Magnetization versus heat treatment in rapidly solidified NdFeB alloys

NdFeB melt-spun amorphous or partially amorphous alloys of four compositions were prepared. Their crystallization kinetics induced by thermal treatment was studied by differential scanning calorimetry and scanning and transmission electron microscopy. Scanning electron microscopy demonstrated that heterogeneous nucleation occurs preferentially at the ribbon surface which was in contact with the wheel. The explicit form of the kinetic equation that best describes the first stage of crystallization under high undercooling conditions was obtained for each alloy. From the crystallization results, the lower part of the experimental time-temperature-transformation curves was deduced for each alloy and extrapolated up to the high-temperature limit of their validity. Microstructural observations showed a typical size of the microcrystals obtained by heat treatment of ~100 nm. From the magnetic properties measured with a vibrating sample magnetometer, the same magnetic behavior of partially crystallized alloys is observed regardless of the temperature of annealing provided the same crystallization fraction, x, is achieved, at least for small values of x (typically ~10%).

High-precision dating and origin of synsedimentary volcanism in the Late Carboniferous Salvan-Dorenaz basin (Aiguilles-Rouges Massif, Western Alps)

Late Variscan volcanic activity is documented in the Late Carboniferous Salvan-Dorenaz sedimentary basin and in the neighboring basement units of the Aiguilles-Rouges and Mont-Blanc crystalline massifs (Western Alps). Precise U/Pb isotopic dating, zircon morphology and geochemical analyses indicate that volcanism occurred during short-lived pulses and that coexisting crustal and mantle sources were involved in the production of melts. Volcanic and subvolcanic products were emplaced along major N-S to NNE-SSW transtensional fracture zones, similar to the ones that governed intense basement exhumation and that favored the formation and filling of the Late Carboniferous Salvan-Dorenaz continental basin. In the Aiguilles-Rouges massif, dacitic flows outcropping at the base of the Salvan-Dorenaz basin erupted at 308 +/- 3 Ma; they represent the surface equivalent of the nearby Vallorcine peraluminous granite and associated rhyolitic dykes (311 +/- 17 Ma). In the Mont Blanc massif, calc-alkaline rhyolitic dykes were emplaced simultaneously (307 +/- 2 Ma) at shallow crustal levels, but they derive from deeper magma sources denoting enhanced mantellic activity. Recently identified tuffs and volcaniclastic layers embedded at different levels of the Salvan-Dorenaz stratigraphic record testify a 295 +3/-4 Ma old episode of highly explosive volcanism from distant volcanic centers, possibly located in the Aar-Gotthard massifs (Central Alps). Their zircon typology is highly heterogeneous. documenting wall-rock contamination of the melts and/or admixture of crustal sediments, whereas consistent subpopulations point to high-temperature magmas of deep-seated origin and alkaline affinity. The dated volcanic layers from the Salvan-Dorenaz basin set the beginning of the detrital sedimentation at 308 +/- 3 Ma and constrain the deposition of 1.5-1.7 km thick of elastic sediments within a time span of 10-15 Ma. These results infer minimum, long-term subsidence rates during basin evolution in the order of >0.1 mm/a, while in the surrounding basement units estimated exhumation rates are in the range of 1 mm/a. All dated rocks contain inherited zircon populations about 350, 450 or 600 Ma old.

Effect of temperature on the electro-oxidation of ethanol on platinum

We present in this work an experimental investigation of the effect of temperature (from 25 to 180 ºC) in the electro-oxidation of ethanol on platinum in two different phosphoric acid concentrations. We observed that the onset potential for ethanol electro-oxidation shifts to lower values and the reaction rates increase as temperature is increased for both electrolytes. The results were rationalized in terms of the effect of temperature on the adsorption of reaction intermediates, poisons, and anions. The formation of oxygenated species at high potentials, mainly in the more diluted electrolyte, also contributes to increase the electro-oxidation reaction rate.

