T_(31)环氧树脂固化过程研究——1.动态扭振法确定最佳固化条件

在新设计制造的HLX-1型树脂固化仪上对T_(31)-环氧树脂E51进行了最佳配方和最佳条件的选择。T_(31)含量为20phr的环氧树脂体系,最佳固化温度为333K,固化反应活化能E=52.7KJ/mol。用非平衡态涨落理论也成功地预估了T_(31)-环氧树脂体系的固化行为。     

酪氨酸-溴酸钾-硫酸-丙酮在三邻菲啰啉合铁(Ⅱ)催化下的B-Z振荡反应

研究了酪氨酸-溴酸钾-硫酸-丙酮在三邻菲啰啉合铁(Ⅱ)催化下的化学振荡反应,对振荡的影响因素进行了研究和讨论.运用正交实验法确立了振荡反应进行的浓度范围,得到一个40多次振荡寿命为60 min的振荡波.获得振荡的诱导期和周期与反应物浓度之间的变化趋势曲线,以及振荡反应在诱导期和振荡期的表观活化能分别为Ein=49.0 kJ/mol和E=57.0 kJ/mol.根据反应过程中的现象和实验数据,建立了振荡反应的模型和反应机理,确定[Br-]是振荡反应自发进行的关键因素.     

Chlorine Dioxide–Iodide–Methyl Acetoacetate Oscillation Reaction Investigated by UV–Vis and an Online FTIR Spectrophotometric Method

In order to study the chemical oscillatory behavior and mechanism of a new chlorine dioxide–iodide ion–methyl acetoacetate reaction system, a series of experiments were done by using UV–vis and an online FTIR spectrophotometric method. The initial concentrations of methyl acetoacetate, chlorine dioxide, potassium iodide, sulfuric acid, and the pH have great influences on the oscillations observed at the wavelength 350 nm. There is a pre-oscillatory or induction period, and the amplitude and number of oscillations are dependent on the initial concentration of the reactants. Equations were obtained for the variation of the triiodide ion reaction rate with the reaction time and the initial concentrations in the oscillation stage. The oscillation reaction was accelerated by increasing the temperature. The apparent activation energies for the induction period and the oscillation period are 55.65 and 33.00 kJ·mol^?1, respectively. The intermediates were detected by the online FTIR analysis. Based upon the experimental data in this work and in the literature, a plausible reaction mechanism is proposed for the oscillation reaction.     

Temperature- and pH-dependent morphology and FT-IR analysis of magnesium carbonate hydrates

Various morphologies of magnesium carbonate hydrates have been synthesized by carefully adjusting the reaction temperature and pH value of the initial reaction solution in the precipitation process. At lower temperatures (from room temperature to 328 K) and lower pH values (variation with the reaction temperature), magnesium carbonate hydrates are prone to display needlelike morphology, and the axis diameter of the particles decreases with the increase of reaction temperature and pH value. With the further increase of the reaction temperature (333-368 K) and pH value, the sheetlike crystallites become the preferred morphology, and at higher temperatures and pH values, these crystallites tend to assemble into layerlike structures with diverse morphologies, such as spherical-like particles with rosette-like structure and cakelike particles built from sheetlike structure. Fourier transform infrared (FT-IR) spectra show that these various morphologies are closely related to their compositions. The needlelike magnesium carbonate hydrate has a formula of MgCO3.xH2O, in which the value x is greatly affected by the experimental conditions, whereas with the morphological transformation from needlelike to sheetlike structure, their corresponding compositions also change from MgCO3.xH2O to Mg5(CO3)4(OH)2.4H2O in the interval of 328-333 K.     

Polymerization of Methyl Methacrylate by Organometallic Compounds. V. Dark Stoichiometric and Polymerization Reactions between Trialkylaluminums and Methyl Methacrylate

The stoichiometric reaction products of the reaction of triethylaluminum and methyl methacrylate (MMA) derive from a different complex to that responsible for the photosensitized, radical polymerization. The stoichiometric products are the result of nucleophilic attack on the carbonyl group of MMA (1,2 addition). No 3,4 nucleophilic adducts are found and it is questioned whether the one product usually believed to be the result of conjugate (1,4) attack does so arise. The reactions have been followed, in situ, using 60 MHz NMR and mechanisms are discussed. The nucleophilic addition reactions do not develop into an anionic polymerization chain. The equilibrium constants governing MMA-triethylaluminium complex formation are such that the 1:1 complex, the precursor of radical polymerization, prevails overwhelmingly in MMA-rich mixtures and the precursor of stoichiometric, nucleophilic, addition reactions prevails in A1-rich mixtures. The validity of diagnostic tests for polymerization mechanism based on the nature of concomitant, low molecular weight products is discussed.

It is confirmed that triethylaluminium does not initiate MMA polymerization in the dark over the temperatures 233-333°K. We find diisobutylalumin-ium hydride inert, in dark or light, at 298 and 333°K. Triisobutylaluminium only initiates MMA when illuminated at 298°K, but at 333°K there is also a significant dark rate. Preliminary copolymerization experiments, devised to elucidate the mechanism of this dark polymerization, suggest that, as in the case of the photo-sensitized, triethylaluminium-initiated, radical polymerization, it proceeds from a 1:1 MMA: trialkylaluminium complex.     

