Kinetic analysis on spherulite growth rate of polypropylene catalloys

The kinetic analysis on melt-crystallization of polypropylene catalloys (PP-cats) was conducted through measuring their spherulite growth rates. A multiple melting behavior of PP-cats was found through differential scanning calorimetry (DSC) and the corresponding crystalline microstructures of PP-cats were studied by wide-angle X-ray diffraction (WAXD). The calculated T_m^o value of propylene homopolymer (PP) suggests an obvious melting point depression of PP-cats. Moreover, it is found that the existence of ethylene-propylene copolymer could result in the changes of crystalline microstructure of PP and the PP crystal is in favor of growing along (040) lattice plane of α-monoclinic crystal. The crystal growth rate of PP-cats decreases with the increase of ethylene-propylene copolymer content in PP-cats. A comparison of crystallization kinetics between PP-cats and virgin iPP through a modified Lauritzen-Hoffman model indicates that there appears a transition from regimes II to III in iPP and PP-cats containing low ethylene-propylene copolymer content. However, for the PP-cats containing high ethylene-propylene copolymer content, crystallization always processes in regime II. In addition, both calculated nucleation parameter (K_g) and the fold surface free energy (σ_e) for PP-cats increase with the increase of ethylene-propylene copolymer content, implying that the existence of ethylene-propylene copolymer is unfavorable for the surface nucleation of PP and regular folding of the molecule chain. It is believed that an increase in viscosity of the melts induced by different compositions could remarkably slow crystallization growth down, because under this condition surface nucleation dominates as compared with crystal growth.     

Influence of molten-state annealing on the phase structure and crystallization behaviour of high impact polypropylene copolymer

The phase structure evolution of high impact polypropylene copolymer (IPC) during molten-state annealing and its influence on crystallization behaviour were studied. An entirely different architecture of the IPC melt was observed after being annealed, and this architecture resulted in variations of the crystallization behaviour. In addition, it was found that the core-shell structure of the dispersed phase was completely destroyed and the sizes of the dispersed domains increased sharply after being annealed at 200 °C for 200 min. Through examination of the coarseness of the phase morphology using phase contrast microscopy (PCM), it was found that a co-continuous structure and an abnormal ‘sea-island’ structure generally appeared with an increase in annealing time. The original matrix PP component appeared as a dispersed phase, whereas the copolymer components formed a continuous ‘sea-island’ structure. This change is ascribed to the large tension induced by solidification at the phase interface and the great content difference between the components. When the temperature was reduced the structure reverted to its original form. With increasing annealing time, the spherulite profiles became more defined and the spherulite birefringence changed from vague to clear. Overall crystallization rates and nucleation densities decreased, but the spherulite radial growth rates remained almost constant, indicating that molten-state annealing mainly affects the nucleation ability of IPC, due to a coarsened microstructure and decreased interface area.     

网络化和拼贴:拯救乡土村落生命之顺德马岗案例

在我国快速城市化进程中和新农村建设高潮来临之际,城市边缘村落和中国广袤大地上的众多村落景观,正面临着前所未有的冲击.尽管有为数不多的古老村落被认定为历史文化名村而得到较好的保护,但大量的一般性传统村落则面临毁灭性的冲击.同时,在城市扩张过程中原居民被迁居到全新的社区中.这种对乡土景观和本土居民的忽视,带来众多严重的社会文化和生态问题.马岗正是一个典型案例.本研究提出了城市边缘村落城市化建设的另一个模式.景观规划师将马岗村作为一个具有历史的生命机体.这一有机系统不应该在城市化过程中被彻底铲平,而应该保持其生命的整体性,并融入到新城市规划之中.同时,马岗的乡土文化遗产不应成为城市化过程的障碍,而应该被看作形成新城社区文化归属感和社会认同感的积极因素,为新社区提供社会草根体系,并提供休闲旅游的机会.     

Fe／HCl体系中缓蚀剂吸脱附诱导的电流／电位振荡

研究了HCl介质中活性电位区有机缓蚀剂在Fe电极表面吸脱附诱导产生的电化学振荡现象，及缓蚀剂浓度、电极电位和溶液搅拌等因素对振荡行为的影响。结果表明，在HCl介质中Fe电极的活性电位区同样得到了规整的电流振荡波，但相同条件下的振荡行为要弱于H2SO4介质中，随缓蚀剂浓度升高，振荡波的周期变长，振荡 减弱；由阴极到阳极，电流振荡波形不同，周期也有所增长，搅拌对电流振荡无明显影响，同时报道了该缓蚀体系中恒电流电位振荡的新现象。     

