The thermodynamics and the growth kinetics of synthesis of the SiC whiskers (SiC w ) from rice hulls are studied in this paper. The results show that the intimate contact of SiO 2 with C in the rice hulls resulted in ...The thermodynamics and the growth kinetics of synthesis of the SiC whiskers (SiC w ) from rice hulls are studied in this paper. The results show that the intimate contact of SiO 2 with C in the rice hulls resulted in the formation of SiC particle (SiC p ) at lower temperature, and the external ash of the hulls (w (SiO 2 )>98%) is the main silicon source for SiCw growth. The metallic composite catalyst increases the selectivity for SiCw growth and the reaction rate. The growth mechanism of the SiCw can be characterized as the VLS (vapour liquid solid) with the presence of the whisker forming catalyst: from SiC nucleation through enlargement and growing with the <1 1 1> crystallographic orientation in a certain diameter, then the SiC w is a complete single crystal of β SiC. The generation reaction of SiO is the rate determing step for synthesis of SiC w .展开更多
In this research,microstructure evaluation,mechanical properties and thermal conductivity of the Mg-SiC_(w)/Cu composite with laminar structure were investigated.For this purpose,SiC whiskers were added to magnesium a...In this research,microstructure evaluation,mechanical properties and thermal conductivity of the Mg-SiC_(w)/Cu composite with laminar structure were investigated.For this purpose,SiC whiskers were added to magnesium alloy by using stir-casting,then the Mg-SiC_(w)composite was bonded to copper layers by warm accumulative roll bonding(ARB).Based on the results of optical microscopy(OM)and scanning electron microscopy(SEM),SiC whiskers were well distributed in the magnesium matrix and they were aligned parallelly when the composites were plastically deformed at higher rolling passes.Furthermore,all layers remained continuous with localized necking sites.Also,no intermetallic compounds and phases were detected by XRD and EDS analyzes.Apart from the significant effect of severe plastic deformation on mechanical properties,the findings of mechanical tests point to the usefulness of reinforcements in improving up to 60%microhardness,Young’s modulus,yield,and up to 41%tensile strengths.Further,thermal conductivities of composites increased by adding reinforcement and above all by increasing the number of rolling passes.This growth is attributed to the higher thermal diffusivity of copper and whiskers as well as the increased number of conductive layers within composite.展开更多
Developing lightweight and flexible thin films for electromagnetic interference(EMI)shielding is of great importance.Porous thin films of reduced graphene oxide containing SiC whiskers(SiC@RGO)for EMI shielding were p...Developing lightweight and flexible thin films for electromagnetic interference(EMI)shielding is of great importance.Porous thin films of reduced graphene oxide containing SiC whiskers(SiC@RGO)for EMI shielding were prepared by a two-step reduction of graphene oxide(GO),in which the two steps were chemical reduction by HI and the solid phase microwave irradiation.A significant increase of the film thickness from around 20 to 200μm was achieved due to the formation of a porous structure by gases released during the 3 s of solid phase microwave irradiation.The total shielding effectiveness(SET)and the reflective SE(SE_(R))of the SiC@RGO porous thin films depended on the GO/SiC mass ratio.The highest SET achieved was 35.6 dB while the SE_(R) was only 2.8 dB,when the GO/SiC mass ratio was 4∶1.The addition of SiC whiskers was critical for the multi-reflection,interfacial po-larization and dielectric attenuation of EM waves.A multilayer film with a gradient change of SE values was constructed using SiC@RGO porous films and multi-walled carbon nanotubes buckypapers.The highest SET of the multilayer films reached 75.1 dB with a SE_(R) of 2.7 dB for a film thickness of about 1.5 mm.These porous SiC@RGO thin films should find use in multilayer or sand-wich structures for EMI absorption in packaging or lining.展开更多
Elucidating the effect of growth periods on the quality of calcium sulfate whiskers(CSWs)prepared from calcium sulfate dihydrate(DH)is imperative.Herein,crystal seeds and whiskers were prepared from DH in a water–gly...Elucidating the effect of growth periods on the quality of calcium sulfate whiskers(CSWs)prepared from calcium sulfate dihydrate(DH)is imperative.Herein,crystal seeds and whiskers were prepared from DH in a water–glycerol system.Longer whiskers were obtained from crystal seeds prepared via hydration of DH for 30 s than via ball milling for 5 min followed by hydration for 20 s.The attachment of cetyltrimethyl ammonium bromide and glycerol additives to the whisker tops promoted whisker growth.The whisker sponges exhibited good thermal barrier properties and compression cycle stability.展开更多
