The technique of creep feed grinding is most suitable for geometrical shaping, and therefore has been expected to improve effectively material removal rate and surface quality of components with complex profile. This ...The technique of creep feed grinding is most suitable for geometrical shaping, and therefore has been expected to improve effectively material removal rate and surface quality of components with complex profile. This article studies experimentally the effects of process parameters （i.e. wheel speed, workpiece speed and depth of cut） on the grindability and surface integrity of cast nickel-based superalloys, i.e. K424, during creep feed grinding with brazed cubic boron nitride （CBN） abrasive wheels. Some important factors, such as grinding force and temperature, specific grinding energy, size stability, surface topography, microhardhess and microstructure alteration of the sub-surface, residual stresses, are investigated in detail. The results show that during creep feed grinding with brazed CBN wheels, low grinding temperature at about 100 ℃ is obtained though the specific grinding energy of nickel-based superalloys is high up to 200-300 J/mm^3. A combination of wheel speed 22.5 m/s, workpiece speed 0.1 m/min, depth of cut 0.2 mm accomplishes the straight grooves with the expected dimensional accuracy. Moreover, the compressive residual stresses are formed in the bum-free and crack-free ground surface.展开更多
As one of the most appealing and attractive technologies, photocatalysis is widely used as a promising method to circumvent the environmental and energy problems. Due to its chemical stability and unique physicochemic...As one of the most appealing and attractive technologies, photocatalysis is widely used as a promising method to circumvent the environmental and energy problems. Due to its chemical stability and unique physicochemical, graphitic carbon nitride (g-C3N4) has become research hotspots in the community. However, g-C3N4 photocatalyst still suffers from many problems, resulting in unsatisfactory photocatalytic activity such as low specific surface area, high charge recombination and insufficient visible light utilization. Since 2009, g-C3N4-based heterostructures have attracted the attention of scientists worldwide for their greatly enhanced photocatalytic performance. Overall, this review summarizes the recent advances of g-C3N4-based nanocomposites modified with transition metal sulfide (TMS), including (1) preparation of pristine g-C3N4,(2) modification strategies of g-C3N4,(3) design principles of TMS-modified g-C3N4 heterostructured photocatalysts, and (4) applications in energy conversion. What is more, the characteristics and transfer mechanisms of each classification of the metal sulfide heterojunction system will be critically reviewed, spanning from the following categories:(1) Type I heterojunction,(2) Type II heterojunction,(3) p-n heterojunction,(4) Schottky junction and (5) Z-scheme heterojunction. Apart from that, the application of g-C3N4-based heterostructured photocatalysts in H2 evolution, CO2 reduction, N2 fixation and pollutant degradation will also be systematically presented. Last but not least, this review will conclude with invigorating perspectives, limitations and prospects for further advancing g-C3N4-based heterostructured photocatalysts toward practical benefits for a sustainable future.展开更多
综述了燃料油(主要是汽油和柴油)深度加氢脱硫催化剂的研究进展。汽油精制的主要问题是在深度加氢脱硫的同时减少由于烯烃饱和造成的辛烷值损失;柴油深度加氢脱硫主要是脱除其中的难脱除硫化物及稠环芳烃加氢饱和。TiO_2和 ZrO_2等载体...综述了燃料油(主要是汽油和柴油)深度加氢脱硫催化剂的研究进展。汽油精制的主要问题是在深度加氢脱硫的同时减少由于烯烃饱和造成的辛烷值损失;柴油深度加氢脱硫主要是脱除其中的难脱除硫化物及稠环芳烃加氢饱和。TiO_2和 ZrO_2等载体负载的金属硫化物催化剂比传统加氢脱硫催化剂的活性高。助剂 P 和 F 能减弱载体-金属间相互作用,在 Co(Ni)-Mo(W)/γ-Al_2O_3催化剂中生成更多的高活性Ⅱ型中心。螯合剂能延迟 Co 的硫化,有利于 Co-Mo-S 活性中心的生成。过渡金属磷化物催化剂表现出更高的脱硫、脱氮活性及良好的活性稳定性,它的主要缺点是金属磷化物的分散度较差,活性中心数目较少。过渡金属碳化物和氮化物催化剂对脱硫、脱氮的初活性较高,但使用后表面金属被硫化,催化活性下降。展开更多