逆向工程中测量数据点的滤波

针对用于曲面拟合的逆向工程散乱数据点云,提出一种先加权中值滤波,再小波包分析滤波的新滤波方法。为避免繁琐的编程,充分利用M atlab中的小波包滤波函数,提出VC 与M atlab混合编程编制数值计算程序的方法,并用实际计算结果验证了该方法的可行性。     

内陆核电厂冷却塔的环境影响预测计算

内陆核电厂通常采用自然通风冷却塔作为散热系统,电厂余热主要通过冷却水释放到大气环境中,由此带来的环境影响包括雾羽、荫屏、盐沉积、噪声等。本文基于美国核管会(NRC)推荐的SACTI计算程序,给出了评价冷却塔造成上述环境影响的计算模式和方法;采用此程序,对我国湖南、湖北和安徽三个拟选内陆核电厂厂址的冷却塔环境影响进行了预测计算,并与美国GGNS电厂的相关计算结果进行了类比分析。     

带侧向抽芯和斜向抽芯的注射模设计

根据塑件的结构特点,设计了带斜向抽芯和侧向抽芯的模具结构。斜向抽芯利用T型块带动斜向滑块作纵向、横向滑动,达到斜向抽芯目的;侧向抽芯则运用T型块在T型槽里滑动,带动侧向滑块作横向运动,完成侧向抽芯。模具结构紧凑,运动平稳可靠。     

Hydrophobically modified poly(sodium 2‐acrylamido‐2‐methylpropanesulfonate): synthesis and viscosity of aqueous solution

BACKGROUND: Hydrophobically modified polyelectrolytes are widely used polymers due to their good water solubility, stretched configuration in water and strong hydrophobic association. The study reported here aimed at researching the double action of hydrophobic association and electrostatic effect of novel hydrophobically modified polyelectrolytes in solution. RESULTS: A series of novel hydrophobically modified polyelectrolytes were synthesized by micellar copolymerization with various feed ratios of sodium 2‐acrylamido‐2‐methylpropanesulfonate, N‐n‐dodecylamine and sodium dodecylsulfonate. Their structure was characterized using Fourier transform infrared spectroscopy, nuclear magnetic resonance and gel permeation chromatography, and the viscosities of their aqueous and salt solutions were studied. CONCLUSION: The results show that the addition of the hydrophobic comonomer results in a decrease in molecular weight (M_w). The smaller the initial number of hydrophobes in one micelle, the higher is M_w of the resulting copolymer. The viscosity of PAD‐1.73 polyelectrolyte is less sensitive to salt than those of the others. According to the zero shear viscosity and corresponding concentration, the critical cluster‐forming concentration, critical overlap concentration and critical entanglement concentration of these polymer solutions were determined. Moreover, in the dilute regime the viscosity decreases with increasing salinity, while in the semi‐dilute regime the viscosity decreases first and then increases. It is suggested that in dilute and semi‐dilute regimes, hydrophobic intramolecular association and intermolecular association dominate, respectively. Copyright © 2009 Society of Chemical Industry     

Extraction of reference lines and items from form document images with complicated background

The extraction of reference lines and items is a fundamental and crucial task in form document analysis. Most of the studies performed so far were done in connection with binary images. This paper proposes a method of extracting lines from gray-level images, by constructing a 2D pseudo Gaussian-Coiflet wavelet with adjustable rectangular support. We also present a method of extracting items using the extracted reference lines and multiresolution wavelet sub-images, which is independent of the intensity of the strokes and backgrounds. The experimental results demonstrate the effectiveness of our proposed methods.     

Modeling of the liquid/solid and the eutectoid phase transformations in spheroidal graphite cast iron

A model of phase transformations in spheroidal graphite (SG) cast iron has been developed to quantitatively describe the microstructural evolution during solidification and the subsequent solid-state phase transformations (eutectoid reaction) during continuous cooling and to predict some of the microstructural characteristics of final phases formed in SG iron castings. Such characteristics include phase fractions, phase spacings, and grain dimensions. In the model, the nucleation and growth of primary dendrites and eutectics were described based on existing theories, whereas the mathematical formulation for the eutectoid reaction,i.e., the formation of pearlite and ferrite from the as-cast austenite, was developed based on theories as well as physical evidence obtained from the experimental work. The Johnson-Mehl equation and the Avrami equation were used to calculate the fraction of transformed phases under continuous cooling conditions. The role of the grain impingement factor used in these two equations and the significance of the additivity principle in treating nonisothermal transformations were briefly discussed. The latent heat method was used for the numerical treatment of the release of latent heat during phase transformations. A two-dimensional finite element code which can be used in either Cartesian or cylindrical coordinates (ALCAST-2D) was used to solve the time-dependent temperature distribution throughout the metal/mold system. Numerical predictions were validated against experimental results, and good agreement was obtained. DONGKAI SHANGGUAN, Previously Assistant Research Engineer, The University of Alabama,