Non-isothermal Method Research Articles

Synthesis and thermal decomposition performance of 3,6,7-triamino-7H-s-triazolo[5,1-c]-s-triazole

3,6,7-Triamino-7H-s-triazolo[5,1-c]-s-triazole was synthesized from triaminoguanidine hydrochloride and cyanogen bromide, and has been prepared at the 30-g scale. A single crystal of 3,6,7-triamino-7H-s-triazolo[5,1-c]-s-triazole was cultivated, and its crystalline density at 293 K was 1.726 g cm−3. Its heat of formation (ΔH f,solid = 470.5 kJ mol−1) was computed by using the density functional theory (DFT) method, and its detonation pressure and detonation velocity were further predicted by EXPLO5 code (D = 9483 m s−1, P = 30.4 GPa). The intermolecular interaction of the title compound was investigated by Hirshfeld surface analysis. Moreover, its thermodynamic performance was evaluated by non-isothermal kinetic methods based on the results of the differential scanning calorimeter (DSC), which shows that the apparent activation energy (E a) obtained by Kissinger, Ozawa and Starink methods is 223.55, 221.61 and 223.73 kJ mol−1, respectively. Meanwhile, the transformation of molecular structure was analyzed by the rapid scanning Fourier transform infrared spectroscopy (RSFT-IR) under the temperature range from 50 to 300 °C. The reaction pathway was further supported by quantum chemical calculations. 3,6,7-Triamino-7H-s-triazolo[5,1-c]-s-triazole processes good vacuum thermal stability, high detonation performance and low sensitivity. It is convincible that these physical–chemical properties make 3,6,7-triamino-7H-s-triazolo[5,1-c]-s-triazole a promising candidate worthy of further investigation.

Mn-Catalyzed Oxidation of Heavy Oil in Porous Media: Kinetics and Some Aspects of the Mechanism

Mn-catalyzed oxidation of the Ashalcha heavy oil in porous media was examined. We used manganese(III) tris(acetylacetonate) as a convinient oil-soluble precatalyst that decomposes to catalytically active species during the temperature ramping. Reaction kinetics in the heavy oil oxidation with air indicated that the presence of the manganese ions changes the mechanism of the oxidation process, especially in the high-temperature region. To study precatalyst transformations in detail, we suggested the approach of combining X-ray powder diffraction (XRPD), thermal analysis, non-isothermal kinetic methods, and electron paramagnetic resonance (EPR). A comprehensive study of the decomposition of pure manganese(III) tris(acetylacetonate) and the subsequent comparison of its behavior to that in porous media in the presence of the oil allows us to shed light on some aspects of the mechanism of catalytic oxidation.

Confined crystallization kinetics and scale of semicrystalline block copolymer via non-isothermal method

In this paper, differential scanning calorimetry (DSC) was used to study non-isothermal crystallization behaviors of tri-block copolymer poly(styrene)-b-poly(ethylene oxide)-b-poly(styrene) (SEOS). Homopolymer poly(ethylene oxide) (PEO) with almost the same molecular weight as PEO block was also studied comparatively under non-isothermal conditions. From final degree of crystalline X c and given degree of polymerization N, relative degree of crystalline X t at different kinetics stage was changed to be monomer units numbers involved in crystallization process. Based on well-recognized model of PEO crystalline structure, X t at specific stage can be used to calculate the scales of PEO crystalline. Comparing the crystallization behaviors of SEOS with those of PEO, it is indicated that confinement from solidified PS block restricts the mobility of PEO chain to form a pre-ordered structure in initial stage and decreases its lamellae thickness of nucleus that dominates the whole crystallization process.

Influence of Ca2+ or Na+ extraframework cations on the thermal dehydration and related kinetic performance of LSX zeolite

Nitrogen adsorption performances of low-silica type X zeolites (LSX) containing Na+ or Ca2+ ions were studied and compared with Li+ ion, and their structural and thermal properties were investigated using various characterizations (XRD, TG-DTG, BET, XPS, SEM, TEM, and EDX with elemental mapping techniques). The kinetics of their thermal dehydration and decomposition was studied using thermogravimetry at three rates (5, 10, and 15K/min) of linear increase of temperature under non-isothermal heating. Two model free procedures named, Kissinger, and Flynn–Wall–Ozawa (iso-conversional) and one model fitting method called Coats–Redfern based on single TG curves, as well as 41 mechanism functions were used. The kinetic parameters (apparent activation energy E, pre-exponential factor A and model) of the three phases for each sample obtained from the non-isothermal methods were then compared with the results from iso-conversional methods this showed that they strongly depend on the selection of appropriate mechanism function and the corresponding kinetic model from the perspective of crystal structure used. The results demonstrated that the E value obtained at low temperature was lower than that at high temperature, implying that the dehydration process of physisorbed water belongs to diffusion-based control, while decomposition of bonded water (chemisorbed) belongs to kinetic-based control at high temperature. These comparisons allow us to underline the strong effect of cations in association with water and their distribution in the micropores of LSX on the N2 adsorption performance.

