Chromium Sulfide Research Articles

Pyrrhotite deposition through thermal projection to simulate iron sulphide slagging in oxyfuel combustion

Oxyfuel combustion is envisaged as one of the main options for near future CO2 reduction in conventional power production. There are many aspects of oxy-combustion still at the research stage. One of those is the issue of boiler materials resistance to corrosion due to solid deposits formed as a consequence of slagging in CO2 rich flue gases. The novel approach to the issue is the simulation of realistic slagging by pyrite (FeS2) projection through an oxyacetylene spray gun, flying along a controlled flame and impacting onto metallic surfaces of selected composition for fireside waterwall construction (F22, P91, 409, 347, 304H, and 800HT). Metallic surface temperatures were kept at 400, 500, 600 or 700°C, and after deposition, metallic coupons were aged for long periods (150 and 1500h) at the selected conditions (O2/N2, CO2/N2). The characterisation of deposits was performed with XRD, SEM-EDX and carburisation tests.The first finding is that the oxidation progression is different when partially transformed pyrite covers metallic surfaces. In that case, no iron oxide (Fe2O3) scale is generated, only the chromium oxide (Cr3O4) grows between the steel and the deposit as a response to oxidation. There is a clear presence of chromium sulphides in competition with the chromium oxide. On the other hand, comparison of scales in CO2 vs. air indicates the same chemical composition but different morphology; in air combustion, corrosion layers are thicker and cracked. These results can improve the prediction of operational problems in coal oxy-fuel combustion.

New Ferromagnetic Chromium Chalcogenides, <i>A</i>Cr<sub>5</sub>Te<sub>8</sub> (<i>A</i> = K, Cs and Rb)

New pseudo-hollandite chromium tellurides, ACr5Te8 (A = K, Cs and Rb), have been synthesized. KCr5Te8 is isostructural (type-A; space group C2/m) to ACr5S8, while RbCr5Te8 and CsCr5Te8 crystallize in a different structure (type-B; space group C2/m). All compounds show ferromagnetic transition, in contrast to antiferromagnetic transition in pseudo-hollandite chromium sulfides and selenides. The ferromagnetism of ACr5Te8 would be related to long Cr-Cr distances, band structure or itinerancy.

Structural and electronic properties of Y2CrS4 from first-principles study

We systematically study the structural, electronic, and magnetic properties of chromium sulfide Y2CrS4 by using density-functional theory. We find that antiferromagnetic order is more energetically favorable than ferromagnetic state and near the Fermi level the main occupation is from Cr 3d states.

Electrochemical deposition and studies on CdCr2S4 thin films

Abstract Cadmium chromium sulphide (CdCr2S4) thin films have prepared on indium doped tin oxide coated conducting glass (ITO) substrates from an aqueous electrolytic bath consists of CdSO4, Cr2O3 and Na2S2O3 using potentiostatic electrodeposition technique. The deposited films are characterized using X-ray diffraction, scanning electron microscopy, energy dispersive analysis by X-rays and optical absorption techniques, respectively. X-ray diffraction pattern reveals that the deposited films possess polycrystalline nature with cubic structure. Surface morphology and film composition shows that the films with smooth surface and better stoichiometry are obtained under optimized deposition condition. The optical parameters such as band gap, refractive index and extinction coefficient are calculated from optical absorption measurements. The experimental observations are discussed in detail.

Sulfidation kinetics of industrial steels in a refinery crude oil at 300 °C: reactivity at the nanometer scale

AbstractHigh temperature sulfidic corrosion has caused safety and reliability issues in refinery units for decades. The objective of the work was to investigate the kinetics of sulfidation under refinery conditions and to characterize, at the nanometer scale, the sulfide layers formed on different steels. The experiments were performed in an autoclave filled with a refinery high‐sulfur crude oil at 300 °C on XC18 carbon steel (Fe–0.18%C), P5 alloy steel (Fe–5% Cr–0.5%Mo) and 304L stainless steel (Fe–18% Cr–8%Ni). The duration of the test ranged from a few hours to a few days.The combination of X‐ray diffraction and transmission electronic microscopy showed the presence of pyrrhotite (Fe1−xS) on XC18, P5 and 304L samples. For all alloys, the S 2p core level decomposition (X‐ray photoelectron spectroscopy) proved the presence of five sulfur species on the surface: sulfide (main species), disulfide, elemental sulfur, sulfite and sulfate. On 304L, the presence of chromium oxide and nickel sulfide was revealed by XPS, whereas chromium sulfide was hardly detected.The macroscopic kinetics of sulfidation was followed by mass loss. The results showed that a parabolic law can fit the kinetics of sulfidation of XC18 and P5 steels. The kinetics of sulfidation of the adherent sulfide layer formed on 304L steel, determined from XPS measurements, follows a logarithmic law. Copyright © 2010 John Wiley & Sons, Ltd.

