Investigation of isothermal and dynamic cure kinetics of epoxy resin/nadic methyl anhydride/dicyandiamide by differential scanning calorimetry (DSC)

Isothermal and dynamic differential scanning calorimetry (DSC) was exploited to study the curing behavior of diglycidyl ether bisphenol-A epoxy resin with various combining ratios of dicyandiamide (DICY) and nadic methyl anhydride (NMA). Curves of prepared samples indicated that the enthalpy of the reaction decreased with increasing the molar ratios (NMA/DICY) up to 40% after which an exothermic peak peculiar to the effect of anhydride appeared at a higher temperature. The curing behavior examination of the samples containing the aforementioned molar ratio of NMA/DICY (= 40%) was carried out using isothermal condition at different temperatures (130–145 °C) and dynamic condition DSC at various heating rates (2.5–20 °C min⁻¹). Under the isothermal condition, by constructing a master curve, the values of activation energy (E_a) and pre-exponential factor (A) were calculated 89.3 kJ mol⁻¹ and 1.2 × 10⁺⁹ s⁻¹, respectively. The activation energy of the curing reactions in a dynamic mode was obtained 85.32 kJ mol⁻¹ and 88.02 kJ mol⁻¹ using Kissinger and Ozawa methods, respectively. Likewise, pre-exponential factors were also calculated 3.35 × 10⁺⁸ and 7.4 × 10 ⁺⁸ s⁻¹, respectively. The overall order of reaction for both conditions was found to be a value around 3.

     

Kinetics and mechanism of formation of gehlenite,Al–Si spinel and anorthite from the mixture of kaolinite and calcite

The kinetics and mechanism of formation of gehlenite, Al–Si spinel phase, wollastonite and anorthite from the mixture of kaolinite and calcite was investigated by differential thermal analysis under the heating rate from 283 to 293 K min⁻¹ using Kissinger equation. The changes in the phase composition of the sample during the thermal treatment were investigated via simultaneous TG-DTA, in situ high-temperature x-ray diffraction analysis and high-temperature heating-microscopy. The crystallizations of gehlenite and Al–Si spinel phase show apparent activation energy of (411 ± 5) kJ mol⁻¹ and (550 ± 9) kJ mol⁻¹, respectively. The value of kinetic exponent corresponds to the process limited by the decreasing nucleation rate for gehlenite while constant nucleation rate is determined for Al–Si spinel phase. Anorthite crystallizes from the eutectic melt and the process shows the apparent activation energy of (1140 ± 25) kJ mol⁻¹. The process is limited by the constant nucleation rate of a new phase.     

Sorption/desorption study of strontium on Ain Oussera soils around the Es-Salam reactor facility

Four types of undisturbed soils around the Es-Salam reactor (Algeria) were used to evaluate the sorption behavior of strontium. The batch study was carried out under different experimental conditions. The kinetics were well fited by pseudosecond order model. Soils’s activation energies were 12.37, 14.76, 15.5 and 16.17 kJ mol⁻¹, corresponding to ion-exchange-type sorption. Sorption was exothermic (ΔH° < 0), spontaneous (ΔG° < 0) and favorable at low temperature. Competing cations, particularly Ca²⁺ reduce the Sr adsorption. Desorption reaction showed a higher value of Sr in the easily extractible phase indicating a relative availability of the element.

     

