Effect of graphene nanoplatelets(GNPs)addition on mechanical properties of magnesium–10wt%Titanium(Mg–10Ti)alloy is investigated in current work.The Mg-(10Ti+0.18GNPs)composite was synthesized using the semi powder ...Effect of graphene nanoplatelets(GNPs)addition on mechanical properties of magnesium–10wt%Titanium(Mg–10Ti)alloy is investigated in current work.The Mg-(10Ti+0.18GNPs)composite was synthesized using the semi powder metallurgy method followed by hot extrusion.Microstructural characterization results revealed the uniform distribution of reinforcement(Ti+GNPs)particles in the matrix,therefore(Ti+GNPs)particles act as an effective reinforcing filler to prevent the deformation.Room temperature tensile results showed that the addition of Ti+GNPs to monolithic Mg lead to increase in 0.2%yield strength(0.2%YS),ultimate tensile strength(UTS),and failure strain.Scanning Electron Microscopy(SEM),Energy-Dispersive X-ray Spectroscopy(EDS)and X-Ray Diffraction(XRD)were used to investigate the surface morphology,elemental dispersion and phase analysis,respectively.展开更多
Epoxy/graphene nanoplatelets(GNPs) powder coatings were fabricated using ultrasonic predispersion of GNPs and melt-blend extrusion method. The isothermal curing kinetics of epoxy/GNPs powder coating were monitored b...Epoxy/graphene nanoplatelets(GNPs) powder coatings were fabricated using ultrasonic predispersion of GNPs and melt-blend extrusion method. The isothermal curing kinetics of epoxy/GNPs powder coating were monitored by means of real-time Fourier transform infrared spectroscopy(FT-IR) with a heating cell. The mechanical properties of the epoxy/GNPs cured coatings had been investigated, by evaluating their fracture surfaces with field-emission scanning electron microscopy(FE-SEM) after three-point-bending tests. The thermal stability of the epoxy/GNPs cured coatings was studied by thermo-gravimetric analysis(TGA). The isothermal curing kinetics result showed that the GNPs would not affect the autocatalytic reaction mechanism, but the loading of GNPs below 1.0 wt % additive played a prompting role in the curing of the epoxy/GNPs powder coatings. The fracture strain, fracture toughness and impact resistance of the epoxy/GNPs cured coatings increased dramatically at low levels of GNPs loading(1 wt %), indicating that the GNPs could improve the toughness of the epoxy/GNPs powder coatings. Furthermore, from FE-SEM studies of the fracture surfaces, the possible toughening mechanisms of the epoxy/GNPs cured coatings were proposed. TGA result showed that the incorporation of GNPs improved the thermal stability of the cured coatings. Hence, the GNPs modified epoxy can be an efficient approach to toughen epoxy powder coating along with improving their thermal stability.展开更多
Variant graphene,graphene oxides(GO),and graphene nanoplatelets(GNP)dispersed in blood-based copper(Cu)nanoliquids over a leaning permeable cylinder are the focus of this study.These forms of graphene are highly benef...Variant graphene,graphene oxides(GO),and graphene nanoplatelets(GNP)dispersed in blood-based copper(Cu)nanoliquids over a leaning permeable cylinder are the focus of this study.These forms of graphene are highly beneficial in the biological and medical fields for cancer therapy,anti-infection measures,and drug delivery.The non-Newtonian Sutterby(blood-based)hybrid nanoliquid flows are generalized within the context of the Tiwari-Das model to simulate the effects of radiation and heating sources.The governing partial differential equations are reformulated into a nonlinear set of ordinary differential equations using similar transformational expressions.These equations are then transformed into boundary value problems through a shooting technique,followed by the implementation of the bvp4c tool in MATLAB.The influences of various parameters on the model’s nondimensional velocity and temperature profiles,reduced skin friction,and reduced Nusselt number are presented for detailed discussions.The results indicated that Cu-GNP/blood and Cu-GO/blood hybrid nanofluids exhibit the lowest and highest velocity distributions,respectively,for increased nanoparticles volume fraction,curvature parameter,Sutterby fluid parameter,Hartmann number,and wall permeability parameter.Conversely,opposite trends are observed for the temperature distribution for all considered parameters,except the mixed convection parameter.Increases in the reduced skin friction magnitude and the reduced Nusselt number with higher values of graphene/GO/GNP nanoparticle volume fraction are also reported.Finally,GNP is identified as the superior heat conductor,with an average increase of approximately 5%and a peak of 7.8%in the reduced Nusselt number compared to graphene and GO nanoparticles in the Cu/blood nanofluids.展开更多