Graphitic carbon nitride nanosheets （g-C3N4 NSs） hybridized nitrogen doped titanium dioxide （N-TiO2） nanofibers （GCN/NT NFs） have been synthesized in situ via a simple electrospinning process combined with a mod...Graphitic carbon nitride nanosheets （g-C3N4 NSs） hybridized nitrogen doped titanium dioxide （N-TiO2） nanofibers （GCN/NT NFs） have been synthesized in situ via a simple electrospinning process combined with a modified heat-etching method. The prepared GCN/NT NFs were characterized by a variety of methods and their photocatalytic activities were evaluated by hydrogen （H2） production from water splitting and degradation of rhodamine B in aqueous solution. It was found that the GCN/NT NFs have a mesoporous structure, composed of g-C3N4 NSs and N-doped TiO2 crystallites. The g-C3N4 NSs synthesized after heat-etching were found to be embedded in, and covered, the hybrid NFs to form stable interfaces. The partial decomposition of g-C3N4 releases its nitrogen content which eventually gets doped into the nearby TiO2 skeleton. The GCN/NT NFs give a high photocatalytic H2 production rate of 8,931.3 μmol·h^-1·g^-1 in aqueous methanol solution under simulated solar light. Such a highly efficient photocatalytic perfor- mance can be ascribed to the combined effects of g-C3N4 NSs and N-doped TiO2 with enhanced light absorption intensity and improved electron transport ability. Also, the large surface area of the mesoporous NFs minimizes light reflection on the surface and provides more surface-active sites. This work highlights the potential of quasi-one dimensional hybrid materials in the field of solar energy conversion.展开更多
A state-of-the-art review on monolayer electroplated and brazed cubic boron nitride（CBN） superabrasive wheels for grinding metallic materials has been provided in this article. The fabrication techniques and mechani...A state-of-the-art review on monolayer electroplated and brazed cubic boron nitride（CBN） superabrasive wheels for grinding metallic materials has been provided in this article. The fabrication techniques and mechanisms of the monolayer CBN wheels are discussed. Grain distribution, wheel dressing, wear behavior, and wheel performance are analyzed in detail. Sample applications of monolayer CBN wheel for grinding steels, titanium alloys, and nickel-based superalloys are also provided. Finally, this article highlights opportunities for further investigation of monolayer CBN grinding wheels.展开更多
Boron nitride(BN) nanostructures with complementary functions to their carbon counterparts are one of the most intriguing nanomaterials.Here we devote a compact review on the syntheses of BN nanomaterials:typical zero...Boron nitride(BN) nanostructures with complementary functions to their carbon counterparts are one of the most intriguing nanomaterials.Here we devote a compact review on the syntheses of BN nanomaterials:typical zero-dimensional(OD) fullerenes and nanoparticles,one-dimensional(1D) nanotubes and nanoribbons,two-dimensional(2D) nanosheets as well as three-dimensional(3D) nanoporous BN.Combining low-dimensional quantum confinement and surface effects with unique physical and chemical properties of BN,e.g.excellent electric insulation,wide band gap,and high chemical and thermal stability,BN nanomaterials have drawn particular attention in a variety of potential applications,e.g.luminescence,functional composites,hydrogen accumulators,and advanced insulators,which are also reviewed.展开更多
Porous carbon nitride(CN)spheres with partially crystalline frameworks have been successfully synthesized via a nanocasting approach by using spherical mesoporous cellular silica foams(MCFs)as a hard template,and ethy...Porous carbon nitride(CN)spheres with partially crystalline frameworks have been successfully synthesized via a nanocasting approach by using spherical mesoporous cellular silica foams(MCFs)as a hard template,and ethylenediamine and carbon tetrachloride as precursors.The resulting spherical CN materials have uniform diameters of ca.4μm,hierarchical three-dimensional(3-D)mesostructures with small and large mesopores with pore diameters centered at ca.4.0 and 43 nm,respectively,a relatively high BET surface area of~550 m^(2)/g,and a pore volume of 0.90 cm^(3)/g.High-resolution transmission electron microscope(HRTEM)images,wide-angle X-ray diffraction(XRD)patterns,and Raman spectra demonstrate that the porous CN material has a partly graphitized structure.In addition,elemental analyses,X-ray photoelectron spectra(XPS),Fourier transform infrared spectra(FT-IR),and CO_(2) temperature-programmed desorption(CO_(2)-TPD)show that the material has a high nitrogen content(17.8 wt%)with nitrogen-containing groups and abundant basic sites.The hierarchical porous CN spheres have excellent CO_(2) capture properties with a capacity of 2.90 mmol/g at 25℃and 0.97 mmol/g at 75℃,superior to those of the pure carbon materials with analogous mesostructures.This can be mainly attributed to the abundant nitrogen-containing basic groups,hierarchical mesostructure,relatively high BET surface area and stable framework.Furthermore,the presence of a large number of micropores and small mesopores also enhance the CO_(2) capture performance,owing to the capillary condensation effect.展开更多
