Al2O3 Cr2O3 Research Articles

Behavior of free-standing atmospheric plasma sprayed Al2O3–Cr2O3 solid solution-based coatings under cyclic heating at 1000 °C

This paper investigates the cyclic heating behavior of free-standing atmospheric plasma sprayed Al2O3 - Cr2O3 coatings containing a solid-solution phase. The coatings are deposited on steels by spraying mechanically blended Al2O3 - Cr2O3 powder mixture with variable Cr2O3 content (2–6 wt%) in the feedstock. The tests are performed up to 50 cycles at 1000 °C temperature in a muffle furnace in a normal atmosphere. After each cycle, the weight gain of the coatings is measured, and the oxidation rate constant (Kp) for each material is estimated. The microstructure and phases of the coatings are studied by using scanning electron microscopy (SEM) and X-ray diffractometry (XRD) techniques respectively. The porosity and crack length are estimated by image analysis (Image J) technique. The hardness of the coatings is measured by Vickers microhardness tester. After 50 cycles, all the free-standing coatings are found to be intact without fragmentation. At higher cycles, the Al2O3 - Cr2O3 coatings form α-Al2O3 and (Al0.9Cr0.1)2O3 solid-solution phase only. The Al2O3 - Cr2O3 coatings gain much less weight than the pure Al2O3 coating due to the major presence of oxidation resistant α-Al2O3 phase in the former. However, among the Al2O3 - Cr2O3 coatings with an increase in Cr2O3 content, the Kp value tends to increase due to the high presence of metastable (Al1.8Cr0.05)2O3 solid-solution phase. On the other hand, the (AlxCr1-x)2O3 phase helps to reduce crack formation due to its high fracture toughness properties. With the highest amount of solid-solution phase content, the Al2O3-4 wt% Cr2O3 coating shows the highest fracture toughness among all. The micro-porosity of the coatings is increased with an increase in the heating cycle, and the coating hardness is reduced accordingly.

High-Temperature Synthesis of Cast Ceramic Material Al2O3–Cr2O3 + ZrO2

High-Temperature Synthesis of Cast Ceramic Material Al2O3–Cr2O3 + ZrO2

Investigating the effects of synthesis parameter on textural and catalytic properties of ZnO–CuO–Al2O3–Cr2O3 mixed oxide in water gas shift reaction

The present study has investigated the influence of preparing conditions, including aging temperature and time, pH, and Tcalcination, on the co-precipitated ZnO–CuO–Al2O3–Cr2O3 mixed oxide at a high-temperature water gas shift reaction. XRD, BET, FTIR, TG-DTA, SEM, TEM, and H2-TPR were used to characterize the relationships between the synthesis parameters and the physicochemical features. The investigation proved that the activity in aging 5 h could be related to higher pore volume and lower crystalline size of 0.24 cm3g-1 and 6.4 nm, respectively. Also found that increasing the aging temperature to 60 °C results in a rise in the surface area and particle size of less than 6 nm, enhancing the catalyst activity. The findings showed that raising the Tcalcination reduced the surface area from 132 to 65 m2 g−1. It has been concluded that the CO conversion of 70 % was obtained when aged at 60 °C and calcination temperature of 400 °C.

Effects of Al2O3 and Cr2O3 on the microstructure and properties of Mo alloys prepared via vacuum sintering

The dilemma of strength and ductility of Mo alloy at ultra-high temperature (above 1300 °C) limits its application in space reactors and other high-temperature environments. Single oxide enhancement has been unable to meet these use requirements. In this research, a strategy of synergistic reinforcement of Mo alloys with nanosized Al2O3 and Cr2O3 ceramic particles was proposed. A 300−400 nm Mo alloy powder was prepared by liquid‒solid doping, and in situ self-generated nanosized oxides were obtained. The grain size of vacuum sintered Mo alloy was very fine, at only 5.3 μm, which was one tenth of the particle size of commercial Mo alloy. Al2O3 and Cr2O3 particles were distributed in the grains of the Mo matrix, which effectively prevented the growth of Mo grains during vacuum sintering and reinforced the Mo alloy. The maximum flow stress of the Mo–Al2O3–Cr2O3 alloy reached 367 MPa at 1000 °C/1 s−1, which was better than that of the single-oxide reinforcement. The ultimate tensile strength (UTS) of the Mo–Al2O3–Cr2O3 alloy was 862 MPa, which was twice that of pure Mo. The preparation process is simple and available for industrial production. Synergistic strengthening of multiple oxides will be the best strategy for strengthening refractory alloys in the future.

