亚麻纤维热解动力学的“model free”法和Coats-Redfern模型拟合法研究

亚麻纤维是一种潜在的气化原料,本文对亚麻纤维的热解行为进行了热重分析研究。10 mg粒径为0.60～0.85 mm的亚麻纤维颗粒在高纯氮气的保护下分别以10、20、30、50 K·min^-1的升温速率线性升温到550℃。使用“model free”方法和Coats-Redfern模型拟合方法分析亚麻纤维的热解过程,并估算出热解反应的表观活化能。本文中“model free”方法包括Friedman、Flynn-wall-Ozawa、Vyazovkin and Wight三种等转化率方法及Kissinger法。三种等转化率方法均得到活化能随着转化率的升高而升高的规律。四种“model free”方法显示亚麻纤维的活化能主要在155～175 kJ·mol^-1之间,使用模型拟合方法所获得亚麻纤维热解反应的活化能值在175 kJ·mol^-1左右,使用模型拟合方法和“model free”方法所得的活化能值接近。这些活化能值可以为亚麻纤维高效的热化学利用提供基础数据。     

Dynamic mechanical analysis and non-isothermal kinetics of EVA/PPy carbon black nanocomposites

Pure ethylene-co-vinyl acetate (EVA) and its conductive blend-nanocomposite with polypyrrole (PPy)/carbon black (CB) were prepared using a melt mixing process. Dynamic mechanical analysis and non-isothermal thermal gravimetrical analysis were performed on the samples. The storage modulus, loss modulus, and damping factor of the EVA/PPy/CB nanocomposites were significantly affected by the incorporation of PPy/CB. Two thermal decomposition stages were detected for pure and blended nanocomposite samples. Peak analysis was used to deconvolve the first complex decomposition stage. The Coats-Redfern method was used to determine the kinetic parameters. Improving the thermal and mechanical properties of the EVA co-polymer will enable the three-phase blend/nanocomposites to be used in several industrial applications.     

聚乙烯与三单体固相接枝物的热分解动力学

采用单体自增溶原位固相接枝法合成了聚乙烯与三单体固相接枝物(PETM)。采用Coats-Redfern法和Doyle-Ozawa法研究了接枝物的热分解动力学。研究表明,受接枝支链的影响,PETM的热分解反应级数介于0~1之间。PETM的热分解活化能比PE高,说明PETM的热稳定性优于PE,随着St在支链中的比例增加,PETM的热稳定性有逐渐增加的趋势,这是由于St能稳定自由基,从而降低PE的热分解速率。     

升温速率对油漆稀料和塑料共热解特性的影响

为研究不同升温速率下油漆稀料与PET塑料共热解特性的变化规律,使用同步热分析仪,测定不同升温速率（10、20、30 K/min）条件下油漆稀料和PET塑料共热解过程中失重（TG）、焓变（DSC）的变化,并采用Coats-Redfern法对样品进行热动力学分析,探究油漆稀料和PET塑料两种材料的共热解行为受升温速率的影响。结果表明：在氮气气氛中,样品的热解过程存在明显的滞后现象;油漆稀料和PET塑料热解过程只存在1个主要失重阶段,混合物存在2个主要失重阶段;油漆稀料和PET塑料的热解活化能随着升温速率的提高而减小,混合物在升温速率低于30 K/min时热解反应受到抑制,在30 K/min升温速率下活化能最低,热解反应最彻底,最终样品残余量为8.4%,火灾危险性强。     

Evaluation of reliability of Coats-Redfern method for kinetic analysis of non-isothermal TGA

A critical examination was made on the reliability of kinetic parameters of nonisothermal thermoanalytical rate measurement by the widely applied Coats-Redfern(CR) equation. For this purpose, simulated TGA curves were made for reactions with different kinetic models, including chemical, diffusion (Janders) and mixed mechanism at different heating rates. The results show that, for reactions controlled kinetically by one mechanism, all solid state reaction models show linear trends by use of CR method and this method can not distinct the correct reaction model. For reactions with mixed mechanism, the CR method shows nonlinear trends and the reaction models and kinetic parameters can not be extracted from CR curves. The overall conclusion from this comparative appraisal of the characteristics of the CR approach to kinetic analysis of TGA data is that the CR approach is generally unsuitable for determination of kinetic parameters.     

