2005 Vol. 22, No. 1
Abstract:
Cyanate esters were modified by carboxyl terminated liquid butadiene-acrylonitrile (CTBN) to improve theirtoughness. Optimized curing parameters were obtained by gel time curves and differential scanning calorimetry (DSC) ofthe systems. Fourier transform infrared spectrometry (FTIR) and DSC were employed to show the curing behavior of thesystems. It was observed , by comparison with purified cyanate esters , that the addition of CTBN has large influence onthe curing behavior of the systems during lower temperature , but little during higher temperature. Scanning electron microscopy (SEM) was employed to show the micro properties of the cured matrixes ; mechanical properties and dielectricproperties of the cured resin were measured. It showed that when 15 % CTBN was added to CE , the best modified systemwas gotten ; its flexural strength and impact strength were increased 39.47 % and 21.92 % , respectively. Additionally , asshown in the TGA curves of the systems , with the increasing content of CTBN from 0 to 15 % , the thermal degradationtemperature decreased from 407 ℃to 383 ℃.
Cyanate esters were modified by carboxyl terminated liquid butadiene-acrylonitrile (CTBN) to improve theirtoughness. Optimized curing parameters were obtained by gel time curves and differential scanning calorimetry (DSC) ofthe systems. Fourier transform infrared spectrometry (FTIR) and DSC were employed to show the curing behavior of thesystems. It was observed , by comparison with purified cyanate esters , that the addition of CTBN has large influence onthe curing behavior of the systems during lower temperature , but little during higher temperature. Scanning electron microscopy (SEM) was employed to show the micro properties of the cured matrixes ; mechanical properties and dielectricproperties of the cured resin were measured. It showed that when 15 % CTBN was added to CE , the best modified systemwas gotten ; its flexural strength and impact strength were increased 39.47 % and 21.92 % , respectively. Additionally , asshown in the TGA curves of the systems , with the increasing content of CTBN from 0 to 15 % , the thermal degradationtemperature decreased from 407 ℃to 383 ℃.
Abstract:
A novel kind of organic montmorillonite (MMT Ⅱ) , modified with the combination of dodecyl benzyldimethyl ammonium chloride (DBDA) and meta-Xylylenediamine (MXDA) , was prepared by a newly designed modification method , and finely exfoliated MMT Ⅱ/ epoxy nanocomposites were achieved by the aid of shearing force of ballmilling. Fourier transform infrared spectroscopy (FTIR) , X-ray diffraction (XRD) and transmission electron microscopy( TEM) were used to characterize the structure of MMTⅡ and the corresponding nanocomposites. The mechanical properties were tested. The results show that large agglomerates of MMT Ⅱ can not be homogeneously dispersed by generalstirring , which only induces an intercalated or partially exfoliated structure of MMT Ⅱin epoxy matrix at most . Whereasthe exfoliation of the retained intercalation structure or agglomerates can be promoted by external shearing force of ballmilling, which induces homogeneously dispersed nano-sheets of MMT Ⅱ and enhances mechanical properties. Impactstrength can be increased up from 3211 kJ / m2 to 4811 kJ / m2 , which is about 50 % higher than that of pristine matrix ,and the flexural strength can also be enhanced by about 8 % higher.
A novel kind of organic montmorillonite (MMT Ⅱ) , modified with the combination of dodecyl benzyldimethyl ammonium chloride (DBDA) and meta-Xylylenediamine (MXDA) , was prepared by a newly designed modification method , and finely exfoliated MMT Ⅱ/ epoxy nanocomposites were achieved by the aid of shearing force of ballmilling. Fourier transform infrared spectroscopy (FTIR) , X-ray diffraction (XRD) and transmission electron microscopy( TEM) were used to characterize the structure of MMTⅡ and the corresponding nanocomposites. The mechanical properties were tested. The results show that large agglomerates of MMT Ⅱ can not be homogeneously dispersed by generalstirring , which only induces an intercalated or partially exfoliated structure of MMT Ⅱin epoxy matrix at most . Whereasthe exfoliation of the retained intercalation structure or agglomerates can be promoted by external shearing force of ballmilling, which induces homogeneously dispersed nano-sheets of MMT Ⅱ and enhances mechanical properties. Impactstrength can be increased up from 3211 kJ / m2 to 4811 kJ / m2 , which is about 50 % higher than that of pristine matrix ,and the flexural strength can also be enhanced by about 8 % higher.
Abstract:
The conductive polyaniline / iron carbonyl powder composite material was prepared based on conductivepolymer and soft magnetic metals , which have very good characteristics of electromagnetic wave absorbing. The conductive polyaniline / iron carbonyl composite powder was prepared under the volume ratio of 2∶8. The composite of wave absorbing dope , which consists of the composite powder and polyurea , was composed under the volume ratio of 2∶8. It indicates that the wave absorbing property of the composite is better than - 10 dB in the frequency range of 2～12 GHz ,while the conductivity of polyaniline was 10-2 S/ cm and the average size of iron carbonyl powder is 1～2μm. The analysis demonstrates that excellent wave absorbing materials with wide frequency characteristic , strong wave absorption abilityand programmable frequency range could be developed based on this technology.
The conductive polyaniline / iron carbonyl powder composite material was prepared based on conductivepolymer and soft magnetic metals , which have very good characteristics of electromagnetic wave absorbing. The conductive polyaniline / iron carbonyl composite powder was prepared under the volume ratio of 2∶8. The composite of wave absorbing dope , which consists of the composite powder and polyurea , was composed under the volume ratio of 2∶8. It indicates that the wave absorbing property of the composite is better than - 10 dB in the frequency range of 2～12 GHz ,while the conductivity of polyaniline was 10-2 S/ cm and the average size of iron carbonyl powder is 1～2μm. The analysis demonstrates that excellent wave absorbing materials with wide frequency characteristic , strong wave absorption abilityand programmable frequency range could be developed based on this technology.