Synthesis of Vegetable Oil‐Based Polyurethane: A Study on Curing Kinetics Behavior

ABSTRACTIn the present study, biobased polyurethane (BPU) samples were synthesized from three different polyols along with polymeric hexamethylene diisocyanate. The three different polyols were synthesized by reacting castor oil with ethylene glycol, triethylene glycol, and triethanolamine. The synthesized polyols were confirmed using proton nuclear magnetic resonance (1H NMR) spectra analysis. BPU samples were confirmed by the disappearance of isocyanate peak in the FTIR spectra. The cross‐linking densities of all BPU samples were determined using swelling studies. Curing kinetics behavior of all BPU samples were analyzed using differential scanning calorimetry at three different heating rates (5, 7.5, and 10°C/min). The curing kinetic parameters were studied using three nonisothermal methods such as Kissinger, Flynn–Wall–Ozawa, and Ozawa, respectively. The activation energies were found to increase with increasing degree of cure (α). Surface properties of all the synthesized BPU samples were evaluated by dynamic mechanical analysis and scanning electron microscopy.

A novel instrument for rapid measurement of temperature-dependent thermal properties of conduction-heated food up to 140 °C

Estimating thermal properties for thick or solid foods at temperatures greater than 100 °C is challenging for two reasons: the long time needed to reach a constant temperature, and the pressure needed to be maintained in the sealed container. An instrument (“Thermal Properties Cell”, or “TPCell”) was developed based on a rapid non-isothermal method to estimate the temperature-dependent thermal properties within a range of commercial food processes (20–140 °C). The instrument design consists of a custom sample holder and special fittings to accommodate the heater within a pressurized environment. The total time of the experiment is less than 1min., compared to existing isothermal instruments requiring 5–6 h to cover a similar temperature range. Thermal conductivities of different food materials were estimated for the temperature range of commercial food processes. The novelty of the instrument lies in its ability to analyze transient temperature data using a nonlinear form of the two-dimensional heat conduction equations.

Catalytic characteristics of the pyrolysis of lignite over oil shale chars

In this paper, the non-isothermal thermogravimetric method (TGA) was applied to study the effect of oil shale chars on catalytic thermal decomposition of lignite. After oil shale chars being added, the trough temperature of the rate of weight loss (Tmax) increased by about 10°C, and corresponding mass loss rate experienced an increase as high as 29.67%. The devolatilization time was longer as well as less concentrated as the value of the characteristic index of the pyrolysis products gained 28.936% increase. The characteristic of oil shale chars’ effect on lengthening the time of pyrolysis indicated that oil shale char compounds may restrain the process of thermal degradation of organic matters in lignite. Noticeable increasing in SO, CO, CH (Both aliphatic and aromatic), CH4 and decreasing in CO2 were observed in the co-pyrolysis of lignite with the oil shale char produced at slow heating rate of 30°C/min from ambient temperature to 510°C. Combining with the appearance of the lowest active energy and the increase of the trace metal concentration (38.89% to Tl and 22.98% to Ga) in the sample of lignite mixed with SC510, a conclusion can be achieve that employing the oil shale char as a catalyst has potential application prospect in co-utilization with other fuels.

Thermal behavior and non-isothermal crystallization kinetics of (Ti41Zr25Be28Fe6)93Cu7 bulk metallic glass

The thermal behavior analysis of (Ti41Zr25Be28Fe6)93Cu7 bulk metallic glass was investigated using the non-isothermal differential scanning calorimetry method. DSC curves at lower heating rates (≤30K·min−1) revealed four exothermic and three endothermic peaks. The middle endothermic peak was characterized as the formation of the CuZr2 Laves phase. The crystallization behavior of the alloy was identified. The first and second exothermic peaks overlapped at all heating rates, therefore the non-isothermal crystallization kinetics of the two peaks were investigated. Using the Kissinger equation the apparent activation energy of the first and second peaks estimated to be 155.6±11.6 and 154.1±4.9kJ·mol−1, respectively. Similar values were also obtained by Ozawa and Boswell methods. The dependence of the local activation energy on the conversion fraction was generalized by the Kissinger-Akahira-Sunose (KAS), Ozawa-Flynn-Wall (OFW) and Friedman methods. The local activation energy remained constant during the first crystallization event and dramatically decreased during the second crystallization reaction. The validity of the JMA model for both transformations was investigated. An autocatalytic behavior of crystallization was observed and the mathematical description of the crystallization using Šesták-Berggren model has been built for the two crystallization reactions. The validity of the proposed models was investigated using the master plot method.