Thermal and exergoeconomic analysis of a dairy food processing plant

The dairy processing industry in India, on an average basis, involves an extensive amount of thermal and electrical energy consumption, i.e. 2.51 × 10⁵ kW MT⁻¹ and 1.44 × 10⁵ kW MT⁻¹, respectively, for an installed milk food processing capacity of 1.21 × 10⁵ TPD. However, energy consumption spectrum depends upon the level of automation along with better utilisation of utility resources. The global ultra-high-temperature (UHT) pasteurised milk trade was valued at € 52.29 billion in 2012 and is expected to reach € 114.38 billion by 2019–2020. In the present work energy, exergy and exergoeconomic evaluation of ultra-high-temperature milk pasteurisation plant have been considered. The overall energy efficiency and efficiency pertaining to executable potential of energy in UHT Milk Processing Unit were reported to be 86.36% and 53.02%. The specific exergy destruction and specific exergy improvement potential were estimated to be 219.23 kJ kg⁻¹ and 137.60 kJ kg⁻¹, respectively. The highest possible retrievable exergy potential of the plant was associated with heating coil, i.e. 158.98 kW, followed by homogeniser (54.62 kW), which pinpointed towards the possibility of huge technical improvement. The processing cost was enumerated to be highest for heating coil (r_k: 38.35%) followed by regeneration-1 (r_k: 23.40%). Further, the total operating cost rate associated with thermodynamic deficiencies of subunits was estimated to be highest for heating coil (4859.82 € H⁻¹) followed by regenerator-2 (1264.88 € H⁻¹) and homogeniser (1187.14 € H⁻¹). The broad survey of thermoeconomic indices of subunits indicated that the level of exergetic destruction was far more on higher side.

     

A study of some kinetic aspects of the CCl4 interaction with oxide ions in KCl-SrCl2 melts with different content of SrCl2

A comparative investigation of a complex process of the interaction between CCl₄ vapor and oxide ions O^2– (carbochlorination) in K₂SrCl₄ and KSr₂Cl₅ melts at 973 K was performed by the potentiometric method using Pt(O₂)|ZrO₂(Y₂O₃) membrane oxygen electrode as reversible to oxide ion. The analysis of the limiting stages of this process was made on the basis of van't Hoff diagrams. The entire process can be divided into three stages with corresponding limiting processes: the rate of CCl₄ dissolution in the melts for stage 1, the chemical reaction in the melts for stage 2, and the rate of the contamination of the melts with oxygen-containing admixtures for the stage 3. The rate constants of the carbochlorination process in both melts at 973 K were calculated using the data corresponding to stage 2 as (4.4 ± 0.25) × 10⁵ kg mol⁻¹ min⁻¹ for K₂SrCl₄ and (1.83 ± 0.5) × 10⁵ kg mol⁻¹ min⁻¹ for KSr₂Cl₅. The final concentration of oxide ions after the treatment is higher ( = (1.6 ± 0.7) × 10⁻⁷ mol kg⁻¹ for KSr₂Cl₅ and  = (2.5 ± 1.3) × 10⁻⁸ mol kg⁻¹ for K₂SrCl₄ melt, respectively). This corresponds to the difference in the oxoacidic properties of the studied melts.     

Crystallization kinetics study of melt-spun Zr66.7Ni33.3 amorphous alloy by electrical resistivity measurements

In this paper, the electronic transport properties of as-spun Zr_66.7Ni_33.3 alloys were studied in detail by a combination of electrical resistivity and absolute thermoelectric power measurements over a temperature range from 25 up to 400 °C. Moreover, the isochronal and isothermal crystallization kinetics of Zr_66.7Ni_33.3 glassy alloy has been investigated based on the electrical resistivity measurements. The comparative study of the crystallization kinetics of these binary amorphous alloys was carried out, for the first time to our knowledge, using an accurate method for electrical resistivity measurements. In the isochronal heating process, the apparent activation energy for crystallization was determined to be, respectively, 371.4 kJ mol⁻¹ and 382.2 kJ mol⁻¹, by means of Kissinger and Ozawa methods. The Johnson–Mehl–Avrami model was used to describe the isothermal transformation kinetics, and the local Avrami exponent has been determined in the range from 2.97 to 3.23 with an average value of 3.1, implying a mainly diffusion-controlled three-dimensional growth with an increasing nucleation rate. Based on an Arrhenius relationship, the local activation energy was analyzed, which yields an average value E_x = 376.2 kJ mol⁻¹.

