Ag precipitation and dissolution reactions in the Cu-3 wt.% Al-4 wt.% Ag alloy

The Ag precipitation and dissolution reactions in the Cu-3 wt.% Al-4 wt.% Ag alloy were studied using isothermal and non-isothermal analyses. The activation energy values, obtained for the Ag precipitation reaction indicated that, when the Kissinger, Ozawa and Johnson-MehI-Avrami methods are compared, the Kissinger method is the most appropriate. Although the Johnson-Mehl-Avrami equation often does not fit precipitation data, the energy values obtained for Ag precipitation kinetics are in agreement with what was experimentally observed. For the dissolution reaction of Ag precipitates the activation energy values obtained from the Kissinger and Ozawa methods are higher than that found in the literature for the Ag dissolution in Cu. This discrepancy seems to be related to the fact that the activation energy is influenced by the heating rate. (c) 2006 Elsevier B.V. All rights reserved.

Influence of Ag additions on the activation energy for the reverse eutectoid reaction in Cu-Al alloys

The eutectoid transformation may be defined as a solid-state diffusion-controlled decomposition process of a high-temperature phase into a two-phase lamellar aggregate behind a migrating boundary on cooling below the eutectoid temperature. In substitutional solid solutions, the eutectoid reaction involves diffusion of the solute atoms either through the matrix or along the boundaries or ledges. The effect of Ag on the non-isothermal kinetics of the reverse eutectoid reaction in the Cu-9 mass%Al, Cu-10 mass%Al, and Cu-11 mass%Al alloys were studied using differential scanning calorimetry (DSC), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The activation energy for this reaction was obtained using the Kissinger and Ozawa methods. The results indicated that Ag additions to Cu-Al alloys interfere on the reverse eutectoid reaction, increasing the activation energy values for the Cu-9 mass%Al and Cu-10 mass%Al alloys and decreasing these values for the Cu-11 mass%Al alloy for additions up to 6 mass%Ag. The changes in the activation energy were attributed to changes in the reaction solute and in Ag solubility due to the increase in Al content.

Decomposition kinetics of iron (III)-diclofenac compound

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Crystallization study of molybdate phosphate glasses by thermal analysis

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Influence of Ag addition on the thermal behavior of the Cu-11 mass% Al alloy

In this work the influence of Ag additions on the thermal behavior of the Cu-11 mass% Al alloy was studied using differential scanning calorimetry, in situ X-ray diffractometry and scanning electron microscopy. The results indicated that changes in the heating rate shift the peak attributed to alpha phase formation to higher temperatures, evidencing the diffusive character of this reaction. The activation energy value for the alpha phase formation reaction, obtained from a non-isotherm kinetic model, is close to that corresponding to Cu atoms self diffusion, thus confirming that this reaction is dominated by Cu atoms diffusion through the martensite matrix.

(alpha + gamma(1)) Complex phase formation in the Cu-10 mass% Al-6mass% Ag alloy

In this work the (alpha + gamma(1)) complex phase formation reaction in the Cu-10mass% Al-6mass% Ag alloy was studied using Differential Scanning Calorimetry (DSC), Differential Thermodilatometry (DTD), X-ray diffractometry (XRD), Optical (OM) and Scanning Electron Microscopies (SEM). The results indicated the presence of two different processes, related to a change in the Ag diffusion route from the alpha matrix to the (alpha + gamma(1)) complex phase.

