Crystallization of Poly(ethylene adipate) within γ-Phase Poly(vinylidene fluoride) Matrix

The effects of PEA on the γ-phase PVDF crystal structure and the crystallization of PEA within the pre-existing γ-phase PVDF spherulites have been investigated by optical microscopy(OM), infrared spectroscopy(IR) and scanning electron microscopy(SEM). The results demonstrate that the γ-phase PVDF spherulites consist of the lamellae exhibiting a highly curved scroll-like morphology and develop preferentially in PEA-rich blend. With increasing PEA concentration, the scroll diameter increases and the scrolls are better separated from each other. PEA crystallizes first in the interspherulitic region and transcrystalline layer develops. Subsequently, the transcrystalline layer of PEA continues to grow within the γ-phase PVDF spherulites, e.g., in the region between the scrolls, until impinging on other PEA transcrystalline layers or spherulites. The crystallization kinetics results indicate that the growth rate of PEA crystals in the intraspherulitic region of γ-phase PVDF shows a positive correlation with content of PEA, but a negative one with the crystallization temperature of γ-phase PVDF.     

Nonlinear frequency response analysis: a recent review and perspectives

The nonlinear frequency response analysis (NFRA) can be seen as an extension of electrochemical impedance spectroscopy. NFRA gives a full and detailed representation of the system response and can establish a connection between model parameters and the experimentally observed phenomena. In this article, different theoretical NFRA approaches and the most recent application examples are discussed. A simple electrochemical example is used to showcase the benefits and disadvantages of analyzing the system response by using different approaches. In addition, it was shown how to extract experimental harmonic values and analyze them.     

Kinetics of phenol hydrogenation over supported palladium catalyst

Kinetics of vapor phase hydrogenation of phenol to cyclohexanone over Pd/MgO system has been studied in a flow microreactor under normal atmospheric pressure. The reaction rate is found to be negative order with respect to the partial pressure of phenol and has increased from −0.5 to 0.5 with increasing temperature (473 to 563 K). The apparent activation energy (E_a) of the process is found to be close to 65 kJ per mol. On the basis of kinetic results a surface mechanism is proposed.     

Roles of SiH4 and SiF4 in growth and structural changes of poly-Si films

The structural properties of polycrystalline silicon films, prepared by plasma enhanced chemical vapor deposition system, with different flow rates of SiH₄/SiF₄ mixtures at 300 °C were investigated. This study indicates that the low hydrogen coverage on the growing surface, under optimum fluorine radicals, will be leaded to an improvement of crystallized area as compared with case of high hydrogen coverage surface. Moreover, the studies of the role of SiH₄ and SiF₄ radicals show that the SiH₄ radicals are important in the nucleation and growth of grains. However, SiF₄ radicals are effective in the structural change of grain boundaries regions and by this way, in the present system, establish the growth of grains under the dominant 〈1 1 0〉 direction. The stress investigation indicates that addition of high flow rate of SiF₄ in amorphous film, results in the nearly stress free films. Finally, we found that the changes in g-value reflect the changes in the intrinsic compressive and tensile stress in the both polycrystalline and amorphous silicon films.     

Physico-chemical aspects of polyethylene processing in an open mixer. Part 26: Formal kinetics of aldehyde and carboxylic acid formation at a constant rate

Formation of carboxylic acids at a constant rate can be easily explained. It seems to result from the formation and decomposition of α,γ-keto-hydroperoxides. Formal kinetics based on formation and decomposition of these structural units is in agreement with the experimental findings. The activation energy deduced from the calculations is negligible, in agreement with the experimental data showing the constant rate to be practically temperature independent. Comparison of the acids with the hydroperoxides and ketones formed initially shows that the rate of oxygen addition to alkyl radicals is significantly smaller than in low molecular mass liquids. The same conclusion is reached on comparing directly the acids formed on decomposition of α,γ-keto-hydroperoxides in polyethylene melt and in hexadecane. The rate of oxygen addition in polyethylene melt is closer to 2 × 10⁵ than to 6 × 10⁵ (s⁻¹) that is valid in hexadecane.It is possible to attribute the relatively small amount of aldehydes that might be formed at a constant rate to different reactions of alkoxy radicals that are not in a cage with other radicals. These alkoxy radicals result from the addition of peroxy radicals to unsaturated bonds. This addition is followed mainly by epoxide formation and simultaneous release of an alkoxy radical.     

