Steam oxidation resistance of Si3N4 and Si2N2O as well as SiAlON bonded SiC refractories at 900℃was tested according to ASTM-C863.Phase composition and microstructure before and after oxidation were analyzed by XRD a...Steam oxidation resistance of Si3N4 and Si2N2O as well as SiAlON bonded SiC refractories at 900℃was tested according to ASTM-C863.Phase composition and microstructure before and after oxidation were analyzed by XRD and SEM.The results show that Si3N4 and Si2N2O bonded SiC refractory presents better steam oxidation resistance than SiAlON bonded SiC.For Si3N4 and Si2N2O bonded SiC,the oxidation speed is higher with more pronounced volume expansion in the early 100 h;afterwards,the volume expansion slows down gradually and starts to level off after 300 h.It is considered that the high silica glass phase formed during the oxidation covers Si3N4 and Si2N2O,and SiC as a protective layer and fills the open pores.But for SiAlON bonded SiC,the volume expands gradually and constantly with the increasing oxidation duration even after 500 h,due to the continuous formation of mullite transformed from oxidation products and Al2O3 in SiAlON.展开更多
High density polyethylene(HDPE)pyrolysis and in-line oxidative steam reforming was carried out in a two-step reaction system consisting of a conical spouted bed reactor and a fluidized bed reactor.Continuous plastic p...High density polyethylene(HDPE)pyrolysis and in-line oxidative steam reforming was carried out in a two-step reaction system consisting of a conical spouted bed reactor and a fluidized bed reactor.Continuous plastic pyrolysis was conducted at 550℃ and the volatiles formed were fed in-line to the oxidative steam reforming step(space-time 3.12 gcat min gHDPE−1;ER=0.2 and steam/plastic=3)operating at 700℃.The influence Ni based reforming catalyst support(Al_(2)O_(3),ZrO_(2),SiO_(2))and promoter(CeO_(2),La_(2)O_(3))have on HDPE pyrolysis volatiles conversion and H_(2) production was assessed.The catalysts were prepared by the wet impregnation and they were characterized by means of N_(2) adsorption-desorption,X-ray fluorescence,temperature-programmed reduction and X-ray powder diffraction.A preliminary study on coke deposition and the deterioration of catalysts properties was carried out,by analyzing the tested catalysts through temperature programmed oxidation of coke,transmission electron microscopy,and N_(2) adsorption-desorption.Among the supports tested,ZrO_(2) showed the best performance,attaining conversion and H_(2) production values of 92.2% and 12.8 wt%,respectively.Concerning promoted catalysts,they led to similar conversion values(around 90%),but significant differences were observed in H_(2) production.Thus,higher H_(2) productions were obtained on the Ni/La_(2)O_(3)-Al_(2)O_(3) catalyst(12.1 wt%)than on CeO_(2) promoted catalysts due to La_(2)O_(3) capability for enhancing water adsorption on the catalyst surface.展开更多
The oxide films of 316L and T91 exposed to 350-500℃ steam were investigated using transmission electron microscopy(TEM).Independent of the exposure temperature,a triplex oxide structure with outer magnetite,inner Cr-...The oxide films of 316L and T91 exposed to 350-500℃ steam were investigated using transmission electron microscopy(TEM).Independent of the exposure temperature,a triplex oxide structure with outer magnetite,inner Cr-rich(Fe_(1.4)Cr_(1.6)O_(4)),and Ni-rich layer formed on 316L,while only a duplex layer with outer magnetite and inner Cr-rich(Fe_(2.2)Cr_(0.8)O_(4))layer formed on T91.As the fast channels for oxidant and the obstacles for solid-state diffusion,nanopores are distributed evenly in the Cr-rich inner layer and are more abundant in 316L than in T91.The oxidation behavior of the materials was understood based on the microscopic characteristics of the oxide films.展开更多