Belousov-Zhabotinskii反应的研究——不同气氛下的振荡现象

本文考察了不同气氛下, 丙二酸(MA)、邻菲罗啉亚铁离子和溴酸根之间反应的振荡现象。结果表明, 氢气与氮气对此反应的振荡基本上是惰性的, 而氧气对此反应的振荡有明显的影响。对氧的影响作了较仔细的研究, 观察到氧气氛下反应出现的一些特殊振荡波形。此外还对邻菲罗啉亚铁离子的离解造成的影响作了初步探讨。结合熟知的反应机理对实验结果进行了若干分析。     

Carotenoids extraction from Japanese persimmon (Hachiya-kaki) peels by supercritical CO(2) with ethanol.

The extraction of carotenoids from Japanese persimmon peels by supercritical fluid extraction (SFE), of which the solvent was CO(2), was performed. In order to enhance the yield and selectivity of the extraction, some portion of ethanol (5 - 20 mol%) was added as an entrainer. The extraction temperature ranged from 313 to 353 K and the pressure was 30 MPa. The effect of temperature on the extraction yield of carotenoids was investigated at 10 mol% of the ethanol concentration in the extraction solvent, and a suitable temperature was found to be 333 K among the temperatures studied with respect to the carotenoid yield. With increasing the entrainer amount from 0 to 10 mol% at a constant temperature (333 K), the carotenoid yield in the extraction was improved, whereas the selectivity of the extracted carotenoids was drastically depressed. We also conducted qualitative and quantitative analyses for the carotenoid components in the extract by HPLC, and analyzed the extraction behavior of each individual carotenoid (alpha-carotene, beta-carotene, beta-cryptoxanthin, lycopene, lutein, and zeaxanthin). The selectivity of each carotenoid changed with the elapsed time and its time evolution was dependent on the carotenoid component, indicating that the location profile and the content can be important factors to understand the SFE behavior of each carotenoid in persimmon peels.     

Self-discharge behavior of LaNi5-based hydrogen storage electrodes in different electrolytes

Nickel–metal hydride (Ni–MH) batteries using hydrogen storage alloys as negative electrode materials have been developed and commercialized because of their high energy density, high rate capability and long cycle life, without causing environmental pollution (Song et al. J Alloys Comp 298:254, 2000; Jang et al. J Alloys Comp 268:290, 1998). However, the self-discharge rate is relatively higher than that of the Ni–Cd batteries, which would certainly be disadvantageous in practical applications. The capacity loss of a battery during storage is often related to self-discharge in the cells. Self-discharge takes place from a highly charged state of a cell to a lower state of charge (SOC) and is typically caused by the highly oxidizing or reducing characteristic of one or both of the electrodes in the cell. This self-discharge behavior may be affected by various factors such as gases, impurities, temperature, type of alloy electrode, electrolytes, or charge/discharge methods. The loss of capacity can be permanent or recoverable, depending on the nature of the mechanism (chemical or electrochemical) and aging condition. In this paper, the effects of electrolyte composition and temperature on self-discharge behavior of LaNi₅-based hydrogen storage alloy electrodes for Ni–MH batteries have been investigated. It was found that both reversible and irreversible capacity loss of MH electrode tested at 333 K were higher than that at 298 K. When tested at 298 K and 333 K, reversible capacity loss was mainly affected by the electrolyte, while the irreversible capacity loss was not affected. The dissolution of Al from the electrode can be reduced more effectively in an electrolyte with Al addition, compared with that in normal electrolyte. This resulted in a lower reversible capacity loss for the electrode exposed in the Al³⁺-rich electrolyte. SEM analysis has shown that some needle shape and hexagonal corrosion products were formed on the surface of the alloy electrodes, especially after storage at high temperature.     

Sorption of Cadmium from Aqueous Solutions at Different Temperatures by Mexican HEU-type Zeolite Rich Tuff

Many factors may affect the heavy metals sorption on natural zeolites among them the temperature, for this reason in this paper the cadmium retention behavior on Mexican zeolitic rich tuff as a function of temperature is considered. The kinetic and the isotherms were determined at 303, 318, and 333 K, the remaining cadmium in the solution samples was analyzed by atomic absorption spectrometry. The pseudo-second order rate constant, k, as well as the apparent diffusion coefficients were calculated from the cadmium uptake by the zeolitic rock as a function of the contact time and temperature, the highest amounts were found for the experiments done at 333 K. The maximum cadmium adsorption capacity by the zeolitic material was 12.2 mg Cd²⁺/g at 318 K corresponding to 20% of the effective ion exchange capacity of the Chihuahua zeolitic rock. In order to explain the cadmium sorption behavior different kinetics and isotherm models were considered.     

Chemical oscillation of vanadium complexes: Simple and aperiodic systems

An oscillatory chemical reaction is an intriguing phenomenon subject to various and often uncontrollable factors. Many oscillatory systems consist of a strong acid, metal ion and an additional species with accessible oxidation states, and restrictive temperature conditions. Thus, an oscillatory system in which all the factors are understood would be useful. In this paper, we describe the first such system based on vanadium chemistry. The V(IV) complex (pale green color) turns dark orange with the production of a V(V) complex. This reaction is affected by many factors such as oxygen, ultraviolet (UV) irradiation, visible irradiation, and aldehyde addition. This oscillation reaction occurs only in a dichloromethane solution, suggesting that the solvent intervenes in the reaction. Examination of the gas phase during the oscillation reaction revealed the formation of carbon monoxide, carbon dioxide, hydrogen chloride, and phosgene. Based on these observations, we propose a plausible oscillation reaction mechanism.The results of this study contribute to the field of nonlinear dynamics. Additionally, this work offers new insights into vanadium chemistry because this oscillation phenomenon is strongly correlated with the electron transfer reaction of the vanadium complex. Moreover, studies using vanadium complexes may help in understanding vanadium-mediated electron transfer systems in vivo, such as vanadium accumulation and storage observed in marine organisms.