BMD/UP体系非等温固化动力学研究

不饱和聚酯是最常用的一种热固性材料,其力学性能和耐热性是较受关注的两个方面,利用双马来酰亚胺作为第二组分对不饱和聚酯进行耐热改性的工作取得了较好的效果。研究其动力学过程对于固化反应温度、时间等工艺合理优化控制,制备高性能复合材料具有重要意义。考虑到BMD／UP体系中反应的复杂性,本文采用n级动力学模型,进行了非等温动力学研究。     

Synthesis,characterization, and non-isothermal curing kinetics of two silicon-containing arylacetylenic monomers

Vinyltri(phenylethynyl)silane ((ph–C≡C)₃–Si–C=CH₂; VTPES) and phenyltri(phenylethynyl)silane ((ph–C≡C)₃–Si–ph; PTPES) were synthesized by Grignard reaction. Their molecular structures were characterized by means of ¹H NMR, ¹³C NMR, ²⁹Si NMR, and FT-IR spectroscopy. Their nonisothermal thermal curing processes were characterized by DSC, and the corresponding kinetic data, for example activation energy (E), pre-exponential factor (A), and the order of the reaction (n), were obtained by the Kissinger method. The results showed that the melting points of VTPES and PTPES were 84 and 116 °C, respectively. Their curing reaction rates were consistent with first-order kinetic equations. VTPES monomer had a lower activation energy and curing temperature as a result of coordination between reactive groups.     

碱式碳酸锌非等温热分解动力学研究

采用TG-DTA曲线分析研究了碱式碳酸锌在氮气气氛中的热分解反应动力学,利用Doyle-Ozawa法和Kissinger法对碱式碳酸锌非等温热分解动力学数据进行了分析,同时运用Satava-Sestak法研究了碱式碳酸锌的热分解机理.结果表明,碱式碳酸锌的热分解反应服从随机成核和随后生长机理.     

火焰原子吸收最佳燃助比的实验方法研究

火焰原子吸收光谱法工作条件的选择对原子吸收光谱分析很重要,但目前用固定助燃气流量、改变燃气流量的方法来选择燃助比,由于燃气流量改变时将引起火焰剧烈变化、从而导致原子化条件不稳定,引起不同文献中实验结果互相矛盾。经过理论讨论,用改进方法,即：固定燃气流量不变、用改变助燃气流量的方法,通过比较单位进样量吸光度来选择燃助比更合理。改进方法实验结果证明：1、现行方法在改变燃气流量时会引起原子化条件改变;2、现行方法在不同的起始实验条件时对实验结果的影响不同;3、改进方法在任意起始条件下结果相同,表明改进方法满足国家标准中“火焰比较稳定”的条件。结论：用改进方法来选择火焰原子吸收光谱法最佳燃助比更合理。     

The mechanism and kinetics of curing reaction of AG-80/SED system by DSC

The mechanism and kinetics of curing reaction of tetrafunctional epoxy resin (Ag-80)/novel diamines curing (SED) system were studied by non-isothermal and isothermal DSC. Different equivalent ratios of amine-epoxide give rise to different curing mechanisms. The main condensation reaction can be attributed to the reactions between the primary amine and epoxide and between the hydroxyl and epoxide when temperature is below 200°C, and to the reaction between the second-ary amine and epoxide when temperature is above 200°C. The corresponding apparent activation energies are 58.3 kJ·mol^?1 and 99.3 kJ·mol^?1 respectively. Apparent activation energies of condensation reactions between primary amine and epoxide and between hydroxyl and epoxide are just the same, which are 47.3 kJ·mol^?1.     

