Determination Of Heat Capacity Research Articles

Hole Transport Materials Based Thin Films: Topographic Structures and Phase Transition Thermodynamics of Triphenylamine Derivatives

The topographic structural analysis of thin films of triphenylamine (TPA) derivatives, obtained by vacuum deposition, is presented. The topology of the films is highly dependent on the number of phenyl rings as well on the presence of methyl groups. The glass transition temperatures can be predicted from the melting temperatures, according to the molecular symmetry, flexibility, and molecular size of the amorphous nonplanar materials suitable for long-time use in OLED based devices. A phase transition thermodynamics study, including vapor pressure and heat capacity determinations of some hole transport materials based triphenylamine derivatives (DDP, p-TTP, TPB, TPD, TDAB, and m-MTDAB) is presented. Analysis of the enthalpic and entropic contributions provides an understanding of the fusion temperature differentiation, which results in higher melting points for TDB and TDAB and lower values for TPD and m-MTDAB, due to the presence of meta-CH3 groups. The thermodynamic parameters of sublimation were used to explain the slightly higher volatility of solid DDP relative to p-TTP and the similarity between the volatilities of solids TPB and TDAB.

Solids Modelling and Capture Simulation of Piperazine in Potassium Solvents

Piperazine is an amine which is used both as an activator or promoter, but also as active component in CO2 capture solvents. High concentrations are being formulated to draw benefit of the PZ properties. This results in a risk of precipitation of PZ and other solid phases during capture. It could be a benefit to the capture process, but it could also result in unforeseen situations of potential hazardous operation, clogging, equipment failure etc.Security of the PZ process needs to be in focus. Flow assurance requires additional attention, especially due to the precipitation phenomenon. This entails all parts of the streams, but also during formulation and transport of the solvent.In this work the extended UNIQUAC thermodynamic model is presented with the addition of piperazine (PZ or PIPH2) in combination with the potassium ion of mixtures with CO2 in equilibration with KOH-KHCO3-K2CO3. Phase boundaries are laid out which shows the concentration regions of solid formation. A special focus will be given to the boundary where precipitations occur.The model is a generic. It builds on consistent parameters of the extended UNIQUAC model previously published. It allows for accurate vapor liquid equilibrium (VLE) calculation, heat capacity determination, and similar thermodynamic properties. It especially allows for determination of solid liquid equilibria (SLE) and heat of absorption/heat of desorption which are core variables in the determination of energy requirements for CO2 capture. In this work the typical phase behavior will be shown for the PZ solvent with potassium (K2CO3/KHCO3) for CO2 capture. Conclusions are given on a solvent compositions resulting in low heat requirements using the predictive nature of the extended UNIQUAC model. Concentration of a PZ/K2CO3 solvent is suggested with a heat of absorption/desorption of 40kJ/mol.

Responses to the comments concerning “Determination of specific heat capacity and standard molar combustion enthalpy of taurine by DSC”

Responses to the comments concerning “Determination of specific heat capacity and standard molar combustion enthalpy of taurine by DSC”

Comments concerning “Determination of specific heat capacity and standard molar combustion enthalpy of taurine by DSC”

In a recent article appearing in this Journal, Han et al. [1] reported the specific heat capacity and standard molar combustion of taurine. There are several errors in the paper, and the quality of the measured calorimetric data is highly questionable. In Table 4 of the manuscript the authors tabulate a numerical of –DcUm/kJ mol -1 = 2545.7 based on four replicate measured values of 2554.5, 2430.5, 2497.9, and 2700.1. The calculated average value and corresponding standard deviation of –DcUm/kJ mol -1 = 2545.7 ± 114.7 shows that the measured values were not very reproducible. Combustion measurements are normally much more reproducible than this. Moreover, Yan et al. [2] reported a numerical of –DcUm/kJ mol -1 = 1611.8 ± 0.1. Han et al. did not reference the earlier work of Yan et al., and their measured value of –DcUm/kJ mol -1 = 2545.7 differs significantly from the published literature, even when the abnormally large standard deviation of 114.7 kJ mol in the Han et al. value is taken into account. Han et al. [1] calculate the standard molar of formation of taurine, based on the following combustion reaction:

High temperature calorimetry and use of magnesium chloride for thermal energy storage

