Silicon-carbide-fiber-reinforced silicon-carbide-ceramic-based matrix(SiC/SiC)composites possess excellent properties such as low density,high strength and high temperature resistance,showing a potential application f...Silicon-carbide-fiber-reinforced silicon-carbide-ceramic-based matrix(SiC/SiC)composites possess excellent properties such as low density,high strength and high temperature resistance,showing a potential application for structural components in the aerospace field,but their oxidation behavior remains largely unknown.In this study,Yb_(2)Si_(2)O_(7)modified SiC/SiC(SiC/SiC-Yb_(2)Si_(2)O_(7))mini-composites were prepared by introducing Yb_(2)Si_(2)O_(7)as anti-oxidation phase into SiC fiber bundles via Sol-Gel and depositing SiC matrix by chemical vapor deposition(CVD).Influence of Yb_(2)Si_(2)O_(7)on microstructure,mechanical property and oxidation behavior of SiC/SiC mini-composites was investigated.The results showed that after oxidation in air at 1200 and 1400℃for 50 h,the tensile strength retentions of SiC/SiC mini-composites were 77%and 69%,respectively,and the fracture morphology exhibited flat.The Yb_(2)Si_(2)O_(7)introduced by Sol-Gel partially distributed in layers,contributing to the toughening of the material.On the fracture surface,there was interlayer debonding,which extended energy dissipation mechanism of SiC/SiC mini-composites.Tensile strength of SiC/SiC-Yb_(2)Si_(2)O_(7)mini-composites at room temperature was 484 MPa.After oxidation in air at 1200 and 1400℃for 50 h,the tensile strengths decreased to 425 and 374 MPa,resulting in retention rates of 88%and 77%,respectively.It displayed typical non-brittle fracture characteristics.The interface oxygen content of SiC/SiC mini-composites at the fracture surface was higher than that of SiC/SiC-Yb_(2)Si_(2)O_(7)mini-composites,indicating that introduction of Yb_(2)Si_(2)O_(7)could alleviate oxygen diffusion towards the interface,and therefore improve the oxidation resistance of SiC/SiC-Yb_(2)Si_(2)O_(7)mini-composites.展开更多
The oxidation behavior of Ti55 alloy and TiBw/Ti55 composites at temperatures ranging from 960 to 1000℃ was investigated by characterizing the surface and cross-section microstructure of specimens.Results showed that...The oxidation behavior of Ti55 alloy and TiBw/Ti55 composites at temperatures ranging from 960 to 1000℃ was investigated by characterizing the surface and cross-section microstructure of specimens.Results showed that TiBw reinforcement accelerated the occurrence of Ti_(6O)/Ti_(3O) by dissolving oxygen in titanium in the starting oxidation stage,and the Ti_(6O)/Ti_(3O) transformed into TiO_(2) with the progression of oxidation.Meanwhile,TiBw reinforcement promoted the formation of(101)crystal planes to be beneficial to the growth of TiO_(2) twins.The cross-sectional characterization showed that the oxide layer of Ti55 alloy and TiBw/Ti55 composites from outside to inside was TiO_(2)+Al_(2)O_(3),TiO_(2),Ti-Sn compounds,Ti_(6O)/Ti_(3O) in sequence,which was confirmed by calculating the standard Gibbs free energy of the oxide nucleation.The TiBw reinforcement accelerated the occurrence of suboxides Ti_(6O)/Ti_(3O) by dissolving oxygen in titanium,and promoted the formation of(101)crystal planes which were beneficial to the growth of TiO_(2) twins.The optimal addition of TiBw induced the TiO_(2) twins,promoted the random orientation of oxides and refined the oxide size of the TiBw/Ti55 composites with 3.5%volume fractions of TiBw,resulting in the best resistance against oxidation.展开更多
The surface of MoSi2-SiB6/phenolic resin matrix composites was modified by mica,and the thermal oxidation behavior of the composites and the mechanical properties of the pyrolysis products were studied.The results sho...The surface of MoSi2-SiB6/phenolic resin matrix composites was modified by mica,and the thermal oxidation behavior of the composites and the mechanical properties of the pyrolysis products were studied.The results showed that the mica improved the thermal properties of the composites,the thermal expansion coefficient decreased,and the liquid phase formation caused the composites to shrink and increase the density.The flexural strength of mica surface modified composites not only increased to 78.64MPa after thermal treatment at 800-1200℃,but reached 83.02 MPa after high temperature treatment at1400℃.The improvement of the mechanical properties of the residual product benefits from the formation of high temperature ceramic phases such as Mo_(2)C and MoB,and the improvement of the shear strength of the composites by the mica.The shear strength of MBm5-2 at room temperature reached 33.08 MPa,indicating that the improvement of the interlayer properties of the composites further improved its mechanical properties.展开更多
The high melting point element W and the rare earth element Ce were added to 18Cr-Mo(444-type)ferritic stainless steel to improve its high-temperature oxidation resistance in exhaust gas.A simulated exhaust gas was fi...The high melting point element W and the rare earth element Ce were added to 18Cr-Mo(444-type)ferritic stainless steel to improve its high-temperature oxidation resistance in exhaust gas.A simulated exhaust gas was filled in the simultaneous thermal analyzer to simulate the service environment,and the oxidation behavior in high-temperature exhaust gas environment of 444-type ferritic stainless steel alloyed with W and Ce was investigated.The oxide structure and composition formed in this process were analyzed and characterized by scanning electron microscopy/energy-dispersive spectroscopy and electron probe analysis,and the mechanism of W and Ce in the oxidation process was revealed.The results show that 18Cr-Mo ferritic stainless steel containing W and Ce has better oxidation resistance in high-temperature exhaust gas.The element W can promote the precipitation of Laves phase at the matrix/interface,inhibit the interface diffusion of oxidizing elements and prevent the inward growth of the oxide film.The element Ce can suppress the volume of SiO_(2)at the oxide film/interface,reducing the breakaway oxidation caused by cracking of the oxide film.The CeO_(2)provides nucleation sites for oxide particles,promoting the healing of cracks and voids within the oxide film.展开更多
Revealing the oxidation behavior of superalloys is crucial for optimizing material properties and extending service life.This study investigated the oxidation behavior of superalloy GH4738 under stress states at 850℃...Revealing the oxidation behavior of superalloys is crucial for optimizing material properties and extending service life.This study investigated the oxidation behavior of superalloy GH4738 under stress states at 850℃.High-throughput specimens were fabricated to withstand different stresses at the same time.Isothermal oxidation s amples were analyzed using the mass gain method to obtain oxidation kinetic curves.The results show that the external stress below 200 MPa could improve the oxidation resistance of the GH4738.With tensile stress increasing,the oxide layer becomes thinner,denser and more complete,while internal oxidation decreases.The tensile stress alters the structure of the external oxide layer from a two-layer to a threelayer configuration.The Cr_(2)O_(3) oxide layer inhibits the outward diffusion of Ti,leading to Ti enrichment at the oxide-matrix interface and altering the oxidation mechanism of GH4738.展开更多
