Specific heat capacities of pure triglycerides by heat-flux differential scanning calorimetry

The specific heat capacities of some triglycerides commonly found in palm oil were determined with a heat-flux differential scanning calorimeter. The specific heat capacity measurements were made under the optimum operating conditions determined earlier: scan rate 17 deg·min^?1, sample mass 21 mg and purge gas (nitrogen) flow rate 50 ml/min. Pure triglycerides (four simple and four mixed) were used in the experiments. The four simple triglycerides were trilaurin, trimyristin, tripalmitin and tristearin, and the mixed triglycerides were 1,2-dimyristoyl-3-oleoyl, 1,2-dimyristoyl-3-palmitoyl, 1,2-dipalmitoyl-3-oleoyl and 1,2-dioleoyl-3-palmitoyl. The results of this study are compared with literature values and also with values obtained by using estimation methods. The experimental specific heat capacities are within ±1% precision with a 95% confidence level.     

Determination of unfrozen matrix concentrations at low temperatures using stepwise DSC

The aim of the current study was to determine whether stepwise DSC (SW-DSC) is a suitable method for measuring the unfrozen matrix concentration (C_g) of binary aqueous solutions at temperatures as low as −50 °C. The optimal experimental conditions were determined using water. Reliable heat capacity values were determined at nominal scanning rates between 10 and 100 K min⁻¹, sample weights between 8 and 15 mg, and with the sample completely covering the base of the DSC pan. These conditions were then applied to aqueous solutions of ethylene glycol, glycerol and sodium chloride.The apparent heat is the sum of all heat including latent heat, heat capacity and heat of dilution. The influence of each term on the apparent heat was discussed in detail. The apparent heat values of the frozen samples were then used to calculate the ice fraction in the solution and were expressed as the C_g. The calculated C_g values were similar to previously published values. This study showed that SW-DSC can be used to determine the C_g over a wide temperature range using only one single solution. This technique is advantageous for solutes that are not available in large quantities.     

Multi-state transition for the thermal unfolding of certain globular proteins as evaluated from the analysis of DSC curve

Differential scanning calorimetry(DSC) has been performed on the thermally induced transitions of soybean trypsin inhibitor(STI) and of Taka-amylase A(TAA) in buffers by using the adiabatic differential heat capacity calorimeter. Thermodynamic parameters have been derived from the excess heat capacity curves and found to be ΔH = 19.8 ± 0.2 J/g and ΔC_p = 0.51 ± 0.02 J/(K g) for STI and ΔH = 37.4 ± 0.7 J/g and ΔC_p= 0.62 ± 0.09 J/(K g) for TAA.The theoretical DSC curves for the unfolding were drawn on the basis of van't Hoff relation and compared with the excess heat capacity curves observed. The unfolding of both the proteins may be characterized by a three-state process rather than a simple two-state process. This was best evident for TAA, but less evident for STI.     

Heat Transfer in a Disc-Type DSC Apparatus IV. Applicability of the coupled cells model to periodic temperature modulation

The application of non-linear heating programs to a heat-flux DSC apparatus has attracted much attention. On the basis of thermodynamics, the change in enthalpy of a sample during a temperature change ΔT is due, on the one hand to the true heat capacity of the sample ΔT C_pξ and on the other, to the enthalpy of some transformation occurring in the sample Δ_rH Δξ. These contributions can be separated on the basis of the kinetics of the transformation. The coupled cells model of a disc type, heat flux DSC apparatus has been tested, using true heat capacities and a sine modulation of the temperature of the furnace around a constant temperature. In the range from 2 to 60 mHz, the amplitude and phase shift of the calorimetric signal were measured at several frequencies. Theoretical equations, based on the model, and using the thermal Ohm's law explains the results with a reasonable accuracy. A non-linear DSC experiment affords two ways of determination of the heat capacity of a sample making possible a distinction between the enthalpic effect and heat capacity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Preparation and thermal properties of a novel flame retardant copolymer

A monomer, acryloxyethyl phenoxy phosphorodiethyl amidate (AEPPA), was synthesized and characterized using Fourier transform infrared (FTIR), ¹H nuclear magnetic resonance spectroscopy (¹H NMR) and ³¹P NMR. The copolymer with various amounts of styrene (St) was obtained by the free radical bulk polymerization between AEPPA and St, and characterized using ¹H NMR. The thermal properties of the copolymers were investigated with thermogravimetric analysis (TGA) in air and nitrogen atmosphere, and differential scanning calorimetry (DSC). The TGA results in air indicated the copolymers with AEPPA show higher thermal stability than those without AEPPA. However, the TGA results in nitrogen showed that the decomposition temperature decreased and the char residue increased with the increase of AEPPA. The glass transition temperature (T_g) of the copolymers from DSC indicated that a inverse proportion was observed between T_g and the amount of AEPPA incorporated. The flammability of the copolymers was evaluated by microscale combustion calorimeter (MCC). The MCC results showed that AEPPA can decrease the peak heat release rate (PHRR) and the heat release capacity (HRC), and the sample CP10 shows the lowest PHRR and HRC.     