Hydrogen production by partial oxidation steam reforming of methanol over a Cu/ZnO/Al2 O3 catalyst has been paid more and more attention. The chemical equilibria involved in the methanol partial oxidation steam reform...Hydrogen production by partial oxidation steam reforming of methanol over a Cu/ZnO/Al2 O3 catalyst has been paid more and more attention. The chemical equilibria involved in the methanol partial oxidation steam reforming reaction network such as methanol partial oxidation, methanol steam reforming, decomposition of methanol and water-gas shift reaction have been examined over the ranges of temperature 473-1073 K under normal pressure. Based on the detailed kinetics of these reactions over a Cu/ZnO/Al2O3 catalyst, and from the basic concept of the effectiveness factor, the intraparticle diffusion limitations were taken into account. The effectiveness factors for each reaction along the bed length were calculated. Then important results were offered for the simulation of this reaction process.展开更多
CuO-CeO2 catalysts were prepared by a urea precipitation method for the oxidative steam reforming of ethanol at low-temperature.The catalytic performance was evaluated and the catalysts were characterized by inductive...CuO-CeO2 catalysts were prepared by a urea precipitation method for the oxidative steam reforming of ethanol at low-temperature.The catalytic performance was evaluated and the catalysts were characterized by inductively coupled plasma atomic emission spectroscopy,X-ray diffraction,temperature-programmed reduction,field emission scanning electron microscopy and thermo-gravimetric analysis.Over CuOCeO2 catalysts,H2 with low CO content was produced in the whole tested temperature range of 250–450 C.The non-noble metal catalyst 20CuCe showed higher H2production rate than 1%Rh/CeO2 catalyst at 300–400 C and the advantage was more obvious after 20 h testing at400 C.These results further confirmed that CuO-CeO2 catalysts may be suitable candidates for low temperature hydrogen production from ethanol.展开更多
A comparative study of high chromium(Super304H)and high manganese low chromium heat-resistant steel(HT630)was carried out at 650℃in steam.Results indicate that the high manganese content in HT630 significantly improv...A comparative study of high chromium(Super304H)and high manganese low chromium heat-resistant steel(HT630)was carried out at 650℃in steam.Results indicate that the high manganese content in HT630 significantly improved its oxidation resistance.It is ascribed to the formation of a dense protective MnCr_(2)O_(4) oxide layer during oxidation.MnCr_(2)O_(4) layer effectively inhibits the diffusion of iron,suppresses the growth of ironrich oxides,promotes the formation of an iron-rich protective interface with the matrix,and improves the overall oxidation resistance.展开更多
The Cr-coated Zr alloys demonstrate excellent resistance to high-temperature steam oxidation.However,the rapid diffusion pathways for oxygen formed by the inter-diffusion between the coating and alloy at high temperat...The Cr-coated Zr alloys demonstrate excellent resistance to high-temperature steam oxidation.However,the rapid diffusion pathways for oxygen formed by the inter-diffusion between the coating and alloy at high temperatures significantly affect the steam oxidation resistance of the coated alloys.To address this issue,we developed a Mo/Cr bilayer coating on Zr alloy by a combination of dc-MS and HiPIMS surface treatments.The coating exhibits outstanding steam oxidation resistance at high temperatures,resulting in a mass gain approximately 86.6%and 44.1%lower than that of the bare Zr alloy and Cr coating,respectively,after 30 min of steam oxidation at 1200℃.This is mainly because,during the oxidation process,the Mo interface layer undergoes a transformation into a thin and high-quality double diffusion layer structure,effectively avoiding high-temperature inter-diffusion between the Cr coating and Zr alloy,thereby inhibiting the formation of oxygen diffusion pathways.展开更多
