Non-isothermal crystallization kinetics of reactive microgel/nylon 6 blends☆

The non-isothermal crystal ization kinetics of reactive microgel/nylon 6 blends was investigated by differential scanning calorimetry (DSC). The Mo equation was employed to analyze the non-isothermal crystallization data. The crystallization activation energies were also evaluated by the Kissinger method. The results show that the crystallization onset temperature (Tonset) and crystallization peak temperature (Tp) decrease with the increase of the content of reactive microgel, whileΔT (Tonset–Tp), the crystallization half-time (t1/2) and the crystal ization enthalpy (ΔHc) increase. The required cooling rates of blends are higher than that of neat nylon 6 in order to achieve the same relative crystallinity in a unit of time. The crystallization activation energies of the reactive microgel/nylon 6 blends are greater than those of the neat nylon 6. When the content of reactive microgel is 30%, the relative crystallinity (Xt) reaches the maximum.     

聚丙烯与超支化聚酯共混物的非等温动力学(英文)

Polypropylene (PP) with different contents of the second generation hyperbranched polyester (HBP) is prepared by melt blending method. The non-isothermal crystallization kinetics of PP and PP/HBP blends is investigated under differential scanning calorimetry (DSC). The Mo equation is used to analyze the DSC data. The results show that the Mo theory is suitable for crystal ization kinetics of the blends. Fast cooling rate is not good for crys-tallizing and nucleating. The values of half crystal ization time (t1/2), crystal ization enthalpy (ΔHc) and temper-ature range (ΔT) of PP/HBP blends decrease when HBP is added. The required cooling rate of PP is higher than that of PP/HBP blends in order to reach the same relative crystal inity. Crystallization rate increases with the ad-dition of HBP. The crystallization rate reaches a maximum when the content of HBP is 5%. In addition, the activa-tion energies of PP and PP/HBP blends are calculated by Kissinger equation, revealing that the content of HBP has a little effect on the crystallization activation energy.     

APPROXIMATE ANALYTICAL SOLUTION OF EFFECTIVENESS FACTOR FOR POROUS CATALYST (Ⅱ) COMPARISON OF APPROXIMATE ANALYTICAL SOLUTION WITH NUMERICAL SOLUTION

Large amounts of calculations on effectiveness factor have been done based on the approximateexpression proposed in Part(Ⅰ)of this work for porous catalyst under isothermal condition at various valuesof Thiele modulus for nonfirst order reaction of power-function and hyperbolic kinetics.Likewise,valuesof effectiveness factor have been obtained under the same conditions from the three expressions found inliterature as well as by numerical method for comparison.The results show that our approximate expressionhas a quite high accuracy and therefore is much superior to the others.The parameter estimation of ourexpression is rather easy doing and has no such difficulties as encountered in handling of the other ex-pressions.     

Influence of Nano-Nd2O3 on Crystallization Mechanism of Fused Quartz

The isothermal crystallization kinetics of pure fused quartz of blank specimen N- 0 and specimen N- 3 in troduced with 3 mass% nano-Nd2O3 was researched by means of XRD and Avrami equation. The results show that crystallization mechanisms of fused quartz in two specimens are both heterogeneous nucleation type caused by surface structure defects,and the grain growth mode of two specimens are both two-dimensional growth ac companied by one-dimensional and three-dimensiona growths,specimen N- 3 has the higher degree of grain growth in one-dimensional and three-dimensional than specimen N- 0; introducing nano-Nd2O3 can obviously reduce the "active nucleation sites"of glass structure on the fused quartz particles surface,enhance the stability o glass structure,increase the activation energy of fused quartz crystallization from 874 k J · mol- 1to 1 270 k J·mol- 1,and decrease the crystallization rate of fused quartz obviously.     