ZrB_(2)-based ceramics typically necessitate high temperature and pressure for sintering,whereas ZrB_(2)-SiC ceramics can be fabricated at 1500℃using the process of reactive melt infiltration with Si.In comparison to...ZrB_(2)-based ceramics typically necessitate high temperature and pressure for sintering,whereas ZrB_(2)-SiC ceramics can be fabricated at 1500℃using the process of reactive melt infiltration with Si.In comparison to the conventional preparation method,reactive synthesis allows for the more facile production of ultra-high temperature ceramics with fine particle size and homogeneous composition.In this work,ZrSi_(2),B4C,and C were used as raw materials to prepare ZrB_(2)-SiC via combination of tape casting and reactive melt infiltration herein referred to as ZBC ceramics.Control sample of ZrB_(2)-SiC was also prepared using ZrB_(2)and SiC as raw materials through an identical process designated as ZS ceramics.Microscopic analysis of both ceramic groups revealed smaller and more uniformly distributed particles of the ZrB_(2)phase in ZBC ceramics compared to the larger particles in ZS ceramics.Both sets of ceramics underwent cyclic oxidation testing in the air at 1600℃for a cumulative duration of 5 cycles,each cycle lasting 2 h.Analysis of the oxidation behavior showed that both ZBC ceramics and ZS ceramics developed a glassy SiO_(2)-ZrO_(2)oxide layer on their surfaces during the oxidation.This layer severed as a barrier against oxygen.In ZBC ceramics,ZrO_(2)is finely distributed in SiO_(2),whereas in ZS ceramics,larger ZrO_(2)particles coexist with glassy SiO_(2).The surface oxide layer of ZBC ceramics maintains a dense structure because the well-dispersed ZrO_(2)increases the viscosity of glassy SiO_(2),preventing its crystallization during the cooling.Conversely,some SiO_(2)in the oxide layer of ZS ceramics may crystallize and form a eutectic with ZrO_(2),leading to the formation of ZrSiO_(4).This leads to cracking of the oxide layer due to differences in thermal expansion coefficients,weakening its barrier effect.An analysis of the oxidation resistance shows that ZBC ceramics exhibit less increase in oxide layer thickness and mass compared to ZS ceramics,suggesting superior oxidation resistance of ZBC ceramics.展开更多
Hf-based carbides are highly desirable candidate materials for oxidizing environments above 2000℃.However,the static oxidation behavior at their potential service temperatures remains unclear.To fill this gap,the sta...Hf-based carbides are highly desirable candidate materials for oxidizing environments above 2000℃.However,the static oxidation behavior at their potential service temperatures remains unclear.To fill this gap,the static oxidation behavior of(Hf,Ti)C and the effect of Ti substitutions were investigated in air at 2500℃ under an oxygen partial pressure of 4.2 kPa.After oxidation for 2000 s,the thickness of the oxide layer on the surface of(Hf,Ti)C bulk ceramic is reduced by 62.29%compared with that on the HfC monocarbide surface.The dramatic improvement in oxidation resistance is attributed to the unique oxide layer structure consisting of various crystalline oxycarbides,HfO_(2),and carbon.The Ti-rich oxycarbide((Ti,Hf)C_(x)O_(y))dispersed within HfO_(2) formed the major structure of the oxide layer.A coherent boundary with lattice distortion existed at the HfO2/(Ti,Hf)C_(x)O_(y) interface along the(111)crystal plane direction,which served as an effective oxygen diffusion barrier.The Hfrich oxycarbide((Hf,Ti)CxOy)together with(Ti,Hf)C_(x)O_(y),HfO_(2),and precipitated carbon constituted a dense transition layer,ensuring favorable bonding between the oxide layer and the matrix.The Ti content affects the oxidation resistance of(Hf,Ti)C by determining the oxide layer's phase distribution and integrity.展开更多
In this work,possible short-term thermal exposure oxidation in hot processing including semi-solid processing is focused.We aim to investigate the short-term oxidation behavior of a novel powder metallurgy Al_(0.8)Co_...In this work,possible short-term thermal exposure oxidation in hot processing including semi-solid processing is focused.We aim to investigate the short-term oxidation behavior of a novel powder metallurgy Al_(0.8)Co_(0.5)Cr_(1.5)CuFeNi high entropy alloy(HEA)in high-temperature solid(1000-1100℃)and semi-solid(1125-1225℃)intervals.From 1000 to 1225℃,mass gain increases from 0.31 to 0.45 mg cm^(-2)after 60 min oxidation,presenting superior oxidation resistance in the semi-solid state compared with other semi-solid alloys.Equiaxedα-Al_(2)O_(3)grains are the predominant component of oxide scales and no obvious internal oxidation layer occurs in both solid and semi-solid intervals.Al_(2)O_(3)scale growth is predominantly determined by outward Al^(3+)diffusion.For solid oxidation,different scale formation kinetics occur on various phases and the BCC(B2)phase has faster scale formation kinetics.This is attributed to outward Al^(3+)diffusion rate differences in various component systems.During semi-solid oxidation,the increased degree of chaos and number of vacancies in the liquid phase provide a diffusion channel,leading to rapid Al_(2)O_(3)formation.Oxidation resistance in the semi-solid state is attributed to dense Al_(2)O_(3)scales formed through selective oxidation of Al.展开更多
The oxidation behavior of Ti?22Al?(27?x)Nb?xZr (x=0, 1, 6) alloys at 800 °C for exposure time up to 100 h was examined. It is shown that oxidation rate of experimental alloys obeys the parabolic kinetics. Ti?22Al...The oxidation behavior of Ti?22Al?(27?x)Nb?xZr (x=0, 1, 6) alloys at 800 °C for exposure time up to 100 h was examined. It is shown that oxidation rate of experimental alloys obeys the parabolic kinetics. Ti?22Al?26Nb?1Zr alloy demonstrates more excellent oxidation resistance than the other two alloys. The main oxidation products are TiO2, Al2O3 and AlNbO4 phases for all these alloys. For the Ti?22Al?26Nb?1Zr alloy, Zr addition can modify the growth mechanism of oxide scale, which can effectively hinder the diffusion of oxygen. Whereas, reaction of Zr with oxygen leads to the formation of ZrO2 precipitates for the Ti?22Al?21Nb?6Zr alloy, which promotes the oxygen ingress into the substrate. Meanwhile, oxidation affected zones, including internal-oxidation layer and oxygen-enriched zone, are present beneath the outmost oxide scale. The difference in these zones is derived from the phase constitution in the starting Ti?22Al?(27?x)Nb?xZr (x=0, 1, 6) alloys.展开更多
