Polypropylene is commonly used as a binder for ceramic injection molding,and rapid cooling is often encountered during processing.However,the crystallization behavior of polypropylene shows a strong dependence on cool...Polypropylene is commonly used as a binder for ceramic injection molding,and rapid cooling is often encountered during processing.However,the crystallization behavior of polypropylene shows a strong dependence on cooling rate due to its semi-crystalline characteristics.Therefore,the influence of cooling rate on the quality of final product cannot be ignored.In this study,the fast differential scanning calorimetry(FSC)test was performed to study the influence of cooling rate on the non-isothermal crystallization behavior and non-isothermal crystallization kinetics of a copolymer polypropylene(PP BC03B).The results show that the crystallization temperatures and crystallinity decrease as the cooling rate increases.In addition,two exothermic peaks occur when cooling rate ranges from 30 to 300 K·s^(-1),indicating the formation of another crystal phase.Avrami,Ozawa and Mo equations were used to explore the non-isothermal crystallization kinetics,and it can be concluded that the Mo method is suitable for this study.展开更多
The non-isothermal crystallization of poly(L-lactide) (PLLA) under quiescent and steady shear flow conditions was in situ investigated by using polarizing optical microscopy (POM) with a hot shear stage and wide...The non-isothermal crystallization of poly(L-lactide) (PLLA) under quiescent and steady shear flow conditions was in situ investigated by using polarizing optical microscopy (POM) with a hot shear stage and wide-angle X-ray diffraction (WAXD). The shear rate and the cooling rate both play a significant role in the final crystalline morphology and crystallinity. Under quiescent conditions, the morphology assumes different sized spherulites, and its crystallinity dramatically reduces with increasing the cooling rate. On the other hand, the shear flow increases the onset crystallization temperature, and enhances the final crystallinity. When the shear rate is above 5 s^-1, cylindrite-like crystals are observed, furthermore, their content depends on the cooling rate.展开更多
The non-isothermal crystallization kinetics of polyamide 6/diamine-modified multi-walled carbon nanotube (PA6/D-MWNT) nanocomposite was investigated by differential scanning calorimetry (DSC). The modified Avrami ...The non-isothermal crystallization kinetics of polyamide 6/diamine-modified multi-walled carbon nanotube (PA6/D-MWNT) nanocomposite was investigated by differential scanning calorimetry (DSC). The modified Avrami equation, the Ozawa equation and the combined Avrami/Ozawa equation were employed to analyze the non-isothermal crystallization data. The crystallization activation energies were also evaluated by the Kissinger method. It was found that the combined Avrami/Ozawa equation could successfully describe the non-isothermal crystallization process. The results showed that D-MWNTs not only acted as effective heterogeneous nucleating agents for PA6 and noticeably increased the crystallization temperature of PA6, but also influenced the mechanism of nucleation and crystal growth of PA6 and then reduced the overall crystallization rate of the neat PA6 matrix. The crystallization activation energy for the nanocomposite sample was greater than that of the neat PA6, which indicated that the addition of D-MWNTs hindered the mobility of PA6 chain segments.展开更多
The non-isothermal crystallization kinetics of polypropylene (PP), PP/anhydrite composites were investigated by differential scanning calorimetry (DSC) with various cooling rates. The Avrami analysis modified by J...The non-isothermal crystallization kinetics of polypropylene (PP), PP/anhydrite composites were investigated by differential scanning calorimetry (DSC) with various cooling rates. The Avrami analysis modified by Jeziorny and a method developed by Mo were employed to describe the non-isothermal crystallization process of these samples. The difference in the exponent n between PP and PP/anhydrite composites indicated that non-isothermal kinetic crystallization corresponded to tri-dimensional growth with heterogeneous nucleation. The values of half-time, Zc and F(T) showed that the crystallization rate increased with the increasing of cooling rates for PP and PP/anhydrite composites, but the crystallization rate of PP/anhydrite composites was faster than that of PP at a given cooling rate. The method developed by Ozawa did not describe the non-isothermal crystallization process of PP very well. Moreover, the method proposed by Kissinger was used to evaluate the activation energy of the mentioned samples. The result showed that the activation energy of PP/anhydrite was greatly larger than that of PP.展开更多
