Automated differential scanning calorimetry at low temperatures

A Perkin-Elmer DSC-2 scanning calorimeter was operated by means of a PDP-11/34 computer with time-shared scanner and voltmeter. Special attention was paid to the problems of measurement below room temperature down to the low-temperature limit. It was found that Ne, rather than He, should be used as a purge gas, that scans should always be started at a standardized liquid nitrogen level, and that gas flow to the dry box should be stopped during measurements. Results on benzoic acid were then accurate to 0.6 % from 120 to 300 K. The specific heat of antimony was measured in the temperature interval 120–720 K.     

The possibility of high-temperature heat capacity measurements by differential scanning calorimetry

We have been conducting series of heat capacity measurements by differential scanning calorimetry (DSC) on various latent thermal storage materials such as NaOH-NaNO₃. Our concern is now shifting to higher temperature applications of latent thermal storage: space solar dynamic power systems (solar thermal electric power generation systems in space) and so on. Such applications require storage materials which can be operated above 1000 K. Needs for heat-capacity measurements at higher temperatures are increasing. In the present paper, some results of our heat capacity measurements by DSC at intermediate temperatures are presented. Several items which should be considered in order to realize the heat capacity measurements above 1000 K by DSC are discussed.Paper presented at the Second U.S.-Japan Joint Seminar on Thermophysical Properties, June 23, 1988, Gaithersburg, Maryland, U.S.A.     

Quantifying low amorphous or crystalline amounts of alpha-lactose-monohydrate using X-ray powder diffraction, near-infrared spectroscopy, and differential scanning calorimetry

Efficient and accurate quantification of low amorphous and crystalline contents within pharmaceutical materials still remains a challenging task in the pharmaceutical industry. Since X-ray powder diffraction (XRPD) equipment has improved in recent years, our aim was 1) to investigate the possibility of substantially lowering the detection limits of amorphous or crystalline material to about 1% or 0.5% w/w respectively by applying conventional Bragg Brentano optics, combined with a fast and simple evaluation technique; 2) to perform these measurements within a short time to make it suitable for routine analysis; and 3) to subject the same data sets to a partial least squares regression (PLSR) in order to investigate whether it is possible to improve accuracy and precision compared to the standard integration method. Near-infrared spectroscopy (NIRS) and differential scanning calorimetry (DSC) were chosen as reference method. As model substance, alpha lactose monohydrate was chosen to create calibration curves based on predetermined mixtures of highly crystalline and amorphous substance. In contrast to DSC, XRPD and NIRS revealed an excellent linearity, precision, and accuracy with the percent of crystalline amount and a detectability down to about 0.5% w/w. Chemometric evaluation (partial least squares regression) applied to the XRPD data further improved the quality of our calibration.     

Prediction of the self-accelerating decomposition temperature (SADT) for liquid organic peroxides from differential scanning calorimetry (DSC) measurements

We present a prediction (estimation, calculation, screening) method for the estimation of the self-accelerating decomposition temperature (SADT) for liquid organic peroxides from differential scanning calorimetry (DSC) measurements based on the concepts of thermal explosion theory originally introduced by Semonov which are adopted to our problem assuming nth-order reaction kinetics. For the peroxides under investigation, we demonstrate good agreement with the experimental SADT. This method can be used as a quick and easy applicable method for the estimation of the critical temperatures.     

Cure rate of DGEBA/MDA/GN/HQ system by differential scanning calorimetry analysis

To compare investigations of the cure kinetics of DGEBA/MDA/GN/HQ system by different methods, the fractional life method, Kissinger equation, Barrett method and integral method were used. From the fractional life method, reaction orders were between 0.77 and 0.93 but had no correlation with cure temperature, and from the Kissinger equation, the activation energy was 11.08 kcal mol⁻¹ and pre-exponential factor was 2.78×10³ s⁻¹. For the second-order reaction by the Barrett method and integral method, the activation energy was 20 kcal mol⁻¹ and the pre-exponential factor was 8.5×10⁸ s⁻¹. By comparison of the Barrett model with experimental data, it was found that the Barrett model was useful for predicting the cure time at a given temperature.     