Effect of tertiary amine accelerators with different substituents on curing kinetics and reactivity of epoxy/dicyandiamide system

Non-isothermal Differential Scanning Calorimetry and gel time measurements were employed to study the effects of four different tertiary amine accelerators with different molecular structure and substituents on the curing behavior and reactivity of epoxy/dicyandiamide (DICY) system. Results showed that the acceleration behavior depends on three factors: the bulkiness, the number of nitrogen atoms in molecular structure and the electron density of accelerator. Among these, the former two factors demonstrated stronger effect. The results of model fitting kinetic demonstrated that Šesták–Berggren model can well simulate the reaction rates especially for the samples accelerated by 2,4,6-tris(dimethylaminomethyl)-phenol and (Dimethylaminomethyl)phenol. The activation energy projected by Flynn-Wall-Ozawa and Kissinger–Akahira–Sunose methods exposed different amounts for each accelerator while both models revealed similar trends. Moreover, 1-methylimidazol-accelerated samples showed shortest storage life and gel time mainly due to the presence of two nitrogen atoms in a compact structure of accelerator.     

Thermal decomposition and non-isothermal decomposition kinetics of carbamazepine

The thermal stability and kinetics of isothermal decomposition of carbamazepine were studied under isothermal conditions by thermogravimetry (TGA) and differential scanning calorimetry (DSC) at three heating rates. Particularly, transformation of crystal forms occurs at 153.75°C. The activation energy of this thermal decomposition process was calculated from the analysis of TG curves by Flynn-Wall-Ozawa, Doyle, distributed activation energy model, ?atava-?esták and Kissinger methods. There were two different stages of thermal decomposition process. For the first stage, E and logA [s^?1] were determined to be 42.51 kJ mol^?1 and 3.45, respectively. In the second stage, E and logA [s^?1] were 47.75 kJ mol^?1 and 3.80. The mechanism of thermal decomposition was Avrami-Erofeev (the reaction order, n = 1/3), with integral form G(α) = [?ln(1 ? α)]^1/3 (α = ～0.1–0.8) in the first stage and Avrami-Erofeev (the reaction order, n = 1) with integral form G(α) = ?ln(1 ? α) (α = ～0.9–0.99) in the second stage. Moreover, ΔH ^≠, ΔS ^≠, ΔG ^≠ values were 37.84 kJ mol^?1, ?192.41 J mol^?1 K^?1, 146.32 kJ mol^?1 and 42.68 kJ mol^?1, ?186.41 J mol^?1 K^?1, 156.26 kJ mol^?1 for the first and second stage, respectively.     

3,4-二硝基吡唑热分解及非等温动力学

采用TG-DSC综合热分析的方法,对3,4-二硝基吡唑(DNP)的热分解和非等温动力学进行了研究。结果表明DNP的热分解分两阶段进行,并且在升温速率达到15K/min时才能明显区分。分别采用Archar微分法和Coats-Redfen积分法计算了DNP第一阶段热分解反应动力学参数:Ea=91.6kJ.mol-1,lnA=42.7s-1。最可能的DNP热分解机理为随机成核和随后生长机理,符合动力学机理函数Avrami-Erofeev方程,n=3。     

Isothermal and non-isothermal pyrolysis kinetics of Kapton polyimide

The kinetics involved in the thermal decomposition of Kapton^® polyimide 100HN under nitrogen atmosphere were studied by applying various fitting techniques to the isothermal and non-isothermal gravimetric data. The correlation of the reaction mechanism fitting, the analytical model fitting and the isoconversional method to these data was examined in relation to the kinetic parameters and the kinetic predictions. The mechanisms for solid-state reactions fit the isothermal data very well but result in highly uncertain values for the kinetic parameters when applied to the non-isothermal data. Isoconversional methods show that the apparent activation energy depends on the extent of conversion but do not provide information for the reaction order and the pre-exponential factor. Three single heating-rate analytical models by Coats-Redfern, MacCallum-Tanner and van Krevelen were analysed using the non-isothermal data. A multi-heating rate model is proposed and its validity is compared to the single-heating rate models on the basis of kinetic predictions.     