With the aim of improving the durability and safety,erosion time,and cost-effective of asphalt road,a composite of modified calcium sulfate whisker-styrene butadiene rubber modified asphalt(MCSWSBRMA)was prepared via ...With the aim of improving the durability and safety,erosion time,and cost-effective of asphalt road,a composite of modified calcium sulfate whisker-styrene butadiene rubber modified asphalt(MCSWSBRMA)was prepared via thermal doping.Firstly,stearic acid and titanate coupling agent(NDZ-201)were used as a modifier to transform calcium sulfate whisker(CSW)into MCSW via wet modification method at 60℃and anhydrous ethanol as a dispersant.What is more,the optimum loading of modifier(a mixture of 25%stearic acid+75%NDZ-201)was found to be at 2%to prepare MCSW.Subsequently,a composite of MCSW-SBRMA was prepared with different loading of MCSW(i.e.2%to 8%)to enhance the softening point of asphalt.In this study,it was found that 4%of modifiers was the best composition to improve the MCSW-SBRMA properties as elucidated in the orthogonal experiment table L_(16)(42).The effects of MCSW and SBR addition on several properties of asphalt were studied by multiple routine tests including penetration,segregation test,and so on.The results show that:2%to 8%MCSW can increase the softening point of SBR modified asphalt(SBRMA)by 7%to 8%.4%MCSW increased the PG of SBRMA from 64 to 70,which greatly improved the high temperature characteristics of asphalt.The 5℃ductility of MCSW-SBRMA is greater than 100 cm,which greatly improves the low temperature performance of asphalt.Through the application of fluorescence microscopy(FM),Fourier transform infrared spectroscopy(FTIR),Scanning electron microscopy(SEM),and energy dispersive spectroscopy(SEM-EDS),it has been demonstrated that MCSW-SBR effectively alters asphalt in a highly uniform manner,with some MCSW still retaining large cross sections,thereby facilitating the dispersion of shear stress and enhancing the durability of asphalt.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
Microstructure evolution and solidification behaviour of ZrB_(2)-SiC composite ceramics fabricated by laser surface zone-melting were investigated.Microstructure coarsening at high scanning speed and mi-crostructure r...Microstructure evolution and solidification behaviour of ZrB_(2)-SiC composite ceramics fabricated by laser surface zone-melting were investigated.Microstructure coarsening at high scanning speed and mi-crostructure refining after turning off the laser was observed due to the changes in the solidification rate.The solidification behaviour from bottom to top of the molten pool was studied,where there are some coarsen eutectic bands caused by the secondary heating of the melting pool on the solidified eu-tectic zone in the molten pool.The deviation of melt composition from the eutectic ratio due to the volatilization of SiC can form a coarse primary ZrB_(2) phase among fine eutectic structure(single-phase instability),and the constitutional supercooling due to the accumulation of impurity elements can form coarse eutectic dendrites among fine eutectic structure(two-phase instability).Both single-phase insta-bility and two-phase instability are adverse to the mechanical properties,which should be prevented by adjusting the composition of raw materials and the solidification process.展开更多
Magnesium carbonate whisker as precursor was prepared from the low-grade magnesite tailings by the route of calcination, hydration, carbonation and thermal decomposition, and then MgO whisker was prepared by calcining...Magnesium carbonate whisker as precursor was prepared from the low-grade magnesite tailings by the route of calcination, hydration, carbonation and thermal decomposition, and then MgO whisker was prepared by calcining the precursor. In addition, the effect of MgO whisker addition on sintering and thermal shock resistance of refractory was also investigated. The results show that the thermal decomposition product is MgCO3·3H2O and its morphology is remarkably influenced by the types of additives, and magnesium carbonate whisker with the length of 10-60 μm and length-diameter ratio of 10-20 is successfully prepared when a type of soluble magnesium salt is added. MgO whisker with the length of 10-40 μm is derived from precursor with the heating rate of 1 ℃/min. The thermal shock resistance of refractory is significantly improved by the addition of MgO whisker due to its effect on binding and preventing crack expanding, and the proper amount of whisker addition is around 3%.展开更多
文摘The thermodynamics and the growth kinetics of synthesis of the SiC whiskers (SiC w ) from rice hulls are studied in this paper. The results show that the intimate contact of SiO 2 with C in the rice hulls resulted in the formation of SiC particle (SiC p ) at lower temperature, and the external ash of the hulls (w (SiO 2 )>98%) is the main silicon source for SiCw growth. The metallic composite catalyst increases the selectivity for SiCw growth and the reaction rate. The growth mechanism of the SiCw can be characterized as the VLS (vapour liquid solid) with the presence of the whisker forming catalyst: from SiC nucleation through enlargement and growing with the <1 1 1> crystallographic orientation in a certain diameter, then the SiC w is a complete single crystal of β SiC. The generation reaction of SiO is the rate determing step for synthesis of SiC w .
