2011 Vol. 28, No. 2
2011, 28(2): 1-9.
Abstract:
Major advancement of TPS (Thermal Protection System) composites at home and aboard is briefly summarized, focusing on ablative TPS composites, non(minimal) ablative TPS composites, high-performance insulative composites and high-temperature microwave transparent composites. Breakthroughs and progress in our country are introduced, and the future development trends of thermal protection composites are discussed.
Major advancement of TPS (Thermal Protection System) composites at home and aboard is briefly summarized, focusing on ablative TPS composites, non(minimal) ablative TPS composites, high-performance insulative composites and high-temperature microwave transparent composites. Breakthroughs and progress in our country are introduced, and the future development trends of thermal protection composites are discussed.
2011, 28(2): 10-15.
Abstract:
UV curing coating of carbon nanotubes/epoxy acrylate (CNTs/EA) was prepared by the molecule group reaction of CNTs with EA. The anti-infrared/ultraviolet property was characterized by UV-vis and FTIR. The results demonstrate that, its transmittance is greater than 85% in visible spectrum, the ratio of wave shielding is 68.55% in near infrared wave range (4000~12000 cm-1) and it shields all of wave in ultraviolet the region (<300 nm). At same time the mechanical property of composite coating is improved. So these new nano-composite materials would be expected to be a wave shielding thin coating in functional applications.
UV curing coating of carbon nanotubes/epoxy acrylate (CNTs/EA) was prepared by the molecule group reaction of CNTs with EA. The anti-infrared/ultraviolet property was characterized by UV-vis and FTIR. The results demonstrate that, its transmittance is greater than 85% in visible spectrum, the ratio of wave shielding is 68.55% in near infrared wave range (4000~12000 cm-1) and it shields all of wave in ultraviolet the region (<300 nm). At same time the mechanical property of composite coating is improved. So these new nano-composite materials would be expected to be a wave shielding thin coating in functional applications.
2011, 28(2): 16-21.
Abstract:
A series of CMWNTs/PA66 composite fibers were melt-spun with the melt-blended PA66 and 0.1 wt%~ 3 wt% of carboxylic multi-walled carbon nanotubes chips. The effects of CMWNTs mass fraction on the morphology and mechanical properties of the composite fibers were characterized using SEM, DMA and a tensile strength tester etc. The results show that the CMWNTs are homogeneously dispersed throughout PA66 matrix. Both the Tg and mechanical properties of the composite fiber increase due to the addition of CMWNTs. When the mass fraction of CMWNTs is 0.5%, the storage modulus of CMWNTs/PA66 composite fiber is the highest, which is 5.5 times that of PA66 fiber. The glass transition temperature of the fiber is 27.6 ℃. When the mass fraction of CMWNTs is 0.3%, the initial modulus of CMWNTs/PA66 composite fiber is the highest with an increase of 101.4%. When the mass fraction of CMWNTs is 1%, the breaking strength is the largest with an increase of 48.8%.
A series of CMWNTs/PA66 composite fibers were melt-spun with the melt-blended PA66 and 0.1 wt%~ 3 wt% of carboxylic multi-walled carbon nanotubes chips. The effects of CMWNTs mass fraction on the morphology and mechanical properties of the composite fibers were characterized using SEM, DMA and a tensile strength tester etc. The results show that the CMWNTs are homogeneously dispersed throughout PA66 matrix. Both the Tg and mechanical properties of the composite fiber increase due to the addition of CMWNTs. When the mass fraction of CMWNTs is 0.5%, the storage modulus of CMWNTs/PA66 composite fiber is the highest, which is 5.5 times that of PA66 fiber. The glass transition temperature of the fiber is 27.6 ℃. When the mass fraction of CMWNTs is 0.3%, the initial modulus of CMWNTs/PA66 composite fiber is the highest with an increase of 101.4%. When the mass fraction of CMWNTs is 1%, the breaking strength is the largest with an increase of 48.8%.
2011, 28(2): 22-26.
Abstract:
The effect of content of porous ePTFE on the mechanical property of the ePTFE/Nafion composite proton exchange membrane was carefully investigated. The results show there is a PTFE content threshold value (ca. 20.7%, volume fraction) beyond which the composite membrane could be reinforced. The tensile strength of the composite membrane goes up with the increasing of ePTFE content when the ePTFE content is greater than the threshold value, and decreases with growing ePTFE content when the ePTFE content does not reach the threshold value. The yield strength change of the composite membranes with the ePTFE content shows similar trend.
The effect of content of porous ePTFE on the mechanical property of the ePTFE/Nafion composite proton exchange membrane was carefully investigated. The results show there is a PTFE content threshold value (ca. 20.7%, volume fraction) beyond which the composite membrane could be reinforced. The tensile strength of the composite membrane goes up with the increasing of ePTFE content when the ePTFE content is greater than the threshold value, and decreases with growing ePTFE content when the ePTFE content does not reach the threshold value. The yield strength change of the composite membranes with the ePTFE content shows similar trend.
2011, 28(2): 27-35.
Abstract:
Poly(ethylene oxide) (PEO)-polypropylene (PP) blends containing organic-montmorillonite (OMMT)/poly(ethylene oxide) (PEO)-polypropylene (PP) composites were prepared using a twin screw extruder followed by the injection molding. The effects of OMMT loading on the morphology and transparent properties of the OMMT/PEO-PP composites were investigated in detail with a combination of TEM and SEM measurements. The crystallization and melt behavior of OMMT/PEO-PP composites were studied by means of DSC and POM. It is found that in all blends the OMMT are preferentially located within the PEO phase and around the interfaces of PEO and PP phases. SEM reveales a large reduction in PEO domain size when OMMT is used. The PP crystal sizes decrease significantly with OMMT content increasing. It is also shown that the incorporation of a small amount of OMMT induces a dramatic transformation from an opaque to a transparent system.
Poly(ethylene oxide) (PEO)-polypropylene (PP) blends containing organic-montmorillonite (OMMT)/poly(ethylene oxide) (PEO)-polypropylene (PP) composites were prepared using a twin screw extruder followed by the injection molding. The effects of OMMT loading on the morphology and transparent properties of the OMMT/PEO-PP composites were investigated in detail with a combination of TEM and SEM measurements. The crystallization and melt behavior of OMMT/PEO-PP composites were studied by means of DSC and POM. It is found that in all blends the OMMT are preferentially located within the PEO phase and around the interfaces of PEO and PP phases. SEM reveales a large reduction in PEO domain size when OMMT is used. The PP crystal sizes decrease significantly with OMMT content increasing. It is also shown that the incorporation of a small amount of OMMT induces a dramatic transformation from an opaque to a transparent system.
2011, 28(2): 36-41.
Abstract:
Ti(OC4H9)4/Ni(CH3COO)2·4H2O PVP fibers were prepared by coaxial electrospinning using PVP/Ni(CH3COO)2·4H2O sol as the core and PVP/Ti(OC4H9)4 sol as the shell, and then Ti(OC4H9)4/ Ni(CH3COO)2·4H2O PVP fibers were heated at 550 ℃ for 6 h to obtain NiO-TiO2 coaxial nanofibers. The structure and properties of the NiO-TiO2 coaxial fibers were investigated using XRD, SEM, FTIR and TG. The photocatalytic properties of NiO-TiO2 coaxial nanofibers were studied by the degradation of methylene blue under UV irradiation. In comparing with TiO2 nanofibers, the NiO-TiO2 coaxial nanofibers exhibite higher photocatalytic activity for the degradation of methylene blue, and the catalyst could be used repeatedly.
Ti(OC4H9)4/Ni(CH3COO)2·4H2O PVP fibers were prepared by coaxial electrospinning using PVP/Ni(CH3COO)2·4H2O sol as the core and PVP/Ti(OC4H9)4 sol as the shell, and then Ti(OC4H9)4/ Ni(CH3COO)2·4H2O PVP fibers were heated at 550 ℃ for 6 h to obtain NiO-TiO2 coaxial nanofibers. The structure and properties of the NiO-TiO2 coaxial fibers were investigated using XRD, SEM, FTIR and TG. The photocatalytic properties of NiO-TiO2 coaxial nanofibers were studied by the degradation of methylene blue under UV irradiation. In comparing with TiO2 nanofibers, the NiO-TiO2 coaxial nanofibers exhibite higher photocatalytic activity for the degradation of methylene blue, and the catalyst could be used repeatedly.
2011, 28(2): 42-48.
