Non-isothermal Kinetic Analysis Research Articles

Nonisothermal crystallization behaviors of nanocomposites prepared by in situ polymerization of high-density polyethylene on tungsten oxide particles

Morphology development and thermal properties of polyolefin composites (tungsten oxide (WO3)/high density polyethylene (HDPE)) were characterized by differential scanning calorimetry, polarized optical microscopy, and nonisothermal crystallization kinetics. Tungsten oxide (WO3) and HDPE composites were prepared by the in situ metallocene polymerization method which consisted of attaching a metallocene catalyst complex onto the surface of the nuclei (WO3) and followed by the surface-initiated polymerization. A kinetic equation proposed by Seo was employed to analyze the nonisothermal crystallization characteristics of the composites. The polarized optical microscopy and the Avrami exponent verified the importance of the interaction between the HDPE molecules and the nuclei surface for the HDPE molecular ordering around the metal powder as well as the morphological development in the early stage. The Avrami exponent, n, determined from the nonisothermal crystallization kinetics analysis indicates random 3-dimentsional morphology development for the WO3/HDPE composites. Dispersed WO3 accelerated the crystallization rate due to heterogeneous nucleation effect as indicated by the shift in the crystallization peaks to higher temperatures. The obtained crystalline structures were compared to those for the neat polyethylene resins and carbon nanotube (CNT)/HDPE composites. Open image in new window

Effects of La3+–Nd3+ ions and pre-calcination on the growth of hexaferrite nanoparticles prepared by gel to crystallization technique: Non-isothermal crystallization kinetics analysis

This is the first report ever on La3+–Nd3+ doped M-type hexaferrite nanoparticles: SrNdxLayFe12−x−yO19 (0 ≤ x ≤ 1) prepared by citrate precursor using the sol–gel technique followed by gel to crystallization. The substitution effects of ions and molar ratio of Fe3+/Sr2+ on the formation of ferrite phase were examined using powder differential thermal analysis (DTA) technique, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (Mid-IR) and vibrating sample magnetometer (VSM). The present work aim to study the crystallization of binary La3+- Nd3+ doped hexaferrite nanoparticles. DTA technique was employed to investigate the formation of nanocrystalline SrNd0.4La0.4Fe11.2O19 and revealed that the formation of ferrite phase was occurred in steps and crystallization take place by the means of endothermic reactions. The value of activation energy and crystallization temperature has been obtained from DTA data using different non-isothermal methods. XRD and Mid-IR studies have confirmed the formation of ferrite phase. Through this work an optimum calcination condition was established for the synthesis of single phase hexaferrite nanoparticles even after the substitution of binary rare earth elements. Magnetic properties were determined by using a vibrating sample magnetometer. The magnetic results revealed that the synthesized nanoparticles are suitable for perpendicular recording media due to their high coercivity value.

Non-isothermal kinetic analysis on the phase transformations of Fe–Co–V alloy

In this study, occurrence of different phase transformations was investigated in a FeCo-7wt% V alloy upon heating to 1200°C by the dilatometry method at different heating rates (5, 10, and 15°Cmin−1). It was found that four phase transformations (including B2-type atomic ordering in α phase, first stage of polymorphic transformation (α→αr+γ), ordering to disordering, and second stage of polymorphic transformation (αr→γ) occur in this alloy up to 1200°C. Two isoconversional methods, as Starink and Friedman, were used to determine variation of the activation energy with temperature, E(T). Moreover, the empirical kinetic triplets (E, A, and g(α)) were calculated by the invariant kinetic parameters (IKP) method and fitting model.

Effect of minor Cu content on microstructure and mechanical property of NiTiCu bulk alloys fabricated by crystallization of metallic glass powder