Molecular structure and thermal behavior of N-Benzoyl-3,3-dinitroazetidine

N-Benzoyl-3,3-dinitroazetidine (BDNAZ) has been synthesized and characterized by elemental analysis, FT-IR spectroscopy, ¹H NMR and X-ray single crystal diffraction technique. BDNAZ crystallizes in the monoclinic space group P2₁/c. Its thermal behavior was studied under a non-isothermal condition by DSC and TG/DTG methods, the value of E _a and A of the exothermic decomposition reaction of BDNAZ are 143.19 kJ mol^?1 and 10^14.34 s^?1, respectively. The specific heat capacity of BDNAZ was determined with a continuous C _p mode of micro-calorimeter and theoretical calculation. The adiabatic time-to-explosion was evaluated as 109.9?C124.4 s.     

Synthesis and thermal characterization of sulfur containing methionine bridged cobalt(III) and copper(II) complex

The sulfur containing amino acid bridging polynuclear transition metal complex has been synthesized and characterized by different measurements such as UV?CVis, FT?CIR, C?CH?CN?CS, TG?CDTA, ICP-AES, differential scanning calorimeter (DSC), and XRD. DSC has showed negative specific heat of this polynuclear system and has used to evaluate some thermodynamic constants like activation energy (E _a), frequency factor (A), enthalpy, and entropy of that system. The specific heat capacity is measured at heating rate of 10?°C?min^?1 in room atmosphere of this polynuclear complex. The characterization of this complex has showed five Co(III) and four Cu(II) atoms and this complex contained ten sulfur containing methionine amino acid units.     

Non-isothermal decomposition of anhydrous silver malonate

The non-isothermal decomposition of anhydrous disilver malonate was studied up to 300°C by means of TG, DTA and DSC techniques in different atmospheres (e.g. N₂, H₂ and air). Acetic acid, CO₂, acetone and CO were identified as the volatile decomposition products using gas chromatography. Silver metal, on the other hand, was identified as the final solid product using X-ray powder diffraction. The mechanism described involves the breakdown of adsorbed radicals, probably including-CH₂COO- and related species, on the surface of the metallic silver product. The activation energy (ΔE) and the frequency factor (InA) were calculated for the decomposition process from the variation of peak temperature (of the DTA curves) with the rate of heating (φ). The enthalpy change (ΔH), the heat capacity (C _p) and entropy change (ΔS) were calculated from the DSC measurements.     

Measuring the Glass Transition of Thermosets by Alternating Differential Scanning Calorimetry

The glass transition temperature of thermosets is determined by alternating differential scanning calorimetry (ADSC), which is a temperature modulated DSC technique. The different values of the glass transition obtained from heat flow measurements (total and reversible) and heat capacity (modulus of the complex heat capacity) are analysed and compared with the values obtained by conventional DSC. The effect of the sample mass on the values of T_g, heat capacity and phase angle has been analysed. The effect of the thermal contact between sample and pan has been studied using samples cured directly inside the pan and disc-shaped samples of different thickness. The results obtained for the thermal properties and the phase angle are compared and analysed. The modulus of the complex heat capacity enables the determination of the dynamic glass transition, T_g, which is frequency dependent. The apparent activation energy ofthe relaxation process associated with the glass transition has been evaluated from the dependence of T_g on the period of the modulation.This revised version was published online in November 2005 with corrections to the Cover Date.     

Synthesis and High-Temperature Heat Capacity of Y<Subscript>2</Subscript>Ge<Subscript>2</Subscript>O<Subscript>7</Subscript>

Yttrium germanate Y₂Ge₂O₇ was prepared by solid-phase synthesis from a stoichiometric Y₂O₃–GeO₂ mixture under multistage calcination in air within a temperature range of 1273–1473 K. The molar heat capacity of polycrystalline samples was measured by differential scanning calorimetry (DSC), and the C _P = f(T) dependence was used to calculate the thermodynamic properties of yttrium digermanates, such as the enthalpy and entropy changes and the reduced Gibbs energy.     