The exploration of the influence of microencapsulation processing parameters on the stabilization of ammonium azide particles

The microencapsulation of ammonium azide particles (NH4N3) with fibrous nitrocellulose has been carried out through a solvent/non-solvent procedure which is based on the coacervation principle. X-ray diffraction, scanning electron microscope, Fourier transform infrared spectroscopy, thermogravimetry–differential thermal analysis and differential scanning calorimetry techniques were used to characterize the structure, morphology and thermal stability of treated ammonium azide particles. Taguchi L-9 orthogonal array design method was exploited for assessment of effectiveness of experimental parameters on the coating properties. The investigated parameters were percent of coating agent, addition time of non-solvent, volume of non-solvent and stirring speed of the mixture (revolutions per minute, rpm). The individual effect of each parameter on the thermal stability of NH4N3 particle, determined by thermal analysis methods, was quantitatively evaluated by the analysis of variance. The statistical results revealed that the most stabilized coated NH4N3 particles can be obtained by using 2 % (w/w) of nitrocellulose as coating agent and by adding of 70 mL n-hexane as non-solvent within 50 min under stirring at 90 rpm, where the sublimation temperature of treated sample increases about 60 °C with respect to uncoated one and reaches to 186.5 °C. Also, the kinetic parameters of the sublimation processes of pure and microencapsulated NH4N3 particles that stabilized at this condition were obtained from the differential scanning calorimetry data by non-isothermal methods proposed by ASTM E696. Finally, the results of this study illustrated that the efficiency of the proposed chemometric method is higher than that of sequential experimental technique.

Screening method for the onset of bonding of molten polyamide resin layers to continuous fiber reinforced laminate sheets

Thermoplastic polymer composites (TPC) with multiple fabric layers of continuous fiber reinforcement are laminate sheets designed to be thermally stamped and overmolded leading to low cycle times and thus high volume composite parts. Injection over-molding is one way to combine the high processability of thermoplastic melts with the less processable TPC sheets, for complex part making. To simulate the adhesion development during processes like over-molding, a non-isothermal screening method for bonding molten polyamide (PA) to a solid TPC surface has been developed and applied to evaluate differences in the threshold temperatures for good bond formation as a function of TPC matrix composition. Pure PA66 and aromatic high temperature nylons (PPA) in addition to miscible PPA blends comprising different ratios of PA66, were used as TPC matrices, and retain most of the very high melting point of 100% PPA. We have devised experiments to address two critical aspects: The first is to develop a screening test that probes very short timescales relevant to practical part making. The second is to investigate various miscible semi-crystalline blend ratios as matrices for the TPC where both blend species are crystalline. This allows us to explore a practical improvement of a lower required bonding temperature without substantially decreasing the high melting point of the PPA. DSC was also used to correlate the various blend melting transitions with the temperature required for the onset of bonding. The interfaces are shown to develop high strength partly because of substantial surface melting of certain blend components of the initially solid TPC, and this quickly allows interpenetration and inter-diffusion across the interface, which then crystallizes and strengthens during cooling.

Crystallization behavior of ZrO2[sbnd]3Y2O3[sbnd]xSrO precursor powders synthesized by a coprecipitation process

Crystallization behaviors of ZrO23Y2O3xSrO precursor powders were studied with zirconium nitrate (Zr(NO3)4·xH2O), yttrium nitrate (Y(NO3)3·6H2O) and strontium nitrate (Sr(NO3)2) constituting the initial materials. Differential thermal analysis (DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), nano beam electron diffraction (NBED) and high-resolution TEM (HRTEM) were utilized to characterize the crystallization behavior of ZrO23Y2O3xSrO precursor powders. The activation energies of tetragonal ZrO2 (t-ZrO2) crystallization were 389.1, 327.6, and 315.1 kJ/mol with SrO content for 1, 2, and 3 mol%, respectively, obtained with a non-isothermal method. The growth morphology parameter and growth mechanism index were close to 2.0 and 1.0, respectively, showing that t-ZrO2 had a plate-like morphology.