Abstract:
Various polyamide-polypropylene (PA1010-PP) blends were prepared by melt mixing using maleic anhydride-grafted ethylene-octene copolymer (POE-g-MAH) as a compatibilizer. In order to investigate the compatibilizing effect of POE-g-MAH on PA1010-PP blends obtained via dynamic packing injection molding (DPIM), morphologies, mechanical and crystallizing properties of the blends were characterized by means of scaning electron microscopy (SEM), mechanical testing and differential scaning calorimetry (DSC), respectively. It is found the tensile strength, tensile modulus and notched impact strength largely increase by applying shear stress during injection molding. SEM results show a remarkable decrease of domain size, more uniform dispersion and more fuzzy interface of the dynamic molded specimens, which indicates that shear stress can accelerate compatibilization. DSC results show that two crystalline peaks appear in dynamic samples when POE-g-MAH reaches 15%, the crystallization of PP at the lower temperature should be assigned to homogeneous nucleation, the other one is heterogeneous nucleation. The appearance of homogeneous nucleation demonstrates that the size of PP particles is very fine in the matrix. The enhancement of compatibilization effect of POE-g-MAH on PA1010-PP blends under shear stress could be due to the effect of shear-induced particular morphologies.
Various polyamide-polypropylene (PA1010-PP) blends were prepared by melt mixing using maleic anhydride-grafted ethylene-octene copolymer (POE-g-MAH) as a compatibilizer. In order to investigate the compatibilizing effect of POE-g-MAH on PA1010-PP blends obtained via dynamic packing injection molding (DPIM), morphologies, mechanical and crystallizing properties of the blends were characterized by means of scaning electron microscopy (SEM), mechanical testing and differential scaning calorimetry (DSC), respectively. It is found the tensile strength, tensile modulus and notched impact strength largely increase by applying shear stress during injection molding. SEM results show a remarkable decrease of domain size, more uniform dispersion and more fuzzy interface of the dynamic molded specimens, which indicates that shear stress can accelerate compatibilization. DSC results show that two crystalline peaks appear in dynamic samples when POE-g-MAH reaches 15%, the crystallization of PP at the lower temperature should be assigned to homogeneous nucleation, the other one is heterogeneous nucleation. The appearance of homogeneous nucleation demonstrates that the size of PP particles is very fine in the matrix. The enhancement of compatibilization effect of POE-g-MAH on PA1010-PP blends under shear stress could be due to the effect of shear-induced particular morphologies.
2011, 28(2): 49-53.
Abstract:
The effect of the fiber microstructure on the fluid flow behavior was investigated. Simulations on the fiber models which have different fiber volume fractions and nearest inter-fiber spacing were performed to calculate the fiber permeability. The results reveal that the permeability is less sensitive to the nearest inter-fiber distance when the volume fraction is low. At the high volume fraction, the permeability declines with the decrease of the nearest inter-fiber spacing. The relation of permeability standard deviation, nearest inter-fiber spacing and volume fraction was studied. The standard deviation of permeability for different fiber microstructures depends only on the nearest inter-fiber spacing when the volume fraction is low, but it is determined by both the nearest inter-fiber spacing and the volume fraction at the high fiber volume fraction.
The effect of the fiber microstructure on the fluid flow behavior was investigated. Simulations on the fiber models which have different fiber volume fractions and nearest inter-fiber spacing were performed to calculate the fiber permeability. The results reveal that the permeability is less sensitive to the nearest inter-fiber distance when the volume fraction is low. At the high volume fraction, the permeability declines with the decrease of the nearest inter-fiber spacing. The relation of permeability standard deviation, nearest inter-fiber spacing and volume fraction was studied. The standard deviation of permeability for different fiber microstructures depends only on the nearest inter-fiber spacing when the volume fraction is low, but it is determined by both the nearest inter-fiber spacing and the volume fraction at the high fiber volume fraction.
2011, 28(2): 54-58.
Abstract:
Mg-PbO2-Ti-PbO2-PTFE composite pyrotechnic thin films were prepared by magnetron sputtering and vacuum evaporation. The component of the thin film was analyzed by X-ray photoelectron spectroscopy (XPS). Combustion linear velocity was measured to analyze its combustion process, and bonding strength between the thin film and the substrate was measured. The results show that PbO2 thin film can be obtained by the vacuum evaporation, and good bonding strength exists between the composite pyrotechnic thin film and the substrate. The combustion linear velocity is (331.82±9.23) mm·s-1 under constraint-free condition and (435.98±18.60) mm·s-1 under constraint condition, with error smaller than 5%, meanwhile, combustion time and length have good linear relationship.
Mg-PbO2-Ti-PbO2-PTFE composite pyrotechnic thin films were prepared by magnetron sputtering and vacuum evaporation. The component of the thin film was analyzed by X-ray photoelectron spectroscopy (XPS). Combustion linear velocity was measured to analyze its combustion process, and bonding strength between the thin film and the substrate was measured. The results show that PbO2 thin film can be obtained by the vacuum evaporation, and good bonding strength exists between the composite pyrotechnic thin film and the substrate. The combustion linear velocity is (331.82±9.23) mm·s-1 under constraint-free condition and (435.98±18.60) mm·s-1 under constraint condition, with error smaller than 5%, meanwhile, combustion time and length have good linear relationship.
Preparation and properties of SiO2/collagen hydrolysate——poly (vinyl alcohol) hybrid composite films
2011, 28(2): 59-63.
Abstract:
With tetraethoxysilane (TEOS) as precursor, SiO2/collagen hydrolysate-poly(vinyl alcohol) hybrid composite films (SiO2/CH-PVA hybrid films) were in-situ prepared using a sol-gel technique. The influences of SiO2 on properties of hybrid films were investigated by means of swelling, thermogravimetry, FTIR spectroscopy, SEM diagram and tensile tests. The results show that the addition of SiO2 decreases the swelling ratio at equilibrium of hybrid films, slows down the swelling process, and effectively restricts the solubility of collagen hydrolysate in aqueous solution. Both adsorption peaks of Si—O—Si and Si—C in FTIR graphs indicate the formation of organic polymer/inorganic hybrid system, and SiO2 significantly improves thermal properties and mechanical properties of the hybrid films, with the increase of the SiO2 mass fractions from 0% to 20%, tensile strength of the hybrid film increases from 18 MPa to 25 MPa, and the elongation at break increases from 510% to 780%.
With tetraethoxysilane (TEOS) as precursor, SiO2/collagen hydrolysate-poly(vinyl alcohol) hybrid composite films (SiO2/CH-PVA hybrid films) were in-situ prepared using a sol-gel technique. The influences of SiO2 on properties of hybrid films were investigated by means of swelling, thermogravimetry, FTIR spectroscopy, SEM diagram and tensile tests. The results show that the addition of SiO2 decreases the swelling ratio at equilibrium of hybrid films, slows down the swelling process, and effectively restricts the solubility of collagen hydrolysate in aqueous solution. Both adsorption peaks of Si—O—Si and Si—C in FTIR graphs indicate the formation of organic polymer/inorganic hybrid system, and SiO2 significantly improves thermal properties and mechanical properties of the hybrid films, with the increase of the SiO2 mass fractions from 0% to 20%, tensile strength of the hybrid film increases from 18 MPa to 25 MPa, and the elongation at break increases from 510% to 780%.
2011, 28(2): 64-69.
Abstract:
The in suit intercalated polymerization of vinyl acetate (VAc) and organophilic montmorillonite (OMMT) was initiated via emulsion polymerization and obtained polyvinylacetate (PVAc)-nano-OMMT hybrid. Twofold blend composed of PVAc-nano-OMMT/PP-EVA was prepared by twin-screw extruder way, and X-ray diffraction (XRD) result shows that the structure of PVAc-nano-OMMT/PP-EVA is be treated as exfoliated nanocomposite structure during application of higher shear stress to system, and transmission electron microscopy (TEM) observation gives the same result directly. Thermo gravimetric analysis (TGA) results show that the initial decomposition temperature of PVAc-nano-OMMT/PP-EVA is greater than that of PP-EVA and nano-OMMT/PP-EVA , the existence of PVAc-nano-OMMT makes composite better thermal stability. In the PVAc-nano-OMMT/PP-EVA composite, PVAc-nano-OMMT has better toughness. Limiting oxygen index (LOI) and cone calorimeter test indicate that LOI of PVAc-nano-OMMT/PP-EVA is 24.1%, and has lower heat release rate, effective heat of combustion, smoke release course, and better flame retardancy.