A METHOD FOR CALCULATING THE EXTENT OF REACTION OF SOLID PARTICLES WITH FLUID IN COMPLETELY MIXED REACTORS CONNECTED IN SERIES

When solid particles react with a fluid,the overall rate is influened by the fraction of the solidunconverted as well as by the operating conditions such as temperature and pressure.Calculation of solidsconversion in the individual reactor of a multi-stage reactor system has therefore to be based upon thesolids residence time distribution (RTD) in the respective stages.By using either the Dirac function δ(0) or the probability density function of the sum of independentrandom variables,the solids RTD in any stage of completely mixed reactors connected in series with nointerstage backflow has been obtained.The latter method has also been used in deriving general formu-las for the calculation of solids conversion when the order of chemical reaction is simple.For complexchemical reaction rate equations a stagewise procedure for numerical computation is proposed,and twocases are discussed according to whether the rate equation is expressed in its integral or differential formrespectively.     

Leaching Kinetics of Calcium Vanadate by Na2CO3 Solution

Leaching kinetics of calcium vanadate by Na2CO3 solution was studied. Kinetic equation was established according to the variation of VO3-concentration with time during the leaching process. The influences of initial pH value and stirring speed on reaction rate constant were examined and the corresponding apparent activation energy was calculated. The results indicate that the leaching process is a 0.68 order reaction, and the reaction rate constant 8.64×10-6 mol/(L-s). It increases with the increase of pH value and stirring speed. And the dissolution rate of calcium vanadate also increases. The apparent activation energy is 38.98 kJ/mol, and temperature has great influence on the leaching rate of calcium vanadate.     

低温水相一步合成钛酸钡:热力学模型化及实验合成研究

A thermodynamic model has been developed to determine the reaction conditions favoring low temperature direct synthesis of barium titanate (BaTiO3). The method utilizes standard-state thermodynamic data for solid and aqueous species and a Debye-Hǔckel coefficients model to represent solution nonideality. The method has been used to generate phase stability diagrams that indicate the ranges of pH and reagent concentrations, for which various species predominate in the system at a given temperature. Also, yield diagrams have been constructed that indicate the concentration, pH and temperature conditions for which different yields of crystalline BaTiO3 can be obtained. The stability and yield diagrams have been used to predict the optimum synthesis conditions (e.g.,reagent concentrations, pH and temperature). Subsequently, these predictions have been experimentally verified.As a result, phase-pure perovskite BaTiO3 has been obtained at temperature ranging from 55 to 85℃ using BaCl2,TiCl4 as a source for Ba and Ti. and NaOH as a orecioitator.     

Effect of wall temperature modulation on the heat transfer characteristics of droplet-train flow inside a rectangular microchannel

The numerical studies of water–oil two-phase slug flow inside a two-dimensional vertical microchannel subjected to modulated wall temperature boundary conditions have been discussed in the present paper. Many researchers have contributed their efforts in exploring the characteristics of Taylor flows inside microchannel under constant wall heat flux or isothermal wall conditions. However, there is no study available in the literature which discusses the impact of modulated thermal wall boundary conditions on the heat transfer behavior of slug flows inside microchannels. Hence, to bridge this gap, an effort has been made to understand the heat transfer characteristics of the flow under sinusoidal wall temperature conditions. Initially, a single phase flow and heat transfer study was performed in microchannels, and the results of the fully developed velocity profile and heat transfer rate were validated with benchmark analytical results. Then an optimal selection of the combination of sinusoidal thermal wall boundary conditions has been made for the two-phase slug flow study. Later, the effects of amplitude(0 b ε b 0.03) and frequency(0 b ω b 750π rad·s~(-1)) of the sinusoidal wall temperature profile on the heat transfer have been studied using the optimal combination of the wall boundary conditions. The results of the numerical study using modulated temperature conditions on channel walls showed a significant improvement in the heat transfer over liquid-only flow by approximately 50% as well as over two-phase flow without wall temperature modulation. The non-dimensional temperature contours obtained for different cases of temperature modulation clearly explain the root cause of such improvement in the heat transfer. Besides,the results based on the hydrodynamics of the flow have also been reported in terms of variation of droplet shapes and film thickness. The influence of Capillary number on the film thickness as well as heat transfer rates has also been discussed. In addition, the measured film thickness has also been compared with that calculated using standard empirical and analytical models available in the literature. The heat transfer rate obtained from the numerical study for the case of unmodulated wall temperature was found to be in a close match with a phenomenological model to evaluate slug flow heat transfer having a mean absolute deviation of 7.56%.     