Transition metal nitrides have been suggested to have both high hardness and good thermal stability with large potential application value, but so far stable superhard transition metal nitrides have not been synthesiz...Transition metal nitrides have been suggested to have both high hardness and good thermal stability with large potential application value, but so far stable superhard transition metal nitrides have not been synthesized. Here, with our newly developed machine-learning accelerated crystal structure searching method, we designed a superhard tungsten nitride, h-WN6, which can be synthesized at pressure around 65 GPa and quenchable to ambient pressure. This h-WN6 is constructed with single-bonded armchair-like N6 rings and presents ionic-like features, which can be formulated as W^2.4＋N^2.4-. It has a band gap of 1.6 eV at 0GPa and exhibits an abnormal gap broadening behavior under pressure. Excitingly, this h-WN6 is found to be the hardest among transition metal nitrides known so far （Vickers hardness around 57 GPa） and also has a very high melting temperature （around 1,900 K）. Additionally, the good gravimet- ric （3.1 kJ/g/and volumetric （28.0 kJ/cm3） energy densities make this nitrogen-rich compound a potential high-energy-density material, These predictions support the designing rules and may stimulate future experiments to synthesize superhard and high-energy-density material.展开更多
A simple one-step thermal polymerization method was developed for synthesis of holey graphitic carbon nitride nanotubes,involving direci eating of mixtures of melamine and urea or melamine and cyanuric acid in specifi...A simple one-step thermal polymerization method was developed for synthesis of holey graphitic carbon nitride nanotubes,involving direci eating of mixtures of melamine and urea or melamine and cyanuric acid in specific mass ratios.Supramolecular structures formed betweer the precursor molecules guided nanotube formation.The porous and nanotubular structure of the nanotubes facilitated efficient charge carrier nigration and separation,thereby enhancing photocatalytic Hz production in 20 vol.%lactic acid under visible light irradiation.Nanotubes synthesized using melamine and urea in a 1:10 mass ratio(denoted herein as CN-MU nanotubes)exhibited a photocatalytic hydroger production rate of 1,073.6μmol·h^-1·^-g with Pt as the cocatalyst,a rate of 4.7 and 3.1 times higher than traditional Pt/g-CN4 photocatalysts prepared from graphitic carbon nitride(g-CN4)obtained by direct thermal polymerization of melamine or urea,respectively.On the basis of their outstanding performance for photocatalytic H2 production,it is envisaged that the holey g-C3N4 nanotubes will find widespread uptake in other areas,including photocatalytic CO2 reduction,dye-sensitized solar cells and photoelectrochemical sensors.展开更多
基金National Basic Research Program of China (2009CB724403)Program for Changjiang Scholars and Innovative Research Team in University (IRT0837)Program for New Century Excellent Talents in University from Ministry of Education of China (NCET-07-0435)
文摘The technique of creep feed grinding is most suitable for geometrical shaping, and therefore has been expected to improve effectively material removal rate and surface quality of components with complex profile. This article studies experimentally the effects of process parameters （i.e. wheel speed, workpiece speed and depth of cut） on the grindability and surface integrity of cast nickel-based superalloys, i.e. K424, during creep feed grinding with brazed cubic boron nitride （CBN） abrasive wheels. Some important factors, such as grinding force and temperature, specific grinding energy, size stability, surface topography, microhardhess and microstructure alteration of the sub-surface, residual stresses, are investigated in detail. The results show that during creep feed grinding with brazed CBN wheels, low grinding temperature at about 100 ℃ is obtained though the specific grinding energy of nickel-based superalloys is high up to 200-300 J/mm^3. A combination of wheel speed 22.5 m/s, workpiece speed 0.1 m/min, depth of cut 0.2 mm accomplishes the straight grooves with the expected dimensional accuracy. Moreover, the compressive residual stresses are formed in the bum-free and crack-free ground surface.