The in suit intercalated polymerization of vinyl acetate (VAc) and organophilic montmorillonite (OMMT) was initiated via emulsion polymerization and obtained polyvinylacetate (PVAc)-nano-OMMT hybrid. Twofold blend composed of PVAc-nano-OMMT/PP-EVA was prepared by twin-screw extruder way, and X-ray diffraction (XRD) result shows that the structure of PVAc-nano-OMMT/PP-EVA is be treated as exfoliated nanocomposite structure during application of higher shear stress to system, and transmission electron microscopy (TEM) observation gives the same result directly. Thermo gravimetric analysis (TGA) results show that the initial decomposition temperature of PVAc-nano-OMMT/PP-EVA is greater than that of PP-EVA and nano-OMMT/PP-EVA , the existence of PVAc-nano-OMMT makes composite better thermal stability. In the PVAc-nano-OMMT/PP-EVA composite, PVAc-nano-OMMT has better toughness. Limiting oxygen index (LOI) and cone calorimeter test indicate that LOI of PVAc-nano-OMMT/PP-EVA is 24.1%, and has lower heat release rate, effective heat of combustion, smoke release course, and better flame retardancy.
2011, 28(2): 70-76.
Abstract:
The bamboo charcoal/phenolic resin conductive composite were prepared by compression molding technology, using bamboo charcoal carbonized at 900 ℃ as the conductive fillers, resin as the binder and carbon black as the additive. The influences of the particle size, resin content, carbon black content, molding pressure and curing temperature on the properties of the composite were investigated. The results show that the flexural strength of the composite increases as the content of phenolic resin increases, and the conductivity of the composite at first increases and then decreases sharply with increasing of the resin content. Increasing molding pressure can improve the conductivity and flexural strength of composite simultaneously. It is beneficial to improve the conductivity of composite by increasing the particle size of bamboo charcoal, black content and curing temperature, but the flexural strength of the composite changes. The optimum particle size, resin content, carbon black content, molding pressure and curing temperature should be ≤75 μm, 30%, 7.5%, 280 MPa and 180 ℃, respectively.
The bamboo charcoal/phenolic resin conductive composite were prepared by compression molding technology, using bamboo charcoal carbonized at 900 ℃ as the conductive fillers, resin as the binder and carbon black as the additive. The influences of the particle size, resin content, carbon black content, molding pressure and curing temperature on the properties of the composite were investigated. The results show that the flexural strength of the composite increases as the content of phenolic resin increases, and the conductivity of the composite at first increases and then decreases sharply with increasing of the resin content. Increasing molding pressure can improve the conductivity and flexural strength of composite simultaneously. It is beneficial to improve the conductivity of composite by increasing the particle size of bamboo charcoal, black content and curing temperature, but the flexural strength of the composite changes. The optimum particle size, resin content, carbon black content, molding pressure and curing temperature should be ≤75 μm, 30%, 7.5%, 280 MPa and 180 ℃, respectively.
Plasma treatment and biomimetic deposition of the 3D braided carbon fiber reinforced PEEK composites
2011, 28(2): 77-81.
Abstract:
In order to improve the bioactivity of the 3D braided carbon fiber reinforced PEEK composites (3D C/PEEK) used for high-performance hard tissue repair materials, the air plasma technology was used to treat the surface of the 3D C/PEEK, and then Ca-P layer on their surface was obtained through immersing in 1.5 times simulated body fluid (SBF) for 7 days. The effect of plasma treatment time on the surface appearance, hydrophility, chemical characterization and biomimetic deposition of the 3D C/PEEK was studied. The results show that the roughness, hydrophility and active groups of the 3D C/PEEK composite surfaces are improved with the increase of plasma treatment time. When 3D C/PEEK composite after plasma treatment is immersed in 1.5 times SBF for 7 days, the Ca-P layer would be formed on their surface, and the Ca-P layer of the 3D C/PEEK composite after plasma treatment for 120 s is more compact than that of after being treated for 30 s.
In order to improve the bioactivity of the 3D braided carbon fiber reinforced PEEK composites (3D C/PEEK) used for high-performance hard tissue repair materials, the air plasma technology was used to treat the surface of the 3D C/PEEK, and then Ca-P layer on their surface was obtained through immersing in 1.5 times simulated body fluid (SBF) for 7 days. The effect of plasma treatment time on the surface appearance, hydrophility, chemical characterization and biomimetic deposition of the 3D C/PEEK was studied. The results show that the roughness, hydrophility and active groups of the 3D C/PEEK composite surfaces are improved with the increase of plasma treatment time. When 3D C/PEEK composite after plasma treatment is immersed in 1.5 times SBF for 7 days, the Ca-P layer would be formed on their surface, and the Ca-P layer of the 3D C/PEEK composite after plasma treatment for 120 s is more compact than that of after being treated for 30 s.
2011, 28(2): 82-87.
Abstract:
The starch/polyvinyl alcohol(PVA) composite membranes were prepared through blending PVA with starch without any chemical treatment. The starch/PVA membranes were characterized by the mechanical assay, swelling test and FTIR analysis. The blood-compatibility of the blending films was evaluated by using the hemolysis assay, dynamic coagulation time and platelet consumption. The results show that the mechanical properties and blood-compatibility of composite membranes are improved as blending starch into PVA. When the mass ratio of PVA and starch is 4∶1, the composite films have quite good tensile strength and tensile strain, reaching to 13.73 MPa and 43.07% respectively, more excellent than those of other composite membranes.
The starch/polyvinyl alcohol(PVA) composite membranes were prepared through blending PVA with starch without any chemical treatment. The starch/PVA membranes were characterized by the mechanical assay, swelling test and FTIR analysis. The blood-compatibility of the blending films was evaluated by using the hemolysis assay, dynamic coagulation time and platelet consumption. The results show that the mechanical properties and blood-compatibility of composite membranes are improved as blending starch into PVA. When the mass ratio of PVA and starch is 4∶1, the composite films have quite good tensile strength and tensile strain, reaching to 13.73 MPa and 43.07% respectively, more excellent than those of other composite membranes.
2011, 28(2): 88-93.
Abstract:
Poly(butylene succinate) (PBS)-silk fibroin (SF) core-shell composite ultrafine fibrous membranes were successfully fabricated by coaxial electrospinning and characterized by FE-SEM and TEM, and the fibrous membranes morphologies prepared at different inner flow rates of spinning were observed.The structure, crystallinity and mechanical properties of the composite ultrafine fibrous membranes before and after treatment with methanol were characterized by means of FTIR, XRD and tensile tester.The results indicate that the typical core-shell structure could be found from observing SF shell layer, PBS core, and the cross-section of the fibers.The average diameter of the core-shell composite ultrafine fibers increases with the increasing of the inner flow rate of spinning.After being treated with methanol, the molecular structure of the shell layer SF changes from random conformation into β-sheet conformation. Because of the increasing of the shell thickness, absorption intensity of X-ray diffraction in the core PBS decreases, but the whole crystallization properties of PBS-SF core-shell ultrafine fibrous membranes does not change significantly.Compared with non-treatment, the tensile strength of the electrospun PBS-SF core-shell composite ultrafine fibrous membranes treated with methanol increases from 14.9 MPa to 17.2 MPa, and the failure strain decreases from 96.8% to 81.8%.
Poly(butylene succinate) (PBS)-silk fibroin (SF) core-shell composite ultrafine fibrous membranes were successfully fabricated by coaxial electrospinning and characterized by FE-SEM and TEM, and the fibrous membranes morphologies prepared at different inner flow rates of spinning were observed.The structure, crystallinity and mechanical properties of the composite ultrafine fibrous membranes before and after treatment with methanol were characterized by means of FTIR, XRD and tensile tester.The results indicate that the typical core-shell structure could be found from observing SF shell layer, PBS core, and the cross-section of the fibers.The average diameter of the core-shell composite ultrafine fibers increases with the increasing of the inner flow rate of spinning.After being treated with methanol, the molecular structure of the shell layer SF changes from random conformation into β-sheet conformation. Because of the increasing of the shell thickness, absorption intensity of X-ray diffraction in the core PBS decreases, but the whole crystallization properties of PBS-SF core-shell ultrafine fibrous membranes does not change significantly.Compared with non-treatment, the tensile strength of the electrospun PBS-SF core-shell composite ultrafine fibrous membranes treated with methanol increases from 14.9 MPa to 17.2 MPa, and the failure strain decreases from 96.8% to 81.8%.