熔融结晶精制高纯对甲酚的参数优化研究(英文)

Laboratory-scale experiments were carried out to evaluate the influences of operational parameters on the melt crystallization efficiency for p-cresol purification.The optimal crystallization conditions were determined:dynamic pulsed aeration at 90 L·h-1 and the cooling rate of 0.6-0.8 ℃·min-1,followed by sweating at 0.2-0.3 ℃·min-1 for 40 min.Results also demonstrate that the melt crystallization efficiency is sensitive to feed concentration,which highlights this technology for separation and purification of high purity products.     

氢气还原氧化铁动力学的研究(英文)

Kinetics parameters of iron oxide reduction by hydrogen were evaluated by the isothermal method in a differential micro-packed bed.Influence of external diffusion,internal diffusion and heat transfer on the intrinsic reaction rate was investigated and the conditions free of internal and external diffusion resistance have been deter-mined.In the experiments,in order to correctly evaluate the intrinsic kinetics parameters for reducing Fe2O3 to Fe3O4,the reaction temperatures were set between 440 °C and 490 °C.However,in order to distinguish the reduc-tion of Fe3O4 to FeO from that of FeO to Fe,the reaction temperature in the experiment was set to be greater than 570 °C.Intrinsic kinetics of iron oxide reduction by hydrogen was established and the newly established kinetic models were validated by the experimental data.     

Melting behavior,isothermal and nonisothermal crystallization kinetics of nylon 1111

The isothermal and nonisothermal crystallization kinetics of nylon 1111 was extensively studied using differential scanning calorimetry (DSC). The equilibrium melting temperature of nylon 1111 was determined to be 188°C. In this article, the Avrami equation was used to describe the isothermal crystallization behavior of nylon 1111. On the basis of the DSC results, the Avrami exponent, n, was determined to be around 3 during the isothermal crystallization process. Nonisothermal crystallization was analyzed using both the Avrami equation as modified by Jeziorny and an equation suggested by Mo. The larger value of the Avrami exponent, n, during the nonisothermal crystallization process indicates that the development of nucleation and crystal growth are more complicated during the nonisothermal crystallization for nylon 1111, and that the nucleation mode might simultaneously include both homogeneous and heterogeneous nucleations. The isothermal and nonisothermal crystallization activation energies of nylon 1111 were determined to be ?132 kJ/mol and ?121 kJ/mol using the Arrhenius equation and the Kissinger method, respectively. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Effect of alkane chain segment length on the crystallization kinetics of nylon 1010, 1013 and 1014

Isothermal and non‐isothermal crystallization kinetics of long alkane chain segment nylon 1010, 1013 and 1014 were investigated by differential scanning calorimetry. The commonly used Avrami equation and that modified by Jeziorny were employed to fit the isothermal and non‐isothermal crystallizations of nylon 1010, 1013 and 1014, respectively. It was found that the crystallization rate of nylon with a longer alkane chain segment was slower than that of nylon with a shorter one at a given cooling rate. The activation energies for the isothermal and non‐isothermal crystallizations determined by the Arrhenius and the Kissinger methods, respectively, decreased with increase of the alkane chain segment length of nylon 1010, 1013 and 1014. Furthermore, the activation energy of the non‐isothermal crystallization process of these nylons, determined by the isoconversional methods of Flynn and Wall and Ozawa, was found to be a decreasing function of the relative degree of crystallinity. © 2014 Society of Chemical Industry     

Isothermal and nonisothermal crystallization kinetics of MC nylon and polyazomethine/MC nylon composites