Abstract:
Polyethylene ( PE ) / maleic anhydride grafted polyethylene ( gPE ) / expanded graphite ( EG) electricallyconductive nanocomposites were prepared by solution intercalation (SI ) and masterbatch melt mixing (MMM ) methods.The electrical conductivity (σ) measurement , TEM , SEM and OM observations as well as DSC analysis were used to examine the influences of preparation methods , EG volume or mass fractions ( ? or fm ) and gPE mass contents ( Cg ) onstructure and σof the nanocomposites , as compared with PE/ gPE/ EG composites and PE/ EG control materials preparedby direct melt mixing (DMM ) method. The percolation thresholds ( ?c )of the SI- , MMM- , DMM-composites with Cg/ fm = 115 and the DMM-PE/ EG controls were determined to be 2.19 % , 3.81 % , 4.68 % and 5.35 % , respectively. Asthe Cg/ fm increased from 1 to 4 , theσof the MMM- , DMM-composites with fm = 9 % rose by 12 and 8 orders of magnitude , respectively. These were closely associated with the morphology and internal microstructure of EG dispersed phasein the composites varying with preparation methods , ? and Cg/ fm , and could be interpreted in terms of percolation theory.
Polyethylene ( PE ) / maleic anhydride grafted polyethylene ( gPE ) / expanded graphite ( EG) electricallyconductive nanocomposites were prepared by solution intercalation (SI ) and masterbatch melt mixing (MMM ) methods.The electrical conductivity (σ) measurement , TEM , SEM and OM observations as well as DSC analysis were used to examine the influences of preparation methods , EG volume or mass fractions ( ? or fm ) and gPE mass contents ( Cg ) onstructure and σof the nanocomposites , as compared with PE/ gPE/ EG composites and PE/ EG control materials preparedby direct melt mixing (DMM ) method. The percolation thresholds ( ?c )of the SI- , MMM- , DMM-composites with Cg/ fm = 115 and the DMM-PE/ EG controls were determined to be 2.19 % , 3.81 % , 4.68 % and 5.35 % , respectively. Asthe Cg/ fm increased from 1 to 4 , theσof the MMM- , DMM-composites with fm = 9 % rose by 12 and 8 orders of magnitude , respectively. These were closely associated with the morphology and internal microstructure of EG dispersed phasein the composites varying with preparation methods , ? and Cg/ fm , and could be interpreted in terms of percolation theory.
Abstract:
The transparent silica / phenolic resole hybrid material was prepared. The relationship between wavelength andtransmittances was measured by the single beam spectrophotometer. The films of the hybrid material and phenolic resole have different colors and transmittances within 460～780nm. The transmittances of the hybrid material film in the range of 460～780nm change with different wavelengths and cannot be compared if the wavelengths are different . The transmittances of phenolicresole decrease with the development of its curing. The transmittances of the hybrid material increase with the development of itscuring and may be a method to characterize the degree of curing of the hybrid material.
The transparent silica / phenolic resole hybrid material was prepared. The relationship between wavelength andtransmittances was measured by the single beam spectrophotometer. The films of the hybrid material and phenolic resole have different colors and transmittances within 460～780nm. The transmittances of the hybrid material film in the range of 460～780nm change with different wavelengths and cannot be compared if the wavelengths are different . The transmittances of phenolicresole decrease with the development of its curing. The transmittances of the hybrid material increase with the development of itscuring and may be a method to characterize the degree of curing of the hybrid material.
Abstract:
The keratoprosthesis was designed , consisting of a transparent core polyvinyl alcohol (PVA) hydrogel with aporous peripheral skirt nano-hydroxyapatite/ polyvinyl alcohol ( n-HA/ PVA) hydrogel sponge. This keratoprosthesisshould improve biocompatibility with the host tissue and ability to interlock with the host cornea. The n-HA/ PVA composite has good homogeneity. Chemical bindings between n-HA and PVA were investigated by IR. The n-HA/ PVAsponges were porous with evenly distributed and interconnected pore structures observed by SEM. The attachment of theskirt to the core was achieved through an interpenetrating polymer network ( IPN) verified by light microscopy techniques. All of the implants have been retained , with no severe complications such as cataract and inflammation. Keratocytes migration into the skirt of the implants and deposition of complex extracellular matrix in the discs were found. Thiskind of keratoprosthesis is a biocompatible , suitable and promising material in its application to the clinic.
The keratoprosthesis was designed , consisting of a transparent core polyvinyl alcohol (PVA) hydrogel with aporous peripheral skirt nano-hydroxyapatite/ polyvinyl alcohol ( n-HA/ PVA) hydrogel sponge. This keratoprosthesisshould improve biocompatibility with the host tissue and ability to interlock with the host cornea. The n-HA/ PVA composite has good homogeneity. Chemical bindings between n-HA and PVA were investigated by IR. The n-HA/ PVAsponges were porous with evenly distributed and interconnected pore structures observed by SEM. The attachment of theskirt to the core was achieved through an interpenetrating polymer network ( IPN) verified by light microscopy techniques. All of the implants have been retained , with no severe complications such as cataract and inflammation. Keratocytes migration into the skirt of the implants and deposition of complex extracellular matrix in the discs were found. Thiskind of keratoprosthesis is a biocompatible , suitable and promising material in its application to the clinic.
Abstract:
The fatigue damage properties of [00 ] single2ply and [ ±200 ] double-ply rubber composite under T-T loading were studied. The results show that the variation of the cycle strain of both kinds of material in the fatigue process exhibits three stages which are corresponding to damage initiation , steady damage propagation and catastrophic failure. Thefatigue damage is controlled by cord properties for the single-ply rubber composites and by matrix properties for the doubleply rubber composite respectively. The logarithmic fatigue life expressed by maximum stress follows a linear trend. Thehysteretic loss keeps constant until the end of the fatigue life. The difference between hysteretic loss and the thermoconductivity results in a difference in the surface temperature between different specimens.