     

An examination of the vaporization enthalpies and vapor pressures of pyrazine, pyrimidine, pyridazine, and 1,3,5-triazine

The vaporization enthalpies and liquid vapor pressures from T = 298.15 K to T = 400 K of 1,3,5-triazine, pyrazine, pyrimidine, and pyridazine using pyridines and pyrazines as standards have been measured by correlation-gas chromatography. The vaporization enthalpies of 1,3,5-triazine (38.8 ± 1.9 kJ mol⁻¹) and pyrazine (40.5 ± 1.7 kJ mol⁻¹) obtained by these correlations are in good agreement with current literature values. The value obtained for pyrimidine (41.0 ± 1.9 kJ mol⁻¹) can be compared with a literature value of 50.0 kJ mol⁻¹. Combined with the condensed phase enthalpy of formation in the literature, this results in a gas-phase enthalpy of formation, Δ_f H _m (g, 298.15 K), of 187.6 ± 2.2 kJ mol⁻¹ for pyrimidine, compared to a value of 195.1 ± 2.1 calculated for pyrazine. Vapor pressures also obtained by correlation are used to predict boiling temperatures (BT). Good agreement with experimental BT (±4.2 K) including results for pyrimidine is observed for most compounds with the exception of the pyridazines. The results suggest that compounds containing one or two nitrogen atoms in the ring are suitable standards for correlating various heterocyclic compounds provided the nitrogen atoms are isolated from each other by carbon. Pyridazines do not appear to be evaluated correctly using pyridines and pyrazines as standards.     

Synthesis and thermal decomposition behavior of nitrogen- and oxygen-rich energetic material N-trinitromethyl-4,5-dicyano-2H-1,2,3-triazole

N-trinitromethyl-4,5-dicyano-2H-1,2,3-triazole was readily synthesized from 4,5-dicyano-2H-1,2,3-triazole. Its crystal structure was obtained for the first time and its crystalline density in 296 K was 1.729 g cm⁻³. It shows high nitrogen and oxygen content up to 77.6%, high calculated solid heat of formation (564 kJ mol⁻¹), and superior detonation pressure and detonation velocity (D = 8619 m s⁻¹, P = 30.8 GPa). This new hydrogen-absent explosive shows high impact and friction sensitivities (IS: 1.25 J, FS: 32 N), which is lower than commercial primary explosive 2-diazonium-4,6-dinitrophenol (DDNP) (IS: 1 J, FS: 5 N). The relationship between intermolecular interaction and sensitivity as well as thermal stability of the title compound was investigated by Hirshfeld surface analysis and fingerprint plot. Its thermodynamic properties were studied by non-isothermal kinetic methods based on the results of differential scanning calorimeter. It is interesting that apparent activation energy (E_a) at T_p1 (210.89–214.17 kJ mol⁻¹) is higher than those at T_p2 (133.90–134.87 kJ mol⁻¹). In addition, gaseous product of this new energetic compound was analyzed by the rapid scanning Fourier transform infrared spectroscopy from 20 to 200 °C and its detonation products was theoretically predicted. Based on the decomposition products, its decomposition mechanism was discussed under inert atmosphere. It is undoubted that these significant physicochemical properties make N-trinitromethyl-4,5-dicyano-2H-1,2,3-triazole a potential hydrogen-absent primary explosive.

     

Two novel algorithms for the thermogravimetric assessment of polymer degradation under non-isothermal conditions

Two novel algorithms are presented for processing thermogravimetric (TG) data obtained during the degradation of a polymer in a single step mechanism under non-isothermal conditions. The first algorithm assesses three characteristics computed from the TG profile against a theoretical data set, and identifies likely kinetic models to fit the experimental data. The second algorithm provides an iterative arithmetic method to extract the apparent activation energy, E_a, and Arrhenius A-factor, A, from TG data without simplifying assumptions. The algorithms are validated using model data and applied to data for the non-isothermal degradation of poly(ethylene adipate), poly(lactic acid) (PLA) and a food packaging PLA composite formulation containing kenaf, a natural fibre. The analysis of poly(ethylene adipate) produced E_a = 137 kJ mol⁻¹ and log₁₀A = 8.71 (first-order kinetic model). The kenaf fibre destabilizes PLA, lowering its E_a from 190 kJ mol⁻¹ to 150 kJ mol⁻¹ (contracting volume model).     