基金supported by Xiamen University Malaysia Research Fund (XMUMRF/2019-C3/IENG/0013)financial assistance and faculty start-up grants/supports from Xiamen University~~
文摘As one of the most appealing and attractive technologies, photocatalysis is widely used as a promising method to circumvent the environmental and energy problems. Due to its chemical stability and unique physicochemical, graphitic carbon nitride (g-C3N4) has become research hotspots in the community. However, g-C3N4 photocatalyst still suffers from many problems, resulting in unsatisfactory photocatalytic activity such as low specific surface area, high charge recombination and insufficient visible light utilization. Since 2009, g-C3N4-based heterostructures have attracted the attention of scientists worldwide for their greatly enhanced photocatalytic performance. Overall, this review summarizes the recent advances of g-C3N4-based nanocomposites modified with transition metal sulfide (TMS), including (1) preparation of pristine g-C3N4,(2) modification strategies of g-C3N4,(3) design principles of TMS-modified g-C3N4 heterostructured photocatalysts, and (4) applications in energy conversion. What is more, the characteristics and transfer mechanisms of each classification of the metal sulfide heterojunction system will be critically reviewed, spanning from the following categories:(1) Type I heterojunction,(2) Type II heterojunction,(3) p-n heterojunction,(4) Schottky junction and (5) Z-scheme heterojunction. Apart from that, the application of g-C3N4-based heterostructured photocatalysts in H2 evolution, CO2 reduction, N2 fixation and pollutant degradation will also be systematically presented. Last but not least, this review will conclude with invigorating perspectives, limitations and prospects for further advancing g-C3N4-based heterostructured photocatalysts toward practical benefits for a sustainable future.
文摘综述了燃料油(主要是汽油和柴油)深度加氢脱硫催化剂的研究进展。汽油精制的主要问题是在深度加氢脱硫的同时减少由于烯烃饱和造成的辛烷值损失;柴油深度加氢脱硫主要是脱除其中的难脱除硫化物及稠环芳烃加氢饱和。TiO_2和 ZrO_2等载体负载的金属硫化物催化剂比传统加氢脱硫催化剂的活性高。助剂 P 和 F 能减弱载体-金属间相互作用,在 Co(Ni)-Mo(W)/γ-Al_2O_3催化剂中生成更多的高活性Ⅱ型中心。螯合剂能延迟 Co 的硫化,有利于 Co-Mo-S 活性中心的生成。过渡金属磷化物催化剂表现出更高的脱硫、脱氮活性及良好的活性稳定性,它的主要缺点是金属磷化物的分散度较差,活性中心数目较少。过渡金属碳化物和氮化物催化剂对脱硫、脱氮的初活性较高,但使用后表面金属被硫化,催化活性下降。
文摘Graphitic carbon nitride nanosheets （g-C3N4 NSs） hybridized nitrogen doped titanium dioxide （N-TiO2） nanofibers （GCN/NT NFs） have been synthesized in situ via a simple electrospinning process combined with a modified heat-etching method. The prepared GCN/NT NFs were characterized by a variety of methods and their photocatalytic activities were evaluated by hydrogen （H2） production from water splitting and degradation of rhodamine B in aqueous solution. It was found that the GCN/NT NFs have a mesoporous structure, composed of g-C3N4 NSs and N-doped TiO2 crystallites. The g-C3N4 NSs synthesized after heat-etching were found to be embedded in, and covered, the hybrid NFs to form stable interfaces. The partial decomposition of g-C3N4 releases its nitrogen content which eventually gets doped into the nearby TiO2 skeleton. The GCN/NT NFs give a high photocatalytic H2 production rate of 8,931.3 μmol·h^-1·g^-1 in aqueous methanol solution under simulated solar light. Such a highly efficient photocatalytic perfor- mance can be ascribed to the combined effects of g-C3N4 NSs and N-doped TiO2 with enhanced light absorption intensity and improved electron transport ability. Also, the large surface area of the mesoporous NFs minimizes light reflection on the surface and provides more surface-active sites. This work highlights the potential of quasi-one dimensional hybrid materials in the field of solar energy conversion.
