Calorimetric studies of natural talc: Enthalpy of dehydroxylation

The standard dehydroxylation enthalpy of natural talc Mg₃[Si₄O₁₀](OH)₂ (87.8 ± 9.0 kJ/mol at 298.15 K) and the enthalpy of formation of dehydrated talc from the elements (Δ_f H _el^o (298.15 K) = −5527.0 ± 9.0 kJ/mol) were determined for the first time using Hess’s law, based on the total values of the enthalpy increments in heating a sample from room temperature to 973 K and the enthalpies of dissolution at 973 K for dehydrated talc measured in this work and those previously determined for talc and corresponding oxides.     

Ytterbium tris(hexafluoroacetylacetonate) Yb(C<Subscript>5</Subscript>O<Subscript>2</Subscript>HF<Subscript>6</Subscript>)<Subscript>3</Subscript>: The composition of overheated vapor and sublimation thermodynamics

A mass spectrometric study of the saturated vapor over ytterbium tris(hexafluoroacetylacetonate) Yb(hfa)₃ (hfa = CF₃-C(O)-CH-C(O)-CF₃) and of the vapor overheated up to the thermal decomposition temperature of the complex is presented. The vapor composition changes markedly with increasing temperature. At T ≈ 370 K, the mass spectrum of the vapor over Yb(hfa)₃ indicates the presence of ions containing one to three metal atoms. As the temperature is raised, the ion currents due to oligomer ions decrease. The oligomers are not detected at T > 440 K. The total decomposition temperature of Yb(hfa)₃ is 663(9) K. The second-law enthalpy of sublimation (ΔH _s^o (380 K)) is 134 ± 7 kJ/mol for the monomer and 138 ± 10 kJ/mol for the dimer. The enthalpy of dissociation of the dimer into monomer molecules is nearly equal to the enthalpy of sublimation of the monomer and dimer: ΔH _dis(380 K) = 130 ± 15 kJ/mol.     

The thermodynamic properties of S-lactic acid

The enthalpies of combustion and formation of S-lactic acid at 298.15 K, Δ_c H _m^o(cr.) = −1337.9 ± 0.8 and Δ_f H _m^o(cr.) = −700.1 ± 0.9 kJ/mol, were determined by calorimetry. The temperature dependence of acid vapor pressure was studied by the transpiration method, and the enthalpy of its vaporization was obtained, Δ_vap H ^o(298.15 K) = 69.1 ± 1.0 kJ/mol. The temperature and enthalpy of fusion, T _m (330.4 K) and Δ_m H ^o(298.15 K) = 14.7 ± 0.2 kJ/mol, were determined by differential scanning calorimetry. The enthalpy of formation of the acid in the gas phase was obtained. Ab initio methods were used to perform a conformational analysis of the acid, calculate fundamental vibration frequencies, moments of inertia, and total and relative energies of the stablest conformers. Thermodynamic properties were calculated in the ideal gas state over the temperature range 0–1500 K. A thermodynamic analysis of mutual transformation processes (the formation of SS- and RS(meso)-lactides from S-lactic acid and the racemization of these lactides) and the formation of poly-(RS)-lactide from S-lactic acid and SS- and RS(meso)-lactides was performed.     

A dielectric study of the structure of propylene glycol

The dielectric spectra of propylene glycol over the frequency and temperature ranges 10 mHz–75 GHz and 175–423 K, respectively, were analyzed using the Dissado-Hill cluster model. A correlation between relaxation processes of breaking and formation of intermolecular H-bonds in clusters was obtained. A correlation of fluctuation processes of synchronous exchange of molecules between neighboring clusters corresponded to the redistribution of H-bonds between them. The Dissado-Hill theory was used to determine the integral relaxation times, n _DH and m _DH parameters and calculate the mean dipole moments of propylene glycol clusters and the energy characteristics of processes of their rearrangement. The mean dipole moments of clusters (23617–18.65 D) were compared with those of molecules in the liquid phase (3.67–3.03 D). The apparent activation enthalpy of processes of cluster rearrangements decreased from 141.8 to 25.2 kJ/mol, the activation energy decreased from 46.03 to 18.47 kJ/mol, and the energy of orientation dipole-dipole interactions, from 3.78 to 3.45 kJ/mol as the temperature increased.     

