Thermal Behavior and Thermolysis Kinetics of the Explosive Trans‐1,4,5,8‐Tetranitro‐1,4,5,8‐Tetraazadecalin (TNAD)

Trans‐1,4,5,8‐Tetranitro‐1,4,5,8‐Tetraazadecalin (TNAD), a cyclic nitroamine, has been studied with regard to the kinetics and mechanism of thermal decomposition, using thermogravimetry (TG), IR spectroscopy, and pressure differential scanning calorimetry (PDSC). The IR spectra of TNAD have also been recorded, and the kinetics of thermolysis has been followed by non‐isothermal TG. The activation energy of the solid‐state process was determined by using the Flynn‐Wall‐Ozawa method. Compared with the activation energy obtained from the Ozawa method, the reaction mechanism of the exothermic process of TNAD was classified by the Coats‐Redfern method as a nucleation and nuclear growth (Avrami equation 1) chemical reaction (α=0.30–0.60) and a 2D diffusion (Valensi equation) chemical reaction (α=0.60–0.90). E_a and ln A were established to be 330.14 kJ mol⁻¹ and 29.93 (α=0.30–0.60) or 250.30 kJ mol⁻¹ and 21.62 (α=0.60–0.90).     

Curing Kinetics and Thermal Properties Characterization of o-Cresol-formaldehyde Epoxy Resin and MeTHPA System

The kinetics of the cure reaction for a system of o-cresol-formaldehyde epoxy resin (o-CFER) with 3-methyl-tetrahydrophthalic anhydride (MeTHPA) as a curing agent and N,N-dimethyl-benzylamine as an accelerator was investigated by means of differential scanning calorimetry (DSC). Analysis of DSC data indicated that an autocatalytic behavior showed in the first stages of the cure for the system, which could be well described by the model proposed by Kamal, which includes two rate constants, k₁ and k₂, and two reaction orders, m and n. The activation energy E₁ and E₂ are 195.84 and 116.54 kJmol^?1, respectively. In the later stages, the reaction is mainly controlled by diffusion, and a diffusion, factor, f(α), was introduced into Kamal's equation. In this way, the curing kinetics were predicted well over the entire range of conversion. Molecular mechanism for the curing reaction was discussed. The glass transition temperature T_g was determined by means of torsional braid analysis (TBA). The results showed that T_gs increased with curing temperature and conversion up to a constant value about 367.1 K. The thermal degradation kinetics of the system was investigated by thermogravimetric analysis (TGA), which revealed two decomposition steps.     

Effect of nickel boride additive on simultaneous densification and phase decomposition of TiB2–WB2 solid solutions by pressureless sintering using induction heating

Short time process of simultaneous densification and phase decomposition of TiB₂–WB₂ solid solutions by pressureless sintering using induction heating has been investigated. The products were obtained by sintering of mixture powder compacts of (Ti,W)B₂ with nickel and boron (Ni/B = 3/1) varying between 0 and 7.5 wt.%. It was found that the presence of nickel boride as an additive markedly enhances the kinetics of the subsequent densification and decomposition from the (Ti,W)B₂ single phase to the two phases of (Ti,W)B₂ and (W,Ti)B₂. The sintered products were evaluated using X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy analysis. In an addition of 7.5 wt.%, the product with a relative density of 91% is produced by induction heating for only 600 s. The mechanical properties of the product, which improved by densification and decomposition of (Ti,W)B₂, is also presented.     

Sintering and Microstructure Modification of Mullite/Zirconia Composites Derived from Silica-Coated Alumina Powders

This paper addresses the densification and microstructure development during firing of mullite/zirconia composites made from silica-coated-alumina (SCA) microcomposite powders. Densification occurs in two stages: in the presence of a silica–alumina mixture and after conversion to mullite. The first stage of densification occurs through transient viscous phase sintering (TVS). This is best promoted by rapid heating, which delays the crystallization of silica to higher temperatures. A further sintering stage is observed following mullitization. The introduction of seeds promotes solid-state sintering, most probably due to refinement of the mullite matrix. For seed concentrations up to about 1% the sintering kinetics depend on seed concentration. This suggests that nucleation still remains the rate-controlling mullitization step. Above this concentration the reaction becomes growth controlled. Introduction of seeds also promotes direct mullitization without transient zircon formation that was observed in a previous study of the same process without seeding. Seeding also promotes the development of elongated grains by way of a solid-state recrystallization process.     

