Kinetic Thermal Analysis Research Articles

Internal hydrophobic treatment for mortar containing supplementary cementitious materials: thermal analysis of kinetics and products of hydration

AbstractThe presented research investigates the application of the organosilicon admixtures based on triethoxyoctylsilane (OTES) on the hydration of the cement-based material with addition of supplementary cementitious materials (SCM) such as blast furnace slag and microsilica. The influence of silane-based admixtures on the kinetics of hydration was investigated by isothermal calorimetry. The calorimetric results disclosed that applied admixtures affect the hydration process of cement paste with SCM. The DTA/TG analysis provided the information about impact of triethoxyoctylsilane on the composition and formation of the mineral phases. The DTA/TG measurements showed noticeable changes in the thermal decomposition of the tested materials and amount of bounded water. The impact of OTES on the microstructure and pore size distribution of pastes was examined by mercury intrusion porosimetry. The result showed significant changes in the range of pore diameters. The influence of organosilicon admixtures on the compressive strength of mortars after 2, 7, 28, 56 and 90 days was also investigated. The effect depended on the mineral additive used. In case of blast furnace slag, the development of compressive strength was only delayed, however, in the case of microsilica, it was stopped.

Investigation of Size-Dependent Sublimation Kinetics of 2,4,6-Trinitrotoluene (TNT) Micro-Islands Using In Situ Atomic Force Microscopy.

Kinetic thermal analysis was conducted using in situ atomic force microscopy (AFM) at a temperature range of 15–25 °C to calculate the activation energy of the sublimation of 2,4,6-trinitrotoluene (TNT) islands. The decay of different diameter ranges (600–1600 nm) of TNT islands was imaged at various temperatures isothermally such that an activation energy could be obtained. The activation energy of the sublimation of TNT increases as the diameter of islands increases. It was found that the coarsening and the sublimation rate of TNT islands can be determined by the local environment of the TNT surface. This result demonstrates that a diffusion model cannot be simply applied to “real world” systems for explaining the sublimation behavior and for estimating the coarsening of TNT.

On the Amorphisation Trajectory of Carbon Nanotubes

ABSTRACTA very simple model for the kinetics of oxidation of carbon Nanotubes (NTs) is proposed which is able to reproduce the main features of their measured kinetic thermal oxidation profiles. Based on this model the resistance to oxidation of NTs is found to decrease with increasing defect density and amorphous phases, i.e. sp3 bonding component. This finding supports the validity of assumptions previously made to explain the correlation between results of Raman Spectroscopy (RS) and Kinetic Thermal Analysis (KTA) on NTs via a three-stage model, inspired to that proposed by Ferrari and Robertson for other nanocarbons.

Do Nanotubes Follow an Amorphization Trajectory as Other Nanocarbons Do?

Various typologies of nanocarbons are considered, including crystalline graphite, amorphous activated carbon, and a large variety of multiwall carbon nanotubes (laboratory-prepared and commercially available, pristine and heat-treated), featured by different purity degree (81.7–99.7 wt %), crystalline quality (amorphous fraction: 0–5 wt %), size (outer diameter: 5–100 nm), and morphology. From the comparative discussion of the results of their systematic investigation by Raman spectroscopy, kinetic thermal analysis, and complementary techniques, the existence of a sharp correlation emerges between the strength of C bonding, as measured by the wavenumber position of the G-band in Raman spectra, and the oxidative resistance of the samples, as monitored by the maximum oxidation-rate temperature. A three-stage model is proposed to account for the effects associated with the increasing localization of states due to the introduction of curvature and lattice defects, accompanying the evolution from crystalline g...

Evaluation of the Overall Crystalline Quality of Amorphous Carbon Containing Multiwalled Nanotubes

A set of nanotubes with moderate contents of amorphous phases (0.4–5.1 wt %) are systematically investigated by Raman spectroscopy, kinetic thermal analysis, and complementary techniques. Results show that, in spite of their small amount, the presence of amorphous phases has a strong impact on the oxidation path of nanotubes. The apparent activation energy for oxidizing them, as inferred from thermal kinetic analysis, decreases linearly with increasing the content of amorphous species. The presence of non-sp2 defects causes the failure of the commonly adopted Raman graphitization indexes, with consequent breakdown of the correlations between crystalline quality and activation energy evidenced in the absence of the amorphous phases. This drawback is overcome by introducing a generalized Raman indicator of the crystalline quality, whose value increases with increasing energy needed for oxidizing nanotubes independently on the typology (sp2 or non-sp2) of defects present in their walls.

