The oxidation kinetic study of mechanically milled ultrafine iron powders by thermogravimetric analysis

Journal of Thermal Analysis and Calorimetry - The effect of mechanical milling on the oxidation kinetics of ultrafine iron powders was investigated by thermogravimetric (TG) analysis. The initial...     

Experimental and theoretical multiple kinetic isotope effects for an SN2 reaction. An attempt to determine transition-state structure and the ability of theoretical methods to predict experimental kinetic isotope effects

The secondary alpha-deuterium, the secondary beta-deuterium, the chlorine leaving-group, the nucleophile secondary nitrogen, the nucleophile (12)C/(13)C carbon, and the (11)C/(14)C alpha-carbon kinetic isotope effects (KIEs) and activation parameters have been measured for the S(N)2 reaction between tetrabutylammonium cyanide and ethyl chloride in DMSO at 30 degrees C. Then, thirty-nine readily available different theoretical methods, both including and excluding solvent, were used to calculate the structure of the transition state, the activation energy, and the kinetic isotope effects for the reaction. A comparison of the experimental and theoretical results by using semiempirical, ab initio, and density functional theory methods has shown that the density functional methods are most successful in calculating the experimental isotope effects. With two exceptions, including solvent in the calculation does not improve the fit with the experimental KIEs. Finally, none of the transition states and force constants obtained from the theoretical methods was able to predict all six of the KIEs found by experiment. Moreover, none of the calculated transition structures, which are all early and loose, agree with the late (product-like) transition-state structure suggested by interpreting the experimental KIEs.     

Isothermal kinetic analysis of the thermal decomposition of magnesium hydroxide using thermogravimetric data

In the present study, the kinetics of the thermal decomposition of magnesium hydroxide is investigated, using isothermal methods of kinetic analysis. For this purpose, experiments in thermogravimetric analyser were carried out in standard values of temperature (350°, 400°, 450° and 500°C) which resulted in weight loss percent as a function of time. The data were further modified to give fraction reacted ‘' versus time to be tested in various forms of ‘' functions. In order to determine the mechanism of the magnesium hydroxide decomposition and the form of the conversion function which governs the dehydroxylation of Mg(OH)₂, four different methods of isothermal kinetic analysis were used. Applying each of these methods to the data, it was concluded that the nucleation mechanism predominates the Mg(OH)₂, decomposition for all values of temperature tested; at 350°C the kinetic model which represents the experimental data is that of reaction at phase boundaries (random nucleation), F₁: ln(1−)=kt) while for the higher temperatures 400°, 450° and 500°C the kinetic equation of nucleation and development in two dimensions, A₂: [−ln (1−)]^1/2=kt was found to fit better the experimental results. The activation energy was evaluated applying two alternative methods; the Arrhenius plot, using maximum rates of reaction, from which the activation energy was evaluated to be 20.54 kcal/mol. An alternative method based on plots of ln t versus 1/T corresponding to the same value of ‘' gave values of 10.72, 13.82 and 16.31 kcal/mol for ‘' values of 0.25, 0.50 and 0.75, respectively.     

Determination of salutary parameters to facilitate bio-energy production from three uncommon biomasses using thermogravimetric analysis

Fuels derived from biomass are renewable as well as environment friendly. In this study, three biomasses viz. husk of areca nut (Areca catheu), trunks of moj (Albizzia lucida), and bon bogori (Ziziphus rugosus) available in North-East region of India were tested as potential biofuel sources. The accentuation of this study was to determine the kinetic parameters using thermogravimetric (TG) technique under air and nitrogen atmosphere. The experiments were carried out within temperature range 300–973 K under air and nitrogen atmosphere at four different heating rates viz. 5, 10, 15, and 20 K min^?1, respectively. The mass losses at different lumps in the TG graphs were estimated. The first-order kinetic parameters such as activation energy and pre-exponential factor were calculated for different reaction zones for all the three biomass samples. Effects of atmosphere on combustion characteristics (e.g., peak temperature, ignition temperature, and reactivity index) of biomasses were also determined in this study. Areca nut husk has highest ignition temperature (526.38 K) and reactivity index (0.21) but moj has highest peak temperature (597.91 K) along with highest activation energy (348.04 kJ mol^?1) and pre-exponential factor (1.12 × 10²⁴ min^?1), respectively.     

