Ultrafine full-vulcanized polybutadiene rubber（UFBR） with particle sizes of ca.50―100 nm were used for modifying mechanical and processing performances of polypropylene（PP） with PP-g-maleic anhydride（PP-g-MA） a...Ultrafine full-vulcanized polybutadiene rubber（UFBR） with particle sizes of ca.50―100 nm were used for modifying mechanical and processing performances of polypropylene（PP） with PP-g-maleic anhydride（PP-g-MA） as a compatibilizer for enhancing the interfacial adhesion between the two components.The morphology,dynamical rheology response and mechanical properties of the blends were characterized by means of SEM,rheometer and tensile test,respectively.The results show that the ternary PP/UFBR blends compatibilized with PP-g-MA possess rheological behaviors like highly branched PP,while no obvious strain hardening is observed in its control binary PP/UFBR blends,a low level of PP-g-MA in PP/UFBR blends can even endow the material with rheological characteristics of high melt strength materials like highly branched PP.The enhancement interfacial interaction between the UFBR particles and PP matrix accounting for the rheological behavior of compatibilized blends and effectiveness of PP-g-MA were proposed and proved.展开更多
Foamable high melt strength polypropylene （HMSPP） was prepared by grafting styrene （St） onto polypropylene （PP） and simultaneously introducing poly- dimethylsiloxane （PDMS） through a one-step melt extru- sion ...Foamable high melt strength polypropylene （HMSPP） was prepared by grafting styrene （St） onto polypropylene （PP） and simultaneously introducing poly- dimethylsiloxane （PDMS） through a one-step melt extru- sion process. The effect of PDMS viscosity on the foaming behavior of HMSPP was systematically investigated using supercritical CO2 as the foaming agent. The results show that the addition of PDMS has little effect on the grafting reaction of St and HMSPP exhibits enhanced elastic response and obvious strain hardening effect. Though the CO2 solubility of HMSPP with PDMS （PDMS-HMSPP） is lower than that of HMSPP without PDMS, especially for PDMS with low viscosity, the PDMS-HMSPP foams exhibit narrow cell size distribution and high cell density. The fracture morphology of PDMS-HMSPP shows that PDMS with low viscosity disperses more easily and uniformly in HMSPP matrix, leading to form small domains during the extrusion process. These small domains act as bubble nucleation sites and thus may be responsible for the improved foaming performance of HMSPP.展开更多
This study investigated that epoxidized soybean oil （ESO） was blended as plasticizer with poly （lactic acid） （PLA） and its effects on the melt rheological properties, such as melt flow index, apparent shear visc...This study investigated that epoxidized soybean oil （ESO） was blended as plasticizer with poly （lactic acid） （PLA） and its effects on the melt rheological properties, such as melt flow index, apparent shear viscosity, and melt strength of the blends. PLA was blended by the twin-screw plastic extruder at five mass fractions： 3%, 6%, 9%, 12%, and 15% （based on PLA mass）. Melt flow index （MFI） was examined with a melt flow indexer. The results indicate that the blends of PLA/ESO had higher MFI than pure PLA, except for MFI at 9% reaching to the lowest point, even lower than that of pure PLA. Melt rheological properties were studied by a capillary rheometer in a temperature range of 160-180℃. The blends exhibited shear-thinning behavior and the apparent shear viscosity was well described by the power law in this shear rate region. The melt strength of PLA plasticized with 6% ESO reached the maximums. ESO was more effective in increasing the melt strength at the mass fractions less than 6%, which could toughen the blends to some extent. Therefore, the authors suggested the optimum addition level of 6%-9% ESO will get good melt rheological performance balance.展开更多
