Studies of thermokinetics in an adiabatic calorimeter

An adiabatic calorimeter in which automation of the control of the adiabatic condition and the thermogram recording is achieved in a simple way has been designed for studies of both thermochemistry and thermokinetics. A new method for specific heat measurements has been proposed and specific heats ofn-heptane were measured to test the reliability of this calorimeter.     

Studies of thermokinetics in an adiabatic calorimeter

Thermokinetic research methods for irreversible and reversible reactions in the adiabatic calorimeter are proposed. Four reaction systems, including an endothermic reaction, have been studied with an adiabatic calorimeter and the validity of these methods is verified.     

Determination of the specific heat capacity of hemoglobin- and methemoglobin-water mixtures using an adiabatic calorimeter

The specific heat capacity of bovine hemoglobin-, methemoglobin-, and thermally denatured hemoglobin-water mixtures were measured in the temperature range from 10 to 80°C. The partial specific heat capacities for mass fractions of the protein between 0 and 1 were computed. Significant differences of the partial quantities were obtained for the native, respectively denatured state of protein and for the protein in the native state in fluid mixtures, respectively in rather dry mixtures. For mixtures with protein mass fractions up to 0.45, exceeding the value in living human red cells, partial specific heat capacities of either components are found to be constant. The accuracy of the used adiabatic calorimeter will be described briefly.     

Thermal hazard evaluations of 18650 lithium-ion batteries by an adiabatic calorimeter

In this study, the thermal hazard features of various lithium-ion batteries, such as LiCoO₂ and LiFePO₄, were assessed properly by calorimetric techniques. Vent sizing package 2 (VSP2), an adiabatic calorimeter, was used to measure the thermal hazards and runaway characteristics of the 18650 lithium-ion batteries under an adiabatic condition. The thermal behaviors of the lithium-ion batteries were obtained at normal and abnormal conditions in this study. The critical parameters for thermal hazardous behavior of lithium-ion batteries were obtained including the exothermic onset temperature (T ₀), heat of decomposition (ΔH), maximum temperature (T _max), maximum pressure (P _max), self-heating rate (dT/dt), and pressure rise rate (dP/dt). Therefore, the result indicates the thermal runaway situation of the lithium-ion battery with different materials and voltages in view the of TNT-equivalent method by VSP2. The hazard gets greater with higher voltage. Without the consideration of other anti-pressure measurements, different voltages involving 3.3, 3.6, 3.7, and 4.2 V are evaluated to 0.11, 0.23, 0.88, and 1.77 g of TNT. Further estimation of thermal runaway reaction and decomposition reaction of lithium-ion battery can also be confirmed by VSP2. It shows that the battery of a fully charged state is more dangerous than that of a storage state. The technique results showed that VSP2 can be used to strictly evaluate thermal runaway reaction and thermal decomposition behaviors of lithium-ion batteries. The loss prevention and thermal hazard assessment are very important for development of electric vehicles as well as other appliances in the future. Therefore, our results could be applied to define important safety indices of lithium-ion batteries for safety concerns.     

Application of an adiabatic precision calorimeter in the field of organic reactions

Adiabatic calorimetry is a suitable method for investigations of reactions because the generated heat remains completely in the reactor. For the investigation of organic reactions, the adiabatic precision calorimeter ACTRON 5 is used. The alcoholyses of phenyl isocyanate and 1,2-butyleneoxide were investigated. The temperature-time course was estimated by means of the nonlinear program TA-kin. Inclusion of the concentration-time course in the estimation procedure led to an increase in the reliability of the parameters. Probes were taken during isoperibolic measurements and were analysed by means of HPLC.     

Enthalpy relaxation of low molecular weight amorphous styrene oligomers measured with an adiabatic calorimeter

Herein, we measured the enthalpy relaxation of three styrene oligomers with different molecular weights (styrene oligomer with M_w?=?4.53?×?10²: PSA-300, styrene oligomer with M_w?=?5.89?×?10²: PSA-500, and styrene oligomer with M_w?=?1.01?×?10³: PSA-1000) near their respective glass transition temperatures (T_g) using an adiabatic calorimeter. We determined the relaxation rates and the amounts of configurational enthalpy released from the temperature dependence of the temperature drift rates around T_g. Based on our experimental findings, we found the amounts of configurational enthalpy release per monomer unit to be 0.8, 3.5, and 1.6 kJ mol^?1 for PSA-300, PSA-500, and PSA-1000, respectively. These values were 3.9–18 times larger than that of glycerol, which is a typical glass-forming liquid.

     

A simple adiabatic low-temperature calorimeter based on a helium refrigerator system

The construction of an adiabatic calorimeter for the 15-300 K range is described. It is fully automated and set up in a helium refrigerator system. The operation of the calorimeter was tested by measuring the specific heat capacity of a pure copper sample. The results show good agreement with the standard literature values. The specific heat capacity of a magnesium hydride sample was also determined. For MgH₂, the standard molar entropy of S⁰(298.15)=30.64 J mol⁻¹ K⁻¹ was calculated from the obtained data.     