Growth, magnetic and transport properties of InSb and II-IV-As2 semiconductors doped with manganese

This thesis is devoted to growth and investigations of Mn-doped InSb and II-IV-As2 semiconductors, including Cd1-xZnxGeAs2:Mn, ZnSiAs2:Mn bulk crystals, ZnSiAs2:Mn/Si heterostructures. Bulk crystals were grown by direct melting of starting components followed by fast cooling. Mn-doped ZnSiAs2/Si heterostructures were grown by vacuum-thermal deposition of ZnAs2 and Mn layers on Si substrates followed by annealing. The compositional and structural properties of samples were investigated by different methods. The samples consist of micro- and nano- sizes clusters of an additional ferromagnetic Mn-X phases (X = Sb or As). Influence of magnetic precipitations on magnetic and electrical properties of the investigated materials was examined. With relatively high Mn concentration the main contribution to magnetization of samples is by MnSb or MnAs clusters. These clusters are responsible for high temperature behavior of magnetization and relatively high Curie temperature: up to 350 K for Mn-doped II-IV-As2 and about 600 K for InMnSb. The low-field magnetic properties of Mn-doped II-IV-As2 semiconductors and ZnSiAs2:Mn/Si heterostructures are connected to the nanosize MnAs particles. Also influence of nanosized MnSb clusters on low-field magnetic properties of InMnSb have been observed. The contribution of paramagnetic phase to magnetization rises at low temperatures or in samples with low Mn concentration. Source of this contribution is not only isolated Mn ions, but also small complexes, mainly dimmers and trimmers formed by Mn ions, substituting cation positions in crystal lattice. Resistivity, magnetoresistance and Hall resistivity properties in bulk Mn-doped II-IV-As2 and InSb crystals was analyzed. The interaction between delocalized holes and 3d shells of the Mn ions together with giant Zeeman splitting near the cluster interface are respond for negative magnetoresistance. Additionally to high temperature critical pointthe low-temperature ferromagnetic transition was observed Anomalous Hall effect was observed in Mn doped samples and analyzed for InMnSb. It was found that MnX clusters influence significantly on magnetic scattering of carriers.

Effect of drying temperature on quality of β-glucan in white oat grains

Oats have received attention because of their nutritional characteristics, especially their high-quality content of β-glucan. The drying process reduces water content; therefore they can be preserved for long periods. However, high-temperature drying process may affect the physical, chemical, and functional properties of the grains. The objective of this study was to evaluate the effect of different drying temperatures on β-glucan quality in oat grains. Grains of oats (Avena sativa, L.), cultivar Albasul, harvested at harvest moisture content of 23% were submitted to stationary drying at air temperatures of 25, 50, 75, and 100 ºC until they reached 13% moisture content. The β-glucan content was determined in samples of oat grains and extraction was performed using water as solvent at 90 ºC. The β-glucan extract was evaluated for water holding capacity, water retention capacity, capacity of displacement, and gelation properties. Stationary of oat grains at air temperatures above 25 ºC decreased the water holding capacity, whereas the content of β-glucan and the water retention capacity of β-glucan extract was affected at temperatures above 50 ºC. Physical changes such as increased gelation capacity of the β-glucan extract occurred following drying at air temperature over 75 ºC.

Drying soybean seed using air ambient temperature at low relative humidity

Under subtropical and tropical environments soybean seed (Glycine max (L.) Merrill) are harvested early to avoid deterioration from weathering. Careful after-harvest drying is required and is an important step in maintaining the physiological quality of the seed. Soybean seed should be harvested when the moisture content is in a range of 16-20%. Traditional drying utilizes a high temperature air stream passed through the seed mass without dehumidification. The drying time is long because the system is inefficient and the high temperature increases the risk of thermal damage to the seed. New technology identified as heat pipe technology (HPT) is available and has the unique feature of removing the moisture from the air stream before it is passed through the seed mass at the same environmental temperature. Two studies were conducted to evaluate the performance of HPT for dry soybean seed. In the first study the seeds were dried from 17.5 to 11.1% in 2 hours and 29 minutes and in the second sudy the seeds were dried from 22.6 to 11.9% in 16 hours and 32 minutes. This drying process caused no reduction in seed quality as measured by the standard germination, tetrazolium-viability, accelerated aging and seedling vigor classification tests. The only parameter that indicated a slight seed quality reduction was tetrazolium vigor in the second study. It was concluded that the HPT system is a promising technology for drying soybean seed when efficiency and maintenance of physiological quality are desired.