纳米TiO_2用于甲基橙溶液的光催化氧化研究

本实验采用纳米级的二氧化钛,对甲基橙溶液进行了紫外光催化氧化处理,探讨了pH的影响和添加Fe3+的效果及反应动力学方程,结果表明,采用UV/O3/TiO2工艺对其进行处理,pH4-5时,10W紫外灯光照60min,CODcr去除率达84%,脱色率达96%以上。添加Fe3+,对溶液的催化降解速度提高不明显。动力学研究表明,CODcr降解速度对CODcr的浓度为一级反应。     

3,7-二硝基亚氨基-2,4-二氮杂双环[3,3,0]辛烷的放热分解反应动力学

在程序升温条件下 ,用DSC研究了标题化合物的放热分解反应动力学 .用线性最小二乘法、迭代法以及二分法与最小二乘法相结合的方法 ,以积分方程、微分方程和放热速率方程拟合DSC数据 .在逻辑选择建立了微分和积分机理函数的最可几一般表达式后 ,用放热速率方程得到相应的表观活化能 (Ea)、指前因子 (A)和反应级数 (n)的值 .结果表明 :该反应的微分形式的经验动力学模式函数、Ea 和A值分别为 (1-α) 0 .44、2 30 .4kJ/mol和 10 18.16s-1.借助加热速率和所得动力学参数值 ,提出了标题化合物放热分解反应的动力学方程 .该化合物的热爆炸临界温度为 30 2 .6℃ .上述动力学参数对分析、评价标题化合物的稳定性和热变化规律十分有用 .     

A differential scanning calorimetry method to determine the isothermal crystallization kinetics of cocoa butter

This research aimed to reduce the variability on the data obtained from differential scanning calorimetric (DSC) analysis of the isothermal crystallization kinetics of cocoa butter.

To enable transformation of the DSC crystallization peak to a sigmoid crystallization curve, the DSC peak area has to be integrated. Usually, the start and end points of the crystallization peak are determined visually. The result of this visual determination appeared to be very much dependent on the operator, but also differed considerably when the same operator performed the integration several times. By proposing an objective calculation algorithm to determine the start and end points of integration, the variability caused by the operator during the integration procedure could be eliminated. Furthermore, sample preparation and the DSC heating protocol to melt the sample prior to crystallization were studied. Three heating protocols (65 °C for 15 min, 65 °C for 30 min and 80 °C for 15 min) were compared and it was shown that holding at 65 °C for 15 min was sufficient to eliminate any influence of sample history. Two different sample preparation procedures were compared and it appeared that a change in sample preparation procedure had a significant influence on the measured crystallization process. It is thus important to keep this method constant to eliminate the variability caused by it.     

Physico-chemical aspects of polyethylene processing in an open mixer. Part 29: Experimental kinetics and mechanisms of γ-lactone formation

The experimental kinetics for γ-lactone formation shows more complexity than that for acids. Nonetheless, it can be concluded to the existence of a constant rate of formation from the beginning of the experiments with polyethylene melts. There is an additional term contributing to γ-lactone formation in the initial stages that is cubic in processing time. In the advanced stages of processing, in the high temperature range (170-200 °C), the concentration of γ-lactones increases linearly with the processing time.There are many mechanisms susceptible to give γ-lactones on polyethylene melt processing. Some of them are based on decomposition of intermediates formed directly on chain propagation. This is so for the α,γ-keto-hydroperoxides in 4-position to hydroxyl groups. Since decomposition of these intermediates is very fast, the reaction might account for a constant rate of γ-lactone formation from the beginning of polyethylene processing. Decomposition of the α,δ-keto-hydroperoxides formed on intramolecular reactions on chain propagation is not so fast as that of the α,γ-keto-hydroperoxides. Nonetheless, it might account for part of the delayed formation of γ-lactones. The same is valid for the mechanisms based on peroxidation of aldehydes and γ-hydroxy trans-vinylene groups that involve intermediates that are formed on polyethylene peroxidation. They might be important for explaining the cubic term as well as γ-lactone formation in the advanced stages of polyethylene processing.     

聚甲醛结晶动力学研究

用解偏振光强法和差示扫描量热法（ＤＳＣ）分别研究了聚甲醛和聚甲醛助剂Ｐ的等温结晶动力学和非等温结晶动力学。探讨了助剂Ｐ对聚甲醛的结晶成核作用。