The oxidation behavior of electroconductive TiN/O′-Sialon ceramics prepared using high titania slag as main starting material was studied at 1 200-1 300 °C in air. The isothermal and non-isothermal oxidation pro...The oxidation behavior of electroconductive TiN/O′-Sialon ceramics prepared using high titania slag as main starting material was studied at 1 200-1 300 °C in air. The isothermal and non-isothermal oxidation processes were investigated by DTA-TG. Phase compositions and morphologies of the oxidized products were analyzed by XRD, SEM and EDS. The results indicate that the oxidation of TiN and O′-Sialon occurs at about 500 °C and 1 050 °C, respectively. After oxidation at 1 200-1 300 °C, a protective scale that consists of Fe2MgTi3O10, SiO2 and TiO2 is formed on the surface of the materials, which effectively prevents the oxidation process. The formation of a protective scale is relative to TiN content and apparent porosity of the samples, the amount of SiO2 and amorphous phase in the oxidation product. At the initial oxidation stage, the oxidation kinetics of the materials follows perfectly the linear law with the apparent activation energy of 1.574×105 J/mol, and at the late-mid stage, the oxidation of the samples obeys the parabolic law with the apparent activation energy of 2.693×105 J/mol. With the increase of TiN content, mass gain of the materials increases significantly.展开更多
By using CeO2 particles instead of part of Al2O3 particles as filler, the CeO2 was successfully entrapped into the outer layer of the chromizing coatings on the as-deposited nanocrystalline （NC） and microcrystalline...By using CeO2 particles instead of part of Al2O3 particles as filler, the CeO2 was successfully entrapped into the outer layer of the chromizing coatings on the as-deposited nanocrystalline （NC） and microcrystalline （MC） Ni films using a conventional pack-cementation method at 800 °C. For comparison, chromizing was also performed under the same condition on MC Ni film using Al2O3 as filler without CeO2 particles. SEM/EDX and TEM results indicate that the refinement of Ni grain and CeO2 entrapped into the chromizing coatings refine the grain of the chromizing coating. Oxidation at 900 °C indicates that compared with the CeO2-free chromizing coating, the CeO2-dispersed chromizing coating exhibits an increased oxidation resistance. For the CeO2-dispersed chromizing coating, the refinement of Ni grain size significantly decreases the transient-oxidation scaling rate of the chromizing coatings. Together with this, the CeO2-dispersed chromizing coating formed on NC Ni exhibits a better oxidation resistance.展开更多
The oxidation behavior of Hastelloy C-2000 alloy was investigated in air at 800 °C and 1000 °C for 100 h, respectively. Oxidation kinetics and oxide scales morphologies were examined by mass gain measurement...The oxidation behavior of Hastelloy C-2000 alloy was investigated in air at 800 °C and 1000 °C for 100 h, respectively. Oxidation kinetics and oxide scales morphologies were examined by mass gain measurement, scanning electron microscopy（SEM）, X-ray diffraction（XRD） and X-ray photoelectron spectroscopy（XPS）. The oxidation behavior of the alloy approximately follows a parabolic rate law. Moreover, annealing twins defect structure in matrix deteriorates the oxidation resistance of alloy due to the improvement of diffusion rates for alloying elements and oxygen atoms. At 800 °C, the microstructure is primarily composed of Ni O and Cr1.3Fe0.7O6 and the initial annealing twins structure is visible and Mo-rich phases are emerged to approach boundary of oxide scales. At 1000 °C, however, the morphology microstructure of oxide scales consists of oxide particle with fine Cr oxides and large Ni oxides by inlaying each other, whilst Mo-rich phases hardly appear closing to the interface of oxide scales.展开更多
The oxidation behavior of a nickel-based superalloy GH738 was studied by isothermal oxidation tests in still air at different temperatures,with exposure time up to 100 h.Oxidation-kinetic curves were plotted using the...The oxidation behavior of a nickel-based superalloy GH738 was studied by isothermal oxidation tests in still air at different temperatures,with exposure time up to 100 h.Oxidation-kinetic curves were plotted using the mass gain method.The surface and cross-sectional morphologies were observed by scanning electron microscopy(SEM).A composition analysis and an oxidation-product identification were conducted using energydispersive X-ray spectroscopy(EDS) and an X-ray diffraction(XRD),respectively.The results showed that GH738 exhibited parabolic oxidation-kinetic curves,with stable parabolic-rate constants at each temperatures.The activation energy of oxide growth was calculated to be329.6 kJ·mol^(-1).Cr_(2) O_(3)(chromia) was the external oxidation product at 800℃.A TiO_(2)-Cr_(2) O_(3) double-layer structure was formed at 900℃.The position of TiO_(2) changed from the oxide-metal interface to the air-oxide interface by the diffusion of Ti atoms in chromia during the oxidation time at this temperature.Spallation was observed in the Cr_(0.12)Ti_(0.78)O_(1.74)-Cr_(2) O_(3) multi-layer oxide of at 1000℃,which increased the oxidation rate.For all the tests,the main internal oxide was always Al_(2) O_(3).The entire GH738 oxidation process was interpreted by the competitive diffusion of elements(Cr,Ti,Ni,etc.) in metal matrix and chromia,while a schematic diagram of oxidation process was proposed.展开更多
In this paper, the isothermal oxidation kinetics and oxidation behavior of GH586 superalloy from 800 to 1000℃ were investigated. The oxide scale morphologies of the surfaces and the cross sections after oxidation wer...In this paper, the isothermal oxidation kinetics and oxidation behavior of GH586 superalloy from 800 to 1000℃ were investigated. The oxide scale morphologies of the surfaces and the cross sections after oxidation were characterized by means of X-ray diffraction （XRD） and scanning electron microscope （SEM） equipped with energy-dispersive spectroscopy （EDS）. The results show that the growth of the oxide scales on the surface of superalloy GH586 obeys a parabolic law with the activa- tion energy of 241.4 kJ.mo1-1 from 800 to 1000℃ The dense oxide scale formed at 800℃ is mainly composed of Cr203, NiCr204 and a small amount of TiO2. At 900℃, the oxide scale is divided into two layers： the outer layer with multiple cracks is mainly composed of ＂Cr203 and TiO2, while the inner is a layer of dense Cr203. Under the oxide scale, aluminum-rich oxides along the grain bound- aries are generated by the internal oxidation. At 1000 ℃for 100 h, cracks throughout the whole oxide film accel- erate the oxidation rate of Ni-based superalloy GH586 and large blocks of TiO2 in the oxide scale are generated, resulting in the spallation of oxide scale.展开更多
