Differential Scanning Calorimetry Cell Research Articles

The insulating effect of the low thermal conductivity of epoxy on the resolution of the heat of reaction during polymerization by differential scanning calorimetry

It is demonstrated that the heat of epoxy cure as measured by isothermal differential scanning calorimetry (DSC), as commonly calibrated by the heat of fusion of an indium standard, is consistently low as compared to methods “directly” calibrated by Joule heating [i.e., isothermal microcalorimetry (IMC)]. The discrepancy between measurement techniques is shown to be on the order of 15% for low thermal conductivity epoxy thermosets. In addition to direct comparisons between DSC and IMC measurements during epoxy polymerization, indium samples embedded in cured epoxy were studied to determine if the DSC was able to accurately capture the total heat of fusion through the polymeric insulating layer. It is found that the indium heat of fusion measured by DSC is lower when the indium is embedded in epoxy than when the indium is in direct contact with a steel sample pan. The fraction of the indium heat of fusion detected through the epoxy insulation by the DSC cell is comparable to the fraction of the heat of reaction detected by DSC during epoxy cure, as determined from the DSC-IMC comparison. It is concluded that the heat flow detected by DSC during epoxy cure must be scaled by a factor of 1.18 in order to accurately portray the full heat of reaction under the conditions used in this work. It is argued that the difference found between DSC and IMC is in reasonable agreement with qualitative heat transfer calculations and with previous thermal conductivity measurement of polymers via DSC. The specific scaling factor is anticipated to depend on the material studied, on the pan type, on the sample geometry, on the purge gas details, and on the instrumentation. Instruments used in this work include a Q2000 DSC and a TAM Air IMC (both TA instruments). The epoxy was diglycidyl ether of bisphenol A (DGEBA) cured with diethanolamine (DEA).

An implicit enthalpy formulation for macroscopic eutectic and progressive melting: DSC (Differential Scanning Calorimetry) applications

In this paper, a physical model is built to study the eutectic and progressive melting of salt solution in DSC (Differential Scanning Calorimetry) cells. The finite volume method is utilized to solve the heat transfer problem, and the general implicit source-based enthalpy method is employed to handle the absorbed latent heat during the phase change process. The resulting numerical solution is implicit in nature and although iteration on the time step is needed at each time level, the tridiagonal matrix algorithm can be utilized within the iterations leading to efficient and accurate solutions. The effects of the heating rate and the initial salt concentration on the kinetics of the melting process are examined.

Effect of molecular architecture on the crystalline structure and stiffness of iPP homopolymers: Modeling based on annealing experiments

ABSTRACTFive polypropylene (PP) homopolymers were selected and their molecular structure was thoroughly characterized to determine the effect of molecular architecture on their annealing behavior and on the ultimate stiffness achieved by heat treatment. Molecular mass and its distribution were characterized by rheological measurements, while chain regularity was determined by differential scanning calorimetry (DSC) using stepwise isothermal segregation technique (SIST). The samples were annealed in two different ways. Tensile bars were treated in an oven at 165 °C for increasing times to determine changes in stiffness. Various defects (microcracks and voids) developed during the annealing of tensile specimens that did not allow the reliable determination of modulus by direct measurement. On the other hand, the second approach, the annealing of small samples in a DSC cell clearly showed the changes occurring in crystalline structure and also the effect of nucleation and molecular architecture on them. The large molecular weight fraction used to facilitate nucleation hinders crystal perfection, whereas the presence of a heterogeneous nucleating agent increases overall crystallinity, but does not influence recrystallization during annealing. Melting traces were transformed into lamella thickness distributions from which average lamella thickness was derived. Lamella thickness and crystallinity, the independent variables of the model equation used for the calculation of modulus, were extrapolated to infinite annealing time to predict maximum stiffness. The value obtained, 3.5 GPa, is very far from the theoretically predicted 40 GPa of oriented crystals, which cannot be achieved under practical conditions. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3365–3373, 2013

