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RESUME Les alliages Cu-Al-Ni sont les seuls à posséder une température de transformation allant jusque 200°C. Ceci leur confère un avantage par rapport aux alliages Cu-Al-Zn ou Ti-Ni dont les températures de transformation ne dépassent pas 100°C. Néanmoins, un chauffage temporaire au dessus de 200°C peut provoquer une perte de l’effet mémoire des alliages Cu-Al-Ni. Nous avons étudié trois alliages aves des teneurs en nickel comprises entre 3 % et 5 %. L’objectif de notre étude est double : • Étudier la cinétique des transformations structurales au cours d’un vieillissement en phase β dans le domaine de températures 200°C-350°C ; • Quantifier la perte de l’effet mémoire au cours du vieillissement afin de déterminer les possibilités d’utilisation de ces alliages au dessus de 200°C. La caractérisation structurale a été effectuée par microscope optique, diffraction des rayons X, microscopie électronique à balayage et microscopie électronique en transmission. Les caractéristiques de la transformation martensitique ont été déterminées par analyse thermomécanique (TMA), par calorimétrie différentielle à balayage (DSC) et par des mesures de résistivité électrique. La perte de l’effet mémoire simple sens a été quantifiée à partir des courbes de transformations obtenues par analyse thermomécanique(TMA) sur des échantillons comprimés. Les résultats principaux sont :  Au dessus de 300°C, la précipitation de la phase d’équilibre у₂ se produit au cours du vieillissement. Elle entraîne une augmentation de la température Mѕ. Nous avons montré que cette augmentation de Ms peut être reliée à la fraction transformée par une loi de puissance.  Il n’y a pas de relation directe, en revanche, entre la perte de l’effet mémoire et la fraction transformée. Cela indique que le nombre et la taille des précipités ont une influence sur la perte de l’effet mémoire.  Pour un vieillissement de 256 minutes à 275°C, la perte de l’effet mémoire est inférieure à 15%. Par contre, au dessus de 300°C, la perte de l’effet mémoire est très rapide. Nous pouvons donc considérer que 275°C est une température limite à ne pas dépasser pour ces alliages. ABSTRACT The shape memory alloys Cu-Al-Ni are the only ones to have a transformation temperature of up to 200°C. This gives them an advantage compared to shape memory alloys Cu-Zn-Al or Ti-Ni whose transformation temperatures do not exceed 100 ° C. However, a temporary heating above 200 ° C can cause a loss of memory effect alloys Cu-Al-Ni. We studied three alloys with nickel content between 3% and 5%. The aim of our study is twofold: • Studying the kinetics of structural changes during aging in β phase in the temperature range 200 °C-350 °C. • Quantifying the loss of memory effect with aging in order to determine the potential use of these alloys above 200°C. The structural characterization was carried out by optical microscope, XR-ray diffraction, scanning electron microscopy and transmission electron microscopy. The characteristics of the martensitic transformation were determined by thermomechanical analysis (TMA), differential scanning calorimetry (DSC) and by measuring the electrical resistivity. The loss of one way shape memory was quantified from the curves obtained by thermomechanical analysis (TMA) on compressed samples. The main results are:  Above 300 ° C, the precipitation of equilibrium phase γ2 occurs during aging. It causes an increase in temperature Mѕ. We showed that this increase of Ms may be related to the fraction transformed by a power law.  There is no direct relationship between the loss of memory effect and the fraction transformed. This indicates that the number and size of the precipitates have an influence on the loss of memory effect.  For 256 minutes of aging at 275°C, loss of memory effect is less than 15%. On the other hand, above 300 ° C, loss of memory effect is very fast. We can therefore consider that 275°C is the temperature limit that not may be exceeded for these alloys.

