DSC Cell Research Articles

Study on the long-term discharge and redox stability of symmetric flat-tube solid oxide fuel cells

In this work, we investigated the stabilities of a newly developed symmetric flat-tube solid oxide fuel cells with double-sided cathodes (DSC cells) for long-term discharge and redox cycling operations. The DSC cell was discharged at 750°Cusing pure H2 fuel for ca. 2030 h and the degradation rate was ca. 10% per one thousand hours. In addition, H2 and air were alternatively supplied to the anode of DSC cells for tens of cycles in order to investigate the redox-stability. The duration time of oxidation process was found to be dominant for the stability of the cell. The microstructure of the DSC cells before and after these tests were investigated in order to clarify the degradation mechanisms. A great number of Ni particles with a diameter of ca. 2 μm was exsolved in the large pores of anode support layer after the redox cycling test with long duration time of oxidation. Such phenomenon induced by redox cycling has not been reported in the literatures. Based on the experimental data, the mechanisms were discussed.

Kinetics of D,L-Lactide Polymerization Initiated with Zirconium Acetylacetonate.

The kinetic of D,L‐lactide polymerization in presence of biocompatible zirconium acetylacetonate initiator was studied by differential scanning calorimetry in isothermal mode at various temperatures and initiator concentrations. The enthalpy of D,L‐lactide polymerization measured directly in DSC cell was found to be ΔH=−17.8±1.4 kJ mol−1. Kinetic curves of D,L‐lactide polymerization and propagation rate constants were determined for polymerization with zirconium acetylacetonate at concentrations of 250–1000 ppm and temperature of 160–220 °C. Using model or reversible polymerization the following kinetic and thermodynamic parameters were calculated: activation energy Ea=44.51±5.35 kJ mol−1, preexponential constant lnA=15.47±1.38, entropy of polymerization ΔS=−25.14 J mol−1 K−1. The effect of reaction conditions on the molecular weight of poly(D,L‐lactide) was shown.

Mechanochemistry of Bi2O3. 2. Mechanical Activation and Thermal Reactions in a High-Energy Al + Bi2O3 System

The regularities of mechanical activation (MA) and the reactivity of an high-energy 15Al + 85Bi2O3 (wt %) system have been studied with the use of X-ray diffraction analysis, synchronous thermal analysis, and the measurement of the ignition temperature upon the contact with a hot surface. For the nonactivated system, the intercomponent interaction has not been recorded upon their heating in a DSC cell up to 760°C. When MA is carried out, the reaction partly occurs directly in the course of grinding and upon the subsequent heating. In the course of heating at a rate of 10°C/min, the intercomponent interaction proceeds to yield Bi metal and amorphous Al2O3 in a temperature range of 350–800°C, with maxima being observed at 520 and 630°C. At temperatures below 480°C, the reaction occurs in nanolayers, as is evident from the position and shape of the melting curve obtained for formed bismuth. The effects of the duration of MA on the conversion of the components, reaction kinetics upon heating in the DSC cell, the temperature of ignition upon the contact of an activated sample with a hot surface, and the rate of mixture combustion have been determined. The optimal duration of MA, at which the ignition temperature is minimum, has been found.

The effect of increasing honey concentration on the properties of the honey/polyvinyl alcohol/chitosan nanofibers

The effect of increasing honey concentrations from 10% to 30% within the Honey (H)/polyvinyl alcohol (P)/chitosan (CS) nanofibers was investigated. Changes in the electrospun nanofiber diameters, crystallinity, thermal behavior, porosity and antibacterial activity have been assessed using SEM, XRD, DSC, TGA, mercury porosimeter and viable cell count technique. The HPCS nanofibers were cross-linked and tested for their swelling abilities and degradation behavior. The mean diameter of HPCS nanofibers increased from 284±97nm to 464±185nm upon increasing the honey concentration from 10% to 30%. Irrespective the honey concentrations, the nanofibers have demonstrated enhanced porosity. Increasing the honey concentration resulted in a reduction in the swelling of the 1h cross-linked HPCS nanofibers containing 10% and 30% H from 520% to 100%; respectively. Degradation after 30days was reduced in the 3h cross-linked HPCS nanofibers compared to the non-crosslinked HPCS nanofibers. Enhanced antibacterial activity was achieved against both Staphylococcus aureus and Escherichia coli upon increasing the honey concentration. Changing the honey concentration and the extent of nanofiber crosslinking can be used to adjust different parameters of the HPCS nanofibers to suit their applications in wound healing and tissue engineering.

