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.     

Kinetics and reaction mechanism of isothermal oxidation of Iranian ilmenite concentrate powder

Thermal oxidation of commercial ilmenite concentrate from Kahnouj titanium mines, Iran, at 500–950 °C was investigated for the first time. Fractional conversion was calculated from mass change of the samples during oxidation. Maximum FeO to Fe₂O₃ conversion of 98.63 % occurred at 900 °C after 120 min. Curve fit trials together with SEM line scan results indicated constant-size shrinking core model as the closest kinetic mechanism of the oxidation process. Below 750 °C, chemical reaction with activation energy of 80.65 kJ mol^?1 and between 775 and 950 °C, ash diffusion with activation energy of 53.50 kJ mol^?1 were the prevailing mechanisms. X-ray diffraction patterns approved presence of pseudobrookite, rutile, hematite, and Fe₂O₃·2TiO₂ phases after oxidation of ilmenite concentrate at 950 °C.     

High temperature oxidation of Cr–Mo–V tool steel in carbon dioxide

This study aims to examine the oxidation resistance and kinetics of Cr, Mo, and V containing tool steel (Calmax) when exposed in CO₂ high temperature environment by thermogravimetric measurements, X-ray diffraction analysis, and microscopic observation. The tool steel samples begin to oxidize at 480 °C while over 600 °C, the oxidation rate increases significantly. Finally, at 900 °C, the oxidation rate is significantly high. The activation energy of the oxidation was calculated as 160.1 kJ mol^?1. Microscopically, the thickness of the scale was found to increase with the exposure temperature, and the as formed scales consisted of two distinguishable oxide layers.     

Kinetics of isothermal oxidation of WC–20Co hot-pressed compacts in air

The present paper presents an isothermal analysis of the oxidation behavior in which hot-pressed compacts rather than powders are used over the temperature range 700–850 °C. This was done to better simulate the extent of oxidation occurring on use. WC–Co powders were first subjected to non-isothermal kinetic analysis to follow the oxidation mechanism. In the isothermal runs, a thermobalance was used to follow up the mass with time at different constant temperatures. The diameter of compacts was measured as function of time at these temperatures, and a simple model was proposed to relate the diameters to extent of oxidation. Two reactions were found to take place that are controlled by chemical reaction at interface: Oxidation of cobalt and oxidation of WC with the formation of WO₃ and CoWO₄. The activation energies for the two steps of oxidation were calculated and found to equal 157 kJ mol^?1 and 205 kJ mol^?1, respectively. These values are in reasonable agreement with published data for WC–Co powders.     

Low-temperature reduction of silver(I) oxide particles with long chain alcohol

The mechanism of reducing silver(I) oxide particles to silver metals was studied using myristyl alcohol as a reducing agent. The reduction temperature of silver oxide with myristyl alcohol decreased to 150 °C from the temperature of silver oxide in air, 400 °C. The reduction temperature was decreased by myristyl alcohol reacting with silver oxide, which was confirmed by our reaction equation model obtained by gas chromatography determination, pyrolysis gas chromatography–mass spectrometry, and Karl Fischer titration. An endothermic of 153.7 kJ mol^?1 in the reduction of silver oxide with myristyl alcohol calculated from the reaction model using Hess’s law was coincident with that obtained experimentally by differential scanning calorimetry measurements.     

Study on the kinetics and reactivity at the ignition temperature of Jurassic coal in North Shaanxi