The fatigue damage properties of [00 ] single2ply and [ ±200 ] double-ply rubber composite under T-T loading were studied. The results show that the variation of the cycle strain of both kinds of material in the fatigue process exhibits three stages which are corresponding to damage initiation , steady damage propagation and catastrophic failure. Thefatigue damage is controlled by cord properties for the single-ply rubber composites and by matrix properties for the doubleply rubber composite respectively. The logarithmic fatigue life expressed by maximum stress follows a linear trend. Thehysteretic loss keeps constant until the end of the fatigue life. The difference between hysteretic loss and the thermoconductivity results in a difference in the surface temperature between different specimens.
Abstract:
The high temperature tensile creep tests were performed on TiB2 ultrafine particulate reinforced ZL109 composite prepared by in situ formation technique. The composite exhibits high values of apparent stress exponent and apparent creep activation energy under constant applied stress at elevated temperatures. These values exceed greatly those forpure aluminum and ZL109 alloy. High temperature creep properties of the in situ TiB2/ ZL109 composite are better thanthose for conventional particulate reinforced composites. By introducing a threshold stress , the creep results of the composite can be explained by a microstructure invariant model , implying that creep of the composite is controlled by lattice diffusion in the matrix. The creep rupture behavior of the composite can be represented by Monkman-Grant empirical equationand the rupture characteristic of the composite is ductile fracture.
The high temperature tensile creep tests were performed on TiB2 ultrafine particulate reinforced ZL109 composite prepared by in situ formation technique. The composite exhibits high values of apparent stress exponent and apparent creep activation energy under constant applied stress at elevated temperatures. These values exceed greatly those forpure aluminum and ZL109 alloy. High temperature creep properties of the in situ TiB2/ ZL109 composite are better thanthose for conventional particulate reinforced composites. By introducing a threshold stress , the creep results of the composite can be explained by a microstructure invariant model , implying that creep of the composite is controlled by lattice diffusion in the matrix. The creep rupture behavior of the composite can be represented by Monkman-Grant empirical equationand the rupture characteristic of the composite is ductile fracture.
Abstract:
Spontaneous infiltration of SiC preforms with FexSiy (Fe3Si , Fe5Si3 and FeSi) melts was employed to produce fully dense ( > 96.5 % theoretical density) SiC/ FexSiy composites1 The phases , microstructures and mechanicalproperties were studied by using conventional materials characterization techniques including X-ray diffraction , optical microscopy , scanning electron microscopy , etc. A key issue behind the whole study is the dissolution and precipitation of SiCin FexSiy melts during infiltration. The dissolution of SiC in Fe3Si melts leads to carbon precipitation and phase changes( Fe3Si disappeared and Fe5Si3 and FeSi formed) . However , Fe5Si3 and FeSi infiltration gives no carbon precipitation , butSiC sintering , particle coalescence and grain growth. Extra-large SiC single crystals are found in fine SiC (0.5μm) infiltrated by Fe5Si3 . The phase equilibrium of Fe-Si-C system is quantitatively analysed at 1873 K using CHEMSAGE. SiCsolubility and the condition for SiC precipitation rather than C in Fe-Si melt are determined. Mechanical properties including micro-hardness , bending strength and Weibull modulus of all infiltrated samples were tested and analyzed on the basisof phase and microstructure observations.
Spontaneous infiltration of SiC preforms with FexSiy (Fe3Si , Fe5Si3 and FeSi) melts was employed to produce fully dense ( > 96.5 % theoretical density) SiC/ FexSiy composites1 The phases , microstructures and mechanicalproperties were studied by using conventional materials characterization techniques including X-ray diffraction , optical microscopy , scanning electron microscopy , etc. A key issue behind the whole study is the dissolution and precipitation of SiCin FexSiy melts during infiltration. The dissolution of SiC in Fe3Si melts leads to carbon precipitation and phase changes( Fe3Si disappeared and Fe5Si3 and FeSi formed) . However , Fe5Si3 and FeSi infiltration gives no carbon precipitation , butSiC sintering , particle coalescence and grain growth. Extra-large SiC single crystals are found in fine SiC (0.5μm) infiltrated by Fe5Si3 . The phase equilibrium of Fe-Si-C system is quantitatively analysed at 1873 K using CHEMSAGE. SiCsolubility and the condition for SiC precipitation rather than C in Fe-Si melt are determined. Mechanical properties including micro-hardness , bending strength and Weibull modulus of all infiltrated samples were tested and analyzed on the basisof phase and microstructure observations.
Abstract:
By squeeze casting technology , industrial pure aluminum L2 , LD11 (Al-12 %Si) and AlSi20 (Al-(18～21) %Si) alloys were reinforced with SiC particles of 20μm and 60μm. And their thermal conduction properties were investigated. On the basis of equal specific interfacial areas , an equivalent particle diameter is brought forward and the thermal conductivity of dual-sized particles reinforced aluminum matrix composites is calculated. The SiCP/ Al composites possess relatively excellent thermal properties , and the thermal conductivities of LD11 and AlSi20 matrix composites are larger than those of matrices. This is attributed to the fact that the equivalent particle diameter of SiC is larger than its criticaldiameter and the thermal conductivity of SiC is higher than those of LD11 and AlSi20. But the thermal conductivities ofSiCP/ Al composites decrease with the increasing of Si additions to the matrix.
By squeeze casting technology , industrial pure aluminum L2 , LD11 (Al-12 %Si) and AlSi20 (Al-(18～21) %Si) alloys were reinforced with SiC particles of 20μm and 60μm. And their thermal conduction properties were investigated. On the basis of equal specific interfacial areas , an equivalent particle diameter is brought forward and the thermal conductivity of dual-sized particles reinforced aluminum matrix composites is calculated. The SiCP/ Al composites possess relatively excellent thermal properties , and the thermal conductivities of LD11 and AlSi20 matrix composites are larger than those of matrices. This is attributed to the fact that the equivalent particle diameter of SiC is larger than its criticaldiameter and the thermal conductivity of SiC is higher than those of LD11 and AlSi20. But the thermal conductivities ofSiCP/ Al composites decrease with the increasing of Si additions to the matrix.
