Thermodynamic properties of carbynoid structures in the 0—340 K range

The temperature dependences of the heat capacity (C _p°) of carbynoid structures prepared by alkaline dehydrochlorination of poly(vinylidene chloride) and 1,1,2- and 1,2,3-polytrichlorobutadienes were studied by adiabatic vacuum calorimetry between 5 and 340 K with an accuracy of 0.2%. The low-temperature relaxation transitions and abnormal patterns of the C _p° vs. T dependences were identified and characterized. The experimental results were used to calculate the thermodynamic functions C _p°(T), H°(T) – H°(0), S°(T) – S°(0), and G°(T) – H°(0) for 0—340 K. These data were compared with the corresponding data for carbyne produced by oxidative dehydropolycondensation of acetylene, which is a mixture of amorphous - and -forms with a minor impurity of crystals of both forms.     

Thermodynamic properties of tetraphenylantimony benzophenoxymate in the region of 0–450 K

Heat capacity of tetraphenylantimony benzophenoxymate Ph₄SbONCPh₂ is measured for first time using adiabatic calorimeter in the range from 6K to 350K and differential scanning calorimeter in the range from 330 K to 450 K. In the range of 400–450 K is revealed a melting accompanied with partial decomposition of the substance. Standard thermodynamic functions of crystalline Ph₄SbONCPh₂ in the range from T → 0 K to 440 K are calculated. Enthalpy of combustion of this compound is measured in a combustion calorimeter with isothermal cover and static bomb. Standard thermodynamic formation functions of crystalline Ph₄SbONCPh₂ at 298.15 K are calculated. Fractal dimension D is revealed.     

Thermodynamic properties of o-semiquinone complex of Co with Di-(2-pyridyl)amine in the temperature range T → 0 to 370 K

The heat capacity of di-(2-pyridyl)amine-bis-(4-methoxy-3,6-di-tert-butyl-o-benzosemiquinone)cobalt in the temperature range from 7 to 370 K was investigated by means of precise adiabatic vacuum calorimetry. It was established that the phase transition associated with the redox-isomeric transformation of the semiquinone-catecholate form of the complex into the bis-semiquinone form is observed above 260 K; this transition is not completed due to thermal destruction that begins at 367 K. The magnetic moment values in the temperature range from 5 to 350 K and the EPR spectra in the temperature range from 130 to 290 K, which confirm the nature of the phase transition, were obtained for the investigated complex. The standard thermodynamic functions C _p ^pO (T), H○(T)-H○(0), S○(T), and G○(T)-H○(0), were calculated from the data on heat capacity in the temperature range from T → 0 to 260 K. Analysis of the low temperature heat capacity on the basis of Debye’s theory of the heat capacity of solids and the multifractional model testifies to the chain-layered structural topology of the investigated complex.     

Thermodynamic Properties of Dibenzo-24-crown-8 in the Range from T → 0 to 500 K

The temperature dependence of the heat capacity of dibenzo-24-crown-8 in the range 6-500 K was measured by adiabatic vacuum and dynamic calorimetry with an accuracy of 0.2-0.5%. The physical transformations of the title compound occurring on its heating and cooling within the above temperature range were revealed and characterized. From the experimental data obtained for dibenzo-24-crown-8, its thermodynamic functions C _4p ⁰(T), H ⁰(T) - H ⁰(0), S ⁰(T) - S ⁰(0), and G ⁰(T) - H ⁰(0) were calculated for the range from T 0 to 500 K; the standard entropy of formation from the elements, _s S ⁰, at T 298.15 K was also calculated. The fractal dimensions D in the heat capacity function of the multifractal version of the Debye heat capacity theory, characterizing the heterodynamic characteristics of the title compound, were calculated.     

Thermodynamic properties of crystalline phosphate Ba0.5Zr2(PO4)3 over the temperature range from T → 0 to 610 K

The temperature dependence of the heat capacity of crystalline barium zirconium phosphate C _p ^o  = f(T) was measured over the temperature range 6–612 K. The experimental data obtained were used to calculate the standard thermodynamic functions C _p ^o (T), H°(T) ? H°(0), S°(T), G°(T) ? H°(0) over the temperature range from T → 0 to 610 K and standard entropy of formation at 298.15 K. The data on the low-temperature (6 ≤ T/K ≤ 50) heat capacity were used to determine the fractal dimension of Ba_0.5Zr₂(PO₄)₃. Conclusions concerning the topology of the structure of phosphate were drawn. Thermodynamic properties of M_0.5Zr₂(PO₄)₃ (M = Ca, Sr, Ba) were compared.     