2011, 28(2): 94-99.
Abstract:
To study the effect of photo degradation on the adhesion at coating/steel interface, the acrylic polyurethane varnish (APV) coatings on the steel were aged under outdoor field environments in the cities of Wuhan and Lhasa and the indoor artificial weathering environments. Pull-off adhesion measurement and electrochemical impedance spectroscopy were applied to investigate the adhesion of dry coating and the wet adhesion at coating/steel interface, respectively. It is found from pull-off measurements that the adhesion decreases with aging time increasing. The same trend is observed in the change of coating delamination area, which is deduced from EIS parameters. That is, the delamination area enlarges with aging time. Based on EIS results, it is found that the delamination area produced by fluorescent UV/condensation weathering device is larger than that by xenon lamp exposure and weathering equipment. This result is also verified by comparing the samples respectively exposed in Lhasa with higher irradiation intensity and Wuhan with less irradiation intensity, which indicates that the enhancement of UV intensity impairs the wet adhesion of coating. Thus, photo degradation undermines the adhesion at the coating/steel interface and further accelerates the underneath corrosion of coatings.
To study the effect of photo degradation on the adhesion at coating/steel interface, the acrylic polyurethane varnish (APV) coatings on the steel were aged under outdoor field environments in the cities of Wuhan and Lhasa and the indoor artificial weathering environments. Pull-off adhesion measurement and electrochemical impedance spectroscopy were applied to investigate the adhesion of dry coating and the wet adhesion at coating/steel interface, respectively. It is found from pull-off measurements that the adhesion decreases with aging time increasing. The same trend is observed in the change of coating delamination area, which is deduced from EIS parameters. That is, the delamination area enlarges with aging time. Based on EIS results, it is found that the delamination area produced by fluorescent UV/condensation weathering device is larger than that by xenon lamp exposure and weathering equipment. This result is also verified by comparing the samples respectively exposed in Lhasa with higher irradiation intensity and Wuhan with less irradiation intensity, which indicates that the enhancement of UV intensity impairs the wet adhesion of coating. Thus, photo degradation undermines the adhesion at the coating/steel interface and further accelerates the underneath corrosion of coatings.
2011, 28(2): 100-104.
Abstract:
The effect of cycles on the flexural fatigue strength for 2D carbon-felt C/C composites at room temperature was studied under the sinusoidal loading frequency of 10 Hz and stress ratio of 0.1.The microstructure of the pyrolytic carbon and the morphology of the fractured surfaces of the samples before and after being fatigued were observed by polarized light microscope(PLM) and SEM. The results show that the pyrolytic carbon consists of smooth laminar and isotropic structure. The fatigue limit of 2D carbon-felt reinforced carbon composites is found to be 76.5 MPa, 90% of the static flexural strength. The residual flexural strength and toughness of the materials after being fatigued are improved. The fiber/matrix interface bonding strength is weaken during fatigue-loading, while collaborative carrying capacity of fiber is improved. Therefore, the fatigue strength-enhancing behavior of C/C composites appears.
The effect of cycles on the flexural fatigue strength for 2D carbon-felt C/C composites at room temperature was studied under the sinusoidal loading frequency of 10 Hz and stress ratio of 0.1.The microstructure of the pyrolytic carbon and the morphology of the fractured surfaces of the samples before and after being fatigued were observed by polarized light microscope(PLM) and SEM. The results show that the pyrolytic carbon consists of smooth laminar and isotropic structure. The fatigue limit of 2D carbon-felt reinforced carbon composites is found to be 76.5 MPa, 90% of the static flexural strength. The residual flexural strength and toughness of the materials after being fatigued are improved. The fiber/matrix interface bonding strength is weaken during fatigue-loading, while collaborative carrying capacity of fiber is improved. Therefore, the fatigue strength-enhancing behavior of C/C composites appears.
2011, 28(2): 105-110.
Abstract:
A short carbon fiber (Cf) reinforced hydroxyapatite (HA) bio-composite was prepared by in-situ processing. In order to improve the interfacial bonding of Cf/HA bio-composite, Cf surface was modified by oxidation treatment. The pure HA structures, Cf surfaces and fracture surface morphologies of the bio-composite were analyzed using XRD, FTIR and SEM, respectively. The mechanical properties of the Cf/HA were tested by a universal testing machine. The result shows that after oxidation treatment the surface of Cf exhibits rough and a lot of —OH, —COOH appears. The bio-composite has the maximum relative density and the excellent mechanical properties when Cf mass fraction is 3%, flexural strength and flexural modulus reach the maximum values of 130 MPa and 36 GPa. SEM fracture surface morphologies of Cf/HA bio-composite indicate that when the mass fraction is less than 6%, Cf uniformly disperses in the HA matrix.
A short carbon fiber (Cf) reinforced hydroxyapatite (HA) bio-composite was prepared by in-situ processing. In order to improve the interfacial bonding of Cf/HA bio-composite, Cf surface was modified by oxidation treatment. The pure HA structures, Cf surfaces and fracture surface morphologies of the bio-composite were analyzed using XRD, FTIR and SEM, respectively. The mechanical properties of the Cf/HA were tested by a universal testing machine. The result shows that after oxidation treatment the surface of Cf exhibits rough and a lot of —OH, —COOH appears. The bio-composite has the maximum relative density and the excellent mechanical properties when Cf mass fraction is 3%, flexural strength and flexural modulus reach the maximum values of 130 MPa and 36 GPa. SEM fracture surface morphologies of Cf/HA bio-composite indicate that when the mass fraction is less than 6%, Cf uniformly disperses in the HA matrix.
2011, 28(2): 111-116.
Abstract:
The surface charge, wettability and roughness of ACA microcapsule membranes were firstly analyzed by streaming potential, contact angle and surface profile measurement. The effect of surface properties on the amount and conformation of fibrinogen adsorbed onto ACA microcapsules was then studied. The results show that there are a negative Zeta potential of ACA microcapsules which decrease with decreasing in chitosan deacetylation degree, indicating less positively charged groups on the surface. The surface wettability of ACA membranes made of chitosans with degree of deacetylation range from 60% to 90% has no statistical difference. ACA membranes have a granular structure surface. The surface roughness decreases with decreasing in chitosan deacetylation degree. Fibrinogen molecules are arranged on the surface of ACA microcapsules in a mixture of side-on and end-on configurations. With the decreasing in deacetylation degree of chitosan, the amount of protein adsorbed decreases, and more fibrinogen molecules adsorbed are in end-on configuration in this case. The results indicate that the surface properties of ACA microcapsules made of chitosans with different deacetylation degree have great effect on the amount and configuration of fibrinogen adsorbed.
The surface charge, wettability and roughness of ACA microcapsule membranes were firstly analyzed by streaming potential, contact angle and surface profile measurement. The effect of surface properties on the amount and conformation of fibrinogen adsorbed onto ACA microcapsules was then studied. The results show that there are a negative Zeta potential of ACA microcapsules which decrease with decreasing in chitosan deacetylation degree, indicating less positively charged groups on the surface. The surface wettability of ACA membranes made of chitosans with degree of deacetylation range from 60% to 90% has no statistical difference. ACA membranes have a granular structure surface. The surface roughness decreases with decreasing in chitosan deacetylation degree. Fibrinogen molecules are arranged on the surface of ACA microcapsules in a mixture of side-on and end-on configurations. With the decreasing in deacetylation degree of chitosan, the amount of protein adsorbed decreases, and more fibrinogen molecules adsorbed are in end-on configuration in this case. The results indicate that the surface properties of ACA microcapsules made of chitosans with different deacetylation degree have great effect on the amount and configuration of fibrinogen adsorbed.
2011, 28(2): 117-122.
Abstract:
The spherical alginate-trypsin microcapsules were prepared by the ionotropic gelation method, which formed the microcapsules by adding sodium alginate-trypsin into aqueous solution containing CaCl2. The infrared analysis shows that the matrix in microspheres is cross-linked by electrostatic attraction existed between Ca2+and—COO- in alginate. The SEM images indicate that "egg-box" structure and holes exist in the microparticles. The experiments were carried out to evaluate the properties of the microparticles such as drug loading rate, encapsulation efficiency rate and in vitro release rate. The results indicate that the in vitro release rate decreases with increasing the sodium alginate concentration, the encapsulation efficiency and the drug loading get the highest point when the mass ratio of sodium alginate to trypsin is 4 and the sodium alginate concentration in water is 4%. As the mass radio of sodium alginate to trypsin increases, the drug loading decreases and the encapsulation efficiency increases at first and then decreases.