Abstract:
The surface of copper alloy was modified using infiltration casting. Fe-based alloy powder was used as infiltrated agent under the condition of negative pressure to form the infiltrated layer on the surface of copper cast . The experimental results show that the surface composites of copper matrix are obtained under the present condition , whose structureis different from that of the substrate. The SEM shows that the interface between the base metal and the penetrated layercontains no exist holes and the structure is compact . Infiltration casting is feasible to fabricate the surface composite of acopper substrate.
The surface of copper alloy was modified using infiltration casting. Fe-based alloy powder was used as infiltrated agent under the condition of negative pressure to form the infiltrated layer on the surface of copper cast . The experimental results show that the surface composites of copper matrix are obtained under the present condition , whose structureis different from that of the substrate. The SEM shows that the interface between the base metal and the penetrated layercontains no exist holes and the structure is compact . Infiltration casting is feasible to fabricate the surface composite of acopper substrate.
Abstract:
The micro-appearance feature , the formation of twin lines of monoclinic , the phase transformation and thecrystal orientation relationship of ZrO2 laminated ceramics were studied by scanning electron micro scope (SEM) ,transmission electron microscope ( TEM) , X-rays instruments , etc1The experiment results show that the interface compressivestresses can decrease the rate of the grains growth , control the transformation of tetragonal during sintering , raise theamount of the transformable tetragonal , strengthen the effect of the transformation effect , but do not change the orientation relation between tetragonal and monoclinic phase , while (100) m/ / (010) t still exist1
The micro-appearance feature , the formation of twin lines of monoclinic , the phase transformation and thecrystal orientation relationship of ZrO2 laminated ceramics were studied by scanning electron micro scope (SEM) ,transmission electron microscope ( TEM) , X-rays instruments , etc1The experiment results show that the interface compressivestresses can decrease the rate of the grains growth , control the transformation of tetragonal during sintering , raise theamount of the transformable tetragonal , strengthen the effect of the transformation effect , but do not change the orientation relation between tetragonal and monoclinic phase , while (100) m/ / (010) t still exist1
Abstract:
TiB2 based cermet with Fe-Ni-Ti-Al as sintering aids was fabricated by hot-pressing. The effects of sinteringtemperature , holding time and sintering aids on microstructure and mechanical properties were investigated. The toughening mechanism of TiB2 based cermet was analysed. Experimental results show that the bending strength of TiB2 cermetdecreases and the Rockwell hardness increases with sintering temperature rising up ; a bending strength peak appears withholding time prolonged. According to the scanning electron microscope (SEM ) and energy dispersive spectrometer (EDS )observation , Ti in sintering aids is essential for avoiding the formation of extremely brittle secondary borides such as Fe2Band Ni23B6 , while Al plays a deoxygen role. Crack deflection and crack bridging are important toughening ways of composite.
TiB2 based cermet with Fe-Ni-Ti-Al as sintering aids was fabricated by hot-pressing. The effects of sinteringtemperature , holding time and sintering aids on microstructure and mechanical properties were investigated. The toughening mechanism of TiB2 based cermet was analysed. Experimental results show that the bending strength of TiB2 cermetdecreases and the Rockwell hardness increases with sintering temperature rising up ; a bending strength peak appears withholding time prolonged. According to the scanning electron microscope (SEM ) and energy dispersive spectrometer (EDS )observation , Ti in sintering aids is essential for avoiding the formation of extremely brittle secondary borides such as Fe2Band Ni23B6 , while Al plays a deoxygen role. Crack deflection and crack bridging are important toughening ways of composite.
Abstract:
e mineral composite particles with rough surfaces and blunt edge angles , coated by nanometer calcium carbonate with a particle size range of 20～100 nm , were successfully prepared by a chemical method in Ca (OH)2-H2O-CO2 system. The specific surface area of the composite powders increased twice or above after coating. It is exhibited thatpolypropylene (PP) composites filled by the composite powders with nano-structure surface have better properties becausethe nano-structured mineral powders have bigger surface areas which would lead to more interfacial compatibility betweenpowders and polymer matrix when the powders are filled into the polymer and moreover , the blunt edge angles would reduce the stress concentration at angles , compared with un-coated powders as filler.
e mineral composite particles with rough surfaces and blunt edge angles , coated by nanometer calcium carbonate with a particle size range of 20～100 nm , were successfully prepared by a chemical method in Ca (OH)2-H2O-CO2 system. The specific surface area of the composite powders increased twice or above after coating. It is exhibited thatpolypropylene (PP) composites filled by the composite powders with nano-structure surface have better properties becausethe nano-structured mineral powders have bigger surface areas which would lead to more interfacial compatibility betweenpowders and polymer matrix when the powders are filled into the polymer and moreover , the blunt edge angles would reduce the stress concentration at angles , compared with un-coated powders as filler.
Abstract:
High-quality SiC/ C composite films were deposited with SiC ultrafine powder as a raw material by thermalplasma physical vapor deposition ( PVD) technique. The maximum deposition rate reached 225 nm/ s. The films werecharacterized with high resolution transmission electron microscope ( HRTEM) , scanning electron microscope ( SEM)and X-ray photoelectron spectrocope (XPS) . The mechanical properties of the deposited films were evaluated with ananoindenter in comparison with that of sintered SiC. The results show that when CH4 is introduced into plasma , the deposition rate and C content of SiC/ C composite film increase , and films with columnar structure are formed. The hardnessand elastic modulus of the deposited films decrease with increasing C content in the SiC/ C composite films. The hardnessevaluated with a nanoindenter at contact depth of 40 nm reaches 38 GPa , which suggests good quality of the depositedfilms.