The exceptional properties of graphene make it ideal as a reinforcement to enhance the properties of aluminum matrices and this critically depends on uniform dispersion. In this study, the dispersion issue was address...The exceptional properties of graphene make it ideal as a reinforcement to enhance the properties of aluminum matrices and this critically depends on uniform dispersion. In this study, the dispersion issue was addressed by sonication and non-covalent surface functionalization of graphite nanoplatelets(GNPs) using two types of surfactant: anionic(sodium dodecyl benzene sulfate(SDBS)) and non-ionic polymeric(ethyl cellulose(EC)). After colloidal mixing with Al powder, consolidation was performed at two sintering temperatures(550 and 620°C). The structure, density, mechanical and wear properties of the nanocomposite samples were investigated and compared with a pure Al and a pure GNPs/Al nanocomposite sample. Noticeably, EC-based 0.5 wt% GNPs/Al samples showed the highest increment of 31% increase in hardness with reduced wear rate of 98.25% at 620°C, while a 22% increase in hardness with reduced wear rate of 96.98% at 550°C was observed, as compared to pure Al. Microstructural analysis and the overall results validate the use of EC-based GNPs/Al nanocomposites as they performed better than pure Al and pure GNPs/Al nanocomposite at both sintering temperatures.展开更多
A 0.3wt%graphene nanoplatelets(GNPs)reinforced 7075 aluminum alloy matrix(7075 Al)composite was fabricated by spark plasma sintering and its strength and wear resistance were investigated.The microstructures of the in...A 0.3wt%graphene nanoplatelets(GNPs)reinforced 7075 aluminum alloy matrix(7075 Al)composite was fabricated by spark plasma sintering and its strength and wear resistance were investigated.The microstructures of the internal structure,the friction surface,and the wear debris were characterized by scanning electron microscopy,X-ray diffraction,and Raman spectroscopy.Compared with the original 7075 aluminum alloy,the hardness and elastic modulus of the 7075 Al/GNPs composite were found to have increased by 29%and 36%,respectively.The results of tribological experiments indicated that the composite also exhibited a lower wear rate than the original 7075 aluminum alloy.展开更多
Lithium–sulfur batteries have great potential for high energy applications due to their high capacities,low cost and eco-friendliness. However, the particularly rapid capacity decay owing to the dissolution and diffu...Lithium–sulfur batteries have great potential for high energy applications due to their high capacities,low cost and eco-friendliness. However, the particularly rapid capacity decay owing to the dissolution and diffusion of polysulfide intermediate into the electrolyte still hamper their practical applications.And the reported preparation procedures to sulfur based cathode materials are often complex, and hence are rather difficult to produce at large scale. Here, we report a simple mechano-chemical sulfurization methodology in vacuum environment applying ball-milling method combined both the chemical and physical interaction for the one-pot synthesis of edge-sulfurized grapheme nanoplatelets with 3D porous foam structure as cathode materials. The optimal sample of 70%S–Gn Ps-48 h(ball-milled 48 h) obtains 13.2 wt% sulfur that chemically bonded onto the edge of Gn Ps. And the assembled batteries exhibit high initial discharge capacities of 1089 mAh/g at 0.1 C and 950 mAh/g at 0.5 C, and retain a stable discharge capacity of 776 mAh/g after 250 cycles at 0.5 C with a high Coulombic efficiency of over 98%. The excellent performance is mainly attributed to the mechano-chemical interaction between sulfur and grapheme nanoplatelets. This definitely triggers the currently extensive research in lithium–sulfur battery area.展开更多