Crystallization kinetics of MC nylon (PA6) and polyazomethine (PAM)/MC nylon (PAM/PA6) both have been isothermally and nonisothermally investigated by different scanning calorimetry (DSC). Two stages of crystallization are observed, including primary crystallization and secondary crystallization. The Avrami equation and Mo's modified method can describe the primary stage of isothermal and nonisothermal crystallization of PA6 and PAM/PA6 composite, respectively. In the isothermal crystallization process, the values of the Avrami exponent are obtained, which range from 1.70 to 3.28, indicating an average contribution of simultaneous occurrence of various types of nucleation and growth of crystallization. The equilibrium melting point of PA6 is enhanced with the addition of a small amount of rigid rod polymer chains (PAM). In the nonisothermal crystallization process, we obtain a convenient method to analyze the nonisothermal crystallization kinetics of PA6 and PAM/PA6 composites by using Mo's method combined with the Avrami and Ozawa equations. In the meanwhile, the activation energies are determined to be ?306.62 and ?414.81 KJ/mol for PA6 and PAM/PA6 (5 wt %) composite in nonisothermal crystallization process from the Kissinger method. Analyzing the crystallization half‐time of isothermal and nonisothermal conditions, the over rate of crystallization is increased significantly in samples with a small content of PAM, which seems to result from the increased nucleation density due to the presence of PAM rigid rod chain polymer. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2844–2855, 2004     

Nonisothermal crystallization behavior of poly(aryl ether ether ketone)

A study has been made of the crystallization behavior of poly(aryl ether ether ketone), PEEK, under nonisothermal conditions. A differential scanning calorimeter (DSC) was used to monitor the energetics of the crystallization process from the melt. For nonisothermal studies, the melt was crystallized by cooling at rates from 1°C/min to 10°C/min. A kinetic analysis based on the recently proposed model for nonisothermal crystallization kinetics to remedy the drawback of the Ozawa equation was applied. The Avrami exponent for the nonisothermal crystallization process was strikingly different from that of the isothermal process, which indicates different crystallization behaviors. The results agree with the morphological observation reported in the literature. This study shows that correct interpretation of the Avrami exponent provides valuable information about the crystal structure and its morphology.     

Isothermal and nonisothermal crystallization kinetics of a semicrystalline copolyterephthalamide based on poly(decamethylene terephthalamide)

The isothermal and nonisothermal crystallization kinetics of a semicrystalline copolyterephthalamide based on poly(decamethylene terephthalamide) (PA‐10T) was studied by differential scanning calorimetry. Several kinetic analyses were used to describe the crystallization process. The commonly used Avrami equation and the one modified by Jeziorny were used, respectively, to describe the primary stage of isothermal and nonisothermal crystallization. The Avrami exponent n was evaluated to be in the range of 2.36–2.67 for isothermal crystallization, and of 3.05–5.34 for nonisothermal crystallization. The Ozawa analysis failed to describe the nonisothermal crystallization behavior, whereas the Mo–Liu equation, a combination equation of Avrami and Ozawa formulas, successfully described the nonisothermal crystallization kinetics. In addition, the value of crystallization rate coefficient under nonisothermal crystallization conditions was calculated. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 819–826, 2004     

Isothermal and nonisothermal crystallization kinetics of novel even‐odd nylon 10 11

Isothermal and nonisothermal crystallization kinetics of even‐odd nylon 10 11 were investigated by differential scanning calorimetry (DSC). Equilibrium melting point was determined to be 195.20°C. Avarmi equation was adopted to describe isothermal and nonisothermal crystallization. A new relation suggested by Mo was used to analyze nonisothermal crystallization and gave a good result. The crystallization activation energies have been obtained to be ?583.75 and ?270.06 KJ/mol for isothermal and nonisothermal crystallization, respectively. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1637–1643, 2005     

Studies on crystallization kinetics of nylon 6-polyoxypropylene-nylon 6 copolymers