High-quality SiC/ C composite films were deposited with SiC ultrafine powder as a raw material by thermalplasma physical vapor deposition ( PVD) technique. The maximum deposition rate reached 225 nm/ s. The films werecharacterized with high resolution transmission electron microscope ( HRTEM) , scanning electron microscope ( SEM)and X-ray photoelectron spectrocope (XPS) . The mechanical properties of the deposited films were evaluated with ananoindenter in comparison with that of sintered SiC. The results show that when CH4 is introduced into plasma , the deposition rate and C content of SiC/ C composite film increase , and films with columnar structure are formed. The hardnessand elastic modulus of the deposited films decrease with increasing C content in the SiC/ C composite films. The hardnessevaluated with a nanoindenter at contact depth of 40 nm reaches 38 GPa , which suggests good quality of the depositedfilms.
Abstract:
TiO2/ Fe2O3 and TiO2/ Fe2O3/ SiO2 nanocomposite photocatalysts were prepared with Na2SiO3 ·9H2O , Fe(NO3 )3·9H2O and TiCl4 as precursors by chemistry coating processes and supercritical fluid drying (SCFD ) methods. Thephotocatalytic activity was evaluated by photocatalytic degradation of phenol as model reaction. Characterizations withXRD , TEM and FTIR show that in addition to anatase type TiO2 is also formed in the range of the studied doping concentration , and SiO2 remains amorphous at all samples. It could hold up the growth of the nanoparticle size and transformation from anatase to rutile. Compared with pure TiO2 , or TiO2/ Fe2O3 catalyst prepared by sol-gel method , nano-composite photocatalyst shows significant improvement in catalytic activity : The photocatalytic degradation rate of phenolin 6 h reached 9519 %. The optimum doping of Fe2O3 is 0106 %. Application of the TiO2/ Fe2O3/ SiO2 composite catalysts for the photocatalytic decomposition of phenol could not only give the same activity relative to pure ultrafine TiO2 ,but also reduce cost . The experimental results prove that the thermal stability of TiO2 is greatly enhanced after mixingwith slight amount of SiO2 . The optimum doping of SiO2 is 1010 %. The photo-catalytic particles prepared by SCFD combination technology have small size , large surface area and high activity.
TiO2/ Fe2O3 and TiO2/ Fe2O3/ SiO2 nanocomposite photocatalysts were prepared with Na2SiO3 ·9H2O , Fe(NO3 )3·9H2O and TiCl4 as precursors by chemistry coating processes and supercritical fluid drying (SCFD ) methods. Thephotocatalytic activity was evaluated by photocatalytic degradation of phenol as model reaction. Characterizations withXRD , TEM and FTIR show that in addition to anatase type TiO2 is also formed in the range of the studied doping concentration , and SiO2 remains amorphous at all samples. It could hold up the growth of the nanoparticle size and transformation from anatase to rutile. Compared with pure TiO2 , or TiO2/ Fe2O3 catalyst prepared by sol-gel method , nano-composite photocatalyst shows significant improvement in catalytic activity : The photocatalytic degradation rate of phenolin 6 h reached 9519 %. The optimum doping of Fe2O3 is 0106 %. Application of the TiO2/ Fe2O3/ SiO2 composite catalysts for the photocatalytic decomposition of phenol could not only give the same activity relative to pure ultrafine TiO2 ,but also reduce cost . The experimental results prove that the thermal stability of TiO2 is greatly enhanced after mixingwith slight amount of SiO2 . The optimum doping of SiO2 is 1010 %. The photo-catalytic particles prepared by SCFD combination technology have small size , large surface area and high activity.
Abstract:
Composite polymer electrolytes (CPE) films consisting of PEO , LiClO4 and self-sintered Li1.3Al0.3Ti1.7 (PO4)3 were prepared by the solution casting method with fixed EO/ Li = 8 but different relative compositions of the twolithium salts1 The CPE films were characterized using DSC and electrical impedance spectroscopy ( EIS) . It is found thatthe incorporation of Li1.3Al0.3Ti1.7 (PO4)3 into PEO by keeping EO/ Li = 8 reduces the crystallinity of PEOfrom 50.34 % to the range of 4.36 %～28.53 % depending upon the relative composition of the two salts. The room temperature impedance spectra of the CPE films all exhibited a shape of depressed semicircle in high frequency range and inclined line in low frequency range , but the high temperature ones were mainly the inclined lines1 The ionic conductivity ofthe CPE films followed Arrhenius law and the activation energy ( Ea) of the films was the lowest , i1e1 4.494425 eV , atthe Li1.3Al0.3Ti1.7 (PO4)3 content of 15 % (Mass fraction) . Meanwhile , the ionic conductivity of the CPE filmsreached the optimal values of 1.161 ×10 -3 S/ cm at 373 K and 7.985 ×10 -5 S/ cm at 298 K when the Li1.3Al0.3Ti1.7 (PO4)3 content is also 15 %1
Composite polymer electrolytes (CPE) films consisting of PEO , LiClO4 and self-sintered Li1.3Al0.3Ti1.7 (PO4)3 were prepared by the solution casting method with fixed EO/ Li = 8 but different relative compositions of the twolithium salts1 The CPE films were characterized using DSC and electrical impedance spectroscopy ( EIS) . It is found thatthe incorporation of Li1.3Al0.3Ti1.7 (PO4)3 into PEO by keeping EO/ Li = 8 reduces the crystallinity of PEOfrom 50.34 % to the range of 4.36 %～28.53 % depending upon the relative composition of the two salts. The room temperature impedance spectra of the CPE films all exhibited a shape of depressed semicircle in high frequency range and inclined line in low frequency range , but the high temperature ones were mainly the inclined lines1 The ionic conductivity ofthe CPE films followed Arrhenius law and the activation energy ( Ea) of the films was the lowest , i1e1 4.494425 eV , atthe Li1.3Al0.3Ti1.7 (PO4)3 content of 15 % (Mass fraction) . Meanwhile , the ionic conductivity of the CPE filmsreached the optimal values of 1.161 ×10 -3 S/ cm at 373 K and 7.985 ×10 -5 S/ cm at 298 K when the Li1.3Al0.3Ti1.7 (PO4)3 content is also 15 %1
Abstract:
Quasi-static uniaxial compression experiments and meso compression-shear experiments were carried out toinvestigate the failure properties of polypropylene micro-fiber and steel fiber reinforced cement and concrete composites.Comparing the effects of two kinds of fibers on the composites under these two loading conditions , experimental resultsshow that under quasi-static uniaxial compression , the effects of steel fiber are evident , and those of Polypropylene microfiber are not ; while under compression and shear loading , steel fiber took on evident effects on the strengthening of thematrix in all of the deformation stages , but polypropylene micro-fiber only reinforced the matrix in the stages before failureand can not improve the ultimate shear strength. The debonding and fracture of steel fiber and gravels in the compositeswere observed in the meso experiments. However , the void collapse phenomenon was observed only in local of the cement . The mechanism that void collapse will lead to the formation of the compaction band needs to be revealed in furtherstudies.