Das hier vorgestellte Vorhaben hat die Entwicklung eines neuartigen Sensor- und Messtechnikkonzepts zur Erfassung der Maximalwerte mechanischer Belastungen von Bauteilen bestehend aus Kohlenstofffaserverbundwerkstoffen mit polymerer Matrix (CFK) zum Ziel. Dazu wurden Untersuchungen zur Anwendbarkeit der spontanen Magnetisierung durch die martensitische Gefügeumwandlung metastabiler Stähle als möglicher Sensoreffekt durchgeführt. Als ein einfaches passives Sensorverfahren hat die Ausbildung einer spontanen Magnetisierung durch die Gefügeumwandlung ein denkbares Anwendungspotenzial. Es ist keine permanente Energieversorgung des Messsystems erforderlich, der Sensor ist vollständig und ohne Kontakt zur Umgebung im Bauteil einbettbar und eine äquivalente Information der maximalen Last ist unauslöschbar im Sensor eingeprägt. Durch kontakt- und zerstörungsfreie Verfahren kann das Auslesen erfolgen. Um die Eignung des Effekts zu überprüfen, erfolgten verschiedene Untersuchungen. Die Ergebnisse von Zugversuchen, durchgeführt an eingebetteten und nicht eingebetteten Sensorproben, und die Messwerte magnetischer Messungen der Sensormagnetisierung wurden zur Ermittlung einer Abhängigkeit zwischen dem Grad der Belastung und der Änderung der Magnetisierung infolge der martensitischen Transformation korreliert. Mittels metallografischer Untersuchungen sowie durch Röntgenbeugung erfolgte zudem der Vergleich zwischen dem Martensitgehalt und den Messergebnissen zur spontanen Magnetisierung. Der vorliegende Artikel beschreibt die Grundlagen des ausgewählten Sensorprinzips, die durchgeführten Arbeiten und erläutert die Ergebnisse der Untersuchungen.

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La dawsonita es un mineral cristalino hallado generalmente en la naturaleza en forma de hidróxicarbonato de sodio y aluminio, NaAlCO3(OH)2. Además del mineral, se han sintetizado diferentes tipos de dawsonitas variando su composición, es decir, cambiando el sodio y/o aluminio por cationes de similar naturaleza. El trabajo descrito en esta tesis se centra en estudiar la química de este tipo de compuestos incluyendo: la estabilidad en medios acuosos de las dawsonitas en condiciones moderadas, la obtención de compuestos nanoestructurados dawsonita-hidrotalcita a partir de hidrotalcita, y el efecto memoria de las alúminas derivadas de dawsonita. El objetivo final es la evaluación de los materiales sintetizados y sus derivados, en catálisis. Estos materiales han resultado ser eficientes o en algunos casos más activos que los catalizadores reportados en la literatura para reacciones básicas (la transesterificación de carbonato de etileno para producir carbonato de dimetilo) y redox (epoxidación de alquenos). Teniendo en cuenta los resultados obtenidos, estos materiales podrían ser utilizados como catalizadores, adsorbentes, y aditivos abriendo así una nueva vía de investigación. / Dawsonites are crystalline minerals generally present in nature as sodium aluminum carbonate hydroxide, NaAlCO3(OH)2. Besides the mineral, a variety of compositions with dawsonite-type structure have been synthesized by changing the nature of sodium or aluminum cations. The work described in this thesis focuses on the chemistry of dawsonite-type compounds including: the stability of dawsonites in aqueous media at mild conditions; the achievement of dawsonite-hydrotalcite nanostructured composites starting from the hydrotalcite; and the memory property of dawsonite-derived aluminas. The final goal is to evaluate the as-synthesized or derived dawsonite-materials in selected catalytic reactions. These materials were efficient or even more active than catalysts in the state-of-the-art in basic (dimethyl carbonate production by transesterification of ethylene carbonate with methanol) and redox (alkene epoxidation of cyclooctene with hydrogen peroxide) reactions. The above findings could have further practical implications as activated dawsonites open a new window of research with potential applications as catalysts, adsorbents, and additives.