Solvent-deficient synthesis of cerium oxide: Characterization and kinetics

The reaction mechanism and kinetics of CeO₂ synthesis using a solvent-deficient method are investigated by simultaneous thermogravimetric analysis (TGA)/differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The decomposition process of the cerium(III) nitrate hexahydrate and ammonium bicarbonate precursor mixture with four observed stages is monitored using TGA/DSC measurements in a nonisothermal regime with heating rates of 5, 10, 15 and 20?°C min^?1. The proposed mechanism indicates a complex synthesis with several parallel reactions, some of which occur at room temperature. A detailed kinetic analysis is performed using isoconversional (expanded Friedman, modified Coats-Redfern and Kissinger) and model fitting (N^th order and nucleation and growth models) methods. The first three stages are best described by the N^th order model with activation energy values of 21, 53 and 90?kJ?mol^?1. The last stage, during which ammonium nitrate decomposition occurs, is best fit by the nucleation and growth model and has an activation energy of 129?kJ?mol^?1. The proposed mechanism, supported by the kinetic analysis in our study, indicates that CeO₂ has already formed before the reaction reaches 200?°C. The average crystallite size of CeO₂ synthesized at 300?°C, which was calculated from the XRD measurements and observed in the SEM and TEM data, is between 10 and 20?nm.     

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.     

聚酰胺12非等温热分解动力学研究

在不同升温速率下,利用热重分析法研究了聚酰胺12（PA12）在氮气氛围中的热分解动力学。运用Freeman Carroll、Kissinger、Ozawa、Achar和Coats Redfern方法计算和确定了PA12在氮气氛围中的热分解活化能和热分解机理及其模型。结果表明,在氮气氛围中,PA12的热分解活化能为246.5 kJ/mol,指前因子为1014.71;PA12热分解机理为收缩球体法则,机理方程的微分形式为f(α)=3(1-α)2/3,积分形式为G(α)=1-(1-α)1/3。     

Selective binding of an imprinted polymer resulted from controlling cobalt coordination to nitric oxide

In this article, the binding characteristics of the imprinted polymer P‐1[Co^II(salen)] (salen: bis(2‐hydroxybenzaldehyde)ethylenediimine) to nitric oxide (NO) have been reported. P‐1[Co^II(salen)] was characterized by Fourier transform infrared analysis, thermogravimetric analysis, and differential scanning calorimetry. Batch‐mode adsorption studies were carried out to investigate binding thermodynamics, kinetics, and selective recognition behavior of P‐1[Co^II(salen)] to NO. The kinetics study indicates that binding of the polymer to NO fits the first‐order reaction kinetics with the rate constant k₁ of 0.087 min^?1. Langmuir and Freundlich equations were used to explain the equilibrium character of P‐1[Co^II(salen)] binding to NO. The r² and χ² values suggest that total amount of NO bound by P‐1[Co^II(salen)] can be best fitted by the Langmuir equation. The binding capacity (B_max) of P‐1[Co^II(salen)] was calculated to be 76.28 μmol/g, very close to the experimental value, 75 μmol/g. The thermodynamics and selectivity experiments showed that the affinity of P‐1[Co^II(salen)] to NO was much higher than carbon dioxide (CO₂) and oxygen (O₂), suggesting that P‐1[Co^II(salen)] is a promising functional material for NO storage and NO sensing. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

十氢十硼酸双四乙基铵热分解特性及其动力学参数

为了解十氢十硼酸双四乙基铵(BHN-10)热分解特性及反应动力学,采用同步热分析-红外质谱联用技术(TG-DSC-MS-FTIR)及热裂解原位池-傅里叶变换红外光谱联用技术(FTIR)对BHN-10热分解过程中间产物和最终产物进行分析;使用Kissinger和Ozawa方法计算两个热分解阶段的动力学参数,并利用Coats-Redfern法拟合得到反应动力学方程。结果表明,BHN-10热分解第一阶段和第二阶段的活化能分别为150.9 kJ/mol和161.7 kJ/mol;第一阶段受随机成核和核增长机理控制,第二阶段遵从幂级数法则(Mampel power);两阶段的动力学机理函数分别为G(α)=[-ln(1-α)]1/3(n=3)和G(α)=α1/4;BHN-10热分解反应第一阶段质量损失2.9%,与理论脱氢质量损失相一致,此阶段发生B10H2-10的脱氢产生氢气和非晶态硼的过程,在热分解第一阶段会生成熔融分解型的中间产物四乙基铵阳离子;第二步反应质量损失39.4%,接近第二阶段气体质量损失的计算值43.4%,是四乙基铵阳离子上的质子转移并通过Hoffman消除反应生成乙烯和Et3N,Et3N进一步分解为C 2H 6、NH3、H2和碳单质。     

