. The current findings might guide the optimized design of future cold-deformed alloys for better corrosion resistance.

The Effect of Heating Time on the Thermal Stability of Chrome-Tanned Leather

Chrome tanning is an essential process to convert raw animal skin into leather, in which collagen, as the main structure of leather, is stabilized against degradation through cross-linking using chromium, consisting of two steps: penetration and basicity. However, the uptake of chrome in leather still needs to be improved. The purpose of this study was to find the best heating time in the chrome tanning process by thermal analysis. Pickled sheepskin was used as raw material for the chromium tanning process. The samples were varied into four categories: heated at the penetration stage of the tanning process (Initial Heating), heated at the basification stage of the tanning process (Final Heating), and heated both at the penetration and basification stage (Continuous Heating). In this study, the thermal stability of wet blue leather was evaluated by shrinkage temperature behavior (Ts), thermogravimetry analysis (TGA/DTG), and differential scanning calorimetry (DSC). The tanning efficiency was measured by Cr2O3 content. The results demonstrated that wet blue samples heated continuously shows better thermal characteristics. In conclusion, the results can be used for finding the best possible technique for the leather tanning process using chrome salts to gain thermal stability.

Passivation Behavior of Different Building Planes of Selective Laser Melting 316L Stainless Steel in 3.5% NaCl Solution

The passivation behavior of selective laser melting 316L stainless steel (SLM 316L SS) on different building planes is studied in 3.5% NaCl solution. The results show that the XOZ and YOZ planes have a semicircular molten pool structure, and the XOY plane shows a columnar molten pool structure. Meanwhile, the XOZ planes have relatively smaller grain sizes and higher low‐angle grain boundaries (LAGBs) proportionate than that of YOZ and XOY planes. The electrochemical testing results illustrate that the XOZ plane has a lower corrosion tendency than that of YOZ and XOY planes, as the thicker passive film with higher content of Cr2O3 is detected on the XOZ plane. The XOZ plane, which has a higher Crox + hy /(Feox + hy + Crox + hy ) ratio, has excellent passivation performance and better electrochemical properties than the other two planes.

Effect of Cr2O3 on the Kinetics Mechanism and Microstructure of Pellet During Oxidation Roasting Process

The oxidation process of iron ore with different Cr2O3 contents is separated into two stages. The Coats–Redfern method is applied to conduct the kinetic analysis, and the restriction links between stages I and II correspond to diffusion control. The apparent activation energy (E) progressively decreases at all stages as the contents of Cr2O3 increase, which is favorable for improving the oxidation kinetics. The fluctuation amplitudes of E in stages I and II are 5.450 and 16.021 kJ mol−1, respectively. The interaction of Fe2O3 and Cr2O3 during oxidation forms a Fe–Cr solid solution, which loosens the internal structure of the pellet and thus increases the number and diameters of the inner pores. This phenomenon facilitates the internal diffusion of oxygen and lowers its concentration inside and outside the pellet. Therefore, the utilization of chromium‐bearing iron ore should be comprehensively considered in terms of its kinetics and microstructure.

Dual roles of Cr2O3 in preparation of glass-ceramics from ferronickel slag

The dual effects of Cr2O3 in the fabrication of glass-ceramics from ferronickel slag (FNS) with the addition of coal fly ash (CFA) were investigated by varying the content of Cr2O3 from 0 wt % to 2.0 wt %. The crystallization kinetics results showed that as the Cr2O3 content increased from 0 wt % to 1.6 wt %, the crystallization activation energy of the parent glass decreased from 448.23 kJ/mol to 232.65 kJ/mol with the change of crystallization mode from surface crystallization to bulk crystallization. When the content of Cr2O3 reached 1.6 wt %, there existed the highest degree of depolymerization of the glass network and the strongest crystallization tendency. The prepared glass-ceramic was composed of enstatite as the main crystalline phase and spinel as the secondary crystalline phase. The microstructure changed from a loose tabular structure to a dense spherical structure. As the Cr2O3 content further increased to 2.0 wt %, the crystallization activation energy increased to 304.21 kJ/mol and the spherical structure became inhomogeneous due to the coexistence of enstatite particles with different sizes. By controlling the Cr2O3 content of 1.6 wt %, an optimal glass-ceramic with density of 3.17 g/cm3, bending strength of 175 MPa, Vickers microhardness of 9.51 GPa, acid resistance of 99.99% and alkali resistance of 99.97% was obtained. This study provided a novel method for promoting conversion of FNS to glass-ceramics.