The purpose of the present study was to assess the feasibility of a laser layer manufacturing technique for realization of shape memory alloy (SMA) components with complex geometry. Pre-placed laser solid freeform fabrication (LSFF) was utilized to produce straight and curvaceous SMA parts from a mixture of 55.2 wt%Ni - 44.8 wt%Ti powder. A pulsed Nd:YAG laser was used; while laser pulse width and frequency were held constant at what are considered their optimal values (4 ms and 50 Hz, respectively), laser energy and scanning speeds were varied across samples to determine appropriate values for fabrication of high quality SMA parts . Different pre-placed powder thicknesses were deposited and then mechanically and physically studied. Optical microscopy, SEM, EDS, and XRD methods, as well as microhardness measurements, were used to examine the microstructural characteristics and hardness of the SMA samples. Also, differential scanning calorimetry (DSC) was performed to determine the transformation temperatures of the fabricated parts. The results confirmed the formation of crack-free solid surfaces in which two types of microstructure exist: solid (non-prose) and dendrite arms. EDS chemical composition analysis confirmed the absence of any impurity or oxidise in the cross section of the samples as well as the presence of only nickel and titanium. XRD spectrum analysis indicated the presence of Ni-Ti intermetallic phases, which are almost Ni-Ti but contain a small amount of Ti2Ni. The XRD results also indicated the presence of austenite and martensite phases, which are exchanged during heating or mechanical deformation. The hardness of these samples varied from 250 to 450 HV0.3. Several tests were carried out to investigate the shape memory effect (SME). It was observed that the fabricated SMAs can recover from the bent condition very quickly (i.e., 1 to 8 seconds) depending on their thickness. In general, the fabricated parts were first bent out of their original shapes then heated, in various ways, above the transformation temperature. To theoretically assess the SME performance of the fabricated SMAs with the proposed geometry two models were developed. The first model was established based upon a lump approach in which the part was exposed to an electrical current. The second model, however, was established based upon a finite element method in which a specific domain at one end of the sample was exposed to a source of heat. It was found that the theoretical outputs from both models were in good agreement with the experimental results.

The purpose of the present study was to assess the feasibility of a laser layer manufacturing technique for realization of shape memory alloy (SMA) components with complex geometry. Pre-placed laser solid freeform fabrication (LSFF) was utilized to produce straight and curvaceous SMA parts from a mixture of 55.2 wt%Ni - 44.8 wt%Ti powder. A pulsed Nd:YAG laser was used; while laser pulse width and frequency were held constant at what are considered their optimal values (4 ms and 50 Hz, respectively), laser energy and scanning speeds were varied across samples to determine appropriate values for fabrication of high quality SMA parts . Different pre-placed powder thicknesses were deposited and then mechanically and physically studied. Optical microscopy, SEM, EDS, and XRD methods, as well as microhardness measurements, were used to examine the microstructural characteristics and hardness of the SMA samples. Also, differential scanning calorimetry (DSC) was performed to determine the transformation temperatures of the fabricated parts. The results confirmed the formation of crack-free solid surfaces in which two types of microstructure exist: solid (non-prose) and dendrite arms. EDS chemical composition analysis confirmed the absence of any impurity or oxidise in the cross section of the samples as well as the presence of only nickel and titanium. XRD spectrum analysis indicated the presence of Ni-Ti intermetallic phases, which are almost Ni-Ti but contain a small amount of Ti2Ni. The XRD results also indicated the presence of austenite and martensite phases, which are exchanged during heating or mechanical deformation. The hardness of these samples varied from 250 to 450 HV0.3. Several tests were carried out to investigate the shape memory effect (SME). It was observed that the fabricated SMAs can recover from the bent condition very quickly (i.e., 1 to 8 seconds) depending on their thickness. In general, the fabricated parts were first bent out of their original shapes then heated, in various ways, above the transformation temperature. To theoretically assess the SME performance of the fabricated SMAs with the proposed geometry two models were developed. The first model was established based upon a lump approach in which the part was exposed to an electrical current. The second model, however, was established based upon a finite element method in which a specific domain at one end of the sample was exposed to a source of heat. It was found that the theoretical outputs from both models were in good agreement with the experimental results.

Porous TiNi alloys (Ti-50.4 at. %Ni and Ti-50.6 at. %Ni) with porosities in the range 21%-81% were prepared successfully applying a new powder metallurgy fabrication route in which magnesium was used as space holder resulting in either single austenite phase or a mixture of austenite and martensite phases dictated by the composition of the starting prealloyed powders but entirely free from secondary brittle intermetallics, oxides, nitrides and carbonitrides. Magnesium vapor do not only prevents secondary phase formation and contamination but also provides higher temperature sintering opportunity preventing liquid phase formation at the eutectic temperature, 1118 &deg / C resulting from Ni enrichment due to oxidation. By two step sintering processing (holding the sample at 1100 &deg / C for 30 minutes and subsequently sintering at temperatures higher than the eutectic temperature, 1118 &deg / C) magnesium may allow sintering probably up to the melting point of TiNi. The processed alloys exhibited interconnected (partially or completely depending on porosity content) open macro-pores spherical in shape and irregular micro-pores in the cell walls resulting from incomplete sintering. It has been found that porosity content of the foams have no influence on the phase transformation temperatures while deformation and oxidation are severely influential. Porous TiNi alloys displayed excellent superelasticity and shape memory behavior. Space holder technique seems to be a promising method for production of porous TiNi alloys. Desired porosity level, pore shape and accordingly mechanical properties were found to be easily adjustable.