The crystllization kinetics of anionic-prepared nylon6-poly(oxypropylene) 1000-nylon 6 (NPN) block copolymers containing 1.20 to 8.76 wt% poly(oxypropylene)(POP) were studied. The thermograms of isothermal and nonisothermal differential scanning calorimetry of NPN block copolymers obtained were used for the study. The Avrami equation was used to analyze the isothermal crystallization of NPN nylon block copolymers. The Avrami exponent n obtained in the temperature range of 180 to 200 °C was 2.0 to 2.5. It was not similar to that for nylon 6 reported in literature. The activation energies of crystallization for the nylon block copolymers were smaller than that of nylon 6, and showed a minimum with POP content. The equilibrium melting point increased as the POP content decreased. For the nylon block copolymers with lower POP content, the slopes of T_c vs. T_m plots were higher than the values reported elsewhere. The Ozawa plot was used to analyze the data of nonisothermal crystallization. The obvious curvature in the plot indicated that the Ozawa model could not fit our system well, and there was an abrupt change of the slope in the Ozawa plot at a critical cooling rate.     

Kinetics of isothermal and nonisothermal crystallization of nylon 1313

The crystallization process of a new polyamide, nylon 1313, from the melt has been thoroughly investigated under isothermal and nonisothermal conditions. During isothermal crystallization, relative crystallinity develops in accordance with the Avrami equation with the exponent n ≈ 2 based on DSC analysis. Under nonisothermal conditions, several different analysis methods were used to elucidate the crystallization process. The Avrami exponent n is greater in the isothermal crystallization process, indicating that the mode of nucleation and the growth of the nonisothermal crystallization for nylon 1313 are more complicated, and that the nucleation mode might include both homogeneous and heterogeneous nucleation simultaneously. The calculated activation energy is 214.25 kJ/mol for isothermal crystallization by Arrhenius form and 135.1 kJ/mol for nonisothermal crystallization by Kissinger method, respectively. In addition, the crystallization ability of nylon 1313 was assessed by using the kinetic crystallizability parameters G. Based on this parameter, the crystallizability of many different polymers was compared theoretically. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1415–1422, 2007     

Isothermal and nonisothermal crystallization kinetics of poly(ϵ‐caprolactone)

With increasing environmental awareness, evaluating the potential of biopolymers as a substitute for traditional materials has been of great interest. Crystallization kinetics provides fundamental knowledge required for evaluation, playing vital role in determining the final properties of the product. In this study, the isothermal and nonisothermal crystallization kinetics of poly(?‐caprolactone) (PCL) were investigated with the help of various models. The Avrami model best described the isothermal crystallization kinetics, suggesting three‐dimensional spherulitic growth, which was in agreement with the morphology studies; whereas the Liu model fit well under nonisothermal crystallization conditions. The failure of the Kissinger model to determine the activation energy was overcome with the Friedman model. The kinetic crystallizability determined by the Ziabacki model indicated a higher crystallization ability of PCL at lower cooling rates. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Isothermal and nonisothermal crystallization of poly(aryl ether ketone ketone) with all‐para phenylene linkage

Isothermal and nonisothermal crystallization behavior for PEKK(T) was studied using differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and electron diffraction (ED). In the isothermal crystallization process, the Avrami parameters obtained were n = 2.33–2.69, which shows crystal growth of two‐dimensional extensions consistent with our observations by TEM. The lamellar thickness increases with the crystallization temperature of PEKK(T) crystallized isothermally from the melt. However, for the nonisothermal crystallization of PEKK(T), the results from the modified Avrami analysis show two different crystallization processes. Avrami exponents n₁ = 3.61–5.30, obtained from the primary crystallization process, are much bigger than are the secondary n₂ = 2.26–3.04 and confirmed by the observation of the spherulite morphology. PEKK(T) crystallized isothermally from the melt possesses the same crystal structure (Form I) as that from nonisothermal melt crystallization. The results from TEM observation show that the spherulite radius decreases with an increasing cooling rate. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3431–3438, 2001