A Mg-Y-Ca-Ce magnesium alloy was optimized for high ignition-proof property, which did not bum in air at 1233 K up to 30 min. Oxidation behavior of the alloy was investigated by X-ray diffraction （XRD）, scanning ele...A Mg-Y-Ca-Ce magnesium alloy was optimized for high ignition-proof property, which did not bum in air at 1233 K up to 30 min. Oxidation behavior of the alloy was investigated by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and thermodynamics calculation at 673, 773 and 873 K. XRD and SEM analysis indicated that dense and compact oxide films composed of MgO, Y203 and CaO formed. The oxidation behavior was characterized by the selective oxidation. Based on Pilling-Bedworth ra- tio （PBR） and energy dispersive spectrometer （EDS） analysis, Y203 contributed more to form the compact surface oxide film, which led to the excellent ignition-proof performance. The thermodynamics analysis and EDS results implied that the Y-rich areas were preferred paths for the selective oxidation.展开更多
The effect of theγ+γtwo-phase structure on the oxidation behaviors of Ni-Al single-crystal alloys at 650℃was investigated by scanning electron microscopy,transmission electron microscopy,atomic force microscopy,X-r...The effect of theγ+γtwo-phase structure on the oxidation behaviors of Ni-Al single-crystal alloys at 650℃was investigated by scanning electron microscopy,transmission electron microscopy,atomic force microscopy,X-ray diffraction and Auger electron spectroscopy.In the initial oxidation stage,the oxidation behavior is primarily determined by the growth pattern of oxides in theγchannel.The outward convex NiO was formed in unprotected wideγchannels.And Ni-Al spinel oxide provides a great number of short-circuit paths,accelerating the inward diffusion of oxygen and outward diffusion of Ni.In the late stage of oxidation,the elongated internal oxide in the largeγphase contributes to the diffusion of oxygen along the oxide/metal interface.Consequently,the Ni-Al single-crystal alloy with wideγchannels and largeγprecipitates exhibited poor oxidation performance.展开更多
Aiming to develop materials for construction of the set-up and electrode of high-temperature molten salt reactors, the effect of Al and Y on the high-temperature oxidation behavior of Ni-11Fe-10Cu at 750 and 950 °...Aiming to develop materials for construction of the set-up and electrode of high-temperature molten salt reactors, the effect of Al and Y on the high-temperature oxidation behavior of Ni-11Fe-10Cu at 750 and 950 °C in air were investigated. The oxidation kinetics of Ni-11Fe-10Cu alloy followed parabolic law at 750 °C without spallation and linear law at 950 °C with severe spallation, while that of Ni-11Fe-10Cu-6Al-3Y alloy followed parabolic law at 750 and 950 °C without spallation. The parabolic rate constant （kp） of Ni-11Fe-10Cu was smaller than that of Ni-11Fe-10Cu-6Al-3Y at 750 °C. The oxide scale formed on Ni-11Fe-10Cu at 750 °C was composed of a CuO outer layer, a NiFe2O4 middle layer and a NiO inner layer. The oxide scale formed on Ni-11Fe-10Cu-6Al-3Y at 750 °C was also composed of the similar triplex layers in addition to an internal oxidation zone containing Al, Ni and Cu oxide and the microstructure of the scale changed with increasing temperature. Although the doping Al and Y could improve the adherence of oxide scale, it could aggravate the extent of internal oxidation. Based on the combination of X-ray diffraction （XRD）, scanning electron mi-croscopy/energy dispersive spectroscopy （SEM/EDX） analysis, the microstructure and growth mechanism of the multi-layer oxide scale was studied and the effect of doping Al and Y on the oxidation behavior of Ni-11Fe-10Cu alloy was also discussed.展开更多
In this study,the CeO_(2)-modified WC-12 Co coatings were deposited on Q345 steel substrate using high-velocity oxygen fuel(HVOF) spraying.Oxidation behavior of the modified coatings was analyzed in the range of 450-...In this study,the CeO_(2)-modified WC-12 Co coatings were deposited on Q345 steel substrate using high-velocity oxygen fuel(HVOF) spraying.Oxidation behavior of the modified coatings was analyzed in the range of 450-900℃ for different oxidation time to investigate the effects of oxidation time and temperature on the coatings.The oxidation kinetics and oxidation mechanism of the modified coatings were clarified.The results show that the oxides are mainly composed of WO_(3) and CoWO_(4) within 450-750℃ while the phases are different at 900 ℃.The CeO_(2)-modified coatings have good oxidation resistance when the oxidation temperature is below550℃ and the oxidation mechanism changes due to the occurrence of anomalous oxidation above 650℃.Moreover,the oxidation mass gain curves obey approximately a parabolic law in the temperature range of 450-650℃ at the initial stage but the later oxidation proceeds by a linear law.In addition,based on the analysis of micromorphology and component of the prepared coating,the role of rare earth(RE) additives is obtained during high-temperature oxidization.展开更多
Excess nitrogenous compounds are detrimental to natural water systems and to human health. To completely realize autohy- drogenotrophic nitrogen removal, a novel 3-dimensional biofilm-electrode reactor was designed. T...Excess nitrogenous compounds are detrimental to natural water systems and to human health. To completely realize autohy- drogenotrophic nitrogen removal, a novel 3-dimensional biofilm-electrode reactor was designed. Titanium was electroplated with ruthenium and used as the anode. Activated carbon fiber felt was used as the cathode. The reactor was separated into two chambers by a permeable membrane. The cathode chamber was filled with granular graphite and glass beads. The cathode and cathode chamber were inhabited with domesticated biofilm. In the absence of organic substances, a nitrogen removal efficiency of up to 91% was achieved at DO levels of 3.42 ± 0.37 mg/L when the applied current density was only 0.02 mA/cm^2. The oxidation of ammonium in biofilmelectrode reactors was also investigated. It was found that ammonium could be oxidized not only on the anode but also on particle electrodes in the cathode chamber of the biofilm-electrode reactor. Oxidation rates of ammonium and nitrogen removal efficiency were found to be affected by the electric current loading on the biofilm-electrode reactor. The kinetic model of ammonium at different electric currents was analyzed by a first-order reaction kinetics equation. The regression analysis implied that when the current density was less than 0.02 mA/cm^2, ammonium removal was positively correlated to the current density. However, when the current density was more than 0.02 mA/cm^2, the electric current became a limiting factor for the oxidation rate of ammonium and nitrogen removal efficiency.展开更多