Simulação do escoamento bifásico da mistura óleo-refrigerante através da folga radial de compressores rotativos de pistão rolante

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Estudo das reações no sistema 'CU'-'AL'-'AG'-'MN'

Pós-graduação em Química - IQ

Desenvolvimento de uma metodologia numérica para escoamentos viscoelásticos não-isotérmicos

Pós-graduação em Matematica Aplicada e Computacional - FCT

Numerical study of Mach number and thermal effects on sound radiation by a mixing layer

Mach number and thermal effects on the mechanisms of sound generation and propagation are investigated in spatially evolving two-dimensional isothermal and non-isothermal mixing layers at Mach number ranging from 0.2 to 0.4 and Reynolds number of 400. A characteristic-based formulation is used to solve by direct numerical simulation the compressible Navier-Stokes equations using high-order schemes. The radiated sound is directly computed in a domain that includes both the near-field aerodynamic source region and the far-field sound propagation. In the isothermal mixing layer, Mach number effects may be identified in the acoustic field through an increase of the directivity associated with the non-compactness of the acoustic sources. Baroclinic instability effects may be recognized in the non-isothermal mixing layer, as the presence of counter-rotating vorticity layers, the resulting acoustic sources being found less efficient. An analysis based on the acoustic analogy shows that the directivity increase with the Mach number can be associated with the emergence of density fluctuations of weak amplitude but very efficient in terms of noise generation at shallow angle. This influence, combined with convection and refraction effects, is found to shape the acoustic wavefront pattern depending on the Mach number.

Thermal decomposition kinetics of Brazilian limestones: effect of CO2 partial pressure

The influence of the partial pressure of carbon dioxide (CO2) on the thermal decomposition process of a calcite (CI) and a dolomite (DP) is investigated in this paper using a thermogravimetric analyser. The tests were non-isothermal at five different heating rates in dynamic atmosphere of air with 0% and 15% carbon dioxide (CO2). In the atmosphere without CO2, the average activation energies (E-alpha) were 197.4 kJ mol(-1) and 188.1 kJ mol(-1) for CI and DP, respectively. For the DP with 15% CO2, two decomposition steps were observed, indicating a change of mechanism. The values of E-alpha for 15% CO2 were 378.7 kJ mol(-1) for the CI, and 299.8 kJ mol(-1) (first decomposition) and 453.4 kJ mol(-1) (second decomposition) for the DP, showing that the determination of E-alpha for DP should in this case be considered separately in those two distinct regions. The results obtained in this study are relevant to understanding the behaviour changes in the thermal decomposition of limestones with CO2 partial pressure when applied to technologies, such as carbon capture and storage (CCS), in which carbon dioxide is present in high concentrations.

Probing the cosmic distance-duality relation with the Sunyaev-Zel'dovich effect, X-ray observations and supernovae Ia

Context. The angular diameter distances toward galaxy clusters can be determined with measurements of Sunyaev-Zel'dovich effect and X-ray surface brightness combined with the validity of the distance-duality relation, D-L(z)(1 + z)(2)/D-A(z) = 1, where D-L(z) and D-A(z) are, respectively, the luminosity and angular diameter distances. This combination enables us to probe galaxy cluster physics or even to test the validity of the distance-duality relation itself. Aims. We explore these possibilities based on two different, but complementary approaches. Firstly, in order to constrain the possible galaxy cluster morphologies, the validity of the distance-duality relation (DD relation) is assumed in the Lambda CDM framework (WMAP7). Secondly, by adopting a cosmological-model-independent test, we directly confront the angular diameters from galaxy clusters with two supernovae Ia (SNe Ia) subsamples (carefully chosen to coincide with the cluster positions). The influence of the different SNe Ia light-curve fitters in the previous analysis are also discussed. Methods. We assumed that eta is a function of the redshift parametrized by two different relations: eta(z) = 1 +eta(0)z, and eta(z) = 1 + eta(0)z/(1 + z), where eta(0) is a constant parameter quantifying the possible departure from the strict validity of the DD relation. In order to determine the probability density function (PDF) of eta(0), we considered the angular diameter distances from galaxy clusters recently studied by two different groups by assuming elliptical and spherical isothermal beta models and spherical non-isothermal beta model. The strict validity of the DD relation will occur only if the maximum value of eta(0) PDF is centered on eta(0) = 0. Results. For both approaches we find that the elliptical beta model agrees with the distance-duality relation, whereas the non-isothermal spherical description is, in the best scenario, only marginally compatible. We find that the two-light curve fitters (SALT2 and MLCS2K2) present a statistically significant conflict, and a joint analysis involving the different approaches suggests that clusters are endowed with an elliptical geometry as previously assumed. Conclusions. The statistical analysis presented here provides new evidence that the true geometry of clusters is elliptical. In principle, it is remarkable that a local property such as the geometry of galaxy clusters might be constrained by a global argument like the one provided by the cosmological distance-duality relation.