Binary Phase Behavior of 1,3-Distearoyl-2-oleoyl-sn-glycerol (SOS) and Trilaurin (LLL)

This paper reports the precise analysis of the eutectic mixing behavior of 1,3-distearoyl-2-oleoyl-sn-glycerol (SOS) and trilaurin (LLL), as a typical model case of the mixture of cocoa butter (CB) and cocoa butter substitute (CBS). SOS was mixed with LLL at several mass fractions of LLL (w_LLL); the mixtures obtained were analyzed for polymorphic phase behavior using differential scanning calorimetry (DSC) and synchrotron radiation X-ray diffractometry (SR-XRD). In melt crystallization with constant-rate cooling, SOS and LLL formed eutectics in their metastable polymorphs, allowing the occurrence of a compatible solid solution at w_LLL ≥ 0.925. With subsequent heating, the resultant crystals transformed toward more stable polymorphs, then melted in a eutectic manner. For mixtures aged at 25 °C after melt crystallization, eutectics were found in the extended w_LLL region, even at w_LLL = 0.975. These results indicate that phase separation between SOS and LLL progressed in their solid solution under stabilization. The crystal growth of the separated SOS fraction may cause fat-bloom formation in compound chocolate containing CB and CBS. To solve this problem, the development of retardation techniques against phase separation is expected.     

Synthesis, structural and thermal characterization of metaphosphatenickel(II) salt

A new inorganically template metaphosphate of Ni(II) complex has been synthesized and characterized by different measurements such as DSC, FT-IR, C?CH?CN?CS, X-RD and ICP-AES. Differential scanning calorimeter (DSC) elucidated negative specific heat of the system and has used to evaluate some thermodynamical constants like specific heat, enthalpy and entropy of that system. The specific heat capacity of the system is measured in atmospheric O₂ at heating rate of 278 and 283?K?min^?1. The specific heat is found both positive and negative at 278?K?min^?1.     

Non-isothermal kinetic and thermodynamic study for the dehydration of copper(II) chloride dihydrate and nickel chloride hexahydrate

Non-isothermal dehydration of copper chloride dihydrate and nickel chloride hexahydrate were studied by using TG, DTG, DTA and DSC measurements. The copper chloride salt loses its two water molecules in one step while nickel chloride salt dehydrates in three consecutive steps. The first two steps involve the loss of 4 water molecules in two overlapped steps while the third step involves the dehydration of the dihydrate salt to give the anhydrous NiCl₂. Activation energies (ΔE) and the frequency factor (A) were calculated from DTG and DTA results. We have also calculated the different thermodynamic parameters, e.g. enthalpy change (ΔH), heat capacity (C _p) and the entropy change (ΔS) from DSC measurements for both reactants. The isothermal rehydration of the completely dehydrated salts was studied in air and under saturated vapour pressure of water. Anhydrous nickel chloride was found to rehydrate in three consecutive steps while the copper salt rehydrated in one step.     

Thermodynamic properties of carbon dioxide derived from the speed of sound

Thermodynamic properties of CO₂ are derived from speed of sound in the temperature range 300 to 360 K (from 0 to 6 MPa), and 300 to 220 K (from 0 to 90% of the saturation pressure). The density, the specific heat capacity at constant pressure, and the specific heat capacity at constant volume are obtained by numerical integration of differential equations connecting the speed of sound with other thermodynamic properties. The set of differential equations is solved as the initial value problem, with the initial values specified along the isotherm at 300 K in terms of several accurate values of the density and the specific heat capacity at constant pressure. The density, the specific heat capacity at constant pressure and the specific heat capacity at constant volume are derived with the absolute average deviations of 0.018%, 0.19%, and 0.18%, respectively. The results of numerical integration are extrapolated to the saturation line for ρ, c _p , and c _v with the absolute average deviations of 0.056%, 2.31%, and 1.32%, respectively.     

Heat capacity measurement by modulated DSC at constant temperature

The mathematical equations for step-wise measurement of heat capacity (C _p ) by modulated differential scanning calorimetry (MDSC) are discussed for the conditions of negligible temperature gradients within sample and reference. Using a commercial MDSC, applications are evaluated and the limits explored. This new technique permits the determination ofC _p by keeping the sample continually close to equilibrium, a condition conventional DSC is unable to meet. Heat capacity is measured at ‘practically isothermal condition’ (often changing not more than ±1 K). The method provides data with good precision. The effects of sample mass, amplitude and frequency of temperature modulation were studied and methods for optimizing the instrument are proposed. The correction for the differences in sample and reference heating rates, needed for high-precision data by standard DSC, do not apply for this method. Presented in preliminary from at the 22nd NATAS Conference in Denver, CO 9/19-22/93 (Proceedings, pages 59–64, editor K. R. Williams).     