Preparation and characterization of supersonic plasma sprayed Al–Al2O3–Cr2O3 composite coatings on magnesium alloy substrate

Magnesium alloys have poor wear and corrosion resistance, which limits their wider industrial applications. In order to improve wear and corrosion resistance, Al–Al2O3–Cr2O3 composite coatings with different Al, Al2O3 and Cr2O3 compositions were prepared on magnesium alloy substrate using supersonic plasma spraying technology. The surface morphology, porosity, and microstructure of Al–Al2O3–Cr2O3 coatings were analyzed. The wear and corrosion resistance of Al–Al2O3–Cr2O3 coatings were evaluated. The results showed the surface morphology of the composite coating was flat, and the cross-sectional structure had a layered structure with close interlayer bonding, and also the structure was uniform and fine. The A70A15C15 coating exhibited the lowest porosity (0.56 %), whereas the porosity of A30A35C35 coating was the highest (only 1.61 %). The wear resistance of the composite coating increased with increasing Al2O3–Cr2O3 compositions, and the A30A35C35 coating showed the best wear resistance, with a 90.58 % reduction in volume wear rate when compared with that of the magnesium alloy substrate. Based on electrochemical impedance spectroscopy testing, the A50A25C25 coating had the slowest corrosion rate and best electrochemical corrosion resistance. Therefore, the preparation of the Al–Al2O3–Cr2O3 coating by supersonic plasma spraying on magnesium alloy substrate is a promising technique for improving its wear and corrosion resistance.

Effect of Mg treatment on inclusion behaviors in 430 ferritic stainless steel during solidification

To understand the effect of Mg treatment on the precipitation, growth, and transformation of inclusions in 430 ferritic stainless steel during solidification, slag refining and Mg treatment experiments with different cooling methods were conducted at 1873 K (1600 °C). Experimental results showed that the oxide inclusions in 430 stainless steel without Mg treatment were mainly Al2O3–SiO2–MnO (slag phase), Al2O3–Cr2O3–MnO (spinel phase), high-Al2O3 (corundum phase) and CaO–SiO2–Al2O3–MnO (slag phase), while all of the oxides except CaO–SiO2–Al2O3–MnO inclusions transformed to MgO–Al2O3–Cr2O3–MnO (spinel phase) after Mg treatment. With water quenching, the average inclusion diameters were about 1.4 μm in both of the Mg-free and Mg-bearing steels, while they increased to approximate 3.1 and 1.9 μm after furnace cooling, separately. With the decrease of cooling rate from 26.2 to 1.24 K s−1, in the Mg-free steel, the average Al2O3 and Cr2O3 contents in the inclusion increased from 19.6 to 42.6 mass% and from 12.22 to 19.44 mass%, respectively, and the average SiO2 content decreased from 43.5 to 17.1 mass%. However, the average composition of inclusions in Mg-bearing steel was relatively stable and independent of cooling rate. A kinetic model was established with the solute micro-segregation model to predict oxide inclusion growth during cooling and solidification. Without and with Mg treatment, under a cooling rate of 1 K s−1, the calculated final sizes of the most stable oxide inclusions were 3.27 and 1.88 μm, respectively. The predicted average compositions and diameters of oxide inclusions were generally consistent with the experimental results.

Evolution Behaviors of Inclusions in Warm‐Rolled L605 Thin‐Walled Tubes and Their Effects on Machinability

This paper investigates the evolution behaviors of inclusions in the warm rolling process of L605 thin‐walled tubes and analyzes their influencing mechanism. Homogeneous spherical and irregular SiO2–Al2O3–Cr2O3(MnO + CaO) inclusions are observed in the cast tubes. After warm rolling, the homogeneous inclusions are changed into heterogeneous spherical ones with gray‐colored (Al2O3)‐rich phase and dark‐colored (SiO2)‐rich phase and Cr2O3(MnO + CaO)‐rich phase due to different deformability of various inclusions under the combined effects of diameter reduction and wall pressure. As the rolling times of tubes increases, large‐sized inclusions are crushed continuously, and the average size of the inclusions gradually decreases. At the same time, the number density of inclusions presents a first increasing and then decreasing trend. It is estimated that the critical size of the inclusions that are hard to further crack in warm rolling is about 0.5 μm. Meanwhile, the inclusions would lead to stress concentration at the positions near large‐sized irregular inclusions, causing cracks and penetrating defects. The simulation results show that the stress near the outer diameter of the inclusions is twice that in the middle and the changes of stress in the 30 μm inclusions and nearby areas exhibit a significant increase compared to the small‐sized 2 μm inclusions.