Synthesis, structures and magnetic properties of pseudo-hollandite chromium sulfides

The pseudo-hollandite chromium sulfides, ACr 5S 8 ( A=K, Rb, Cs) and A′ 0.5Cr 5S 8 ( A′=Sr, Ba), have been synthesized and investigated in structural and magnetic properties. All the compounds crystallize in the isostructure with a monoclinic C2/ m. Its crystal structure has triangular lattices and double chains made of Cr 3+ (d 3; S=3/2) triangles. The magnetic susceptibilities of all compounds behave as Curie–Weiss types in high temperature region. From magnetic susceptibility and specific heat measurements, all the compounds have antiferromagnetic ground states. The Néel temperatures are rather low compared to Weiss temperatures, reflecting magnetic frustration in the triangular lattices and double chains. The magnetic transitions in KCr 5S 8 and Ba 0.5Cr 5S 8 are a two-step transition around 50 and 60 K, respectively, while RbCr 5S 8 shows a sharp magnetic transition at 42 K, accompanied by magnetoelastic behavior. CsCr 5S 8 shows a structural transition around 100 K, followed by a magnetic transition at 10 K. In Sr 0.5Cr 5S 8, ferromagnetic interaction develops below 100 K and then a three-dimensional antiferromagnetic order takes place at 30 K. These magnetic properties are discussed from A-cation dependences of local structures and a model of magnetic structure for RbCr 5S 8 is proposed on the basis of the arguments of magnetic interactions and neutron diffraction data. It is different from the known magnetic structure of TlCr 5Se 8.

Properties of Ni-based self-lubricating composite

Ni-Cr based alloy were fabricated using powder metallurgy method. It was found that the composites were mainly consisted of nickel-based solution, chromium sulfide et al., the strengthening phases can improve the hardness of alloy obviously, but decreases the bending strength. Both the wear and friction of alloy with strengthening phase was improved.

Some tribological properties of SHS-produced chromium sulfide

Oxidation resistance and tribological properties of SHS-produced chromium sulfide have been explored. The material was oxidized up to 5 to 7 μm thick from its surface upon heat treatment at 1000°C for a short time. It also exhibited a unique compositional change in sulfur and chromium at the interface between matrix and oxide layer formed during heat treatment. Meanwhile, the synthesized material showed the coefficient of kinetic friction of below 0.18, which is an acceptable value for a solid lubricant. Although the friction coefficient of CrS was initially low, it was found to grow upon high-temperature oxidation of the CrS surface. This fluctuation in the tribological property seems to depend on both the crystal structures of chromium sulfide and chromium oxide and of the interface between the oxide and matrix.

Evaluation of the Corrosion Resistance of Fe–Al–Cr Alloys in Simulated Low NO x Environments

The first part of this manuscript presented SEM analysis of corrosion products formed on iron-aluminum-chromium alloys that were exposed to a simulated low NO x combustion environments. In Part II, results from electron microprobe analysis (EMPA) and scanning transmission electron microscopy (STEM) analyses of select as-corroded coupons from the long tem tests are discussed. Despite the formation of thick iron sulfide films one of the alloys, EMPA did not detect any measurable depletion of aluminum near the surface of this alloy. STEM analysis revealed that chromium was able to form chromium sulfides only on the higher aluminum content alloys, thereby preventing the formation of deleterious iron sulfides and reducing the overall corrosive attack on this alloy. Also observed in the STEM analysis was the encapsulation of external iron sulfide products with a thin layer of aluminum oxide, which may serve as a secondary layer of corrosion protection in these regions.