Based on the pseudo potential plane-wave method of density functional theory （DFT）, Ti1-xNbxAk （x=0, 0.062 5, 0.083 3, 0.125, 0.250） crystals＇ geometry structure, elastic constants, electronic structure and Mulli...Based on the pseudo potential plane-wave method of density functional theory （DFT）, Ti1-xNbxAk （x=0, 0.062 5, 0.083 3, 0.125, 0.250） crystals＇ geometry structure, elastic constants, electronic structure and Mulliken populations were calculated, and the effects of doping on the geometric structure, electronic structure and bond strength were systematically analyzed. The results show that the influence of Nb on the geometric structure is little in terms of the plasticity, and with the increase of Nb content, the covalent bond strength remarkably reduces, and Ti-Al, Nb-M （M=Ti, Al） and other hybrid bonds enhance; meanwhile, the peak district increases and the pseudo-energy gap first decreases and then increases, the overall band structure narrows, the covalent bond and direction of bonds reduce. The population analysis also shows that the results are consistent with the electronic structure analysis. The density of states of TiAINb shows that Nb doping can enhance the activity of Al and benefit the form of Al2O3 film. All the calculations reveal that the room temperature plasticity and the antioxidation properties of the compounds can be improved with the Nb content of 8.33%-12.5% （mole fraction）.展开更多
基金National Natural Science Foundation of China(52222202)National Key R&D Program of China(2022YFB3707700)+2 种基金Project of Shanghai Science and Technology Innovation Action Plan(21511104800)Shanghai Pilot Program for Basic Research-Chinese Academy of Science,Shanghai Branch(JCYJ-SHFY-2021-001)Science Center for Gas Turbine Project(P2022-B-Ⅳ-001-001)。
文摘Silicon-carbide-fiber-reinforced silicon-carbide-ceramic-based matrix(SiC/SiC)composites possess excellent properties such as low density,high strength and high temperature resistance,showing a potential application for structural components in the aerospace field,but their oxidation behavior remains largely unknown.In this study,Yb_(2)Si_(2)O_(7)modified SiC/SiC(SiC/SiC-Yb_(2)Si_(2)O_(7))mini-composites were prepared by introducing Yb_(2)Si_(2)O_(7)as anti-oxidation phase into SiC fiber bundles via Sol-Gel and depositing SiC matrix by chemical vapor deposition(CVD).Influence of Yb_(2)Si_(2)O_(7)on microstructure,mechanical property and oxidation behavior of SiC/SiC mini-composites was investigated.The results showed that after oxidation in air at 1200 and 1400℃for 50 h,the tensile strength retentions of SiC/SiC mini-composites were 77%and 69%,respectively,and the fracture morphology exhibited flat.The Yb_(2)Si_(2)O_(7)introduced by Sol-Gel partially distributed in layers,contributing to the toughening of the material.On the fracture surface,there was interlayer debonding,which extended energy dissipation mechanism of SiC/SiC mini-composites.Tensile strength of SiC/SiC-Yb_(2)Si_(2)O_(7)mini-composites at room temperature was 484 MPa.After oxidation in air at 1200 and 1400℃for 50 h,the tensile strengths decreased to 425 and 374 MPa,resulting in retention rates of 88%and 77%,respectively.It displayed typical non-brittle fracture characteristics.The interface oxygen content of SiC/SiC mini-composites at the fracture surface was higher than that of SiC/SiC-Yb_(2)Si_(2)O_(7)mini-composites,indicating that introduction of Yb_(2)Si_(2)O_(7)could alleviate oxygen diffusion towards the interface,and therefore improve the oxidation resistance of SiC/SiC-Yb_(2)Si_(2)O_(7)mini-composites.
基金supported by the Special Project of the Central-Guided Local Science and Technology Development(Grant No.2022ZY2-JCYJ-01-06)the Key Research and Development Program(Grant No.2020-xxx-ZD-179-00-05)Prof.Lujun Huang Group at Harbin Institute of Technology for providing the TiBw/Ti55 composites.
文摘The oxidation behavior of Ti55 alloy and TiBw/Ti55 composites at temperatures ranging from 960 to 1000℃ was investigated by characterizing the surface and cross-section microstructure of specimens.Results showed that TiBw reinforcement accelerated the occurrence of Ti_(6O)/Ti_(3O) by dissolving oxygen in titanium in the starting oxidation stage,and the Ti_(6O)/Ti_(3O) transformed into TiO_(2) with the progression of oxidation.Meanwhile,TiBw reinforcement promoted the formation of(101)crystal planes to be beneficial to the growth of TiO_(2) twins.The cross-sectional characterization showed that the oxide layer of Ti55 alloy and TiBw/Ti55 composites from outside to inside was TiO_(2)+Al_(2)O_(3),TiO_(2),Ti-Sn compounds,Ti_(6O)/Ti_(3O) in sequence,which was confirmed by calculating the standard Gibbs free energy of the oxide nucleation.The TiBw reinforcement accelerated the occurrence of suboxides Ti_(6O)/Ti_(3O) by dissolving oxygen in titanium,and promoted the formation of(101)crystal planes which were beneficial to the growth of TiO_(2) twins.The optimal addition of TiBw induced the TiO_(2) twins,promoted the random orientation of oxides and refined the oxide size of the TiBw/Ti55 composites with 3.5%volume fractions of TiBw,resulting in the best resistance against oxidation.
基金Funded by the National Natural Science Foundation of China(Nos.52171045,52162013,and 51932006)。
文摘The surface of MoSi2-SiB6/phenolic resin matrix composites was modified by mica,and the thermal oxidation behavior of the composites and the mechanical properties of the pyrolysis products were studied.The results showed that the mica improved the thermal properties of the composites,the thermal expansion coefficient decreased,and the liquid phase formation caused the composites to shrink and increase the density.The flexural strength of mica surface modified composites not only increased to 78.64MPa after thermal treatment at 800-1200℃,but reached 83.02 MPa after high temperature treatment at1400℃.The improvement of the mechanical properties of the residual product benefits from the formation of high temperature ceramic phases such as Mo_(2)C and MoB,and the improvement of the shear strength of the composites by the mica.The shear strength of MBm5-2 at room temperature reached 33.08 MPa,indicating that the improvement of the interlayer properties of the composites further improved its mechanical properties.
基金the joint financial support from the National Natural Science Foundation of China and Baowu Group Co.,Ltd.(Grant No.U1660205)the Fundamental Research Funds for the Central Universities(Grant No.N2007001).
文摘The high melting point element W and the rare earth element Ce were added to 18Cr-Mo(444-type)ferritic stainless steel to improve its high-temperature oxidation resistance in exhaust gas.A simulated exhaust gas was filled in the simultaneous thermal analyzer to simulate the service environment,and the oxidation behavior in high-temperature exhaust gas environment of 444-type ferritic stainless steel alloyed with W and Ce was investigated.The oxide structure and composition formed in this process were analyzed and characterized by scanning electron microscopy/energy-dispersive spectroscopy and electron probe analysis,and the mechanism of W and Ce in the oxidation process was revealed.The results show that 18Cr-Mo ferritic stainless steel containing W and Ce has better oxidation resistance in high-temperature exhaust gas.The element W can promote the precipitation of Laves phase at the matrix/interface,inhibit the interface diffusion of oxidizing elements and prevent the inward growth of the oxide film.The element Ce can suppress the volume of SiO_(2)at the oxide film/interface,reducing the breakaway oxidation caused by cracking of the oxide film.The CeO_(2)provides nucleation sites for oxide particles,promoting the healing of cracks and voids within the oxide film.