Determination of the oxidative stability by DSC of vegetable oils from the Amazonian area

Differential scanning calorimetry (DSC) and a Rancimat method apparatus were applied to evaluate the oxidative stability of buriti pulp oil ( Mauritia flexuosa Mart), rubber seed oil ( Hevea brasiliensis), and passion fruit oil ( Passiflora edulis). The Rancimat measurements taken for the oxidative induction times were performed under isothermal conditions at 100 °C and in an air atmosphere. The DSC technique involved the oxidation of oil samples in an oxygen-flow DSC cell. The DSC cell temperature was set at five different isothermal temperatures: 100, 110, 120, 130 and 140 °C. During the oxidation reaction, an increase in heat was observed as a sharp exothermic curve. The value T 0 represents the oxidative induction time, which is determined from the downward extrapolated DSC oxidative curve verses the time axis. These curves indicate a good correlation between the DSC T 0 and oxidative stability index (OSI) values. The DSC method is useful because it consumes less time and less sample.

ChemInform Abstract: Effect of Decationation and Dealumination of Zeolite Y on Its Acidity as Assessed by Ammonia Desorption Measured by Differential Scanning Calorimetry (DSC).

Abstract Zeolite NaY was decationated step-wise until the H-form was obtained (HY), and zeolite HY was dealuminated step-wise to increase its SiO2/Al2o3 ratio from 4.8 to 8.5. Ammonia was adsorbed on all the zeolite forms and was then desorbed thermally in a DSC cell, making use of the programmed temperature-increasing facility available in the DSC system. The total acidity of the zeolite was found to increase with decationation and decrease with dealumination. Strong acidity was found to increase with both decationation and dealumination, whereas weaker acidity decreased. The strength of strong acid sites increased further, whereas that of weaker acid sites decreased in both treatments.

Heat transfer in salt solutions enclosed in DSC cells

This study addresses the heat transfer in differential scanning calorimetry (DSC) cells during the melting process of an eutectic solution. The energy and entropy equations for two-dimensional transient thermal analysis with associated boundary and initial conditions are solved numerically using a fixed grid numerical model with the finite control volume approach. Proper trends and a good agreement between the results of theoretical modeling and experiment results are obtained. A parametric study with various associated parameters is performed and results are illustrated.

Oxidative stability assessment of Bauhinia purpurea seed oil in comparison to two conventional vegetable oils by differential scanning calorimetry and Rancimat methods

The differential scanning calorimetry (DSC) and oxidative stability index (OSI) techniques were applied for evaluating the oxidative stability of Bauhinia purpurea, rice bran and cotton seed oil. The DSC cell temperature was adjusted at four isothermal temperatures (110, 120, 130, and 140 °C) and oxidative DSC curves were obtained under oxygen flow rate of 50 ml/min. During the oxidation reaction the increase of heat was observed with sharp exothermic curve. T 0 was the oxidative induction time determined by the downward extrapolated DSC oxidative curve to time axis. The oxidation times ( T 0) acquired from each oil demonstrated a good correlation, r > 0.99, with the oxidative stability measured by Rancimat method. DSC method is concluded to be useful by consuming shorter time with lesser amount of sample.

Quenching of polymer inside aluminum DSC pans: Origin of an apparent artifact

To obtain amorphous polymer samples for thermal analysis by differential scanning calorimetry (DSC), a typical procedure involves quenching the sample, which is encapsulated inside an aluminum DSC pan and lid, into liquid nitrogen or liquid nitrogen-cooled glass beads. We demonstrate that this procedure can cause an artifact endotherm in the subsequent DSC scan of the polymer. The artifact is not related to the polymer sample itself, but is possibly due to phase change of surface moisture introduced during the process of transferring into the DSC cell. A procedure to eliminate the artifact is discussed.