Quantum hydrodynamic models for semiconductors with and without collisions

In dieser Arbeit werden Quantum-Hydrodynamische (QHD) Modelle betrachtet, die ihren Einsatz besonders in der Modellierung von Halbleiterbauteilen finden. Das QHD Modell besteht aus den Erhaltungsgleichungen für die Teilchendichte, das Momentum und die Energiedichte, inklusive der Quanten-Korrekturen durch das Bohmsche Potential. Zu Beginn wird eine Übersicht über die bekannten Ergebnisse der QHD Modelle unter Vernachlässigung von Kollisionseffekten gegeben, die aus ein­em Schrödinger-System für den gemischten-Zustand oder aus der Wigner-Glei­chung hergeleitet werden können. Nach der Reformulierung der eindimensionalen QHD Gleichungen mit linearem Potential als stationäre Schrö­din­ger-Gleichung werden die semianalytischen Fassungen der QHD Gleichungen für die Gleichspannungs-Kurve betrachtet. Weiterhin werden die viskosen Stabilisierungen des QHD Modells be­rück­sich­tigt, sowie die von Gardner vorgeschlagene numerische Viskosität für das {sf upwind} Finite-Differenzen Schema berechnet. Im Weiteren wird das viskose QHD Modell aus der Wigner-Glei­chung mit Fokker-Planck Kollisions-Ope­ra­tor hergeleitet. Dieses Modell enthält die physikalische Viskosität, die durch den Kollision-Operator eingeführt wird. Die Existenz der Lösungen (mit strikt positiver Teilchendichte) für das isotherme, stationäre, eindimensionale, viskose Modell für allgemeine Daten und nichthomogene Randbedingungen wird gezeigt. Die dafür notwendigen Abschätzungen hängen von der Viskosität ab und erlauben daher den Grenzübergang zum nicht-viskosen Fall nicht. Numerische Simulationen der Resonanz-Tunneldiode modelliert mit dem nichtisothermen, stationären, eindimensionalen, viskosen QHD Modell zeigen den Einfluss der Viskosität auf die Lösung. Unter Verwendung des von Degond und Ringhofer entwickelten Quanten-Entropie-Minimierungs-Verfahren werden die allgemeinen QHD-Gleichungen aus der Wigner-Boltzmann-Gleichung mit dem BGK-Kollisions-Operator hergeleitet. Die Herleitung basiert auf der vorsichtige Entwicklung des Quanten-Max­well­ians in Potenzen der skalierten Plankschen Konstante. Das so erhaltene Modell enthält auch vertex-Terme und dispersive Terme für die Ge­schwin­dig­keit. Dadurch bleibt die Gleichspannungs-Kurve für die Re­so­nanz-Tunnel­diode unter Verwendung des allgemeinen QHD Modells in einer Dimension numerisch erhalten. Die Ergebnisse zeigen, dass der dispersive Ge­schwin­dig­keits-Term die Lösung des Systems stabilisiert.