A kinetic equation of non-isothermal crystamzation was derived by extending Avrami's equation to the non-isothermal situation. More crystallization information can be obtained from this kinetic equation. The curve...A kinetic equation of non-isothermal crystamzation was derived by extending Avrami's equation to the non-isothermal situation. More crystallization information can be obtained from this kinetic equation. The curves of non-isothermal and isothermal crystallizations were analysed and compared for poly (ethylene terephthalate) (PET), and the results were discussed.展开更多
Fiber-class modified kaolin and PET have been blended in the twin-screw and granulated to chips containing 4 wt% of kaolin.Non-isothermal crystallization process of kaolin modified polyester was investigated using a d...Fiber-class modified kaolin and PET have been blended in the twin-screw and granulated to chips containing 4 wt% of kaolin.Non-isothermal crystallization process of kaolin modified polyester was investigated using a differential scanning calorimetry (DSC),and the addition of kaolin enhances either the melting temperature (Tm) or the crystallization temperature (Tc).The morphology of kaolin modified polyester,the melt of which is cooled at different cooling rate,was observed by scanning electron microscope (SEM).The relationship between Tc and cooling rate F was studied.Semi-crystalline phase t1/2 makes an exponential decline with increasing F,and the higher the cooling rate,the shorter the time of crystallization completion.Non-isothermal crystallization kinetics parameters and the activation energy were calculated,indicating that the higher rate of cooling needs the higher relative crystallinity in the unit crystallization time,the crystallization rate increased while speeding up the temperature reduction,and the activation energy ΔE was calculated to be-204.1566 kJ/mol for the non-isothermal crystallization processes by the Kissinger's methods.展开更多
An equation of non-isothermal crystallization kinetics was derived according to a new model and the crystallizations of both the PET samples under solid state polycon-densation and the pre-orientation yarn of high spe...An equation of non-isothermal crystallization kinetics was derived according to a new model and the crystallizations of both the PET samples under solid state polycon-densation and the pre-orientation yarn of high speeding spinning PET were studied with this equation. The results show that there is a good linear relationship between In {-In[1-X(T)]} and lnΦ. The index m in the equation approximately equals to 3 for PET chips and 1. 3 for pre-orientated yarn. At the same temperature, Q(T) decreases with the increase of PET M. W. and the kinetics parameters obtained by Jeziorny' s method indicate that G also decreases with the increase of PET M. W.. Q(T) and Gc show the same varying tendency in the non-isothermal crystallization process.展开更多
In this paper we have presented the results of acoustic emission (AE) during non-isothemal crystallization of polypropylene (PP) melt with mean cooling rate 4℃/min, and discussed the effects of molecular weight (MW) ...In this paper we have presented the results of acoustic emission (AE) during non-isothemal crystallization of polypropylene (PP) melt with mean cooling rate 4℃/min, and discussed the effects of molecular weight (MW) on AE activity. It is shown that the amount of AE ring-down counts during whole crystallization of PP depends on the MW strongly.The copious AE bursts have been observed at the late stage of PPcrystallization. AE bursts are caused by cracking, crazing and cavitation between spherulites and inside spherulites.展开更多
The non-isothermal crystallization kinetics of modified poly(ethylene terephthalate) (PET) with the function of ultraviolet (UV) protection was studied by means of differential scanning calorimetry. The kinetics of th...The non-isothermal crystallization kinetics of modified poly(ethylene terephthalate) (PET) with the function of ultraviolet (UV) protection was studied by means of differential scanning calorimetry. The kinetics of the modified polymer under non-isothermal crystallization was analyzed by Ozawa equation. The crystallization behavior of the modified polymer obeyed Ozawa theory. The additives in the polymer whose function was UV-resistant acted as crystal nucleus in the processing of crystallization, which resulted in the increase of Avrami index and the crystallization rate of the cooling system.展开更多
The kineties of non-isothermal crystallization of Nylon-1010 has been investigated by using differential scanning calorimetry(DSC), DSC curves were obtained under cooling rate(R): 2. 5, 5, 10, 20, 40K/min. Applying Ma...The kineties of non-isothermal crystallization of Nylon-1010 has been investigated by using differential scanning calorimetry(DSC), DSC curves were obtained under cooling rate(R): 2. 5, 5, 10, 20, 40K/min. Applying Mandelkern and Ziabicki theories, the values of the Z kinetic parameter and G the kinetic crystalllzab- ility have been determined. Expenents of Avrami obtained in this work decrease with increase of cooling rate and then level off. The experimental results show disagreements with the Ozawa equation.展开更多