Thermal behavior and phase identification of Valsartan by standard and temperature-modulated differential scanning calorimetry

Thermal behavior of angiotensin II type 1 (AT₁) receptor antagonist, Valsartan (VAL), was examined employing thermogravimetric analysis (TGA), standard differential scanning calorimetry (DSC) and temperature-modulated differential scanning calorimetry (TMDSC). The stability of VAL was measured by TGA from 25 to 600°C. Decomposition of Valsartan starts around 160°C. The DSC curve shows two endotherms, occurring around 80°C and 100°C, related to evaporation of water and enthalpy relaxation, respectively. Valsartan was identified by DSC as an amorphous material and it was confirmed by X-ray powder diffraction. The glass transition of fresh Valsartan appears around 76°C (fictive temperature). TMDSC allows separation of the total heat flow rate into reversing and nonreversing parts. The nonreversing curve corresponds to the enthalpy relaxation and the reversing curve shows changes of heat capacity around 94°C. In the second run, TMDSC curve shows the glass transition process occurring at around 74°C. Results from standard DSC and TMDSC of Valsartan were compared over the whole range of temperature.     

Permeability of naphthalene in different types of polymeric food packaging materials

The relative permeabilities of naphthalene through different types of common polymeric food packaging materials were determined by migration studies in a controlled environment. The results illustrate that polyolefins, such as low density polyethylene (LDPE), have a higher relative permeability than other polymers, such as polyethylene terephthalate (PET) or polyvinylchloride co-polymer (PVC). This was explained by the correlation between the permeability of the migrant and the glass transition temperature (Tg) of the different polymers, as well as their polarity.     

Special features characteristic of the use of differential scanning calorimetry for the investigation of the kinetics of thermal decomposition of energetic materials

The results of analysis of mathematical models of “ideal” differential scanning calorimeter are used for determining the experimental conditions which provide for the minimal level of errors of determination of the kinetic constants of exothermal reactions of thermal decomposition of energetic materials under conditions of constant-rate heating of samples and in the isothermal mode. The predicted estimates of admissible values of the basic parameters of models (mass of samples, rate of heating, temperature range of investigations, and so on) are based on the experimental data largely obtained in the investigation of cyclotetramethylenetetranitramine (HMX).     

Component migration from adhesives used in paper and paperboard packaging for foodstuffs

This paper presents the first results of research on the migration of adhesive components in the paper and paperboard packaging sector. It examines components that can migrate from a variety of commonly used adhesives in the framework of a ‘worst case’ scenario in respect of the contents. The report also explains the methodology used to analyse extraction and migration and the model used for calculating the transfers. Copyright © 1999 John Wiley & Sons, Ltd.     

Coupling of conductivity to the relaxation process in polymer electrolytes

Conductivity relaxation using modulus formalism has been used to explore the coupling of ionic conductivity to dielectric relaxation in polymer electrolyte based on polyethylene oxide complexed with various content of LiAsF₆. The temperature dependence of conductivity followed the VTF behavior suggesting close correlation between conductivity and the segmental relaxation process in polymer electrolytes. The coupling of conductivity to the segmental process has been discussed in terms of coupling index. For all compositions studied, the coupling index was within the range of 1–11 in the temperature range of investigation, which was in agreement with the coupled systems.     

Nature and density of lattice defects in ball milled nanostructured copper

Copper powder of 99.9% purity with particle size in the micrometer range was subjected to high energy ball milling by milling times between 2 and 24 h applying stearic acid as surfactant. The nature and density of lattice defects were determined using differential scanning calorimetry (DSC) and X-ray line profile analysis (XPA). The DSC measurements exhibit a considerable drop of the total stored energy with increasing ball milling time indicating a surprising decrease of lattice defect concentrations by more than one order of magnitude. The results from XPA, however, show that neither the dislocation density, nor the crystallite size can account for this behavior. Rather it is to be attributed to a high concentration of deformation induced vacancy type defects, with their density gradually decreasing during ongoing milling.     