Thermochemical Properties and Decomposition Kinetics of Ammonium Magnesium Phosphate Monohydrate

Ammonium magnesium phosphate monohydrate NH4MgPO4·H2O was prepared via solid state reaction at room temperature and characterized by XRD, FT-IR and SEM. Thermochemical study was performed by an isoperibol solution calorimeter, non-isothermal measurement was used in a multivariate non-linear regression analysis to determine the kinetic reaction parameters. The results show that the molar enthalpy of reaction above is （28.795 ± 0.182） kJ/mol （298.15 K）, and the standard molar enthalpy of formation of the title complex is （-2185.43 ± 13.80） kJ/mol （298.15 K）. Kinetics analysis shows that the second decomposition of NH4MgPO4·H2O acts as a double-step reaction： an nth-order reaction （Fn） with n=4.28, E1=147.35 kJ/mol, A1=3.63×10^13 s^-1 is followed by a second-order reaction （F2） with E2=212.71 kJ/mol, A2= 1.82 × 10^18 s^-1.     

Sorption,diffusion, and permeation of ethylbenzene in poly(1‐trimethylsilyl‐1‐propyne)

The solubility, diffusivity, and permeability of ethylbenzene in poly(1‐trimethylsilyl‐1‐propyne) (PTMSP) at 35, 45 and 55 °C were determined using kinetic gravimetric sorption and pure gas permeation methods. Ethylbenzene solubility in PTMSP was well described by the generalized dual‐mode model with χ = 0.39 ± 0.02, b = 15 ± 1, and C^′_H = 45 ± 4 cm³ (STP)/cm³ PTMSP at 35 °C. Ethylbenzene solubility increased with decreasing temperature; the enthalpy of sorption at infinite dilution was −40 ± 7 kJ/mol and was essentially equal to the enthalpy change upon condensation of pure ethylbenzene. The diffusion coefficient of ethylbenzene in PTMSP decreased with increasing concentration and decreasing temperature. Activation energies of diffusion were very low at infinite dilution and increased with increasing concentration to a maximum value of 50 ± 10 kJ/mol at the highest concentration explored. PTMSP permeability to ethylbenzene decreased with increasing concentration. The permeability estimated from solubility and diffusivity data obtained by kinetic gravimetric sorption was in good agreement with permeability determined from direct permeation experiments. Permeability after exposure to a high ethylbenzene partial pressure was significantly higher than that observed before the sample was exposed to a higher partial pressure of ethylbenzene. Nitrogen permeability coefficients were also determined from pure gas experiments. Nitrogen and ethylbenzene permeability coefficients increased with decreasing temperature, and infinite dilution activation energies of permeation for N₂ and ethylbenzene were −5.5 ± 0.5 kJ/mol and −74 ± 11 kJ/mol, respectively. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1078–1089, 2000     

The sublimation enthalpy of dimethyl oxalate

The sublimation enthalpy of dimethyl oxalate has been measured by calorimetric and head space analysis. These results along with vaporization enthalpy measured by correlation gas chromatography and fusion enthalpy measurements are compared to results predicted by two estimation techniques. A previous experimental measurement was found to be in error. A mean value of (75.2±0.5) kJ/mol was obtained which results in a corrected molar value of (–681.5±0.8) kJ/mol for the enthalpy of formation of gaseous dimethyl oxalate, _f H _m ^o (g, 298.15 K). This new value of _f H _m ^o (g, 298.15 K) for dimethyl oxalate, in combination with other enthalpies of formation, suggests that the ground state of oxalates are destabilized relative to -diketones by approximately 25 kJ/mol.     

