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.     

Heats of melting of sodium nitrate and indium by differential scanning calorimetry: a suggestion for a new calibration substance

Measurments with a Perkin-Elmer DSC-2 differential scanning calorimeter that has been calibrated with indium, tin, and lead have yielded values for the heat of melting of sodium nitrate. Analysis of these results along with those from earlier investigations gives ΔH_m ? 3615 cal mol^?1 as a recommended “best” value for the heat of melting of NaNO₃. The consistency of our results over a period of three years in which many samples were investigated, in combination with results of earlier investigations, leads us to suggest that NaNO₃ is a useful substance for calibration of differential scanning calorimeters. Results of our measurements of the heat of melting of indium are presented and discussed in relation to earlier investigations.     

Determination of the purity,melting point and heat of melting of cyclic polyethers

Conclusions Differential scanning calorimeter was used to determine the thermal stability, purity, melting point, and heat of melting of benzo-15-crown-5, dibenzo-18-crown-6, and dibenzo-24-crown-8. These crown ethers have relatively high heats of melting.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 691–692, March, 1986.     

A new approach for estimating the recrystallization rate and equilibrium melting temperature

A method is described for measuring the heat and rate of recrystallization following partial melting. The method uses a specific sequence of temperatures with a differential scanning calorimeter, and the melting and recrystallization processes were confirmed by optical observations. The method was applied to poly(butylene terephthalate). The rate of recrystallization was found to be roughly two orders of magnitude faster than isothermal crystallization from the melt. The melting temperatures obtained from recrystallization were used in the Hoffman–Weeks equation to deduce 236°C as the equilibrium melting temperature for poly(butylene terephthalate). © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36 : 133–141, 1998     

Tetrachlorobisphenol-A adipate polymers. I. Crystallization of poly(tetrachlorobisphenol-A adipate)

The properties of melt-crystallized poly(tetrachlorobisphenol-A adipate) were studied by using a differential scanning calorimeter. The dependence of melting point and the degree of crystallinity are reported as a function of the crystallization conditions. The heat of fusion is equal to 8.1 kcal/mole, while the equilibrium melting point, as determined by extrapolation, is 283°C. The polymer crystallized from the melt has a maximum degree of crystallinity of 0.53.     

Low Temperature Specific Heat and Thermal Stability of Fe–B Ultrafine Amorphous Alloy Particles

Fe–B ultrafine amorphous alloy particles (UFAAP) were prepared by chemical reduction of Fe³⁺ with NaBHO₄ and confirmed to be ultrafine amorphous particles by transmission electron microscopy and X-ray diffraction. The specific heat of the sample was measured by a high precision adiabatic calorimeter, and a differential scanning calorimeter was used for thermal stability analysis. A topological structure of Fe-B atoms is proposed to explain two crystallization peaks and a melting peak observed at T=600, 868 and 1645 K, respectively. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermodynamic investigations of uranium-rich binary and ternary alloys

Uranium–zirconium, uranium niobium, and uranium–zirconium–niobium alloys were synthesized by the arc melting technique and their phase transition temperatures were determined using a high temperature calorimeter. Heat capacities of U–7 wt%Zr, U–7 wt%Nb, U–5 wt%Zr–2 wt%Nb, U–3.5 wt%Nb–3.5 wt%Zr, and U–2 wt%Zr–5 wt%Nb were measured using a differential scanning calorimeter in the temperature range 303–921 K. A set of self-consistent thermodynamic functions such as entropy, enthalpy, and Gibbs energy function data for these binary and ternary alloys were reported for the first time using heat capacity data obtained in this study and required literature data.     

RheoDSC: design and validation of a new hybrid measurement technique

A newly developed hyphenated technique is presented that combines an existing rheometer and differential scanning calorimeter (DSC) into a single experimental setup. Through the development of a fixation accessory inside the cell of the calorimeter and the introduction of an add-on unit for the rheometer, the simultaneous calorimetric and rheological measurement inside the well-controlled thermal environment of a Tzero™ DSC cell opens new experimental possibilities. The evolution of thermal and flow properties of a material can be simultaneously monitored during steady or oscillatory shear flow and regular or modulated temperature DSC measurements. The technique offers interesting opportunities for the investigation of flow-induced transitions, such as crystallization or phase separation, and provides a possibility for high-throughput screening of materials. The signal quality of the novel technique in comparison to the stand-alone techniques is demonstrated by the evaluation of the calibration factors and by measurements on standard materials. Finally, combined rheological and calorimetric melting and crystallization experiments on polycaprolacton are performed.     

