The Experts below are selected from a list of 249 Experts worldwide ranked by ideXlab platform
Zhengyang Li - One of the best experts on this subject based on the ideXlab platform.
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investigation of the tribology behaviour of the graphene nanosheets as oil additives on textured Alloy Cast Iron surface
Applied Surface Science, 2016Co-Authors: Dan Zheng, Mingxue Shen, Zhengyang LiAbstract:Abstract Tribological properties of graphene nanosheets (GNS) as lubricating oil additives on textured surfaces were investigated using a UMT-2 tribotester. The lubricating fluids keeping a constant temperature of 100 °C were applied to a GCr15 steel ball and an RTCr2 Alloy Cast Iron plate with various texture designs (original surface, dimple density of 22.1%, 19.6% and 44.2%). The oil with GNS adding showed good tribological properties (wear reduced 50%), especially on the textured surfaces (the reduction in wear was high at over 90%). A combined effect between GNS additives and laser surface texturing (LST) was revealed, which is not a simple superposition of the two factors mentioned. A mechanism is proposed to explain for these results −the graphene layers sheared at the sliding contact interfaces, and form a protective film, which is closely related with the GNS structures and surface texture patterns.
S.k. Schaefer - One of the best experts on this subject based on the ideXlab platform.
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Wear and Wear Mechanism Simulation of Heavy-Duty Engine Intake Valve and Seat Inserts
Journal of Materials Engineering and Performance, 1997Co-Authors: Y.s. Wang, S. Narasimhan, J.m. Larson, S.k. SchaeferAbstract:A silicon-chromium Alloy frequently used for heavy-duty diesel engine intake valves was tested against eight different insert materials with a valve seat wear simulator. Wear resistance of these combinations was ranked. For each test, the valve seat temperature was controlled at approximately 510 °C, the number of cycles was 864,000 (or 24 h), and the test load was 17,640 N. The combination of the silicon-chromium valve against a Cast Iron insert produced the least valve seat wear, whereas a cobalt-base Alloy insert produced the highest valve seat wear. In the overall valve seat recession ranking, however, the combination of the silicon-chromium valve and an Iron-base chromium-nickel Alloy insert had the least total seat recession, whereas the silicon-chromium valve against cobalt-base Alloy, Cast Iron, and nickel-base Alloy inserts had significant seat recession. Hardness and microstructure compatibility of valve and insert materials are believed to be significant factors in reducing valve and insert wear. The test results indicate that the mechanisms of valve seat and insert wear are a complex combination of adhesion and plastic deformation. Adhesion was confirmed by material transfer, while plastic deformation was verified by shear strain (or radial flow) and abrasion. The oxide films formed during testing also played a significant role. They prevented direct metal-to-metal contact and reduced the coefficient of friction on seat surfaces, thereby reducing adhesive and deformation-controlled wear.
Dan Zheng - One of the best experts on this subject based on the ideXlab platform.
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investigation of the tribology behaviour of the graphene nanosheets as oil additives on textured Alloy Cast Iron surface
Applied Surface Science, 2016Co-Authors: Dan Zheng, Mingxue Shen, Zhengyang LiAbstract:Abstract Tribological properties of graphene nanosheets (GNS) as lubricating oil additives on textured surfaces were investigated using a UMT-2 tribotester. The lubricating fluids keeping a constant temperature of 100 °C were applied to a GCr15 steel ball and an RTCr2 Alloy Cast Iron plate with various texture designs (original surface, dimple density of 22.1%, 19.6% and 44.2%). The oil with GNS adding showed good tribological properties (wear reduced 50%), especially on the textured surfaces (the reduction in wear was high at over 90%). A combined effect between GNS additives and laser surface texturing (LST) was revealed, which is not a simple superposition of the two factors mentioned. A mechanism is proposed to explain for these results −the graphene layers sheared at the sliding contact interfaces, and form a protective film, which is closely related with the GNS structures and surface texture patterns.
Qiu Ji - One of the best experts on this subject based on the ideXlab platform.