The non-isothermal crystallization kinetics of poly(ethylene terephthalate) (PET) modified by poly (ethlene glycol) (PEG) were determined by DSC. The dual linear regression method was used to evaluate the relationship...The non-isothermal crystallization kinetics of poly(ethylene terephthalate) (PET) modified by poly (ethlene glycol) (PEG) were determined by DSC. The dual linear regression method was used to evaluate the relationship between the reciprocal of t 1/2 ( the half life of crystallization) and the appropriate temperature variable. The parameters such as the activation energy (Ed) for transport, the equilibrium melting temperature (T_m^0),the nucleation parameter (ψ),themaximum crystallization temperature (T_(e, max)), and the kinetic crystallizability (G) for the copolyesters were obtained. The influence of the PEG content in PET chains on the parameters characterizing crystallization kinetics and crystallization thermodynamics was discussed.展开更多
This work deals with isothermal and non-isothermal crystallization kinetics of electrically conductive polyvinylidene fluoride/poly(ethylene terephthalate) (PVDF/PET) based composites. It completes our previous work i...This work deals with isothermal and non-isothermal crystallization kinetics of electrically conductive polyvinylidene fluoride/poly(ethylene terephthalate) (PVDF/PET) based composites. It completes our previous work in which we related the crystallinity of these conductive PVDF/PET based composites to their through-plane resistivity [1]. Isothermal crystallization was described using the logarithmic form of the Avrami equation and it was observed that the crystallization rate of the PVDF phase inside the composite became slower compared to that of neat PVDF. In non-isothermal crystallization, the Avrami exponent of PVDF phase did not show any noticeable variation;however, that of PET phase, which contains the major part of the conductive carbon black (CB) and graphite (GR) additives, showed an evident decrease compared with neat PET. It was also observed that, at the same cooling rate, the crystallization rate of PVDF and PET phases inside the composite was slower than that of neat PVDF and PET.展开更多
In this article, we prove the global existence of weak solutions to the non- isothermal nematic liquid crystal system on T2, on the basis of a new approximate system which is different from the classical Ginzburg-Land...In this article, we prove the global existence of weak solutions to the non- isothermal nematic liquid crystal system on T2, on the basis of a new approximate system which is different from the classical Ginzburg-Landau approximation. Local in space energy inequalities are employed to recover the estimates on the second order spatial derivatives of the director fields locally in time, which cannot be derived from the basic energy balance. It is shown that these weak solutions satisfy the temperature equation, and also the total energy equation but away from at most finite many "singular" times, at which the energy concentration occurs and the director field losses its second order derivatives.展开更多
In this paper, we study the low Mach number limit of a compressible nonisothermal model for nematic liquid crystals in a bounded domain. We establish the uniform estimates with respect to the Mach number, and thus pro...In this paper, we study the low Mach number limit of a compressible nonisothermal model for nematic liquid crystals in a bounded domain. We establish the uniform estimates with respect to the Mach number, and thus prove the convergence to the solution of the incompressible model for nematic liquid crystals.展开更多
Al-12Zn-3Mg-2.5Cu alloy was prepared using a liquid metallurgy route under the optimized conditions. A sample cut from the ingot was rolled non-isothermally from 400℃ to 100℃ in 100℃ steps, with 15% reduction in th...Al-12Zn-3Mg-2.5Cu alloy was prepared using a liquid metallurgy route under the optimized conditions. A sample cut from the ingot was rolled non-isothermally from 400℃ to 100℃ in 100℃ steps, with 15% reduction in thickness; it was then cold rolled isothermally at room temperature for 85% reduction. The cold-rolled alloys were characterized by electron microscopy, hardness test, and tensile test to elucidate their structural evolution and evaluate their mechanical behavior. In the results, the cast alloy consists of a-aluminum and various intermetallic compounds. These compounds are segregated along the grain boundaries, which makes the alloy difficult to roll at room tem- perature. The combined effect of non-isothermal step rolling and cold rolling results in the nano/microsized compounds distributed uniformly in the matrix. The hardness is substantially increased after rolling. This increase in hardness is attributed to the ultra-fine grain size, fine-scale intermetallic compounds, and structural defects (e.g., dislocations, stacking faults, and sub-grains). The ultimate tensile strength of the rolled alloy is approximately 628 MPa with 7% ductility.展开更多