The thermodynamic properties of bis(η6-o-xylene)chromium(I) fulleride over the temperature range from T → 0 to 340 K

The temperature dependence of the heat capacity of bis(η⁶-o-xylene)chromium(I) fulleride, [(η⁶-(o-xylene))₂Cr]^+?[C₆₀]^??, over the temperature range 6–340 K was measured on an adiabatic vacuum calorimeter. The low-temperature (20 K ≤ T ≤ 50 K) heat capacity was subjected to multifractal processing; conclusions about the heterodynamic character of the structure were drawn. The experimental data were used to calculate the standard thermodynamic functions C _p ^° (T), H ^°(T)-H ^°(0), S ^°(T), and G ^°(T)-H ^°(0) over the temperature range from T → 0 to 340 K and estimate the standard entropy of fulleride formation from simple substances at 298.15 K. The standard thermodynamic characteristics of [(η⁶-(o-xylene))₂Cr]^+?[C₆₀]^?? were compared with those of the initial fullerene C₆₀.     

Thermodynamic properties of o-semiquinonato complexes of cobalt, nickel, and copper in the range T → 0 to 350 K

The heat capacity of bis(3,6-di-tert-butyl-o-benzosemiquinonato)copper, (triethylarsine)bis(3,6-di-tert-butyl-o-benzosemiquinonato)nickel, and (triphenylphosphine)bis(3,6-di-tert-butyl-o-benzosemiquinonato)cobalt was determined in the range of 0 to 350 K by precision adiabatic vacuum calorimetry. The temperature dependences of magnetic moments were studied for the last two complexes. The G-transition in nickel complex, which is presumably caused by a loosening of the molecular degrees of freedom, was determined. The standard thermodynamic functions of complexes were calculated according to the obtained data: C _p ^○ , H○(T)-H○(0), S○(T), and G○(T)-H○(0) for the range of T → 0 to 350 K. It was concluded that our analysis of low-temperature heat capacity based on the Debye theory of the heat capacity of solids and the multifractal model confirms the chain-layer topologies of the structures of the investigated complexes.     

Thermodynamic properties of cellulose of various structures in the temperature range 5–370 K

The energies of combustion of cellulose samples with different supramolecular structures were determined, and the enthalpies of formation of these substances were calculated. Reliable values of the heat capacity were obtained.     

FT-IR spectra of NaCl�CH2O in the region from near to beyond the critical state

Water and NaCl?CH₂O solutions and their molecular spectra at high temperatures and pressures were observed and examined using a new design of hydrothermal diamond anvil cell (HDAC) connected to both a light and an infrared microscope. We have modified the diamond window of the HDAC to have a wide angle to allow the infrared beam to pass the window. Fourier-transform infrared (FT-IR) spectra of NaCl?CH₂O?CD₂O were examined at high temperatures and pressures up to 850 °C and 3 GPa. The effect of increasing temperature on water spectra differed from that of increasing pressure. The O?CH stretching frequency of water molecules increases with increasing temperature (from 20 to 600 °C), and also with increasing salinity of the solution.     

Thermodynamic quantities for the ionization of nitric acid in aqueous solution from 250 to 319°C

The aqueous reaction, HNO₃(aq)=H⁺+NO ₃ ^– was studied as a function of ionic strength I at 250, 275, 300 and 319°C using a flow calorimeter and the equilibrium constant K and enthalpy change (H) at I=0 were determined. Using these experimental values, equations describing logK, H, the entropy change S and the heat capacity change C _p of reaction at I=0 and temperatures from 250 to 319°C were derived. The increasing importance of ion association as temperature rises was discussed. The use of an equation containing identical numbers of positive and identical numbers of negative charges on both sides of the equal sign (isocoulombic reaction principle) was applied to the logK values reported here and to those determined by others. The resulting plot of logK for the isocoulombic reaction vs. 1/T was fairly linear which supports the postulate that the principle is a useful technique for the extrapolation of logK values from low to high temperatures.Presented at the Second International Symposium on Chemistry in High Temperature Water, Provo, UT, August 1991.     

Phase diagram of the ethylene glycol-dioxane system in the temperature range from ?90 to 25°C

The ethylene glycol-1,4-dioxane system is studied by means of differential scanning calorimetry over a wide range of temperatures (?90 to 25°C) and is found to be a simple eutectic with the eutectic point at 10 mol % of dioxane (?16.5°C). Unlike a water-dioxane system, in which the clathrate with dioxane: H₂O = 1: 34 ratio is formed, the observed phase diagram showed no evidence of clathrate formation, due presumably to its hydrogen bond geometry and the intermolecular interaction properties of ethylene glycol.     

Thermodynamic stability of solid phases in the system Cu–O–Al2O3 by means of the EMF and DSC-TGA techniques

Journal of Solid State Electrochemistry - Thermodynamic properties of solid phases in the Cu–O–Al2O3 system were measured by means of the EMF method with oxygen concentration galvanic...     