Thermal analysis of seven Jurassic coal samples from North Shaanxi in West China and three permo-carboniferous coal samples from East China was studied to identify ignition temperatures in the process of the oxidation and spontaneous combustion. The experiments were carried out under non-isothermal heating conditions up to 700 °C at the heating rates of 5, 10, 15, and 20 °C min^?1 in an air atmosphere. Through the FTIR spectrometer experiments, the absorbance peaks of functional groups of coal samples were analyzed at the ignition temperatures, pre-ignition of the 10 °C, post-ignition of the 10 °C at the heating rate of 10 °C min^?1. By the differential spectrum method, the changes of functional groups were discussed with the aim to determine characteristics and reactivity of the ignition temperature around. The results showed that ignition temperatures of experimental coal samples increased with the rising heating rates, and ignition temperatures of Jurassic coals were lower than that of the permo-carboniferous coal samples at the same heating rate. Apparent activation energy of experimental Jurassic coals at the ignition temperatures was calculated by Ozawa method based on the non-isothermal and differential heating rates, ranging from 80 to 105 kJ mol^?1, which were lower than that of the eastern permo-carboniferous samples. On the basis of Pearson correlation coefficient method which can signify the degree of correlations ranging from ?1 to 1, the correlation analyses were conducted between activation energy and functional groups variation within 10 °C before and after ignition temperature. It was concluded that the key functional groups of Jurassic coals in the oxidation and ignition reaction were methyl and alkyl ether within 10 °C before ignition temperature, and carboxyl and carbonyl within 10 °C after ignition temperature.     

Thermal Behavior of 2‐(Dinitromethylene)‐1,3‐diazacyclopentane

A new compound, 2‐(dinitromethylene)‐1,3‐diazacyclopentane (DNDZ), was prepared by the reaction of 1,1‐diamino‐2,2‐dinitroethylene (FOX‐7) with 1,2‐diaminoethane in N‐methylpyrrolidone (NMP). Thermal decomposition of DNDZ was studied under non‐isothermal conditions by DSC, TG/DTG methods, and the enthalpy, apparent activation energy and pre‐exponential factor of the exothermic decomposition reaction were obtained as 317.13 kJ·mol^?1, 269.7 kJ·mol^?1 and 10^24.51 s^?1, respectively. The critical temperature of thermal explosion was 261.04°C. Specific heat capacity of DNDZ was determined with a micro‐DSC method and a theoretical calculation method, and the molar heat capacity was 205.41 J·mol^?1·K^?1 at 298.15 K. Adiabatic time‐to‐explosion was calculated to be a certain value between 263–289 s. DNDZ has higher thermal stability than FOX‐7.     

Study of the adsorbent properties of nickel oxide for phenol depollution

Phenol and its derivatives are considered as dangerous pollutants due to these harmful effects on health and the environment. Treatment of the waters charged by these compounds by adsorption remains very important. For these reasons, this study was designed to prepare nickel oxide by precipitation method in order to remove these pollutants from aquatic environments. Indeed, structural and textural properties of this solid have been determined by various physicochemical methods (X-ray diffraction, Fourier transform in the infrared, N2 adsorption/desorption (BET), ATD / ATG thermal analysis and scanning electron microscopy (SEM)). In addition, several adsorption tests were carried out in order to show the effectiveness of this solid for the elimination of phenol in aqueous solution and to determine the physicochemical parameters which affect adsorption. Our results have shown 5.29 mg·g⁻¹ of adsorption capacity with 98% of yield. Furthermore, it was shown that adsorption process was endothermic. For the kinetic study, it was demonstrated that phenol adsorption on NiO follows the pseudo-second-order and the Langmuir model better adaptable for the isotherm of desorption. Moreover, thermodynamic study shows positive values of ΔS ° (266.6 JK⁻¹·mol⁻¹) suggesting a randomness increase of the solid/liquid interface. ΔH ° (60.41 kJ·mol⁻¹) was also positive confirming the endothermic nature of the adsorption processes. However, ΔG ° (kJ·mol⁻¹) was negative suggesting the spontaneity of the phenol adsorption. In summary, this work suggests that phenol adsorption on NiO was linked to the chemical adsorbate/adsorbent interactions.     