Cu-Zr-Al-(Y, Ag) amorphous alloy ribbons of Cu_(50)Zr_(42)Al_8, Cu_(46)Zr_(47-x)Al_7Y_x(x=2, 5), Cu_(43)Zr_(42)Al_8Ag_7, and Cu_(43)Zr_(42)Al_8Ag_5Y_2 were prepared using the single roller melt-spi...Cu-Zr-Al-(Y, Ag) amorphous alloy ribbons of Cu_(50)Zr_(42)Al_8, Cu_(46)Zr_(47-x)Al_7Y_x(x=2, 5), Cu_(43)Zr_(42)Al_8Ag_7, and Cu_(43)Zr_(42)Al_8Ag_5Y_2 were prepared using the single roller melt-spinning method. The glass forming ability and non-isothermal crystallization behavior of the amorphous alloys were investigated by means of X-ray diffraction(XRD) and differential scanning calorimetry(DSC) in a continuous heating mode. The experimental results show that the glass forming ability and thermal stability of Cu-Zr-Al amorphous alloys are improved by adding minor amounts of Y and Ag, and the effect of Ag on the glass forming ability is more significant than that of Y. Compared to the Cu_(50)Zr_(42)Al_8 alloy, the width of the supercooled liquid region of the Cu_(46)Zr_(47-x)Al_7Y_x(x =2 and 5) alloys increased by 19 K and 30 K, respectively. The reduced glass transition temperature(Trg) and the parameter γ of the two alloys enhanced separately. Compared to the Cu_(50)Zr_(42)Al_8 alloy, the Trg and γ values of both Cu_(43)Zr_(42)Al_8Ag_7 and Cu_(43)Zr_(42)Al_8Ag_5Y_2 alloys enhanced noticeably up to 0.619, 0.417, and 0.609, 0.412, respectively. The crystallization activation energies of the amorphous alloys calculated by the Kissinger and Flynn Wall Ozawa equations increased with the addition of minor Y and Ag into the Cu_(50)Zr_(42)Al_8 alloy. The addition of Y and Ag significantly improved the thermal stability of the Cu_(50)Zr_(42)Al_8 amorphous alloy.展开更多
With the means of electron backscattered diffraction(EBSD),mechanical properties test and digital eddy current metal conductivity,the single crystal copper cold-welded joint was tested and analyzed,the structure chang...With the means of electron backscattered diffraction(EBSD),mechanical properties test and digital eddy current metal conductivity,the single crystal copper cold-welded joint was tested and analyzed,the structure change of cold-welded joint and the effect of heat treating on the structure and property of cold-welded joint were discussed.The results show that:The deformation area of the single crystal copper cold welded joint is broken,the crystalline grain at the interface of the joint is refined,and the single crystal structure is still maintained in the base metal area.The hardness of the deformation area increases greatly,the conductivity of the joint does not change much,and the tensile strength of the joint reaches about 70%of that of the base metal.At the interface of the heat treating joint,the single crystal structure of the deformation area and the base metal area are destroyed,and the grains grow up at the interface and the orientation is different.The hardness of the joint interface is much lower than that of the non-heat treating joint,the electrical conductivity of the joint is good,and the tensile strength of the joint is higher than that of the base metal.展开更多
The non-isothermal crystallization kinetics, isothermal crystallization and the morphology of crystals of the copolymer poly (ethylene terephthalate/ isophthalate )(IPET) were studied by DSC and polarized-light micros...The non-isothermal crystallization kinetics, isothermal crystallization and the morphology of crystals of the copolymer poly (ethylene terephthalate/ isophthalate )(IPET) were studied by DSC and polarized-light microscopy in this paper. DSC results indicate that the glass transition temperature Tg of IPET is slightly lower than that of poly(ethylene terephthalate) (PET), but the melting temperature Tm and the crystallization temperature Tc of PET and IPET have much difference.The difference of Tc between PET and IPET2 is about 7℃, and the difference of Tm between PET and IPET2 is about 16℃. From the kinetics analysis of the crystallization, the crystallization mechanism of all samples is of three-dimension spherulitic growth from instantaneous nuclei and the incorporation of isophthalate (IPA) decreases the crystallization rate of IPET greatly. The isothermal results indicate that the morphologies of PET and IPET crystals are all spherulite, which is in conformity to the results of nonisothermal dynamic crystallization. At the same time,the spherulite of IPET grows slower and has longer incubation time than the spherulite of PET under the same crystallization condition.展开更多