Effect of graphene on the microstructure, mechanical properties, and wear behavior of plasma‐sprayed Al2O3–Cr2O3 coating

AbstractIn this study, plasma‐sprayed Al2O3–Cr2O3 coatings with different contents of graphene nanosheets were prepared for investigating effects of the graphene on microstructure, mechanical properties, and wear behavior of the coating. The experimental results showed that graphene increased the porosity and the microhardness of the coating. But excessive graphene decreased the microhardness remarkably. Besides, the anti‐crack initiation and propagation abilities of the coatings with graphene improved significantly. The wear rate of the coatings decreased first, and then increased with increasing the graphene content. Impressively, the wear rates of the coating with 2.9% graphene decreased by 33.5% and 36.7%, compared with those of the coating without graphene under normal loads of 5 and 15 N, respectively. The main wear mechanisms of the coatings with and without graphene are brittle fracture and abrasive wear.

Effects of TiO2 addition on phase, mechanical properties, and microstructure of Cr2O3–Al2O3 ceramic composite

TiO2 is a sintering additive that can significantly improve the sintering and mechanical properties of Cr2O3–Al2O3 refractory materials with high Cr2O3 contents. In this study, TiO2-reinforced Cr2O3–Al2O3 composite refractories were prepared using a reaction-sintering process. The microstructure, phase composition, mechanical properties, and strengthening mechanism of the TiO2-reinforced Cr2O3–Al2O3 composite refractories were investigated. The results indicated that the Al2O3–Cr2O3–TiO2 composite refractory with a TiO2 content of 3.0–4.5 wt% had good compactness (porosity of 5.89%), hardness (17.21 GPa), wear resistance (wear rate of 0.4 mm3/Nm), flexural strength (101.10 MPa), and compressive strength (420.90 MPa). This is mainly because when the added amount of TiO2 was <3.0 wt%, TiO2 was solidly soluble in the matrix, forming a Ti3+-doped (Cr, Al)2O3 solid solution, inhibiting abnormal grain growth, rapidly increasing the sintering shrinkage of the sample, rapidly increasing the bulk density, rapidly decreasing the apparent porosity, and improving the sintering and mechanical properties of the composite resistant material. When the TiO2 addition exceeded 4.5 wt%, a large amount of (Cr, Al)2TiO5 phase was distributed between the grain boundaries of the solid solution, and its bulk density started to decrease. The sintering shrinkage and apparent porosity did not change significantly, and the bonding between the solid solution was not improved. Thus, the sintering and mechanical properties of the composite resistant material deteriorated. Taking into account the slag resistance and mechanical properties of the material, Al2O3–Cr2O3–TiO2 with a TiO2 content of 3.0–4.5 wt% can meet the service requirements for mechanical properties of the lining of smelting reduction ironmaking furnaces.

Microstructure, phase evolution, mechanical properties and slag corrosion resistance of ZrO2 reinforced Al2O3–Cr2O3 composites

Al2O3–Cr2O3 refractories have excellent slag corrosion resistance and can adapt to the oxidation/reduction atmosphere in the smelting reduction ironmaking furnace. Improving the corrosion resistance of chrome corundum refractories is of great significance for extending the life length of industrial kilns and decreasing carbon emissions. In this work, the influences of ZrO2 content on the phase evolution, microstructure, physicochemical properties, mechanical properties and slag corrosion resistance of the ZrO2 reinforced Al2O3–Cr2O3 composite refractories were investigated. The results show that the ZrO2 reinforced Al2O3–Cr2O3 composites are primarily composed of (Al, Cr)2O3 solid solution and m-ZrO2. The compressive strength, flexural strength and hardness of the composite refractories can be improved by adding 2.5 wt% ZrO2. However, adding more ZrO2 will reduce its mechanical properties. This is due to ZrO2 excessive content will augement the porosity of the composite refractories, and the phase transformation of ZrO2 will also lead to the formation of microcracks during the cooling process. It is worth noting that higher ZrO2 content improves the thermal shock resistance of the composites, which is primarily put down to the microcrack toughening mechanism of ZrO2. The corrosion tests show that the thicknesses of the corrosion and infiltration layers of composite refractories are significantly decreased accompanied by ZrO2 content increase. This is because the formation of high melting point CaZr4O9 reduces the CaO content and slag alkalinity, and inhibits the dissolution of Al2O3 into the slag to a certain extent. Therefore, the slag corrosion/penetration resistance of the of the composites are obviously improved with the increase of ZrO2 addition.