It is important, for electronic application, to decrease the melting point of Sn-5Sb solder alloy because it is relatively high as compared with the most popular eutectic Pb-Sn solder alloy. Adding Au or Ag can decrea...It is important, for electronic application, to decrease the melting point of Sn-5Sb solder alloy because it is relatively high as compared with the most popular eutectic Pb-Sn solder alloy. Adding Au or Ag can decrease the onset melting temperature （233℃） of this alloy to 203,5℃ and 216℃, respectively. The results indicate that the Sn-5Sb-i.5Au alloy has very good ultimate tensile strength （UTS）, ductility, and fusion heat, which are better than both those of the Sn-5Sb-3.SAg and Sn-5Sb alloys. The formation of intermetallic compounds （IMCs） AuSn4 and Ag3Sn enhanced the SbSn precipitates in the solidification microstructure microstructure stability, while retained the formation of thus significantly improved the strength and ductility For all alloys, both UTS and yield stress （σy） increase with increasing strain rate and decrease with increasing temperature in tensile tests, but changes of ductility are generally small with inconsistent trends.展开更多
The porcelain fracture caused by low metal-ceramic bond strength is a critical issue in porcelain fused to metal（PFM） restorations. Surface roughening methods, such as sand blasting, acid etching and alkaline degrea...The porcelain fracture caused by low metal-ceramic bond strength is a critical issue in porcelain fused to metal（PFM） restorations. Surface roughening methods, such as sand blasting, acid etching and alkaline degreasing for the metal matrix are used to increase bond strength. However, the metal matrix of PFM processed by selective laser melting（SLM） has natural rough surface. To explore the effect of the original roughness on metal-ceramic bond strength, two groups of specimen are fabricated by SLM. One group of specimen surface is polished smooth while another group remains the original rough surface. The dental porcelain is fused to the specimens＇ surfaces according to the ISO 9693：1999 standard. To gain the bond strength, a three-point bending test is carried out and X ray energy spectrum analysis（EDS）, scanning electron microscope（SEM） are used to show fracture mode. The results show that the mean bond strength is 116.5 16 MPa of the group with rough surface（Ra= 17.2）, and the fracture mode is cohesive. However, when the surface is smooth （Ra =3.8）, the mean bond strength is 74.5 MPa _＋ 5 MPa and the fracture mode is mixed. The original surface with prominent structures formed by the partly melted powder particles, not only increases surface roughness but also significantly improves the bond strength by forming strong mechanical lock effect. Statistical analysis （Student＇s t-test） demonstrates a significant difference （p〈0.05） of the mean value of bond strength between the two groups. The experiments indicate the natural rough surface can enhance the metal-ceramic bond strength to over four times the minimum value （25 MPa） of the ISO 9693：1999 standard. It is found that the natural rough surface of SLM-made PFM can eliminate the porcelain collapse defect produced by traditional casting method in PFM restorations.展开更多
An aromatic azo-polymer, poly（thiourea-azo-sulfone） （PTAS）, has been prepared using 4-（4- aminophenylsulfonyl）benzenamine and diazonium salt solution of 2,6odiaminopyridine. PTAS was easily processable using pol...An aromatic azo-polymer, poly（thiourea-azo-sulfone） （PTAS）, has been prepared using 4-（4- aminophenylsulfonyl）benzenamine and diazonium salt solution of 2,6odiaminopyridine. PTAS was easily processable using polar solvents and had high molar mass 63 × 103 g.mo1-1 according to GPC. Mechanically and thermally stable and electrically conducting polymer/CNTs nano-composites were obtained via melt processing technique. Fine distribution of CNTs in a polymer matrix performed an essential role in the preparation of polymer/CNTs nano-composites based on interfacial interaction between CNTs and polymer matrix. Scanning electron micrographs showed good dispersion of filler and adhesion of matrix on the surface of nanotubes. Accordingly, increasing the amount of CNTs from 0.1 wt% to 5 wt% increased the electrical conductivity from 2.99 S.cm-1 to 3.56 S.cm-1. Mechanical strength of functional nanotubes-based hybrids was enhanced from 43.22 MPa to 65.02 MPa compared with that of hybrids with non-functional filler in matrix 37.21 MPa. A rapport between nanotube loading and thermal stability of the materials was also observed. 10% gravimetric loss temperature was increased from 528 ~C to 578 ~C, while glass transition was improved from 241 ℃ to 271 ℃. Adding up of small quantity of functional CNTs strongly affected the tensile, electrical and thermal properties of materials. Improvement of the physical properties of CNT-reinforced polymer nano-composites was ascribed to the melt processing technique.展开更多