Heterogeneity of laser‐irradiated films of polyvinyl alcohol/starch blends: effect of glycerol content

The present paper reports the results of studies on the effect of laser irradiation on the morphology and thermal properties of starch/polyvinyl alcohol (PVA) blend, with varying glycerol concentration. Differential scanning calorimeter results showed that laser irradiation increased the heat of fusion (ΔH_fus), heat of crystallization (ΔH_cry), temperature of melting (T_m), temperature of crystallization (T_cry) and percentage crystallinity as a function of the amount of glycerol. It is believed that breakdown of the intermolecular hydrogen bonding between the starch and PVA causes an increase in the blend heterogeneity. These results are corroborated with the findings from thermogravimetric analysis and scanning electron microscope images. Copyright © 2013 John Wiley & Sons, Ltd.     

硝酸肼的量热研究

用精密自动绝热量热计测定了在220 K—370 K温度范围内硝酸肼的热容、熔化热、熔化温度和熔化熵。所得热容数据的精密度以百分偏差的均方根值表示为±0.2％。三次熔化热测定的相对偏差为±0.1％。为验证结果的可靠性, 用该装置测定了冰的熔化热和熔化温度, 其结果与文献值一致; 又用法国SETARAM公司的高温量热计测定了硝酸肼的熔化热和熔化温度, 其结果与我们用量热法测定的结果一致; 从量热结果计算出了该试样的纯度, 该结果亦与化学分析的结果一致。这些均可说明我们所测得的数据是可靠的。     

苯氧威 (C17H19NO4) 的热容和热力学性质

通过小样品精密自动绝热量热计测定了自己合成并提纯的苯氧威 (C₁₇H₁₉NO₄) 在79 ～ 360 K温区的低温摩尔热容。量热实验发现, 该化合物在320 ~ 330 K温区, 有一固 - 液熔化相变过程, 其熔化温度为（326.31±0.14）K, 摩尔熔化焓、摩尔熔化熵及化合物的纯度分别为：(26.98±0.04) kJ• mol^-1和（82.69 0.09）J•mol^-1•K^-1和 (99.53±0.01 )%。并计算出了80-360 K的热力学参数。用分步熔化法得到绝对纯化和物的熔点为326.60±0.06 K。用差示扫描量热 (DSC) 技术对该物质的固-液熔化过程作了进一步研究，结果与绝热量热法一致。     

4,4'-二羟基二苯硫醚对聚甲醛结晶和熔融行为的影响

为了探究4,4'-二羟基二苯硫醚(TDP)的添加对聚甲醛(POM)熔融与结晶行为的影响,本文利用熔融共混的方法制备了POM/TDP共混材料。通过差示扫描量热仪(DSC)对共混材料的熔融与结晶行为进行了研究,利用广角X射线衍射仪(WAXD)对共混材料的晶体结构进行了研究。结果表明,在POM中添加TDP后,POM的晶面间距变大,晶体结构变的疏松,使POM的结晶温度(Tc)、结晶焓(ΔHc)、熔融温度(Tm)与熔融焓(ΔHm)均降低。当TDP质量分数增加到30%时,共混物的熔点与结晶温度较纯POM分别下降了15.2和12.8℃。在等温结晶过程中,随着TDP含量的增大,POM完成结晶所需的时间显著加长,共混物的结晶速率逐渐降低,结晶活化能逐渐升高,但TDP的加入对POM的晶型并没有影响。以上结果说明TDP的添加对POM的熔融与结晶行为影响很大,这将为POM结晶行为的调控提供依据。     

Modulated capillary titration calorimeter

A modulated capillary titration calorimeter has been developed. New software and optimization of the calorimetric unit CTD2156 are used as a basis of the modulated capillary titration calorimeter. The scanning mode of the calorimeter has been theoretically substantiated. The scanning of chambers temperature is provided due to the fact that the shield temperature is linearly varied at heating and cooling. The reversing and kinetic part of the total heat flow are measured at heating of a diluted collagen solution. The main advantage of the calorimeter is its ability to operate in a modulation mode, in an isothermal mode, in modes of linear heating and cooling of homogeneous and dispersoid liquid samples at an effective mixing of reagents in calorimetric chambers.     