Interaction of long-chain nicotinates with dipalmitoylphosphatidylcholine

The interaction of four long-chain nicotinates, compounds that are of interest as potential chemopreventive agents, with dipalmitoylphosphatidylcholine (DPPC) was investigated in monolayers at the air-water interface and in fully hydrated bilayers. For the monolayer studies, the compression isotherms of mixtures of the respective nicotinate with DPPC were recorded at various compositions on a hydrochloric acid subphase (pH 1.9-2.1, 37 +/- 2 degrees C). The headgroup of the nicotinates (24-29 A2/molecule) is larger than that of the hydrophobic tail (20 A2/molecule). The pure nicotinates exhibit a temperature- and chain length-dependent transition from an expanded to a condensed phase. Analysis of the concentration dependence of the average molecular area at constant film pressure and the concentration dependence of the breakpoint of the phase transition from the expanded to the condensed state suggests that all four DPPC-nicotinate mixtures are partially miscible at the air-water interface. Although a complex phase behavior with several phase transitions was observed, differential scanning calorimetry studies of the four mixtures are also indicative of the partial miscibility of DPPC and the respective nicotinate. Overall, the complex phase behavior most likely results from the head-tail mismatch of the nicotinates and the geometric packing constraints in the two-component lipid bilayer.

Comparative studies of oxidative stability of edible oils by differential scanning calorimetry and oxidative stability index methods

A comparative study was conducted to determine the oxidative stability of twelve different edible oils with two different instruments: a differential scanning calorimeter and an oxidative stability index (OSI) instrument. The OSI instrument temperature was set at 110 °C. The differential scanning calorimetry (DSC) technique involved oxidation of oil samples in an oxygen-flow DSC cell. The DSC cell temperature was set at four different isothermal temperatures: 110, 120, 130 and 140 °C. A dramatic increase of evolved heat was observed with the appearance of a sharp exothermic curve during initiation of the oxidation reaction. The oxidative induction time (T0) was automatically determined by extrapolation of the downward portion of the DSC oxidation curve to the time axis. There was a good correlation (P<0.0001) between the DSC T0 and OSI values. The decrease in log10 (T0) with increasing DSC isothermal temperature was best fitted by a linear equation. DSC evidently provides a convenient way to determine the oxidative stability of various edible oils.

Formation of nano-scale icosahedral quasicrystalline phase in amorphous Zr60Ni25Ti15 alloy

The precipitation of icosahedral quasicrystalline phases (I-phase) from Zr-based amorphous alloys was reported initially by Koster et al. [1]. Recently, much attention has been paid to amorphous Zr–Al–TM– M (TM = Co, Ni, Cu, M = Ag, Pd, Au, or Pt) system [2–4] and Zr–TM–M system [5–7] for the formation of I-phases from amorphous phases by crystallization. A typical alloy composition for the Zr–Al–TM–M system is Zr65Al7.5Ni10Cu12.5M5. In these alloys, noble metals (Pd, Pt, Au and Ag) are added to the wellknown good metallic glass former Zr65Al7.5Ni10Cu17.5 [8] in order to stabilize I-phases. For the Zr–TM– M system, the noble metals also play an important role in the formation of I-phases. It is noticed that most of the above amorphous alloys exhibit a large supercooled liquid region, Tx(=Tx − Tg), where Tx and Tg are the crystallization and glass transition temperature, respectively. Such a large supercooled region means good glass-forming ability for an amorphous alloy. It also seems that the addition of noble metals is essential for the formation of I-phases in these Zr-based amorphous alloys. For example, no icosahedral phase was observed in the Zr70(Ni, Cu)30 amorphous alloy, while I-phases could be acquired in the quaternary, ternary, and even binary Zr70(Ni, Cu, Pd)30 amorphous alloys [7]. In order to determine the possibility of getting an I-phase from a Zr-based amorphous alloy without a significant supercooled liquid region and noble metals, a study was undertaken on the formation of a nano-scale I-phase in amorphous Zr60Ni25Ti15 alloy. The Zr60Ni25Ti15 alloy ingot was prepared by arc melting a mixture of pure Zr, Ni and Ti. From the alloy ingot, a ribbon with a cross section of 0.03 × 1 mm2 was produced by a single roller melt-spinning method in an argon atmosphere. Annealing of the specimen was performed in a differential scanning calorimetry (DSC) at a heating rate of 0.67 K/s. The microstructure was examined by a transmission electron microscope (TEM). The sample for TEM observation was prepared by the ion milling technique. The XRD pattern of the melt-spun Zr60Ni25Ti15 ribbon is shown in Fig. 1. The existence of a broad peak indicates the formation of an amorphous state. It is very clear that the as-quenched ribbon only contains a single amorphous phase. The DSC curve of the melt-spun Zr60Ni25Ti15 ribbon is shown in Fig. 2. We can see from this figure that the crystallization proceeds through two Figure 1 XRD patterns of the Zr60Ni25Ti15 ribbon: (a) melt-spun, (b) annealed to 685 K, and (c) annealed to 900 K at a heating rate of 0.67 K/s and then cooled rapidly in the DSC cell.