Tibetan butter(TB),generally called butter,is a solid oil product extracted from yak milk in the QinghaiTibet plateau area.However,due to the limitations of raw material sources and production technology,there is a sh...Tibetan butter(TB),generally called butter,is a solid oil product extracted from yak milk in the QinghaiTibet plateau area.However,due to the limitations of raw material sources and production technology,there is a shortage of TB,so it is important to find substitutes of TB.This paper studied the crystallization behavior of six kinds of commercial TB products in Tibet to provide the theoretical basis for the development of TB substitutes for the production of TB lamps and flowers.This study assessed the crystallization behaviors of the TB samples,including isothermal crystallization process and non-isothermal crystallization process.The microstructure,isothermal crystallization of TB were evaluated by polarized light microscopy and low-pulse NMR spectrometry,respectively.The non-isothermal crystallization process of TB under temperature scanning were investigated using Rheometer,and the crystallization behavior under different cooling rates were determined by diferential scanning calorimetry(DSC)procedures.The results showed that the TB was crystallized at a higher supercooling(-10,0 and 10℃).Dimensional growth is dominant;at 20℃,spiral growth dominates.The TB has complex crystallization nucleation behavior.The crystal types of TB are mainlyβ’-crystal form andβ’-like crystal form.The lower the cooling rate,the shorter the crystallization induction time,and the more the number of crystal nuclei.Therefore,during producing TB substitutes in the factory,the cooling rate can be controlled at10℃/min to reduce energy consumption and production costs.展开更多
基金financially supported by a grant provided by Mitsubishi Heavy Industries。
文摘Polypropylene is commonly used as a binder for ceramic injection molding,and rapid cooling is often encountered during processing.However,the crystallization behavior of polypropylene shows a strong dependence on cooling rate due to its semi-crystalline characteristics.Therefore,the influence of cooling rate on the quality of final product cannot be ignored.In this study,the fast differential scanning calorimetry(FSC)test was performed to study the influence of cooling rate on the non-isothermal crystallization behavior and non-isothermal crystallization kinetics of a copolymer polypropylene(PP BC03B).The results show that the crystallization temperatures and crystallinity decrease as the cooling rate increases.In addition,two exothermic peaks occur when cooling rate ranges from 30 to 300 K·s^(-1),indicating the formation of another crystal phase.Avrami,Ozawa and Mo equations were used to explore the non-isothermal crystallization kinetics,and it can be concluded that the Mo method is suitable for this study.
基金supported by the National Natural Science Foundation of China(No.50527301)
文摘The non-isothermal crystallization of poly(L-lactide) (PLLA) under quiescent and steady shear flow conditions was in situ investigated by using polarizing optical microscopy (POM) with a hot shear stage and wide-angle X-ray diffraction (WAXD). The shear rate and the cooling rate both play a significant role in the final crystalline morphology and crystallinity. Under quiescent conditions, the morphology assumes different sized spherulites, and its crystallinity dramatically reduces with increasing the cooling rate. On the other hand, the shear flow increases the onset crystallization temperature, and enhances the final crystallinity. When the shear rate is above 5 s^-1, cylindrite-like crystals are observed, furthermore, their content depends on the cooling rate.
基金Guoxin Sui would like to acknowledge the financial supports of the Hundreds’ Talents Program of Chinese Academy of Sciences.
文摘The non-isothermal crystallization kinetics of polyamide 6/diamine-modified multi-walled carbon nanotube (PA6/D-MWNT) nanocomposite was investigated by differential scanning calorimetry (DSC). The modified Avrami equation, the Ozawa equation and the combined Avrami/Ozawa equation were employed to analyze the non-isothermal crystallization data. The crystallization activation energies were also evaluated by the Kissinger method. It was found that the combined Avrami/Ozawa equation could successfully describe the non-isothermal crystallization process. The results showed that D-MWNTs not only acted as effective heterogeneous nucleating agents for PA6 and noticeably increased the crystallization temperature of PA6, but also influenced the mechanism of nucleation and crystal growth of PA6 and then reduced the overall crystallization rate of the neat PA6 matrix. The crystallization activation energy for the nanocomposite sample was greater than that of the neat PA6, which indicated that the addition of D-MWNTs hindered the mobility of PA6 chain segments.