Recommendations on DSC calibration

The enthalpy of fusion of indium was measured at the heating rates of 3, 9, and 15 K min−1 according to two procedures, with and without replacing the crucible with the sample in DSC cell. Repeatability in the enthalpies after these two procedures differs by ten times. Placing the crucible with a sample into its position inside DSC was concluded to generate a random error of about 0.5 % in the enthalpy due to the irreproducibility in the thermal conduction. The error in a single value measured after single run can be as high as 2–3 %. If that value is used for the evaluation of the calibration coefficient, the random error of the sample positioning becomes systematic error of the calibration. The ways of escaping such a flaw are discussed.

Thermally induced crystallization of amorphous Fe40Ni40P14B6 alloy

The crystallization mechanism and kinetics of Fe40Ni40P14B6 amorphous alloy were studied under non-isothermal conditions. Thermal stabilization of this alloy manifests in DSC through two complex peaks, corresponding to crystallization and recrystallization, respectively. The complex crystallization DSC peak was deconvoluted into individual steps corresponding to crystallization of individual phases, where the results using both Gaussian–Lorentzian cross-product and Fraser–Suzuki function were compared. It was determined that the values of kinetic triplets of the individual steps did not exhibit any significant difference, depending on the deconvolution function. Anisotropic growth was indicated to be the prevailing type of impingement for all crystallization steps. Using the calculated values of the respective kinetic triplets and the mechanisms determined from the value of Avrami exponent, distinct values of activation energies for nucleation and crystal growth for crystallization of each individual phase were calculated, showing significantly higher values for nucleation than those for crystal growth. Alloy samples treated non-isothermally in the DSC cell exhibit inhomogeneous surface morphology with highly granulated structure dependent on heating rate.

Kinetics and thermodynamics of l-lactide polymerization studied by differential scanning calorimetry

Kinetics of l-lactide polymerization was studied by differential scanning calorimetry in isothermal mode at various temperatures and catalyst concentrations. The enthalpy of l-lactide polymerization measured directly in DSC cell was found to be ΔH=−19±0.5kJmol−1. Kinetic curves of l-lactide polymerization and propagation rate constants were determined for polymerization with stannous octoate at concentrations 200–1100ppm at temperatures 180, 190, 200 and 220°C. Using model or reversible polymerization the following kinetic and thermodynamic parameters were calculated: activation energy Ea=50±5kJmol−1, preexponential constant lnA=18±1, entropy of polymerization ΔS=−12±1Jmol−1K−1.

RheoDSC: Design optimisation by heat transfer modelling

RheoDSC is a novel thermal analysis technique that permits simultaneous rheometry and calorimetry on one sample. By combining two instruments in a single setup, introducing a rotor assembly and an insert for fixing sample plates into the DSC cell, an operational instrument was developed. As design and material selection greatly influence the calorimetric performance of this combined technique, several designs were evaluated through numerical simulation of experiments. Finite element based heat transfer modelling, in some cases combined with chemical reaction modelling, is used to evaluate the quality of the calorimetric response, supporting the instrument design.

Time–temperature-transformation (TTT) and temperature–conversion-transformation (TxT) cure diagrams by RheoDSC: Combined rheometry and calorimetry on an epoxy-amine thermoset

A novel hyphenated RheoDSC combines rheological and calorimetric analyses of samples by performing rheological experiments inside a DSC cell. This enables direct studies of the chemorheological changes of epoxy-amine thermosets during crosslinking. The rheological and calorimetric information can be presented in time–temperature-transformation (TTT) cure diagrams, without the need for making interpretations based on experiments performed on different samples in the different thermal environments of individual rheometers and calorimeters.