Al-SBA-15 as a support of catalysts based on chromium sulfide for sulfur removal

SBA-15 doped with aluminium supported Cr catalysts were prepared with different chromium contents by the wetness impregnation method. The materials in oxidic and sulfided states were characterized by X-ray diffraction (XRD), N 2 adsorption–desorption isotherms at 77K, NH 3-TPD, XPS analysis and H 2-TPRS. The catalytic properties of these materials with the hydrodesulfurization (HDS) of dibenzothiophene (DBT) were tested at 260–340 °C under a hydrogen pressure of 3.0 MPa. The catalytic behaviour was studied as a function of the Cr loading and the support. A mesoporous silica (SBA-15) was also used to prepare the Cr catalysts in order to study the influence of the support on the catalytic performance. The catalyst based on SBA-15 showed very low catalytic activity in the reaction conditions studied whereas the AlSBA-15 based catalyst showed very good performance in hydrotreating, depending on the Cr loading. These results suggest that catalytic activity, which is directly related to the amount of labile sulfur, can vary not only as a function of the Cr content, but also with the incorporation of aluminium to the mesoporous silica. This highly modifies the nature of the acidic properties of the support, providing a stronger metal–support interaction, allowing better dispersion of the chromium species and specific electronic properties of the active species that affect the catalyst performance.

Structural, Magnetic, and Electronic Properties of VxCr2−xS3(0 < x < 2)

A new family of vanadium-substituted chromium sulfides (VxCr2-xS3, 0 < x < 2) has been prepared and characterized by powder X-ray and neutron diffraction, SQUID magnetometry, electrical resistivity, and Seebeck coefficient measurements. Vanadium substitution leads to a single-phase region with a rhombohedral Cr2S3 structure over the composition range 0.0 < x e 0.75, while at higher vanadium contents (1.6 e x < 2.0) a second single-phase region, in which materials adopt a cation-deficient Cr3S4 structure, is observed. Materials with the Cr2S3 structure all exhibit semiconducting behavior. However, both transport and magnetic properties indicate an increasing degree of electron delocalization with increasing vanadium content in this compositional region. Materials that adopt a Cr3S4-type structure exhibit metallic behavior. Magnetic susceptibility data reveal that all materials undergo a magnetic ordering transition at temperatures in the range 90–118 K. Low-temperature magnetization data suggest that this involves a transition to a ferrimagnetic state.

長期間運転された電力貯蔵用 NAS 電池のアルミニウム円筒容器の内壁面に施工された高 Cr-Fe 合金プラズマ溶射皮膜の耐硫化腐食性と密着強さ

The characteristics and adhesive strength of a high Cr-Fe alloy plasma spray coating applied to the inner surface of cylindrical aluminum containers of 17 NAS battery cell used to leveling electrical power for 0.2 to 10 years were studied. The operating temperature of the batteries was 593 K±15 K, and the number of charge/discharge cycles per year was 300 on average. A Sulfide layers consisting mainly of Cr2S3 and Cr3S4 was formed on the surface of the high Cr-Fe alloy plasma spray coating, and the growth rate of sulfide layer was approximately 2 μm per year. Chromium sulfides also formed within the spray coating. Molten sulfur and Na2Sx which are positive electrode active materials, penetrated the coating through the interfaces of the sprayed particles. The deepest sulfides almost reached the wall surface of the aluminum container. The adhesive strength of high Cr-Fe alloy plasma spray coatings operating history of 3, 5, and 10 years, was in the range of 42-44 MPa, showing that the adhesive strength from the time of coating was maintained. After tensile testing, peeling only occurred at the middle region of the sprayed layer, indicating that the reason for the peeling of the coating was formation of chromium sulfide formed at the interfaces of the sprayed particles.

High-Pressure Synthesis and Structures of New Barium Chromium Sulfides, BaCr4S7 and Ba2Cr5S10, with New Type Face-Sharing CrS6 Structure Units

Abstract Two new ternary barium chromium sulfides, BaCr4S7 and Ba2Cr5S10, were synthesized by reactions of barium sulfide, sulfur, and chromium metal under high-pressure and high-temperature conditions. Single crystals of BaCr4S7 were obtained from a starting mixture with a molar ratio of Ba:Cr:S = 2:5:10 after reacting at 1200 °C and under a pressure of 5 GPa. It crystallizes in the monoclinic space group P21⁄c (No. 14) with a=6.739(4) Å, b=22.665(9) Å, c=5.907(3) Å, β=90.1(4)°, V=902.2(7) Å3, and Z=4. It contains CrS2 sheets composed of edge-sharing CrS6 octahedra. The sheets are connected by wall-shaped subunits composed of face-sharing CrS6 octahedra to form a tunnel structure. Ba atoms are situated in the tunnels. Single crystals of Ba2Cr5S10 were synthesized by heating a mixture with a molar ratio of Ba:Cr:S = 1:1:3 under a pressure of 5 GPa at 1200 °C. It crystallizes in the triclinic space groupa=5.940(4) Å, b=6.645(5) Å, c=17.39(2) Å, α=95.19(3)°, β=91.67(3)°, γ=90.16(2)°, V=683.1(9) Å3, and Z=2. The structure is composed of CrS2 sheets and the wall-shaped subunits, like as in BaCr4S7, but the subunits do not connect the adjacent CrS2 sheets. It has a two-dimensional structure, and Ba atoms are situated in interlayer regions.(No. 2) with