Drying peanut seed using air ambient temperature at low relative humidity

The moisture content of peanut kernel (Arachis hypogaea L.) at digging ranges from 30 to 50% on a wet basis (w.b.). The seed moisture content must be reduced to 10.5% or below before seeds can be graded and marketed. After digging, peanuts are cured on a window sill for two to five days then mechanically separated from the vine. Heated air is used to further dry the peanuts from approximately 18 to 10% moisture content w.b. Drying is required to maintain peanut seed and grain quality. Traditional dryers pass a high temperature and high humidity air stream through the seed mass. The drying time is long because the system is inefficient and the high temperature increases the risk of thermal damage to the kernels. New technology identified as heat pipe technology (HPT) is available and has the unique feature of removing the moisture from the air stream before it is heated and passed through the seed. A study was conducted to evaluate the performance of the HPT system in drying peanut seed. The seeds inside the shells were dried from 17.4 to 7.3% in 14 hours and 11 minutes, with a rate of moisture removal of 0.71% mc per hour. This drying process caused no reduction in seed quality as measured by the standard germination, accelerated ageing and field emergence tests. It was concluded that the HPT system is a promising technology for drying peanut seed when efficiency and maintenance of physiological quality are desired.

Calculation of the magnetic field penetration depth for high-Tc cuprate superconductors based on the Interlayer Pair Tunneling model /

In this work, the magnetic field penetration depth for high-Tc cuprate superconductors is calculated using a recent Interlayer Pair Tunneling (ILPT) model proposed by Chakravarty, Sudb0, Anderson, and Strong [1] to explain high temperature superconductivity. This model involves a "hopping" of Cooper pairs between layers of the unit cell which acts to amplify the pairing mechanism within the planes themselves. Recent work has shown that this model can account reasonably well for the isotope effect and the dependence of Tc on nonmagnetic in-plane impurities [2] , as well as the Knight shift curves [3] and the presence of a magnetic peak in the neutron scattering intensity [4]. In the latter case, Yin et al. emphasize that the pair tunneling must be the dominant pairing mechanism in the high-Tc cuprates in order to capture the features found in experiments. The goal of this work is to determine whether or not the ILPT model can account for the experimental observations of the magnetic field penetration depth in YBa2Cu307_a7. Calculations are performed in the weak and strong coupling limits, and the efi"ects of both small and large strengths of interlayer pair tunneling are investigated. Furthermore, as a follow up to the penetration depth calculations, both the neutron scattering intensity and the Knight shift are calculated within the ILPT formalism. The aim is to determine if the ILPT model can yield results consistent with experiments performed for these properties. The results for all three thermodynamic properties considered are not consistent with the notion that the interlayer pair tunneling must be the dominate pairing mechanism in these high-Tc cuprate superconductors. Instead, it is found that reasonable agreement with experiments is obtained for small strengths of pair tunneling, and that large pair tunneling yields results which do not resemble those of the experiments.

Composition analysis of high-Tc superconducting thin films by quantitative x-ray fluorescence

A method is presented for determining the composition of thin films containing the elements Bi, Sr, Br, Cu, and Ca. Quantitative x-ray fluorescence (XRF) consisting of radioactive sources (secondary foil excitor 241Am-Mo source and 55Pe source), a Si(Li) detector, and a multichannel analyzer were employed. The XRF system was calibrated by using sol gel thin films of known element composition and also by sputtered thin films analyzed by the conventional Rutherford Back Scattering (RBS). The XRF system has been used to assist and optimize the sputter target composition required to produce high-Tc BiSrCaCuO films with the desired metal composition.

The effects of temperature on nickel tocicity in goldfish (carassius auratus L.)