Correlation between processing parameters and microstructure of electrospun poly( D, l-lactic acid) nanofibers

Using dimethyl formamide as the solvent, electrospinning of poly( D, l-lactic acid) (PDLLA, d-lactide content:10%) solutions with various concentrations was performed by means of a heating jacket for controlling the solution temperature range from 25 to 104 °C. In addition, an IR emitter was used to control the surrounding temperature at ∼110 °C. The effects of solution properties and processing variables on the morphologies of the cone/jet/fiber were investigated, and the internal structure of the electrospun fibers was characterized using polarized FTIR, WAXD and DSC. A sufficient entanglement density existing in a given solution was an important requirement for successfully obtaining uniform fibers without beads. The log–log plot of specific viscosity ( η sp) versus PDLLA volume fraction ( ϕ v) provided us with a useful guideline to determine the entanglement concentration ( c e) for preparing fiber-shaped electrospun products. The ϕ v-dependence of η sp varied from η sp ∼ ϕ v 1.1 for a dilute solution to η sp ∼ ϕ v 4.7 for a solution possessing entangled chains. From the incipient concentration of entanglements, the determined c e was ∼10 wt%, which was in fair agreement with what was predicted theoretically by a simple relation of 2 M e/ M w, where M e and M w were the molecular weight between melt entanglements and the average molecular weight of PDLLA, respectively. To obtain uniform PDLLA fibers without beads, however, a minimum concentration of ∼1.9 c e was required for the entangled solutions possessing sufficient network strength to prohibit the capillary instability during jet whipping. The log–log plots of the jet diameter ( d j) and fiber diameter ( d f) versus zero shear viscosity ( η o) showed two scaling laws existing for the present solution, that is, d j ∼ η o 0.07 and d f ∼ η o 0.45 . For a given solution, an intimate relation between d j and d f was derived to be d f ∼ d j 0.61 , regardless of the variations of processing variables applied. High-temperature electrospinning produced small diameter fibers because of the reduction of η o, but the effect was gradually diminished for solution temperatures higher than 56 °C owing to the enhanced solvent evaporation. The as-spun nanofibers of this thermally slow-crystallizing PDLLA species were amorphous, and the Hermans orientation function calculated from the polarized FTIR results was ca. −0.063 regardless of the electrospinning conditions applied. This suggests that there was no preferential chain orientation developed in the nanofibers. In the heating in a DSC cell at a rate of 10 °C/min, however, rapid crystallization took place at 97 °C, followed by two well-separated melting endotherms centered at 121 and 148 °C, respectively. WAXD and FTIR results exhibited the exclusive presence of α-form crystals. These unique features were attributed to the occurrence of phase separation during electrospinning, which interrupted the chain orientation along the fiber during jet stretching, and yielded more trans–trans conformers with more extended chain structure to readily facilitate the cold crystallization during post-heating.

DSC Analysis of the precipitation reactions in the alloy AA6082

The deformation introduced during the sample preparation had a high impact on the response of the alloy AA6082 to heating in the DSC cell. The DSC curve was strikingly different when DSC samples of this alloy were punched after the solution treatment. Dislocations introduced by punching have annihilated the quenched-in vacancies and have suppressed clustering initially. Dislocations have also provided heterogeneous nucleation sites for the GP-1 zones that readily grew to become stable nuclei for the β" phase owing to the enhanced atomic transport. β" as well as the β' precipitation kinetics were thus accelerated leading to a substantial change in the DSC peak arrangement. Deformation introduced during sample preparation by gentle grinding alone, on the other hand, did not suffice to alter the precipitation sequence, producing a DSC curve very similar to that obtained with samples punched before the solution treatment.

Calibration coefficient of a heat-flow DSC. Part I. Relation to the Sensitivity of a thermocouple

Abstract Relation between the calibration coefficient of a DSC sensor k(T) and the sensitivity of a thermocouple e(T) which the sensor is made from was derived from the analysis of a heat transfer inside a DSC cell. Ratio e(T)/k(T) is equal to A+BT 3. The first component depends on heat conduction and the second one on radiation. The relationship was tested for DSC-204 Netzsch using (i) data on calibration vs. enthalpies of phase transitions (reference samples) and (ii) measurements of heat capacity of corundum. Both tests show very good agreement between experimental data and predicted theoretical function.