The melt spun ribbons of Al-La-Y-Ni(Fe)quaternary alloys were prepared by a single- roller melt spinning technique in vacuum.Their amorphous nature,mechanical properties and tensile fracture surface morphology were in...The melt spun ribbons of Al-La-Y-Ni(Fe)quaternary alloys were prepared by a single- roller melt spinning technique in vacuum.Their amorphous nature,mechanical properties and tensile fracture surface morphology were investigated.The experimental results show that amorphous alloys with high strength and good ductility as well as good thermal stability can be achieved in Al-La-Y-Ni(Fe)system,when the alloy contains 85—90 at.-% Al and less than 10 at.-% La+Y.The maximum tensile fracture strength(σ_f) and microhardness(HV)are as high as 760 MPa and 294 DPN,respectively.The as- quenched ribbons can be bent 180 degree without fracturing.The dominant factors for formation of amorphous Al-La-Y-Ni(Fe)are the strong attractive interaction among Al, La,Y and a decrease of melting temperature.展开更多
As the aircraft and aerospace industry and the automobile industry are developed, the demand of reliable materials with high strength and high toughness is steadily increased. The grain miniature method which improves...As the aircraft and aerospace industry and the automobile industry are developed, the demand of reliable materials with high strength and high toughness is steadily increased. The grain miniature method which improves the ductility and the toughness simultaneously under high strength is the miniature of the casting microstructure. In this paper, the Nb which affects the austenite grain miniature is added by 0.00%, 0.03% and 0.06% in this steel and the ingot is manufactured in a vacuum induction melting furnace （VIM）. The casting microstructure and the mechanical property of the maraging steel according to Nb contents are analyzed by conducting the solution annealing and the age hardening after hot rolling. In this result, a specimen containing 0.03% Nb is most miniature. When it does the long time age hardening, the precipitation estimated as the carbide is appeared. The mechanical properties are excellent if a specimen containing 0.06% Nb does the age hardening during 8 h in 482℃.展开更多
基金Supported by the National High Technology Research and Development Program of China(No.2002AA333040)the Special Funds of Science and Technology Bureau of Harbin for Hi-Tech Research,China(No.2007AA4BG140)
文摘Ultrafine full-vulcanized polybutadiene rubber（UFBR） with particle sizes of ca.50―100 nm were used for modifying mechanical and processing performances of polypropylene（PP） with PP-g-maleic anhydride（PP-g-MA） as a compatibilizer for enhancing the interfacial adhesion between the two components.The morphology,dynamical rheology response and mechanical properties of the blends were characterized by means of SEM,rheometer and tensile test,respectively.The results show that the ternary PP/UFBR blends compatibilized with PP-g-MA possess rheological behaviors like highly branched PP,while no obvious strain hardening is observed in its control binary PP/UFBR blends,a low level of PP-g-MA in PP/UFBR blends can even endow the material with rheological characteristics of high melt strength materials like highly branched PP.The enhancement interfacial interaction between the UFBR particles and PP matrix accounting for the rheological behavior of compatibilized blends and effectiveness of PP-g-MA were proposed and proved.
基金Acknowledgements This work was financially supported by National Natural Science Foundation of China （Grant Nos. 21476085 and 21306047）, Fundamental Research Funds for the Central Universities of China （22A201514016 222201314051）.