Hydrophobic interaction chromatography of proteins: Studies of unfolding upon adsorption by isothermal titration calorimetry

Heat of adsorption is an excellent measure for adsorption strength and, therefore, very useful to study the influence of salt and temperature in hydrophobic interaction chromatography. The adsorption of bovine serum albumin and β‐lactoglobulin to Toyopearl Butyl‐650 M was studied with isothermal titration calorimetry to follow the unfolding of proteins on hydrophobic surfaces. Isothermal titration calorimetry is established as an experimental method to track conformational changes of proteins on stationary phases. Experiments were carried out at two different salt concentrations and five different temperatures. Protein unfolding, as indicated by large changes of molar enthalpy of adsorption Δh_ads, was observed to be dependent on temperature and salt concentration. Δh_ads were significantly higher for bovine serum albumin and ranged from 578 (288 K) to 811 (308 K) kJ/mol for 1.2 mol/kg ammonium sulfate. Δh_ads for β‐lactoglobulin ranged from 129 kJ/mol (288 K) to 186 kJ/mol (308 K). For both proteins, Δh_ads increased with increasing temperature. The influence of salt concentration on Δh_ads was also more pronounced for bovine serum albumin than for β‐lactoglobulin. The comparison of retention analysis evaluated by the van't Hoff algorithm shows that beyond adsorption other processes occur simultaneously. Further interpretation such as unfolding upon adsorption needs other in situ techniques.     

Enthalpy of formation of talc Mg<Subscript>3</Subscript>[Si<Subscript>4</Subscript>O<Subscript>10</Subscript>](OH)<Subscript>2</Subscript> according to dissolution calorimetry

A thermochemical study of natural talc was performed by high-temperature melt dissolution calorimetry on a Tian-Calvet calorimeter. Based on the total values of the increment in enthalpy upon heating the sample from room temperature to 973 K, and of the dissolution enthalpy at 973 K measured in this work for talc and gibbsite (along with those determined for tremolite, brucite, and their corresponding oxides), the enthalpy of formation was calculated for talc composed of elements, Mg₃[Si₄O₁₀](OH)₂, at 298.15 K: Δ_f H _el^o(298.15 K) = −5900.6 ± 4.7 kJ/mol.     

Calorimetric determination of the enthalpy of formation for pyrophyllite

A calorimetric study of the natural pyrophyllite was performed by high-temperature melt calorimetry on a Tian-Calvet calorimeter. Based on experimentally determined in this work for pyrophyllite and gibbsite, as well as previously obtained for corundum and quartz, the total value of the enthalpy increment for the sample heated from room temperature to 973 K and the enthalpy of dissolution at 973 K by Hess’s law, the enthalpy of formation of pyrophyllite of Al₂[(OH)₂/Si₄O₁₀] composed of elements was calculated at 298.15 K: Δ_f H _el^o(298.15 K) = −5639.8 ± 5.7 kJ/mol.     

Synthesis and characterization of new soluble thermally stable poly(azomethine‐ether‐imide)s: discerning the possibility for high temperature applications

A new series of polyimides was synthesized by the condensation of monomers (azomethine‐ether diamine, DA‐1 and DA‐2) with pyromelliticdianhydride (PMDA), 3,4,9,10‐perylenetetracarboxylic dianhydride (PD) and 3,3′4,4′‐benzophenonetetracarboxylic dianhydride (BD). The structural explications of monomers and polyimides was conducted by FT‐IR, ¹H NMR and elemental analysis. All polyimides were found soluble in polar aprotic solvents and found to be semicrystalline in nature confirmed by XRD. The inherent viscosities were found in the range of 0.67–0.77 g/dl. %. Average molecular weight (M_W) and number average molecular weight (Mn) of the polyimides were found in the range of 5.72 × 10⁵ g/mol–6.58 × 10⁵ g/mol and 3.79 × 10⁵ g/mol 4.11 × 10⁵ g/mol respectively. The polyimides exhibited excellent thermal properties having a glass transition temperature T_g in the range of 230–290°C and the 10% weight loss temperature was above 450°C. The values of thermodynamic parameters, activation energy, enthalpy and entropy fall in the range of 45.2–53.90 kJ/mol, 43.5–52.30 kJ/mol and 0.217 kJ/mol k to 0.261 kJ/mol k respectively. Copyright © 2015 John Wiley & Sons, Ltd.     