Radiation effects on alanine; thermal approach for estimation of low absorbed radiation doses

Irradiated alanine when heated in differential scanning calorimetry cell (DSC) gives thermal profiles which have varying decomposition temperatures correlated to absorbed radiation dose between 0 to 250 Gy with high precision. Higher absorbed doses give characteristic decomposition peaks in DSC thermal profile. DSC studies indicate that changes in the thermal profiles are mainly due to exothermic decomposition of peroxides. Based on the information, it may be possible to develop a low cost and simple thermal device for estimating low absorbed doses in industrial radiation processing applications.

Determination of the melting and solidification characteristics of solders using differential scanning calorimetry

Differential scanning calorimetry (DSC) is used in the present study to determine the onset temperature of phase transformation and the enthalpy of fusion of various solder alloys. The solders studied are Sn-Pb, Sn-Bi, Ag-Sn, In-Ag, and Sn-Pb-Bi alloys. Very notable undercooling, such as 35 °C, is observed in the solidification process; however, a superheating effect is not as significant in the heating process. Besides the direct measurements of reaction temperature and heat of fusion, the fraction solid vs temperature has also been determined using a DSC coupled with a mathematical-model method. The heating and cooling curves of the solders are first determined using DSC. By mathematically modeling the heat transfer of the DSC cells, the heat evolution and absorption can be calculated, and then the melting and solidification curves of the solder alloys are determined. The three ternary alloys, Sn-35 wt pct Pb-10 wt pct Bi, Sn-45 wt pct Pb-10 wt pct Bi, and Sn-55 wt pct Pb-10 wt pct Bi, displayed similar DSC cooling curves, which had three reaction peaks. However, the solid fractions of the three alloys at the same temperature in the semisolid state, which had been determined quantitatively using the DSC coupled with a mathematical method, were different, and their primary solidification phases were also different.

Measuring Protein Thermostability by Differential Scanning Calorimetry

Differential scanning calorimetry (DSC) the method of choice to study the conformational stability of biological macromolecules and proteins in particular. This unit presents step-by-step protocols for DSC, including sample preparation and interpretation of the results in the simplest cases as well as calibration of the apparatus and maintenance of DSC cells. Various general experimental considerations, including possible pitfalls and errors, are also discussed.

Frictional surface temperature determination of high-temperature-resistant semicrystalline polymers by using their double melting features

Most semicrystalline polymers exhibit multiple melting peaks in the course of normal differential scanning calorimetry (DSC) measurements. When their amorphous versions are annealed above the glass transition temperatures, the lower endothermic temperatures (Tm1) appearing on the subsequent DSC heating traces are highly dependent on the annealing temperature (Ta). In consideration of the fact that temperature is the critical environmental factor controlling polymer crystallization, thermal history experienced by the material during annealing in the DSC cell is basically equivalent to that under frictional heating, and the surface temperature prevailing under sliding wear can be estimated from DSC scans taken on the worn surface. In this case, the lower melting peak temperature observed (which can be correlated with the annealing temperature) serves as an indicator for the flash temperature. In addition, this thermoanalytical method can also provide information about microstructural changes due to wearing. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 589–593, 1997