基金financial support for this work by the National Natural Science Foundation of China (Nos. 51235004 and 51375235)the Fundamental Research Funds for the Central Universities (Nos. NE2014103 and NZ2016107)
文摘A state-of-the-art review on monolayer electroplated and brazed cubic boron nitride（CBN） superabrasive wheels for grinding metallic materials has been provided in this article. The fabrication techniques and mechanisms of the monolayer CBN wheels are discussed. Grain distribution, wheel dressing, wear behavior, and wheel performance are analyzed in detail. Sample applications of monolayer CBN wheel for grinding steels, titanium alloys, and nickel-based superalloys are also provided. Finally, this article highlights opportunities for further investigation of monolayer CBN grinding wheels.
基金financial support of International Center for Young Scientists(ICYS)World Premier International Center for Materials Nanoarchitectonics(WPI-MANA) in National Institute for Materials Science(NIMS)financial support from KAKENHI project(Grant-in-Aid for Young Scientists,26820322) of Japan Society for the Promotion of Science(JSPS)
文摘Boron nitride(BN) nanostructures with complementary functions to their carbon counterparts are one of the most intriguing nanomaterials.Here we devote a compact review on the syntheses of BN nanomaterials:typical zero-dimensional(OD) fullerenes and nanoparticles,one-dimensional(1D) nanotubes and nanoribbons,two-dimensional(2D) nanosheets as well as three-dimensional(3D) nanoporous BN.Combining low-dimensional quantum confinement and surface effects with unique physical and chemical properties of BN,e.g.excellent electric insulation,wide band gap,and high chemical and thermal stability,BN nanomaterials have drawn particular attention in a variety of potential applications,e.g.luminescence,functional composites,hydrogen accumulators,and advanced insulators,which are also reviewed.
基金This work was supported by the National Natural Science Foundation of China(NSFC)(Nos.2089012,20721063,20821140537,20871030)State Key Basic Research Program of PRC(Nos.2006CB932302 and 2009AA033701)+3 种基金Shanghai Leading Academic Discipline Project(No.B108)Science&Technology Com-mission of Shanghai Municipality(No.08DZ2270500)C.S.Ha also thanks the National Research Foundation(NRF)of Korea for support through the Korea-China Joint Research Center Program on Mesoporous Thin Films(No.K20803001459-10B1200-00310)the Acceleration Research Program(No.2010-0000790).
文摘Porous carbon nitride(CN)spheres with partially crystalline frameworks have been successfully synthesized via a nanocasting approach by using spherical mesoporous cellular silica foams(MCFs)as a hard template,and ethylenediamine and carbon tetrachloride as precursors.The resulting spherical CN materials have uniform diameters of ca.4μm,hierarchical three-dimensional(3-D)mesostructures with small and large mesopores with pore diameters centered at ca.4.0 and 43 nm,respectively,a relatively high BET surface area of~550 m^(2)/g,and a pore volume of 0.90 cm^(3)/g.High-resolution transmission electron microscope(HRTEM)images,wide-angle X-ray diffraction(XRD)patterns,and Raman spectra demonstrate that the porous CN material has a partly graphitized structure.In addition,elemental analyses,X-ray photoelectron spectra(XPS),Fourier transform infrared spectra(FT-IR),and CO_(2) temperature-programmed desorption(CO_(2)-TPD)show that the material has a high nitrogen content(17.8 wt%)with nitrogen-containing groups and abundant basic sites.The hierarchical porous CN spheres have excellent CO_(2) capture properties with a capacity of 2.90 mmol/g at 25℃and 0.97 mmol/g at 75℃,superior to those of the pure carbon materials with analogous mesostructures.This can be mainly attributed to the abundant nitrogen-containing basic groups,hierarchical mesostructure,relatively high BET surface area and stable framework.Furthermore,the presence of a large number of micropores and small mesopores also enhance the CO_(2) capture performance,owing to the capillary condensation effect.