Evaluation of CO2 adsorption capacity of solid sorbents

The CO₂ adsorption capacity of the low-cost solid sorbents of waste tire char (TC) and chicken waste char (CW) was compared with commercial active carbon (AC) and 5 ? zeolite (ZA) using thermogravimetric analysis (TG), pressurized TG, and differential scanning calorimetry (DSC). The sorbents were degassed in a TG up to 150 °C to release all gases on the surface of the sample, then cooled down to the designed temperature for adsorption. TG results indicated that the CO₂ adsorption capacity of TC was higher than that of CW, but lower than those of AC and ZA. The maximum adsorption rate of TC at 50 °C was 0.61% min⁻¹, lower than that of AC, but higher than that of CW, 0.44% min⁻¹. The maximum adsorption rate of ZA at 50 °C was 3.1% min⁻¹. When the pressure was over 4 bar, the adsorption rate of ZA was lower than that of TC and AC. At 30 bar, the total CO₂ uptake of TC was 20 wt%, higher than that of CW and ZA but lower than that of AC. The temperature, nitrogen concentration, and water content also influenced the CO₂ adsorption capacity of sorbents to some extent. DSC results showed that adsorption was an exothermic process. The heat of CO₂ adsorption per mole of CO₂ of TC at 50 °C was 24 kJ mol⁻¹ while the ZA had the largest heat of adsorption at 38 kJ mol⁻¹. Comparing the characteristics of TC and CW, TC may be a promising sorbent for removal of CO₂.     

Kinetic study of crystallization of PHB in presence of hydroxy acids

Poly(3-hydroxybutyrate), PHB, has been structurally modified through reaction with hydroxy acids (HA) such as tartaric acid (TA) and malic acid (MA). The crystallization kinetic of the samples was evaluated by isoconversional method through nonlinear fitting to obtain the estimation for activation energy (E _a ) and pre-exponential (A) values. The thermal behavior of the crystallization temperature, 44.8 and 58.9 °C at 5 °C/min, and results obtained to the average activation energy, 73 ± 9 kJ mol⁻¹ and 63 ± 1 kJ mol⁻¹, to PHB/MA and PHB, respectively, are suggesting that malic acid may be deriving plasticizer units from its own PHB chain. PHB/TA show increase in the medium value of E _a, 119 ± 2 kJ mol⁻¹ and T _c = 48.2 °C (at 5 °C/min), indicating that tartaric acid is probably interacts in different way to the of PHB chain (E _a=73 ± 9 kJ mol⁻¹, T _c = 44.8 °C at 5 °C/min).     

A variable temperature 1H NMR and DFT study of procyanidin B2 conformational interchange

Two procyanidin B2 conformers were identified in a relative abundance ratio of approximately 3:1 at 298 K by ¹H NMR experiments in acetonitrile. The conformational interchange reactions between these two conformers are 1st order in both reactions, with ?G^? for forward and reverse of 57.12?±?5.62 and 54.56?±?5.48 kJ mol^?1, respectively. The experimentally obtained standard thermodynamic energies for this reaction are ΔH⁰_rxn (3.67?±?0.22 kJ mol^?1), ΔS⁰_rxn (4.05?±?1.57 kJ mol^?1 K^?1), and ΔH⁰_rxn (2.96?±?0.33 kJ.mol^?1). Conformational search results at the DFT (PBE, PBE-D2, and B3LYP with 6-311++g**) level of theory yielded four novel conformations, named fully compact (FC), partially compact (PC), partially extended (PE), and fully extended (FE). Although the FC conformer is electronically the most stable of the four as a result of extensive intramolecular non-covalent interactions, the PC and FE conformers are thermodynamically favored in a 5:1 ratio (B3LYP), with the FC and PE conformers present in negligible amounts at equilibrium. The DFT computed standard reaction energies using the B3LYP functional for the PC_major to FE_minor conformational interchange reaction compare exceptionally well with experimental data at 298 K: ?G⁰_rxn (3.86 kJ mol^?1), ΔH⁰_rxn (5.34 kJ mol^?1), and ?S⁰_rxn (4.97 kJ mol^?1 K^?1). It was found that inclusion of solvation energies is crucial to obtain accurate thermodynamic energies. The secondary equilibria found in chromatographic separations are predicted to be highly dependent on solvent polarity and temperature. Similar conformational diversity and hierarchies should exist for all non-rigid procyanidin oligomers and the unique chromatographic behavior of these compounds may be a result of conformational interchange.