Quasi-static uniaxial compression experiments and meso compression-shear experiments were carried out toinvestigate the failure properties of polypropylene micro-fiber and steel fiber reinforced cement and concrete composites.Comparing the effects of two kinds of fibers on the composites under these two loading conditions , experimental resultsshow that under quasi-static uniaxial compression , the effects of steel fiber are evident , and those of Polypropylene microfiber are not ; while under compression and shear loading , steel fiber took on evident effects on the strengthening of thematrix in all of the deformation stages , but polypropylene micro-fiber only reinforced the matrix in the stages before failureand can not improve the ultimate shear strength. The debonding and fracture of steel fiber and gravels in the compositeswere observed in the meso experiments. However , the void collapse phenomenon was observed only in local of the cement . The mechanism that void collapse will lead to the formation of the compaction band needs to be revealed in furtherstudies.
Abstract:
A three-phase composite sphere model is presented for the prediction of Young ’s modulus of concrete1 At amesoscopic level , concrete was considered as a three-phase composite material with aggregates as dispersed phase , interfacial transition zone ( ITZ) as interphase and cement paste as continuous phase1 Applying the simulation technique of concrete mesostructure , the ITZ volume fraction was obtained for a given aggregate grading1 Simulation results show that Li’s approximate method overestimates the ITZ volume fraction and that the ITZ volume fraction is dependant on the ITZthickness , largest aggregate diameter and aggregate grading to a great extent1 By introducing a three-phase compositesphere model , the analytical solution of Young’s modulus of concrete was given1 By comparing the results of both the analytical solution and laboratory experiment , the validity of the model presented is verified1 It is also demonstrated by numerical results that , for a given aggregate volume fraction , the Young’s modulus of concrete increases with the increase ofthe largest aggregate diameter and ITZ Young’s modulus , but decreases with the increase of the ITZ thickness. The aggregate grading also has a greater influence on the Young’s modulus of concrete1
A three-phase composite sphere model is presented for the prediction of Young ’s modulus of concrete1 At amesoscopic level , concrete was considered as a three-phase composite material with aggregates as dispersed phase , interfacial transition zone ( ITZ) as interphase and cement paste as continuous phase1 Applying the simulation technique of concrete mesostructure , the ITZ volume fraction was obtained for a given aggregate grading1 Simulation results show that Li’s approximate method overestimates the ITZ volume fraction and that the ITZ volume fraction is dependant on the ITZthickness , largest aggregate diameter and aggregate grading to a great extent1 By introducing a three-phase compositesphere model , the analytical solution of Young’s modulus of concrete was given1 By comparing the results of both the analytical solution and laboratory experiment , the validity of the model presented is verified1 It is also demonstrated by numerical results that , for a given aggregate volume fraction , the Young’s modulus of concrete increases with the increase ofthe largest aggregate diameter and ITZ Young’s modulus , but decreases with the increase of the ITZ thickness. The aggregate grading also has a greater influence on the Young’s modulus of concrete1
Abstract:
On the basis of the large unit cell of two-step rectangular three-dimensional braided composites , the finite element model of a spatial truss consisting of beam elements is developed to model the effective mechanical properties of thecomposites under the uniaxial tension. Yarns and resin are treated as beam elements. The finite element method can beemployed for predicting the mechanical properties of the composites. The uniaxial tensile tests of samples are simulated utilizing the software MARC. Results of the effective elastic properties and Poisson ratios predicted by this approach compare favorably with the experiment data. Parametric studies show that the axial elastic modulus of the composites increaseswith increasing the linear density ratio of axial yarn to braider yarns and pitch length.
On the basis of the large unit cell of two-step rectangular three-dimensional braided composites , the finite element model of a spatial truss consisting of beam elements is developed to model the effective mechanical properties of thecomposites under the uniaxial tension. Yarns and resin are treated as beam elements. The finite element method can beemployed for predicting the mechanical properties of the composites. The uniaxial tensile tests of samples are simulated utilizing the software MARC. Results of the effective elastic properties and Poisson ratios predicted by this approach compare favorably with the experiment data. Parametric studies show that the axial elastic modulus of the composites increaseswith increasing the linear density ratio of axial yarn to braider yarns and pitch length.
Abstract:
The Ladeveze’s damage model of the uni-ply for laminated plates is developed , and it is used to damageanalysis of the generally laminated plates including shear viscoelasticity. On the basis of the Von Karman theory , the non-linear equations of viscoelastic laminated composite plates with damage are derived , and by using the finite differencemethod and iteration method , these equations are solved. Numerical results show that the dynamic responses of the structure will change remarkably when considering the damage and damage evolution.
The Ladeveze’s damage model of the uni-ply for laminated plates is developed , and it is used to damageanalysis of the generally laminated plates including shear viscoelasticity. On the basis of the Von Karman theory , the non-linear equations of viscoelastic laminated composite plates with damage are derived , and by using the finite differencemethod and iteration method , these equations are solved. Numerical results show that the dynamic responses of the structure will change remarkably when considering the damage and damage evolution.