文摘Foamable high melt strength polypropylene （HMSPP） was prepared by grafting styrene （St） onto polypropylene （PP） and simultaneously introducing poly- dimethylsiloxane （PDMS） through a one-step melt extru- sion process. The effect of PDMS viscosity on the foaming behavior of HMSPP was systematically investigated using supercritical CO2 as the foaming agent. The results show that the addition of PDMS has little effect on the grafting reaction of St and HMSPP exhibits enhanced elastic response and obvious strain hardening effect. Though the CO2 solubility of HMSPP with PDMS （PDMS-HMSPP） is lower than that of HMSPP without PDMS, especially for PDMS with low viscosity, the PDMS-HMSPP foams exhibit narrow cell size distribution and high cell density. The fracture morphology of PDMS-HMSPP shows that PDMS with low viscosity disperses more easily and uniformly in HMSPP matrix, leading to form small domains during the extrusion process. These small domains act as bubble nucleation sites and thus may be responsible for the improved foaming performance of HMSPP.
基金Supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China (20030561014)
文摘This study investigated that epoxidized soybean oil （ESO） was blended as plasticizer with poly （lactic acid） （PLA） and its effects on the melt rheological properties, such as melt flow index, apparent shear viscosity, and melt strength of the blends. PLA was blended by the twin-screw plastic extruder at five mass fractions： 3%, 6%, 9%, 12%, and 15% （based on PLA mass）. Melt flow index （MFI） was examined with a melt flow indexer. The results indicate that the blends of PLA/ESO had higher MFI than pure PLA, except for MFI at 9% reaching to the lowest point, even lower than that of pure PLA. Melt rheological properties were studied by a capillary rheometer in a temperature range of 160-180℃. The blends exhibited shear-thinning behavior and the apparent shear viscosity was well described by the power law in this shear rate region. The melt strength of PLA plasticized with 6% ESO reached the maximums. ESO was more effective in increasing the melt strength at the mass fractions less than 6%, which could toughen the blends to some extent. Therefore, the authors suggested the optimum addition level of 6%-9% ESO will get good melt rheological performance balance.
文摘It is important, for electronic application, to decrease the melting point of Sn-5Sb solder alloy because it is relatively high as compared with the most popular eutectic Pb-Sn solder alloy. Adding Au or Ag can decrease the onset melting temperature （233℃） of this alloy to 203,5℃ and 216℃, respectively. The results indicate that the Sn-5Sb-i.5Au alloy has very good ultimate tensile strength （UTS）, ductility, and fusion heat, which are better than both those of the Sn-5Sb-3.SAg and Sn-5Sb alloys. The formation of intermetallic compounds （IMCs） AuSn4 and Ag3Sn enhanced the SbSn precipitates in the solidification microstructure microstructure stability, while retained the formation of thus significantly improved the strength and ductility For all alloys, both UTS and yield stress （σy） increase with increasing strain rate and decrease with increasing temperature in tensile tests, but changes of ductility are generally small with inconsistent trends.
基金supported by the Royal Academy of Engineering Research Exchanges with China and UK(Grant No.2012-P02)National Key Technology R&D Program of Ministry of Science and Technology of China(Grant No.2012BAF08B03)National Natural Science Foundation of China(Grant No.51375189)
文摘The porcelain fracture caused by low metal-ceramic bond strength is a critical issue in porcelain fused to metal（PFM） restorations. Surface roughening methods, such as sand blasting, acid etching and alkaline degreasing for the metal matrix are used to increase bond strength. However, the metal matrix of PFM processed by selective laser melting（SLM） has natural rough surface. To explore the effect of the original roughness on metal-ceramic bond strength, two groups of specimen are fabricated by SLM. One group of specimen surface is polished smooth while another group remains the original rough surface. The dental porcelain is fused to the specimens＇ surfaces according to the ISO 9693：1999 standard. To gain the bond strength, a three-point bending test is carried out and X ray energy spectrum analysis（EDS）, scanning electron microscope（SEM） are used to show fracture mode. The results show that the mean bond strength is 116.5 16 MPa of the group with rough surface（Ra= 17.2）, and the fracture mode is cohesive. However, when the surface is smooth （Ra =3.8）, the mean bond strength is 74.5 MPa _＋ 5 MPa and the fracture mode is mixed. The original surface with prominent structures formed by the partly melted powder particles, not only increases surface roughness but also significantly improves the bond strength by forming strong mechanical lock effect. Statistical analysis （Student＇s t-test） demonstrates a significant difference （p〈0.05） of the mean value of bond strength between the two groups. The experiments indicate the natural rough surface can enhance the metal-ceramic bond strength to over four times the minimum value （25 MPa） of the ISO 9693：1999 standard. It is found that the natural rough surface of SLM-made PFM can eliminate the porcelain collapse defect produced by traditional casting method in PFM restorations.