Fully densified zircon co-doped with iron and aluminium prepared by sol–gel processing

A sol–gel technique has been used to prepare Fe and Al doped zircon. Structural properties have been studied by X-ray diffraction, nuclear magnetic resonance, scanning electron microscopy and transmission electron microscopy (TEM). Fully densified zircon was produced with high zircon yield and promising microstructures. The presence of Fe promotes zircon formation, while Al improves densification. The zircon phase starts to form at 1215 °C, with almost single phase zircon obtained at 1400 °C when heated for 1 h. Densification increases very significantly (to 99.7% of theoretical density) when the holding time was increased to 48 h from 1 h. TEM micrographs reveal a crystalline grain boundary phase containing some Fe and Al.     

三元硝酸熔盐高温热稳定性实验研究与机理分析

通过熔盐质量损失率和试样中NO2-含量变化状况,以及熔盐材料的热重(TG)曲线,研究了三元硝酸熔盐(53%KNO3-40%NaNO2-7%NaNO3)在空气和氮气气氛中高温条件下的热稳定性性能。结果表明,三元硝酸熔盐空气中的上限使用温度为773K,高温时存在劣化现象;而在氮气气氛中三元熔盐的热分解温度为723K。同时,从热力学和动力学角度分析得到,三元硝酸熔盐在773K以下空气中发生的反应为亚硝酸钠的分解和氧化;而在氮气气氛中三元熔盐723K以下时主要发生的是亚硝酸钠的分解反应。在氧气含量一定的情况下,氧气的扩散和亚硝酸盐的分解反应符合一级反应动力学模型。     

化合物[NH_3CH_2CH_2NH_3][CuCl_4]的热稳定性及其分解动力学研究

利用液相法合成了[NH3CH2CH2NH3][CuCl4],并对化合物的热稳定性、热分解及其动力学进行了研究。采用TG-DTG技术研究化合物[NH3CH2CH2NH3][CuCl4]的热分解,并应用微分法（Achar法）、Coast-Redfern法、Kissinger法、Ozawa法对非等温动力学数据进行处理,发现晶体的第一步分解是二维扩散反应,n=2,机理函数积分形式g（α）=[1-（1-α）1/2]2和微分形式f（α）=（1-α）1/2[1-（1-α）1/2]-1,表观活化能Ea=192.56 kJ.mol-1,指前因子A=2.13×1016s-1。标题化合物的第二步分解是化学反应,机理函数积分形式g（α）=（1-α）-1-1和微分形式f（α）=（1-α）2,表观活化能Ea=164.70 kJ.mol-1,指前因子A=2.90×1012s-1。     

Influence of zircon particle size on conventional and microwave assisted reaction sintering of in-situ mullite–zirconia composites

Mullite–zirconia composites were fabricated by reaction sintering of ZrSiO₄ and α-Al₂O₃ using conventional heating and microwave processing. The powder mixtures were prepared from sub-micron zircon powders with three different particle sizes and CIPed as coin shaped samples. The samples sintered both in a muffle furnace and microwave furnace. The open porosities, bulk and true densities were measured. Phase transformations were characterized by X-ray diffraction and microstructures were evaluated by scanning electron microscopy. The effects of zircon particle size on the in-situ transformation system and mullitization was evaluated for both methods. As a result, decreasing zircon particle size decreases the in-situ transformation temperature for 25 °C (1575 °C) in conventional heating. Microwave assisted sintering (MAS) lowers the transformation temperature at least 50 °C by lowering the activation energy more efficiently and gives better densification than conventional sintering. Furthermore, milling also produces structures having finer mullite grains.     