An aluminide（AlFe and α-（FeAl）） surface layer containing lower-Al was formed on ferritic-martensitic steel P92 by means of surface mechanical attrition treatment（SMAT） combined with a duplex aluminization proce...An aluminide（AlFe and α-（FeAl）） surface layer containing lower-Al was formed on ferritic-martensitic steel P92 by means of surface mechanical attrition treatment（SMAT） combined with a duplex aluminization process at lower temperatures,i.e.a packed aluminization followed by a diffusion annealing treatment below its tempering temperature.Indentation tests indicated that the lower-Al surface layer formed on the SMAT sample is more resistant to cracking and has better adhesion to the substrate in comparison with the Al 5Fe 2 layer formed on the as-received sample after the duplex aluminization process.Isothermal steam oxidation measurements showed that the oxidation resistance is increased significantly by the lower-Al surface layer due to the formation of a protective（Fe,Cr）Al 2O 4 layer.The rate constant of oxidation was estimated to decrease from-0.849 mg^2 cm^-4h^-1 of the as-received material to^0.011 mg^2 cm^-4 h^-1 of the AlFe layer at 700 ℃.展开更多
Surface-modified Zr-based alloy(ZIRLO)claddings with advanced ceramic coatings are increasingly required for accident-tolerant fuel(ATF)systems in light-water reactors.Cr_(2)AlC MAX phase coatings are promising for th...Surface-modified Zr-based alloy(ZIRLO)claddings with advanced ceramic coatings are increasingly required for accident-tolerant fuel(ATF)systems in light-water reactors.Cr_(2)AlC MAX phase coatings are promising for this purpose owing to their remarkable properties combining radiation/oxidation/corrosion resistance.However they are suffering from weak interface compatibility to ZIRLO substrate and poor structural densities for long-term services.Herein,we fabricated densely high-purity Cr_(2)AlC MAX phase coatings with uniquely designed Cr/CrC_(x)interfacial layers.The oxidation behavior of the coatings was focused under steam environments at 1000–1200℃.Results showed that Cr_(2)AlC coatings exhibited an oxidation mass gain of 8.9 mg/cm^(2)and an oxide thickness of 680 nm after oxidation at 1200℃ for 30 min,which were about 10%and 0.5%of ZIRLO substrate,respectively.Based on microstructural evolutions,the embedded interfacial layers significantly suppressed the rapid diffusion of Al in Cr_(2)AlC coatings to the substrate and the premature delamination of oxidized coatings.Particularly,the formed oxides were identified as dense yet pure α-Al_(2)O_(3),which endowed the protection against further oxidation and excellent resistance to high-temperature steam corrosion.展开更多
The oxidation behavior of welded joints with or without heat-treatment of HT700 alloy was studied in 700℃saturated water vapor with regards to oxidation kinetics,oxide film composition,and microstructure.The results ...The oxidation behavior of welded joints with or without heat-treatment of HT700 alloy was studied in 700℃saturated water vapor with regards to oxidation kinetics,oxide film composition,and microstructure.The results show that the oxide film compositions of the as-welded joints and heat-treated welded joints were basically the same.The oxide film is composed of a small amount of iron oxide,NiCr_(2)O_(4),and a large amount of Cr_(2)O_(3) from the outer layer to the inner layer,with a small amount of internal oxidation products Al_(2)O_(3).At the beginning of the oxidation process,the double layer oxide film grew at the same time,so that the as-welded joint had better performance in the later stage of oxidation.The formation of a continuous internal oxidation layer was later in heat-treated welded joints as compared to the as-welded joint,resulting in a larger thickness of the oxide film.The oxidation behavior of the welded seams in different regions of as-welded state and heat treatment state after welding displayed the following characteristics:small grain size,thin oxide film,and the weld fusion line with thin oxide film.展开更多
Hydrogen production from butanol is a promising alternative when it is obtained from bio-butanol or bio-oil due to the higher hydrogen content compared to other oxygenates such as methanol,ethanol or propanol.Catalyst...Hydrogen production from butanol is a promising alternative when it is obtained from bio-butanol or bio-oil due to the higher hydrogen content compared to other oxygenates such as methanol,ethanol or propanol.Catalysts and operating conditions play a crucial role in hydrogen production.Ni and Rh are metals mainly used for butanol steam reforming,oxidative steam reforming and partial oxidation.Additives such as Cu can improve catalytic activity in many folds.Moreover,support-metal