Synthesis, characterization and crystallization of bionanocomposites based on PLLA, PCL and nanocellulose

In recent years, environmental concerns and the expected shortage in the fossil reserves have increased further development of biomaterials. Among them, poly(lactide) PLA possess some potential properties such as good ability process, excellent tensile strength and stiffness equivalent to some commercial petroleum-based polymers (PP, PS, PET, etc.). This biobased polymer is also biodegradable and biocompatible However, one great disadvantage of commercial PLA is slow crystallization rate, which restricts its use in many fields. Using of nanofillers is viewed as an efficient strategy to overcome this problem. In this thesis, the effect of bionanofillers in neat PLA and in blends of poly (L-lactide)(PLA)/poly(ε-Caprolactone) (PCL) has been investigated. The used nanofillers are: poly(L-lactide-co-ε-caprolactone) and poly(L-lactide-b-ε-caprolactone) grafted on cellulose nanowhiskers and neat cellulose nanowhiskers (CNW). The grafting reaction of poly(L-lactide-co-caprolactone) and poly (L-lactide-b-caprolactone) on the nanocellulose has been performed by the grafting from technique. In this way the polymerization reaction it is directly initiated on the substrate surface. The condition of the reaction were chosen after a temperature and solvent screening. By non-isothermal an isothermal DSC analysis the effect of bionanofillers on PLA and 80/20 PLA/PCL was evaluated. Non-isothermal DSC scans show a nucleating effect of the bionanofillers on PLA. This effect is detectable during PLA crystallization from the glassy state. Cold crystallization temperature is reduced upon the addition of the poly(L-lactide-b-caprolactone) grafted on cellulose nanowhiskers that is most performing bionanofiller in acting as a nucleating agent. On the other hand, DSC isothermal analysis on the overall crystallization rate indicate that cellulose nanowhiskers are best nucleating agents during isothermal crystallization from the melt state. In conclusion, nanofillers have different behavior depending on the processing conditions. However, the efficiency of our nanofillers as nucleating agent was clearly demonstrated in both isothermal as in non-isothermal condition.

Bionanocomposites based on Plla, Pcl and montmorillonite: synthesis, characterization and crystallization

Poly(lactide) is one of the best candidate to replace conventional petroleum-based polymers, since it is biobased, biocompatible and biodegradable. However, commercial PLA materials typically have low crystallization rate resulting in long processing time and low production efficiency. In this work the effects of two nanofillers MMT30B and MMT30B-g-P(LA-co-CL) on the crystallization rate of neat PLA and PLA/PCL blend were investigated. MMT30B-g-P(LA-co-CL) was synthetized by in situ grafting reaction. The synthesis was carried in xylene at 140°C, upon the results of a screening. The grafted copolymers were evaluated by 1H-NMR ,ATR–IR and TGA. Solvent casted films were obtained by mixing MMT30B-g-P(LA-co-CL) at 5% (w/w) with neat PLA and PLA/PCL blend, comparing the properties with the corresponding blends with and without a 5% of (w/w) unmodified clay. SEM images on PLA based blends shows that MMT30B is aggregated into larger particles compared to MMT30B-g-P(LLA-co-CL). This behavior is correlated to the better exfoliation of MMT30B-g-P(LA-co-CL) clay layers. SEM images on PLA/PCL based blends exhibit the typical sea-island morphology, characteristic of immiscible blends. PLA is the matrix while PCL is finely dispersed in droplets. MMT30B does not reduce PCL droplets size, while MMT30B-g-P(LA-co-CL) reduces the size of PCL droplets. This means that MMT30B-g-P(LA-co-CL) can migrate to the PLA-PCL interface, acting as a compatibilizer. Non-isothermal DSC cooling scans show a fractionated crystallization of the PCL phase in PLA/PCL/MMT30B-g-P(LA-co-CL), confirming the compatibilizer effect of MMT30B-g-P(LA-co-CL). At the same timeMMT30B-g-P(LA-co-CL) can better nucleate the PLA phase, both in neat PLA and PLA/PCL blend, promoting the crystallization during the heating scans. In isothermal condition, both the nanofillers increase the crystallization rate of PLA phase in neat PLA, while in PLA/PCL blends the effect is covered by the nucleating effect of PCL.