Metallothermic SHS of Al2O3–Cr2O3 + TiC ceramic composite material

Ceramic composite material Al2O3–Cr2O3 + TiC was prepared by metallothermic self-propagating high-temperature synthesis (SHS) under 5 MPa of Ar pressure from green mixtures containing TiO2, Al, and C powders, and additive of CrO3 + Al blend. An increase in the mass fraction α of CrO3 + Al in the general charge was found to raise the synthesis temperature. For α < 0.2, sintered multiphase products were formed. In case of high additive content (α > 0.2), the combustion products were separated into two layers: carbide and oxide phases. Optimum synthesis conditions for forming the cast product consisting of Al2O3–Cr2O3 solid solution (“ruby”) and uniformly distributed TiC particles were found. In order to evaluate the possibility of using this material as a cutting tool, physical and mechanical properties were determined. SHS-prepared Al2O3–Cr2O3 + TiC composite after 24-h milling in a planetary mill, pressing under a pressure of 200 MPa, and sintering at 1460°С was found to possess density of 4.55 g/cm3, hardness of 20 GPa, flexural strength of 680 MPa, and crack resistance of 4.2 MPa m1/2.

Effects of air annealing treatments on the microstructure, components, and mechanical properties of magnetron sputtered Al2O3–Cr2O3–ZrO2 composite coatings

To investigate the effects of air annealing on the microstructure, components, and mechanical properties of ceramic composite coatings, Al2O3–Cr2O3–ZrO2 composite coatings were prepared on silicon substrate using radio frequency magnetron sputtering at room temperature, and then air-annealed in a temperature range of 450–850 °C for 30 min. The results indicated that the phase-structure and superficial characteristics, including morphology and surface roughness, were not visibly altered in the annealed coatings up to 600 °C; the elemental component distributions remained uniform. The improvement in the mechanical properties was attributed to the growth of oxide grains. There were no significant changes in the components of Al, Cr, Zr, and O in the annealed coatings. However, an increase in the Cr component and a decrease in the Zr component occurred on the coating surface; the overall structure of the composite coatings possessed a favorable heat resistance. Upon annealing at 750 °C, the thermally-driven formation of uniform and refined nanoparticles on the coating surface was responsible for the effective enhancement of the mechanical properties. Furthermore, annealing at 850 °C induced the enlargement of the precipitated Cr2O3 nanoparticles and the generation of micro-defects, resulting in a drastic morphological evolution, an evident increase in the surface roughness, and a significant decrease in the mechanical properties. This study provides new perspectives on designing novel thermal barrier coatings and understanding the role of high temperature air annealing on the microstructural transformation.

Microstructure and corrosion behavior of Al2O3–Cr2O3 composites with various Cr2O3 content in Al2O3–SiO2–CaO–FeO slag

The corrosion of refractory materials by high-temperature slag has caused severe technical challenges and economic losses to the metallurgical industry. In this study, the microstructure and mechanical properties of Al2O3–Cr2O3 composites were investigated. The static crucible method was used to investigate the corrosion and infiltration behavior of a typical smelting reduction ironmaking slag for the Al2O3–Cr2O3 refractory. Corrosion test results indicate that the corrosion region of Cr2O3–Al2O3 composites is mainly composed of a corrosion and infiltration layer, and the thickness of the corrosion layer decreases significantly with increasing Cr2O3 content in the sample, whereas the thickness of the infiltration layer increases gradually. The dissolution of Al2O3 into the slag is the main reason for the severe erosion of Al2O3–Cr2O3 composites with a low Cr2O3 content. Increasing the amount of Cr2O3 can significantly improve the slag corrosion resistance of Cr2O3–Al2O3 composites, however will have a negative effect on the slag infiltration resistance, which is mainly owing to the increase in porosity of the composite refractory. The formation of the (Al, Cr)2O3 solid solution effectively inhibited the dissolution of alumina in the slag. In addition, excessive Cr2O3 content can also consume Al2O3 in the slag and form an (Al, Cr)2O3 solid solution, which improves the slag corrosion resistance of the aluminum chromium composite refractory.

