Analysis of thermal properties of phase change materials (PCM) using differential scanning calorimeter (DSC)

Commercially available PCM RT 20, RT 27, SP 22, A17 and SP 25 A8. Were analyzed using dynamic and step method of heat flux DSC. The results of the dinamic and step method were compared with commercial valures. It was found that RT 20 & RT 27 showed good conforming of results with commercial values while SP 22 A17 & SP 25 A8 did not show conformity.

Calorimetry of dehydrogenation and dangling-bond recombination in several hydrogenated amorphous silicon materials

Differential scanning calorimetry (DSC) was used to study the dehydrogenation processes that take place in three hydrogenated amorphous silicon materials: nanoparticles, polymorphous silicon, and conventional device-quality amorphous silicon. Comparison of DSC thermograms with evolved gas analysis (EGA) has led to the identification of four dehydrogenation processes arising from polymeric chains (A), SiH groups at the surfaces of internal voids (A'), SiH groups at interfaces (B), and in the bulk (C). All of them are slightly exothermic with enthalpies below 50 meV/H atoms , indicating that, after dissociation of any SiH group, most dangling bonds recombine. The kinetics of the three low-temperature processes [with DSC peak temperatures at around 320 (A),360 (A'), and 430°C (B)] exhibit a kinetic-compensation effect characterized by a linea relationship between the activation entropy and enthalpy, which constitutes their signature. Their Si-H bond-dissociation energies have been determined to be E (Si-H)0=3.14 (A), 3.19 (A'), and 3.28 eV (B). In these cases it was possible to extract the formation energy E(DB) of the dangling bonds that recombine after Si-H bond breaking [0.97 (A), 1.05 (A'), and 1.12 (B)]. It is concluded that E(DB) increases with the degree of confinement and that E(DB)>1.10 eV for the isolated dangling bond in the bulk. After Si-H dissociation and for the low-temperature processes, hydrogen is transported in molecular form and a low relaxation of the silicon network is promoted. This is in contrast to the high-temperature process for which the diffusion of H in atomic form induces a substantial lattice relaxation that, for the conventional amorphous sample, releases energy of around 600 meV per H atom. It is argued that the density of sites in the Si network for H trapping diminishes during atomic diffusion

Calorimetry of hydrogen desorption from a-Si nanoparticles

The process of hydrogen desorption from amorphous silicon (a-Si) nanoparticles grown by plasma-enhanced chemical vapor deposition (PECVD) has been analyzed by differential scanning calorimetry (DSC), mass spectrometry, and infrared spectroscopy, with the aim of quantifying the energy exchanged. Two exothermic peaks centered at 330 and 410 C have been detected with energies per H atom of about 50 meV. This value has been compared with the results of theoretical calculations and is found to agree with the dissociation energy of Si-H groups of about 3.25 eV per H atom, provided that the formation energy per dangling bond in a-Si is about 1.15 eV. It is shown that this result is valid for a-Si:H films, too.

Calorimetry of hydrogen desorption from ɑ-Si nanoparticles

The process of hydrogen desorption from amorphous silicon (ɑ-Si) nanoparticles grown by plasmaenhanced chemical vapor deposition (PECVD) has been analyzed by differential scanning calorimetry (DSC), mass spectrometry, and infrared spectroscopy, with the aim of quantifying the energy exchanged. Two exothermic peaks centered at 330 and 410 °C have been detected with energies per H atom of about 50 meV. This value has been compared with the results of theoretical calculations and is found to agree with the dissociation energy of Si-H groups of about 3.25 eV per H atom, provided that the formation energy per dangling bond in ɑ-Si is about 1.15 eV. It is shown that this result is valid for ɑ-Si:H films, too

Stone-ground wood pulp-reinforced polypropylene composites: water uptake and thermal properties

Two of the drawbacks of using natural-based composites in industrial applications are thermal instability and water uptake capacity. In this work, mechanical wood pulp was used to reinforce polypropylene at a level of 20 to 50 wt. %. Composites were mixed by means of a Brabender internal mixer for both non-coupled and coupled formulations. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to determine the thermal properties of the composites. The water uptake behavior was evaluated by immersion of the composites in water until an equilibrium state was reached. Results of water absorption tests revealed that the amount of water absorption was clearly dependent upon the fiber content. The coupled composites showed lower water absorption compared to the uncoupled composites. The incorporation of mechanical wood pulp into the polypropylene matrix produced a clear nucleating effect by increasing the crystallinity degree of the polymer and also increasing the temperature of polymer degradation. The maximum degradation temperature for stone ground wood pulp–reinforced composites was in the range of 330 to 345 ºC