Ultrafine-grained Ni50.2−xTi49.8Cux (x = 0, 2.5, 5, and 7.5) bulk shape memory alloys were fabricated by sintering of metallic glass (MG) powder and crystallization of amorphous phase. Non-isothermal crystallization kinetic analysis reveals that the crystallization mechanism of the synthesized x = 5 MG powder is typical interface-controlled two dimensional growth of nuclei followed by volume diffusion-controlled three dimensional growth of nuclei. In contrast, the crystallization mechanism of the synthesized x = 7.5 MG powder is typical volume diffusion-controlled three dimensional growth of nuclei in whole crystallization process. Correspondingly to different crystallization mechanisms, the two sintered and crystallized (SCed) bulk alloys have the same crystallized phases of bcc B2, fcc NiTi2 phases, and monoclinic B19′, but these phases display different morphologies and distributions. The SCed x = 5 bulk alloy has a microstructure of bcc B2 matrix surrounding fcc NiTi2 phase region, while the SCed x = 7.5 bulk alloy possesses discontinuous bcc B2 phase region. Consequently, the different crystallization mechanisms and microstructures causes extreme high yield strength and large plasticity for the SCed x = 5 bulk alloy and low strength and no plasticity for the SCed x = 7.5 bulk alloy. Especially, the yield strength of the SCed x = 5 bulk alloy is at least two times of that of the counterpart alloy prepared by melt solidification. The results provide a method fabricating high performance bulk alloys by tailoring crystallization mechanism using powder metallurgy.

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.

Two coordination polymers with 3-hydrazino-4-amino-1,2,4-triazole as ligand: synthesis, crystal structures, and non-isothermal kinetic analysis

Two coordination polymers, [Mn2(HATr)4(NO3)4·2H2O]n (1) and [Cd2(HATr)4(NO3)4·H2O]n (2), were obtained from the corresponding metal nitrate with 3-hydrazino-4-amino-1,2,4-triazole (HATr) and characterized through elemental analysis and IR spectroscopy. The structures were determined by single-crystal X-ray diffraction. The results show that both complexes crystallize in the triclinic P-1 space group and have six-coordinate distorted octahedral structures, which are made up of infinite 1-D chains running along the a axis of metals linked by bridging-chelating HATr ligands. The coordination sites are in agreement with the computational results. Additionally, the decomposition temperatures were determined by differential scanning calorimetry and the kinetic parameters were calculated using Kissinger’s and Ozawa–Doyle’s methods; the energies of combustion for 1 and 2 were −7186.25 and −6922.53 kJ M−1 and the enthalpies of formation were obtained as −1002.35 and −457.27 kJ M−1, respectively.

Non-isothermal kinetic analysis of thermal decomposition of the Ca-bentonite from Santai, China

The thermal decompositions of Ca-bentonites (CaB) from Santai, Shichuan Province, China, over the temperature range of 30–1,100 °C were investigated by simultaneous thermal analyzer. Non-isothermal kinetic analysis was employed to study the thermal decomposition mechanism by using Netzsch Thermokinetics software. Flynn-Wall-Ozawa and Friedman isoconversional methods were used to calculate the activation energy and analyze the reaction steps. The probable mechanism and the corresponding kinetic parameters were determined by multivariate non-linear regression program. The results show that the thermal decomposition process of CaB over the temperature range of 30–800 °C is a kind of six-step, competitive reaction (F 1 D 3 F n C 1E F n F n model). The dehydration reaction is controlled by two consecutive mechanisms, nucleation and growth, followed by a diffusion-controlled reaction (F 1 D 3 model), the first step: E = 61.68 kJ mol−1, logA = 6.75 s−1; the second step: E = 50.73 kJ mol−1, logA = 3.11 s−1. The dehydroxylation reaction is controlled by three-step competitive mechanisms, an autocatalytically activated, initial reaction followed by n-order competitive reaction (C 1E F n F n model), the first step: E = 124.74 kJ mol−1, logA = 5.67 s−1; the second step: E = 245.29 kJ mol−1, logA = 11.69 s−1; the third step : E = 261.73 kJ mol−1, logA = 11.23 s−1. A combination reaction of the dehydration and dehydroxylation is observed, and controlled by one n-order reaction (F n model), E = 8.99 kJ mol−1, logA = −1.91 s−1.

Non-isothermal free-models kinetic analysis on crystallization of europium-doped phosphate glasses

A kinetic analysis under non-isothermal conditions has been performed on europium-doped phosphate glasses with molar composition 20.42 Li2O–10.25 Al2O3–58.49 P2O5–7.23 BaO–1.44 La2O3–2.16 Eu2O3 and particle size <30µm, >50µm. Differential scanning calorimetry measurements at four heating rates, from room temperature up to 900°C using synthetic air have revealed that no significant mass change occurs during the heat treatment, as normally expected for glass samples. The step changes in heat flow signals are associated with the presence of three important effects: the first one, that occurs as a slope corresponds to the glass transition effect (Tg) is followed by two exothermic peaks, first of them more pronounced, associated with the first crystallization process (Tp1), while, the second one, lower in intensity corresponds to the second crystallization (Tp2) process. As expected, all peaks (Tg, Tp1 and Tp2) increase with the increasing of the heating rate. Both the activation energy of crystallization process and the crystallization mechanism were comparatively analyzed by two free-model estimations and using the formal theory of transformations for heterogeneous nucleation.