Featuring exceptional mechanical and functional performance, MWCNTs and graphene(nano)platelets(GNPs or Gn Ps;each platelet below 10 nm in thickness) have been increasingly used for the development of polymer nanocomp...Featuring exceptional mechanical and functional performance, MWCNTs and graphene(nano)platelets(GNPs or Gn Ps;each platelet below 10 nm in thickness) have been increasingly used for the development of polymer nanocomposites. Since MWCNTs are now cost-effective at US$30 per kg for industrial applications, this work starts by briefly reviewing the disentanglement and surface modification of MWCNTs as well as the properties of the resulting polymer nanocomposites. GNPs can be made through the thermal treatment of graphite intercalation compounds followed by ultrasonication;GNPs would have lower cost yet higher electrical conductivity over 1,400 S cmthan MWCNTs. Through proper surface modification and compounding techniques, both types of fillers can reinforce or toughen polymers and simultaneously add anti-static performance. A high ratio of MWCNTs to GNPs would increase the synergy for polymers. Green, solvent-free systhesis methods are desired for polymer nanocomposites. Perspectives on the limitations, current challenges and future prospects are provided.展开更多
In aiming to obtain fibers with enhanced thermal and mechanical properties,graphene based textile fibers with 144 filaments were developed using an approach in which the PP/GnP(polypropylene/graphene nanoplatelets)nan...In aiming to obtain fibers with enhanced thermal and mechanical properties,graphene based textile fibers with 144 filaments were developed using an approach in which the PP/GnP(polypropylene/graphene nanoplatelets)nanocomposite was employed as conductive material in a fiber with circular cross-section geometry.The kinetics of thermal degradation was evaluated by the Broido method using thermogravimetric analysis(TGA).Activation energy was enhanced from 260.6 kJ·mol^-1 to 337.4 kJ·mol^-1 compared to the neat PP.GnP increased the thermal stability of the PP,slowing its degradation by thermal depolymerization.Furthermore,the degree of crystallization declined as the GnP content increased,reducing the tenacity of the yarn,but improving its elastic modulus from 91.9 to 95.9 cN/tex,being a promising alternative to produce smart textiles.In conclusion,it has been confirmed that GnP loading up to 1%(w/w)can be incorporated into polypropylene by melt spinning and that the resulting nanocomposite fibers are suitable for several applications in the textile industry.展开更多
A powder thixoforging route combined with slurry based mixing process was proposed to fabricate graphene nanoplatelets(GNPs) reinforced magnesium matrix composites(MgMCs). The originally spherical and ball-milled ZK60...A powder thixoforging route combined with slurry based mixing process was proposed to fabricate graphene nanoplatelets(GNPs) reinforced magnesium matrix composites(MgMCs). The originally spherical and ball-milled ZK60 powders were used as matrices, respectively.The mixing of 0.05 wt.% GNPs with the spherical powder led to GNPs clusters and degraded the mechanical properties of the composite.In contrast, with the addition of an optimal content(0.1 wt.%) of GNPs, the composite fabricated from ball-milled powder achieved a joint enhancement in tensile yield strength(52%) and fracture toughness(19%), demonstrating a pronounced strengthening efficiency of 650% and a good balance between strength and toughness. The ball-milled powder endowed the composite with a homogenous distribution of GNPs and a denser microstructure with reduced Mg-Zn eutectics, and the thixoforging process offered a well-bonded Mg/GNP interface, making full use of the strengthening and toughening potential of GNPs. Theoretical predication based on a modified shear-lag model suggested that load transfer dominated the strengthening mechanisms. In-situ tensile tests verified that crack deflection, secondary cracks and GNPs bridging mainly accounted for the toughening mechanisms. A numerical model with consideration of GNPs orientations was also established to understand the toughening effect from GNPs bridging.展开更多
Thermal energy storage(TES) systems use solar energy despite its irregular availability and day-night temperature difference.Current work reports the thermal characterizations of solar salt-based phase change composit...Thermal energy storage(TES) systems use solar energy despite its irregular availability and day-night temperature difference.Current work reports the thermal characterizations of solar salt-based phase change composites in the presence of graphene nanoplatelets(GNP).Solar salt(60:40 of NaNO_(3):KNO_(3)) possessing phase transition temperature and melting enthalpy of 221.01℃ and 134.58 kJ/kg is proposed as a phase change material(PCM) for high-temperature solar-based energy storage applications.Thermal conductivity must be improved to make them suitable for widespread applications