     

Thermal stability and lifetime of [AMIM]Cl-PFSA composite membranes

1-Allyl-3-methylimidazolium chloride [AMIM]Cl hybrid perfluorosulfonic acid (PFSA) composite electrolyte membrane was prepared and characterized by TG and FTIR technique. The conductivity was measured using AC impedance method. The results showed that when raised from 20 to 90 °C, the conductivity of composite membrane was increased from 4.50 × 10⁻⁶ to 1.34 × 10⁻⁵ S cm⁻¹, before and after the modification of triethylamine, the thermal stability of composite membrane was not changed, but the TEA-PFSA with [AMIM]Cl reactivity was a little difference. However, the heat resistance of composite membrane was significantly enhanced compared with that of PFSA membrane, the peak temperature of composite membrane almost disappeared in first stage, and offset to the high-temperature zone. When heated at 350 °C, the decomposition rate of PFSA, 10%[AMIM]Cl-PFSA and 10%[AMIM]Cl-TEA-PFSA membrane was 13.71, 3.67 and 1.26%, respectively. If the decomposition process follows isothermal first-order reaction and the conversion rate α is 10%, the activation energy E _α of the composite membrane is 97.4 kJ mol⁻¹. Besides, the isothermal lifetime of composite membrane was also measured.

     

Molecular docking analysis and spectroscopic investigations of zinc(II), nickel(II) N-phthaloyl-β-alanine complexes for DNA binding: Evaluation of antibacterial and antitumor activities

Herein, computational molecular docking, UV/visible and fluorescence spectroscopic techniques have been used to explore the DNA binding interactions of N-phthaloyl-β-alanine (NPA) ligand and its Zn(II) and Ni(II) complexes (NPAZn, NPANi). The compounds were further tested for anti-bacterial and anti-tumor activities. Docking analysis depicted that ligand NPA interacted with DNA via intercalation, while its metal complexes showed mixed mode of interactions. Spectroscopic experiments for DNA binding studies were run under physiological conditions of pH (stomach; 4.7, blood; 7.4) and temperature (37 °C). Based on changes in spectral responses, binding parameters for all the compounds were obtained which showed comparatively greater binding constant values (K_b: UV; 1.16 × 10⁵ M⁻¹, Flu; 1.35 × 10⁵ M⁻¹) and more negative free energy changes (ΔG: UV; −30.00 kJ mol⁻¹, Flu; −30.44 kJ mol⁻¹) for NPAZn at pH 4.7. The overall, binding results were also found more significant at stomach pH. Dynamic “K_D” and bimolecular “K_B” constants were evaluated, and the values affirmed the participation of static process for each compound–DNA binding. The greater binding site size values (n > 1) of metal complexes NPAZn and NPANi indicated other sites availability of intercalative compounds. DNA viscosity variation by increasing compound’s concentration further verified the compound–DNA interaction. Antibacterial and tumor inhibitory activities were observed significant for both metal complexes, while ligand has shown no activity. The greater binding affinity of metal complexes, as evaluated both computationally and spectroscopically, further validated the lower IC50 values of complexes as compared to ligand.     