Thermally induced polymerization of isobutylene in the presence of SnCl4: Kinetic study of the polymerization and NMR structural investigation of low molecular weight products

The polymerization reactivity of isobutylene/SnCl₄ mixtures in the absence of polar solvent, was investigated in a temperature interval from −78 to 60 °C. The mixture is nonreactive below −20 °C but slow polymerization proceeds from −20 to 20 °C with the initial rate r₀ of the order 10⁻⁵ mol · l⁻¹ · s⁻¹. The rate of the process increases with increasing temperature up to ∼10⁻² mol · l⁻¹ · s⁻¹ at 60 °C. Logarithmic plots of r₀ and M̄_n versus 1/T exhibit a break in the range from 20 to 35 °C. Activation energy is positive with values E = 21.7 ± 4.2 kJ/mol in the temperature interval from −20 to 35 °C and E = 159.5 ± 4.2 kJ/mol in the interval from 35 to 60 °C. The values of activation enthalpy difference of molecular weights in these temperature intervals are ΔH_Mn = −12.7 ± 4.2 kJ/mol and −38.3 ± 4.2 kJ/mol, respectively. The polymerization proceeds quantitatively, the molecular weights of products are relatively high, M̄_n = 1500–2500 at 35 °C and about 600 at 60 °C. It is assumed that initiation proceeds via [isobutylene · SnCl₄] charge transfer complex which is thermally excited and gives isobutylene radical‐cations. Oxygen inhibits the polymerization from −20 to 20 °C. Possible role of traces of water at temperatures above 20 °C is discussed. It was verified by NMR analysis that only low molecular weight polyisobutylenes are formed with high contents of exo‐ terminal unsaturated structures. In addition to standard unsaturated groups, new structures were detected in the products. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1568–1579, 2000     

Correlation between the equilibrium and relaxation dielectric properties of 1,2-ethanediol

The data on the dispersion of the permittivity ?*(ω) of 1,2-ethanediol over the temperature range 161–453 K and the frequency range 0.1 Hz–150 GHz were analyzed using the Dissado-Hill cluster model. The relaxation frequency ω_p = τ _DH ^?1 and intra-(n _DH) and intercluster (m _DH) correlation parameters were calculated. The energy barrier to the libration of molecular axes in clusters was found to be B _DH = 2.96 kJ/mol. The apparent enthalpy of activation was determined; it increased from ΔH _{DH exp} ^# = 22.18 kJ/mol to ΔH _{DH exp} ^# = 129.19 kJ/mol close to the glass transition temperature. The mean dipole moments $ \bar \mu _c The data on the dispersion of the permittivity ɛ*(ω) of 1,2-ethanediol over the temperature range 161–453 K and the frequency range 0.1 Hz–150 GHz were analyzed using the Dissado-Hill cluster model. The relaxation frequency ω_p = τ_DH⁻¹ and intra-(n _DH) and intercluster (m _DH) correlation parameters were calculated. The energy barrier to the libration of molecular axes in clusters was found to be B _DH = 2.96 kJ/mol. The apparent enthalpy of activation was determined; it increased from ΔH _{DH exp}^# = 22.18 kJ/mol to ΔH _{DH exp}^# = 129.19 kJ/mol close to the glass transition temperature. The mean dipole moments of 1,2-ethanediol clusters were calculated; they decreased from 162920 to 18.08 D as the temperature increased from 161 to 453 K. According to approximate estimates, the number of 1,2-ethanediol molecules in a cluster /μ_v decreased from 72405 at 161 K to 8.04 at 453 K (μ_v is the dipole moment of the molecule in the vacuum), which substantiated the suggestion of the existence of a spatial structure close to the boiling point. Original Russian Text ? N.V. Lifanova, T.M. Usacheva, V.I. Zhuravlev, V.K. Matveev, 2008, published in Zhurnal Fizicheskoi Khimii, 2008, Vol. 82, No. 10, pp. 1973–1981.     