The spherical alginate-trypsin microcapsules were prepared by the ionotropic gelation method, which formed the microcapsules by adding sodium alginate-trypsin into aqueous solution containing CaCl2. The infrared analysis shows that the matrix in microspheres is cross-linked by electrostatic attraction existed between Ca2+and—COO- in alginate. The SEM images indicate that "egg-box" structure and holes exist in the microparticles. The experiments were carried out to evaluate the properties of the microparticles such as drug loading rate, encapsulation efficiency rate and in vitro release rate. The results indicate that the in vitro release rate decreases with increasing the sodium alginate concentration, the encapsulation efficiency and the drug loading get the highest point when the mass ratio of sodium alginate to trypsin is 4 and the sodium alginate concentration in water is 4%. As the mass radio of sodium alginate to trypsin increases, the drug loading decreases and the encapsulation efficiency increases at first and then decreases.
2011, 28(2): 123-129.
Abstract:
Calcium phosphate microfibrils were fabricated by a homogeneous low-temperature deposition method in an aqueous solution. Chitosan (CS) rods were prepared via an in-situ precipitation processing, and hydroxyapatite(HA*)/CS composite rods were prepared on the base of the in-situ precipitation processing. The calcium phosphate microfibrils were transformed to hydroxyapatite style through the in-situ precipitation method. X-ray diffractometer (XRD) and scanning electron microscope (SEM) were performed to characterize structure and morphology of the calcium phosphate microfibrils and the hydroxyapatite crystals. Moreover, the transformation mechanism from calcium phosphate to hydroxyapatite was also discussed. XRD results show that the calcium phosphate transforms to hudroxyapatite through the in-situ precipitation processing. SEM results exhibit that the hydroxyapatite crystals are dispersed uniformly in the composites and formed an inlayed and occlusive structure with the CS matrix, which led to significant improvement in mechanical properties of the HA*/CS composite rods. Results indicate that the HA*/CS composites show much better mechanical properties than a commercial HA reinforced CS matrix composites. Flexural properties of the HA*/CS composites are increased with increasing HA* concentration within its saturated solubility, mass fraction 3.3%. Flexural strength and flexural modulus of the HA*/CS composites with 3.3% hydroxyapatite are 159.6 MPa and 5.1 GPa, respectively, which are 85.6% and 54.5% higher than the neat CS rod. The mechanical properties of the HA*/CS composites are much higher than cancellous bone, and close to compact bone.
Calcium phosphate microfibrils were fabricated by a homogeneous low-temperature deposition method in an aqueous solution. Chitosan (CS) rods were prepared via an in-situ precipitation processing, and hydroxyapatite(HA*)/CS composite rods were prepared on the base of the in-situ precipitation processing. The calcium phosphate microfibrils were transformed to hydroxyapatite style through the in-situ precipitation method. X-ray diffractometer (XRD) and scanning electron microscope (SEM) were performed to characterize structure and morphology of the calcium phosphate microfibrils and the hydroxyapatite crystals. Moreover, the transformation mechanism from calcium phosphate to hydroxyapatite was also discussed. XRD results show that the calcium phosphate transforms to hudroxyapatite through the in-situ precipitation processing. SEM results exhibit that the hydroxyapatite crystals are dispersed uniformly in the composites and formed an inlayed and occlusive structure with the CS matrix, which led to significant improvement in mechanical properties of the HA*/CS composite rods. Results indicate that the HA*/CS composites show much better mechanical properties than a commercial HA reinforced CS matrix composites. Flexural properties of the HA*/CS composites are increased with increasing HA* concentration within its saturated solubility, mass fraction 3.3%. Flexural strength and flexural modulus of the HA*/CS composites with 3.3% hydroxyapatite are 159.6 MPa and 5.1 GPa, respectively, which are 85.6% and 54.5% higher than the neat CS rod. The mechanical properties of the HA*/CS composites are much higher than cancellous bone, and close to compact bone.
2011, 28(2): 130-135.
Abstract:
The hydrothermal synthesis of hydroxyapatite whiskers (HAW) and the slurry-and-powder-metallurgy preparation of the hydroxyapatite whisker reinforced magnesium matrix composite (HAW/Mg) were described. The structures and the associated properties of HAW and HAW/Mg composites were characterized by XRD, FTIR, FESEM and TG. The relationship between urea content and crystal structure of HAW was explored. The thermal stability and microstructure of HAW/Mg composites were investigated. The results show that pure carbonate-containing HAW with belt-like morphology are acquired in this study; that the length and crystallinity of HA increase with the increase of urea content; that no chemical reaction occurs between HAW and Mg under 600 ℃ and oxidation of Mg is not deteriorated by HA; that HAW with high toughness distribute evenly in HAW/Mg composites.
The hydrothermal synthesis of hydroxyapatite whiskers (HAW) and the slurry-and-powder-metallurgy preparation of the hydroxyapatite whisker reinforced magnesium matrix composite (HAW/Mg) were described. The structures and the associated properties of HAW and HAW/Mg composites were characterized by XRD, FTIR, FESEM and TG. The relationship between urea content and crystal structure of HAW was explored. The thermal stability and microstructure of HAW/Mg composites were investigated. The results show that pure carbonate-containing HAW with belt-like morphology are acquired in this study; that the length and crystallinity of HA increase with the increase of urea content; that no chemical reaction occurs between HAW and Mg under 600 ℃ and oxidation of Mg is not deteriorated by HA; that HAW with high toughness distribute evenly in HAW/Mg composites.
2011, 28(2): 136-141.
Abstract:
A novel magnetoelectric (ME) composite which is suitable for magnetic sensor was fabricated, its structure is different from conventional ME composites. The strip PZT (Pb(ZrTi)O3) and Terfenol-D were laminated bonded with the thermoset epoxy. Terfenol-D layer was magnetized in its longitudinal direction and piezoelectric PZT strips were polled in their transverse direction. Every PZT strip was electrical series connected together, different from conventional 1-3 type ME composite. It gets much larger voltage output which is 2.2 times of conventional ME composite in the same magnetic field. The novel ME composite has higher magnetic field sensitivity and enhances the anti-noise characteristic. It’s a new way of using ME composite for small magnetic field sensor.
A novel magnetoelectric (ME) composite which is suitable for magnetic sensor was fabricated, its structure is different from conventional ME composites. The strip PZT (Pb(ZrTi)O3) and Terfenol-D were laminated bonded with the thermoset epoxy. Terfenol-D layer was magnetized in its longitudinal direction and piezoelectric PZT strips were polled in their transverse direction. Every PZT strip was electrical series connected together, different from conventional 1-3 type ME composite. It gets much larger voltage output which is 2.2 times of conventional ME composite in the same magnetic field. The novel ME composite has higher magnetic field sensitivity and enhances the anti-noise characteristic. It’s a new way of using ME composite for small magnetic field sensor.
2011, 28(2): 142-148.
Abstract:
SiC self-healing coatings containing borosilicate glass were prepared by polymer plyen on the 2D C/SiC composites. The microstructure morphologies of the 2D C/SiC composites with SiC coating containing borosilicate glass before and after oxidation were analyzed by SEM. The oxidation behaviors of the C/SiC composites with SiC coating containing borosilicate glass were studied at 700℃, 1000℃ and 1200℃ in static air and the oxidation behaviors resulted by different layers were analyzed. The results show that the glass phase produced by the SiC coating containing borosilicate glass can seal the defections (cracks and pores) existed in the coating, and with increasing the temperature and number of the coating layers, the C/SiC composites have lower mass loss during the oxidation and higher strength retention after oxidized.
SiC self-healing coatings containing borosilicate glass were prepared by polymer plyen on the 2D C/SiC composites. The microstructure morphologies of the 2D C/SiC composites with SiC coating containing borosilicate glass before and after oxidation were analyzed by SEM. The oxidation behaviors of the C/SiC composites with SiC coating containing borosilicate glass were studied at 700℃, 1000℃ and 1200℃ in static air and the oxidation behaviors resulted by different layers were analyzed. The results show that the glass phase produced by the SiC coating containing borosilicate glass can seal the defections (cracks and pores) existed in the coating, and with increasing the temperature and number of the coating layers, the C/SiC composites have lower mass loss during the oxidation and higher strength retention after oxidized.