Study on thermal decomposition and oxidation kinetics of cation exchange resins using non-isothermal TG analysis

Kinetics of two successive thermal decomposition reaction steps of cationic ion exchange resins and oxidation of the first thermal decomposition residue were investigated using a non-isothermal thermogravimetric analysis. Reaction mechanisms and kinetic parameters for three different reaction steps, which were identified from a FTIR gas analysis, were established from an analysis of TG analysis data using an isoconversional method and a master-plot method. Primary thermal dissociation of SO₃H⁺ from divinylbenzene copolymer was well described by an Avrami–Erofeev type reaction (n = 2, g(α) = [?ln(1 ? α)]^1/2]), and its activation energy was determined to be 46.8 ± 2.8 kJ mol^?1. Thermal decomposition of remaining polymeric materials at temperatures above 400 °C was described by one-dimensional diffusion (g(α) = α ²), and its activation energy was determined to be 49.1 ± 3.1 kJ mol^?1. The oxidation of remaining polymeric materials after thermal dissociation of SO₃H⁺ was described by a phase boundary reaction (contracting volume, g(α) = 1?(1 ? α)^1/3). The activation energy and the order of oxygen power dependency were determined to be 101.3 ± 13.4 and 1.05 ± 0.17 kJ mol^?1, respectively.     

Isothermal and non-isothermal crystallisation kinetics of pCBT and PBT

The crystallisation behaviour of in situ polymerised cyclic butylene terephthalates (pCBT) and poly(butylene terephthalate)s (PBT) were studied by differential scanning calorimetry (DSC) both under isothermal and non-isothermal conditions. The crystallisation was analysed by adopting the Avrami, Ozawa and Kissinger methods for the isothermal and non-isothermal crystallisations, respectively. An Avrami exponent n between 2 and 3 was found for the pCBTs whereas the exponent ranged between 3 and 4 for the PBTs. The Ozawa exponent m varied for all materials between 2 and 3. Differences in the crystallisation kinetics were also reflected in the related activation energy data.     

Preparation and curing kinetics of intrinsic flame retardant epoxy resin system based on polyoxometalates

Journal of Thermal Analysis and Calorimetry - In this work, phosphomolybdic acid (PMoA) was used as a kind of eco-friendly flame retardant precursor. Then, a green intrinsic flame...     

On the dependence of kinetic parameters and functions in non-isothermal kinetics

The approaches to overcoming local ambiguity due to the dependence of the kinetic equation parameters are considered. The application of the mathematical apparatus of the Jacobi matrices enables one to determine the number of both independent kinetic parameters and kinetic functions used to describe a process. No more than five parameters in the Šestak-Berggren equation and only some kinetic functions are found to possess independence.     

Criterion of the existence of compensation relationship for non-isothermal kinetics

If, for a series of similar-type chemical transformations in non-isothermal kinetics, identical or closely similar values of T _cr are observed in the equation 1/T _cr =1/T _si + + (R/E _i)·ln (E _i q/RT _si ² the existence of the compensation relationship lnA _i= =E _i/RT _cr may regularly be assumed.     

Mechanism and kinetics of thermal decomposition of precipitates of the zinc oxide-aluminium oxide system from non-isothermal tg curves

Kinetics of decomposition of the precipitates of the ZnO&2sbndAl₂O₃ system, prepared by coprecipitation and mechanical mixing of the individual precipitates, have been studied. The decomposition of zinc basic carbonate is a first order rate process with an activation energy of 34.5 kcal/mole (Coats and Redfern equation). The decomposition of aluminium hydroxide is also best described as a first order rate process with one break in the Coats and Redfern plot corresponding to activation energies of 29.4 and 8.3 kcal/mole respectively. The entire course of decomposition of coprecipitated as well as mechanically mixed samples cannot be described by any one of the many rate equations available. Consequently, the Coats and Redfern equation has been employed. The plots indicate one or two breaks and thus two to three values of activation energy are reported. From the results it is to be concluded that decomposition of these precipitates is a heterogeneous process. The first step is definitely the decomposition of zinc basic carbonate followed by decomposition of aluminium hydroxide and/or interaction of the two precipitates resulting in the formation of “precursor” to spinel. The results of our earlier investigation on the same system (especially the formation of precursors) are well supported by the results reported in this investigation. p]A new equation (a modified form of the Elovich equation) has been proposed for such heterogeneous decomposition processes. The proposed equation also appears to be the general form of the equations where diffusion is the rate controlling process.