The effect of temperature on lithium intercalation into carbon materials

The effects of temperature on lithium intercalation into non-graphitized carbonized cloth from various electrolytes have been studied. The open-circuit potential (o.c.p.) of the intercalates shifts in the negative direction as the temperature is raised. The average temperature coefficient of the o.c.p. is equal to −0.04 mV·K⁻¹ in the range from −35 to +45 °C. Intercalation-deintercalation kinetics was studied by the galvanostatic technique. It was shown that this process is quasi-ohmic at room and higher temperatures and has activation-ohmic control at lower temperatures. The effective activation energy of intercalation-deintercalation is about 20kJ·mol⁻¹. Intercalates are corroded in all electrolytes, the corrosion rate being drastically increased as the temperature is raised. The apparent activation energy of corrosion is 120–150 kJ·mol⁻¹. The corrosion rate is suggested to be controlled by cathodic reduction of electrolyte components. Received: 11 April 1997 / Accepted: 8 September 1997     

Kinetics and Mechanism of the Exothermic First-stage Decomposition Reaction of Dinitroglycoluril

Introduction Dinitroglycoluril (DINGU) is a typical cyclourea nitramine. Its crystal density is 1.94 gcm-3. The detonation velocity corresponding to =1.94 gcm-3 is about 8450 ms-1. Its sensitivity to impact is better than that of cyclotrimethylenetrinitramine. It has the potential for possible use as high explosive from the point of view of the above-mentioned high performance. Its preparation,1-4 properties1-4 and hydrolytic behavior4 have been reported. In the present paper, we report i…     

Mechanism of Oxidation of Ketorolac by Hexacyanoferrate(III) in Aqueous Alkali: A Thermodynamics and Kinetics Study

The kinetics of the oxidation of ketorolac by hexacyanoferrate(III) (HCF) in aqueous alkaline medium at a constant ionic strength of 0.75 mol·dm^?3 was studied spectrophotometrically at 300 K. A plausible mechanism was proposed and the rate law was derived. The mechanism of oxidation of ketorolac (KET) in alkaline medium has been shown to proceed via a KET-HCF complex, which decomposes in a slow step followed by other fast steps to give the products. The main oxidative product was identified as (2,3-dihydro-1-hydroxy-1H-pyrrolizin-5-yl-)(phenyl)methanone and is characterized by its LC–ESI–MS spectrum. Thermodynamic parameters of various equilibria of the mechanism were calculated and activation parameters ΔH ^≠, ΔS ^≠, ΔG ^≠ and log₁₀ A were found to be 29.9 kJ·mol^?1, ?220 J·K^?1·mol^?1, 96 kJ·mol^?1 and 2.70 respectively.     

Thermogravimetric analysis of cellulose insulation and determination of activation energy of its thermo‐oxidation using non‐isothermal,model‐free methods

The aim of the work was to determine the effect of heating rate on initial decomposition temperature and phases of thermal decomposition of cellulose insulation. The activation energy of thermo‐oxidation of insulation was also determined. Individual samples were heated in the air flow in the thermal range of 100°C to 500°C at rates from 1.9°C min^?1 to 20.1°C min^?1. The initial temperatures of thermal decomposition ranged from 220°C to 320°C, depending on the heating rate. Three regions of thermal decomposition were observed. The maximum rates of mass loss were measured at the temperatures between 288°C and 362°C. The activation energies, which achieved average values between 75 and 80.7 kJ mol^?1, were calculated from the obtained results by non‐isothermal, model‐free methods. Copyright © 2014 John Wiley & Sons, Ltd.     

Near‐infrared electrochromic poly(aryl ether)s based on isolated electroactive tetraphenyl‐p‐phenylenediamine moieties

A series of near‐infrared (NIR) electrochromic aromatic poly(aryl ether)s containing N,N,N′,N′‐tetraphenyl‐p‐phenylenediamine (TPPA) moieties in the backbone were prepared from the high‐temperature polycondensation reactions of a biphenol monomer, 2,5‐bis(diphenylamino)hydroquinone, with difluoro compounds. The obtained polymers were readily soluble in many organic solvents and showed useful levels of thermal stability associated with high glass‐transition temperatures (182–205 °C) and high char yields (higher than 40% at 800 °C in nitrogen). The polymer films showed reversible electrochemical oxidation with high contrast ratio both in the visible range and NIR region, and also exhibited high coloration efficiency (CE), low switching time, and stability for electrochromic operation. The polyether TPPA‐a thin film revealed good CE in visible (CE = 217 cm²/C) and NIR (CE = 192 cm²/C) region with reversible electroactive stability (over 500 times within 5% loss relative to its initial injected charge). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5378–5385, 2009     