Tribological properties of nickel-based self-lubricating composite at elevated temperature and counterface material selection

Solid lubricating materials are necessary for development of new generation gas turbine engines. Nickel-based self-lubricating composites with graphite and molybdenum disulfide as lubricant were prepared by powder metallurgy (P/M) method. Their tribological properties were tested by a MG-2000 high-temperature tribometer from room temperature to 600 °C. The structure of the composite was analyzed by XRD and worn surface morphologies were observed by optical microscope. The effects of counterface materials on tribological behavior of composites were investigated. It was found that chromium sulfide and tungsten carbide were formed in the composite by adding molybdenum disulfide and graphite, which were responsible for low-friction and high wear-resistance at elevated temperatures, respectively. The average friction coefficients (0.14–0.27) and wear rates (1.0–3.5 × 10 −6 mm 3/(N m)) were obtained for Ni–Cr–W–Fe–C–MoS 2 composite when rubbed against silicon nitride from room temperature to 600 °C due to a synergetic lubricating action of graphite and molybdenum disulfide. The optimum combination of Ni–Cr–W–Fe–C–MoS 2/Ni–Cr–W–Al–Ti–C showed lower friction than other counter pairs. The graphite played the main role of lubrication at room temperature, while sulfides were responsible for low friction at high temperature.

Crystal and magnetic structures of Y 2CrS 4

Chromium(II) sulfide, Y 2CrS 4, prepared by a solid-state reaction of Y 2S 3 and CrS, showed an antiferromagnetic transition at 65 K. The neutron diffraction patterns at 10 and 90 K were both well refined with the space group Pca2 1. At 90 K, cell parameters were a=12.5518(13) Å, b=7.5245(8) Å, and c=12.4918(13) Å. At 10 K, magnetic peaks were observed, which could be indexed on the same unit cell. Magnetic moments of chromium ions were parallel to the b-axis and antiferromagnetically ordered in each set of the 4 a sites.

Advanced burner-rig test for oxidation–corrosion resistance evaluation of MCrAlY/superalloys systems

Protective coatings are used on gas turbine components to enable them to survive in engine-operating conditions. This study presents a recently developed cyclic burner-rig test that is used to simulate helicopter engine conditions and to assess the oxidation and hot corrosion behaviour of MCrAlY coatings on nickel-base superalloys. A diluted sea-salt solution is atomised into the burner-rig to simulate hot-corrosion. Each cycle lasts 1 h with temperatures varying in the range of 900 °C to 1000 °C followed by 15 min cooling to room temperature. Specimens are tested up to 1000 such cycles. Three different NiCoCrAlYTa coating thicknesses are used to determine the influence of the Al reservoir on the lifetime of the coated MC2 superalloy. The evolving microstructural features are identified using high resolution scanning electron microscopy and energy dispersive spectroscopy and compared with isothermal testing in pure oxidising conditions. The NiCoCrAlYTa microstructure obtained after the burner-rig test has typical features of a Type 1 hot corrosion degradation, with internal oxidation and nitruration and a front of chromium and yttrium-rich sulphides. This type of advanced burner-rig test cycle is successful in reproducing the accelerated combined hot-corrosion/oxidation damage.

Pyridine-2,6-bis(thiocarboxylic acid) Produced by Pseudomonas stutzeri KC Reduces Chromium(VI) and Precipitates Mercury, Cadmium, Lead and Arsenic

Interactions of the Pseudomonas stutzeri KC siderophore pyridine-2,6-bis(thiocarboxylic acid) (pdtc) with chromium(VI), mercury(II), cadmium(II), lead(II), and arsenic(III) are described. Pdtc was found to reduce Cr(VI) to Cr(III) in both bacterial cultures and in abiotic reactions with chemically synthesized pdtc. Cr(III) subsequently formed complexes with pdtc and pdtc hydrolysis products, and their presence was confirmed using electrospray ionization-mass spectrometry (ESI-MS). Cr(III):pdtc complexes were found to slowly release Cr(III) as chromium sulfide and possibly Cr(III) oxides. Pdtc also formed poorly soluble complexes with Hg, Cd, Pb, and As(III). Hydrolysis of those complexes led to the formation of their respective metal sulfides as confirmed by energy dispersive X-ray spectroscopy (EDS) elemental analysis. The pdtc-producing strain P. stutzeri KC showed higher tolerance to most of these metals as compared to a pdtc-negative mutant. A novel role of pdtc is postulated as its involvement in providing an extracellular pool of thiols that are used for redox processes in detoxification of the bacterial extracellular environment. These redox processes can be mediated by transition metal:pdtc complexes.