New modulated DSC measurement technique

The introduction of modulated DSC (MDSC) increased the utility of DSC by adding the ability to separate the sample heat flows resulting from time dependent and time independent processes. The time independent sample heat flow rate is just that which is due to the sample heat capacity. MDSC is based on conventional DSC where the measured signal is the temperature difference between the sample and reference positions of the sensing apparatus. The measured heat flow rates display significant dependence on the period of the modulation, as demonstrated by the well-known decrease of measured heat capacity with decreasing modulation period. To reduce the frequency dependence, MDSC experiments are usually performed using rather long periods, typically 60 s or more, or various calibration or correction techniques may be applied. Long periods require low average heating rates and result in rather lengthy experiments that reduce the productivity of the DSC. A new MDSC heat flow measuring technique has been developed that greatly reduces the frequency dependence of the heat flow measurement. It includes three components: (1) a new DSC cell that has independent sample and reference calorimeters and includes two differential temperature measurements, (2) a new DSC heat flow measurement method that is based upon independent sample and reference heat flow rates and (3) a new MDSC heat flow calculation method that uses the independent sample and reference heat flow rate measurements. MDSC experiments using this new technique display greatly reduced period dependence, allowing modulation periods as short as 20 s to be used. Higher average heating rates may be used and productivity of the DSC is increased as much as threefold or more. 1 Patents applied for. 1

Phase transitions of pigskin gelatin

Edible films are flexible thin materials based on biopolymers. It is therefore necessary to know the physicochemical properties of those macromolecules in order to obtain films with desirable characteristics. Dried gelatin is a partially crystalline polymer that exhibits glass and helix–coil transitions. The knowledge of phase properties is important for the choice of the type and concentration of the plasticizer to be utilized to obtain a flexible and easy-to-handle film. The objective of this work is to determine the phase transitions of pigskin gelatin as a function of moisture content in the hygroscopic domain. Pure gelatin was conditioned over different saturated salt solutions at 25°C to allows samples with various moisture content. After equilibrium was established, the samples and an empty pan, as reference, were heated twice between −100 and 250°C at the rate of 5°C/min, in a DSC (TA 2010) after quench-cooling with liquid nitrogen. Gelatin was placed in a pan with a perforated cover, and maintained at 105°C for 24 h in the DSC cell before thermal analyses, to obtain completely dried samples. The glass transition temperature of these samples was found to be 220.2°C. The DSC traces obtained in the first scan, except those conditioned at 11% relative humidity, showed a glass transition followed by two endothermic peaks due to two sol–gel transitions in the gelatin. The plasticizing effect of moisture on Tg was observed in all the samples conditioned by absorption and in the second scan with the samples conditioned by desorption. This behavior was well represented by the Gordon and Taylor model, with κ=5.26 and R 2=0.96. Also, a plasticizing effect of moisture over the sol–gel transitions was observed. The Flory-Huggins model was applied to experimental data with: χ 1=1.94 and R 2=0.999, for the first peak Tm, and χ 1=1.90 and R 2=0.989, for the second peak.

Synchrotron studies of polymers at DND-CAT

Two examples are presented that illustrate the capabilities of DND-CAT instrumentation for the study of the effects of processing on polymers. Firstly, a thermoplastic elastomer, Hytrel®, was stretched while 2-D data were collected simultaneously. The Hytrel® data show that the yield point of the stress-strain curve is associated with the sudden appearance of a four-point pattern. At higher deformations, strain-induced crystallization and the destruction of the hard segment domains lead to a substantial decrease of the contrast as monitored by the SAXS invariant. Prior to breakage, the extent and intensity of an equatorial streak develops as the material fibrillates. Secondly, SAXS and WAXS data were collected from quenched and annealed Poly(ethylene terephthalate) (PET) samples mounted on a DSC cell, to characterize the pre-melting shoulder in this material. Results show that substantial melting and re-crystallization occurs within the range of this shoulder in the quenched sample.