Abstract:
The thermo-mechanical behaviors of shape memory alloy (SMA) fiber reinforced smart structure with damages were analyzed through variational principle. Mathematical expressions for meso-displacement field , stress-strain fieldof typical element with damages were presented , and a failure criterion for interface failure between SMA fibers and matrix was established. The failure criterion was geometrically characterized with an example. The results may provide atheoretical foundation for further studying on integrity of SMA smart structures.
The thermo-mechanical behaviors of shape memory alloy (SMA) fiber reinforced smart structure with damages were analyzed through variational principle. Mathematical expressions for meso-displacement field , stress-strain fieldof typical element with damages were presented , and a failure criterion for interface failure between SMA fibers and matrix was established. The failure criterion was geometrically characterized with an example. The results may provide atheoretical foundation for further studying on integrity of SMA smart structures.
Abstract:
Materials with zero thermal expansion coefficients benefit to improve the geometrical stabilities of aeronauticand astronautic structures and electric equipment under great temperature changes. The microstructure of materials withzero thermal expansion coefficients is designed using a topology optimization method which consists of finding the distribution of three material phases in the design domain. These material phases include two different material phases and a voidphase. The effective properties of material structures are determined using the numerical homogenization method based ona finite-element discretization of the base cell , and the optimization problem is solved with the feasible direction method.The dependence on initial design is investigated , and some possible reasons causing the problem are discussed. The thermalexpansion behavior of the material with designed microstructures is tested by numerically simulated experiments and , thethermal expansion coefficients are obtained through analyzing the deformation of the materials caused by temperaturechange. These numerically simulated experiments verified the characteristic of zero (low) thermal expansion behavior ofthe designed material , which shows that the topology optimization method is a valid and effective method for microstructure design of materials with zero thermal expansion coefficients.
Materials with zero thermal expansion coefficients benefit to improve the geometrical stabilities of aeronauticand astronautic structures and electric equipment under great temperature changes. The microstructure of materials withzero thermal expansion coefficients is designed using a topology optimization method which consists of finding the distribution of three material phases in the design domain. These material phases include two different material phases and a voidphase. The effective properties of material structures are determined using the numerical homogenization method based ona finite-element discretization of the base cell , and the optimization problem is solved with the feasible direction method.The dependence on initial design is investigated , and some possible reasons causing the problem are discussed. The thermalexpansion behavior of the material with designed microstructures is tested by numerically simulated experiments and , thethermal expansion coefficients are obtained through analyzing the deformation of the materials caused by temperaturechange. These numerically simulated experiments verified the characteristic of zero (low) thermal expansion behavior ofthe designed material , which shows that the topology optimization method is a valid and effective method for microstructure design of materials with zero thermal expansion coefficients.
Abstract:
A unit cell geometrical model for 4-step 3D 4-directional rectangular braided composites is proposed. The effect of bending and cross-sectional variation of the yarns due to their mutual squeeze is considered in the model. A model topredict stiffness is then established based on the stiffness volume average method and on the laminated plate theory by assuming that differential yarns are straight . Thus the elastic material constants can be obtained. Numerical results show theeffectiveness of the model. The influences of the technics parameters and the cross-sectional shape of yarn on the engineering elastic constants are also studied , and some conclusions are drawn based on the results reported herein.
A unit cell geometrical model for 4-step 3D 4-directional rectangular braided composites is proposed. The effect of bending and cross-sectional variation of the yarns due to their mutual squeeze is considered in the model. A model topredict stiffness is then established based on the stiffness volume average method and on the laminated plate theory by assuming that differential yarns are straight . Thus the elastic material constants can be obtained. Numerical results show theeffectiveness of the model. The influences of the technics parameters and the cross-sectional shape of yarn on the engineering elastic constants are also studied , and some conclusions are drawn based on the results reported herein.
Abstract:
The dynamic response and loading capacity of the stiffened delaminated penetration composite plates werestudied by finite element method. Using the first-order shear deformation theory derives a formula of element stiffness andmass matrices for the composite laminated plate and beam. A damping model is deduced by using Rayleigh damping modeltogether with Adams’strain energy method (MSE) . A delaminated constrained model and a virtual interface element arealso developed to avoid the overlap and penetration phenomenon between the upper and lower sub-laminates at the delaminated region. The failure analysis method for the stiffened delaminated plates under dynamic load is established by Tsai’sfailure criterion and corresponding reduced stiffness role. By some numerical examples , the effects of frequency of dynamicload , delamination depth , stiffener location and reduction of structure stiffness during the failure process upon dynamic behavior of the delaminated composite laminates are discussed. The method and conclusions would be useful for compositestructures designers.
The dynamic response and loading capacity of the stiffened delaminated penetration composite plates werestudied by finite element method. Using the first-order shear deformation theory derives a formula of element stiffness andmass matrices for the composite laminated plate and beam. A damping model is deduced by using Rayleigh damping modeltogether with Adams’strain energy method (MSE) . A delaminated constrained model and a virtual interface element arealso developed to avoid the overlap and penetration phenomenon between the upper and lower sub-laminates at the delaminated region. The failure analysis method for the stiffened delaminated plates under dynamic load is established by Tsai’sfailure criterion and corresponding reduced stiffness role. By some numerical examples , the effects of frequency of dynamicload , delamination depth , stiffener location and reduction of structure stiffness during the failure process upon dynamic behavior of the delaminated composite laminates are discussed. The method and conclusions would be useful for compositestructures designers.
Abstract:
A kind of three layered 32-node temperature shell element is presented for the transient temperature fieldFEM analysis of the honeycomb sandwich composite shell. The temperature distribution in the thickness direction of thetop and bottom face sheets and the core layer was assumed , respectively , to satisfy the thermal boundary conditions of thetop and bottom surfaces and the condition of continuous temperature at the interfaces and to reduce the total number of thedegrees of freedom. The considered thermal boundary conditions on the inner and outer surfaces of the shell may includeheat flux , convection and radiation at the same time. The post processing was carried out so that the temperature distribution in the core layer also satisfies the condition of continuous heat flux at the interfaces and the accuracy of the temperature result is further improved. Two examples are provided to show the reliability and validity of the element .