Effect of decationation and dealumination of zeolite Y on its acidity as assessed by ammonia desorption measured by differential scanning calorimetry (DSC)

Zeolite NaY was decationated step-wise until the H-form was obtained (HY), and zeolite HY was dealuminated step-wise to increase its SiO 2/Al 2o 3 ratio from 4.8 to 8.5. Ammonia was adsorbed on all the zeolite forms and was then desorbed thermally in a DSC cell, making use of the programmed temperature-increasing facility available in the DSC system. The total acidity of the zeolite was found to increase with decationation and decrease with dealumination. Strong acidity was found to increase with both decationation and dealumination, whereas weaker acidity decreased. The strength of strong acid sites increased further, whereas that of weaker acid sites decreased in both treatments.

Thermal and mechanical properties of single- and double-layer amorphous Se1−x Te x photoreceptors

Single and multilayer photoreceptor devices based on various compositions of amorphous selenium alloyed with tellurium and arsenic have been tested recently in a number of laboratories for use in laser and LEDtype printers employing the xerographic process, as well as for use in vidicon image tubes. Monolayer a-Sel_xTex alloys form one of the most widely used commercial xerographic photoreceptors and hence have been extensively examined for electrical and optical properties by a number of research organizations. There is, however, very little information available on the thermal stability and mechanical durability of these amorphous semiconductors, particularly in machine operating conditions where they are subjected to temperature variations, humidity changes, mechanical wear and scratching dUring the cleaning cycle and other environmental influences. In fact it was the proneness to crystallization and the weakness to mechanical wear and tear which led to the abandonment of pure a-Se as a viable xerographic photoreceptor in the 1960s. It was replaced by a-Se alloyed with 0.5 to 1% As which has a higher resistance to crystallization. The purpose of this letter is to provide some useful comparative data on the thermal and mechanical behaviour of singleand double-layer photoreceptor films from differential scanning calorimetry (DSC) and microhardness measurements. Inasmuch as a-As 2 Se 3 is another commercial amorphous photoconductor competing directly with the a-Se~_xTex system, we will also give data on its thermal and mechanical characteristics. Singleand double-layer a-Se~_xTe~ photoreceptor films were fabricated by vacuum evaporation of vitreous pellets from long stainless steel boats on to heated (~ 70 ° C) aluminium substrates. The stainless steel coating plant pumped by a conventional silicone diffusion pump (10-6torr) was equipped with a set of independently controlled boats and a shutter system to enable the fabrication ofmultilayers. Pure selenium pellets of xerographic grade (99.999%) were loaded into one boat and a mixture of selenium and prealloyed Se: Te pellets in correct proportions into another. The two sources were then evaporated sequentially without breaking the vacuum. Typical coating rates were 1 to 2 #m rain~ and the film thicknesses were 50 to 70/tm. Preparation and characterization of monolayer xerographic photoreceptors have already been reported [1]. Typical composition variation with distance in a singleand two doublelayer photoreceptors are shown in Fig. 1. In doublelayer photoreceptor structures the thin a-Se:Te top coating serves as the photogeneration layer (PGL) whereas the thicker a-Se coating between the PGL and the aluminium substrate acts as the charge transport layer (TL). The tellurium concentration profile was obtained from scanning electron microprobe (SEM) analysis. Films of a-As2Se3 were also prepared by vacuum evaporation on to heated aluminium substrates. The substrate temperature in the latter case was ~ 185 ° C. All the samples were well aged at room temperature to allow the physical properties to stabilize via structural relaxation processes. DSC studies were carried out on a DuPont differential thermal analyser, Type 990, equipped with the DSC cell attachment as described previously and also by others [1]. The films were stripped of their substrates and placed in Smallaluminium pans and then sealed. An empty pan Was used as a reference. A typical specimen weight was in the range 5 to 20 rag. The observed DSC thermograms were unaffected when the samples were preilluminated under highintensity light or dark-rested inthe pan for many days. The microhardness tests were carried Out on a Leitz (Wetzlar, Germany) miniload hardness tester with a 25g load which was the minimum available. The equipment operates a diamond pyramidal indenter for Vickers indentations on the sample under the selected load. For the softest films (a-Se) the measured indent diameters were ~ 35/~m which implies that the indentation depth was less than the film thickness. The quoted Vickers hardness number, Hv, for each sample is a mean over a number of random indentations. The variation was within ~ 10%. Fig. 2 shows three typical DSC thermograms at a heating rate of 5°Cmin -~ on (a) pure a-Se, (b) a-Se: 10wt % Te/Se double-layer and (c) a-Se: 10wt % Te single-layer photoreceptor films. The various characteristic temperatures are defined on thermogram (a). It is apparent from Fig. 2 that both the glass transition temperature, Tg, and the peak crystallization rate temperature, To, are shifted to higher temperatures with 10wt % Te alloying. Because of the broadening of the exotherms with tellurium addition the crystallization onset temperatures, Tff and To, however, are only slightly affected. By applying thermoanalytical methods developed for non-isothermal crystallization transformations based on nucleation and growth, we were able to show that the crystallization