Glass transition and crystallization study of chalcogenide Se<Subscript>70</Subscript>Te<Subscript>15</Subscript>In<Subscript>15</Subscript> glass

Differential scanning calorimetry data at different heating rates (5, 10, 15 and 20 °C min⁻¹) of Se₇₀Te₁₅In₁₅ chalcogenide glass is reported and discussed. The crystallization mechanism is explained in terms of recent analyses developed for use under non-isothermal conditions. The value of Avrami exponent (n) indicates that the glassy Se₇₀Te₁₅In₁₅ alloy has three-dimensional growth. The average values of the activation energy for glass transition, E _g, and crystallization process, E _c, are (154.16 ± 4.1) kJ mol⁻¹ and (98.81 ± 18.1) kJ mol⁻¹, respectively. The ease of glass formation has also been studied. The reduced glass transition temperature (T _rg), Hruby’ parameter (K _gl) and fragility index (F _i) indicate that the prepared glass is obtained from a strong glass forming liquid.     

O3 and SO2 sensing concept on extended surface of B12N12 nanocages modified by Nickel decoration: A comprehensive DFT study

Adsorption of SO₂ and O₃ molecules on pristine boron nitride (B₁₂N₁₂) and Ni-decorated B₁₂N₁₂ nano-cages has been systemically investigated through density functional theory (DFT) methods. Adsorption energies (thermodynamics), bond distances, charge analysis, dipole moments, orbital analysis and density of states are calculated by van der Waals DFT method (MPW1PW91) functional. The adsorption energies of O₃ and SO₂ on pristine B₁₂N₁₂ are about −143.8 and −14.0 kJ mol⁻¹, respectively. The interaction energies of O₃ and SO₂ with pristine B₁₂N₁₂ are indicative of chemisorption and physisorption, respectively. Ni-decorated B₁₂N₁₂ (Ni@BN) enhances adsorption of both O₃ and SO₂ species. The interaction energies for adsorption of SO₂ are about −166 and −277 kJ mol⁻¹ whereas the corresponding energies for O₃ are −362 and −396 kJ mol⁻¹ for configuration A and B, respectively. These observations show that functionalized B₁₂N₁₂ are highly sensitive toward SO₂ and O₃ molecules.     

Standard molar enthalpy of formation of [(C12H8N2)2Bi(O2NO)3] and its biological activity on Schizosaccharomyces pombe

The title complex [(C₁₂H₈N₂)₂Bi(O₂NO)₃] was synthesized by reaction of 1,10-phenanthroline (phen) and Bi(NO₃)₃·5H₂O. The structure of the complex was characterized by single-crystal X-ray diffraction, IR spectroscopy, and elemental analysis. An advanced solution-reaction isoperibol microcalorimeter was applied to determine the standard molar enthalpies of formation at 298.15 K of the complex and Bi(NO₃)₃·5H₂O, giving –(798.92 ± 5.99) and –(1986.87 ± 0.20) kJ mol⁻¹, respectively. The biological effect of the complex was evaluated by microcalorimetry on the growth of Schizosaccharomyces pombe (S. pombe). According to thermogenic curves, the corresponding thermokinetics and thermodynamic parameters were derived. The complex had good bioactivity on the growth metabolism of S. pombe, with the value of IC₅₀ being 2.8 × 10⁻⁵ mol L⁻¹.

     

The thermodynamic properties of DyBr3(s) and DyI3(s) from T=5 K to their melting temperatures