Determination of thallium is important due to its toxic effects on the environment and human health. Extremely low abundance of thallium in earth crust requires very sensitive and accurate methods for determination of this element. Although volatile compound generation is a sensitive, fast and economical method, thallium determination by this method has not been sufficiently investigated in literature, because of the fact that the formation of volatile forms of this element is a difficult task. A continuous flow volatile compound generation system was developed and parameters that affect the analytical signal were optimized. Sample solutions were acidified with 0.5 mol/L HNO3 and prepared in 0.0005% (v/v) rhodamine B and 1.0 mg/L Pd while 0.5% (m/v) NaBH4 stabilized in 0.5% (m/v) NaOH was used as reductant. Fast decomposition and unstability of thallium volatile species affected system performance negatively. Flow injection volatile compound generation studies were carried out with a special system. After optimizations, LOD and LOQ values were calculated as 12 ng/mL and 40 ng/mL according to peak height values in HNO3 medium. Similarly, in HCl medium LOD and LOQ values were calculated as 14 ng/mL and 45 ng/mL. Addition of Te and Pd to the sample solution containing co-enhancement reagent rhodamine B improved volatile compound generation efficiency in peak height by 3.6 and 9.3, respectively. Type of the acid used was affected peak heights and peak shapes of Tl+ and Tl3+ volatile species and HNO3 medium gave better results. By changing the location of introduction for Ar gas, the sources of memory effects and reasons of peak broadening were investigated. Most of the memory effects were coming from the gas-liquid separator (GLS) or before the GLS, as well as T-tube atomizer. Nature and behavior of Tl volatile species were also investigated and it was found that Tl and also Pd were generated in the form of nanoparticles. Transmission electron microscopic (TEM) measurements prove the presence of Tl nanoparticles in the analyte species transported to the atomizer by the effect of carrier Ar gas.

Alzheimer's disease (AD) is associated with decreased brain energy metabolism. Hypometabolism in the posterior cingulate cortex (PCC) occurs before the onset of memory deficits in subjects at genetic risk for AD who are not yet cognitively impaired. There is a specific inhibition in cytochrome oxidase (C.O.) in the PCC, an area involved in spatial navigation. Creating an animal model that exhibits the early pathophysiology of AD is important for developing and testing drugs that could reverse memory problems associated with such deficits. Methylene blue (MB) is a compound that improves C.O. activity and memory retention in rats. This dissertation had three specific aims: 1) to examine if isolated PCC hypometabolism causes spatial memory deficits in rats; 2) to find a dose of MB that improves memory without nonspecific behavioral effects; and 3) to prevent memory deficits from PCC hypometabolism with low dose MB. PCC hypometabolism was produced by focal administration of sodium azide, an inhibitor of C.O. activity. PCC hypometabolism resulted in impaired spatial memory in a hole board food-search task, increased oxidative damage, and neurotoxicity in the PCC. In addition, PCC hypometabolism resulted in reduced inter-regional correlations in brain activity. Our second set of studies examined the dose-response effects of MB. Our findings demonstrated that a low dose of MB: 1) enhanced memory in open field habituation and object recognition tasks; 2) did not affect general locomotor activity, exploration, motivation, or anxiety; and 3) increased brain oxygen consumption 24 hr after in vivo administration. Finally, our last study found that low dose MB prevented the deficits caused by PCC hypometabolism. MB did not prevent PCC inhibition or cell loss caused by sodium azide. Inter-regional correlations of brain metabolic activity suggested that rats treated with MB were using a different, but equally efficient, strategy for memory retrieval. This animal model of C.O. hypometabolism in the PCC can provide information to understand the mechanisms that regulate early pathological degeneration and reveal new therapeutic strategies aimed at reducing or preventing cognitive decline. Studies of low dose MB in humans are needed to examine its effects in AD patients.