Thermochemistry of iron manganese oxide spinels

Oxide melt solution calorimetry has been performed on iron manganese oxide spinels prepared at high temperature. The enthalpy of formation of (MnxFe1−x)3O4 at 298 K from the oxides, tetragonal Mn3O4 (hausmannite) and cubic Fe3O4 (magnetite), is negative from x=0 to x=0.67 and becomes slightly positive for 0.670.6) spinels of intermediate compositions. The enthalpies of formation are discussed in terms of three factors: oxidation–reduction relative to the end-members, cation distribution, and tetragonality. A combination of measured enthalpies and Gibbs free energies of formation in the literature provides entropies of mixing. ΔSmix, consistent with a cation distribution in which all trivalent manganese is octahedral and all other ions are randomly distributed for x>0.5, but the entropy of mixing appears to be smaller than these predicted values for x<0.4

Gibbs free energy difference between the undercooled liquid and the beta-phase of a Ti-Cr alloy

The heat of fusion and the specific heats of the solid and liquid have been experimentally determined for a Ti60Cr40 alloy. The data are used to evaluate the Gibbs free energy difference, DELTA-G, between the liquid and the beta-phase as a function of temperature to verify a reported spontaneous vitrification (SV) of the beta-phase in Ti-Cr alloys. The results show that SV of an undistorted beta-phase in the Ti60Cr40 alloy at 873 K is not feasible because DELTA-G is positive at the temperature. However, DELTA-G may become negative with additional excess free energy to the beta-phase in the form of defects

Safer Sodium Battery: Thermal and electrochemical studies of Na-ion based batteries

In the recent decade, the community emphasizes the crucial need for the improvement of battery safety and safety remains a critical barrier for this technology. Despite safer battery materials, battery thermal management could be a key to safer post Lithium technology. In that respect, sodium ion based batteries were studied using different electrolyte routes. Thermo-physical and electrochemical analyses depicted the performance of the battery material and the coin cell characteristics. The safety related parameters including the heat generation during charging-discharging and thermal abuse test have been executed by the means of sophisticated calorimetry instruments. Quantitative measurement of the thermal data was performed, and out-gasing during thermal decomposition of the electrolytes has been analysed in order to design a safer battery. This work helps finding new and quantitative correlations between different critical thermal and safety related issues in future post Li batteries. The determined thermal data, gas compositions and safety parameters on coin cell level are needed for the design of a safer battery, the safe upscaling and for the adaptation of the thermal management system

Dehydration kinetics and thermochemistry of selected hydrous phases, and simulated gas release pattern in carbonaceous chondrites

As part of our continued program of study on the volatile bearing phases and volatile resource potential of carbonaceous chondrite, results of our experimental studies on the dehydration kinetics of talc as a function of temperature and grain size (50 to 0.5 microns), equilibrium dehydration boundary of talc to 40 kbars, calorimetric study of enthalpy of formation of both natural and synthetic talc as a function of grain size, and preliminary results on the dehydration kinetics of epsomite are reported. In addition, theoretical calculations on the gas release pattern of Murchison meteorite, which is a C2(CM) carbonaceous chondrite, were performed. The kinetic study of talc leads to a dehydration rate constant for 40-50 microns size fraction of k = (3.23 x 10(exp 4))exp(-Q/RT)/min with the activation energy Q = 376 (plus or minus 20) kJ/mole. The dehydration rate was found to increase somewhat with decreasing grain size. The enthalpy of formation of talc from elements was measured to be -5896(10) kJ/mol. There was no measurable effect of grain size on the enthalpy beyond the limits of precision of the calorimetric studies. Also the calorimetric enthalpy of both synthetic and natural talc was found to be essentially the same, within the precision of measurements, although the natural talc had a slightly larger field of stability in our phase equilibrium studies. The high pressure experimental data the dehydration equilibrium of talc (talc = enstatite + coesite + H2O) is in strong disagreement with that calculated from the available thermochemical data, which were constrained to fit the low pressure experimental results. The calculated gas release pattern of Murchison meteorite were in reasonable agreement with that determined by stepwise heating in a gas chromatograph

Ověřování náchylnosti uhlí k samovznícení v OKR

Spontaneous combustion of coal mass represents a considerable health hazard of workers and endangering mining operations, which is often connected with a failure of coal mining and costs of endogenous fire suppression. Prompt recognition of spontaneous combustion plays a very important role in deep working coal seams prone to spontaneous combustion. The susceptibility of coal to a spontaneously combustible process is considered as a feature of coal mass that can be specified by a laboratory test. Since seventies of the last century in OKR (Ostrava-Karvina Coal Field) methods according to the author Olpinski and the oxidation method under adiabatic conditions have already been used to verify the tendency of coal to spontaneous combustion. Later the method of pulse calorimetry and the CPT (Crossing Point Temperature) method were used for the OKR coal. Experimentally the method according to the author Veselovskij was verified. The presented paper describes the objective methods, their technical performance and criteria of assessment of susceptibility of coal to spontaneous combustion.Samovznícení uhelné hmoty představuje značné riziko spojené s ohroţením zdraví pracovníků a důlního provozu, coţ je často spojeno s výpadkem těţby a s náklady na likvidaci endogenního poţárů. Včasné rozpoznání samovznícení má velice důleţitou roli v hlubinném dobývání uhelných slojí náchylných k samovznícení. Náchylnost uhlí k samovzněcovacímu procesu je povaţována za vlastnost uhelné hmoty, kterou lze stanovit laboratorní zkouškou. V OKR jsou jiţ od sedmdesátých let minulého století pouţívány pro ověřování náchylnosti uhlí k samovznícení metoda podle autora Olpinského a metoda oxidace za adiabatických podmínek. Později byla pro uhlí OKR ověřena metoda pulsní kalorimetrie a průsečíková metoda CPT (Crossing Point Temperature). Experimentálně byla ověřena metoda podle autora Veselovského. Předloţený článek popisuje předmětné metody, jejich technické provedení a stupnice hodnocení náchylnosti uhlí k samovznícení

Thermophysical properties of nickel-based cast superalloys

The article presents tests results of specific heat storage capacity and oxidation resistance of nickel - based cast Mar M - 200, Mar - M - 247 and Rene 80 superalloys. Specific heat measurements were conducted with the use of differential scanning calorimetry (DSC), with the use of high - temperature calorimeter multi (HTC) Setaram. Oxidation resistance tests were conducted with the use of cyclic temperature change method. Each cycle consisted of heating by temperature of 1 100 °C and next quick cooling in air. It was proved that the biggest value of specific heat Cp was found in alloy Mar - M - 200, and the lowest in alloy Mar - M - 247. Relatively good oxidation resistance has been found in alloy Mar - M - 247