The primary objective of this study is to develop encapsulated phase change materials (EPCMs) capable of storing thermal energy at temperatures above 750 °C. EPCM with magnesium chloride as phase change material (PCM) are considered here for application in concentrated solar power (CSP) systems. MgCl2 is an effective storage medium because of its high melting temperature, 714 °C, and high latent heat of fusion, 454 kJ/kg. A specialized calorimeter with requisite size and high temperature capability is designed and built to prove the storage capability of MgCl2 EPCM. The calorimeter is also used to determine heat capacities for MgCl2 in both liquid and solid states as well as its latent heat of fusion. Calorimetric tests for the thermal storage capacities of three MgCl2 EPCM samples show excellent agreement with published data. Based on the measured properties, the latent heat of phase change can contribute about 84% of the storage capacity of MgCl2 PCM for a 100 °C temperature swing bracketing the salt's melting point. Repeated thermal-cycles show sustained performance of MgCl2 EPCM capsules with no discernible diminishment in storage capacity.

Determination of effective thermal conductivity and specific heat capacity of wood pellets

Effective thermal conductivity and specific heat capacity are important properties for studying the self-heating during wood pellets storage. A modified line heat source within a wood pellets container was used to determine the thermal conductivity and specific heat capacity of wood pellets with moisture content ranging from 1.4% to 9%w.b. A second order partial differential equation describing transient temperature distribution within the test container was numerically solved for temporal and spatial temperatures. The difference between experimental and numerical temperatures was minimized to estimate an effective thermal conductivity and specific heat capacity for the bulk pellets. The estimated thermal conductivity ranged from 0.146 to 0.192W/(mK) increasing with moisture content. An empirical relationship among effective thermal conductivity, moisture content and porosity was developed. The dependence of effective thermal conductivity on pellets size was negligible. The estimated specific heat capacity of pellets ranged from 1.074 to 1.253kJ/(kgK) in the tested range. A relation between specific heat capacity and moisture content was developed for general wood pellets.

A New Method for the Determination of the Specific Heat Capacity Using Laser-Flash Calorimetry Down to 77K

A new method for evaluation of the specific heat capacity in the temperature regime between 77K and 330K using laser-flash calorimetry is presented. Usually, laser-flash calorimetry is accomplished by performing an additional laser-flash measurement on a reference specimen with a known specific heat capacity and by comparing the maximum rear-side temperatures rises. In this study, the calibration is achieved by comparison of the rear-side temperature rise to specific-heat-capacity data determined by other methods in an adjacent temperature regime. Subsequently, the thus yielded proportional factor is used for the evaluation of the specific heat capacity from laser-flash measurements at temperatures where no specific-heat-capacity data are available. The reliability of this method is shown by performing measurements on a material with known specific heat capacity, aluminum oxide. Furthermore, the specific heat capacity and thermal conductivity of borosilicate crown glass (BK7) was determined experimentally.

Comment on “Rapid chemical and topological ordering in supercooled liquid Cu46Zr54”

In their recent publication, Wessels et al. [Phys. Rev. B 83, 094116 (2011)] present evidence of rapid ordering in a supercooled Cu${}_{46}$Zr${}_{54}$ liquid. A part of their supporting argument is based on an experimentally observed peak in the specific heat capacity of a Cu${}_{46}$Zr${}_{54}$ melt as a function of temperature. The experimental observations are supported by classical molecular dynamics (MD) simulations for which the phase trajectory is modeled using an embedded-atom model. We believe that (i) the hypothesis that has led to the determination of the specific heat capacity as a function of temperature, (ii) the MD general simulation procedure, and (iii) the interpretation of the experimental evidence are not fully justified, and this alters some of the conclusions of their paper.

Calculation of the standard molal thermodynamic properties of crystalline peptides

To augment the relatively sparse set of thermodynamic data available for high molecular weight biopolymers, group additivity algorithms have been developed to estimate the heat capacity power function coefficients and standard molal thermodynamic properties of crystalline peptides in the multitude of biogeochemical environments in which they are found. Group contributions representing the 20 common amino acids plus 5-hydroxylysine and 4-hydroxyproline for each coefficient and property were generated using the thermodynamic properties of crystalline amino acids, polypeptides and other organic compounds. These group contributions were in turn used to compute the thermodynamic properties of naturally occurring proteins that are found in a crystalline state in cells. The coefficients and properties of the model compounds, group contributions and proteins are tabulated. In a demonstration of the uncertainty of the thermodynamic properties of the groups generated in this study, experimentally determined heat capacities and entropies of crystalline homopolypeptides and proteins taken from the literature have been compared to estimates of these quantities. Additionally, standard molal volumes for 24 amino acids have been recalculated in light of inconsistencies in an earlier analysis, and the standard molal thermodynamic properties of aqueous and crystalline methionine at 25°C and 0.1MPa have been reassessed. Calculations of this kind can be carried out to thermodynamically describe the biogeochemical interactions throughout the broad range of environmental settings in which they are known to occur.