Study of carbon black oxidation behavior under different heating rates

The thermodynamic methods of the Arrhenius and Achar-Brindley-Sharp-Wendworth are employed to investigate the influence of the heating rate on oxidation characteristics of three carbon samples. High resolution transmission electron microscopy, Raman spectroscopy, and specific surface area measurements using Brunauer–Emmett–Teller theory are applied to evaluate the influence of the graphitization degree, the microcrystalline length, and the microstructure on the oxidation of carbon black. The results show that with the increase in heating rate, the reaction rate of carbon black increases and the oxidation activation energy gradually decreases; the fitted values of the activation energy range from 136.4 to 221.3 kJ mol^?1 with the heating rate is <100 K min^?1. Besides, the evaporation and oxidation of simulating soluble organic fractions absorbed on carbon samples can change its internal microstructure, which could influence carbon oxidation. All experimental results indicate that carbon black would sequentially take those steps during oxidation: volatile substance evaporation or oxidation, amorphous carbon oxidation, graphitization, and combustion finally.     

Pyrolysis of the hybrid energy cane: thermal decomposition and kinetic modeling using non-isothermal thermogravimetric analysis

Journal of Thermal Analysis and Calorimetry - This work aims to investigate the thermal decomposition and reaction kinetics of the hybrid energy cane, as well as its thermochemical properties....     

A computer program system for kinetic analysis of non-isothermal thermogravimetric data: II. Generalized kinetic analysis and application to coal pyrolysis

A FORTRAN program is presented which enables the kinetic analysis of extent and rate of reaction data resulting from transposed experimental TG/DTG data obtained under non-isothermal conditions. This software allows one to perform Arrhenius, Friedman and Kissinger analyses for up to nine different solid-state rate-controlling reactions, including nth order, Avrami-Erofeev, phase boundary movement and diffusional models. Data from an investigation of the pyrolysis of a bituminous coal serve as an example of the application of the program.     

Computer-aided treatment of thermogravimetric data and calculation of effective kinetic parameters of thermal decomposition processes

Separate stages of mathematical processing of thermogravimetric data, the difficulties most often encountered, and typical error sources are considered. A complex procedure of automatic acquisition and editing of experimental data, including calculation of effective kinetic parameters, is described and an appropriate algorithm for the 15 BCM-5 microcomputer is presented. The computer calculation of the kinetic parameters of the multistage thermal decomposition of a polyamide fibre is given as an example.

---

Zusammenfassung Verschiedene Phasen der mathematischen Behandlung von thermogravimetrischen Daten, am häufigsten auftretende Schwierigkeiten und typische Fehlerquellen werden erörtert. Das komplexe Verfahren der automatischen Eingabe und Ausgabe experimenteller Daten wird, einschliessliche der Berechnung von effektiven kinetischen Parametern, beschrieben. Ein entsprechender Algorithmus wird für den Mikrokomputer 15 BCM-5 angegeben. Als Beispiel wird die Berechnung der kinetischen Parameter der mehrstufigen thermischen Zersetzung von Polyamidfasern ausgeführt.

---

, . , , - 15 BCM-5. .

     

Surface modification and characterization of carbon black through oxidation

This study focuses on modifying the surface of carbon black (CB) with hydrogen peroxide to raise light absorbance of dispersed CB in water without capping agent. Four kinds of commercial CB, trademarked as M900, M1000, M1100, and Mogul L, respectively, were used as study materials. The ultrasonic bath was utilized to disperse the treated CB in de-ionic (DI) water in the absence of capping agent. The surface properties of treated CB were characterized by thermal gravimetric analysis, X-ray photoelectron spectroscope, and Fourier transform infrared spectroscopy, as well as the light absorbance, stability, and morphology of treated CB particles dispersed in DI water were analyzed by ultraviolet-visible light absorption spectroscopy, dynamic light scattering, and transmission electron microscopy. As shown in the results, in particular, it was found that the oxygen on the surface of CB could be increased by the treatment of peroxide hydrogen, resulting in stable dispersion without capping agent to sharply increase light absorption value of Mogul L CB in DI water from 38 to 545 g⁻¹ dm².     

Thermal decomposed behavior and kinetic study for untreated and flame retardant treated regenerated cellulose fibers using thermogravimetric analysis

Journal of Thermal Analysis and Calorimetry - In the present work, pyrolysis kinetic mechanism was studied for regenerated cellulosic fiber (RCF) and composite RCF containing silicon/nitrogen flame...     

Hydrogenation of single-wall carbon nanotubes using polyamine reagents: combined experimental and theoretical study

We combine experimental observations with ab initio calculations to study the reversible hydrogenation of single-wall carbon nanotubes using high boiling polyamines as hydrogenation reagents. Our calculations characterize the nature of the adsorption bond and identify preferential adsorption geometries at different coverages. We find the barrier for sigmatropic rearrangement of chemisorbed hydrogen atoms to be approximately 1 eV, thus facilitating surface diffusion and formation of energetically favored, axially aligned adsorbate chains. Chemisorbed hydrogen modifies the structure and stability of nanotubes significantly and increases the inter-tube distance, thus explaining the improved dispersability in solvents like methanol, ethanol, chloroform, and benzene.     