Crystallization kinetic and thermal and electrical properties of β-spodumeness/cordierite glass–ceramics

The aim of the present work was to investigate the crystallization kinetic of spodumene-/cordierite-based glass–ceramics. Thus, three glasses were prepared with compositions based predominantly on cordierite and β-spodumeness crystalline phases, and a mass ratio 1:1 of both phases. The kinetic parameters were determined by means of non-isothermal methods using differential thermal analysis. A multi-peaks fit method was used based on the Fraser–Suzuki equation to determine the crystallization temperature peak. The crystallization kinetic was investigated using the Ozawa and Kissinger methods. The samples were crystalized according to DTA analyses and characterized by using X-ray diffraction. Additionally, the coefficient of thermal expansion and electrical properties of the glass–ceramics was determined. The results showed activation energy for crystallization ranging from 121 to 333 kJ mol−1. The main crystalline phases were β-spodumeness to composition L, cordierite and β-quartzss to composition C and β-quartzss and spinel to composition CL. Taking into account the thermal and electrical properties of the heat-treated samples, these glass–ceramics show potential to LTCC (low thermal co-fired ceramics) application.

Using rheometry to study the curing kinetics of glycidyl azide polymer spherical propellant by non-isothermal method

The curing kinetics of GAP spherical propellant was studied by rheological non-isothermal measurement. The kinetic parameters were determined by rheometry based on conversion degree α described by storage modulus. The non-isothermal method was first used in rheometry as conversion α determined by a novel method, considering that storage modulus variation was a complex process which increased with polymerization and decreased as the temperature increased. The variation of apparent activation energy was obtained by the isoconversional method of Kissinger–Akahira–Sunose. It was found that Ea is little lower in the range of 0.05 < α < 0.50 than it is in the range of 0.50 < α < 0.70. During the complete curing process, apparent activation energy can be considered a constant. A new kinetic equation had been established and showed great agreement with experimental data. Altogether, the rheological non-isothermal method can be used to investigate the mechanism and kinetics of thermosetting reactions, and the obtained knowledge of the curing kinetic will form a contribution to the study of GAP spherical propellant.

Kinetics of Pyrolysis and Gasification Using Thermogravimetric and Thermovolumetric Analyses

Abstract The carbon dioxide gasification process of Miscanthus giganteus biomass was examined using two methods. First an isothermal thermovolumetric method was applied. The measurement was conducted at 950°C and pressure of 0.1 MPa. Based on the continuous analysis of different kinds of gases formed during the gasification process, the thermovolumetric method allowed the determination of yields and composition of the resulting gas as well as the rate constant of CO formation. Then a non-isothermal thermogravimetric method was applied, during which the loss of weight of a sample as a function of temperature was recorded. In the course of the measurement, the temperature was raised from ambient to 950°C and the pressure was 0.1 MPa. As a result, a change in the carbon conversion degree was obtained. Moreover, TGA methods allow distinguishing various stages of the gasification process such as primary pyrolysis, secondary pyrolysis and gasification, and determining kinetic parameters for each stage. The presented methods differs from each other as they are based either on the analysis of changes in the resulting product or on the analysis of changes in the supplied feedstock, but both can be successfully used to the effective examination of kinetics of the gasification process. In addition, an important advantage of both methods is the possibility to carry out the gasification process for different solid fuels as coal, biomass, or solid waste in the atmosphere of a variety of gasification agents.

Synthesis, characterization, thermal stability and compatibility properties of new energetic polymers

Four new cross-linked polymers poly(vinyl m-nitrobenzene)-polyglycidylazides (PVMNB-GAPs) were successfully synthesized using toluene diisocyanate as the cross-linking agent. Their structure was confirmed by their FTIR, UV–Vis, 1H and 13C NMR spectroscopy. Moreover, the thermal properties of cross-linked polymers were evaluated by DTA, TGA and DSC techniques, which confirmed that synthesized polymers exhibited good resistance to thermal decomposition up to 200°C. In addition, their compatibility with the main energetic components of 2,4,6-trinitrotoluene-based melt-cast explosives were also evaluated by the non-isothermal differential thermal analysis method.

Synthesis, kinetic analysis and electrical characterization of (Ca0.8Sr0.2)0.6La0.267TiO3 by polymeric precursor method

(Ca0.8Sr0.2)0.6La0.267TiO3 microwave dielectric ceramic was synthesized by a polymeric precursor method. The kinetic and thermodynamic parameters of the reaction were determined by a non-isothermal method. The activation energy of thermal decomposition of the polymeric precursor was found to be 70.97 ± 5.67 kJ/mol and 63.62 ± 6.03 kJ/mol using FWO and KAS models respectively. The average values of thermodynamic parameters were; ΔH* = 120.57 kJ/mol, ΔG* = 282.94 kJ/mol and ΔS* = −223.93 J/mol K. The particle size of the synthesized powder was <100 nm with orthorhombic (Pbnm) symmetry. The sintered ceramic exhibited εr = 116.2, Q × ƒ = 15730 and τƒ = +231 ppm/°C. Analysis of impedance data obtained in the temperature range 200–500 °C revealed that the ceramic exhibited negative temperature coefficient resistor (NTCR) characteristics.