Study of chemical modification of alkaline lignin by the glyoxalation reaction

In this study, glyoxalated alkaline lignins with a non-volatile and non-toxic aldehyde, which can be obtained from several natural resources, namely glyoxal, were prepared and characterized for its use in wood adhesives. The preparation method consisted of the reaction of lignin with glyoxal under an alkaline medium. The influence of reaction conditions such as the molar ratio of sodium hydroxide-to-lignin and reaction time were studied relative to the properties of the prepared adducts. The analytical techniques used were FTIR and 1H-NMR spectroscopies, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Results from both the FTIR and 1H-NMR spectroscopies showed that the amount of introduced aliphatic hydroxyl groups onto the lignin molecule increased with increasing reaction time and reached a maximum value at 10 h, and after they began to decrease. The molecular weights remained unchanged until 10 h of reaction time, and then started to increase, possibly due to the repolymerization reactions. DSC analysis showed that the glass transition temperature (Tg) decreased with the introduction of glyoxal onto the lignin molecule due to the increase in free volume of the lignin molecules. TGA analysis showed that the thermal stability of glyoxalated lignin is not influenced and remained suitable for wood adhesives. Compared to the original lignin, the improved lignin is reactive and a suitable raw material for adhesive formula

Characterization of alkaline lignins for use in penol-formaldehyde and epoxy resins

Besides polyurethanes and polyesters, phenolic and epoxy resins are the most prominent applications for technical lignins in thermosetting materials. To evaluate the potential application of lignin raw materials in phenol formaldehyde and epoxy resins, three types of alkaline lignins were characterized in terms of their structures and thermal properties. The lignin samples analyzed were kraft lignin (LIG-1), soda–rice straw lignin (LIG-2), and soda-wheat straw lignin (LIG-3). FTIR and 1H-NMR methods were used to determine their structure. Gel permeation chromatography (GPC) was used to determine the molecular weight distribution (MWD). Differential scanning calorimetry (DSC) was used to measure the glass transition temperature (Tg), and thermogravimetric analysis (TGA) to determine the thermal stability of lignin samples. Results showed that kraft lignin (LIG-1) has moderate hydroxyl-group content, is rich in G-type units, and has good thermal stability. These properties make it more suitable for direct use in phenol formaldehyde resins, and it is therefore a good raw material for this purpose. The alkaline soda-rice straw lignin (LIG-2) with a high hydroxyl-group content and excellent thermal stability is most suited to preparing lignin-based epoxy resin

Análisis de sistemas bucoadhesivos

[spa]Objetivo: El objetivo de este estudio es el diseño de un parche bucoadhesivo para la administración transbucal de clorhidrato de doxepina utilizando diferentes polímeros así como la caracterización de dichos sistemas en cuanto al análisis calorimétrico y la capacidad de hinchamiento.Materiales y métodos: Se ha utilizado clorhidrato de doxepina y diferentes polímeros, carboximetilcelulosa sódica, hidroxipropilmetilcelulosa y chitosan. La calorimetría diferencial de barrido (DSC) se ha realizado en un dispositivo Mettler FP 80 equipado con un horno FP 85 y la capacidad de hinchamiento utilizando placas de agar.Resultados: Se obtienen termogramas de los parches y las mezclas físicas donde se observan transiciones endotérmicas entre 30 y 120º C y el pico endotérmico del principio activo en las mezclas físicas binarias. La entalpía de deshidratación es similar en los polímeros de carboximetilcelulosa sódica y chitosan (281 J/g) siendo menor en la película de hidroxipropilmetilcelulosa (251 J/g), al igual que el porcentaje de hidratación donde se demuestra que los parches elaborados con hidroxipropilmetilcelulosa presenta menor tendencia a captar agua (55,91 %) frente al 67,04 % y 67,30 % de la carboximetilcelulosa sódica y chitosan, respectivamente.Conclusión: Los resultados obtenidos muestran que existe compatibilidad entre los componentes de la formulación y los datos de entalpía se correlacionan con los datos obtenidos en el ensayo de hinchamiento.[eng]The aim of this study is to design a bucoadhesive patch for the transbuccal administration of doxepin hydrochloride using different polymers as well as the characterization of these systems for calorimetric analysis and the swelling capacity. Materials and methods: Doxepin hydrochloride was used as well as various polymers; carboxymethylcellulose sodium, hydroxypropylmethyl cellulose and chitosan. Differential scanning calorimetry (DSC) was carried out using a Mettler FP 80 device equipped with a FP 85 oven and the swelling capacity using agar plates. Results: Thermograms obtained patches and physical mixtures where there are endothermic transitions between 30 and 120º C and the endothermic peak of the active principle in binary physical mixtures. Dehydration enthalpy is similar in polymers of carboxymethylcellulose sodium and chitosan (281 J/g), the film having less hydroxypropylmethylcellulose (251 J/g), the percentage of moisture shows that the patches prepared with hydroxypropylmethylcellulose have less tendency to collect water (55.91 %) compared to 67.04 % and 67.30 % with sodium carboxymethylcellulose and chitosan, respectively. Conclusion: The results show that there is compatibility between the components of the formulation and the enthalpy data correlate