and to close the gap between the system needs where they are employed.GNP is added at weight concentrations of 0.1%,0.3%,and 0.5% with solar salt using the ball milling method to boost its thermal conductivity.Morphological studies indicated the formation of a uniform surface of GNP on solar salt.FTIR spectrum peaks identified the physical interaction between salt and GNP.Thermal characterization of the composites,such as thermal conductivity,DSC and TGA was carried out for the samples earlier and later 300 thermal cycles.0.5% of GNP has improved the thermal conductivity of salt by 129.67% and after thermal cycling,the enhancement reduced to 125.21% indicating that thermal cycling has a minor impact on thermal conductivity.Phase change temperature decreased by around 2.32% in the presence of0.5% GNP and the latent heat reduced by 4.34% after thermal cycling.TGA thermograms depicted the composites initiated the weight loss at around 550℃ after which it was rapid.After thermal cycling,the weight loss initiated at ~40℃ lower compared to pure salt,which was found to be a minor change.Thermal characterization of solar salt and GNP-based solar salt composites revealed that the composites can be used for enhanced heat transfer in high-temperature solar-based heat transfer and energy storage applications.展开更多
Over the span of years, improvements over various synthesis methods of graphene are constantly pursued to provide safer and more effective alternatives. Though the extraction of graphene through Hummers method is one ...Over the span of years, improvements over various synthesis methods of graphene are constantly pursued to provide safer and more effective alternatives. Though the extraction of graphene through Hummers method is one of the oldest techniques yet it is one of the most suitable methods for the formation of bulk graphene. Graphene can be obtained in the form of reduced Graphite oxide, sometimes also referred as Graphene oxide. The effectiveness of this oxidation process can be evaluated by the magnitude of carbon/oxygen ratio of the obtained graphene. Here, graphene oxide (GO) was prepared by oxidizing the purified natural flake graphite (NFG) by a modified Hummers method. The attempts have been made to synthesize GO having few layers by using a modified Hummers method where the amount of NaNO3 has been decreased, and the amount of KMnO4 is increased. The reaction has been performed in a 9:1 (by volume) mixture of H2SO4/H3PO4. This modification is successful in increasing the reaction yield and reducing the toxic gas evolution while using a varied proportion of KMnO4 and H2SO4 as those required by Hummers method. A new component of K2S2O8 has been introduced to the reaction system to maintain the pH value. Reduced graphene oxide (rGO) was thereafter extracted by thermal modification of GO. Here, GO has been used as a precursor for graphene synthesis by thermal reduction processes. The results of FTIR and Raman spectroscopy analysis show that the NFG when oxidized by strong oxidants like KMnO4 and NaNO3, introduced oxygen atoms into the graphite layers and formed bonds like C=O, C-H, COOH and C-O-C with the carbon atoms in the graphite layers. The structure and morphology of both GO and rGO were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy, Raman spectroscopy, Brunauer-Emmett-Teller (BET) surface area analysis and differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).展开更多
基金The present work was supported by the National Natural Science Funds of China(No.50725413)the Ministry of Science and Technology of China(MOST)(No.2010DFR50010 and 2011FU125Z07)Chongqing Science and Technology Commission(CSTC2013jcyjC60001).
文摘Effect of graphene nanoplatelets(GNPs)addition on mechanical properties of magnesium–10wt%Titanium(Mg–10Ti)alloy is investigated in current work.The Mg-(10Ti+0.18GNPs)composite was synthesized using the semi powder metallurgy method followed by hot extrusion.Microstructural characterization results revealed the uniform distribution of reinforcement(Ti+GNPs)particles in the matrix,therefore(Ti+GNPs)particles act as an effective reinforcing filler to prevent the deformation.Room temperature tensile results showed that the addition of Ti+GNPs to monolithic Mg lead to increase in 0.2%yield strength(0.2%YS),ultimate tensile strength(UTS),and failure strain.Scanning Electron Microscopy(SEM),Energy-Dispersive X-ray Spectroscopy(EDS)and X-Ray Diffraction(XRD)were used to investigate the surface morphology,elemental dispersion and phase analysis,respectively.