Kinetic and thermodynamic parameters of volatilization of biodiesel from babassu, palm oil and mineral diesel by thermogravimetric analysis (TG)

The boiling point and volatility are important properties for fuels, as it is for quality control of the industry of petroleum diesel and biofuels. In addition, through the volatility is possible to predict properties, such as vapor pressure, density, latent heat, heat of vaporization, viscosity, and surface tension of biodiesel. From thermogravimetry analysis it is possible to find the kinetic parameters (activation energy, pre-exponential factor, and reaction order), of thermally simulated processes, like volatilization. With the kinetic parameters, it is possible to obtain the thermodynamic parameters by mathematical formula. For the kinetic parameters, the minor values of activation energy were found for mineral diesel (E = 49.38 kJ mol−1), followed by babassu biodiesel (E = 76.37 kJ mol−1), and palm biodiesel (E = 87.00 kJ mol−1). Between the two biofuels studied, the babassu biodiesel has the higher minor value of activation energy. The thermodynamics parameters of babassu biodiesel are, ΔS = −129.12 J mol−1 K−1, ΔH = +80.38 kJ mol−1 and ΔG = +142.74 kJ mol−1. For palm biodiesel ΔS = −119.26 J mol−1 K−1, ΔH = + 90.53 kJ mol−1 and ΔG = +141.21 kJ mol−1, and for diesel ΔS = −131.3 J mol−1 K−1, ΔH = +53.29 kJ mol−1 and ΔG = +115.13 kJ mol−1. The kinetic thermal analysis shows that all E, ΔH, and ΔG values are positive and ΔS values are negative, consequently, all thermodynamic parameters indicate non-spontaneous processes of volatilization for all the fuels studied.

Improvement of weldability and evaluation criteria for high-strength pipe steel heat-affected zone reliability

Criteria are formulated for evaluating weldability on the basis of methods simulating welding thermal cycles and analysis of austenite polymorphic transformation kinetics in the thermally affected zone. Results are provided for evaluating the joint heat-affected zone (HAZ) cold resistance under the influence of thermal action during welding of thick-walled pipes for considerable heat input and the tendency for cold cracks during welding with small heat input. The effect of alloying elements, i.e., nickel and chromium, and also vanadium and molybdenum in steels microalloyed with niobium on ductile-brittle failure parameters during impact testing is demonstrated. Microalloying niobium-containing steels with vanadium and molybdenum leads to HAZ metal embrittlement. Optimum cooling rates after welding are determined with which HAZ metal cold resistance at down to –30°C is provided are determined.

Thermal analysis of kinetics of coal oxidation

Thermal analysis was used to study the oxidation and thermal degradation reaction of Yangquan coal. One method is that the coal was heated to a certain temperature and held at that temperature for 45 min; Another method is that coal was heated to a temperature and held for 45 min, then it was taken out and the new coal sample was re-put with other temperature's experiments. Two different experiments and their dynamic characterizes were compared, showing that the change degree of TG curve is different from each other. The process of coal oxygenolysis belongs to the first-order of chemical reaction. The activation energy increases along with the reaction process. Moreover, the oxidation of coal is a process that contains lots of reaction steps which mutually promote and connect.

Chitosan and N‐carboxymethylchitosan: I. The role of N‐carboxymethylation of chitosan in the thermal stability and dynamic mechanical properties of its films

AbstractChitosan (degree of deacetylation of 90.2%) and N‐carboxymethylchitosan (N‐CMCh) (degree of substitution of 18.5%) were analyzed using thermogravimetric analysis in order to determine their thermal stability. Also, their films were evaluated using scanning electron microscopy (SEM) and mechanical and dynamic mechanical analysis (DMA). Both polymers showed a thermal degradation peak at Tm ∼ 250 °C, with Tonset and weight loss of 175 °C and 62% and 190 °C and 35% for chitosan and N‐CMCh, respectively. N‐CMCh showed a second thermal degradation peak at Tm = 600 °C, with an additional weight loss of 25%. Kinetic thermal analysis showed a slower process of degradation at 100 °C for N‐CMCh compared with chitosan, and an activation energy 13 times higher for the former, confirming the higher stability of N‐CMCh. Analysis of chitosan and N‐CMCh films showed that the latter support a high tension, with lower elasticity, and, as revealed by DMA, N‐CMCh has a more compact film structure, with a crossing arrangement of N‐CMCh fibers, as compared with the chitosan films which were determined from SEM analysis to have fibers in one direction only. Copyright © 2006 Society of Chemical Industry

