Injection effect on the sensitivity in an isothermal titration calorimeter

By using electrical calibrations and with the injection of liquids with very different heating capacities (water and cyclohexane), it is made a thorough evaluation of the ‘injection effect’ in terms of the parameter ρc _p f (ρc _p – volumetric heat capacity, f – injection flow) in an isothermal titration calorimeter. This effect can be evaluated accurately in the case of non-volatile liquids, however, when dealing with volatile liquids, the uncertainty in their determination increases because of the vaporization heat.     

Flow microcalorimeter for heat capacities of solutions

A new type of flow microcalorimeter for measuring heat capacities at constant pressure of liquids and solutions was constructed. This calorimeter is the similar in design to Picker's except for the flow system, which consists of two syringe type of pumps and two flowing paths in each flow cell. It was found that the magnitude of heat loss from cells depended on liquids themselves used and the flow rates of sample liquids. The molar heat capacities, C_p of benzene and ethanol were determined relative to those of cyclohexane and water, respectively. The excess molar heat capacities, C_p(E) for the systems of benzene + cyclohexane and water + ethanol were also determined at 298.15K by the direct mixing method. An inaccuracy for C_p(E) was estimated to be within ± 1%.     

Comparing Methods for Calculating the Heat Flow Rate of Reactions in Different Bench-Scale Calorimeters

Summary: A transfer function of the RC1e™ (Mettler-Toledo) calorimeter was obtained by calibration with a heating cartridge. With this function it was possible to determine the heat flow rate and total heat of different polymerization reactions. The calorimeter operates in isothermal as well as in isoperibolic mode. Additionally, 1-vinyl-2-pyrrolidone and acrylic acid were polymerized in a three-neck flask. In this common laboratory device the heat flow rate was obtained by using a transfer function calculated by calibration with a heating cartridge. Thus, the heat of polymerization can be obtained without using a calorimeter and without solving the heat balance equation.     

Study on thermodynamic properties of glyphosate by oxygen-bomb calorimeter and DSC

The combustion enthalpy of glyphosate was determined by XRY-1C oxygen-bomb calorimeter at a constant volume. The standard mole combustion enthalpy and the standard mole formation enthalpy have been calculated to be ?1702.19 and ?1478.36 kJ mol^?1, respectively. For testing the reliability of instrument, glycine and naphthalene were used as reference materials by comparing the measured values with the literature values, the absolute error and relative error are 2.58 kJ mol^?1 and 0.26 % for glycine, respectively, and these of naphthalene are 4.08 kJ mol^?1 and 0.08 %, respectively. Moreover, the constant-pressure heat capacities c _p of glyphosate were measured by differential scanning calorimetry in the temperature range 303.15–365.15 K, and the relationship between c _p and temperature was established. These related studies can provide a thermodynamic basis for their further application.     

High-precision adiabatic calorimetry and the specific heat of cyclopentane at low temperature

We describe a fully automated adiabatic calorimeter designed for high-precision covering the temperature range 15 to 300 K. Initial measurements were performed on synthetic sapphire (20 g). The statistical error of the apparatus estimated from the scattering of theC _p data of sapphire is about 0.1% and the average absolute error of specific heat between 100 and 300 K was 0.7% compared to values given in the literature. The heat capacity and the three phase transitions of cyclopentane (C₅H₁₀) which is recommended as a standard for the temperature calibration of scanning calorimeters have also been measured. The transition temperatures were determined to be (literature values in parentheses): 122.23 K (122.39 K) 138.35 K (138.07 K) and 178.59 K (179.69 K), with an experimental error of ±40 mK.     

Thermodynamic Properties of Liquid n-Pentadecane

Abstract

This paper reports experimental results concerning the isobaric heat capacity C_p of Liquid n-pentadecane as a function of pressure (up to 100 MPa) and temperature (313.15 to 373.15 K). The measurements were performed with a modified C80 SETARAM calorimeter based on the Calvet principle. These calorimetric data, combined with density data, were used to evaluate derived thermophysical properties such as the isochoric heat capacity C_v , the isentropic compressibility k_s and the speed of sound u in the same ranges of pressure and temperature. The pressure-temperature behaviour of these properties was then discussed as a model for simple organic liquids.     