A computer program system for kinetic analysis of non-isothermal thermogravimetric data: I. Data acquisition and preparation for kinetic analysis

FORTRAN software is described which enables the generation of rate of weight change data (DTG) from percentage weight change measurements (TG), obtained under non-isothermal conditions. The program also transposes this information into the dimensionless extent and rate of reaction at unit temperature intervals by means of a cubic spline interpolation. A simple search routine identifies all DTG spikes in the thermogravimetric record, and the temperature and extent of reaction at which the rate attains its maximum value. This total information serves as input data for the kinetic analysis software to be discussed in part II of this communication. An example of the application of this program to the pyrolysis of bituminous coal is presented.     

Engineering delivery of pantaprazole drug using multi-walled carbon nanotubes: an experimental and theoretical study

Structural Chemistry - Todays, using nano-based drug delivery systems as suitable carriers can help in controlling release of drug to target cells. In current study, multi-walled carbon nanotube...     

Thermal stability and degradation kinetic study of white and colored cotton fibers by thermogravimetric analysis

Complexation of neptunium(V) with fluoride in aqueous solutions at elevated temperatures was studied by spectrophotometry and microcalorimetry. Two successive complexes, NpO₂F(aq) and NpO₂F₂⁻, were identified by spectrophotometry in the temperature range of 10–70°C. Thermodynamic parameters, including the equilibrium constants and enthalpy of complexation between Np(V) and fluoride at 10–70°C were determined. Results show that the complexation of Np(V) with fluoride is endothermic and that the complexation is enhanced by the increase in temperature — a two-fold increase in the stability constants of NpO₂F(aq) and more than five-fold increase in the stability constants of NpO₂F₂⁻ as the temperature is increased from 10 to 70°C.     

Thermal degradation behaviour and kinetic analysis of unsaturated polyester-based composites and IPNs by conventional and modulated thermogravimetric analysis

The thermal degradation behaviour of epoxy/unsaturated polyester based polymer interpenetrating networks (IPNs), and unsaturated polyester containing various flame-retardants have been investigated by TGA and Py/GC/MS. The kinetic parameters of various polymers were analysed by conventional and modulated thermogravimetric analysis (MTGA) methods. The activation energies of degradation were calculated by the Coats-Redfern and MTGA methods, respectively. The results of both conventional and MTGA analyses reveal that the decomposition of IPNs consists of two non-interfering decomposition processes for epoxy polymer and cured unsaturated polyester, respectively. For the flame-retardant containing unsaturated polyesters, ammonium polyphosphate (APP) played an important role in the second-step of the pyrolysis reaction of APP-containing samples. It is important to note that the possibilities of reaction order for these pyrolysis processes are significantly distinguishable by Coats-Redfern method. Furthermore, the activation energies for various samples calculated by MTGA method are on average larger than those calculated from the Coats-Redfern method. The results also reveal that when either the flame-retardant or the epoxy was added to the unsaturated polyester, the heat resistance of the unsaturated polyester was enhanced.     

Thermal and kinetic behaviors of pyrolytic carbon black and gas coal in co-combustion

Journal of Thermal Analysis and Calorimetry - In this study, a combustion study of tire pyrolytic carbon black (CBp), gas coal (GC), and their blends was carried out by thermogravimetric analysis...     

Non-isothermal oxidation and kinetic analysis of pure magnesium powder

Journal of Thermal Analysis and Calorimetry - With high energy densities, metals appear as innovative energy carriers. In the present study, magnesium powder is considered as fuel for energy...     

Gas chromatographic analysis of water phenolic pollutants using acid-washed graphitised carbon black

Summary The fractionation of eleven phenols which may be contaminants in drinking water has been accomplished by using acid-washed graphitised carbon black modified with trimesic acid and PEG 20 M.     

Assessment of the sorption capacity and regeneration of carbon dioxide sorbents using thermogravimetric methods

Adsorption methods using solid sorbents are an alternative to the absorption technology in the processes of purification gases from carbon dioxide. There is a need to rapidly assess the suitability of sorbents for use it in PSA, TSA, or VPSA installations. Important parameters which determine the quality of the sorbent are the sorption capacity of sorbent, selectivity to CO₂ and the possibility of regeneration. This paper presents the results of sorption/desorption of CO₂ study on the impregnated porous materials using thermogravimetric methods. Thermogravimetry allows for rapid assessment of sorption capacity and regeneration of the sorbents. Specially selected temperature program allowed to determine the sorption capacity of sorbents depending on the concentration of CO₂ in the gas mixture and temperature. Degree of sorbent purification was determined in desorption process.