Kinetic thermal analysis of glass ceramics from industrial wastes

To recycle inorganic industrial solid wastes, the use of glass ceramics has been proposed as a useful choice. In this work, a pyroxene glass ceramic of the CaO–MgO–Al 2O 3–SiO 2 family was synthesized by mixing three industrial wastes of high production rate generated in northeast Mexico. A kinetic study was carried out by a non-isothermal differential thermal analysis technique (DTA) from which the kinetic parameters, activation energy for crystallization, E a, of 534 ± 4 kJ mol −1, frequency factor, ν, of 5.60 × 10 20 min −1 and Avrami factor, n, values between 1.2 ± 0.2 and 1.3 ± 0.1 were estimated, corresponding to a surface crystallization mechanism.

Fourier thermal analysis of solidification kinetics in molten aluminium and in presence of ultrasonic field

In this paper a comparison between the Newtonian and Fourier method analysis available in thermal analysis techniques is reported. The experimental solidification of liquid aluminium under various conditions has been studied. Thermal analysis is a tool in elucidating the thermal events involved in liquid to solid transformation. The Newtonian method predicts a maximum in heat generation at the onset of solidification, while the Fourier method incorporates the effect of thermal gradient and predicts two heat generation peaks during the solidification process. This comparison between the Fourier and Newtonian method indicates that their predictions are appreciably different. In order to elucidate the effect of ultrasonic waves on solidification process, the measurements were carried out under similar conditions both with and without sonication. Our studies have shown that in presence of the ultrasonic field the kinetics of solidification is changed, leading namely to a decreased undercooling degree of the melt and thermal diffusivity.

Numerical simulation and fourier thermal analysis of solidification kinetics in high-carbon Fe-C alloys

The aim of this work was to carry out both experimental and numerical simulations of cast iron solidification under various conditions. The experimental work was based on a novel technique of thermal analysis known as the Fourier method, whereas solidification modeling was possible by solving the Fourier equation with a heat source. Moreover, a comparison between the Fourier and the Newtonian method indicated that their predictions are appreciably different. The Newtonian method is rather insensitive to the actual thermal gradients and predicts a clear maximum in heat generation at the onset of solidification. In contrast, the Fourier method incorporates the effect of actual thermal gradients and predicts two successive heat generation peaks of increasing magnitude as solidification proceeds. In particular, it was found that the experimental outcome of solidified volume fractions agrees closely with the predictions of the Fourier method. In this case, both experimental and computer simulations on 30- and 40-mm-diameter cylindrical specimens indicated that the solidified fraction followed a sinusoidal trend. Moreover, it was found that under normal solidification conditions, secondary nucleation of fine grains can occur near the center of a cylindrical cast iron specimen. Secondary grain nucleation is attributed to the development of a second under-cooling maximum which easily exceeds the initial one. Finally, the effects of inoculation were investigated in plain cast iron and as a function of the inoculation time. Accordingly, in all cases, the computer simulations were in close agreement with the experimental outcome.

Thermal analysis study of the influence of rapid solidification on the precipitation kinetics of theδ′ (Al3Li) Metastable phase in an Al-Mn-Li Alloy

The precipitation kinetics of theδ′ (Al3Li) phase in two rapidly solidified and one conventionally cast samples of an Al-2.3Li-6.5Mn (in wt%) alloy are compared. Following high cooling rates, manganese is retained in solid solution in the aluminium matrix (αAl) up to 6.0 wt%, far beyond the thermodynamic equilibrium value (0.36 wt% at 500°). Extended solid solution of manganese in aluminium induces strain gradients, similar to those produed by dislocations. The effect of such gradients, the size of which is proportional to the solute atomic fraction, is to enhance lithium precipitation, by lowering the activation energy, as observed, and also by affecting the rate parameter. Kinetic thermal analysis has been performed in a series of nonisothermal DTA experiments, operated in the heat flux DSC mode. The precipitation of theδ′ (Al3Li) phase is evidenced by an exothermic peak whose characteristics were analyzed. The rate of transformation (precipitation) is assumed to obey the Johnson-Mehl-Avrami equation. The activation energy for the precipitation process, as well as the kinetic rate parameter have been evaluated for the rapidly solidified and the conventionally cast specimens. The activation energy for precipitation is lowered, from 105 kJ·mol−1 for the conventionally cast material, down to 77 kJ·mol−1 for a sample that exhibits manganese solid solubility extension of 6.00 wt%. The rate parameter for the precipitation reaction is reduced from about 1.40 for the slowly cast sample to 1.20 the rapidly solidified sample, as a result of additional stress-assisted precipitation.