Low-temperature calorimetric measurements have been performed on DyBr₃(s) in the temperature range (5.5 to 420 K ) and on DyI₃(s) from T=4 K to T=420 K. The data reveal enhanced heat capacities below T=10 K, consisting of a magnetic and an electronic contribution. From the experimental data on DyBr₃(s) a C⁰_p,m (298.15 K) of (102.2±0.2) J·K⁻¹·mol⁻¹ and a value for {S⁰_m (298.15 K) − S⁰_m (5.5 K)} of (205.5±0.5) J·K⁻¹·mol⁻¹, have been obtained. For DyI₃(s), {S⁰_m (298.15 K) − S⁰_m (4 K)} and C⁰_p,m (298.15 K) have been determined as (226.9±0.5) J·K⁻¹·mol⁻¹ and (103.4±0.2) J·K⁻¹·mol⁻¹, respectively. The values for {S⁰_m (5.5 K) − S⁰_m (0)} for DyBr₃(s) and {S⁰_m (4 K) − S⁰_m (0)} for DyI₃(s) have been calculated, giving S⁰_m (298.15 K)=(212.3±0.9) J·K⁻¹·mol⁻¹ in case of DyBr₃(s) and S⁰_m (298.15 K) =(233.1±0.7) J·K⁻¹·mol⁻¹ for DyI₃(s). The high-temperature enthalpy increment has been measured for DyBr₃(s) in the temperature range (525 to 799 K) and for DyI₃(s) in the temperature range (525 to 627 K). From the results obtained and enthalpies of formation from the literature, thermodynamic functions for DyBr₃(s) and DyI₃(s) have been calculated from T→0 to their melting temperatures at 1151.0 K and 1251.5 K, respectively.     

How reliable is DFT in predicting relative energies of polycyclic aromatic hydrocarbon isomers? comparison of functionals from different rungs of jacob's ladder

Density functional theory (DFT) is the only quantum‐chemical avenue for calculating thermochemical/kinetic properties of large polycyclic aromatic hydrocarbons (PAHs) such as graphene nanoflakes. Using CCSD(T)/CBS PAH isomerization energies, we find that all generalized gradient approximation (GGA) and meta GGA DFT functionals have severe difficulties in describing isomerization energies in PAHs. The poor performance of these functionals is demonstrated by the following root‐mean‐square deviations (RMSDs) obtained for a database of C₁₄H₁₀ and C₁₈H₁₂ isomerization energies. The RMSDs for the GGAs range between 6.0 (BP86‐D3) and 23.0 (SOGGA11) and for the meta GGAs they range between 3.5 (MN12‐L) and 11.9 (τ‐HCTH) kJ mol⁻¹. These functionals (including the dispersion‐corrected methods) systematically and significantly underestimate the isomerization energies. A consequence of this behavior is that they all predict that chrysene (rather than triphenylene) is the most stable C₁₈H₁₂ isomer. A general improvement in performance is observed along the rungs of Jacob's Ladder; however, only a handful of functionals from rung four give good performance for PAH isomerization energies. These include functionals with high percentages (40–50%) of exact Hartree–Fock exchange such as the hybrid GGA SOGGA11‐X (RMSD = 1.7 kJ mol⁻¹) and the hybrid‐meta GGA BMK (RMSD = 1.3 kJ mol⁻¹). Alternatively, the inclusion of lower percentages (20–30%) of exact exchange in conjunction with an empirical dispersion correction results in good performance. For example, the hybrid GGA PBE0‐D3 attains an RMSD of 1.5 kJ mol⁻¹, and the hybrid‐meta GGAs PW6B95‐D3 and B1B95‐D3 result in RMSDs below 1 kJ mol⁻¹. © 2016 Wiley Periodicals, Inc.     

Thermal analysis of dehydroxylation of Algerian kaolinite

Thermal analysis techniques remain important tools amongst the large variety of methods used for analysis of the dehydroxylation of kaolinite. In the present study, the kinetics of dehydroxylation of Algerian kaolinite, wet ball milled for 5 h followed by attrition milling for 1 h, was investigated using differential thermal analysis (DTA) and thermogravimetry (TG). Experiments were carried out between room temperature and 1350 °C at heating rates of 5, 10 and 20 °C min⁻¹. The temperature of dehydroxylation was found to be around 509 °C. The activation energy and frequency parameter evaluated through isothermal DTA treatment were 174.69 kJ mol⁻¹ and 2.68 × 10⁹ s⁻¹, respectively. The activation energies evaluated through non-isothermal DTA and TG treatments were 177.32 and 177.75 kJ mol⁻¹, respectively. Growth morphology parameters n and m were found to be almost equal to 1.5.