Synthesis of nanocrystalline yttria doped ceria powder by urea-formaldehyde polymer gel auto-combustion process

Nanocrystalline yttria doped ceria powder has been prepared by auto-combustion of a transparent gel formed by heating an aqueous acidic solution containing methylol urea, urea, cerium(III) nitrate and yttrium(III) nitrate. The TGA and DSC studies showed the combustion reaction of the gel initiated at 225 °C and completed within a short period of time. XRD spectrum of the combustion product reveals the formation of phase pure cubic yttria doped ceria during the combustion process. Loose agglomerate of yttria doped ceria particle obtained by the combustion reaction could be easily deagglomerated by planetary ball milling and the powder obtained contains particles in the size range of 0.05-3.3 μm with D₅₀ value of 0.13 μm. The powder particles are aggregate of nanocrystallites with a wide size range of 14-105 nm. Pellets prepared by pressing the yttria doped ceria powder sintered to 95.2% TD at 1400 °C.     

紫外光分光光度法测定食品包装纸用天然色素虎杖黄酮含量的研究

研究了紫外光分光光度法测定食品包装纸用色素虎杖黄酮含量的方法,以芦丁为参照品,测量波长为359nm,平均回收率为99.96%,精密度为1.34%,说明紫外分光光度法是一种较理想的测定方法.     

Generalized numerical modelling of unsteady heat transfer during cooling and freezing using an improved enthalpy method and quasi-one-dimensional formulation

A numerical solution of a generalized Stefan problem is presented. It covers a great variety of unsteady heat conduction cases accompanied by phase transformations. A mathematical model is developed for determination of the unsteady-state temperature and enthalpy fields (as well as the space-time evolution of the phase content) and of the cooling and freezing (heating and thawing) times of food materials and other bodies of various configuration (representing multicomponent two-phase systems having one freezable component). An improved enthalpy method is proposed by which all non-linearities, caused by the temperature dependence of the thermophysical coefficients, are introduced in a functional relationship between the volumetric specific enthalpy and the Kirchhoff function. Thus the non-linearities are eliminated as a factor making the solution difficult. The applied approach possesses great adaptivity and flexibility in solving complicated moving boundary problems: it is suitable for both isothermal and non-isothermal phase change, reaches a high degree of correspondence between the real physical phenomenon and its mathematical formalization, uses uniform and easy fixed-grid computational techniques, makes it possible to avoid complications and to eliminate possible errors caused by ‘jumping’ of the equivalent specific heat capacity peak at the maximum of the latent heat effect, etc. Efficient procedures and algorithms for computer simulation of complex refrigerating technological processes are created. Experimental verification demonstrating the applicability and accuracy of the model is carried out.     

Characterization of the evolution of the volume fraction of precipitates in aged AlMgSiCu alloys using DSC technique

Differential scanning calorimetry is used to quantify the evolution of the volume fraction of precipitates during age hardening in AlMgSiCu alloys. The calorimetry tests are run on alloy samples after aging for various times at 180 °C and the change in the collective heat effects from the major precipitation and dissolution processes in each run are used to determine the precipitation state of the samples. The method is implemented on alloys with various thermal histories prior to artificial aging, including commercial pre-aging histories. The estimated values for the relative volume fraction of precipitates are compared with the results from a newly developed analytical method using isothermal calorimetry and a related quantitative transmission electron microscopy work. Excellent agreement is obtained between the results from various methods.     

Facile synthesis of MOF-5 structure with large surface area in the presence of benzoyl peroxide by room temperature synthesis

In this study, for the first time, the uniform cylindrical MOF-5-BPO (Zn₄O(BDC)₃(H₂O)·0.5ZnO, BDC = 1,4-benzenedicarboxylate, BPO = benzoyl peroxide) crystals with large Brunauer–Emmett–Teller (BET) surface area (3210.2 m² g⁻¹) was successfully synthesized by room temperature synthesis in the presence of BPO using zinc nitrate hexahydrate (Zn(NO₃)₂·6H₂O) as the zinc source. The pore volumes of MOF-5-BPO materials prepared with different concentrations of BPO were 0.84–1.07 cm³ g⁻¹, higher than that of MOF-5-NP (0.68 cm³ g⁻¹, Zn₄O(BDC)₃(H₂O)₃·2ZnO) and MOF-5-H₂O₂ (0.84 cm³ g⁻¹, Zn₄O(BDC)₃(H₂O)₂·2ZnO, H₂O₂ = hydrogen peroxide). The addition of the peroxides created new pores, which possessed the same diameters as the existing ones, thus increased the pore volume of the product. The concentration of BPO was critical for the pore texture of MOF-5-BPO. Moreover, MOF-5-BPO could store 1.24 wt% hydrogen at 77 K and 100 kPa. Thus, this study points out some information for one to realize the influence of the peroxides over MOF-5 structure and promises the potentiality of large-scale production of MOF-5 structure with large surface area.     