A constant heat-flux calorimeter for measuring heat transfer data

A new isothermal calorimeter, designed especially for simultaneously measuring the heat of reaction and the heat transfer data in a reaction solution, is described. The system, called a Constant Heat-Flux Calorimeter, is similar to a differential scanning calorimeter in terms of direct calorimetric measurement of the energies of reaction, but differs from the conventional calorimeters described in the literature. With this device, one recorded output in a temperature control circuit is a linear function of change in energies of reaction, and second in a differential temperature control circuit is found to be proportional to a resistance to heat transfer in a solution. The performance of the calorimeter was evaluated on the basis of some results on heat transfer data of aqueous solution of polyethylene glycol and on solution polymerization of styrene at constant temperatures.     

Reaction calorimetry for the development of chemical reactions

A new reaction calorimeter is described that has been developed to study chemical reaction processes on a laboratory scale. It provides precise measurements of kinetic and thermal data, of heat transfer data, as well as of the physical properties of the reaction product. The reaction calorimeter is applied successfully in the development of chemical processes, in the evaluation of hazards and risks of chemical synthesis.Working principles and evaluation are described using the example of the nitration of benzaldehyde.     

A Method for Analysis of the Measured Curves of TMDSC Investigation in the Melting Region of Polymers

The measured signal of the temperature-modulated differential scanning calorimetry (TMDSC) is discussed in the case of polymer melting. The common data evaluation procedure of TMDSC-signals is the Fourier analysis. The resulting information is the amplitude and the phase shift of the first harmonic of the periodic heat flow component. It is shown that this procedure is not sufficient for quantitative discussions if deviations from the symmetric curve shape occur in the measured heat flow curves. For polymer melting it is demonstrated that asymmetric curves will be measured if the experimental temperature amplitude is too large. In this paper a data evaluation method is presented, which is based on the Fourier transform of the measured curves. The peaks of the first and second harmonics in the resulting spectra are used for the analysis of the asymmetry of the measured curves. In the case of polymer melting this analysis yields the maximum temperature amplitude which follows a correct linear data evaluation. This maximum temperature amplitude depends on the material. This revised version was published online in July 2006 with corrections to the Cover Date.     

Temperature-modulated differential scanning calorimetry of reversible and irreversible first-order transitions

Temperature-modulated differential scanning calorimetry of first-order transitions has led to many new observations. Some of these involve non-linear processes or deal with transformations of practically instantaneous response. The latter may cause serious lags within the calorimeter due to limited thermal conductivity of the sample and the instrument. In both cases the “reversing heat capacity” or a “complex heat capacity” is not a precise representation of the transition since both are computed from abbreviated Fourier transforms, limited to the evaluation of the first harmonic component. One has in these cases to work in the time-domain with the raw output. But even from these analyses in the time-domain many interesting new insights about the transition and the calorimeter performance can be generated.     

Equilibrium melting parameters of poly(ethylene terephthalate)

The equilibrium melting temperature, volume, and enthalpy and entropy changes on melting of poly(ethylene terephthalate) have been analyzed and heats of fusion have been newly measured with an automated scanning calorimeter to yield the following data: 553°K, 16.9 cm³/mole, 2.69 kJ/mole, and 48.6 J/deg/mole, respectively. A more detailed discussion of annealed samples obtained from etched starting materials shows that the density of the noncrystalline regions may be variable.     

Simultaneous differential scanning calorimetry and small-angle x-ray scattering

A method is described for performing simultaneous measurements of small-angle x-ray scattering and differential scanning calorimetry. The experiment is made possible through a combination of the high flux afforded by the storage ring at the Stanford Synchrotron Radiation Laboratory, a linear position-sensitive detector with rapid response time, and a differential scanning calorimeter developed for optical microscopy. The feasibility of the technique is illustrated by examining the melting and crystallization of a polyethylene specimen. This example demonstrates the power of the technique and the accuracy and reliability of the scattering and thermal data.