interaction and catalyst preparation technique also play a decisive role in the stability and hydrogen production capacity of catalyst.Steam reforming technique as an option is more frequently researched due to higher hydrogen production capability in comparison to other thermochemical techniques despite its endothermic nature.The use of the oxidative steam reforming and partial oxidation has the advantages of requiring less energy and longer stability of catalysts.However,the hydrogen yield is less.This article brings together and examines the latest research on hydrogen production from butanol via steam reforming,oxidative steam reforming and partial oxidation reactions.In addition,the review examines a few thermodynamic studies based on sorption-enhanced steam reforming and dry reforming where there is potential for hydrogen extraction.展开更多
文摘Steam oxidation resistance of Si3N4 and Si2N2O as well as SiAlON bonded SiC refractories at 900℃was tested according to ASTM-C863.Phase composition and microstructure before and after oxidation were analyzed by XRD and SEM.The results show that Si3N4 and Si2N2O bonded SiC refractory presents better steam oxidation resistance than SiAlON bonded SiC.For Si3N4 and Si2N2O bonded SiC,the oxidation speed is higher with more pronounced volume expansion in the early 100 h;afterwards,the volume expansion slows down gradually and starts to level off after 300 h.It is considered that the high silica glass phase formed during the oxidation covers Si3N4 and Si2N2O,and SiC as a protective layer and fills the open pores.But for SiAlON bonded SiC,the volume expands gradually and constantly with the increasing oxidation duration even after 500 h,due to the continuous formation of mullite transformed from oxidation products and Al2O3 in SiAlON.
文摘High density polyethylene(HDPE)pyrolysis and in-line oxidative steam reforming was carried out in a two-step reaction system consisting of a conical spouted bed reactor and a fluidized bed reactor.Continuous plastic pyrolysis was conducted at 550℃ and the volatiles formed were fed in-line to the oxidative steam reforming step(space-time 3.12 gcat min gHDPE−1;ER=0.2 and steam/plastic=3)operating at 700℃.The influence Ni based reforming catalyst support(Al_(2)O_(3),ZrO_(2),SiO_(2))and promoter(CeO_(2),La_(2)O_(3))have on HDPE pyrolysis volatiles conversion and H_(2) production was assessed.The catalysts were prepared by the wet impregnation and they were characterized by means of N_(2) adsorption-desorption,X-ray fluorescence,temperature-programmed reduction and X-ray powder diffraction.A preliminary study on coke deposition and the deterioration of catalysts properties was carried out,by analyzing the tested catalysts through temperature programmed oxidation of coke,transmission electron microscopy,and N_(2) adsorption-desorption.Among the supports tested,ZrO_(2) showed the best performance,attaining conversion and H_(2) production values of 92.2% and 12.8 wt%,respectively.Concerning promoted catalysts,they led to similar conversion values(around 90%),but significant differences were observed in H_(2) production.Thus,higher H_(2) productions were obtained on the Ni/La_(2)O_(3)-Al_(2)O_(3) catalyst(12.1 wt%)than on CeO_(2) promoted catalysts due to La_(2)O_(3) capability for enhancing water adsorption on the catalyst surface.
基金supported by the National Natural Science Foundation of China(Nos.12005269 and U1832206).
文摘The oxide films of 316L and T91 exposed to 350-500℃ steam were investigated using transmission electron microscopy(TEM).Independent of the exposure temperature,a triplex oxide structure with outer magnetite,inner Cr-rich(Fe_(1.4)Cr_(1.6)O_(4)),and Ni-rich layer formed on 316L,while only a duplex layer with outer magnetite and inner Cr-rich(Fe_(2.2)Cr_(0.8)O_(4))layer formed on T91.As the fast channels for oxidant and the obstacles for solid-state diffusion,nanopores are distributed evenly in the Cr-rich inner layer and are more abundant in 316L than in T91.The oxidation behavior of the materials was understood based on the microscopic characteristics of the oxide films.
基金the grant of Post-Doc. Program, Kyungpook National University (1999).