Estimation of the curing rate of acrylamide used as a consolidant in heritage sandstone conservation

An investigation of the curing (polymerisation) rate of acrylamide was carried out using isothermal and non-isothermal DSC in order to estimate the time for complete conversion of monomer at ambient temperatures. The non-isothermal data were used to model the rate using integral isoconversional and incremental isoconversional kinetic methods. Applying the equations for integral isoconversional methods and extrapolating to ambient temperatures resulted in non-sensical conversion–time curves, where the time estimated decreased for increasing degree of conversion to be reached. This odd behaviour was attributed to the incorrectness of the integration where the kinetic parameters (e.g. the activation energy) are a function of conversion. The problem was addressed by applying incremental methods which provided more reasonable results as the integration is carried out over small conversion increments where the kinetic parameters are assumed to be constant. Estimates of the conversion were compared to isothermal measurements and, although isothermal DSC produced significant variability in the data, extrapolated estimates from non-isothermal kinetic analysis produced, at best, an upper boundary for the estimation of the time to reach a fixed degree of conversion.

In Situ Monitoring of Thermal Crystallization of Ultrathin Tris(8-Hydroxyquinoline) Aluminum Films Using Surface-Enhanced Raman Scattering

Thermal crystallization of 3, 10, and 60 nm-thick tris(8-hydroxyquinoline)aluminum (Alq3) films is studied using surface-enhanced Raman scattering with a constant heating rate. An abrupt higher frequency shift of the quinoline-stretching mode is found to be an indication of a phase transition of Alq3 molecules from amorphous to crystalline. While the 60 nm-thick film shows the same crystallization temperature as a bulk sample, the thinner films were found to have a lower crystallization temperature and slower rate of crystallization. Non-isothermal kinetics analysis is performed to quantify kinetic properties such as the Avrami exponent constants and crystallization rates of ultrathin Alq3 films.

Thermal Degradation and Kinetic Parameters of Polyester and Poly(Lactic Acid) Blends Used in Shopping Bags in Brazil

In this work, synthetic polyester and poly(lactic acid) blends used as biodegradable shopping plastic bags were studied, together with control samples of polyethylene containing pro-oxidant catalysts (called “oxidegradable bags” in the market). Samples of these materials were weighed and buried in simulated soil for 3 months, and then studied by Thermal Analysis including a non-isothermal kinetic analysis. It was observed that although there was no significant mass loss in the period of the ageing, the activation energies for the thermal decomposition processes were substantially reduced for the biodegradable samples, but not for the oxidegradable ones.

Effect of the TiO2 nanoparticle size on the decomposition behaviors in aluminum matrix composites

The decomposition behaviors and the effect of particle size on the kinetic rate are studied for Al–3 vol.% titanium dioxide (TiO2) composites by using three different types of TiO2 particles (15, 50, and 300 nm). Thermal analysis shows that the reaction is stepwise with the first reaction starting before the melting temperature of Al. Since the high chemical potential of nanoparticles enhances reactivity, the TiO, Al3Ti, and α-Al2O3 phases are found to be formed during the first reaction regardless of particle size. Based on observations of microstructure, the formation mechanism of Al3Ti and α-Al2O3 is understood to be solution precipitation. Non-isothermal kinetic analysis reveals that the reaction mechanism is closely related to the three-dimensional continuous nucleation and the growth limited by diffusion. Particle size is found to be having considerable effect on the kinetic rate. As the particle size decreases, the rate constant increases, while the pre-exponential factor and the activation energy decreases. A non-linear relationship between the rate constant and the reciprocal of the size is found and evaluated.