文摘The non-isothermal crystallization kinetics of polypropylene (PP), PP/anhydrite composites were investigated by differential scanning calorimetry (DSC) with various cooling rates. The Avrami analysis modified by Jeziorny and a method developed by Mo were employed to describe the non-isothermal crystallization process of these samples. The difference in the exponent n between PP and PP/anhydrite composites indicated that non-isothermal kinetic crystallization corresponded to tri-dimensional growth with heterogeneous nucleation. The values of half-time, Zc and F(T) showed that the crystallization rate increased with the increasing of cooling rates for PP and PP/anhydrite composites, but the crystallization rate of PP/anhydrite composites was faster than that of PP at a given cooling rate. The method developed by Ozawa did not describe the non-isothermal crystallization process of PP very well. Moreover, the method proposed by Kissinger was used to evaluate the activation energy of the mentioned samples. The result showed that the activation energy of PP/anhydrite was greatly larger than that of PP.
文摘A kinetic equation of non-isothermal crystamzation was derived by extending Avrami's equation to the non-isothermal situation. More crystallization information can be obtained from this kinetic equation. The curves of non-isothermal and isothermal crystallizations were analysed and compared for poly (ethylene terephthalate) (PET), and the results were discussed.
文摘Fiber-class modified kaolin and PET have been blended in the twin-screw and granulated to chips containing 4 wt% of kaolin.Non-isothermal crystallization process of kaolin modified polyester was investigated using a differential scanning calorimetry (DSC),and the addition of kaolin enhances either the melting temperature (Tm) or the crystallization temperature (Tc).The morphology of kaolin modified polyester,the melt of which is cooled at different cooling rate,was observed by scanning electron microscope (SEM).The relationship between Tc and cooling rate F was studied.Semi-crystalline phase t1/2 makes an exponential decline with increasing F,and the higher the cooling rate,the shorter the time of crystallization completion.Non-isothermal crystallization kinetics parameters and the activation energy were calculated,indicating that the higher rate of cooling needs the higher relative crystallinity in the unit crystallization time,the crystallization rate increased while speeding up the temperature reduction,and the activation energy ΔE was calculated to be-204.1566 kJ/mol for the non-isothermal crystallization processes by the Kissinger's methods.
文摘An equation of non-isothermal crystallization kinetics was derived according to a new model and the crystallizations of both the PET samples under solid state polycon-densation and the pre-orientation yarn of high speeding spinning PET were studied with this equation. The results show that there is a good linear relationship between In {-In[1-X(T)]} and lnΦ. The index m in the equation approximately equals to 3 for PET chips and 1. 3 for pre-orientated yarn. At the same temperature, Q(T) decreases with the increase of PET M. W. and the kinetics parameters obtained by Jeziorny' s method indicate that G also decreases with the increase of PET M. W.. Q(T) and Gc show the same varying tendency in the non-isothermal crystallization process.
基金This work was supported by Academia Sinica selected Research Program and National Natural Science Foundation of China
文摘In this paper we have presented the results of acoustic emission (AE) during non-isothemal crystallization of polypropylene (PP) melt with mean cooling rate 4℃/min, and discussed the effects of molecular weight (MW) on AE activity. It is shown that the amount of AE ring-down counts during whole crystallization of PP depends on the MW strongly.The copious AE bursts have been observed at the late stage of PPcrystallization. AE bursts are caused by cracking, crazing and cavitation between spherulites and inside spherulites.
文摘The non-isothermal crystallization kinetics of modified poly(ethylene terephthalate) (PET) with the function of ultraviolet (UV) protection was studied by means of differential scanning calorimetry. The kinetics of the modified polymer under non-isothermal crystallization was analyzed by Ozawa equation. The crystallization behavior of the modified polymer obeyed Ozawa theory. The additives in the polymer whose function was UV-resistant acted as crystal nucleus in the processing of crystallization, which resulted in the increase of Avrami index and the crystallization rate of the cooling system.
文摘The kineties of non-isothermal crystallization of Nylon-1010 has been investigated by using differential scanning calorimetry(DSC), DSC curves were obtained under cooling rate(R): 2. 5, 5, 10, 20, 40K/min. Applying Mandelkern and Ziabicki theories, the values of the Z kinetic parameter and G the kinetic crystalllzab- ility have been determined. Expenents of Avrami obtained in this work decrease with increase of cooling rate and then level off. The experimental results show disagreements with the Ozawa equation.