基金Funded by the National Natural Science Foundation of China(No.51473104)
文摘Epoxy/graphene nanoplatelets(GNPs) powder coatings were fabricated using ultrasonic predispersion of GNPs and melt-blend extrusion method. The isothermal curing kinetics of epoxy/GNPs powder coating were monitored by means of real-time Fourier transform infrared spectroscopy(FT-IR) with a heating cell. The mechanical properties of the epoxy/GNPs cured coatings had been investigated, by evaluating their fracture surfaces with field-emission scanning electron microscopy(FE-SEM) after three-point-bending tests. The thermal stability of the epoxy/GNPs cured coatings was studied by thermo-gravimetric analysis(TGA). The isothermal curing kinetics result showed that the GNPs would not affect the autocatalytic reaction mechanism, but the loading of GNPs below 1.0 wt % additive played a prompting role in the curing of the epoxy/GNPs powder coatings. The fracture strain, fracture toughness and impact resistance of the epoxy/GNPs cured coatings increased dramatically at low levels of GNPs loading(1 wt %), indicating that the GNPs could improve the toughness of the epoxy/GNPs powder coatings. Furthermore, from FE-SEM studies of the fracture surfaces, the possible toughening mechanisms of the epoxy/GNPs cured coatings were proposed. TGA result showed that the incorporation of GNPs improved the thermal stability of the cured coatings. Hence, the GNPs modified epoxy can be an efficient approach to toughen epoxy powder coating along with improving their thermal stability.
基金funded by the Ministry of Higher Education,Malaysia,through the Research Fund of Fundamental Research Grant Scheme (FRGS/1/2020/STG06/UM/02/1:FP009-2020).
文摘Variant graphene,graphene oxides(GO),and graphene nanoplatelets(GNP)dispersed in blood-based copper(Cu)nanoliquids over a leaning permeable cylinder are the focus of this study.These forms of graphene are highly beneficial in the biological and medical fields for cancer therapy,anti-infection measures,and drug delivery.The non-Newtonian Sutterby(blood-based)hybrid nanoliquid flows are generalized within the context of the Tiwari-Das model to simulate the effects of radiation and heating sources.The governing partial differential equations are reformulated into a nonlinear set of ordinary differential equations using similar transformational expressions.These equations are then transformed into boundary value problems through a shooting technique,followed by the implementation of the bvp4c tool in MATLAB.The influences of various parameters on the model’s nondimensional velocity and temperature profiles,reduced skin friction,and reduced Nusselt number are presented for detailed discussions.The results indicated that Cu-GNP/blood and Cu-GO/blood hybrid nanofluids exhibit the lowest and highest velocity distributions,respectively,for increased nanoparticles volume fraction,curvature parameter,Sutterby fluid parameter,Hartmann number,and wall permeability parameter.Conversely,opposite trends are observed for the temperature distribution for all considered parameters,except the mixed convection parameter.Increases in the reduced skin friction magnitude and the reduced Nusselt number with higher values of graphene/GO/GNP nanoparticle volume fraction are also reported.Finally,GNP is identified as the superior heat conductor,with an average increase of approximately 5%and a peak of 7.8%in the reduced Nusselt number compared to graphene and GO nanoparticles in the Cu/blood nanofluids.
文摘The exceptional properties of graphene make it ideal as a reinforcement to enhance the properties of aluminum matrices and this critically depends on uniform dispersion. In this study, the dispersion issue was addressed by sonication and non-covalent surface functionalization of graphite nanoplatelets(GNPs) using two types of surfactant: anionic(sodium dodecyl benzene sulfate(SDBS)) and non-ionic polymeric(ethyl cellulose(EC)). After colloidal mixing with Al powder, consolidation was performed at two sintering temperatures(550 and 620°C). The structure, density, mechanical and wear properties of the nanocomposite samples were investigated and compared with a pure Al and a pure GNPs/Al nanocomposite sample. Noticeably, EC-based 0.5 wt% GNPs/Al samples showed the highest increment of 31% increase in hardness with reduced wear rate of 98.25% at 620°C, while a 22% increase in hardness with reduced wear rate of 96.98% at 550°C was observed, as compared to pure Al. Microstructural analysis and the overall results validate the use of EC-based GNPs/Al nanocomposites as they performed better than pure Al and pure GNPs/Al nanocomposite at both sintering temperatures.
基金This work was financially supported by the Program for New Century Excellent Talents in University(No.NCET-11-0951).
文摘A 0.3wt%graphene nanoplatelets(GNPs)reinforced 7075 aluminum alloy matrix(7075 Al)composite was fabricated by spark plasma sintering and its strength and wear resistance were investigated.The microstructures of the internal structure,the friction surface,and the wear debris were characterized by scanning electron microscopy,X-ray diffraction,and Raman spectroscopy.Compared with the original 7075 aluminum alloy,the hardness and elastic modulus of the 7075 Al/GNPs composite were found to have increased by 29%and 36%,respectively.The results of tribological experiments indicated that the composite also exhibited a lower wear rate than the original 7075 aluminum alloy.