Coarse-grained model for protein folding based on structural profiles

We study a coarse-grained protein model whose primary characteristics are (i) a tubelike geometry to describe the self-avoidance effects of the polypeptide chain and (ii) an energy function based on a one-dimensional structural representation. The latter specifies the connectivity of a sequence in a given conformation, so that the energy function, rather than favoring the formation of specific native pairwise contacts, promotes the establishment of a specific target connectivity for each amino acid. We show that the resulting dynamics is in good agreement with both experimental observations and the results of all-atoms simulations. In contrast to the latter, our coarse-grained approach provides the possibility to explore longer time scales and thus enables one to access, albeit in less detail, larger regions of the conformational space. We illustrate our approach by its application to the villin headpiece domain, a three-helix protein, by studying its folding behavior and determining heat capacities and free-energy landscapes in various reaction coordinates.

Experimental determination of heat capacities and their correlation with theoretical predictions

We discuss an experiment for determining the heat capacities of various solids based on a calorimetric approach where the solid vaporizes a measurable mass of liquid nitrogen. We demonstrate our technique for copper and aluminum, and compare our data with Einstein’s model of independent harmonic oscillators and the more accurate Debye model. We also illustrate an interesting material property, the Verwey transition in magnetite.

Determination of the individual specific heat capacities of solids from multi-component powder mixtures and polymorphic mixtures

This study describes a method to determine the specific heat capacities of individual solids from multi-component solid mixtures. To achieve this end, powder X-ray diffraction measurements are used to provide information on the number and identity of constituents as well as their compositions while calorimetry measurements give the specific heat capacities of the bulk solid mixtures. The method is applied to investigate three different solid mixture systems, namely (i) ternary organic mixtures containing α-glycine, α-lactose monohydrate, and paracetamol; (ii) ternary inorganic mixtures containing calcium fluoride, titanium nitride, and tungsten carbide; and (iii) polymorphic mixtures of α- and γ-glycine. All systems are investigated at 298.15 K and at atmospheric pressure. The results show that the specific heat capacities of individual solids determined from multi-component solid mixtures are in good agreement with those directly determined from pure solid compounds.

Quaternary phosphonium-based ionic liquids: Thermal stability and heat capacity of the liquid phase

In spite of the great importance of calorimetric data on phosphonium-based ionic liquids (PBILs), the information available in the literature is quite limited. This work reports the study of the thermal stability and the determination of heat capacity of the following (PBILs): tributyl(methyl)phosphonium methyl sulfate, [(C 4) 3PC 1][MeSO 4], trihexyl-tetradecylphosphonium chloride, [(C 6) 3PC 14][Cl], trihexyl-tetradecyl-phosphonium dicyanamide, [(C 6) 3 PC 14][DCA], trihexyl-tetradecylphosphonium bis((trifluoromethyl)sulfonyl) imide, [(C 6) 3 PC 14][NTf 2], and trihexyl-tetradecylphosphonium tris(pentafluoroethyl)trifluorophosphate, [(C 6) 3 PC 14][FAP]. Measurements on the well-known IL 1-ethyl-3-methylimidazoliumbis((trifluoromethyl)sulfonyl)imide, [EMIM][NTf 2], were also performed for comparative purposes. The thermal stability was assessed by conventional and high resolution modulated thermogravimetric analysis within the interval (303 to 873) K. The heat capacity was measured by modulated differential scanning calorimetry within the range (310 to 515) K with an uncertainty in the range (1 to 5) J · K −1 · mol −1. The experimental results were correlated using polynomial expressions. The Joback method for predicting ideal gas heat capacities was used in conjunction with the principle of corresponding states and the modified Lydersen–Joback–Reid method to predict the heat capacity of the ILs. The methods due to Valderrama et al. were also used with the same purpose.