Non-Isothermal Kinetic Analysis of Oxidation of Pure Aluminum Powder Particles

Non-isothermal kinetic analysis of oxidation of aluminum powder particles (100–200 μm) was investigated by simultaneous thermogravimetry (TG) and differential thermal analysis under linear temperature programming (ranging from 25 to 1,400 °C) at different heating rates (10, 20 and 30 °C/min). In addition, the rate of oxidation reaction (rate of thermogravimetry; RTG) was obtained by the RTG curves. It was found that the oxidation of aluminum powders took place over several stages and the complete oxidation process did not occur even up to 1,400 °C. Among different stages, the temperature ranging from 1,000 to 1,150 °C was identified as the main stage for oxidation process. Hence, kinetic analysis of non-isothermal was determined to be carried out in this region only. Therefore, non-isothermal kinetic analysis of oxidation of pure aluminum powder particles was performed using isoconversional methods (Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose, Friedman ), Markworth and Coats–Redfern methods. Also, the empirical kinetic triplets [Ea, A, and f(α)] have been calculated.

Thermal and spectroscopic measurements of some energetic compositions and corresponding aerosols obtained

Studies on specific thermochemical processes contribute to the understanding of combustion processes and, meanwhile, to the calculus of the safety characteristics and the systems design parameters. In this paper, five different compositions have been studied through TGA and DTA. The reaction rate constants and the activation energies have been determined. Also, the solid combustion products obtained have been evaluated through SEM, EDX, and XPS. Nonisothermal kinetic analyses performed yield results that prove an important difference among the first fire compositions, where the activation energies are considerable, up to 400 kJ/mol, in comparison with the activation energies of the flare compositions, which are lower, 150–250 kJ/mol.

Thermal characteristics of the combustion process of biomass and sewage sludge

The combustion of two kinds of biomass and sewage sludge was studied. The biomass fuels were wood biomass (pellets) and agriculture biomass (oat). The sewage sludge came from waste water treatment plant. The biomass and sludge percentage in blends with coal were 10 %. The studied materials were characterised in terms of their proximate and ultimate analysis and calorific value. The composition of the ash of the studied fuels was also carried out. The behaviour of studied fuels was investigated by thermogravimetric analysis (TG, DTG and DTA). The samples were heated from an ambient temperature up to 1,000 °C at a constant three rates: 10, 40 and 100 °C min−1 in 40 mL min−1 air flow. TG, DTG and DTA analysis showed differences between coal, biomass fuels and sewage sludge. 10 % addition of studied fuels to the mixture with coal changed its combustion profile in the case of sewage sludge addition. The combustion characteristics of fuel mixtures showed, respectively, qualitative summarise behaviour based on single fuels. Evolved gaseous products from the decomposition of studied samples were identified. This study showed that thermogravimetric analysis connected with mass spectrometry is useful techniques to investigate the combustion and co-combustion of biomass fuels, and sewage sludge, together with coal. Non-isothermal kinetic analysis was used to evaluate the Arrhenius activation energy and the pre-exponential factor. The kinetic parameters were calculated using Kissinger–Akahira–Sunose model.

A kinetic study of the formation of smectic phases in novel liquid crystal ionogens

A multi-rate non-isothermal kinetic analysis of the isotropic-melt to liquid crystalline phase transition of novel liquid crystalline ionogenic copolymers, LCIs, the 10-(4-methoxyazobenzene-4′-oxy)decyl methacrylate]-co-2-(acrylamido-2-methyl-1-propanesulfonic acid)s, 10-MeOAzB/AMPS, copolymers, has been performed by means of calorimetric experiments. An analytical methodology which includes the study of the phase transition rate parameter, the determination of the activation energies by using Kissinger and Flynn–Wall–Ozawa models, and the study of the phase transition kinetics by the use of the Avrami theory, has been applied. The formation of the mesophases from the isotropic state occurred close to thermodynamic equilibrium. The results evidence the presence of several individual processes in the formation of liquid crystalline phases from the melt and a strong dependence of phase transition rates and activation energies with acid contents. A decrease in the phase transition rate, related to a decrease in the overall change of the transition entropy, has been observed. The final inhibition of the liquid crystal (LC) behaviour is ascribed to an exponential increase in the activation energy of the phase transition, promoted by strong acid aggregation. An optimum composition of the 10-MeOAzB/AMPS copolymers to achieve the dual characteristics of LCIs (ionogenic and liquid crystalline behaviour) requires acid concentrations capable of promoting structure-forming effects on the LC phases and the evolution of phase separated morphologies.