High-temperature oxidation behaviour of low-entropy alloy to medium- and high-entropy alloys

The high-temperature oxidation behaviour of CoCrNi, CoCrNiMn, and CoCrNiMnFe equimolar alloys was investigated. All three alloys have a single-phase face-centred cubic structure. Thermogravimetric analyses (TGA) were conducted at temperatures ranging from 800 to 1000 °C for 24 h in dry air. The kinetic curves of the oxidation were measured by TGA, and the microstructure and chemical element distribution in different regions of the specimens were analysed. The oxidation kinetics of the three alloys followed the two-stage parabolic rate law, with rate constants generally increasing with increasing temperature. CoCrNi displayed the highest resistance to oxidation, followed by CoCrNiMnFe and CoCrNiMn exhibiting the least resistance to oxidation. The addition of Mn to CoCrNi increased the oxidation rate. The oxidation resistance of CoCrNiMn was enhanced by the addition of Fe. Less Mn Content and the formation of more Cr₂O₃ were responsible for the reduction in the oxidation rates of CoCrNiMnFe. The calculated activation energies of CoCrNiMn and CoCrNiMnFe at 800, 850 and 900 °C were 108 and 137 kJ mol^?1, respectively, and are comparable to that of Mn diffusion in Mn oxides. The diffusion of Mn through the oxides at 800–900 °C is considered to be the rate-limiting process. The intense diffusion of Cr at 1000 °C contributed to the formation of CrMn_1.5O₄ spinel with Mn in the outer layer of CoCrNiMn and Cr₂O₃ in the outer layer of CoCrNiMn.     

Kinetic Study on the Exothermic First-stage Decomposition Reaction of 2,4,8,10-Tetranitro-2,4,8,10-tetraaza- spiro[5,5]undecane-3,9-dione

Introduction 2,4,8,10-Tetranitro-2,4,8,10-tetraazaspiro[5,5]udecane- 3,9-dione is a typical cyclourea nitramine (Figure 1). Its crystal density is 1.91 gcm-3. The detonation velocity according to =1.90 gcm-3 is about 8670 ms-1. Its sensitivity to impact is better than that of cyclotrimethy- lenetrinitramine. So it is the potential high explosive. Its preparation,1-3 properties,1-3 hydrolytic behavior4 and electronic structure3 have been reported. In the present work, we report its kinetic pa…     

Decoupling Study of Melt Polycondensation of Polycarbonate: Experimental and Modeling of Reaction Kinetics and Mass Transfer in Thin Films Polycondensation Process

During the melt polycondensation process of polycarbonate, reaction and mass transfer are deeply coupled owing to relatively high melt viscosity. In this work, the polycondensation reaction kinetics and mass transfer behavior of volatile phenol are decoupling studied in detail by using thin‐film experiments with 250–280 °C, 10–1000 Pa and 0.085–0.68 mm film thickness. A realistic apparent rate model coupled the reaction kinetics with thermodynamic equilibrium and diffusion behavior is developed to describe the polycondensation process, while the diffusion characteristic of small molecule (phenol) is further obtained based on penetration theory. The obtained polycondensation equilibrium constant ranges from 0.3 to 0.55, while the activation energy and pre‐exponential factor of temperature‐dependent diffusion coefficients of phenol are 87.9 kJ mol⁻¹ and 5.08 × 10² m² s⁻¹, respectively. It is also observed that the overall apparent rate of polycarbonate (PC) polycondensation process increases with higher temperature, lower pressure, and thinner film thickness. Coupling the reaction kinetics with mass transfer, the predictions of the realistic apparent rate model are in quite satisfactory agreement with experimental data.     