基金the Link Project of the National Natural Science Foundation of China and Guangdong Province(Grant no.U1301244)the National Natural Science Foundation of China(Grant nos.51573215,21506260)+2 种基金Guangdong Province Science&Technology Foundation(2011B050300008)Guangdong Natural Science Foundation(Grant nos.2014A030313159,2016A030313354)Guangzhou Scientific and Technological Planning Project(2014J4500002,201607010042)for financial support of this work
文摘Lithium–sulfur batteries have great potential for high energy applications due to their high capacities,low cost and eco-friendliness. However, the particularly rapid capacity decay owing to the dissolution and diffusion of polysulfide intermediate into the electrolyte still hamper their practical applications.And the reported preparation procedures to sulfur based cathode materials are often complex, and hence are rather difficult to produce at large scale. Here, we report a simple mechano-chemical sulfurization methodology in vacuum environment applying ball-milling method combined both the chemical and physical interaction for the one-pot synthesis of edge-sulfurized grapheme nanoplatelets with 3D porous foam structure as cathode materials. The optimal sample of 70%S–Gn Ps-48 h(ball-milled 48 h) obtains 13.2 wt% sulfur that chemically bonded onto the edge of Gn Ps. And the assembled batteries exhibit high initial discharge capacities of 1089 mAh/g at 0.1 C and 950 mAh/g at 0.5 C, and retain a stable discharge capacity of 776 mAh/g after 250 cycles at 0.5 C with a high Coulombic efficiency of over 98%. The excellent performance is mainly attributed to the mechano-chemical interaction between sulfur and grapheme nanoplatelets. This definitely triggers the currently extensive research in lithium–sulfur battery area.
基金financial support by the Australian Research Council (LP180100005 & DP200101737)。
文摘Featuring exceptional mechanical and functional performance, MWCNTs and graphene(nano)platelets(GNPs or Gn Ps;each platelet below 10 nm in thickness) have been increasingly used for the development of polymer nanocomposites. Since MWCNTs are now cost-effective at US$30 per kg for industrial applications, this work starts by briefly reviewing the disentanglement and surface modification of MWCNTs as well as the properties of the resulting polymer nanocomposites. GNPs can be made through the thermal treatment of graphite intercalation compounds followed by ultrasonication;GNPs would have lower cost yet higher electrical conductivity over 1,400 S cmthan MWCNTs. Through proper surface modification and compounding techniques, both types of fillers can reinforce or toughen polymers and simultaneously add anti-static performance. A high ratio of MWCNTs to GNPs would increase the synergy for polymers. Green, solvent-free systhesis methods are desired for polymer nanocomposites. Perspectives on the limitations, current challenges and future prospects are provided.
基金financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior-Brasil(CAPES)-Finance Code 001.
文摘In aiming to obtain fibers with enhanced thermal and mechanical properties,graphene based textile fibers with 144 filaments were developed using an approach in which the PP/GnP(polypropylene/graphene nanoplatelets)nanocomposite was employed as conductive material in a fiber with circular cross-section geometry.The kinetics of thermal degradation was evaluated by the Broido method using thermogravimetric analysis(TGA).Activation energy was enhanced from 260.6 kJ·mol^-1 to 337.4 kJ·mol^-1 compared to the neat PP.GnP increased the thermal stability of the PP,slowing its degradation by thermal depolymerization.Furthermore,the degree of crystallization declined as the GnP content increased,reducing the tenacity of the yarn,but improving its elastic modulus from 91.9 to 95.9 cN/tex,being a promising alternative to produce smart textiles.In conclusion,it has been confirmed that GnP loading up to 1%(w/w)can be incorporated into polypropylene by melt spinning and that the resulting nanocomposite fibers are suitable for several applications in the textile industry.