Análisis de sistemas bucoadhesivos

[spa]Objetivo: El objetivo de este estudio es el diseño de un parche bucoadhesivo para la administración transbucal de clorhidrato de doxepina utilizando diferentes polímeros así como la caracterización de dichos sistemas en cuanto al análisis calorimétrico y la capacidad de hinchamiento.Materiales y métodos: Se ha utilizado clorhidrato de doxepina y diferentes polímeros, carboximetilcelulosa sódica, hidroxipropilmetilcelulosa y chitosan. La calorimetría diferencial de barrido (DSC) se ha realizado en un dispositivo Mettler FP 80 equipado con un horno FP 85 y la capacidad de hinchamiento utilizando placas de agar.Resultados: Se obtienen termogramas de los parches y las mezclas físicas donde se observan transiciones endotérmicas entre 30 y 120º C y el pico endotérmico del principio activo en las mezclas físicas binarias. La entalpía de deshidratación es similar en los polímeros de carboximetilcelulosa sódica y chitosan (281 J/g) siendo menor en la película de hidroxipropilmetilcelulosa (251 J/g), al igual que el porcentaje de hidratación donde se demuestra que los parches elaborados con hidroxipropilmetilcelulosa presenta menor tendencia a captar agua (55,91 %) frente al 67,04 % y 67,30 % de la carboximetilcelulosa sódica y chitosan, respectivamente.Conclusión: Los resultados obtenidos muestran que existe compatibilidad entre los componentes de la formulación y los datos de entalpía se correlacionan con los datos obtenidos en el ensayo de hinchamiento.[eng]The aim of this study is to design a bucoadhesive patch for the transbuccal administration of doxepin hydrochloride using different polymers as well as the characterization of these systems for calorimetric analysis and the swelling capacity. Materials and methods: Doxepin hydrochloride was used as well as various polymers; carboxymethylcellulose sodium, hydroxypropylmethyl cellulose and chitosan. Differential scanning calorimetry (DSC) was carried out using a Mettler FP 80 device equipped with a FP 85 oven and the swelling capacity using agar plates. Results: Thermograms obtained patches and physical mixtures where there are endothermic transitions between 30 and 120º C and the endothermic peak of the active principle in binary physical mixtures. Dehydration enthalpy is similar in polymers of carboxymethylcellulose sodium and chitosan (281 J/g), the film having less hydroxypropylmethylcellulose (251 J/g), the percentage of moisture shows that the patches prepared with hydroxypropylmethylcellulose have less tendency to collect water (55.91 %) compared to 67.04 % and 67.30 % with sodium carboxymethylcellulose and chitosan, respectively. Conclusion: The results show that there is compatibility between the components of the formulation and the enthalpy data correlate

Characterization of Mechanically Alloyed Nanocrystalline Fe(Al): Crystallite Size and Dislocation Density

A nanostructured disordered Fe(Al) solid solution was obtained from elemental powders of Fe and Al using a high-energy ball mill. The transformations occurring in the material during milling were studied with the use of X-ray diffraction. In addition lattice microstrain, average crystallite size, dislocation density, and the lattice parameter were determined. Scanning electron microscopy (SEM) was employed to examine the morphology of the samples as a function of milling times. Thermal behaviour of the milled powders was examined by differential scanning calorimetry (DSC). The results, as well as dissimilarity between calorimetric curves of the powders after 2 and 20 h of milling, indicated the formation of a nanostructured Fe(Al) solid solution