Garnet composition from the Reflejos de Mar LCT-pegmatite, Ancasti district, Argentina and its implication for exploration of primary deposits of lithium

The Reflejos de Mar Li-pegmatite, located in northwestern Argentina, is part of the Villismán pegmatite group, Ancasti District, Pampean Pegmatite Province. Four garnet crystals from the outermost part of the pegmatite were analyzed by major and minor elements (SiO2, TiO2, Al2O3, Cr2O3, MgO, CaO, MnO, FeO) using electron microprobe. The pegmatite belongs to the rare-element class, spodumene type, LCT (Li-Cs-Ta) petrogenetic family. Based on their Mn and Fe contents, the analyzed garnet can be assigned to the spessartine-almandine serie. The cores and rims of the analyzed garnets show significant differences for the divalent components in VIII-coordination, especially, Mn and Fe. The average MnO and FeO contents in the cores of the grains is 34.6 and 8.29 wt%, respectively, while in the rims is 29.31 and 12.95 wt%, respectively. The Fe/Mn ratio at the core of the grains is 0.24 while at the rims it is 0.44. Cr2O3 and TiO2 contents are very low (˂0.17 wt%) and the values of SiO2 and Al2O3 are ~36 and ~21 wt%, respectively. The mean chemical and molecular formulas of the core can be expressed: [(Mn2.40 Fe0.57 Ca0.02 Mg0.02)3.01 (Al1.99 Cr0.002)2.00 (Si2.99 Ti0.01)3.00 O12]; {Sps79.8 Alm18.9 Grs0.7 Prp0.5}; and the rim as: [(Mn2.04 Fe0.89 Ca0.05 Mg0.04)3.02 (Al2.00 Cr0.002)2.00 (Si2.98 Ti0.005)3.00 O12]; {Sps67.6 Alm29.5 Grs1.6 Prp1.3}. The chemical composition of garnet from the Reflejos de Mar pegmatite is similar to other worldwide examples in similar rocks, especially LCT pegmatites, which are highly evolved and associated with Li mineralization. Therefore, its composition could be used as an additional tool in the exploration of Li-bearing pegmatites in the Pampean Pegmatite Province. The differences in Fe-Mn contents between core and rim of the crystals would be controlled by variations in composition of the pegmatitic melt and, in addition, by the simultaneous precipitation of other mineral phases, for example, schorl and Mn-Fe-bearing phosphates.

The effects of the source composition on the origin of orthopyroxene-bearing adakitic granitoid in West Qinling, Central China

Orthopyroxene-bearing granodiorite (sometimes referred to as ‘charnockite’) with an adakitic affinity is a rare type of granitoid. It is generally accepted that the stabilization of orthopyroxene in igneous charnockites essentially requires low aH2O and/or high temperatures in a closed system. However, orthopyroxene can be an antecryst in a trans-crustal magmatic system. In this regard, orthopyroxene-bearing granitoids are somewhat analogous to pseudo-charnockites, where the orthopyroxene stems from a mafic reservoir. On the other hand, the source compositions of continental adakites can vary, which is often ignored in the interpretation of their contribution to the adakitic geochemical signature. In this study, we have investigated a rare orthopyroxene-bearing felsic pluton from the Zhuyuan area of West Qinling, Central China. The Zhuyuan pluton was emplaced in the Middle–Late Triassic (222 Ma–217 Ma) and is mainly composed of metaluminous to weakly peraluminous granodiorites belonging to the high-K calc-alkaline series. Moreover, they are characterized by high Mg# values (49.7–60.9) and Sr contents (471–697 ppm), low Y (12.2–15.4 ppm) and Yb (1.03–1.24 ppm) contents, high Sr/Y (33.2–46.2) and (La/Yb)N (15.3–21.4) ratios, and weakly negative Eu anomalies (Eu/Eu* = 0.78–0.89). The Zhuyuan adakitic granodiorites exhibit fairly limited Sr–Nd–Pb isotopic ratios and variable zircon initial Hf isotopes, indicating a major contribution from the Neoproterozoic basement of the Qinling Orogenic Belt. There is no evidence of any formation through high-pressure magmatic processes, and we propose that the adakitic signature of the Zhuyuan pluton could have been inherited from its source rocks (i.e., from the Neoproterozoic basement). The orthopyroxenes in the Zhuyuan granodiorites display poikilitic textures with high MgO, NiO and Cr2O3 contents, indicating that they have an antecrystic origin. Studies of regional tectonic evolution have shown that the Zhuyuan granodiorites formed during the tearing stage of the A'nimaque–Mianlue oceanic subduction slab. Therefore, this study emphasizes the effect of source inheritance on the formation of pseudo-charnockite with an adakitic signature.