基金financially supported by the National natural Science Foundation of China (Grant No.51761028)。
文摘A powder thixoforging route combined with slurry based mixing process was proposed to fabricate graphene nanoplatelets(GNPs) reinforced magnesium matrix composites(MgMCs). The originally spherical and ball-milled ZK60 powders were used as matrices, respectively.The mixing of 0.05 wt.% GNPs with the spherical powder led to GNPs clusters and degraded the mechanical properties of the composite.In contrast, with the addition of an optimal content(0.1 wt.%) of GNPs, the composite fabricated from ball-milled powder achieved a joint enhancement in tensile yield strength(52%) and fracture toughness(19%), demonstrating a pronounced strengthening efficiency of 650% and a good balance between strength and toughness. The ball-milled powder endowed the composite with a homogenous distribution of GNPs and a denser microstructure with reduced Mg-Zn eutectics, and the thixoforging process offered a well-bonded Mg/GNP interface, making full use of the strengthening and toughening potential of GNPs. Theoretical predication based on a modified shear-lag model suggested that load transfer dominated the strengthening mechanisms. In-situ tensile tests verified that crack deflection, secondary cracks and GNPs bridging mainly accounted for the toughening mechanisms. A numerical model with consideration of GNPs orientations was also established to understand the toughening effect from GNPs bridging.
文摘Thermal energy storage(TES) systems use solar energy despite its irregular availability and day-night temperature difference.Current work reports the thermal characterizations of solar salt-based phase change composites in the presence of graphene nanoplatelets(GNP).Solar salt(60:40 of NaNO_(3):KNO_(3)) possessing phase transition temperature and melting enthalpy of 221.01℃ and 134.58 kJ/kg is proposed as a phase change material(PCM) for high-temperature solar-based energy storage applications.Thermal conductivity must be improved to make them suitable for widespread applications and to close the gap between the system needs where they are employed.GNP is added at weight concentrations of 0.1%,0.3%,and 0.5% with solar salt using the ball milling method to boost its thermal conductivity.Morphological studies indicated the formation of a uniform surface of GNP on solar salt.FTIR spectrum peaks identified the physical interaction between salt and GNP.Thermal characterization of the composites,such as thermal conductivity,DSC and TGA was carried out for the samples earlier and later 300 thermal cycles.0.5% of GNP has improved the thermal conductivity of salt by 129.67% and after thermal cycling,the enhancement reduced to 125.21% indicating that thermal cycling has a minor impact on thermal conductivity.Phase change temperature decreased by around 2.32% in the presence of0.5% GNP and the latent heat reduced by 4.34% after thermal cycling.TGA thermograms depicted the composites initiated the weight loss at around 550℃ after which it was rapid.After thermal cycling,the weight loss initiated at ~40℃ lower compared to pure salt,which was found to be a minor change.Thermal characterization of solar salt and GNP-based solar salt composites revealed that the composites can be used for enhanced heat transfer in high-temperature solar-based heat transfer and energy storage applications.
文摘Over the span of years, improvements over various synthesis methods of graphene are constantly pursued to provide safer and more effective alternatives. Though the extraction of graphene through Hummers method is one of the oldest techniques yet it is one of the most suitable methods for the formation of bulk graphene. Graphene can be obtained in the form of reduced Graphite oxide, sometimes also referred as Graphene oxide. The effectiveness of this oxidation process can be evaluated by the magnitude of carbon/oxygen ratio of the obtained graphene. Here, graphene oxide (GO) was prepared by oxidizing the purified natural flake graphite (NFG) by a modified Hummers method. The attempts have been made to synthesize GO having few layers by using a modified Hummers method where the amount of NaNO3 has been decreased, and the amount of KMnO4 is increased. The reaction has been performed in a 9:1 (by volume) mixture of H2SO4/H3PO4. This modification is successful in increasing the reaction yield and reducing the toxic gas evolution while using a varied proportion of KMnO4 and H2SO4 as those required by Hummers method. A new component of K2S2O8 has been introduced to the reaction system to maintain the pH value. Reduced graphene oxide (rGO) was thereafter extracted by thermal modification of GO. Here, GO has been used as a precursor for graphene synthesis by thermal reduction processes. The results of FTIR and Raman spectroscopy analysis show that the NFG when oxidized by strong oxidants like KMnO4 and NaNO3, introduced oxygen atoms into the graphite layers and formed bonds like C=O, C-H, COOH and C-O-C with the carbon atoms in the graphite layers. The structure and morphology of both GO and rGO were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy, Raman spectroscopy, Brunauer-Emmett-Teller (BET) surface area analysis and differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).