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Abstract  

The complex (C11H18NO)2CuCl4(s) was synthesized. Chemical analysis, elemental analysis, and X-ray crystallography were used to characterize the structure and composition of the complex. Low-temperature heat-capacities of the compound were measured by an adiabatic calorimeter in the temperature range from 77 to 400 K. A phase transition of the compound took place in the region of 297–368 K. Experimental molar heat-capacities were fitted to two polynomial equations of heat-capacities as a function of the reduced temperature by least square method. The peak temperature, molar enthalpy, and entropy of phase transition of the compound were calculated to be T trs = 354.214 ± 0.298 K, Δtrs H m = 76.327 ± 0.328 kJ mol−1, and Δtrs S m = 51.340 ± 0.164 J K−1 mol−1.

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Summary Heat capacity measurements of the two-dimensional metal-assembled complex, (NEt4)[{MnIII(salen)}2FeIII(CN)6] [Et=ethyl, salen= N,N’-ethylenebis(salicylideneaminato) dianion], were performed in the temperature range between 0.2 and 300 K by adiabatic calorimetry. A ferrimagnetic phase transition was observed at T c1=7.51 K. Furthermore, another small magnetic phase transition appeared at T c2=0.78 K. Above T c1, a heat capacity tail arising from the short-range ordering of the spins characteristic of two-dimensional magnets was found. The magnetic enthalpy and entropy were evaluated to be ΔH=291 J mol-1 and ΔS=27.4 J K-1 mol-1, respectively. The experimental magnetic entropy agrees roughly with ΔS=Rln(5·5·2) (=32.5 J K-1 mol-1; R being the gas constant), which is expected for the metal complex with two Mn(III) ions in high-spin state (spin quantum number S=2) and one Fe(III) ion in low-spin state (S=1/2). The heat capacity tail above T c1 became small by grinding and pressing the crystal. This mechanochemical effect would be attributed to the increase of lattice defects and imperfections in the crystal lattice, leading not only to formation of the crystal with a different magnetic phase transition temperature but also to decrease of the magnetic heat capacity and thus the magnetic enthalpy and entropy.

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Abstract  

The aim of this study was to correlate the results of experimental data using DTA method and predictions of artificial neural network (ANN) and multivariate linear regression (MLR). Thermal decomposition of polymers was analyzed by simultaneous DTA method, and kinetic parameters (critical points, the change of enthalpy and entropy) of polymers were investigated. A computer model based on multilayer feed forwarding back propagation and multilayer linear regression model were used for the prediction of critical points, phase transitions of low-density polyethylene (LDPE) and mid-density polyethylene. As a result of our study, we concluded that ANN model is more suitable than MLR about prediction of experimental data.

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The influence of the temperature program parameters of an ODSC experiment on the calculated “reversing” and “kinetic” signals has been studied. Mixed orthophosphate salts of KMPO4 (where M=Ni2+, Co2+ and Fe2+) which present at least one structural phase transition have been used for this purpose. On these crystalline compounds we have shown that the non reversing heat flow is partly associated with the formation and disappearance of ferroelastic and ferroelectric domain walls. However a proper choice of the temperature program parameters is important so that the calculated “reversing” and “kinetic” curves have the supposed physical meaning according to the assumptions made for the calculations.

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Abstract  

Molar enthalpies of solid-solid and solid-liquid phase transitions of the LaBr3, K2LaBr5, Rb2LaBr5, Rb3LaBr6 and Cs3LaBr6 compounds were determined by differential scanning calorimetry. K2LaBr5 and Rb2LaBr5 exist at ambient temperature and melt congruently at 875 and 864 K, respectively, with corresponding enthalpies of 81.5 and 77.2 kJ mol-1. Rb3LaBr6 and Cs3LaBr6 are the only 3:1 compounds existing in the investigated systems. The first one forms from RbBr and Rb2LaBr5 at 700 K with an enthalpy of 44.0 kJ mol-1 and melts congruently at 940 K with an enthalpy of 46.7 kJ mol-1. The second one exists at room temperature, undergoes a solid-solid phase transition at 725 K with an enthalpy of 9.0 kJ mol-1 and melts congruently at 1013 K with an enthalpy of 57.6 kJ mol-1. Two other compounds existing in the CsBr-based systems (Cs2LaBr5 and CsLa2Br7) decompose peritectically at 765 and 828 K, respectively. The heat capacities of the above compounds in the solid as well as in the liquid phase were determined by differential scanning calorimetry. A special method - 'step method' developed by SETARAM was applied in these measurements. The heat capacity experimental data were fitted by a polynomial temperature dependence.

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Abstract  

A general feature of temperature-induced reversible denaturation of small globular proteins is its all-or-none character. This strong cooperativity leads to think that protein molecules, possessing only two accessible thermodynamic states, the native and the denatured one, resemble ‘crystal molecules’ that melt at raising temperature. An analysis, grounded on mean field theory, allows to conclude that the two-state transition is a first-order phase transition. The implication of this conclusion are briefly discussed.

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Differential thermal analysis and differential scanning calorimetry techniques have been used to study the kinetics of phase transitions. The aragonite/calcite transformation was chosen as test reaction.

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212 222 Gallyas, F., Pál, J. (2008) Whole-cell phase transition in neurons and its possible role in apoptotic cell death. In: Pollack, G. H., Chin, W.-C. (eds) Phase Transition

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Orientation, phase composition and phase transitions of a series of long chain low molecular weight compounds (LMC), such as heneicosane, cetyl alcohol, normal fatty acids, introduced into porous structure (crazes) of polymeric matrices oriented in liquid medium have been studied by means of DSC and SAXS techniques. Different types of LMC crystallites orientation in crazes of polymeric matrices have been observed. LMC phase state in crazes is shown to be characterized by higher stability of high-temperature polymer midifications. LMC melting temperature in crazes usually decreases as well as melting enthalpy (heat) and entropy. The origin of LMC properties changes observed is high dispersity (40–100nm) of LMC particles in crazes resulting in a marked growth of polymer/LMC interface influence on principal thermodynamic parameters of the systems studied.

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Abstract  

Fourier transform far- and mid-infrared (FT-FIR and FT-MIR) and Fourier transform Raman scattering (FT-RS) spectra of [Fe(H2O)6](ClO4)3 and [Cr(H2O)6](ClO4)3 indicate that these compounds are ionic molecular crystals built from complex cations and complex anions of octahedral (T h) and tetrahedral (T d) symmetry, respectively. The thermodynamic parameters for two phase transitions in polycrystalline [Fe(H2O)6](ClO4)3 and [Cr(H2O)6](ClO4)3 were determined by differential scanning calorimetry (DSC): melting of the crystals (at T m=359.2 and 363.1 K) and solid-solid phase transition (at T C1=126.5 and 139.4 K), respectively.

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