Ozawa’s kinetic method for analyzing thermoanalytical curves

By reviewing the history of thermal analysis and its application to the kinetic analysis of the solid-state processes, we investigate the theoretical basis and historical perspective of Ozawa’s kinetic method for analyzing thermoanalytical curves. Ozawa’s nonisothermal kinetic method is demonstrated using thermoanalytical data for the thermal decomposition of sodium hydrogencarbonate and the crystallization of anhydrous magnesium acetate glass as examples. Through investigating recent theoretical advancements in nonisothermal kinetic analysis in view of the theoretical fundamentals of Ozawa’s kinetic method, it is indicated that they are in line with Ozawa’s kinetic theory. On the basis of the above investigations, we discuss the role of Ozawa’s kinetic theory in advancing the analysis of complex reaction kinetics.

Dispersion and reaggregation of nanoparticles in the polypropylene copolymer foamed by supercritical carbon dioxide

For the preparation of nanocomposites, we conducted environmentally benign foaming processing on polypropylene (PP) copolymer/clay nanocomposites via a batch process in an autoclave. We investigated the dispersion and the exfoliation of the nanoclay particles. Full exfoliation was achieved by the foamability of the matrix PP copolymer using supercritical carbon dioxide (sc CO2) and subcritical carbon dioxide (sub CO2). More and smaller cells were observed when the clay was blended as heterogeneous nuclei and sc CO2 was used. Small angle X-ray scattering showed that highly dispersed states (exfoliation) of the clay particles were obtained by the foaming process. Since the clay particles provided more nucleating sites for the foaming of the polymer, a well dispersed (or fully exfoliated) nanocomposite exhibited a higher cell density and a smaller cell size at the same clay particle concentration. Expansion of the adsorbed CO2 facilitated the exfoliation of the clay platelets; thus, sc CO2 at lower temperature was more efficient for uniform foaming-cell production. Fully dispersed clay platelets were, however, re-aggregated when subjected to a further melting processing. The reprocessed nanocomposites still had some exfoliated platelets as well as some aggregated intercalates. The dual role of the nanoclay particles as foaming nucleus and a crystallization nucleus was confirmed by cell growth observation and nonisothermal crystallization kinetics analysis. A low foaming temperature and a high saturation pressure were more favorable for obtaining a uniform foam. The PP copolymer was found to be foamed more easily than polypropylene. A small amount of other olefin moieties in the backbone of the polymer facilitated better foamability than the neat polypropylene.

Microstructure and hydrogen storage properties of MgH2–TiB2–SiC composites

Abstract The influence of TiB2 and SiC ceramics on H-desorption kinetics from MgH2 based composites was investigated and correlated with the microstructure and morphology of the composites. The mechanism of desorption and the activation energy for desorption was investigated by applying non-isothermal kinetic analysis of thermodesorption spectra. It has been shown that TiB2 addition leads to significant decrease of the activation energy for desorption, while SiC addition has effect on the interface reaction between hydride and hydroxide. The mechanism of desorption change from Avrami–Erofeev n=3 for pure MgH2 to Avrami–Erofeev n=4 for composite materials. The change from 3 to 4 can be due to the modification of the nucleation process or a change in the dimensionality of the growth. Those high values of n discard a diffusion control as a rate limiting step.

New Nonisothermal Arrhenius Temperature Integral Approximate Formula

A new formula for approximating the Arrhenius temperature integral for nonisothermal analysis has been developed, using the Solver algorithm. The new formula takes the form p(u)=(e−u/u2)×[(1−2/u)/(1−λ/u2)], where λ=0.33 ln(u)+4.48. Applicability of the formula has been proven by conducting thermogravimetric analysis experiments on polypropylene material. When simulated thermogravimetric analysis curves derived from the proposed approximation were compared with curves obtained from other published approximate formulae, the new approximation fit the experimental data very well. Numerical analysis was used to test accuracy of the proposed formula, and its deviation from the numerical value was compared with those of other published approximation formulae. Results show that the new formula is a suitable solution for the evaluation of kinetic parameters for nonisothermal kinetic analysis, for example, pyrolysis of polymeric wastes and biomass fuel or to produce biomass fuel. Its use will result in significant improvement in plastic resource recycling and could also be helpful in biomass energy production.