文摘Hydrogen production by partial oxidation steam reforming of methanol over a Cu/ZnO/Al2 O3 catalyst has been paid more and more attention. The chemical equilibria involved in the methanol partial oxidation steam reforming reaction network such as methanol partial oxidation, methanol steam reforming, decomposition of methanol and water-gas shift reaction have been examined over the ranges of temperature 473-1073 K under normal pressure. Based on the detailed kinetics of these reactions over a Cu/ZnO/Al2O3 catalyst, and from the basic concept of the effectiveness factor, the intraparticle diffusion limitations were taken into account. The effectiveness factors for each reaction along the bed length were calculated. Then important results were offered for the simulation of this reaction process.
基金supported by the National Basic Research Program of China (2010CB732304)the National Natural Science Foundation of China (21177142 and 20973193)
文摘CuO-CeO2 catalysts were prepared by a urea precipitation method for the oxidative steam reforming of ethanol at low-temperature.The catalytic performance was evaluated and the catalysts were characterized by inductively coupled plasma atomic emission spectroscopy,X-ray diffraction,temperature-programmed reduction,field emission scanning electron microscopy and thermo-gravimetric analysis.Over CuOCeO2 catalysts,H2 with low CO content was produced in the whole tested temperature range of 250–450 C.The non-noble metal catalyst 20CuCe showed higher H2production rate than 1%Rh/CeO2 catalyst at 300–400 C and the advantage was more obvious after 20 h testing at400 C.These results further confirmed that CuO-CeO2 catalysts may be suitable candidates for low temperature hydrogen production from ethanol.
基金financially supported by the Excellent Youth Science and Technology Fund Project of Xi’an University of Science and Technology(6310221009)
文摘A comparative study of high chromium(Super304H)and high manganese low chromium heat-resistant steel(HT630)was carried out at 650℃in steam.Results indicate that the high manganese content in HT630 significantly improved its oxidation resistance.It is ascribed to the formation of a dense protective MnCr_(2)O_(4) oxide layer during oxidation.MnCr_(2)O_(4) layer effectively inhibits the diffusion of iron,suppresses the growth of ironrich oxides,promotes the formation of an iron-rich protective interface with the matrix,and improves the overall oxidation resistance.
基金financially supported by the National Natural Science Foundation of China(U22A20111)the Key Research and Development Program of Ningbo(20232ZDYF020062)
文摘The Cr-coated Zr alloys demonstrate excellent resistance to high-temperature steam oxidation.However,the rapid diffusion pathways for oxygen formed by the inter-diffusion between the coating and alloy at high temperatures significantly affect the steam oxidation resistance of the coated alloys.To address this issue,we developed a Mo/Cr bilayer coating on Zr alloy by a combination of dc-MS and HiPIMS surface treatments.The coating exhibits outstanding steam oxidation resistance at high temperatures,resulting in a mass gain approximately 86.6%and 44.1%lower than that of the bare Zr alloy and Cr coating,respectively,after 30 min of steam oxidation at 1200℃.This is mainly because,during the oxidation process,the Mo interface layer undergoes a transformation into a thin and high-quality double diffusion layer structure,effectively avoiding high-temperature inter-diffusion between the Cr coating and Zr alloy,thereby inhibiting the formation of oxygen diffusion pathways.
基金Financial supports from the Ministry of Science and Technology of the People’s Republic of China (No.2012CB932201)the National Natural Science Foundation of China (No.91226204)the Key Research Program of Chinese Academy of Sciences (No.KGZD-EW-T06)
文摘An aluminide（AlFe and α-（FeAl）） surface layer containing lower-Al was formed on ferritic-martensitic steel P92 by means of surface mechanical attrition treatment（SMAT） combined with a duplex aluminization process at lower temperatures,i.e.a packed aluminization followed by a diffusion annealing treatment below its tempering temperature.Indentation tests indicated that the lower-Al surface layer formed on the SMAT sample is more resistant to cracking and has better adhesion to the substrate in comparison with the Al 5Fe 2 layer formed on the as-received sample after the duplex aluminization process.Isothermal steam oxidation measurements showed that the oxidation resistance is increased significantly by the lower-Al surface layer due to the formation of a protective（Fe,Cr）Al 2O 4 layer.The rate constant of oxidation was estimated to decrease from-0.849 mg^2 cm^-4h^-1 of the as-received material to^0.011 mg^2 cm^-4 h^-1 of the AlFe layer at 700 ℃.