基金financially supported by the National Key R&D Program of China(No.2021YFB3700401)Shandong Provincial Natural Science Foundation for Youths(No.ZR2022QE234)+1 种基金Zhejiang Provincial Natural Science Foundation(No.LQ21E030002)the Youth Innovation team Project of Higher Education Institutions in Shandong Province(No.2022KJ272)。
文摘Revealing the oxidation behavior of superalloys is crucial for optimizing material properties and extending service life.This study investigated the oxidation behavior of superalloy GH4738 under stress states at 850℃.High-throughput specimens were fabricated to withstand different stresses at the same time.Isothermal oxidation s amples were analyzed using the mass gain method to obtain oxidation kinetic curves.The results show that the external stress below 200 MPa could improve the oxidation resistance of the GH4738.With tensile stress increasing,the oxide layer becomes thinner,denser and more complete,while internal oxidation decreases.The tensile stress alters the structure of the external oxide layer from a two-layer to a threelayer configuration.The Cr_(2)O_(3) oxide layer inhibits the outward diffusion of Ti,leading to Ti enrichment at the oxide-matrix interface and altering the oxidation mechanism of GH4738.
基金National Key R&D Program of China(2022YFB3707700)Shanghai Science and Technology Innovation Action Plan(21511104800)+3 种基金National Natural Science Foundation of China(52172111)National Science and Technology Major Project(2017-IV-0005-0042)Key Research Program of the Chinese Academy of Sciences(ZDRW-CN-2021-2-2)Science Center for Gas Turbine Project(P2022-B-IV-001-001)。
文摘ZrB_(2)-based ceramics typically necessitate high temperature and pressure for sintering,whereas ZrB_(2)-SiC ceramics can be fabricated at 1500℃using the process of reactive melt infiltration with Si.In comparison to the conventional preparation method,reactive synthesis allows for the more facile production of ultra-high temperature ceramics with fine particle size and homogeneous composition.In this work,ZrSi_(2),B4C,and C were used as raw materials to prepare ZrB_(2)-SiC via combination of tape casting and reactive melt infiltration herein referred to as ZBC ceramics.Control sample of ZrB_(2)-SiC was also prepared using ZrB_(2)and SiC as raw materials through an identical process designated as ZS ceramics.Microscopic analysis of both ceramic groups revealed smaller and more uniformly distributed particles of the ZrB_(2)phase in ZBC ceramics compared to the larger particles in ZS ceramics.Both sets of ceramics underwent cyclic oxidation testing in the air at 1600℃for a cumulative duration of 5 cycles,each cycle lasting 2 h.Analysis of the oxidation behavior showed that both ZBC ceramics and ZS ceramics developed a glassy SiO_(2)-ZrO_(2)oxide layer on their surfaces during the oxidation.This layer severed as a barrier against oxygen.In ZBC ceramics,ZrO_(2)is finely distributed in SiO_(2),whereas in ZS ceramics,larger ZrO_(2)particles coexist with glassy SiO_(2).The surface oxide layer of ZBC ceramics maintains a dense structure because the well-dispersed ZrO_(2)increases the viscosity of glassy SiO_(2),preventing its crystallization during the cooling.Conversely,some SiO_(2)in the oxide layer of ZS ceramics may crystallize and form a eutectic with ZrO_(2),leading to the formation of ZrSiO_(4).This leads to cracking of the oxide layer due to differences in thermal expansion coefficients,weakening its barrier effect.An analysis of the oxidation resistance shows that ZBC ceramics exhibit less increase in oxide layer thickness and mass compared to ZS ceramics,suggesting superior oxidation resistance of ZBC ceramics.
基金This work was supported by the National Natural Science Foundation of China grant numbers[52072410].
文摘Hf-based carbides are highly desirable candidate materials for oxidizing environments above 2000℃.However,the static oxidation behavior at their potential service temperatures remains unclear.To fill this gap,the static oxidation behavior of(Hf,Ti)C and the effect of Ti substitutions were investigated in air at 2500℃ under an oxygen partial pressure of 4.2 kPa.After oxidation for 2000 s,the thickness of the oxide layer on the surface of(Hf,Ti)C bulk ceramic is reduced by 62.29%compared with that on the HfC monocarbide surface.The dramatic improvement in oxidation resistance is attributed to the unique oxide layer structure consisting of various crystalline oxycarbides,HfO_(2),and carbon.The Ti-rich oxycarbide((Ti,Hf)C_(x)O_(y))dispersed within HfO_(2) formed the major structure of the oxide layer.A coherent boundary with lattice distortion existed at the HfO2/(Ti,Hf)C_(x)O_(y) interface along the(111)crystal plane direction,which served as an effective oxygen diffusion barrier.The Hfrich oxycarbide((Hf,Ti)CxOy)together with(Ti,Hf)C_(x)O_(y),HfO_(2),and precipitated carbon constituted a dense transition layer,ensuring favorable bonding between the oxide layer and the matrix.The Ti content affects the oxidation resistance of(Hf,Ti)C by determining the oxide layer's phase distribution and integrity.
基金supported by the National Natural Science Foun-dation of China(NSFC)under Grant No.52071113.
文摘In this work,possible short-term thermal exposure oxidation in hot processing including semi-solid processing is focused.We aim to investigate the short-term oxidation behavior of a novel powder metallurgy Al_(0.8)Co_(0.5)Cr_(1.5)CuFeNi high entropy alloy(HEA)in high-temperature solid(1000-1100℃)and semi-solid(1125-1225℃)intervals.From 1000 to 1225℃,mass gain increases from 0.31 to 0.45 mg cm^(-2)after 60 min oxidation,presenting superior oxidation resistance in the semi-solid state compared with other semi-solid alloys.Equiaxedα-Al_(2)O_(3)grains are the predominant component of oxide scales and no obvious internal oxidation layer occurs in both solid and semi-solid intervals.Al_(2)O_(3)scale growth is predominantly determined by outward Al^(3+)diffusion.For solid oxidation,different scale formation kinetics occur on various phases and the BCC(B2)phase has faster scale formation kinetics.This is attributed to outward Al^(3+)diffusion rate differences in various component systems.During semi-solid oxidation,the increased degree of chaos and number of vacancies in the liquid phase provide a diffusion channel,leading to rapid Al_(2)O_(3)formation.Oxidation resistance in the semi-solid state is attributed to dense Al_(2)O_(3)scales formed through selective oxidation of Al.
基金Project(2011CB605503)supported by the National Basic Research Program of China
文摘The oxidation behavior of Ti?22Al?(27?x)Nb?xZr (x=0, 1, 6) alloys at 800 °C for exposure time up to 100 h was examined. It is shown that oxidation rate of experimental alloys obeys the parabolic kinetics. Ti?22Al?26Nb?1Zr alloy demonstrates more excellent oxidation resistance than the other two alloys. The main oxidation products are TiO2, Al2O3 and AlNbO4 phases for all these alloys. For the Ti?22Al?26Nb?1Zr alloy, Zr addition can modify the growth mechanism of oxide scale, which can effectively hinder the diffusion of oxygen. Whereas, reaction of Zr with oxygen leads to the formation of ZrO2 precipitates for the Ti?22Al?21Nb?6Zr alloy, which promotes the oxygen ingress into the substrate. Meanwhile, oxidation affected zones, including internal-oxidation layer and oxygen-enriched zone, are present beneath the outmost oxide scale. The difference in these zones is derived from the phase constitution in the starting Ti?22Al?(27?x)Nb?xZr (x=0, 1, 6) alloys.