Preparació de materials híbrids orgànico-inorgànics a partir de sals d'imidazoli

Estudi elaborat a partir d’una estada a l’ Ecole Nationale Supérieure de Chimie de Montpellier, França, durant 2006. S’han sintetitzat materials híbrids orgànico-inorgànics mitjançant el procés sol-gel i altres estratègies sintètiques. En alguns casos, s’ha intentat estructurar aquests materials, ja sigui per autoestructuració o per mitjà de tensioactius. Com a catalitzadors de les reaccions d'hidròlisi i policondensació s’han utilitzat àcids, bases i fluorurs. Els materials obtinguts s’han caracteritzat mitjançant diferents tècniques: BET (Brunauer-Emmett-Teller), TEM (microscopia electrònica de transmissió), SEM (microscòpia electrònica de rastreig), raigs X en pols , IR i RMN (ressonància magnètica nuclear) en estat sòlid. Amb aquests materials es pretén preparar catalitzadors heterogenis de Pd per reaccions d’acoblament creuat, i de Ru per reaccions de metàtesi. També s’han sintetitzat sals d'imidazoli amb cadenes hidrocarbonades llargues amb l'objectiu de preparar gels de sílice amb aquestes molècules atrapades dins la matriu inorgànica. Aquests materials s’utilitzaran com a organocatalitzadors i també es prepararan els corresponents catalitzadors de Pd per reaccions de Heck, Suzuki i Sonogashira. Les sals d’imidazoli s’han utilitzat com a tensioactius en la preparació de gels de sílice estructurats. Aquestes molècules han resultat ser cristalls líquids i s’han caracteritzar mitjançant DSC (differential scanning calorimetry), microscopia òptica i raigs X.

A high-sensitivity differential scanning calorimeter with magnetic field for magnetostructural transitions

We have developed a differential scanning calorimeter capable of working under applied magnetic fields of up to 5 T. The calorimeter is highly sensitive and operates over the temperature range 10¿300 K. It is shown that, after a proper calibration, the system enables determination of the latent heat and entropy changes in first-order solid¿solid phase transitions. The system is particularly useful for investigating materials that exhibit the giant magnetocaloric effect arising from a magnetostructural phase transition. Data for Gd5(Si0.1Ge0.9)4 are presented.

A high-sensitivity differential scanning calorimeter with magnetic field for magnetostructural transitions

We have developed a differential scanning calorimeter capable of working under applied magnetic fields of up to 5 T. The calorimeter is highly sensitive and operates over the temperature range 10¿300 K. It is shown that, after a proper calibration, the system enables determination of the latent heat and entropy changes in first-order solid¿solid phase transitions. The system is particularly useful for investigating materials that exhibit the giant magnetocaloric effect arising from a magnetostructural phase transition. Data for Gd5(Si0.1Ge0.9)4 are presented.

Entropy change and magnetocaloric effect in Gd5(SixGe1-x)4

Isothermal magnetization curves up to 23 T have been measured in Gd5Si1.8Ge2.2. We show that the values of the entropy change at the first-order magnetostructural transition, obtained from the Clausius-Clapeyron equation and the Maxwell relation, are coincident, provided the Maxwell relation is evaluated only within the transition region and the maximum applied field is high enough to complete the transition. These values are also in agreement with the entropy change obtained from differential scanning calorimetry. We also show that a simple phenomenological model based on the temperature and field dependence of the magnetization accounts for these results.

Martensitic transitions and the nature of ferromagnetism in the austenitic and martensitic states of Ni-Mn-Sn alloys

Structural and magnetic transformations in the Heusler-based system Ni0.50Mn0.50¿xSnx are studied by x-ray diffraction, optical microscopy, differential scanning calorimetry, and magnetization. The structural transformations are of austenitic-martensitic character. The austenite state has an L21 structure, whereas the structures of the martensite can be 10M , 14M , or L10 depending on the Sn composition. For samples that undergo martensitic transformations below and around room temperature, it is observed that the magnetic exchange in both parent and product phases is ferromagnetic, but the ferromagnetic exchange, characteristic of each phase, is found to be of different strength. This gives rise to different Curie temperatures for the austenitic and martensitic states.