E. Wilhelm and T. M. Letcher (eds): Heat capacities: liquids, solutions and vapours

Chemical thermodynamics continues to be a subject of major importance for the understanding of phase transitions, chemical reactions, and (increasingly) biophysical processes, as well as its fundamental role in discussion of alternative future energy sources. This volume, which is published under the auspices of the International Union of Pure and Applied Chemistry and the International Association of Chemical Thermodynamics, is the latest in a series of volumes to be published by these organisations that describe the state of the art instrumentation and experimental techniques for acquisition of thermodynamic property data for fluids, the critical evaluation of these data and the representation by equations of their dependence on variables such as temperature, pressure, and composition. The practical realization of these equations lies in their incorporation in computer simulation packages of chemical engineering processes. The importance of heat capacities arises because they are intimately related to the temperature dependence of thermodynamic functions, and because they link thermodynamics with microscopic fluid structure. The topics covered in the 22 chapters in this volume include the underlying theory and the most important experimental techniques for direct and indirect determination of heat capacities; their application to gases at low and high pressure, to liquids at low and high pressure, to electrolyte and non-electrolyte solutions, to polymeric systems, to proteins and liquid crystals, plastic crystals and ionic liquids, and molten salts. There is a discussion of heat capacities in the critical region, of computer simulation studies of heat capacity effects associated with hydrophobic effects and of partial molar heat capacity changes of gases dissolved in liquids. The coverage by an international team of 35 authors, is wide-ranging though it should be mentioned that some topics, such as chemically reactive systems, are not included. This book will be welcomed by researchers in chemical thermodynamics in academia and in the chemical industry.

Determination of Accurate Specific Heat Capacities of Liquids in a Reaction Calorimeter, by Statistical Design

A method using statistical design is proposed to determine the measurement error of specific heat capacities (Cp) of liquids in any reaction calorimeter. This method only takes into account the experimental specific heat of the liquid, its volume and the reactors stirring rate. With the RC1e calorimeter used in this study, the Cp measured by its QuickCal mode was overestimated by up to 0.4 J·g–1·K–1, whereas with its RTCal mode, more accurate values of Cp (± 0.2 J·g–1·K–1) were obtained. The statistical model obtained based on the QuickCal mode predicts experimental conditions which improve the accuracy of Cp, and could also be used to correct the value of Cp in the rest of the experimental domain. The corrected values of Cp for test solvents using this model were close to those cited in literature (≤5%). As an application, the specific heat capacities at 25 °C of less well documented solvents were determined: anisole, ethyl-tertiobutylether, methyl-tetrahydrofurane, diethoxymethane, dimethyl-ethyleneurea...

Determination of specific heat capacity and standard molar combustion enthalpy of taurine by DSC

Abstract Using XRY-1C calorimeter, the standard molar enthalpy of taurine was determined to be −2546.2 kJ mol−1. The reliability of the instrument used was tested by using naphthalene as reference material; and through comparing the molar combustion enthalpy of naphthalene measured with its standard value found in literature, the absolute error and relative error were found to be 4.53 kJ mol−1 and 0.09%, respectively. The melting point and melting enthalpy of taurine were determined by Differential Scanning Calorimetry (DSC), which was found to be 588.45 K and −22.197 kJ mol−1, respectively. Moreover, using the DSC method, the specific heat capacities Cp of taurine was measured and the relationship between Cp and temperature was established. The thermodynamic basic data obtained are available for the exploiting new synthesis method, engineering design and industry production of taurine.

Thermal Relaxation and Heat Transport in the Spin Ice Material Dy2Ti2O7

The thermal properties of single crystalline Dy2Ti2O7 have been studied in a temperature range from 0.3 K to 30 K and magnetic fields applied along [110] direction up to 1.5 T. Based on a thermodynamic field theory various heat relaxation and thermal transport measurements were analysed. So we were able to present not only the heat capacity of Dy2Ti2O7 in the whole temperature and magnetic field range, but also the different contributions of the magnetic excitations and their corresponding relaxation times in the spin ice phase. In addition, the thermal conductivity and the shortest relaxation time were determined by thermodynamic analysis of steady state heat transport measurements. Finally, we were able to reproduce the temperature profiles recorded in heat pulse experiments on the basis of the thermodynamic field theory using the previously determined heat capacity and thermal conductivity data without additional parameters. Thus, the thermodynamic field theory has been proved to be thermodynamically consistent in describing three thermal transport experiments on different time scales. The observed temperature and field dependencies of heat capacity contributions and relaxation times indicate the magnetic excitations in the spin ice material Dy2Ti2O7 as thermally activated monopole-antimonopole defects.