2011, 28(2): 149-154.
Abstract:
3D needled C/SiC-TaC composites were prepared by slurry infiltration combined with reactive melt infiltration (RMI). The coefficient of thermal expansion (CTE) of the composites was tested from room temperature to 1400 ℃ using a thermal dilatometer before and after heat treatment. The CTE value of C/SiC-TaC is higher than that of C/SiC composites. The thermal expansion behavior was qualitatively analyzed from thermal stress, preparation method and composition. The results show that the CTE of the composites increases slowly as the temperature increases at low temperature range (below 1100 ℃). The increase in CTE is contributed by the thermal expansion of 90° non-woven cloth, TaC and SiC. The fluctuations of CTE are related to the structural stress, residual silicon and asymmetrical distribution of porosities. In high temperature range (above 1100 ℃), the controlling factors of thermal expansion are 0° non-woven cloth and interfacial thermal stress. The heat-treatment resulted in the decrease in CTE values at temperatures below 1100℃ and also change the CTE behavior of the composites at temperatures higher than 1100 ℃.
3D needled C/SiC-TaC composites were prepared by slurry infiltration combined with reactive melt infiltration (RMI). The coefficient of thermal expansion (CTE) of the composites was tested from room temperature to 1400 ℃ using a thermal dilatometer before and after heat treatment. The CTE value of C/SiC-TaC is higher than that of C/SiC composites. The thermal expansion behavior was qualitatively analyzed from thermal stress, preparation method and composition. The results show that the CTE of the composites increases slowly as the temperature increases at low temperature range (below 1100 ℃). The increase in CTE is contributed by the thermal expansion of 90° non-woven cloth, TaC and SiC. The fluctuations of CTE are related to the structural stress, residual silicon and asymmetrical distribution of porosities. In high temperature range (above 1100 ℃), the controlling factors of thermal expansion are 0° non-woven cloth and interfacial thermal stress. The heat-treatment resulted in the decrease in CTE values at temperatures below 1100℃ and also change the CTE behavior of the composites at temperatures higher than 1100 ℃.
2011, 28(2): 155-159.
Abstract:
Al2O3/Mo5Si3 nanocomposite powders was synthesized by mechanochemical reduction method using MoO3, Mo, Si and Al powders as the raw materials. The solid-state reaction process were studied. The results indicate that a mechanically induced self-propagation reaction is triggered during mechanical alloying of MoO3-Mo-Al-Si powders. The main phase of composite powders are Mo5Si3、 Mo3Si and Al2O3 after milling for 30 h. The content of Mo3Si and the burning loss of Si increase in the composite powder with the increase of Al2O3 content. The particle size of the composite powder is small which between 1 μm and 3 μm. The grain size of Mo5Si3、 Mo3Si and Al2O3 are 31~79.3 nm with nano-crystalline structure of the Al2O3/Mo5Si3 composite powders with mass fraction of 20%~40% Al2O3 after milling for 30 h. Al2O3/Mo5Si3 composite powder is very stable during annealing at 1000 ℃ for 1 h and no transformation takes place.
Al2O3/Mo5Si3 nanocomposite powders was synthesized by mechanochemical reduction method using MoO3, Mo, Si and Al powders as the raw materials. The solid-state reaction process were studied. The results indicate that a mechanically induced self-propagation reaction is triggered during mechanical alloying of MoO3-Mo-Al-Si powders. The main phase of composite powders are Mo5Si3、 Mo3Si and Al2O3 after milling for 30 h. The content of Mo3Si and the burning loss of Si increase in the composite powder with the increase of Al2O3 content. The particle size of the composite powder is small which between 1 μm and 3 μm. The grain size of Mo5Si3、 Mo3Si and Al2O3 are 31~79.3 nm with nano-crystalline structure of the Al2O3/Mo5Si3 composite powders with mass fraction of 20%~40% Al2O3 after milling for 30 h. Al2O3/Mo5Si3 composite powder is very stable during annealing at 1000 ℃ for 1 h and no transformation takes place.
2011, 28(2): 160-164.
Abstract:
The Al2O3/Ni-Co composites with different additives were fabricated by pulse current electrodeposition, the microstructures of Al2O3/Ni-Co composites were studied by TEM and EDS. The effects of additives on the smoothness, microhardness, plasticity at room temperature and at high temperature were compared. SEM was employed to examine the microstructures of the deformed samples. The hardness, fracture strength, elongation at room temperature and at superplastic temperature of the Al2O3/Ni-Co composite reach HV469, 1150 MPa, 7% and 417% respectively, when the saccharin was used as additive.
The Al2O3/Ni-Co composites with different additives were fabricated by pulse current electrodeposition, the microstructures of Al2O3/Ni-Co composites were studied by TEM and EDS. The effects of additives on the smoothness, microhardness, plasticity at room temperature and at high temperature were compared. SEM was employed to examine the microstructures of the deformed samples. The hardness, fracture strength, elongation at room temperature and at superplastic temperature of the Al2O3/Ni-Co composite reach HV469, 1150 MPa, 7% and 417% respectively, when the saccharin was used as additive.
2011, 28(2): 165-169.
Abstract:
In order to investigate the damage evolution of 3-dimensional braided carbon-fiber reinforced SiC matrix composite (3D C/SiC) during fatigue and establish the model of relationship between variation rate of electrical resistance (ΔR/R0) and fatigue cycles, tension-tension fatigue tests of 3D C/SiC were carried out under a maximum stress of 250, 255, 260 MPa, a sinusoidal loading frequency of 20 Hz, a stress ratio of 0.1. ΔR/R0 was measured by electrical resistance appearance. The experimental results show that its ΔR/R0 decreases at the first cycle and then monotonic increases with the increase of fatigue cycles, which mainly consist of steady increases, spurting and abrupt increases. Finally, based on the damage mechanics theory, ΔR/R0 is selected as the fatigue damage variable, and the relationship between ΔR/R0 and fatigue cycles was obtained, the modeling results have good agreement with the experimental results.
In order to investigate the damage evolution of 3-dimensional braided carbon-fiber reinforced SiC matrix composite (3D C/SiC) during fatigue and establish the model of relationship between variation rate of electrical resistance (ΔR/R0) and fatigue cycles, tension-tension fatigue tests of 3D C/SiC were carried out under a maximum stress of 250, 255, 260 MPa, a sinusoidal loading frequency of 20 Hz, a stress ratio of 0.1. ΔR/R0 was measured by electrical resistance appearance. The experimental results show that its ΔR/R0 decreases at the first cycle and then monotonic increases with the increase of fatigue cycles, which mainly consist of steady increases, spurting and abrupt increases. Finally, based on the damage mechanics theory, ΔR/R0 is selected as the fatigue damage variable, and the relationship between ΔR/R0 and fatigue cycles was obtained, the modeling results have good agreement with the experimental results.
2011, 28(2): 170-173.
Abstract:
Hydroxyapatite-zirconia composite powders were prepared using the hydrothermal-deposition in-situ stepwise reaction method. The XRD and TEM were employed to characterize the phase, morphology and size of the resulting powders. The composite ceramic samples were fabricated via moulding and thermal treatment of the composite powders. The results show that the as-synthesized powders with nanosize are composed of well-crystallized tetragonal phase ZrO2 core clad with hydroxyapatite shells to fabricate the core-shell structure (HA-n-ZrO2). With the increase of HA mass fraction from 0 to 100%, the as-clad HA shells get thicker gradually, but the bending strength and the mean Vickers hardness of the resulting ceramic samples moulded by the composite powders become lower from 183 MPa to 61 MPa and 781.75 MPa to 131.76 MPa, respectively.
Hydroxyapatite-zirconia composite powders were prepared using the hydrothermal-deposition in-situ stepwise reaction method. The XRD and TEM were employed to characterize the phase, morphology and size of the resulting powders. The composite ceramic samples were fabricated via moulding and thermal treatment of the composite powders. The results show that the as-synthesized powders with nanosize are composed of well-crystallized tetragonal phase ZrO2 core clad with hydroxyapatite shells to fabricate the core-shell structure (HA-n-ZrO2). With the increase of HA mass fraction from 0 to 100%, the as-clad HA shells get thicker gradually, but the bending strength and the mean Vickers hardness of the resulting ceramic samples moulded by the composite powders become lower from 183 MPa to 61 MPa and 781.75 MPa to 131.76 MPa, respectively.
2011, 28(2): 174-178.