Although it is widely assumed that temperature affects pollutant toxicity, few studies have actually investigated this relationship. Moreover, such research as has been done has involved constant temperatures; circumstances which are rarely, if ever, actually experienced by north temperate, littoral zone cyprinid species. To investigate the effects of temperature regime on nickel toxicity in goldfish (Carassius auratus L.), 96- and 240-h LCSO values for the heavy metal pollutant, nickel (NiCI2.6H20), were initially determined at 2DoC (22.8 mg/L and 14.7 mg/L in artificially softened water). Constant temperature bioassays at 10°C, 20°C and 30°C were conducted at each of 0, 240-h and 96-h LCSO nickel concentrations for 240 hours. In order to determine the effects of temperature variation during nickel exposure it was imperative that the effects of a single temperature change be investigated before addressing more complex regimes. Single temperature changes of + 10°C or -10°C were imposed at rates of 2°C/h following exposures of between 24 hand 216 h. The effects of a single temperature change on mortality, and duration of toxicant exposure at high and low temperatures were evaluated. The effects of fluctuating temperatures during exposure were investigated through two regimes. The first set of bioassays imposed a sinewave diurnal cycle temperature (20.±.1DOC) throughout the 10 day exposure to 240-h LeSO Ni. The second set of investigations approximated cyprinid movement through the littoral zone by imposing directionally random temperature changes (±2°C at 2-h intervals), between extremes of 10° and 30°C, at 240-h LC50 Ni. Body size (i.e., total length, fork length, and weight) and exposure time were recorded for all fish mortalities. Cumulative mortality curves under constant temperature regimes indicated significantly higher mortality as temperature and nickel concentration were increased. At 1DOC no significant differences in mortality curves were evident in relation to low and high nickel test concentrations (Le., 16 mg/L and 20 mg/L). However at 20°C and 30°C significantly higher mortality was experienced in animals exposed to 20 mg/L Ni. Mortality at constant 10°C was significantly lower than at 30°C with 16 mg/L and was significantly loWer than each of 2DoC and 39°C tanks at 20 mg/L Ni exposure. A single temperature shift from 20°C to 1DoC resulted in a significant decrease in mortality rate and conversely, a single temperature shift from 20°C to 30°C resulted in a significant increase in mortality rate. Rates of mortality recorded during these single temperature shift assays were significantly different from mortality rates obtained under constant temperature assay conditions. Increased Ni exposure duration at higher temperatures resulted in highest mortality. Diurnally cycling temperature bioassays produced cumulative mortality curves approximating constant 20°C curves, with increased mortality evident after peaks in the temperature cycle. Randomly fluctuating temperature regime mortality curves also resembled constant 20°C tanks with mortalities after high temperature exposures (25°C - 30°C). Some test animals survived in all assays with the exception of the 30°C assays, with highest survival associated with low temperature and low Ni concentration. Post-exposure mortality occurred most frequently in individuals which had experienced high Ni concentrations and high temperatures during assays. Additional temperature stress imposed 2 - 12 weeks post exposure resulted in a single death out of 116 individuals suggesting that survivors are capable of surviving subsequent temperature stresses. These investigations suggest that temperature significantly and markedly affects acute nickel toxicity under both constant and fluctuating temperature regimes and plays a role in post exposure mortality and subsequent stress response.

Effets des recuits ultra-rapides (10^5 K/s) sur la formation des siliciures métalliques en phase solide

