H.A.J. Oonk

Synthesis of strontium and barium cerate and their reaction with carbon dioxide

The log p co2 versus 1/T relationships of the equilibria (1) ACO 3 +CeO 2 ⇄ACeO 3 +CO 2 and (2) ACO 3 ⇄AO+CO 2 , in whichA=Sr or Ba, were investigated. The methods which have been used are: thermodynamic equilibrium calculations, simultaneous thermogravimetry-differential thermal analysis and high-temperature X-ray diffraction. In pure N 2 atmosphere, the synthesis of the cerates proceeds via (1) ACO 3 -AO+CO 2 and (2) AO+CeO 2 -ACeO 3 , which is not calculated thermodynamically, but is apparently kinetically more favourable at low temperatures. SrCeO 3 and BaCeO 3 react with 1 atm CO 2 below 1190 o C and 1185 o C,respectively. For mixtures of CO 2 with other gases, the decomposition temperatures can be estimated from the figures presented

A new equation of state based on Grover, Getting and Kennedy's empirical relation between volume and bulk modulus. The high-pressure thermodynamics of MgO

The empirical linear relation between volume and logarithm of bulk modulus, discovered by Grover, Getting and Kennedy, is taken as the basis for a new pressure–volume equation of state. This linear relation and the equation of state have the same two substance-dependent parameters, the values of which can be derived from low-pressure data. For MgO, in the temperature range 100–3100 K and the pressure range 0–225 GPa, it is shown that the new methodology allows the careful calculation of high-pressure thermodynamic properties: all available experimental data are reproduced with great precision.

Polymorphism of even saturated carboxylic acids from n-decanoic to n-eicosanoic acid

The polymorphism of normal saturated even carboxylic acids from n-decanoic to n-eicosanoic acid is discussed. Seven crystal modifications, including polymorphs and polytypes, were identified and fully characterized by the combination of calorimetric measurements (DSC) at atmospheric and high pressures, X-ray powder diffraction, FT-IR spectroscopy and scanning electron microscopy (SEM). All seven crystal forms, including polymorphs and polytypes, are observed at room temperature. Forms A2 and Asuper are triclinic, form C is monoclinic and forms E and B show both a monoclinic and an orthorhombic polytype. The triclinic modifications A2 and Asuper predominate for acids up to n-tetradecanoic acid (C14H27O2H). The orthorhombic and the monoclinic forms predominate for acids from n-hexadecanoic (C16H31O2H) up to n-eicosanoic acid (C20H39O2H). When the temperature is increased, all the crystal modifications transform irreversibly to the C form. In the first part of this paper, cell parameters for the different forms are given, the observed temperatures and enthalpies of the transitions are reported and the stability of the different forms is discussed. In the second part, we state the main contribution of each technique for the identification and interpretation of the polymorphism of even numbered carboxylic acids.

Liquid–vapour equilibria of the methyl esters of alkanoic acids: vapour pressures as a function of temperature and standard thermodynamic function changes

Abstract The vapour pressures as a function of temperature of the methyl esters of alkanoic acids from butanoic to eicosanoic acid, have been measured using two different techniques: the static diaphragm and spinning rotor manometry and the combined torsion mass-loss effusion. Combined with data available from literature, the new data have been processed using the thermodynamic regression equation proposed by Clarke and Glew. The results of this research are reliable vapour pressures and the thermodynamic properties of vaporisation.

Protection of temperature sensitive biomedical products using molecular alloys as phase change material.

In this paper we present an example of the application of molecular alloys for thermal protection of biomedical products during transport or storage. Particularly, thermal protection of blood elements have been considered at different temperatures. All steps from basic research to marketing have been addressed. The high latent heat of fusion of the components allows us to propose molecular alloys as materials for thermal energy storage and also for thermal protection over a large range of temperatures, which can be used in many industrial sectors.

Perfect families of mixed crystals: The rotator I N-alkane case

The experimental systems considered in this paper are isobaric binary mixed crystals, and their properties studied are the thermodynamic mixing properties, actually the excess enthalpy and excess entropy. More in particular, the excess behavior is examined for families of systems where the components of each of the member systems belong to a group of chemically coherent substances. The accent is on a group of 18 systems composed of n-alkanes in the range from C11H24 to C26H54, such that the components of an individual system are either neighbors or next nearest neighbors. In these systems mixed crystalline solid forms are stable in which the molecules have rotational freedom around their long axis. One of these forms is rotator I, and it is this form for which thermodynamic mixing properties have been determined. The magnitudes of the excess enthalpy and excess entropy are system-dependent and can be correlated to the geometric mismatch, i.e., the relative difference in number of carbon atoms of the molec...

A thermodynamic method for the derivation of the solidus and liquidus curves from a set of experimental liquidus points

A thermodynamic method is presented which makes possible the correct derivation of solidus and liquidus curves from a set of experimental liquidus points. In an iterative procedure, which is based on the equal-G curve and which uses intermediate phase diagram calculations, the liquidus of the calculated phase diagram is made to run through the experimental liquidus points. In addition, information about the thermodynamic mixing properties of the system is obtained. Results are given for the system p-dichlorobenzene + p-dibromobenzene, K2CO3 + K2SO4, KCl + NaCl.

Enthalpies of sublimation and dimerization in the vapour phase of formic, acetic, propanoic, and butanoic acids

Abstract Combined torsion- and weighing-effusion techniques are used to measure saturation vapour pressures as function of temperature for four solid carboxylic acids: formic, acetic, propanoic, and butanoic acid. By means of a theoretical analysis, which is given first, it is shown that the enthalpy of sublimation and the monomer/dimer ratio of the vapour phase are related to measured vapour pressures for both techniques but in a somewhat different manner. As a result, the combination of the two sets permits the determination of not only the enthalpy of sublimation but also of the monomer/dimer ratio of the vapour phase in equilibrium with the solid phase. It is found that the first three acids are highly dimerized and butanoic acid to a less extent.

A realistic equation of state for solids. the high pressure and high temperature thermodynamic properties of MGO

As has been found for pure metals, there exists a linear relationship between molar volume and the logarithm of bulk modulus. This relation is also valid for oxide and silicate substances. From the relationship, an equation of state has been developed and applied to the substance MgO. With this equation of state and by using experimental thermodynamic data at 1 bar pressure only, it is possible to make accurate predictions of thermodynamic properties at very high pressures and temperatures. Thermodynamic anomalies encountered in using e.g. a Birch-Murnaghan equation of state do not occur and the number of adjustable parameters is reduced.

Phase diagrams of scalemic mixtures: A Monte Carlo simulation study

In this paper, a simplified model was used to describe the interactions between the enantiomers in a scalemic mixture. Monte Carlo simulations were performed to determine several thermodynamic properties as a function of temperature and mole fraction of solid, liquid, and gas phase. Phase diagrams were constructed using a macroscopic thermodynamic program, PROPHASE. The model consists of spherical D and L molecules interacting via modified Lennard–Jones potentials (σDD=σLL, eDD=eLL, eDL=eeDD, and σDL=sσDD.) The two heterochiral interaction parameters, e and s, were found to be sufficient to produce all types of phase diagrams that have been found for these systems experimentally. Conglomerates were found when the heterochiral interaction strength was smaller than the homochiral value, e<1. A different heterochiral interaction distance, s≠1, led to racemic compounds, with an ordered distribution of D and L molecules. The CsCl-structured compound was found to be stable for short DL interactions, s<1 (e=1), ...