Search results for "Enthalpy"
showing 10 items of 199 documents
Heats and Entropies of Reaction of Transition Metal Ions with Ethylenediamine
1960
THE heats of formation of complexes between ligands and metal ions are very important to further the ligand field-theory and check its implications. Until now, only the heats of hydration of the first transition group ions have been used for this purpose1 as the thermochemical data on the complexes formed by ligands other than water are very incomplete. The transition metal complexes of ethylenediamine, which have a very nearly octahedral configuration, could also be fruitfully studied in terms of ligand field-theory. Unfortunately only the thermal data on nickel (II), copper (II) and zinc (II) complexes are known2, and so the formation constants have been used instead of the values of enth…
Spin crossover in solid solution
1980
Abstract The temperature dependent high spin (HS) ⇌ low spin (LS) transition, otherwise called spin crossover, has been well established for many first-row transition metal complexes, particularly for complexes of iron(II) [1]. The phenomenon has been observed mostly in the crystalline state, but also in solution. The spin crossover characteristics have been found to depend on various chemical influences, such as ligand substitution, the nature of the non-coordinating anion and the crystallizing solvent. It has been shown by 57Fe Mossbauer spectroscopy that the spin crossover behaviour in the solid solutions of [FexZn1−x(2-pic)3] Cl2·EtOH (2-pic = 2-picolylamine) is also susceptible to meta…
Recombination studies of photodissociated MbCO by Mössbauer spectroscopy at low temperatures
1990
Rebinding of carbonmonoxide to myoglobin after photodissociation has been studied by Mossbauer spectroscopy at 57.6 K and below for up to 9 days. The time dependence is reproduced by a set of exponentials representing a distribution of activation enthalpies. A shift to smaller values of these activation enthalpies and of the preexponential factor compared to optical studies at higher temperatures has been observed as well as pumping into long-living states.
Attempts to chemically investigate element 112
2006
Summary Two experiments aiming at the chemical investigation of element 112 produced in the heavy ion induced nuclear fusion reaction of 48Ca with 238U were performed at the Gesellschaft für Schwerionenforschung (GSI), Darmstadt, Germany. Both experiments were designed to determine the adsorption enthalpy of element 112 on a gold surface using a thermochromatography setup. The temperature range covered in the thermochromatography experiments allowed the adsorption of Hg at about 35 °C and of Rn at about -180 °C. Reports from the Flerov Laboratory for Nuclear Reactions (FLNR), Dubna, Russia claim production of a 5-min spontaneous fission (SF) activity assigned to 283112 for the 238U(48Ca,3n)…
Retention of aroma compounds: an interlaboratory study on the effect of the composition of food matrices on thermodynamic parameters in comparison wi…
2010
BACKGROUND: Partition coefficients give an indication of the retention of aroma compounds by the food matrix. Data in the literature are obtained by various methods, under various conditions and expressed in various units, and it is thus difficult to compare the results. The aim of the present study was first to obtain gas/water and gas/matrix partition coefficients of selected aroma compounds, at different temperatures, in order to calculate thermodynamic parameters and second to compare the retention of these aroma compounds in different food matrices. RESULTS: Yogurts containing lipids and proteins induced a higher retention of aroma compounds than model gel matrices. The observed effect…
Influence of temperature and background electrolyte on the sorption of neptunium(V) on Opalinus Clay
2012
Abstract The temperature dependence of the sorption of 8 μM neptunium(V) on Opalinus Clay (OPA, Mont Terri, Switzerland) was investigated between 40 and 80 °C and compared to previous results for 20 °C. The batch experiments were performed under ambient air conditions in synthetic pore water (pH = 7.6, I = 0.4 M) under variation of the solid-to-liquid ratio between 2 and 20 g/L. Under these conditions the sorption of Np(V) on OPA was found to be an endothermic process as the average distribution coefficient (K d ) increases continuously with increasing temperature from 23 ± 4 L/kg at 40 °C to 678 ± 254 L/kg at 80 °C. In the temperature range of 40-80 °C, the plot of log(K d ) vs. 1/T could …
Microstructure, calorimetric and dielectric investigation of hafnium doped barium titanate ceramics
2013
Ferroelectric properties of BaTi1− x Hf x O3 ceramics with Hf content x = 0, 0.001, and 0.025 were examined. It was found that the substitution of Hf4+ for Ti4+ in BaTiO3 resulted in shifting the two low-temperature transitions (T 1, T 2) of the investigated samples to higher temperatures and decreasing the tetragonal-cubic phase transition temperature (T c). This is a well-known pinching effect. Thermal parameters of the transitions, such as the enthalpy ΔH and the entropy ΔS, were also estimated and discussed.
Influence of molecular weight and polydispersity on phase behaviour of polyesters with laterally fixed or cross-shaped mesogens
1991
Abstract To supplement previous studies of polyesters with laterally attached and cross-shaped mesogens the influence of molecular weight and molecular weight distribution on the phase behaviour has been investigated. For that purpose two polyesters have been fractionated by preparative gel permeation chromatography under high pressure and observed by polarizing microscopy and DSC measurements. A monotropic nematic polyester with laterally attached mesogens shows changing phase transitions up to a molecular weight of 10 000 (Mw); at higher molecular weight only the clearing transition is still slightly influenced. The molecular weight distribution at an average molecular weight of 15 000 (M…
Structural, magnetic, dielectric and mechanical properties of (Ba,Sr)MnO3 ceramics
2017
The authors acknowledge the CPU time allocation at Academic Computer Centre CYFRONET AGH in Cracow. This work was supported in part by PL-Grid Infrastructure and the European Regional Development Fund under the Infrastructure and Environment Programme [grant number UDA-POIS.13.01-023/09-00]. The research was partially carried out with the equipment purchased thanks to the financial support of the European Regional Development Fund in the framework of the Polish Innovation Economy Operational Program (contract no. POIG.02.01.00-12-023/08). L. Vasylechko acknowledges partial support of the Ukrainian Ministry of Education and Sciences under the Projects ?RZE?, ?KMON?, and ICDD Grant-in-Aid pro…
Investigation of Solid-Liquid Phase Transition for Sn-54wt%In Alloy by Positron Anihilation Spectroscopy
1995
The peak coincidence counting rate F(T) was measured for Sn-54wt%In alloy at the temperature range from room temperature to 400°C. It was observed that for both heating and cooling run, F(Τ) parameter changes . in the liquid phase. These changes were related to disintegration of SnII microcrystals. From a simple trapping model the defect disintegration enthalpy, H1,, was calculated. For heating and cooling run, the value of H1 was 0.53 ± 0.03 eV and 0.67 ± 0.07 eV, respectively. For well-annealed and cold rolled samples we find only one component, equal 200 ps, in the lifetime spectrum. PACS numbers: 64.70.Dv, 61.72.Cc, 78.70.Bj.