文摘The non-isothermal crystallization kinetics of poly(ethylene terephthalate) (PET) modified by poly (ethlene glycol) (PEG) were determined by DSC. The dual linear regression method was used to evaluate the relationship between the reciprocal of t 1/2 ( the half life of crystallization) and the appropriate temperature variable. The parameters such as the activation energy (Ed) for transport, the equilibrium melting temperature (T_m^0),the nucleation parameter (ψ),themaximum crystallization temperature (T_(e, max)), and the kinetic crystallizability (G) for the copolyesters were obtained. The influence of the PEG content in PET chains on the parameters characterizing crystallization kinetics and crystallization thermodynamics was discussed.
文摘This work deals with isothermal and non-isothermal crystallization kinetics of electrically conductive polyvinylidene fluoride/poly(ethylene terephthalate) (PVDF/PET) based composites. It completes our previous work in which we related the crystallinity of these conductive PVDF/PET based composites to their through-plane resistivity [1]. Isothermal crystallization was described using the logarithmic form of the Avrami equation and it was observed that the crystallization rate of the PVDF phase inside the composite became slower compared to that of neat PVDF. In non-isothermal crystallization, the Avrami exponent of PVDF phase did not show any noticeable variation;however, that of PET phase, which contains the major part of the conductive carbon black (CB) and graphite (GR) additives, showed an evident decrease compared with neat PET. It was also observed that, at the same cooling rate, the crystallization rate of PVDF and PET phases inside the composite was slower than that of neat PVDF and PET.
基金Hong Kong RGC Earmarked Research Grants 14305315,CUHK4041/11P and CUHK4048/13PThe Chinese University of Hong Kong,a Croucher Foundation-CAS Joint Grant,and a NSFC/RGC Joint Research Scheme(N-CUHK443/14)
文摘In this article, we prove the global existence of weak solutions to the non- isothermal nematic liquid crystal system on T2, on the basis of a new approximate system which is different from the classical Ginzburg-Landau approximation. Local in space energy inequalities are employed to recover the estimates on the second order spatial derivatives of the director fields locally in time, which cannot be derived from the basic energy balance. It is shown that these weak solutions satisfy the temperature equation, and also the total energy equation but away from at most finite many "singular" times, at which the energy concentration occurs and the director field losses its second order derivatives.
基金supported by NSFC(11171154)supported in part by by NSFC(11671193)A Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘In this paper, we study the low Mach number limit of a compressible nonisothermal model for nematic liquid crystals in a bounded domain. We establish the uniform estimates with respect to the Mach number, and thus prove the convergence to the solution of the incompressible model for nematic liquid crystals.
文摘Al-12Zn-3Mg-2.5Cu alloy was prepared using a liquid metallurgy route under the optimized conditions. A sample cut from the ingot was rolled non-isothermally from 400℃ to 100℃ in 100℃ steps, with 15% reduction in thickness; it was then cold rolled isothermally at room temperature for 85% reduction. The cold-rolled alloys were characterized by electron microscopy, hardness test, and tensile test to elucidate their structural evolution and evaluate their mechanical behavior. In the results, the cast alloy consists of a-aluminum and various intermetallic compounds. These compounds are segregated along the grain boundaries, which makes the alloy difficult to roll at room tem- perature. The combined effect of non-isothermal step rolling and cold rolling results in the nano/microsized compounds distributed uniformly in the matrix. The hardness is substantially increased after rolling. This increase in hardness is attributed to the ultra-fine grain size, fine-scale intermetallic compounds, and structural defects (e.g., dislocations, stacking faults, and sub-grains). The ultimate tensile strength of the rolled alloy is approximately 628 MPa with 7% ductility.
基金the National Natural Science Foundation of China(No.51208288)the SDUST Research Fund(No.2014TDJH104)
文摘Cu-Zr-Al-(Y, Ag) amorphous alloy ribbons of Cu_(50)Zr_(42)Al_8, Cu_(46)Zr_(47-x)Al_7Y_x(x=2, 5), Cu_(43)Zr_(42)Al_8Ag_7, and Cu_(43)Zr_(42)Al_8Ag_5Y_2 were prepared using the single roller melt-spinning method. The glass forming ability and non-isothermal crystallization behavior of the amorphous alloys were investigated by means of X-ray diffraction(XRD) and differential scanning calorimetry(DSC) in a continuous heating mode. The experimental results show that the glass forming ability and thermal stability of Cu-Zr-Al amorphous alloys are improved by adding minor amounts of Y and Ag, and the effect of Ag on the glass forming ability is more significant than that of Y. Compared to the Cu_(50)Zr_(42)Al_8 alloy, the width of the supercooled liquid region of the Cu_(46)Zr_(47-x)Al_7Y_x(x =2 and 5) alloys increased by 19 K and 30 K, respectively. The reduced glass transition temperature(Trg) and the parameter γ of the two alloys enhanced separately. Compared to the Cu_(50)Zr_(42)Al_8 alloy, the Trg and γ values of both Cu_(43)Zr_(42)Al_8Ag_7 and Cu_(43)Zr_(42)Al_8Ag_5Y_2 alloys enhanced noticeably up to 0.619, 0.417, and 0.609, 0.412, respectively. The crystallization activation energies of the amorphous alloys calculated by the Kissinger and Flynn Wall Ozawa equations increased with the addition of minor Y and Ag into the Cu_(50)Zr_(42)Al_8 alloy. The addition of Y and Ag significantly improved the thermal stability of the Cu_(50)Zr_(42)Al_8 amorphous alloy.