Silt erosion performance of high velocity oxy fuel- (HVOF) sprayed Al2O3–Cr2O3 composite coatings on turbine steel

PurposeThe purpose of this paper is to investigate the erosion performance of high velocity oxy fuel- (HVOF) sprayed Al2O3–Cr2O3 composite coatings under silt slurry conditions.Design/methodology/approachThe requisite HVOF composite coatings has been deposited on the stainless steel substrate (SS-304). The slurry erosion pot tester of make Ducom was used for conducting the silt slurry erosion tests on the required substrates. The comprehensive experiments were conducted at different particle size of silt in the range 212–250, 150–212, 53–106 µm, and the concentration of the silt ranged from 10%–40% by weight. The rotational speed of the pot tester has been varied between 500 and 1,500 revolutions per minute, and the test duration has been kept to 4 h.FindingsThe erosion wear resistance of the uncoated SS-304 has been greatly enhanced by the application of HVOF-sprayed Al2O3–Cr2O3 composite coatings. The addition of CeO2 has a significant impact in reducing the erosive wear caused by silt slurry. The composite coating powder composition of 65%Cr2O3 + 34.5%Al2O3 + 0.5%CeO2 has shown the highest erosion resistance.Practical implicationsThe developed coatings have the potential to be used for hydro turbines as subjected to silt slurry conditions.Originality/valueThe erosion wear experiments are conducted comprehensively for coated and uncoated samples and the scanning electron micrographs supports the findings.

Preparation of Al2O3–Cr2O3 Solid Solutions as Buoyancy Markers and Their High Pressure Synchrotron X-ray Diffraction Analysis

Preparation of Al2O3–Cr2O3 Solid Solutions as Buoyancy Markers and Their High Pressure Synchrotron X-ray Diffraction Analysis

High-temperature performance in Al2O3–Cr2O3 refractories: Effect of Al2TiO5

In an effort to reduce resource consumption through recycling, Al 2 O 3 –Cr 2 O 3 refractories were prepared by sintering a mixture of brown corundum and recycled aluminum chromium slag at 1600 °C. To elucidate the significance of TiO 2 in refractory, the effect of TiO 2 addition on the room- and high-temperature mechanical properties of these refractories was investigated. The observed stepwise progression in the high-temperature mechanical properties of the specimens was explained by considering the results of thermodynamic simulations, as well as those of phase and microstructural analyses. This behavior was ascribed to the generation of Al 2 TiO 5 in the matrix of the specimens. Moreover, the addition of TiO 2 increased the content of undecomposed Al 2 TiO 5 , and it was accompanied by the appearance of several microcracks in the matrix portion. The high temperatures caused the integration of microcracks and counteracted the thermal stresses in the specimens, which considerably improved the high-temperature mechanical properties and the thermal shock resistance.

Comprehensive study on corrosion protection properties of Al2O3, Cr2O3 and Al2O3–Cr2O3 ceramic coatings deposited by plasma spraying on carbon steel

In this study, individual Al 2 O 3 and Cr 2 O 3 coatings and Cr 2 O 3 -25, 50, 75 wt% Al 2 O 3 composite coatings were applied on carbon steel by atmospheric plasma spraying method. Corrosion experiments were performed on as-sprayed and epoxy resin sealed coatings including potentiodynamic polarization, electrochemical impedance spectroscopy and long-term immersion in 3.5 wt% NaCl solution. Phase composition and microstructure of the coatings were investigated by x-ray diffraction, optical microscopy and scanning electron microscopy, before and after the corrosion experiment. The results showed that the Cr 2 O 3 coating exhibited the best corrosion resistance, due to the densest microstructure and highest adhesion strength. The Cr 2 O 3 -25 wt% Al 2 O 3 coating had the highest interconnected porosities and thus had the least corrosion resistance compared to other coatings. In general, the as-sprayed coatings induced a maximum increase of 3.93 times the polarization resistance (R p ) in the polarization experiment and a 3.5 times increase in the charge transfer resistance (R ct ) in the EIS experiment, which was not significant. Stresses caused by increased volume of corrosion products in the coating-substrate interface resulted in the spallation of Cr 2 O 3 -25, 50 wt% Al 2 O 3 coatings from the substrate over long-term of immersion. The adhesion strength of the coatings was a determining criterion for the long-term durability of the coatings. The sealing treatment resulted in a significant increase in R p and R ct .