Differential scanning calorimetry study of Ge1−xSnxSe2.5 glasses

The glass-forming tendency and specific heat in ice cold water-quenched Ge_1?xSn_xSe_2.5 glassy alloys with 0H _f, the heat ΔH _c associated with the crystallization of an amorphous phase and the glass transition temperatureT _g were deduced from the DSC curves. The composition dependence of glass forming ability,T _g and crystallization behavior has been discussed.     

Thermochemical studies on Bi4Ge3O12 and Bi4Ti3O12 single crystals

The specific heat values of Bi₄Ge₃O₁₂ and Bi₄Ti₃O₁₂ single crystals have been studied using a DSC instrument in the temperature range from 323 to 1273 K. The temperature range at which the anomaly associated with transition from polarized to non-polarized phase in Bi₄Ti₃O₁₂ occurred, has been estimated using the shape of the Bi₄Ge₃O₁₂ heat capacity curve as a “normal” one. The heat effect and the entropy change of the transition were evaluated.     

DSC investigation of the polystyrene films filled with fullerene

Polystyrene composite films with different content of C₆₀?+?C₇₀ fullerene mix have been obtained from o-xylene solutions. The mass fraction of fullerene was varied from 0.01 to 0.1 mass%. The glass transition temperatures and specific heat capacities in range of 293?C423?K have been determined for the films by DSC method. The plasticization of the polymer is observed in thermal properties of the films under influence of small fullerene additions. The values of T _g and C _P decrease and thermal coefficient of heat capacity b increase as fullerene content increases up to 0.02 mass%. The effect of interaction between polymer and fullerene molecules on thermal properties becomes evident at higher fullerene content in range from 0.02 to 0.1 mass%. At this the values of T _g and C _P increase and b coefficient decrease with increasing content of fullerene. Concentration dependence of C _P and b values is less steep for polymer composite films in elastic state at temperatures above T _g. Molecular interactions in the composites are discussed in view of our-self and literature data.     

Measurement of thermal diffusivity and specific heat capacity of polymers by laser flash method

We measured thermal diffusivity and heat capacity of polymers by laser flash method, and the effects of measurement condition and sample size on the accuracy of the measurement are discussed. Thermal diffusivities of PTFE films with thickness 200–500 μm were the same as those data that have been reported. But, the data for film thickness less than 200 μm have to be corrected by an equation to cancel thermal resistance between sample film and graphite layers for receiving light and detecting temperature. Thermal diffusivity was almost unaffected by the size of area vertical to the direction of laser pulse, because heat flow for the direction could be negligible. Specific heat capacity of polymer film was exactly measured at room temperature, provided that low absorbed energy (< 0.3 J) and enough sample mass (> 25 mg) were satisfied as measuring conditions. Thermal diffusivity curve of PS or PC versus temperature had a terrace around T_g, whereas that of PE decreased monotonously with increasing in temperature until T_m. Further, we estimated relative specific heat capacity (RC_p) by calculating ratios of heat capacities at various temperatures to the one at 299 K. RC_p for PS obtained by laser flash method was larger than that obtained by DSC method, whereas the RC_ps for PE obtained by the both methods agreed with one another until T_m (305 K). RC_p for PS decreased linearly, with increase in temperature after it increased linearly until T_g (389 K), showing similarity to temperature dependency of thermal conductivity. RC_p for PE also decreased until T_m, similar to thermal conductivity. ©1995 John Wiley & Sons, Inc.     

Synthesis and thermal behaviors of 1,3-bis(4-aminophenoxy)benzene (TPER) and polyimide based on TPER and pyromellitic dianhydride

1,3-Bis(4-aminophenoxy)benzene (TPER) and poly(amic acid) based on TPER and pyromellitic dianhydride (PMDA) were synthesized. After imidization of the poly(amic acid), polyimide based on TPER and PMDA was obtained. The melting process and the specific heat capacity (C _p) of TPER were examined by DSC and microcalorimetry, respectively. The melting enthalpy, the melting entropy, and the C _p for TPER were obtained. The enthalpy change, the entropy change, and the Gibbs free energy change for TPER were obtained within 283 and 353 K. The thermal decomposition reaction mechanism of the polyimide is classified from the TG–DTG experimental data, and the thermokinetic parameters of the thermal decomposition reaction are E _a = 296.87 kJ mol^?1and log (A/s^?1) = 14.41.