Application of a novel type of adiabatic scanning calorimeter for high-resolution thermal data near the melting point of gallium

A novel type of adiabatic scanning calorimeter (ASC) based on Peltier elements (PEs) is used to obtain high-resolution enthalpy and heat capacity data on the melting transition of gallium. The accuracy of the specific heat capacity and specific enthalpy is about 2 %, for a sub-mK temperature resolution. The simultaneously determined equilibrium specific heat capacity and specific enthalpy are used to determine the heat of fusion and the purity. In addition, the use of the PE-based ASC as a classical heat step calorimeter and as a constant rate (DSC-type) calorimeter is discussed. A comparison of the ASC results with literature data and DSC data shows the advantages of ASC for the study of phase transitions.     

An adiabatic low-temperature calorimeter for heat capacity measurement of small samples

A small sample adiabatic calorimeter for measuring heat capacities in the temperature range 60–350 K using the Nernst method has been constructed. The sample cell of the calorimeter is 6 cm³ in the internal volume, equipped with a miniature platinum thermometer and surrounded by two adiabatic shields. Two sets of 6-junction chromel-copel thermocouples were mounted between the cell and the shields to indicate the temperature differences between them. The adiabatic conditions of the cell were automatically controlled by two sets of temperature controller. A mechanical pump was used to pump out the vapour of liquid nitrogen in the cryostat to solidify N₂ (1), and 60 K or even lower temperature was obtained. The performance of this apparatus was evaluated by heat capacity measurements on α-alumina. The deviations of experimental results from a smoothed curve lie within ±0.2%, while the inaccuracy is within ±0.5% compared with the recommended reference data in the wole temperature range.     

Thermal risk evaluation of organic peroxide by automatic pressure tracking adiabatic calorimeter

An automatic pressure tracking adiabatic calorimeter (APTAC) has been developed to obtain the thermokinetic and vapor pressure data during runaway reactions. The heat onset temperature is important data for estimating the thermal hazardous materials. DTBP(di-tert-butyl peroxide)/toluene was chosen for evaluating the measurement values and the thermokinetic parameters. The relationships between the sample mass and the heat onset temperature in the addition to the maximum temperature were investigated to explain the heat of reaction measured by the APTAC. The apparatus properties and the reliability of the data obtained by the APTAC were examined on the basis of the experimental data.     

Thermodynamic investigation of the liquid PbS system by using a drop calorimeter

Heat contents of the PbS system were measured by a drop calorimeter in the composition range of sulfur X_s = 0 to 0.5 (PbS) and in the temperature range of 560 to 1500 K, and a heat content-temperature-composition ternary diagram was constructed. By using a quantitative thermodynamic analysis method, free energy, heat and entropy of mixing in the liquid PbS binary and PbPbS pseudo-binary systems were derived from the measured heat contents. The obtained partial molar free energies of mixing (activities) are considerably different from those estimated by the use of a regular solution model.     

Conditions for calibration of an isothermal titration calorimeter using chemical reactions

The reaction of protonation of 2-amino-2-(hydroxymethyl)-1,3-propanediol (TRIS) is a suitable one for the calibration of isothermal titration calorimeter (ITC), providing that experimental conditions are appropriately chosen. The conditions and methods for handling experimental data from a nanowatt-ITC are discussed. Also, the binding of Ba²⁺ to 18-Crown-6 is successfully used to check the accuracy and precision of the chemical calibration performed with TRIS. This latter reaction has the additional advantage that the data can also be used for a check on the determination of the value of a binding constant. The anomaly of the first injection in ITC is analyzed and, by combining calorimetric and spectroscopic measurements, it is shown that it mainly results from a backlash effect of the syringe plunger rather than from a diffusion effect.     

Thermal runaway and fire behavior investigation of lithium ion batteries using modified cone calorimeter

The lithium ion battery has been widely used, but it has high fire risk due to its flammable materials. In this study, a series of combustion tests are conducted on the 18650-type lithium ion batteries using the modified cone calorimeter. The temperature and voltage variation of the battery, heat release rate and gas generation during combustion are measured in this study. The battery is heated evenly by the self-made heater, and the reliable trigger temperatures of thermal runaway are obtained for different states of charge (SOCs) batteries in this study. The fire behavior of the 100% SOC batteries is shown in this paper. The net heat absorption by the battery before thermal runaway is calculated based on the heat transfer theory. It ranges from 56.81 to 64.05 kJ for 0 to 100% SOC batteries, which shows a decreasing trend as SOC increases. The peak combustion heat release rate of 100% SOC batteries is 3.747?±?0.858 kW. CH₄ and CO gases are detected before and after thermal runaway. The generation of CO shows an increasing trend as SOC increases. Some suggestions on the early warning system of battery thermal runaway are proposed based on this study.