Calculation of eutectics temperatures and compositions of multicomponent sections of the system (Mg, Ca, Sr, Ba)O—Al2O3—Cr2O3

With change in the structure of metallurgical production in Ukraine, the range of used refractory materials is expanding: the share of unshaped highquality refractories is growing, since this eliminates the time-consuming and energy-consuming operation of firing piece products, and also simplifies the operation of creating a lining layer. To establish the maximum possible operating temperature of materials developed on the basis of compositions of the optimal regions of multicomponent oxide system (Mg, Ca, Sr, Ba)O— Al2O3—Cr2O3, it was necessary to calculate the temperatures and compositions of the eutectics of binary, ternary and four-component sections, which was the purpose of this study.&#x0D; For calculations in binary sections, the Epstein — Howland method is most acceptable, and in three- and four-component sections — the solution of nonlinear equations system. It was found that to obtain a refractory unshaped material based on calcium aluminium chromite cement with periclase as a filler, it is necessary to adjust the phase composition of the cement towards an increased CaCr2O4 content, and the total composition must contains at least 75 wt. % periclase or magnesium spinel. In addition, in the case of alumina hydrates formation as a result of cement hydration processes, magnesium spinel will be synthesized as part of a refractory unshaped material during service. To obtain refractory unshaped materials based on strontium aluminium chromite cement and periclase as filler, it is necessary to increase the SrAl2O4 content and minimize the Sr3Al2O6 content in the cement composition, while the filler content in the composition can vary within wide limits, since the melting temperature of such compositions will be more than 1700 °C. To create refractory unshaped materials based on barium aluminium chromite cements, it is necessary to increase the content of BaAl2O4 in the cement composition as the most hydraulically active and refractory component and the composition of the composite material should be low- or ultra-low-cement in order to increase the operating temperature. In addition, in the case of chromium hydroxides formation during the hydration of aluminium chromite cement, chromium spinel will be synthesized in the composition during service, increasing the refractoriness of resulting composition. Thus, by varying the type and phase composition of cement and the ratio of cement and aggregates in the concrete composition, it is possible to obtain unshaped materials with a wide operating temperature range for use in heat-stressed areas of high-temperature aggregates.

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.

Understanding the solidification and leaching behavior of synthesized Cr-containing stainless steel slags with varying Al2O3/SiO2 mass ratios

This study investigated the effect of Al2O3/SiO2 mass ratios on the equilibrium crystallization behavior of synthesized CaO–SiO2–MgO–Al2O3–Cr2O3 stainless steel slags to understand the selective concentration behavior of Cr into a primary Mg(Cr,Al)2O4 spinel phase during slag solidification and to determine the leaching stability of Cr-containing slags. The spinel solid solution was precipitated within the temperature range of 1600-1400 °C, where the Cr/(Cr+Al) mole ratio in the Mg(Cr,Al)2O4 spinel phase gradually decreased for slags with higher Al2O3/SiO2 mass ratios. When the Al2O3/SiO2 mass ratio increased from 0.125 to 0.5, the Cr content in the amorphous glass phase gradually decreased, with a subsequent increase in the Cr content in the crystalline phase. For slags with a unit Al2O3/SiO2 mass ratio and MgO mole percent comprising less than the combined sum of the Cr2O3 and Al2O3 mole percents, the Cr content in the amorphous glass phase increased, which was correlated with the enhanced substitution of Cr3+ with Al3+ in the spinel. The trend of the amount of Cr-related ions in the leachate was consistent with the trend of Cr in the amorphous glass phase: the amount decreased for slags with Al2O3/SiO2 mass ratios from 0.125 to 5 and then increased for slags with an Al2O3/SiO2 mass ratio of 1. The results suggest that the addition of appropriate amounts of Al2O3 to stainless steel slags could be conducive to stabilizing Cr into the primary spinel phase to minimize Cr leaching into the environment.