On the kinetics of the δ′ (Al3Li) phase precipitation in a rapidly solidified Al–Mn–Li–Zr alloy

The precipitation kinetics of the δ′ (Al3Li) phase in two rapidly solidified samples and one conventionally cast sample of an Al–2.3Li–6.5Mn–0.65Zr (in wt. %) alloy are compared. Following high cooling rates, manganese is retained in solid solution in the aluminum matrix (αAl) up to 6.0 wt.%, far beyond the thermodynamic equilibrium value (0.36 wt.% at 500 °C). Extended solid solution of manganese in aluminum induces strain gradients, similar to those produced by dislocations. The effect of such gradients, the size of which is proportional to the solute atomic fraction, is to enhance lithium precipitation by lowering the activation energy, as observed, and also by affecting the rate parameter. Kinetic thermal analysis has been performed in a series of nonisothermal experiments in the heat flux differential scanning calorimetry (DSC) mode. The precipitation of the δ′ (Al3Li) phase is evidenced by an exothermic peak whose characteristics were analyzed. The rate of transformation (precipitation) is assumed to obey the Johnson–Mehl–Avrami equation. The activation energy for the precipitation process as well as the kinetic rate parameter have been evaluated for the rapidly solidified and the conventionally cast specimens. The activation energy for precipitation is lowered, from 107.0 kJ mol−1 for the conventionally cast material, down to 81.8 kJ mol−1 and 77.0 kJ mol−1 for samples that exhibit manganese solid solubility extensions of 2.10 and 6.00 wt.%, respectively. The rate parameter for the precipitation reaction, which has the generally admitted value of 1.50, for a transformation involving diffusion controlled growth, is affected by the strain gradients, too. Its value is reduced from 1.40 for the slowly cast sample to 1.32 and 1.20, respectively, for the two rapidly solidified samples, as a result of competing mechanisms, namely: growth controlled by diffusion and strain-assisted precipitation.

Theory of thermal analysis of non-isothermal crystallization kinetics of amorphous solids

The theoretical basis of thermal analysis of crystallization kinetics occurring by nucleation and growth under non-isothermal conditions of constant heating rate β has been studied by integrating the fundamental equation describing the crystallized volume fraction, x. Assuming a thermally activated growth rate of the form u=u0 exp (–EG/kT) two specific cases have been considered: (i) growth from a constant number of nuclei or growth following the saturation of nucleation sites and (ii) a temperature-dependent nucleation rate whose functional form over a limited temperature range is approximated by Iv=I0 exp (–EN/kT).It is shown that the expression for the crystallized fractional volume x(T) contains a function φn of the initial temperature T0. Except for one-dimensional growth under case (i), the rate of transformation x is also a function of T0, which implies that a Johnson–Mehl–Avrami type of description of the kinetics is inappropriate.The limits of applicability of current thermoanalytical methods of the following groups: Kissinger, Borchardt–Piloyan, Ozawa, Chen and Coats–Redfern–Sestak, have been critically examined and modifications have been proposed to include the effect of the initial temperature. A method of thermal analysis has been developed to determine the nature of the crystallization kinetics.

Differential thermal analysis of reaction kinetics in pseudo‐isothermal state Part 1. Simple reaction

AbstractA new method for the evaluation of kinetic parameters is proposed, in which differential thermal analysis (DTA) is carried out under psuedo‐isothermal conditions, that is, both sample and reference materials are not heated and the temperatures remain as isothermal as possible. The hydrolysis of acetic anhydride was used as a model of simple reaction for the DTA experiment. The kinetic parameters such as the rate constant, the heat of reaction and the activation energy, evaluated from the proposed method were in good agreement with those obtained from conventional titration measurements. Systematic errors in the rate constant evaluation are discussed in order to enable the kinetic parameters to be evaluated accurately.

Differential thermal analysis of reaction kinetics in pseudo‐isothermal state Part 2. Complex reaction

AbstractThe complex reaction between urea and formaldehyde is studied by the simultaneous method of DTA in pseudoisothermal state and conventional titration, and the kinetic parameters and the heat of reaction are evaluated. This reaction is technically important in the production of urea‐formaldehyde resins. The conversions were determined from both the experimental DTA data and the concentration change of formaldehyde with time. By using the available values of the heat of reaction, the rate constants then could be obtained. The experimentally determined activation energies were in good agreement with those reported in the literature.