The non-isothermal kinetics of cordierite formation in mechanically activated talc–kaolinite–alumina ceramics system

The non-isothermal kinetics of cordierite formation from both non-activated and mechanically activated kaolinite + talc + alumina ceramic system was studied by differential thermal analysis (DTA). The mixture of kaolinite, talc and alumina was activated mechanically in a planetary mill, while amorphisation in the kaolinite, talc and alumina structure was studied by X-ray diffraction analysis. The activation energies depending on the conversion for cordierite formation were calculated from the DTA curves by using the non-isothermal method of Coats and Redfern at heating rates of 5, 10, 15 and 20 °C min−1. The mechanical activation of the kaolinite, talc and alumina mixture resulted in the decrease in activation energy values for cordierite formation.

Approximation-based integral versus differential isoconversional approaches to the evaluation of kinetic parameters from thermogravimetry

The relative accuracies of approximation-based integral versus differential isoconversional approaches for ‘actual’ E determination were investigated on experimental dehydration data of roxithromycin monohydrate from thermogravimetric (TG) analysis. The dehydration kinetic parameters and the relationship to the structural characteristics of the monohydrate and anhydrate forms from differential scanning calorimetry (DSC) and single-crystal X-ray diffractometry (SC-XRD) are also reported. Integral methods versus the differential Friedman isoconversional method evaluated E correspondences in both iso- and non-isothermal TG methods. The reliability in E from Friedman approached that of estimates from current most accepted integral isoconversional methods and was even superior to methods (for non-isothermal studies) that employ an approximation to the temperature integral (modified Kissinger–Akahira–Sunose, Senum–Yang fourth degree). Structural characterization (DSC, SC-XRD) and kinetic analysis from generalized kinetic master plots concluded that coordinated water occupied interlinked voids in crystal structure which may have facilitated the multidimensional diffusional loss of water upon heating without disruption of the crystal structure.

Kinetic Analysis of the Thermal Decomposition of Latex Foam according to Thermogravimetric Analysis

The thermal decomposition of latex foam was investigated under nonisothermal conditions. Pieces of commercial mattress samples were subjected to thermogravimetric analysis (TG) over a heating range from 5°C min−1 to 20°C min−1. The morphology of the latex foam before and after combustion was observed by scanning electron microscopy (SEM), and the primary chemical composition was investigated via infrared spectroscopy (FT-IR). The kinetic mechanism and relevant parameters were calculated. Results indicate that the decomposition of latex foam in the three major degradation phases is controlled by third-order reaction (F3) and by Zhuravlev’s diffusion equation (D5). The mean E values of each phase as calculated according to a single heating rate nonisothermal method are equal to 41.91 ± 0.06 kJ mol−1, 86.32 ± 1.04 kJ mol−1, and 19.53 ± 0.11 kJ mol−1, respectively. Correspondingly, the preexponential factors of each phase are equal to 300.39 s−1, 2355.65 s−1, and 27.90 s−1, respectively. The mean activation energy E and preexponential factor A of latex foam estimated according to multiple heating rates and a nonisothermal method are 92.82 kJ mol−1 and 1.12 × 10−3 s−1, respectively.

Thermal Characteristics of 1-Butyl-3-Methylimimidazolium Based Oxidant Ionic Liquids

This study investigates the thermal properties of a series of 1-butyl-3-methylimizolium based ionic liquids (ILs) possessing various oxidative anions such as dichromate (Cr2O72-), nitrate (NO3-), hydrogen sulphate (HSO4- ), tetrafluoroborate (BF4-), perchlorate (ClO4-) and hexafluorophosphate (PF6-). The synthesized ILs was defined by their thermal properties in terms of glass transitions, melting and decomposition temperatures. The effect of oxidant anions on activation energy of ILs were computed by non-isothermal kinetic methods i.e., through were of Ozawa and Kissinger’s methods. The most thermally stable IL was seen to be the transition metal-containing IL [bmim] Cr2O72- where it recorded the highest activation energy of 11.65 kJ/mole using Ozawa method and 15.71 kJ/mole using Kissinger method compared to other ILs. The lowest activation energy was obtained for [bmim]BF4 and [bmim] PF6. Based on the detailed thermal behavior of this high temperature oxidant ILs, it can potentially be beneficial for desulfurization applications.