Effects of alumina sols on the sintering of α-alumina ceramics

The effects of two kinds of alumina sols on the densification behavior of sub-micron grain sized α-alumina ceramics have been investigated. Composition of the sol-derived gels was investigated by energy dispersive spectra and Fourier transform infrared spectra. Structural evolution of the gels at different temperatures was characterized by a combination of X-ray diffraction and ²⁷Al magic angle spinning nuclear magnetic resonance spectroscopy. Results showed that the gel containing chlorine and carbon transformed to α-alumina at about 950 °C, significantly lower than the other gel which transformed at about 1050 °C. Density measurements and scanning electron microscopy analyses were used to investigate the sintering of alumina ceramics with or without alumina sols. It was found that the alumina sols had profound effects on the densification of alumina ceramics. The ceramic displayed the best densification behavior when the sol containing chlorine and carbon was added.     

菱镁矿热分解的动力学研究

利用热重(TG)分析法,对不同粒度菱镁矿的热分解过程进行研究.根据Flynn-Wall-Ozawa法,拟合计算得到不同粒度菱镁矿热分解的活化能和指前因子.采用Thermo-kinetics软件对可能性最大的5种动力学机理函数进行拟合,根据相关系数最大的原则确定最佳分解机理.研究结果表明:菱镁矿热分解的活化能随菱镁矿粒度的增大而减小,当菱镁矿的粒度由小增大时,控制其热分解过程的机理由化学反应逐渐向颗粒内部的传热和CO2的扩散传质转变;其热分解过程的最可几机理函数为R3模型,即三级相边界扩散反应,函数方程为G(α)=1-(1-α)1/3.     

CURING KINETICS AND THERMAL PROPERTY CHARACTERIZATION OF BISPHENOL-F EPOXY RESIN AND DDS SYSTEM

The curing kinetics of bisphenol-F epoxy resin (BPFER)/4,4′-diaminodiphenyl sulfone (DDS) system were studied by isothermal experiments using a differential scanning calorimeter (DSC). Autocatalytic behavior was shown in the first stages of the cure for the system, which could be well described by the model proposed by Kamal that includes two rate constants, k ₁ and k ₂, and two reaction orders, m and n. The curing reaction at the later stages was practically diffusion-controlled due to the onset of gelation and vitrification. To consider the diffusion effect more precisely, diffusion factor, f(α), was introduced into Kamal's equation. Thus, the curing kinetics could be predicted well over the whole range of conversion covering both pre- and postvitrification stages. The glass transition temperatures (T_gs) of the BPFER/DDS system isothermally cured partially were determined by means of torsional braid analysis (TBA), and the results showed that T_gs increased with conversion up to a constant value. The highest T_g was 406.2 K. The thermal degradation kinetics of cured BPFER were investigated by thermogravimetric analysis (TGA), revealing two decomposition steps.     

Segregation-controlled densification and grain growth in rare earth-doped Y2O3

Cation doping of Y₂O₃ is an established approach for tailoring densification and grain growth during sintering. However, the segregation of doped cations to the grain boundary and their impact on processing are still not completely understood. Segregation can be driven by electrostatic effects due to charge mismatch with the host lattice or elastic effects induced by ion size mismatch. While segregation is caused by thermodynamics, it impacts diffusion and the kinetics of grain boundaries during densification and microstructure evolution. In this study, we utilize two isovalent dopants (La³⁺ and Gd³⁺), that is we focus on the elastic component of segregation. We investigate the densification as well as the grain growth kinetics of both doped and undoped Y₂O₃ during field-assisted sintering/spark plasma sintering (FAST/SPS). While Gd³⁺ is showing no significant effect on densification, La³⁺ resulted in a strongly reduced sintering activity. Furthermore, the analysis of the grain growth behavior during sintering and on predensified samples revealed a decrease in the grain growth coefficient, with La³⁺ having the strongest impact. The structure and chemistry at the grain boundary were observed by aberration-corrected TEM. While no structural change was caused by doping, the chemical analysis showed a strong segregation of La³⁺ to the grain boundary, which could not be observed for Gd³⁺. The results indicate that segregated La³⁺ causes a drastic decrease in grain boundary migration rates through solute drag as well as much slower sintering kinetics, likely caused by a decrease in the grain boundary self-diffusion due to segregation. This study further underlines the importance of the elastic contribution to cation segregation and establishes a clear relationship to grain growth and sintering kinetics, which are both decreased by segregation.     