Simultaneous Differential Scanning Calorimetry (DSC) and Infrared Spectroscopy Using an Infrared Microsampling Accessory (IRMA) and FT-IR

The capability of simultaneously measuring thermal property response and infrared spectra on specimens of microscopic dimensions can provide important insight into structural changes associated with thermal response for a wide range of systems. The simultaneous measurement of the thermal response in a differential scanning calorimeter (DSC) and the infrared spectra in an FT-IR can provide this capability. In particular, the use of a DSC cell adapted for microscopic observation during thermal treatment, combined with an infrared microsampling accessory (IRMA) in an FT-IR, permits the simultaneous collection of such data. The range of applications of such a technique is undoubtedly immense. The various phase transitions and thermal responses of crystalline and amorphous polymers, polymer blends and copolymers, and liquid crystalline polymers, as well as small molecules, could be correlated with the structural information derivable from the simultaneously collected infrared spectra. This would permit studies of reaction and crystallization kinetics, oxidation, efficacy of additives, etc.

The DSC cell—a versatile tool to study thermal-oxidative degradation of lubricants and related problems

The versatility of a differential scanning calorimetry (DSC) cell in studying thermal and/or thermal-oxidative degradation of lubricants is shown using ester based aviation turbine oils as an example. The following applications are discussed: 1. quality control of used oils by pressure differential scanning calorimetry (PDSC); 2. influence of metal catalysis on oil degradation; 3. identification of volatile degradation products by PDSC—gas chromatography (GC)—mass spectrometry (MS) via a TENAX GC trap.

Amorphous to crystalline transformation in bulk electroless nickel by differential scanning calorimetry

Differential scanning calorimetry (DSC) in conjunction with X-rays and transmission electron microscopy were employed to elucidate the mechanism of amorphous to crystalline transformation in bulk electroless nickel (Ni—10.9 wt. % P) alloy. As-deposited amorphous electroless nickel was heated from room temperature to 650°C in a DSC cell in an argon atmosphere at 20°C min −1. Three exothermic reactions were observed. Heating runs were interrupted after each reaction for microstructural and crystal structure determinations. It was found that the first reaction was associated with the precipitation of fine nickel particles in an amorphous Ni 3P matrix, the second with crystallization of the amorphous Ni 3P matrix into spherulitic grains, and the third with recrystallization and grain growth of the Ni 3P matrix and coarsening of nickel precipitates. The transformation temperatures and heats of reaction were also determined. This demonstrates the application of high sensitivity differential scanning calorimetry to the study of solid state reactions in general.