Abstract:
With Al-SiO2-sucrose as reactive system, Al2O3-Si hollow ceramic microspheres were synthesized using SHS flame quenched technology. Reaction mechanism of hollow ceramic microspheres was studied. The results show that sphere, similar sphere and irregular powders constitute the spraying products. The sphere and similar sphere powders are hollow structure and constitutive of Al2O3-Si diphase and maybe a few unreactive SiO2. The irregular powders are constitutive of SiC、 C and maybe some SiO2 and reactive but not spherical particles. High reactive heat quantity and fast reaction rate make for the formation of ceramic droplets and the gas produced by carbon is the key factor to form hollow structure. All above three factors determine the formation of hollow ceramic microspheres.
With Al-SiO2-sucrose as reactive system, Al2O3-Si hollow ceramic microspheres were synthesized using SHS flame quenched technology. Reaction mechanism of hollow ceramic microspheres was studied. The results show that sphere, similar sphere and irregular powders constitute the spraying products. The sphere and similar sphere powders are hollow structure and constitutive of Al2O3-Si diphase and maybe a few unreactive SiO2. The irregular powders are constitutive of SiC、 C and maybe some SiO2 and reactive but not spherical particles. High reactive heat quantity and fast reaction rate make for the formation of ceramic droplets and the gas produced by carbon is the key factor to form hollow structure. All above three factors determine the formation of hollow ceramic microspheres.
2011, 28(2): 179-184.
Abstract:
Rare earth (RE) oxides doping yttria stabilized zirconia (YSZ) is an effective path to improve the thermal-resistance and high-temperature stability of traditional ceramic YSZ thermal barrier coatings. Gd2O3-Yb2O3 co-doped YSZ (contain 3.5%Y2O3, mole fraction) (GY-YSZ) was prepared by sintering at 1500 ℃ for 24 h. The crystal structure and phase composition of the GY-YSZ were studied by XRD analysis. Laser flash method was used to investigate the effects of doping rare earth oxides on the thermophysical property of GY-YSZ. The results show that the thermal conductivity of the GY-YSZ doped with 2.0%~3.0% mole fraction of Gd2O3 and Yb2O3 is 0.90~1.15 W·(m·K)-1, which is reduced by 30% at least than that of YSZ and proves the higher thermal-resistance property of the GY-YSZ. The influence mechanism of doping rare earth oxides on the thermal physical property of YSZ is that co-doping with Gd2O3 and Yb2O3 results in lattice distortion and content variation of monoclinic phase (M), tetragonal phase (T) and cubic phase (C) in YSZ.
Rare earth (RE) oxides doping yttria stabilized zirconia (YSZ) is an effective path to improve the thermal-resistance and high-temperature stability of traditional ceramic YSZ thermal barrier coatings. Gd2O3-Yb2O3 co-doped YSZ (contain 3.5%Y2O3, mole fraction) (GY-YSZ) was prepared by sintering at 1500 ℃ for 24 h. The crystal structure and phase composition of the GY-YSZ were studied by XRD analysis. Laser flash method was used to investigate the effects of doping rare earth oxides on the thermophysical property of GY-YSZ. The results show that the thermal conductivity of the GY-YSZ doped with 2.0%~3.0% mole fraction of Gd2O3 and Yb2O3 is 0.90~1.15 W·(m·K)-1, which is reduced by 30% at least than that of YSZ and proves the higher thermal-resistance property of the GY-YSZ. The influence mechanism of doping rare earth oxides on the thermal physical property of YSZ is that co-doping with Gd2O3 and Yb2O3 results in lattice distortion and content variation of monoclinic phase (M), tetragonal phase (T) and cubic phase (C) in YSZ.
2011, 28(2): 185-190.
Abstract:
In order to prepare composites with fine grains, uniform microstructure, and improving the mechanics performance significantly, different contents of carbon nanotubes (CNTs) reinforced aluminum matrix composites were prepared by friction stir processing (FSP). The microstructure, tensile properties and morphologies of tensile fracture surface were analyzed. The results show that CNTs are embedded in the aluminum matrix. The grain size is fine in the center of the friction stir zone. CNTs and matrix have a good combination. There are no obvious defects in the composites. CNTs improve the mechanics performance of the matrix. The tensile strength of aluminum matrix increases with the increasing of CNTs contents. The tensile strength reaches to 201 MPa when the volume fraction of CNTs is 7%, which is 2.2 times than that of matrix. The composites show the characteristics of brittle fracture at the macrostructure and plastic fracture at the microstructure. The fracture mechanism dominates by CNTs/Al interface debonding, matrix tearing and reinforced fiber fracturing.
In order to prepare composites with fine grains, uniform microstructure, and improving the mechanics performance significantly, different contents of carbon nanotubes (CNTs) reinforced aluminum matrix composites were prepared by friction stir processing (FSP). The microstructure, tensile properties and morphologies of tensile fracture surface were analyzed. The results show that CNTs are embedded in the aluminum matrix. The grain size is fine in the center of the friction stir zone. CNTs and matrix have a good combination. There are no obvious defects in the composites. CNTs improve the mechanics performance of the matrix. The tensile strength of aluminum matrix increases with the increasing of CNTs contents. The tensile strength reaches to 201 MPa when the volume fraction of CNTs is 7%, which is 2.2 times than that of matrix. The composites show the characteristics of brittle fracture at the macrostructure and plastic fracture at the microstructure. The fracture mechanism dominates by CNTs/Al interface debonding, matrix tearing and reinforced fiber fracturing.
2011, 28(2): 191-195.
Abstract:
The nanocomposite oxides (Fe2O3-CuO)as anode materials for lithium-ion batteries were synthesized via the hydrothermal method and the precipitation method. The crystalline structure and the electrochemical performance of the as-synthesized samples were investigated. The results show that the nano Fe2O3-CuO composite oxides obtained by the hydrothermal method are blocky, with narrow size distribution around 30 nm, while spherical, with narrow size distribution around 90 nm by the precipitation method. It is also found that the discharge capacity of the samples via the precipitation method is better than those of the samples obtained via the hydrothermal method.
The nanocomposite oxides (Fe2O3-CuO)as anode materials for lithium-ion batteries were synthesized via the hydrothermal method and the precipitation method. The crystalline structure and the electrochemical performance of the as-synthesized samples were investigated. The results show that the nano Fe2O3-CuO composite oxides obtained by the hydrothermal method are blocky, with narrow size distribution around 30 nm, while spherical, with narrow size distribution around 90 nm by the precipitation method. It is also found that the discharge capacity of the samples via the precipitation method is better than those of the samples obtained via the hydrothermal method.
2011, 28(2): 196-200.
Abstract:
A high temperature infrared radiat coating for energy saving was developed with iron chromium based high emissivity powder, binder, additives and sintering aids. The coatings were sintered at different temperatures. The changes of microstructures, phase compositions and the bonding interface between the coating and firebrick were investigated by thermal analysis, SEM, XRD and electron microprobe analysis. The results indicate that the spinel phase formed by iron chromium based high emissivity powder is uniformly distributed in the Al-Si matrix phase, the entire infrared radiation emissivity of the coating is 0.89.The electron microprobe analysis and thermal shock tests show high bonding strength between the coating and the firebrick.
A high temperature infrared radiat coating for energy saving was developed with iron chromium based high emissivity powder, binder, additives and sintering aids. The coatings were sintered at different temperatures. The changes of microstructures, phase compositions and the bonding interface between the coating and firebrick were investigated by thermal analysis, SEM, XRD and electron microprobe analysis. The results indicate that the spinel phase formed by iron chromium based high emissivity powder is uniformly distributed in the Al-Si matrix phase, the entire infrared radiation emissivity of the coating is 0.89.The electron microprobe analysis and thermal shock tests show high bonding strength between the coating and the firebrick.
2011, 28(2): 201-205.
Abstract:
The global buckling is one of the important failure modes of stitched foam-core composite sandwich plates. Considering the characters that the thicknesses of stitched foam-core composite sandwich are always relatively large and the thicknesses of face panel and core are obviously different, in addition that the stitching process influences the property evidently, the finite element program for stability analysis of stitched foam-core composite sandwich plates was written based on higher-order shear deformation theory. The calculation results revealed the consistency with the results in references and experiments. The relationship between the stability of stitched foam-core composite sandwich plates and stitching parameters (including step, space and radius of needle) and structural parameters (including stacking angles in face panel, thickness of the core and length of the sandwich) was discussed.