基金Project (2007CB613504) supported by the National Basic Research Program of ChinaProject (20070145041) supported by the Specialized Research Fund for the Doctoral Program of Higher Education, China
文摘The oxidation behavior of electroconductive TiN/O′-Sialon ceramics prepared using high titania slag as main starting material was studied at 1 200-1 300 °C in air. The isothermal and non-isothermal oxidation processes were investigated by DTA-TG. Phase compositions and morphologies of the oxidized products were analyzed by XRD, SEM and EDS. The results indicate that the oxidation of TiN and O′-Sialon occurs at about 500 °C and 1 050 °C, respectively. After oxidation at 1 200-1 300 °C, a protective scale that consists of Fe2MgTi3O10, SiO2 and TiO2 is formed on the surface of the materials, which effectively prevents the oxidation process. The formation of a protective scale is relative to TiN content and apparent porosity of the samples, the amount of SiO2 and amorphous phase in the oxidation product. At the initial oxidation stage, the oxidation kinetics of the materials follows perfectly the linear law with the apparent activation energy of 1.574×105 J/mol, and at the late-mid stage, the oxidation of the samples obeys the parabolic law with the apparent activation energy of 2.693×105 J/mol. With the increase of TiN content, mass gain of the materials increases significantly.
基金Project(11531319)supported by Scientific Research Fund of Heilongjiang Provincial Education Department,China
文摘By using CeO2 particles instead of part of Al2O3 particles as filler, the CeO2 was successfully entrapped into the outer layer of the chromizing coatings on the as-deposited nanocrystalline （NC） and microcrystalline （MC） Ni films using a conventional pack-cementation method at 800 °C. For comparison, chromizing was also performed under the same condition on MC Ni film using Al2O3 as filler without CeO2 particles. SEM/EDX and TEM results indicate that the refinement of Ni grain and CeO2 entrapped into the chromizing coatings refine the grain of the chromizing coating. Oxidation at 900 °C indicates that compared with the CeO2-free chromizing coating, the CeO2-dispersed chromizing coating exhibits an increased oxidation resistance. For the CeO2-dispersed chromizing coating, the refinement of Ni grain size significantly decreases the transient-oxidation scaling rate of the chromizing coatings. Together with this, the CeO2-dispersed chromizing coating formed on NC Ni exhibits a better oxidation resistance.
基金Project(2013AA031004)supported by the National High-tech Research and Development Program of China
文摘The oxidation behavior of Hastelloy C-2000 alloy was investigated in air at 800 °C and 1000 °C for 100 h, respectively. Oxidation kinetics and oxide scales morphologies were examined by mass gain measurement, scanning electron microscopy（SEM）, X-ray diffraction（XRD） and X-ray photoelectron spectroscopy（XPS）. The oxidation behavior of the alloy approximately follows a parabolic rate law. Moreover, annealing twins defect structure in matrix deteriorates the oxidation resistance of alloy due to the improvement of diffusion rates for alloying elements and oxygen atoms. At 800 °C, the microstructure is primarily composed of Ni O and Cr1.3Fe0.7O6 and the initial annealing twins structure is visible and Mo-rich phases are emerged to approach boundary of oxide scales. At 1000 °C, however, the morphology microstructure of oxide scales consists of oxide particle with fine Cr oxides and large Ni oxides by inlaying each other, whilst Mo-rich phases hardly appear closing to the interface of oxide scales.
基金financially supported by the Scientific Research Fund of Nanjing Institute of Technology(No.CKJA201802)the Opening Project of Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology(No.ASMA201802)。
文摘The oxidation behavior of a nickel-based superalloy GH738 was studied by isothermal oxidation tests in still air at different temperatures,with exposure time up to 100 h.Oxidation-kinetic curves were plotted using the mass gain method.The surface and cross-sectional morphologies were observed by scanning electron microscopy(SEM).A composition analysis and an oxidation-product identification were conducted using energydispersive X-ray spectroscopy(EDS) and an X-ray diffraction(XRD),respectively.The results showed that GH738 exhibited parabolic oxidation-kinetic curves,with stable parabolic-rate constants at each temperatures.The activation energy of oxide growth was calculated to be329.6 kJ·mol^(-1).Cr_(2) O_(3)(chromia) was the external oxidation product at 800℃.A TiO_(2)-Cr_(2) O_(3) double-layer structure was formed at 900℃.The position of TiO_(2) changed from the oxide-metal interface to the air-oxide interface by the diffusion of Ti atoms in chromia during the oxidation time at this temperature.Spallation was observed in the Cr_(0.12)Ti_(0.78)O_(1.74)-Cr_(2) O_(3) multi-layer oxide of at 1000℃,which increased the oxidation rate.For all the tests,the main internal oxide was always Al_(2) O_(3).The entire GH738 oxidation process was interpreted by the competitive diffusion of elements(Cr,Ti,Ni,etc.) in metal matrix and chromia,while a schematic diagram of oxidation process was proposed.
基金financially supported by the National Natural Science Foundation of China (No.51641102)the Natural Science Foundation of Jiangsu Province (No.16KJB430035)the Nantong Science and Technology Project (No. GY12015032)
文摘In this paper, the isothermal oxidation kinetics and oxidation behavior of GH586 superalloy from 800 to 1000℃ were investigated. The oxide scale morphologies of the surfaces and the cross sections after oxidation were characterized by means of X-ray diffraction （XRD） and scanning electron microscope （SEM） equipped with energy-dispersive spectroscopy （EDS）. The results show that the growth of the oxide scales on the surface of superalloy GH586 obeys a parabolic law with the activa- tion energy of 241.4 kJ.mo1-1 from 800 to 1000℃ The dense oxide scale formed at 800℃ is mainly composed of Cr203, NiCr204 and a small amount of TiO2. At 900℃, the oxide scale is divided into two layers： the outer layer with multiple cracks is mainly composed of ＂Cr203 and TiO2, while the inner is a layer of dense Cr203. Under the oxide scale, aluminum-rich oxides along the grain bound- aries are generated by the internal oxidation. At 1000 ℃for 100 h, cracks throughout the whole oxide film accel- erate the oxidation rate of Ni-based superalloy GH586 and large blocks of TiO2 in the oxide scale are generated, resulting in the spallation of oxide scale.