     

Characterisation of an exothermic reaction using adiabatic and isothermal calorimetry

A simple esterification reaction is used to demonstrate standard procedures for determining the thermokinetic parameters of an exothermic reaction from adiabatic calorimetric data. The influence of variations in the heat capacity of the sample due to changes in temperature and concentration is explored. Shortcomings in the simple interpretation of adiabatic data are identified and isothermal heatflow calorimetry is used to reveal autocatalytic effects which were not apparent from the adiabatic experiments. A more rigourous interpretation of the adiabatic and isothermal data is outlined and used to predict the conditions which can lead to exothermic runaway in a batch reactor. Mathematical simulation of the conditions in a jacketed reactor is used to demonstrate the importance of developing reliable kinetic expressions before assessing the safety of a batch process.

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Zusammenfassung Anhand einer einfachen Veresterungsreaktion wurden Standardverfahren zur Ermittlung thermokinetischer Parameter exothermen Reaktionen aus adiabatischen kalorimetrischen Daten demonstriert. Dabei wurde der Einfluß von Temperatur und Konzentration auf Änderungen der Wärmekapazität untersucht. Fehler bei der einfachen Interpretation adiabatischer Daten wurden identifiziert und isotherme Wärmeflußkalorimetrie wurde angewendet, um autokatalytische Effekte aufzuzeigen, die sich anhand der adiabatischen Experimente nicht ersehen lassen. Es wurde eine gründlichere Interpretation adiabatischer und isothermer Daten umrissen und verwendet, um die Bedingungen vorherzusagen, die in einem Kesselreaktor zu einem exothermen Davonlaufen der Reaktion führen. Mathematische Simulation der Bedingungen in einem Mantelkessel wurde angewendet, um zu zeigen, von welch großer Bedeutung die Entwicklung zuverlässiger kinetischer Ausdrücke ist, bevor man die Sicherheit einer Reaktion in einem Kesselreaktor beurteilt.

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A new technique of analysis for the investigation of kinetic data using the differential scanning calorimeter

This method of analysis for kinetic data of solid state chemical reactions takes advantage of the binomial series expansion to normalize various mathematical expressions related to various solid state models into a power series. This facilitates analysis by computer methods, in that deviations of the various models will be perceptible at the outset.     

An investigation of the adiabatic potential energy surface of a Pseudo-Jahn-Teller complex using X-ray diffraction

X-ray diffraction combined with theoretical results obtained for isolated molecules can reveal many topologic features of the adiabatic potential energy surface (APS) of pseudo-Jahn-Teller Cu(II) complexes. Single-crystal x-ray results of acetatobis (1,10-phenanthroline)copper(II) perchlorate from 10 to 351 K are presented. The observed Cu-O bond length changes of 0.26 and 0.38 Å are rationalized in terms of a one-dimensional APS with two nonequivalent minima. The Silver and Getz model of vibronic coupling applied to the temperature variation of the Cu-O bond lengths is not obeyed. The actual structures of the conformers associated with the energy minima were determined from the x-ray data. A means of estimating the pseudo-Jahn-Teller radius using mean-square vibrational amplitudes along the Cu-O bonds is also discussed.     

过氧化苯甲酰的热分解研究

The thermal decomposition process of benzoyl peroxide was investigated by Accelerating Rate Calorimeter. The curves of thermal decomposition temperature and pressure versus time for the systems were obtained. The curves of temperature rising-rate versus thermal decomposition temperature were also obtained. After the data revision disposal and analysis processing, thermal decomposition parameters and kinetic data of benzoyl peroxide were calculated, respectively.     

An adiabatic calorimeter for use at intermediate and higher temperatures The heat capacity of synthetic sapphire (α-Al2O3) from 70 to 700 K

A vacuum adiabatic calorimeter for measurement of heat capacity was constructed, and has been successfully operated over the temperature range from 70 to 700 K. Its performance was examined by measurements on the standard reference sample of synthetic sapphire (NBS SRM 720). The accuracy was proved to be better than 0.2 per cent, which is comparable with that of the best calorimeters hitherto reported.     

Asymmetric synthesis of an enantiomerically pure rivastigmine intermediate using ketoreductase

A novel chemo-enzymatic synthesis of (S)-rivastigmine using ketoreductases with NADH/NADPH as the proton donor has been demonstrated. An exclusive enzymatic process has been developed by exploring the possible ketoreductases by screening to identify enzymes useful for the preparation of the (S)-isomer intermediate, and scaling up of the enzymatic process for the production of an adequate, enantiomerically pure precursor of rivastigmine and for the total synthesis of (S)-rivastigmine.