La synthèse de siliciures métalliques sous la forme de films ultra-minces demeure un enjeu majeur en technologie CMOS. Le contrôle du budget thermique, afin de limiter la diffusion des dopants, est essentiel. Des techniques de recuit ultra-rapide sont alors couramment utilisées. Dans ce contexte, la technique de nanocalorimétrie est employée afin d'étudier, in situ, la formation en phase solide des siliciures de Ni à des taux de chauffage aussi élevés que 10^5 K/s. Des films de Ni, compris entre 9.3 et 0.3 nm sont déposés sur des calorimètres avec un substrat de a-Si ou de Si(100). Des mesures de diffraction de rayons X, balayées en température à 3 K/s, permettent de comparer les séquences de phase obtenues à bas taux de chauffage sur des échantillons de contrôle et à ultra-haut taux de chauffage sur les calorimètres. En premier lieu, il est apparu que l'emploi de calorimètres de type c-NC, munis d'une couche de 340 nm de Si(100), présente un défi majeur : un signal endothermique anormal vient fausser la mesure à haute température. Des micro-défauts au sein de la membrane de SiNx créent des courts-circuits entre la bande chauffante de Pt du calorimètre et l'échantillon métallique. Ce phénomène diminue avec l'épaisseur de l'échantillon et n'a pas d'effet en dessous de 400 °C tant que les porteurs de charge intrinsèques au Si ne sont pas activés. Il est possible de corriger la mesure de taux de chaleur en fonction de la température avec une incertitude de 12 °C. En ce qui a trait à la formation des siliciures de Ni à ultra-haut taux de chauffage, l'étude montre que la séquence de phase est modifiée. Les phases riches en m étal, Ni2Si et théta, ne sont pas détectées sur Si(100) et la cinétique de formation favorise une amorphisation en phase solide en début de réaction. Les enthalpies de formation pour les couches de Ni inférieures à 10 nm sont globalement plus élevées que dans le cas volumique, jusqu' à 66 %. De plus, les mesures calorimétriques montrent clairement un signal endothermique à haute température, témoignant de la compétition que se livrent la réaction de phase et l'agglomération de la couche. Pour les échantillons recuits a 3 K/s sur Si(100), une épaisseur critique telle que décrite par Zhang et Luo, et proche de 4 nm de Ni, est supposée. Un modèle est proposé, basé sur la difficulté de diffusion des composants entre des grains de plus en plus petits, afin d'expliquer la stabilité accrue des couches de plus en plus fines. Cette stabilité est également observée par nanocalorimétrie à travers le signal endothermique. Ce dernier se décale vers les hautes températures quand l'épaisseur du film diminue. En outre, une 2e épaisseur critique, d'environ 1 nm de Ni, est remarquée. En dessous, une seule phase semble se former au-dessus de 400 °C, supposément du NiSi2.

Optical and electrical properties of amorphous zinc tin oxide thin films examined for thin film transistor application

Structural, electronic, and optical properties of amorphous and transparent zinc tin oxide films deposited on glass substrates by pulsed laser deposition (PLD) were examined for two chemical compositions of Zn:Sn=1:1 and 2:1 as a function of oxygen partial pressure PO2 used for the film deposition and annealing temperature. Different from a previous report on sputter-deposited films Chiang et al., Appl. Phys. Lett. 86, 013503 2005 , the PLD-deposited films crystallized at a lower temperature 450 °C to give crystalline ZnO and SnO2 phases. The optical band gaps Tauc gaps were 2.80−2.85 eV and almost independent of oxygen PO2 , which are smaller than those of the corresponding crystals 3.35−3.89 eV . Films deposited at low PO2 showed significant subgap absorptions, which were reduced by postthermal annealing. Hall mobility showed steep increases when carrier concentration exceeded threshold values and the threshold value depended on the film chemical composition. The films deposited at low PO2 2 Pa had low carrier concentrations. It is thought that the low PO2 produced high-density oxygen deficiencies and generated electrons, but these electrons were trapped in localized states, which would be observed as the subgap absorptions. Similar effects were observed for 600 °C crystallized films and their resistivities were increased by formation of subgap states due to the reducing high-temperature condition. High carrier concentrations and large mobilities were obtained in an intermediate PO2 region for the as-deposited films.

Temporal and Spatial Behavior of Electron Density and Temperature in a Laser-Produced Plasma from YBa2Cu3O7

Spectroscopic studies of laser -induced plasma from a high-temperature superconducting material, viz., YBa2Cu3O7 (YBCO), have been carried out. Electron temperature and electron density measurements were made from spectral data. The Stark broad ening of emission lines was used to determine the electron density, and the ratio of line in tensities was exploited for the determination of electron temperature. An initial electron temperature of 2.35 eV and electron density of 2.5 3 1017 cm2 3 were observed. The dependence on electron temperature and density on different experimental parameters such as distance from the target, delay time after the in itiation of the plasm a, and laser irradiance is also discussed in detail. Index Headings: Laser -plasma spectroscopy; Plasma diagnostics; Emission spectroscop y; YBa2Cu3O7.

On the role of acoustic plasmons in high Tc superconductors

The role of acoustic plasmons in the recently discovered high Tc superconductors is discussed. It is shown that the exchange of acoustic plasmons together with the usual phonon exchange between electrons can give rise to a Tc - 100 K.