Synthesis,crystal structure and dehydration kinetics of NaB(OH)<Subscript>4</Subscript>·2H<Subscript>2</Subscript>O

Sodium metaborate tetrahydrate (NaB(OH)₄·2H₂O) was synthesized by reaction of anhydrous borax (Na₂O·2B₂O₃) with sodium hydroxide (NaOH) under conditions at 90 °C for 150 min. The structure was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscope (SEM) and Thermogravimetric (TG) analyses. Moreover, dehydration kinetics of NaB(OH)₄·2H₂O was carried out under non-isothermal conditions and the Coats-Redfern method was applied to analyze the TG data for calculation of activation energies (E _a ) and pre-exponential factors (k _o ) for different heating rates. It was determined that dehydration of sodium metaborate tetrahydrate occurred in five steps. According to the Coats-Redfern non-isothermal model, E _a and k _o were calculated as 50.89 kJ/mol and 26×10⁴ min⁻¹ for region I, 18.51 kJ/mol and 0.87×10³ min⁻¹ for region II, 15.72 kJ/mol and 0.52×10³ min⁻¹ for region III, 4.37 kJ/mol and 0.04×10³ min⁻¹ for region IV and 37.42 kJ/mol and 8.56×10³ min⁻¹ for region V, respectively.     

酒糟非等温热解动力学研究

酒糟气化是酒糟高效利用的一种方式。文章对酒糟的热解行为进行了热重分析研究。在高纯氮气的保护下,将10 mg酒糟分别以10,20,30 K/min的升温速率线性升温到923 K。结果显示,酒糟热分解的主要阶段为453～743 K,试样的大部分失重发生在该区域,失重率达67%以上。使用Coats-Redfern模型拟合方法分析酒糟的热解过程,确定了反应的动力学参数。在此阶段,酒糟热分解的级数为2.1级,表观活化能为69.31 kJ/mol,指前因子为4.92×105min-1。此热解动力学模型可以为酒糟的热化学转化有效利用提供基础数据。     

油页岩燃烧反应活化能不同求解方法的比较

利用热重分析仪在非等温条件下测得的桦甸油页岩燃烧试验数据，分别采用Coats-Redfern法和等转化率法（KAS法）对油页岩燃烧反应的表现活化能进行了求取，并对结果进行了比较。结果发现，用两种方法得出的活化能都表明油页岩燃烧分为两个阶段，且燃烧前期的活化能低于燃烧后期；等转化率法分析的结果表明，油页岩燃烧是一个复杂的多步反应过程，而C-R法将反应的机理简单假设为遵循反应级数模型，本身就存在问题，所以其得出的活化能值可靠性不高。     

Kinetic analysis of thermal decomposition of boric acid from thermogravimetric data

The kinetic parameters of the thermal decomposition of boric acid have been investigated by using TGA data. Suzuki and Coats-Redfern methods have been applied for the kinetic investigation. It was determined that decomposition kinetics of boric acid occurred in two steps and both regions suitably fit a first-order kinetic model. According to Coats-Redfern method, the activation energy and frequency factor were found as 79.85 kJ·mol^-1 and 3.82x 10⁴ min^-1 for region I and 4.79 kJ·mol^-1 and 4.045 x 10^-5 min^-1 for region II, respectively. The activation energies and frequency factors were found as 4.45 kJ·mol^-1 and 4.08 x10⁸ min^-1 for the Suzuki method.     

KINETIC STUDY OF SPINEL LiMn2O4 SYNTHESIZED BY SOLID REACTION WITH SOFT-CHEMICAL METHOD

1. IntroductionLithium -ion battery is the third generation rechargeable battery follow ing nickel-cadm ium batteryand m etal-hydrogen nickelbattery. Itisapplied in m any fields, such as portable notebook com puter,electro-m obile, space airship and m edi…