文摘In this research,microstructure evaluation,mechanical properties and thermal conductivity of the Mg-SiC_(w)/Cu composite with laminar structure were investigated.For this purpose,SiC whiskers were added to magnesium alloy by using stir-casting,then the Mg-SiC_(w)composite was bonded to copper layers by warm accumulative roll bonding(ARB).Based on the results of optical microscopy(OM)and scanning electron microscopy(SEM),SiC whiskers were well distributed in the magnesium matrix and they were aligned parallelly when the composites were plastically deformed at higher rolling passes.Furthermore,all layers remained continuous with localized necking sites.Also,no intermetallic compounds and phases were detected by XRD and EDS analyzes.Apart from the significant effect of severe plastic deformation on mechanical properties,the findings of mechanical tests point to the usefulness of reinforcements in improving up to 60%microhardness,Young’s modulus,yield,and up to 41%tensile strengths.Further,thermal conductivities of composites increased by adding reinforcement and above all by increasing the number of rolling passes.This growth is attributed to the higher thermal diffusivity of copper and whiskers as well as the increased number of conductive layers within composite.
文摘Developing lightweight and flexible thin films for electromagnetic interference(EMI)shielding is of great importance.Porous thin films of reduced graphene oxide containing SiC whiskers(SiC@RGO)for EMI shielding were prepared by a two-step reduction of graphene oxide(GO),in which the two steps were chemical reduction by HI and the solid phase microwave irradiation.A significant increase of the film thickness from around 20 to 200μm was achieved due to the formation of a porous structure by gases released during the 3 s of solid phase microwave irradiation.The total shielding effectiveness(SET)and the reflective SE(SE_(R))of the SiC@RGO porous thin films depended on the GO/SiC mass ratio.The highest SET achieved was 35.6 dB while the SE_(R) was only 2.8 dB,when the GO/SiC mass ratio was 4∶1.The addition of SiC whiskers was critical for the multi-reflection,interfacial po-larization and dielectric attenuation of EM waves.A multilayer film with a gradient change of SE values was constructed using SiC@RGO porous films and multi-walled carbon nanotubes buckypapers.The highest SET of the multilayer films reached 75.1 dB with a SE_(R) of 2.7 dB for a film thickness of about 1.5 mm.These porous SiC@RGO thin films should find use in multilayer or sand-wich structures for EMI absorption in packaging or lining.
基金supported by the Degradable Plastics Engineering Research Center of Yunnan Provincial Education Department(KKPU202205001).
文摘Elucidating the effect of growth periods on the quality of calcium sulfate whiskers(CSWs)prepared from calcium sulfate dihydrate(DH)is imperative.Herein,crystal seeds and whiskers were prepared from DH in a water–glycerol system.Longer whiskers were obtained from crystal seeds prepared via hydration of DH for 30 s than via ball milling for 5 min followed by hydration for 20 s.The attachment of cetyltrimethyl ammonium bromide and glycerol additives to the whisker tops promoted whisker growth.The whisker sponges exhibited good thermal barrier properties and compression cycle stability.