Low-temperature heat capacities and derived thermodynamic functions of cyclohexane

The low-temperature heat capacities of cyclohexane were measured in the temperature range from 78 to 350 K by means of an automatic adiabatic calorimeter equipped with a new sample container adapted to measure heat capacities of liquids. The sample container was described in detail. The performance of this calorimetric apparatus was evaluated by heat capacity measurements on water. The deviations of experimental heat capacities from the corresponding smoothed values lie within ±0.3%, while the inaccuracy is within ±0.4%, compared with the reference data in the whole experimental temperature range. Two kinds of phase transitions were found at 186.065 and 279.684 K corresponding solid-solid and solid-liquid phase transitions, respectively. The entropy and enthalpy of the phase transition, as well as the thermodynamic functions {H_(T)-H _{298.15 K}} and {S _(T)-S_{298.15 K}}, were derived from the heat capacity data. The mass fraction purity of cyclohexane sample used in the present calorimetric study was determined to be 99.9965% by fraction melting approach. This revised version was published online in July 2006 with corrections to the Cover Date.     

Advanced Calorimetric Techniques in Polymer Engineering

Summary: In polymer synthesis, reaction calorimetry (RC) is an appropriate technique for on-line process monitoring, since polymerization reactions are highly exothermic. Measurements are noninvasive, rapid, and straightforward. Nowadays RC is the technique recognized as the most powerful way to study such process in near-to-the- industrial conditions. Our approach was focused on temperature oscillation calorimetry (TOC). Two different reaction calorimeters were used, i.e. a isoperibolic calorimeter and a Calvet type high sensitivity differential calorimeter, respectively. A special attention was paid to the interpretation of the measured signals in order to obtain reliable calorimetric data. The evolution of heat transfer coefficient UA was followed by performing appropriate Joule effect calibrations, before and after the reaction. A convolution differential method of the measured heat flow by the generated one was used for determining the time constants and deconvoluting the measured heat flow.     

Thermochemistry study on H2O/NaY zeolite adsorption system

By using an automatic adiabatic calorimeter the heat capacity measurements in the temperature range of 220—320K for H₂O/NaY zeolite adsorption system with various amounts of adsorbed water have been made. In c_p-T curves obtained, there is no peak for solid-liquid phase transition of the adsorbed water. But for H₂O-NaY zeolite system which consists of a saturated H₂O/NaY adsorption system mixed mechanically with a certain amount of water, there are distinct peaks in their c_p-T curves. The peak in the c_p-T curve disappeared as soon as the mixed water in the latter system was evacuated. The facts mentioned above have been discussed from the point of view of the structure of the adsorbed layer and the pore size of zeolite.     

Standard enthalpy of formation of fluorinated graphite CF0.96

The energy of combustion ?? _c U ⁰ of fluorinated graphite CF_0.96 has been determined using an isoperibolic calorimeter with a rotating platinized bomb and the enthalpy of formation ?? _f H ⁰ thereof has been calculated. The enthalpy of the dissociation of the C-F bond has been calculated from the obtained value of ?? _f H⁰(CF_0.96) and compared with analogous values for the previously investigated C₆₀ fullerene fluorides.     

Changes in the Transfer Function of a flow microcalorimeter

Flow microcalorimeters are used to determine thermodynamic properties of liquid mixtures, the accuracy of these measures depends on the right calibration of the instrument. In this work the system is identified by means of the transfer functions of the two poles, it is proven that the first time constant and the sensitivity change with the value of rc _p f of the injected liquids (r - density, c _p - heat capacity, f - injection flow), and that the sensitivities obtained in the electrical and chemical calibrations are different for the same value of rc _p f because the dissipation in each case does not occur in the same place. As a summary of the calibration carried out, it is proposed a sensitivity value of 313±4 mV W^-1 for rc _p f<15 mW K^-1 that permits to make thermal measures with an uncertainty of 3%. This revised version was published online in July 2006 with corrections to the Cover Date.     

The enthalpy of formation of fullerene fluoride C<Subscript>60</Subscript>F<Subscript>18</Subscript> and the C-F bond energy

The enthalpy of combustion of crystalline fullerene fluoride C₆₀F₁₈ was determined in an isoperibolic calorimeter with a rotating platinized bomb, and the enthalpy of formation of the compound was calculated. The enthalpy of sublimation of C₆₀F₁₈ measured earlier was used to calculate the enthalpy of formation of fullerene fluoride in the gas phase and the mean enthalpy of dissociation of C-F bonds in this compound.     