Determination of heat capacities and thermodynamic properties of two structurally unrelated but isotypic calcium and manganese(II) 2,6-naphthalene dicarboxylate-based MOFs

Abstract Two metal-organic frameworks, Ca(2,6-NDC)(DMF) (1) and Mn3(2,6-NDC)3(DMF)4 (2) (where 2,6-NDC = 2,6-naphthalene dicarboxylate and DMF = N,N′-dimethylformamide) have been solvothermally synthesized under optimized conditions and characterized by X-ray powder diffraction, elemental analysis, FT-IR spectroscopy, and TG analysis. The thermal decomposition characteristics were investigated under air atmosphere from 300 to 1,170 K (for 1) and from 300 to 971 K (for 2). The molar heat capacities were measured from 198 to 548 K (for 1) and from 198 to 448 K (for 2) by temperature modulated differential scanning calorimetry (TMDSC) for the first time. The fundamental thermodynamic parameters such as entropy and enthalpy variations with temperature were calculated based on the experimentally determined molar heat capacities.

Studi Transformasi Fasa Sistem Besi Karbon Dengan Pengamatan Thermal Diferensial

Phase Transformation Studies of Fe-C System with Differential Thermal Analyzer: Phase transformation studies for ironcarbon (Fe-C) system have been done by means of Differential Thermal Analyzer, DTA. Fe-C samples of nominal compositions for respectively low carbon containing alloy (0.1 wt.%), hypo eutectoid (0.4 wt.%), and eutectoid (0.8 wt.%) were prepared by powder metallurgy process using pure Fe and C powder materials (>99 %) as the feed stock. Measurement by DTA in the temperature range 25 oC–1100 oC for the samples indicated that there are two endothermic temperatures transition in pure Fe sample respectively at 773.8 oC associated with phase transformation of ferromagnetic (α) to paramagnetic (β) and at 930 oC due to a phase transformation of β-ferrite to austenite (γ). The two transition temperature was also consistently observed in all Fe-C samples but with one additional temperature transition at about 753 oC associated with a phase transformation of pearlite to austenite. Data of heat change measurement in the temperature range 25 oC-1100 oC were subsequently used for determination of heat capacity, Cp for the Fe-C samples as the function of T. Cp (T) curves when fi tted by polynomial regression have resulted in regression coeffi cients between 0.8 and 1.0. Keywords: Pearlite, eutectoid, ferromagnetic, entalphy, iron-carbon system, phase transformation

Solvated Crystalline Forms of Nevirapine: Thermoanalytical and Spectroscopic Studies

The study is aimed at exploring the utility of thermoanalytical methods in the solid-state characterization of various crystalline forms of nevirapine. The different forms obtained by recrystallization of nevirapine from various solvents were identified using differential scanning calorimetry and thermogravimetric analysis (TGA). The appearance of desolvation peak accompanied by weight loss in TGA indicated the formation of solvates: hemi-ethanolate (Form I), hemi-acetonitrilate (Form II), hemi-chloroformate (Form III), hemi-THF solvate (Form IV), mixed hemi-ethanolate hemi-hydrate (Form V), and hemi-toluenate (Form VI). The higher desolvation temperatures of all the solvates except toluenate than their respective boiling point indicate tighter binding of solvent. Emphasis has been laid on the determination of heat capacity and heat of solution utilizing microreaction calorimeter to further distinguish the various forms. The enthalpy of solution (ΔH(sol)), an indirect measure of the lattice energy of a solid, was well correlated with the crystallinity of all the solid forms obtained. The magnitude of ΔH(sol) was found to be -14.14 kJ/mol for Form I and -2.83 kJ/mol for Form V in phosphate buffer of pH 2, exhibiting maximum ease of molecular release from the lattice in Form I. The heat capacity for solvation (ΔC(p)) was found to be positive, providing information about the state of solvent molecules in the host lattice. The solubility and dissolution rate of the forms were also found to be in agreement with their enthalpy of solution. Form (I), being the most exothermic, was found to be the most soluble of all the forms.