文摘With the aim of improving the durability and safety,erosion time,and cost-effective of asphalt road,a composite of modified calcium sulfate whisker-styrene butadiene rubber modified asphalt(MCSWSBRMA)was prepared via thermal doping.Firstly,stearic acid and titanate coupling agent(NDZ-201)were used as a modifier to transform calcium sulfate whisker(CSW)into MCSW via wet modification method at 60℃and anhydrous ethanol as a dispersant.What is more,the optimum loading of modifier(a mixture of 25%stearic acid+75%NDZ-201)was found to be at 2%to prepare MCSW.Subsequently,a composite of MCSW-SBRMA was prepared with different loading of MCSW(i.e.2%to 8%)to enhance the softening point of asphalt.In this study,it was found that 4%of modifiers was the best composition to improve the MCSW-SBRMA properties as elucidated in the orthogonal experiment table L_(16)(42).The effects of MCSW and SBR addition on several properties of asphalt were studied by multiple routine tests including penetration,segregation test,and so on.The results show that:2%to 8%MCSW can increase the softening point of SBR modified asphalt(SBRMA)by 7%to 8%.4%MCSW increased the PG of SBRMA from 64 to 70,which greatly improved the high temperature characteristics of asphalt.The 5℃ductility of MCSW-SBRMA is greater than 100 cm,which greatly improves the low temperature performance of asphalt.Through the application of fluorescence microscopy(FM),Fourier transform infrared spectroscopy(FTIR),Scanning electron microscopy(SEM),and energy dispersive spectroscopy(SEM-EDS),it has been demonstrated that MCSW-SBR effectively alters asphalt in a highly uniform manner,with some MCSW still retaining large cross sections,thereby facilitating the dispersion of shear stress and enhancing the durability of asphalt.
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supported by the National Natural Science Foundation of China(Nos.52130204,52174376,52202070)the Guangdong Basic and Applied Basic Research Foundation(No.2021B1515120028)+5 种基金the TQ Innovation Foundation(No.23-TQ09-02-ZT-01-005)the Aeronautical Science Foundation of China(No.20220042053001)the Science and Technology Innovation Team Plan of ShaanXi Province(No.2021TD-17)the Thousands Person Plan of Jiangxi Province(No.JXSQ2020102131)the Xi’an Science and Technology Program(No.21ZCZZHXJS-QCY6-0005)the Fundamental Research Funds for the Central Universities(Nos.D5000230348 and D5000220057).
文摘Microstructure evolution and solidification behaviour of ZrB_(2)-SiC composite ceramics fabricated by laser surface zone-melting were investigated.Microstructure coarsening at high scanning speed and mi-crostructure refining after turning off the laser was observed due to the changes in the solidification rate.The solidification behaviour from bottom to top of the molten pool was studied,where there are some coarsen eutectic bands caused by the secondary heating of the melting pool on the solidified eu-tectic zone in the molten pool.The deviation of melt composition from the eutectic ratio due to the volatilization of SiC can form a coarse primary ZrB_(2) phase among fine eutectic structure(single-phase instability),and the constitutional supercooling due to the accumulation of impurity elements can form coarse eutectic dendrites among fine eutectic structure(two-phase instability).Both single-phase insta-bility and two-phase instability are adverse to the mechanical properties,which should be prevented by adjusting the composition of raw materials and the solidification process.
基金Projects(50874130,50974034)supported by the National Natural Science Foundation of ChinaProject(FMRU2008K01)supported by the Open Research Fund of Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education,Wuhan University of Science and Technology,China
文摘Magnesium carbonate whisker as precursor was prepared from the low-grade magnesite tailings by the route of calcination, hydration, carbonation and thermal decomposition, and then MgO whisker was prepared by calcining the precursor. In addition, the effect of MgO whisker addition on sintering and thermal shock resistance of refractory was also investigated. The results show that the thermal decomposition product is MgCO3·3H2O and its morphology is remarkably influenced by the types of additives, and magnesium carbonate whisker with the length of 10-60 μm and length-diameter ratio of 10-20 is successfully prepared when a type of soluble magnesium salt is added. MgO whisker with the length of 10-40 μm is derived from precursor with the heating rate of 1 ℃/min. The thermal shock resistance of refractory is significantly improved by the addition of MgO whisker due to its effect on binding and preventing crack expanding, and the proper amount of whisker addition is around 3%.