A kind of three layered 32-node temperature shell element is presented for the transient temperature fieldFEM analysis of the honeycomb sandwich composite shell. The temperature distribution in the thickness direction of thetop and bottom face sheets and the core layer was assumed , respectively , to satisfy the thermal boundary conditions of thetop and bottom surfaces and the condition of continuous temperature at the interfaces and to reduce the total number of thedegrees of freedom. The considered thermal boundary conditions on the inner and outer surfaces of the shell may includeheat flux , convection and radiation at the same time. The post processing was carried out so that the temperature distribution in the core layer also satisfies the condition of continuous heat flux at the interfaces and the accuracy of the temperature result is further improved. Two examples are provided to show the reliability and validity of the element .
Abstract:
Based on the homogenization theory , the multi-scale analysis methods of the viscoelastic property , and theeffective thermal stress relaxation laws are studied. By defining the concepts , the effective thermal stress relaxation modulus ( ETSRM) and the effective time-dependent coefficients of thermal expansion ( ETCTE) , the thermal viscoelastic constitutive equation is expressed in the same form as that of conventional materials. Besides , a homogenization-based methodfor predicting the effective viscoelastic relaxation modulus , ETSRM and ETCET is given. It is pointed out that , for viscoelastic composite materials , the thermal expansion coefficients are time-dependent , and the thermal expansion processcan not be completed instantaneously , exhibiting an obvious time-delay effect . The analysis of several kinds of specialcomposite materials shows that : (1) The thermal expansion of porous material has an instantaneous character , its ETCTEis the same as that of the matrix material which is time-independent , and its thermal stress relaxation law is also the sameas that of the matrix material ; (2) For a special kind of composite materials of which the relaxation moduli of all the components can be expressed as the products of different individual time-independent coefficients and a same time-dependentfunction , the effective time-dependent thermal expansion coefficient is time-independent , and the character of the relaxation laws is the same as that of conventional materials.
Based on the homogenization theory , the multi-scale analysis methods of the viscoelastic property , and theeffective thermal stress relaxation laws are studied. By defining the concepts , the effective thermal stress relaxation modulus ( ETSRM) and the effective time-dependent coefficients of thermal expansion ( ETCTE) , the thermal viscoelastic constitutive equation is expressed in the same form as that of conventional materials. Besides , a homogenization-based methodfor predicting the effective viscoelastic relaxation modulus , ETSRM and ETCET is given. It is pointed out that , for viscoelastic composite materials , the thermal expansion coefficients are time-dependent , and the thermal expansion processcan not be completed instantaneously , exhibiting an obvious time-delay effect . The analysis of several kinds of specialcomposite materials shows that : (1) The thermal expansion of porous material has an instantaneous character , its ETCTEis the same as that of the matrix material which is time-independent , and its thermal stress relaxation law is also the sameas that of the matrix material ; (2) For a special kind of composite materials of which the relaxation moduli of all the components can be expressed as the products of different individual time-independent coefficients and a same time-dependentfunction , the effective time-dependent thermal expansion coefficient is time-independent , and the character of the relaxation laws is the same as that of conventional materials.
Abstract:
The finite element processes for predicting the effective viscoelastic relaxation modulus , the effective thermalstress relaxation modulus and the effective time-dependent thermal expansion coefficient are given. The thermal viscoelastic constitutive equations including temperature change , the effective thermal stress relaxation laws and the time-dependentcharacter of the thermal expansion coefficients of unidirectional fiber reinforced composite materials are studied. The deformation analysis of a one-dimensional structure of unidirectional fiber reinforced composites shows that the thermal straindepends on time intensively. The numerical results illustrate that the time-dependency of the effective thermal stress relaxation modulus of unidirectional fiber reinforced composites is slight ; its impact modulus is only 0.4 % more than its asymptotic modulus.
The finite element processes for predicting the effective viscoelastic relaxation modulus , the effective thermalstress relaxation modulus and the effective time-dependent thermal expansion coefficient are given. The thermal viscoelastic constitutive equations including temperature change , the effective thermal stress relaxation laws and the time-dependentcharacter of the thermal expansion coefficients of unidirectional fiber reinforced composite materials are studied. The deformation analysis of a one-dimensional structure of unidirectional fiber reinforced composites shows that the thermal straindepends on time intensively. The numerical results illustrate that the time-dependency of the effective thermal stress relaxation modulus of unidirectional fiber reinforced composites is slight ; its impact modulus is only 0.4 % more than its asymptotic modulus.
Abstract:
A piezoelectric-mechanical coupled high order model of composite plates with embedded piezoelectric patcheswas presented. The third-order laminate theory was used to describe the displacement field and a high order electric potential field was assumed to accurately describe the nonuniform distribution of an electric field through the thickness of piezoelectric patches. The simplified constitutive equations of piezoelectric material were presented upon the plane-stress stateassumption , and then the finite element formulas were deduced based on this high order model. The performance of themodel and the formula developed were validated by application in calculating the deformation of a bimorph beam and incontrolling the deflection of a square composite plate with piezoelectric actuators.
A piezoelectric-mechanical coupled high order model of composite plates with embedded piezoelectric patcheswas presented. The third-order laminate theory was used to describe the displacement field and a high order electric potential field was assumed to accurately describe the nonuniform distribution of an electric field through the thickness of piezoelectric patches. The simplified constitutive equations of piezoelectric material were presented upon the plane-stress stateassumption , and then the finite element formulas were deduced based on this high order model. The performance of themodel and the formula developed were validated by application in calculating the deformation of a bimorph beam and incontrolling the deflection of a square composite plate with piezoelectric actuators.