基金financially supported by the National Natural Science Foundation of China(52171090,U22A20111)the National Science Fund for Distinguished Young Scholars of China(52025014)the Municipal Natural Science Foundation of Ningbo(2023J410,2022J305)
文摘Surface-modified Zr-based alloy(ZIRLO)claddings with advanced ceramic coatings are increasingly required for accident-tolerant fuel(ATF)systems in light-water reactors.Cr_(2)AlC MAX phase coatings are promising for this purpose owing to their remarkable properties combining radiation/oxidation/corrosion resistance.However they are suffering from weak interface compatibility to ZIRLO substrate and poor structural densities for long-term services.Herein,we fabricated densely high-purity Cr_(2)AlC MAX phase coatings with uniquely designed Cr/CrC_(x)interfacial layers.The oxidation behavior of the coatings was focused under steam environments at 1000–1200℃.Results showed that Cr_(2)AlC coatings exhibited an oxidation mass gain of 8.9 mg/cm^(2)and an oxide thickness of 680 nm after oxidation at 1200℃ for 30 min,which were about 10%and 0.5%of ZIRLO substrate,respectively.Based on microstructural evolutions,the embedded interfacial layers significantly suppressed the rapid diffusion of Al in Cr_(2)AlC coatings to the substrate and the premature delamination of oxidized coatings.Particularly,the formed oxides were identified as dense yet pure α-Al_(2)O_(3),which endowed the protection against further oxidation and excellent resistance to high-temperature steam corrosion.
基金supported by the Natural Science Basic Research Program of Shaanxi(No.2020JM-716)the Youth Special Support Program of Shaanxi Province(No.ZD18SST05)the Science and Technology Project of China Huaneng Group(No.HNKJ40-H43)
文摘The oxidation behavior of welded joints with or without heat-treatment of HT700 alloy was studied in 700℃saturated water vapor with regards to oxidation kinetics,oxide film composition,and microstructure.The results show that the oxide film compositions of the as-welded joints and heat-treated welded joints were basically the same.The oxide film is composed of a small amount of iron oxide,NiCr_(2)O_(4),and a large amount of Cr_(2)O_(3) from the outer layer to the inner layer,with a small amount of internal oxidation products Al_(2)O_(3).At the beginning of the oxidation process,the double layer oxide film grew at the same time,so that the as-welded joint had better performance in the later stage of oxidation.The formation of a continuous internal oxidation layer was later in heat-treated welded joints as compared to the as-welded joint,resulting in a larger thickness of the oxide film.The oxidation behavior of the welded seams in different regions of as-welded state and heat treatment state after welding displayed the following characteristics:small grain size,thin oxide film,and the weld fusion line with thin oxide film.
文摘Hydrogen production from butanol is a promising alternative when it is obtained from bio-butanol or bio-oil due to the higher hydrogen content compared to other oxygenates such as methanol,ethanol or propanol.Catalysts and operating conditions play a crucial role in hydrogen production.Ni and Rh are metals mainly used for butanol steam reforming,oxidative steam reforming and partial oxidation.Additives such as Cu can improve catalytic activity in many folds.Moreover,support-metal interaction and catalyst preparation technique also play a decisive role in the stability and hydrogen production capacity of catalyst.Steam reforming technique as an option is more frequently researched due to higher hydrogen production capability in comparison to other thermochemical techniques despite its endothermic nature.The use of the oxidative steam reforming and partial oxidation has the advantages of requiring less energy and longer stability of catalysts.However,the hydrogen yield is less.This article brings together and examines the latest research on hydrogen production from butanol via steam reforming,oxidative steam reforming and partial oxidation reactions.In addition,the review examines a few thermodynamic studies based on sorption-enhanced steam reforming and dry reforming where there is potential for hydrogen extraction.