Calorimetric determination enthalpy of the formation of natural pyromorphite

A calorimetric study of natural pyromorphite Pb₅[PO₄]₃Cl was performed. Its enthalpy of formation was determined by melt solution calorimetry from elements Δ_f H _el^∘(298.15 K) = −4124 ± 20 kJ/mol. Value Δ_f G _el^o(298.15 K) = −3765 ± 20 kJ/mol was calculated.     

Kinetic modeling of ZnO-rGO catalyzed degradation of methylene blue

Photodegradation of organic pollutants strongly depends on design of metal oxide semiconductor photocatalysts. Graphene, if composited with ZnO, can effectively enhance its photocatalytic performance for the eradication of pollutants from aqueous medium. Here in, ZnO-rGO is reported as highly active catalyst for degradation of methylene blue. A 200-mg/L solution of methylene blue dye was completely degraded within 1 h in comparison to 74% and 56% degradation over ZnO and rGO, respectively. The commonly used mechanisms of heterogeneous catalytic reactions, the Langmuir-Hinshelwood mechanism, and the Eley-Rideal mechanisms, were used to describe the reaction kinetics. The Langmuir-Hinshelwood mechanism was found as more favorable in this study. Apparent activation energy, E_ap, true activation energy, E_T, entropy, ΔS, and enthalpy, ΔH were calculated as 36.2 kJ/mol, 13.1 kJ/mol, 197.5 J/mol, and 23.1 kJ/mol, respectively.     

The thermodynamic properties of Ba2SrUO6

The standard enthalpy of formation of crystalline Ba₂SrUO₆ at 298.15 K was determined by reaction calorimetry (-2940.0 ± 8.5 kJ/mol). The heat capacity of the compound was measured over the temperature range 8-330 K by adiabatic vacuum calorimetry. The thermodynamic functions of Ba₂SrUO₆ were calculated. The standard entropy (-558.6 ± 2.1 J/(mol K)) and Gibbs function of formation at 298.15 K (-2773.5 ± 9.0 kJ/mol) were determined.     

Thermal stability of ammonium chlorocobaltates(II)

The thermal destruction of ammonium penta-, tetra-, and trichlorocobaltates(II) was studied. Thermogravimetric analysis (TGA) data was used to calculate the thermal destruction activation energy, which was 8.6 kJ/mol for (NH₄)₃CoCl₅, 14.8 kJ/mol for (NH₄)₂CoCl₄, and 117.4 kJ/mol for NH₄CoCl₃. The decomposition enthalpy of 35.9 kJ/mol for (NH₄)₃CoCl₅, 12.1 kJ/mol for (NH₄)₂CoCl₄, and 166.3 kJ/mol for NH₄CoCl₃ was determined from differential scanning calorimetry (DSC) data.     

The thermodynamic properties of magnesium uranoborate

The standard enthalpy of formation of crystalline Mg(BUO₅)₂ at 298.15 K (?4347.5 ± 8.0 kJ/mol) was determined by reaction calorimetry. The heat capacity of magnesium uranoborate was studied by adiabatic vacuum calorimetry over the temperature range 8–330 K. The thermodynamic functions of the compound were calculated. The standard entropy and Gibbs energy of formation at 298.15 K were found to be ?903.0 ± 2.1 J/(mol K) and ?4078.5 ± 9.0 kJ/mol, respectively.     

The thermodynamic properties of magnesium uranoborate tetrahydrate

The standard enthalpy of formation of crystalline Mg(BUO₅)₂ · 4H₂O at 298.15 K (?5563 ± 10 kJ/mol) was determined by reaction calorimetry. The heat capacity of the compound was studied over the temperature range 8–340 K by adiabatic vacuum calorimetry, and its thermodynamic functions were calculated. The standard entropy and Gibbs function of formation at 298.15 K (?1692.2 ± 3.4 J/(mol K) and ?5059 ± 11 kJ/mol, respectively) were determined.     

Standard enthalpy of formation of nickel trifluoride by isothermal calorimetry

The change in enthalpy in reactions of NiF₃(s) with water and aqueous solution of potassium hydroxide are measured in the isothermal calorimetry mode at 298.15 K. The standard enthalpy of formation Δ_f H° of nickel trifluoride was found to be −816 ± 6 kJ/mol.