Construction,calibration and testing of a micro-combustion calorimeter

An isoperibolic micro-combustion calorimeter was designed, built and set up in our laboratory, taking as base a 1107 Parr combustion bomb of 22 cm³ of volume. Taken into account the geometrical form of the bomb, it was designed and constructed a vessel and a submarine chamber in brass. All of the pieces of the calorimeter were chromium-plated to reduce heat loss by radiation. The calorimeter was calibrated by using pellets of standard benzoic acid (mass approximate of 40 mg) leading to the energy equivalent of ε(calor) = (1283.8 ± 0.6) J · K⁻¹. In order to test the calorimeter, combustion experiments of salicylic acid were performed leading to a value of combustion energy of Δ_cu^∘ = −(21,888.8 ± 10.9) J · g⁻¹, which agrees with the reported literature values. The combustion of piperonylic acid was carried out as a further test leading to a value of combustion energy of Δ_cu^∘ = −(20,215.9 ± 10.4) J · g⁻¹ in accordance with the reported literature value. The uncertainty of the calibration and the combustion of salicylic acid and piperonylic acid was 0.05%.     

A reinvestigation of the hypersonic properties and the specific heat capacity of PMMA around the quasi-static glass transition II. High performance caloric investigations

To continue dynamicc _p measurements in the range of smallest temperature rates and non-linear thermal relaxation investigations into the linear range, simultaneousc _p and thermal relaxation measurements were carried out in an adiabatic vacuum calorimeter, using the pulse heating method. The rate-dependentc _p behaviour, known from dynamic measurements, does not continue at small temperature rates. This is confirmed by the relaxation process which is observed. The results suggest an extended interpretation of the glass transition in atactic polymethylmethacrylate (PMMA).     

Low‐Temperature Heat Capacities and Standard Molar Enthalpy of Formation of Gramine (C11H14N2)

Low‐temperature heat capacities of gramine (C₁₁H₁₄N₂) were measured by a precision automated adiabatic calorimeter over the temperature range from 78 to 401 K. A polynomial equation of heat capacities as a function of temperature was fitted by least squares method. Based on the fitted polynomial, the smoothed heat capacities and thermodynamic functions of the compound relative to the standard reference temperature 298.15 K were calculated and tabulated at 5 K intervals. The constant‐volume energy of combustion of the compound at T=298.15 K was measured by a precision oxygen‐bomb combustion calorimeter as Δ_cU=−(35336.7±13.9) J·g⁻¹. The standard molar enthalpy of combustion of the compound was determined to be Δ_cH_m⁰=−(6163.2±2.4) kJ·mol⁻¹, according to the definition of combustion enthalpy. Finally, the standard molar enthalpy of formation of the compound was calculated to be Δ;_cH_m⁰=−(166.2±2.8) kJ·mol⁻¹ in accordance with Hess law.     

烟酸的低温热容和标准摩尔生成焓

利用精密自动绝热热量计测量了分析纯烟酸在78～400 K温区的低温热容. 用最小二乘法将实验摩尔热容对温度进行拟合, 得到了热容随温度变化的多项式方程. 用此方程进行数值积分, 得到在此温区每隔5 K的舒平热容值和相对于298.15 K时的热力学函数值. 利用精密静止氧弹燃烧热量计测定了烟酸在298.15 K时的恒体积燃烧能为 Δ_cU＝ －(24528.3±16.1) J•g^－1. 依据物质燃烧焓定义计算出烟酸的标准摩尔燃烧焓为: Δ_cH_m^o＝－(3019.05±1.98) kJ•mol^－1. 最后, 依据Hess定律计算出烟酸的标准摩尔生成焓为: Δ_fH_m^o＝－(56.76±2.13) kJ•mol^－1.     

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.     

Standard formation enthalpies for α-amino acids: L-serine,L-arginine,and L-tyrosine

The energies of combustion, Δ _c U ⁰, of three amino acids: L-serine (I), L-arginine (II) and L-tyrosine (III) in the crystalline state at 298.15 K were determined using a static-bomb isoperibolic calorimeter. From these data, the enthalpies of combustion, Δ _c H ⁰, and the enthalpies of formation, Δ _f H ⁰, are calculated. The Δ _f H ⁰ values are compared with the published data.     

Thermochemical study of aqueous solutions of lithium diclofenac at 293.15–318.15 K

The enthalpies of solution and dilution of aqueous solutions of lithium diclofenac (LiDC) are measured in the concentration range of 0.002–0.047m at 293.15, 298.15, 308.15, and 318.5 K using an isoperibolic calorimeter. The heat capacity of solid LiDC in the temperature range of 273.15–373.15 K is determined using a DSC 204 F1 Phoenix differential scanning calorimeter (NETZSCH, Germany). The virial coefficients of the enthalpy characteristics of a water-LiDC solution are derived in terms of the Pitzer model to calculate a wide range of thermodynamic properties of both the solution and its components. Changes in these characteristics as a function of concentration and temperature are discussed.