文摘With the means of electron backscattered diffraction(EBSD),mechanical properties test and digital eddy current metal conductivity,the single crystal copper cold-welded joint was tested and analyzed,the structure change of cold-welded joint and the effect of heat treating on the structure and property of cold-welded joint were discussed.The results show that:The deformation area of the single crystal copper cold welded joint is broken,the crystalline grain at the interface of the joint is refined,and the single crystal structure is still maintained in the base metal area.The hardness of the deformation area increases greatly,the conductivity of the joint does not change much,and the tensile strength of the joint reaches about 70%of that of the base metal.At the interface of the heat treating joint,the single crystal structure of the deformation area and the base metal area are destroyed,and the grains grow up at the interface and the orientation is different.The hardness of the joint interface is much lower than that of the non-heat treating joint,the electrical conductivity of the joint is good,and the tensile strength of the joint is higher than that of the base metal.
文摘The non-isothermal crystallization kinetics, isothermal crystallization and the morphology of crystals of the copolymer poly (ethylene terephthalate/ isophthalate )(IPET) were studied by DSC and polarized-light microscopy in this paper. DSC results indicate that the glass transition temperature Tg of IPET is slightly lower than that of poly(ethylene terephthalate) (PET), but the melting temperature Tm and the crystallization temperature Tc of PET and IPET have much difference.The difference of Tc between PET and IPET2 is about 7℃, and the difference of Tm between PET and IPET2 is about 16℃. From the kinetics analysis of the crystallization, the crystallization mechanism of all samples is of three-dimension spherulitic growth from instantaneous nuclei and the incorporation of isophthalate (IPA) decreases the crystallization rate of IPET greatly. The isothermal results indicate that the morphologies of PET and IPET crystals are all spherulite, which is in conformity to the results of nonisothermal dynamic crystallization. At the same time,the spherulite of IPET grows slower and has longer incubation time than the spherulite of PET under the same crystallization condition.
基金funding from the MPOB(PORTSIM 045/2016)the National Key R&D Program of China(2016YFD041404)。
文摘Tibetan butter(TB),generally called butter,is a solid oil product extracted from yak milk in the QinghaiTibet plateau area.However,due to the limitations of raw material sources and production technology,there is a shortage of TB,so it is important to find substitutes of TB.This paper studied the crystallization behavior of six kinds of commercial TB products in Tibet to provide the theoretical basis for the development of TB substitutes for the production of TB lamps and flowers.This study assessed the crystallization behaviors of the TB samples,including isothermal crystallization process and non-isothermal crystallization process.The microstructure,isothermal crystallization of TB were evaluated by polarized light microscopy and low-pulse NMR spectrometry,respectively.The non-isothermal crystallization process of TB under temperature scanning were investigated using Rheometer,and the crystallization behavior under different cooling rates were determined by diferential scanning calorimetry(DSC)procedures.The results showed that the TB was crystallized at a higher supercooling(-10,0 and 10℃).Dimensional growth is dominant;at 20℃,spiral growth dominates.The TB has complex crystallization nucleation behavior.The crystal types of TB are mainlyβ’-crystal form andβ’-like crystal form.The lower the cooling rate,the shorter the crystallization induction time,and the more the number of crystal nuclei.Therefore,during producing TB substitutes in the factory,the cooling rate can be controlled at10℃/min to reduce energy consumption and production costs.
基金the financial support of the Natural Science Foundation of Chongqing(project No.CSTC2006BA6031)the Program for New Century Excellent Talents in Chinese Universities(project No.NCET-04-1002)