Quantitative determination of acetaminophen in pharmaceutical formulations using differential scanning calorimetry. Comparison with spectrophotometric method

In this paper our previous researches dealing with compatibility, thermoanalytical characterization, the kinetics of thermal degradation of acetaminophen, either pure or contained in some commercial pharmaceutical formulations, have found applications outlets. In a previous investigation the possible interactions between acetaminophen and four excipients contained in the commercial pharmaceutical formulations were tested. As a continuation of this research in the present study an analytical method based on differential scanning calorimetry (DSC) was applied to determine the acetaminophen content of four commercial pharmaceutical formulations. For a fifth drug it was shown that the method is not applicable owing to observed incompatibility with one of the excipients. Finally, the analytical results obtained were compared with those derived from two UV spectrophotometric methods (one, i.e., “direct method,” recommended by the Pharmacopeia and the other based on the first-order derivative UV spectra).     

Aging and overaging processes in Pb-0.08%Ca-x%Sn alloys using transmission electron microscopy and differential scanning calorimetry

The precipitation hardening and overaging mechanisms in three Pb-0.08%Ca-x%Sn alloys were investigated by means of hardness and calorimetric measurements (DSC) and transmission electron microscopy (TEM) observations. It is found that the highest tin content, close to 2 wt.%, allows delaying the overaging phenomenon in ternary Pb–Ca–Sn alloys. DSC studies show that tin has a favourable effect on the aging by providing further nucleation sites. Furthermore, the precipitate coarsening due to overaging shifts to higher temperatures upon increasing the Sn content. Using TEM to observe the microstructural transformations shows the presence of an epitaxial relationship between precipitates and the matrix during both aging and overaging. In the course of overaging, coarse precipitates adopt a lamellar morphology and their growth occurs preferentially along the [111] compact atomic plane direction. The tin content of coarse precipitates of (Pb_1−xSn_x)₃Ca increases with rising overaging time and follows the tin content of the initial alloy.     

Exfoliation of clay layers in polypropylene matrix using potassium succinate-g-polypropylene as compatibilizer

The efficiency of potassium succinate-g-polypropylene (KPPSA) as compatibilizer for the dispersion of clay in a high molecular weight polypropylene during melt mixing for the preparation of nanocomposites was evaluated and compared with maleic anhydride-g-polypropylene (PPMA). Nanocomposites were prepared by direct melt mixing and by masterbatch methods and the structure obtained was characterized by WAXD and TEM. The exfoliation and better dispersion of the organoclay was observed with KPPSA than PPMA. The dispersion of clay was found to be dependent on the method of preparation, type and the amount of compatibilizer used. The dispersion was better when the nanocomposites were prepared by two step masterbatch route than the single step direct mixing method. Flexural moduli and crystallization behavior were studied and correlated with the dispersion of organoclay in the PP matrix.     

Microstructure and martensitic transformation in Si-coated TiNi powders prepared by ball milling

Si was coated on the surface of Ti–49Ni (at%) alloy powders by ball milling in order to improve the electrochemical properties of the Si electrodes of secondary Li ion batteries and then the microstructure and martensitic transformation behavior were investigated by means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Ti–Ni powders coated with Si were fabricated successfully by ball milling. As-milled powders consisted of highly deformed Ti–Ni powders with the B2 phase and amorphous Si layers. The thickness of the Si layer coated on the surface of the Ti–Ni powders increased from 3–5 μm to 10–15 μm by extending the milling time from 3 h to 48 h. However, severe contamination from the grinding media, ZrO₂ occurred when the ball milling time was as long as 48 h. By heating as-milled powders to various temperatures in the range of 673–873 K, the highly deformed Ti–Ni powders were recovered and Ti₄Ni₄Si₇ was formed. Two-stage B2–R–B19′ transformation occurred when as-milled Si-coated Ti–49Ni alloy powders were heated to temperatures below 873 K, above this temperature one-stage B2–B19′ transformation occurred.