文摘An aromatic azo-polymer, poly（thiourea-azo-sulfone） （PTAS）, has been prepared using 4-（4- aminophenylsulfonyl）benzenamine and diazonium salt solution of 2,6odiaminopyridine. PTAS was easily processable using polar solvents and had high molar mass 63 × 103 g.mo1-1 according to GPC. Mechanically and thermally stable and electrically conducting polymer/CNTs nano-composites were obtained via melt processing technique. Fine distribution of CNTs in a polymer matrix performed an essential role in the preparation of polymer/CNTs nano-composites based on interfacial interaction between CNTs and polymer matrix. Scanning electron micrographs showed good dispersion of filler and adhesion of matrix on the surface of nanotubes. Accordingly, increasing the amount of CNTs from 0.1 wt% to 5 wt% increased the electrical conductivity from 2.99 S.cm-1 to 3.56 S.cm-1. Mechanical strength of functional nanotubes-based hybrids was enhanced from 43.22 MPa to 65.02 MPa compared with that of hybrids with non-functional filler in matrix 37.21 MPa. A rapport between nanotube loading and thermal stability of the materials was also observed. 10% gravimetric loss temperature was increased from 528 ~C to 578 ~C, while glass transition was improved from 241 ℃ to 271 ℃. Adding up of small quantity of functional CNTs strongly affected the tensile, electrical and thermal properties of materials. Improvement of the physical properties of CNT-reinforced polymer nano-composites was ascribed to the melt processing technique.
文摘The melt spun ribbons of Al-La-Y-Ni(Fe)quaternary alloys were prepared by a single- roller melt spinning technique in vacuum.Their amorphous nature,mechanical properties and tensile fracture surface morphology were investigated.The experimental results show that amorphous alloys with high strength and good ductility as well as good thermal stability can be achieved in Al-La-Y-Ni(Fe)system,when the alloy contains 85—90 at.-% Al and less than 10 at.-% La+Y.The maximum tensile fracture strength(σ_f) and microhardness(HV)are as high as 760 MPa and 294 DPN,respectively.The as- quenched ribbons can be bent 180 degree without fracturing.The dominant factors for formation of amorphous Al-La-Y-Ni(Fe)are the strong attractive interaction among Al, La,Y and a decrease of melting temperature.
基金supported by Research Funds from Chosun University,2007.
文摘As the aircraft and aerospace industry and the automobile industry are developed, the demand of reliable materials with high strength and high toughness is steadily increased. The grain miniature method which improves the ductility and the toughness simultaneously under high strength is the miniature of the casting microstructure. In this paper, the Nb which affects the austenite grain miniature is added by 0.00%, 0.03% and 0.06% in this steel and the ingot is manufactured in a vacuum induction melting furnace （VIM）. The casting microstructure and the mechanical property of the maraging steel according to Nb contents are analyzed by conducting the solution annealing and the age hardening after hot rolling. In this result, a specimen containing 0.03% Nb is most miniature. When it does the long time age hardening, the precipitation estimated as the carbide is appeared. The mechanical properties are excellent if a specimen containing 0.06% Nb does the age hardening during 8 h in 482℃.