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Microstructure and formation mechanism of the low temperature plasma sulphurized layer of CrMoCu Alloy Cast Iron
Heat Treatment of Metals, 2011Co-Authors: Qiu Ji, Liu Qian, Liu JiyanAbstract:The sulphurized layer was prepared on the surface of CrMoCu Alloy Cast Iron by plasma sulphurization.Surface analysis methods such as SEM,TEM,electron diffraction pattern,EDS and XRD were employed.The microstructure of the sulphurized layer was systematically investigated and the formation mechanism of the sulphurized layer was discussed.The results show that the sulphurized surface makes up of 200~300 nm even sulphide granules,which contain the phases of α-Fe、Fe1-xS and FeS.The sulphur content of sulphurized layer gradually decreases from surface to inner.By the Electron diffraction pattern of TEM,FeS noncrystal phases was found in the sulphurized layer and the reason of formation was analyzed.
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Study on Tribological Properties of Nitrocarburizing-Sulphurizing Layer of CrMoCu Alloy Cast Iron
China Surface Engineering, 2004Co-Authors: Qiu JiAbstract:A compound layer with nitrocarbonide and sulfide has been made on the surface of CrMoCu Alloy Cast Iron by the combined treatment of ion nitrocarburizing and sulphurizing. The compound layer is composed of sulfide surface layer, nitrocarbonide layer and diffusing layer. The size of sulfide grains on the surface is in nano-micron-scale, and the phase structure of the compound layer is composed of FeS、FeS1-x、Fe2C and Fe3N. Under oil lubrication, the sulphurized surface shows good friction-reduction behavior, but its service time cant last very long, While the nitrocarburized+sulphurized surface can greatly improve the wear-resistance and the friction coeeficient of CrMoCu Alloy Cast Iron, under load 80 N and sliding velocity 0.3 m/s condition, its integrated friction and wear properties are better than that of plain and sulphurized surfaces?
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Study on Friction and Wear Characteristics and Structure of Compound Layer from Combined Treatment of Ion Nitrocarburizing-Ion Sulphurizing of CrMoCu Alloy Cast Iron
Transactions of Materids and Heat Treatment, 2004Co-Authors: Qiu JiAbstract:The technics of combined treatment of ion nitrocarburizing-ion sulphurizing of CrMoCu Alloy Cast Iron has been investigated and the compound layer with nitrocarbonide and sulphide has been made on the surface of CrMoCu Alloy Cast Iron. The compound layer is composed of sulfide surface layer and the nitrocarbonide hypo-surface layer and its diffusing layer. The size of sulfide globular grains distributing equably on the surface is in nano-rnicron-scale, and the phase structure of the compound layer is composed of FeS^ FeSi^ Fe2C and Fe3N. Under dry sliding condition, the friction-reducing of sulphurized surface is good, but its function time can't last very long. The nitrocarbonided+sulphurized surface can greatly improve the wear-resistance and the friction-reducing of CrMoCu Alloy Cast Iron, and its integrated friction and wear properties are better than plain and sulphurized surfaces'.
Harry G Preuss - One of the best experts on this subject based on the ideXlab platform.
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cytotoxicity and oxidative mechanisms of different forms of chromium
Toxicology, 2002Co-Authors: Debasis Bagchi, Bernard W. Downs, Sidney J. Stohs, Manashi Bagchi, Harry G PreussAbstract:Abstract Chromium exists mostly in two valence states in nature: hexavalent chromium [chromium(VI)] and trivalent chromium [chromium(III)]. Chromium(VI) is commonly used in industrial chrome plating, welding, painting, metal finishes, steel manufacturing, Alloy, Cast Iron and wood treatment, and is a proven toxin, mutagen and carcinogen. The mechanistic cytotoxicity of chromium(VI) is not completely understood, however, a large number of studies demonstrated that chromium(VI) induces oxidative stress, DNA damage, apoptotic cell death and altered gene expression. Conversely, chromium(III) is essential for proper insulin function and is required for normal protein, fat and carbohydrate metabolism, and is acknowledged as a dietary supplement. In this paper, comparative concentration- and time-dependent effects of chromium(VI) and chromium(III) were demonstrated on increased production of reactive oxygen species (ROS) and lipid peroxidation, enhanced excretion of urinary lipid metabolites, DNA fragmentation and apoptotic cell death in both in vitro and in vivo models. Chromium(VI) demonstrated significantly higher toxicity as compared with chromium(III). To evaluate