Effect of shear on the crystallization of the poly(ether ether ketone)

The effect of shear on the crystallization behavior of the poly(ether ether ketone) (PEEK) has been investigated by means of ex situ wide‐angle X‐ray diffraction (WAXD), small‐angle X‐ray scattering, and differential scanning calorimetry (DSC). The changes of the intensity of WAXD patterns along shear direction of the PEEK induced by short‐term shear were observed when the samples crystallized at 330 °C. The results showed that the dimensions of the crystallites perpendicular to the (110) and (111) planes reduced with the increase of shear rate, whereas the dimensions of the crystallites perpendicular to (200) plane increased with the increase of shear rate. Moreover, increasing shear rate can lead to the increase of the crystallinity as well as the average thickness of the crystalline layers. Correspondingly, a new melting peak at higher temperature was found during the subsequent DSC scanning when the shear rate was increased to 30 s^?1. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 220–225, 2010     

Characteristics and kinetics analysis of Codonopsis pilosula pyrolysis

Eight kinds of Radix Codonopsis (RC) from different origins in China were selected as the experimental samples fort his study. Their pyrolysis processes were researched by the method of thermogravimetry analysis, in which the heating course was set in the ways of programming temperature from room temperature to 500 °C at different heating rates. Research results show that the process in the heating period of RC includes three stages: water loss, fast pyrolysis, and medium rate decomposition. For cultivated RC, the average initial decomposition temperature in the fast pyrolysis stage is 115 °C, whereas the peak temperature of the fast pyrolysis stage is changed from 189 to 225 °C, in which stage the alcohol-soluble substances are mainly decomposed. It is required to control the operational temperatures of drying and concocting processes according to initial decomposition temperature. Kissinger–Akahira–Sunose model can be used to describe the process mechanism of RC pyrolysis, and the kinetic analyses based on the fast pyrolysis stage thermogravimetric data show that the activation energies change from 141 to 207 kJ mol^?1 for cultivated RC samples and 122 to 131 kJ mol^?1for wild RC samples. The alcohol-soluble extract (ASE) content of wild RC samples is lower than that of cultivated RC samples; their thermal stability is also relatively poor.     

Thermal Behavior of N,N＇Bis[N-（2,2,2-trinitroethyl）-N-nitro]ethylenediamine

The thermal behavior and kinetic parameters of the exothermic decomposition reaction of N‐N‐bis[N‐(2,2,2‐tri‐nitroethyl)‐N‐nitro]ethylenediamine in a temperature‐programmed mode have been investigated by means of differential scanning calorimetry (DSC). The results show that kinetic model function in differential form, apparent activation energy E_a and pre‐exponential factor A of this reaction are 3(1 ‐α)^2/3, 203.67 kJ·mol^?1 and 10^20.61s^?1, respectively. The critical temperature of thermal explosion of the compound is 182.2 °C. The values of ΔS^≠ ΔH^≠ and ΔG^≠ of this reaction are 143.3 J·mol^?1·K^?1, 199.5 kJ·mol^?1 and 135.5 kJ·mol^?1, respectively.     

Aerobic oxidation of cumene to cumene hydroperoxide catalyzed by metalloporphyrins

A protocol for the aerobic oxidation of cumene to cumene hydroperoxide (CHP) catalyzed by metalloporphyrins is reported herein. Typically, the reaction was performed in an intermittent mode under an atmospheric pressure of air and below 130°C. Several important reaction parameters, such as the structure and concentration of metalloporphyrin, the air flow rate, and the temperature, were carefully studied. Analysis of the data obtained showed that the reaction was remarkably improved by the addition of metalloporphyrins, in terms of both the yield and formation rate of CHP while high selectivity was maintained. It was discovered that 4 or 5 h was the optimal reaction time when the reaction was catalyzed by monomanganese-porphyrin ((p-Cl)TPPMnCl) (7.20 × 10^?5 mol/l) at 120°C with the air flow rate being 600 ml/min. From the results, we also found that higher concentration of (p-Cl)TPPMnCl, longer reaction time and higher reaction temperature were all detrimental to the production of CHP from cumene. Studies of the reaction kinetics revealed that the activation energy of the reaction (E) is around 38.9 × 10⁴ kJ mol^?1. The low apparent activation energy of the reaction could explain why the rate of cumene oxidation to CHP in the presence of metalloporphyrins was much faster than that of the non-catalyzed oxidation.