基金financially supported by the Ministry of Science and Technology of the People’s Republic of China (2016YFA0300404 and 2015CB921202)the National Natural Science Foundation of China (51372112 and 11574133)+2 种基金the NSF of Jiangsu Province (BK20150012)the Fundamental Research Funds for the Central Universities,the Science Challenge Project (TZ2016001)Special Program for Applied Research on Super Computation of the NSFC-Guangdong Joint Fund (the second phase) under Grant No.U1501501
文摘Transition metal nitrides have been suggested to have both high hardness and good thermal stability with large potential application value, but so far stable superhard transition metal nitrides have not been synthesized. Here, with our newly developed machine-learning accelerated crystal structure searching method, we designed a superhard tungsten nitride, h-WN6, which can be synthesized at pressure around 65 GPa and quenchable to ambient pressure. This h-WN6 is constructed with single-bonded armchair-like N6 rings and presents ionic-like features, which can be formulated as W^2.4＋N^2.4-. It has a band gap of 1.6 eV at 0GPa and exhibits an abnormal gap broadening behavior under pressure. Excitingly, this h-WN6 is found to be the hardest among transition metal nitrides known so far （Vickers hardness around 57 GPa） and also has a very high melting temperature （around 1,900 K）. Additionally, the good gravimet- ric （3.1 kJ/g/and volumetric （28.0 kJ/cm3） energy densities make this nitrogen-rich compound a potential high-energy-density material, These predictions support the designing rules and may stimulate future experiments to synthesize superhard and high-energy-density material.
基金The authors are grateful for the financial support from the National Key R&D Program of China(Nos.2018YFB1502002,2017YFA0206904,2017YFA0206900,and 2016YFB0600901)the National Natural Science Foundation of China(Nos.51825205,U1662U&51772305,51572270,21871279,and 21802154)+4 种基金the Beijing Natural Science Foundation(Nos.2191002,218207&and 2194089)the Beijing Municipal Science and Technology Project(No.Z181100005118007)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB17000000)the Royal Society-Newton Advanced Fellowship(No.NA170422)the International Partnership Program of Chinese Academy of Sciences(No.GJHZ1819)and the K.C.Wong Education Foundation.G.I.N.W.acknowledges funding support from the Energy Education Trust of New Zealand and the University of Auckland Faculty Research Development Fund.
文摘A simple one-step thermal polymerization method was developed for synthesis of holey graphitic carbon nitride nanotubes,involving direci eating of mixtures of melamine and urea or melamine and cyanuric acid in specific mass ratios.Supramolecular structures formed betweer the precursor molecules guided nanotube formation.The porous and nanotubular structure of the nanotubes facilitated efficient charge carrier nigration and separation,thereby enhancing photocatalytic Hz production in 20 vol.%lactic acid under visible light irradiation.Nanotubes synthesized using melamine and urea in a 1:10 mass ratio(denoted herein as CN-MU nanotubes)exhibited a photocatalytic hydroger production rate of 1,073.6μmol·h^-1·^-g with Pt as the cocatalyst,a rate of 4.7 and 3.1 times higher than traditional Pt/g-CN4 photocatalysts prepared from graphitic carbon nitride(g-CN4)obtained by direct thermal polymerization of melamine or urea,respectively.On the basis of their outstanding performance for photocatalytic H2 production,it is envisaged that the holey g-C3N4 nanotubes will find widespread uptake in other areas,including photocatalytic CO2 reduction,dye-sensitized solar cells and photoelectrochemical sensors.