The global buckling is one of the important failure modes of stitched foam-core composite sandwich plates. Considering the characters that the thicknesses of stitched foam-core composite sandwich are always relatively large and the thicknesses of face panel and core are obviously different, in addition that the stitching process influences the property evidently, the finite element program for stability analysis of stitched foam-core composite sandwich plates was written based on higher-order shear deformation theory. The calculation results revealed the consistency with the results in references and experiments. The relationship between the stability of stitched foam-core composite sandwich plates and stitching parameters (including step, space and radius of needle) and structural parameters (including stacking angles in face panel, thickness of the core and length of the sandwich) was discussed.
2011, 28(2): 206-210.
Abstract:
A micromechanical finite element method——parameterized double-random distribution model of virtual reality was developed. Integrated with the real microstructure character of fiber reinforced resin matrix composites and discrete characteristics of testing results about mechanical properties for monofilaments, random distribution of fiber arrangement and fiber strength were both simulated in the model. The reliability of parameter random distribution model was studied with moving window method and the size of its representative volume element was determined. The predicted formulas of elastic modulus for unidirectional composites were derived based on energy method. Combined with energy method and progressive failure analysis, elastic modulus and strength properties of unidirectional fiber reinforced resin matrix composite T300/5228 were respectively predicted by the micromechanical finite element method. The numerical results agree well with most experimental data, which shows that the micromechanical finite element method can predict the mechanical properties of composites correctly.
A micromechanical finite element method——parameterized double-random distribution model of virtual reality was developed. Integrated with the real microstructure character of fiber reinforced resin matrix composites and discrete characteristics of testing results about mechanical properties for monofilaments, random distribution of fiber arrangement and fiber strength were both simulated in the model. The reliability of parameter random distribution model was studied with moving window method and the size of its representative volume element was determined. The predicted formulas of elastic modulus for unidirectional composites were derived based on energy method. Combined with energy method and progressive failure analysis, elastic modulus and strength properties of unidirectional fiber reinforced resin matrix composite T300/5228 were respectively predicted by the micromechanical finite element method. The numerical results agree well with most experimental data, which shows that the micromechanical finite element method can predict the mechanical properties of composites correctly.
2011, 28(2): 211-216.
Abstract:
The tearing properties and the punch properties were investigated on the flexible composites from the aerostat by experiments and numerical simulations. For tearing tests of specimens with different quench width and total width, the typical brittle fracture is displayed in the crack propagation process. The tearing fracture process from the numerical simulations with linear fracture model is consistent with the experimental results. With the stress intensity factor calculated, the maximum loading level for the tearing tests reduce with the increment of the quench width ratio which agree well with the experimental results. The FEA simulations with the fracture strain as the crack propagation criteria rebuilt the experimental results of the punch tests. Larger displacement is needed for the specimens with larger diameter to perform the same fracture strain at the punch center while the maximum loading level is the same for different specimens for the stress at the punch center.
The tearing properties and the punch properties were investigated on the flexible composites from the aerostat by experiments and numerical simulations. For tearing tests of specimens with different quench width and total width, the typical brittle fracture is displayed in the crack propagation process. The tearing fracture process from the numerical simulations with linear fracture model is consistent with the experimental results. With the stress intensity factor calculated, the maximum loading level for the tearing tests reduce with the increment of the quench width ratio which agree well with the experimental results. The FEA simulations with the fracture strain as the crack propagation criteria rebuilt the experimental results of the punch tests. Larger displacement is needed for the specimens with larger diameter to perform the same fracture strain at the punch center while the maximum loading level is the same for different specimens for the stress at the punch center.
2011, 28(2): 217-221.
Abstract:
Based on thin-wall vessel theory and null-unloading-residual-strain assumption, a simplified engineering formula for autofrettage pressure of composite overwrapped pressure vessels (COPV) was deduced, in which the effects of bilinear isotropic and kinetic hardening behavior for metal inner were considered respectively. The validity of the engineering formula was verified through comparing with FEM. As an example, the residual strain field after autofrettage technique and corresponding stress field under the service loading case for a typical COPV were studied. The results indicate that the load capacity of COPV significantly increases by means of the autofrettage technique provide in this paper.
Based on thin-wall vessel theory and null-unloading-residual-strain assumption, a simplified engineering formula for autofrettage pressure of composite overwrapped pressure vessels (COPV) was deduced, in which the effects of bilinear isotropic and kinetic hardening behavior for metal inner were considered respectively. The validity of the engineering formula was verified through comparing with FEM. As an example, the residual strain field after autofrettage technique and corresponding stress field under the service loading case for a typical COPV were studied. The results indicate that the load capacity of COPV significantly increases by means of the autofrettage technique provide in this paper.
2011, 28(2): 222-230.
Abstract:
A representative volume element (RVE) taking account of the contact and jamming of yarns, coupled with the periodical boundary condition was chosen to simulate the progressive damage behavior of 3D braided composites. The tensile strengths were predicted from the calculated stress-strain curves. The stiffness matrix of the damaged material was established by the method of introducing damage variables to the strain energy density function. The damage evolvement method by introducing damage variables of different damage modes were considered as the progressive damage of the material integral points. Hashin and Tsai-Wu failure criterions were adopted to identify damage initiation of the braiding yarns. They were analyzed and discussed by comparing numerical predictions with two typical specimens’ experimental data. The results indicate that numerical simulation based on Tsai-Wu failure criteria with various damage modes gives good agreement compared to experimental results, Hashin criteria is not suitable for predicting the occurring of damage of braiding yarns. Specimens with different braided angles show different damage mechanisms.
A representative volume element (RVE) taking account of the contact and jamming of yarns, coupled with the periodical boundary condition was chosen to simulate the progressive damage behavior of 3D braided composites. The tensile strengths were predicted from the calculated stress-strain curves. The stiffness matrix of the damaged material was established by the method of introducing damage variables to the strain energy density function. The damage evolvement method by introducing damage variables of different damage modes were considered as the progressive damage of the material integral points. Hashin and Tsai-Wu failure criterions were adopted to identify damage initiation of the braiding yarns. They were analyzed and discussed by comparing numerical predictions with two typical specimens’ experimental data. The results indicate that numerical simulation based on Tsai-Wu failure criteria with various damage modes gives good agreement compared to experimental results, Hashin criteria is not suitable for predicting the occurring of damage of braiding yarns. Specimens with different braided angles show different damage mechanisms.
2011, 28(2): 231-234.
Abstract:
A honeycomb sandwich structure embedded with the microstrip antenna of conformal load-bearing antenna structure (CLAS) was designed and fabricated. The mechanical property was analyzed by finite element method (FEM). Compared with the 3-point bending test, the calculated results from FEM are agree well with those from experiments. The influences of honeycomb thickness on the mechanical and electric properties were investigated. The results show that the CLAS with 8~14 mm thick honeycomb has not only have high gain and low return loss, but also have good mechanical properties.
A honeycomb sandwich structure embedded with the microstrip antenna of conformal load-bearing antenna structure (CLAS) was designed and fabricated. The mechanical property was analyzed by finite element method (FEM). Compared with the 3-point bending test, the calculated results from FEM are agree well with those from experiments. The influences of honeycomb thickness on the mechanical and electric properties were investigated. The results show that the CLAS with 8~14 mm thick honeycomb has not only have high gain and low return loss, but also have good mechanical properties.
2011, 28(2): 235-241.
Abstract:
Based on the 2D finite element model, changes of the fibre distortion region in the preform were investigated during the Z-pinning process. The shape and size of the resin zone were quantitatively characterized. Characteristic parameters of the fibre misalignment angle and the non-uniform distribution of local fibre content were made, and the rule of the fibre non-uniform distribution was obtained. On this basis, influence of the Pin diameter on the microstructure of the laminates was numerically analyzed. The results show that the Pin diameter has a great impact on the resin rich zone. The misalignment angle and fibre volume fraction increase with the Pin diameter, however, the maximum does not change significantly.
Based on the 2D finite element model, changes of the fibre distortion region in the preform were investigated during the Z-pinning process. The shape and size of the resin zone were quantitatively characterized. Characteristic parameters of the fibre misalignment angle and the non-uniform distribution of local fibre content were made, and the rule of the fibre non-uniform distribution was obtained. On this basis, influence of the Pin diameter on the microstructure of the laminates was numerically analyzed. The results show that the Pin diameter has a great impact on the resin rich zone. The misalignment angle and fibre volume fraction increase with the Pin diameter, however, the maximum does not change significantly.