the role of p53 gene, the dose-dependent effects of chromium(VI) were assessed in female C57BL/6Ntac and p53-deficient C57BL/6TSG p53 mice on enhanced production of ROS, lipid peroxidation and DNA fragmentation in hepatic and brain tissues. Chromium(VI) induced more pronounced oxidative damage in multiple target organs in p53 deficient mice. Comparative studies of chromium(III) picolinate and niacin-bound chromium(III), two popular dietary supplements, reveal that chromium(III) picolinate produces significantly more oxidative stress and DNA damage. Studies have implicated the toxicity of chromium picolinate in renal impairment, skin blisters and pustules, anemia, hemolysis, tissue edema, liver dysfunction; neuronal cell injury, impaired cognitive, perceptual and motor activity; enhanced production of hydroxyl radicals, chromosomal aberration, depletion of antioxidant enzymes, and DNA damage. Recently, chromium picolinate has been shown to be mutagenic and picolinic acid moiety appears to be responsible as studies show that picolinic acid alone is clastogenic. Niacin-bound chromium(III) has been demonstrated to be more bioavailable and efficacious and no toxicity has been reported. In summary, these studies demonstrate that a cascade of cellular events including oxidative stress, genomic DNA damage and modulation of apoptotic regulatory gene p53 are involved in chromium(VI)-induced toxicity and carcinogenesis. The safety of chromium(III) is largely dependent on the ligand, and adequate clinical studies are warranted to demonstrate the safety and efficacy of chromium(III) for human consumption.
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Cytotoxicity and oxidative mechanisms of different forms of chromium
Toxicology, 2002Co-Authors: Debasis Bagchi, Bernard W. Downs, Sidney J. Stohs, Manashi Bagchi, Harry G PreussAbstract:Chromium exists mostly in two valence states in nature: hexavalent chromium [chromium(VI)] and trivalent chromium [chromium(III)]. Chromium(VI) is commonly used in industrial chrome plating, welding, painting, metal finishes, steel manufacturing, Alloy, Cast Iron and wood treatment, and is a proven toxin, mutagen and carcinogen. The mechanistic cytotoxicity of chromium(VI) is not completely understood, however, a large number of studies demonstrated that chromium(VI) induces oxidative stress, DNA damage, apoptotic cell death and altered gene expression. Conversely, chromium(III) is essential for proper insulin function and is required for normal protein, fat and carbohydrate metabolism, and is acknowledged as a dietary supplement. In this paper, comparative concentration- and time-dependent effects of chromium(VI) and chromium(III) were demonstrated on increased production of reactive oxygen species (ROS) and lipid peroxidation, enhanced excretion of urinary lipid metabolites, DNA fragmentation and apoptotic cell death in both in vitro and in vivo models. Chromium(VI) demonstrated significantly higher toxicity as compared with chromium(III). To evaluate the role of p53 gene, the dose-dependent effects of chromium(VI) were assessed in female C57BL/6Ntac and p53-deficient C57BL/6TSG p53 mice on enhanced production of ROS, lipid peroxidation and DNA fragmentation in hepatic and brain tissues. Chromium(VI) induced more pronounced oxidative damage in multiple target organs in p53 deficient mice. Comparative studies of chromium(III) picolinate and niacin-bound chromium(III), two popular dietary supplements, reveal that chromium(III) picolinate produces significantly more oxidative stress and DNA damage. Studies have implicated the toxicity of chromium picolinate in renal impairment, skin blisters and pustules, anemia, hemolysis, tissue edema, liver dysfunction; neuronal cell injury, impaired cognitive, perceptual and motor activity; enhanced production of hydroxyl radicals, chromosomal aberration, depletion of antioxidant enzymes, and DNA damage. Recently, chromium picolinate has been shown to be mutagenic and picolinic acid moiety appears to be responsible as studies show that picolinic acid alone is clastogenic. Niacin-bound chromium(III) has been demonstrated to be more bioavailable and efficacious and no toxicity has been reported. In summary, these studies demonstrate that a cascade of cellular events including oxidative stress, genomic DNA damage and modulation of apoptotic regulatory gene p53 are involved in chromium(VI)-induced toxicity and carcinogenesis. The safety of chromium(III) is largely dependent on the ligand, and adequate clinical studies are warranted to demonstrate the safety and efficacy of chromium(III) for human consumption. © 2002 Elsevier Science Ireland Ltd. All rights reserved.