The development of gas-flow modulation for high-frequency MTDSC measurements

The purpose of this study was to investigate the feasibility of modulating the temperature programme of a conventional DSC by use of an alternating gas-flow system. Modulated temperature differential scanning calorimetry (MTDSC) is an important thermal analysis technique but suffers from a limited applicable frequency range due to the mass of the sample and DSC cell leading to the impingement of thermal conductivity effects. We suggest that the frequency limit can be increased by replacing the cell as the source of temperature modulation with an external gaseous source, directed towards the sample and reference pans. In this evaluation, an alternating gas-flow was passed through a line to a forced gas-flow accessory (FGFA). The FGFA consisted of two matched cylinders containing chambers that allowed pre-temperature-equilibration of the stream of gas before it was passed over the sample and reference pans. The development of this device revealed the essential practical requirements of gas-flow modulation for high-frequency temperature modulation. These include the following: an appropriately sealed tunable gas supply to both sample and reference pans, an effective method for high-frequency cycling of the gas-flow rate, a small aperture to deliver the flowing gas directly over the pan and a temperature equilibration chamber. The results from samples of quenched PET and amorphous Saquinavir indicate that gas-flow modulation is indeed feasible, with the FGFA able to raise the attainable temperature modulation frequency by an order of magnitude compared to conventional MTDSC.

High-pressure DSC study of thermal transitions of a poly(ethylene terephthalate)/carbon dioxide system

The thermal transitions of a poly(ethylene terephthalate)/carbon dioxide (PET/CO 2) system were investigated by using a differential scanning calorimeter accessorized with a high-pressure DSC cell. It was found that the glass transition temperature of PET decreases with an increase in the CO 2 pressure due to the plasticization effect, which is quite noticeable even at rather low CO 2 pressures. The sorbed CO 2 enhances the mobility of the chain segments and depresses the crystallization temperature of the PET. The CO 2-induced crystallization of PET at high pressure is attributed mainly to the plasticization effect, which causes a lower T g than room temperature for PET, and hence crystallization of PET can occur at room temperature. The sorbed CO 2 was also found to be able to induce the crystallization of PET at temperatures lower than the glass transition temperature of PET. The results of high-pressure DSC were supported by measurements of wide-angle X-ray diffraction (WAXD).

Derivation of Temperature-Modulated DSC Thermal Conductivity Equations

One of the benefits of temperature-modulated DSC (TMDSC) is its ability to measure thermal conductivity and thermal diffusivity without DSC cell modifications or additional accessories. Thermal conductivity of solid materials from 0.1 to about 1 W m-1 K-1 measured. Applications of this approach have been discussed in the literature but no description is yet available concerning the derivation of the working equations. This presentation provides a detailed derivation of the working equations used to obtain thermal conductivity and thermal diffusivity from TMDSC data.

DSC characterisation of urea/formaldehyde condensates, II. Experiences with high pressure DSC cell

At anisothermic thermograms registered when curing the urea/formaldehyde (UF) resins in high pressure DSC cell the endothermic effects, such as evaporation of water and elimination of formaldehyde shift to temperatures higher by about 40°C in comparison to the thermograms received using the cell without pressure. The temperature for the exotherma of curing remains unchanged. Due to the shift of decomposition temperature the elimination of formaldehyde takes place at more agreeable conditions: as the resin is more rigid the risk of additional endothermic effect connected with bubble blowing is diminished. The shift of water elimination temperature however disturbs at clear recognition of the base line of the endotherma. Preliminary treating of samples with inert gas before the measurements helps to improve the measurement conditions.

Evaluation of systems for use in DSC measurements on energetic materials

Tray and tube holders for microampoules containing energetic material were fabricated for use in DSC measurements. Comparison with earlier, independent studies using an aluminum tube holder demonstrated that equivalent performance was obtained. While the system with the tray holder provided statistically improved results over those obtained using the tube holder, it clearly afforded less protection for the DSC cell in the event of a microampoule rupture. Results obtained for a number of energetic materials including t -butyl peroxide and the explosives, tetryl, nitrocellulose and pentaerythritol tetranitrate are specifically described. In addition, explosion tests conducted using 2,4,6-trinitrotoluene enabled the elucidation of a qualitative ranking scale for potential damage to the DSC cell based on the deformation of the tray holder.