Commercial Diatomite for Adsorption of Tetracycline Antibiotic from Aqueous Solution

Extensive use of antibiotics in human therapy and farming industry has resulted in their accumulation and potential hazards to the environment. In this study, diatomite, which is a siliceous rock with large surface area and high adsorptivity towards organic compounds, was used to adsorb the antibiotic tetracycline (TC) from aqueous media. The adsorption kinetics, isotherms, thermodynamics, and effects of the adsorbent amount and ionic strength were evaluated in batch adsorption experiments. The adsorption of TC onto diatomite followed the pseudo-second-order kinetics model, and the sorption equilibrium was reached in 120 min. The perfect adsorbent amount could be selected within the range of 1 ? 20 g·L^?1. The equilibrium data at different temperatures was satisfactorily fitted to the Langmuir isotherm equation with high R² above 0.999, and the maximum monolayer adsorption capacity of 303.03 mg·g^?1 was obtained at 318 K using 1 g·L^?1 diatomite. Thermodynamic parameters showed that the adsorption reaction was spontaneous and endothermic. Moreover, the adsorption of TC was insignificantly affected by the ionic strength of 0.05-1% NaCl and CaCl₂, indicating that diatomite has a potential practical application as adsorbent media for removing TC from real water.     

An optimization study on microwave irradiated decomposition of phenol in the presence of H2O2

BACKGROUND Removal of phenol from industrial waste waters involves basic techniques namely extraction, biodegradation, photocatalytic degradation, etc. Among the available processes, the oxidation of phenols using H₂O₂ is a suitable alternative because of low cost and high oxidizing power. The application of an oxidation process for the decomposition of stable organic compounds in waste water leads to the total degradation of the compounds rather than transferring from one form to another. Since oxidation using Fenton's reagent is more dependent on pH, in this present work it was proposed to use H₂O₂ coupled with microwave irradiation. The effects of initial phenol concentration, microwave power and the irradiation time on the amount of decomposition were studied. RESULTS: In the present work experiments were conducted to estimate the percentage degradation of phenol for different initial concentrations of phenol (100, 200, 300, 400 and 500 mg L^?1), microwave power input (180, 360, 540, 720 and 900 W) for different irradiation times. The kinetics of the degradation process were examined through experimental data and the decomposition rate follows first‐order kinetics. Response surface methodology (RSM) was employed to optimize the design parameters for the present process. The interaction effect between the variables and the effect of interaction on to the responses (percentage decomposition of phenol) of the process was analysed and discussed in detail. The optimum values for the design parameters of the process were evaluated (initial phenol concentration 300 mg L^?1, microwave power output 668 W, and microwave irradiation time 60 s, giving phenol degradation 82.39%) through RSM by differential approximation, and were confirmed by experiment. CONCLUSION: The decomposition of phenol was carried out using H₂O₂ coupled with microwave irradiation for different initial phenol concentrations, microwave power input and irradiation times. The phenol degradation process follows first‐order kinetics. Optimization of the process was carried out through RSM by forming a design matrix using CCD. The optimized conditions were validated using experiments. The information is of value for the scale up of the oxidation process for the removal of phenol from wastewater. Copyright © 2008 Society of Chemical Industry     

A chelating cellulose adsorbent for the removal of Cu(II) from aqueous solutions

Regenerated cellulose wood pulp was grafted with the vinyl monomer glycidyl methacrylate (GMA) using ceric ammonium nitrate as initiator and was further fuctionalised with imidazole to produce a novel adsorbent material, cellulose‐g‐GMA‐imidazole. All cellulose, grafted cellulose and functionalized cellulose grafts were physically and chemically characterized using a number of analytical techniques, including elemental analysis, Fourier transform infrared spectroscopy, thermogravimetric analysis, differential thermal analysis, and scanning electron microscopy. The cellulose‐g‐GMA material was found to contain 1.75 mmol g^?1 epoxy groups. These epoxy groups permitted introduction of metal binding functionality to produce the cellulose‐g‐GMA‐imidazole final product. Following characterization, a series of adsorption studies were carried out on the cellulose‐g‐GMA‐imidazole to assess its capacity in the removal of Cu²⁺ ions from solution. Cellulose‐g‐GMA‐imidazole sorbent showed an uptake of ～70 mg g^?1 of copper from aqueous solution. The adsorption process is best described by the Langmuir model of adsorption, and the thermodynamics of the process suggest that the binding process is mildly exothermic. The kinetics of the adsorption process indicated that copper uptake occurred within 30 min and that pseudo‐second‐order kinetics best describe the overall process. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 2006