基金Project supported by the National Key Technology R&D Program(2011BAE22B06)National Natural Science Foundation of China(51101100)
文摘A Mg-Y-Ca-Ce magnesium alloy was optimized for high ignition-proof property, which did not bum in air at 1233 K up to 30 min. Oxidation behavior of the alloy was investigated by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and thermodynamics calculation at 673, 773 and 873 K. XRD and SEM analysis indicated that dense and compact oxide films composed of MgO, Y203 and CaO formed. The oxidation behavior was characterized by the selective oxidation. Based on Pilling-Bedworth ra- tio （PBR） and energy dispersive spectrometer （EDS） analysis, Y203 contributed more to form the compact surface oxide film, which led to the excellent ignition-proof performance. The thermodynamics analysis and EDS results implied that the Y-rich areas were preferred paths for the selective oxidation.
基金supported financially by the National Natural Science Foundation of China(No.51774212)。
文摘The effect of theγ+γtwo-phase structure on the oxidation behaviors of Ni-Al single-crystal alloys at 650℃was investigated by scanning electron microscopy,transmission electron microscopy,atomic force microscopy,X-ray diffraction and Auger electron spectroscopy.In the initial oxidation stage,the oxidation behavior is primarily determined by the growth pattern of oxides in theγchannel.The outward convex NiO was formed in unprotected wideγchannels.And Ni-Al spinel oxide provides a great number of short-circuit paths,accelerating the inward diffusion of oxygen and outward diffusion of Ni.In the late stage of oxidation,the elongated internal oxide in the largeγphase contributes to the diffusion of oxygen along the oxide/metal interface.Consequently,the Ni-Al single-crystal alloy with wideγchannels and largeγprecipitates exhibited poor oxidation performance.
基金supported by the National Natural Science Foundation of China(51325102)the International Science and Technology Cooperation Program of Ministry of Science and Technology(2015DFA90750)
文摘Aiming to develop materials for construction of the set-up and electrode of high-temperature molten salt reactors, the effect of Al and Y on the high-temperature oxidation behavior of Ni-11Fe-10Cu at 750 and 950 °C in air were investigated. The oxidation kinetics of Ni-11Fe-10Cu alloy followed parabolic law at 750 °C without spallation and linear law at 950 °C with severe spallation, while that of Ni-11Fe-10Cu-6Al-3Y alloy followed parabolic law at 750 and 950 °C without spallation. The parabolic rate constant （kp） of Ni-11Fe-10Cu was smaller than that of Ni-11Fe-10Cu-6Al-3Y at 750 °C. The oxide scale formed on Ni-11Fe-10Cu at 750 °C was composed of a CuO outer layer, a NiFe2O4 middle layer and a NiO inner layer. The oxide scale formed on Ni-11Fe-10Cu-6Al-3Y at 750 °C was also composed of the similar triplex layers in addition to an internal oxidation zone containing Al, Ni and Cu oxide and the microstructure of the scale changed with increasing temperature. Although the doping Al and Y could improve the adherence of oxide scale, it could aggravate the extent of internal oxidation. Based on the combination of X-ray diffraction （XRD）, scanning electron mi-croscopy/energy dispersive spectroscopy （SEM/EDX） analysis, the microstructure and growth mechanism of the multi-layer oxide scale was studied and the effect of doping Al and Y on the oxidation behavior of Ni-11Fe-10Cu alloy was also discussed.
基金financially supported by the National Natural Science Foundation of China (No.51505393)。
文摘In this study,the CeO_(2)-modified WC-12 Co coatings were deposited on Q345 steel substrate using high-velocity oxygen fuel(HVOF) spraying.Oxidation behavior of the modified coatings was analyzed in the range of 450-900℃ for different oxidation time to investigate the effects of oxidation time and temperature on the coatings.The oxidation kinetics and oxidation mechanism of the modified coatings were clarified.The results show that the oxides are mainly composed of WO_(3) and CoWO_(4) within 450-750℃ while the phases are different at 900 ℃.The CeO_(2)-modified coatings have good oxidation resistance when the oxidation temperature is below550℃ and the oxidation mechanism changes due to the occurrence of anomalous oxidation above 650℃.Moreover,the oxidation mass gain curves obey approximately a parabolic law in the temperature range of 450-650℃ at the initial stage but the later oxidation proceeds by a linear law.In addition,based on the analysis of micromorphology and component of the prepared coating,the role of rare earth(RE) additives is obtained during high-temperature oxidization.
基金supported by the Water Special Project(No.2009ZX07104 002)the Fundamental Research Funds for the Central Universities of China(No.CQDXWL2012-040)
文摘Excess nitrogenous compounds are detrimental to natural water systems and to human health. To completely realize autohy- drogenotrophic nitrogen removal, a novel 3-dimensional biofilm-electrode reactor was designed. Titanium was electroplated with ruthenium and used as the anode. Activated carbon fiber felt was used as the cathode. The reactor was separated into two chambers by a permeable membrane. The cathode chamber was filled with granular graphite and glass beads. The cathode and cathode chamber were inhabited with domesticated biofilm. In the absence of organic substances, a nitrogen removal efficiency of up to 91% was achieved at DO levels of 3.42 ± 0.37 mg/L when the applied current density was only 0.02 mA/cm^2. The oxidation of ammonium in biofilmelectrode reactors was also investigated. It was found that ammonium could be oxidized not only on the anode but also on particle electrodes in the cathode chamber of the biofilm-electrode reactor. Oxidation rates of ammonium and nitrogen removal efficiency were found to be affected by the electric current loading on the biofilm-electrode reactor. The kinetic model of ammonium at different electric currents was analyzed by a first-order reaction kinetics equation. The regression analysis implied that when the current density was less than 0.02 mA/cm^2, ammonium removal was positively correlated to the current density. However, when the current density was more than 0.02 mA/cm^2, the electric current became a limiting factor for the oxidation rate of ammonium and nitrogen removal efficiency.
基金Project(07JJ3102) supported by Hunan Provincial Natural Science Foundation,ChinaProject(k0902132-11) supported by Changsha Municipal Science and Technology,China
文摘Based on the pseudo potential plane-wave method of density functional theory （DFT）, Ti1-xNbxAk （x=0, 0.062 5, 0.083 3, 0.125, 0.250） crystals＇ geometry structure, elastic constants, electronic structure and Mulliken populations were calculated, and the effects of doping on the geometric structure, electronic structure and bond strength were systematically analyzed. The results show that the influence of Nb on the geometric structure is little in terms of the plasticity, and with the increase of Nb content, the covalent bond strength remarkably reduces, and Ti-Al, Nb-M （M=Ti, Al） and other hybrid bonds enhance; meanwhile, the peak district increases and the pseudo-energy gap first decreases and then increases, the overall band structure narrows, the covalent bond and direction of bonds reduce. The population analysis also shows that the results are consistent with the electronic structure analysis. The density of states of TiAINb shows that Nb doping can enhance the activity of Al and benefit the form of Al2O3 film. All the calculations reveal that the room temperature plasticity and the antioxidation properties of the compounds can be improved with the Nb content of 8.33%-12.5% （mole fraction）.