Phase equilibria in the CsUO system in the temperature range from 873 to 1273 K

Portions of the cesium-uranium-oxygen system have been investigated between 873 and 1273 K and a phase diagram has been constructed using our data and the data of other workers in the field. A consistent set of measured and estimated thermodynamic data for cesium uranates has been used to calculate the equilibrium cesium partial pressure and the equilibrium oxygen partial pressure over two and three phase regions in the CsUO system. For a given temperature, the equilibrium cesium partial pressure in a two phase region decreases as the equilibrium oxygen partial pressure increases.     

Standard thermodynamic functions of CaNi0.5Zr1.5(PO4)3 crystalline phosphate in the range of T → 0 to 640 K

The temperature dependence of the heat capacity C _p ^○ = f(T) of CaNi_0.5Zr_1.5(PO₄)₃ crystalline phosphate is studied by precision adiabatic vacuum and differential scanning calorimetry over the temperature range of 7–640 K. Its standard thermodynamic functions C _p ^○ (T), H ^○(T)-H ^○(0), S ^○(T), and G ^○(T)-H ^○(0) for the region T → 0 to 640 K and the standard entropy of formation at T = 298.15 K are calculated from the obtained experimental data. Using data on the low-temperature (30–50 K) heat capacity, the D fractal dimension of phosphate is determined and conclusions about the character of the topology of its structure have been made. The final results are compared to data from thermodynamic investigations of the structurally related crystalline phosphates Zr₃(PO₄)₄, Ni_0.5Zr₂(PO₄)₃, and Ca_0.5Zr₂(PO₄)₃.     

Thermodynamic properties of the ternary oxides in the Eu–Ru–O system by using solid-state electrochemical cells

The Gibbs free energies of formation of Eu₃RuO₇(s) and Eu₂Ru₂O₇(s) have been determined using solid-state electrochemical technique employing oxide ion conducting electrolyte. The reversible electromotive force (e.m.f.) of the following solid-state electrochemical cells have been measured:

Thermodynamic properties of solid solutions in the PbSe—AgSbSe2 system

The results of the study of the PbSe—AgSbSe₂ system by measuring the emf of concentration chains with respect to PbSe in a temperature range of 300–450 K are presented. The formation in the system of a wide (37–100 mol.% AgSbSe₂) region of solid solutions based on AgSbSe₂ is shown. The partial thermodynamic functions of PbSe and lead in the alloys are calculated from the equations of the temperature dependences of the emf. The standard thermodynamic functions of formation and standard entropies of solid solutions (2PbSe)_x(AgSbSe₂)_1?x (x = 0.4, 0.6, 0.8, and 0.9) are calculated by the integration of the Gibbs—Duhem equation over the PbSe—AgSbSe₂ section using the literature data on the corresponding thermodynamic data for compounds PbSe and AgSbSe₂.

     

Non-ideal properties of the TRIS—TRIS·HCl−NaCl−H2O buffer system in the 0–40 °C temperature interval. Application of the pitzer equations

The buffer solution TRIS—TRIS·HCl−NaCl−H₂O was studied in the 0–40 °C temperature region and ionic strength interval of (0.1–4)m (m is molality) by the e.m.f. method using two types of cells without liquid junction composed of platinum-hydrogen, silverchloride, and sodium-glass electrodes. For temperatures of 5 and 15 °C and the (1–4)m concentration region, the osmotic coefficients of the TRIS·HCl−H₂O solutions were measured by the isopiestic method. The results were processed in the framework of the Pitzer method, and the parameters of interaction of the components of the buffer system were calculated. The associative character of the interactions in the TRIS·HCl−H₂O solution was shown. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 670–675, April, 2000.     

The thermodynamic properties of 2-ethylhexyl acrylate over the temperature range from <Emphasis Type="Italic">T</Emphasis> → 0 to 350 K

The temperature dependence of the heat capacity C _p ^o= f(T) 2 of 2-ethylhexyl acrylate was studied in an adiabatic vacuum calorimeter over the temperature range 6–350 K. Measurement errors were mainly of 0.2%. Glass formation and vitreous state parameters were determined. An isothermic shell calorimeter with a static bomb was used to measure the energy of combustion of 2-ethylhexyl acrylate. The experimental data were used to calculate the standard thermodynamic functions C _p ^o(T), H ^o(T)-H ^o(0), S ^o(T)-S ^o(0), and G ^o(T)-H ^o(0) of the compound in the vitreous and liquid states over the temperature range from T → 0 to 350 K, the standard enthalpies of combustion Δ_c H ^o, and the thermodynamic characteristics of formation Δ_f H ^o, Δ_f S ^o, and Δ_f G ^o at 298.15 K and p = 0.1 MPa.