Corrosion mechanism of magnesia-chrome refractory bricks with FetO-SiO2-Cr2O3 copper converter slag

The paper investigates the effect of Cr2O3 on the resistance of magnesia-chrome refractory bricks to copper converter slag. The static crucible method was employed to carry out the slag resistance experiment. The corrosion of magnesia-chrome refractory bricks under the action of FetO-SiO2-xCr2O3 (x = 0–5 wt%) slag at 1300 °C was discussed. The microstructure of the corroded sample was analyzed by XRD and SEM-EDS to elucidate the corrosion mechanisms of magnesia-chrome refractory bricks with FetO-SiO2-Cr2O3 slag. The results indicated that the permeability index of the slag-resistant samples gradually decreased with increasing Cr2O3 content in the FetO-SiO2-Cr2O3 slag. Combined with SEM and XRD characterization, the MgO in the refractory reacted with FeO and SiO2 in the molten slag, leading to dissolution and reaction corrosion of the refractories. Meanwhile, forming a (Mg, Fe)O solid solution layer in corroded samples can prevent further chemical reactions and high-temperature dissolution between the FetO-SiO2-Cr2O3 slag and refractories. With the addition of Cr2O3 in the FetO-SiO2-Cr2O3 slag, the corrosion effect of slag on refractories was weakened, and the (Mg, Fe)O solid solution layer became thinner. The magnesia-chrome refractory bricks showed excellent slag resistance when the Cr2O3 content in the copper converter slag was 5 wt%.

The peridotite-pyroxenite sequence of Rocca d'Argimonia (Ivrea-Verbano Zone, Italy): Evidence for reactive melt flow and slow cooling in the lowermost continental crust

The present study investigates the origin of a ∼ 400 m thick peridotite-pyroxenite sequence, locally known as Rocca d'Argimonia, which is encased within the lowest levels of the ∼8 km thick Mafic Complex, a gabbro-dioritic batholith from the lower continental crust section of the Ivrea-Verbano Zone (Southern Alps). The broad purpose of this work is to elucidate the evolution of mantle-derived magmas emplaced in the lowermost continental crust. We also wish to provide new geochronological constraints on the intrusion and the cooling evolution of the Lower Mafic Complex, which are still mostly unknown.Zircon grains separated from two gabbronorites enclosing the peridotite-pyroxenite sequence document a whole reset of the original UPb isotopic system at 286 ± 2 Ma. A Rocca d'Argimonia peridotite provided a consistent age of 296 ± 19 Ma, based on a LuHf clinopyroxene-amphibole alignment (initial εHf = +7.9). These results are interpreted to date the early cooling evolution of the Lower Mafic Complex. The clinopyroxene-amphibole peridotite pair also gave a RbSr alignment corresponding to an age of 250 ± 16 Ma (initial 87Sr/86Sr = 0.7045), which is reconciled with the subsequent, slow cooling evolution of the Lower Mafic Complex.The Rocca d'Argimonia peridotites (dunites to harzburgites and lherzolites) have whole-rock εNd(286 Ma) and εHf(286 Ma) values ranging from +0.4 to −1.1 and from +8.8 to +3.4, respectively, and 87Sr/86Sr(286 Ma) ratios varying from 0.7048 to 0.7060. The peridotites are crosscut by gabbronorite dykes and associated with olivine-free orthopyroxene-dominated pyroxenites. The gabbronorite dykes and the pyroxenites share the Nd-Hf-Sr signature of the peridotites. The gabbronorites enclosing the peridotite-pyroxenite sequence differ in the relatively enriched Nd-Hf-Sr isotopic fingerprint (εNd(286 Ma) = −4.5 to −5.6, εHf(286 Ma) = +0.2 to −2.5, 87Sr/86Sr(286 Ma) = 0.7073 to 0.7086). Remarkably, pyroxenes from the pyroxenites typically contain higher Cr2O3 than the peridotite counterparts (e.g., 0.23–0.37 wt% Cr2O3 in peridotite orthopyroxenes and 0.43–0.50 wt% Cr2O3 in pyroxenite orthopyroxenes).We propose that the peridotite-pyroxenite sequence formed by reactive melt percolation through an olivine-rich spinel-bearing matrix. In particular, the relatively high Cr2O3 content of the pyroxenitic pyroxenes is attributed to redistribution of Cr released by the breakdown of accessory spinel that was originally present in the olivine-dominated matrix, in response to a high melt/solid ratio. The melt residual after the crystallization of the pyroxenites continued to percolate the olivine-dominated matrix, thereby forming spinel-bearing lherzolites, harzburgites and dunites with the progression of the melt migration process. The chemically most primitive dunite records Nd-Hf-Sr isotopic disequilibrium conditions, thereby providing further information about the process of reactive melt flow. It is inferred that the original olivine-dominated matrix crystallized from a mantle magma having a slightly enriched Nd-Hf-Sr isotopic signature, whereas the percolating melts overall had a relatively depleted Nd-Hf-Sr isotopic fingerprint, despite being variably contaminated by the continental crust.