The effects of titanium additions on AF1410 ultra-high-strength steel

The mechanical properties and microstructure of two heats of AF1410 steel were compared. The first heat, heat 811, contained a titanium addition of 0.02 wt pct, while the second heat, heat 91, contained no titanium, manganese, or other strong sulfide formers. The sulfur in heat 811 was gettered as titanium carbosulfide, while in heat 91 the sulfides were chromium sulfide. The toughness of heat 811 was found to be much enhanced compared to heat 91, with Charpy impact energies of 176 J and 79 J and KIC fracture toughness values of 235 MPa.m1/2 and 170 MPa.m1/2, respectively. This significant difference in fracture toughness is attributed to the fact that titanium carbosulfide particles are more resistant to void nucleation than the chromium sulfide particles, which appear to nucleate voids at the onset of plastic strain. In addition to altering the sulfide particle type, the titanium addition also results in the presence of undissolved MC carbides in the titanium-modified steel in addition to the M2C carbides found in heat 91. These carbides act as grain growth inhibitors, resulting in a finer prior austenite grain size and martensite packet size in heat 811.

Effect of alloying additions and preoxidation on high temperature sulphidation resistance of iron–chromium alloys

High temperature corrosion of structural alloys in sulphur bearing environments is many orders of magnitude higher than in oxidising environments. Efforts to increase sulphidation resistance of these alloys include addition of alloying elements. This paper reports the effect of yttrium, aluminium and yttrium plus aluminium addition on the sulphidation behaviour of an Fe–20Cr alloy in H2–2%H2S at 700 and 800°C. The effect of preoxidation of these alloys on sulphidation behaviour was also investigated. The initial stages of sulphidation of these alloys were observed and overall sulphidation kinetics was determined. In the presence of yttrium, the sulphidation rate of the alloy decreased by an order of magnitude, and the sulphide layer on the FeCrY alloy was significantly thinner than that formed on the FeCr alloy. Aluminium addition increased sulphidation resistance even more. The FeCrAl and FeCrAlY alloys exhibited parabolic sulphidation kinetics at the two temperatures. On both alloys, initial chromium sulphide (Cr2S3) formation at grain boundaries and Al2S3 and FeCr2S4 formation over the grains was followed by formation of an outer Cr2S3 layer over a mixed sulphide layer. Preoxidation of the two alloys resulted in an ‘incubation period’ with practically no sulphidation during subsequent exposure to S bearing environments. After this incubation period, the sulphidation behaviour of the FeCr alloy was similar to that when the alloy was not preoxidised. The incubation period of the FeCrAl alloy was significantly longer, over 45 h, compared with 2 h for the Al free alloy. Based on thermogravimetric as well as SEM, energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) data, sulphidation mechanisms have been proposed for the alloys before and after preoxidation.

High Temperature Corrosion of Chromium–Manganese Steels in Sulfur Dioxide

This work was aimed at explaining the corrosion mechanism of commercial Cr–Mn steels at 1073, 1173 and 1273 K in the atmospheres containing oxygen and sulfur. Three steels were selected for the investigations, two single-phase austenitic steels (Cr17Mn17 and Cr13Mn19SiCa) and a two-phase austenitic-ferritic steel Cr15Mn19. On all studied steels triplex scales were formed. The inner very thin, fine-grained part of the scale contained manganese, chromium and iron sulfides and oxides, the intermediate layer was built mainly of the MnCr2O4 spinel while MnO was the predominant constituent of the outer scale layer. According to the gravimetric measurements, after an initial incubation period, the oxidation of steel follows a parabolic rate law. Thermodynamic and kinetic aspects of the formation of oxide-sulfide and oxide layers were discussed. Oxidation was accompanied by depletion of the subscale region of the metallic core in manganese, which is the austenite former. Consequently austenite transformed into ferrite.