Crystallization mechanism and properties of a blast furnace slag glass

The complex crystallization process of a Brazilian blast-furnace slag glass was investigated using differential scanning calorimetry (DSC), X-ray diffraction, optical microscopy, transmission electron microscopy (TEM), selected area diffraction (SAD), energy dispersive spectroscopy (EDS) and micro-Raman spectroscopy. Three crystalline phases (merwinite, melilite and larnite) were identified after heat treatment between Tg (742°C) and the DSC crystallization peak (T = 1000°C). Merwinite was identified as a metastable phase. A small amount (0.004 wt%) of metallic platinum was found in the glass composition. Particles of Pt3Fe, detected by EDS and SAD-TEM, were the starting points of crystallization acting, therefore, as heterogeneous nucleating sites. Only melilite and larnite precipitated in a glass sample heat-treated at 1000°C for 1 h. The flexural strength of this crystallized sample was less than that of the glass, probably due the allotropic phase transformation of larnite. © 2000 Published by Elsevier Science B.V. All rights reserved.

Crystallization of amorphous GaAs films prepared onto different substrates

This work reports changes in structural properties produced by thermal annealing of flash evaporated amorphous GaAs films using the micro-Raman scattering and the X-ray diffraction (XRD) techniques. Films of about 1 μm were grown on c-Si and glass substrates. The crystallization process is less effective for samples deposited on c-Si. This could be due to the ordering in the first layers of the film imposed by the oriented Si substrates. We propose that this ordering makes the growth of crystallites in these films more restrained than the growth occurring in the completely amorphous films on glass substrates. © 2002 Elsevier Science B.V. All rights reserved.

Magnetic resonance study of the crystallization behavior of InF3-based glasses doped with Cu2+, Mn2+ and Gd3+

The crystallization of fluoroindate glasses doped with Gd3+, Mn2+ and Cu2+ heat treated at different temperatures, ranging from the glass transition temperature (Tg) to the crystallization temperature (Tc), are investigated by electron paramagnetic resonance (EPR) and 19F nuclear magnetic resonance (NMR). The EPR spectra indicate that the Cu2+ ions in the glass are located in axially distorted octahedral sites. In the crystallized glass, the g-values agreed with those reported for Ba2ZnF6, which correspond to Cu2+ in a tetragonal compressed F- octahedron and to Cu2+ on interstitial sites with a square-planar F- co-ordination. The EPR spectra of the Mn2+ doped glasses exhibit a sextet structure due to the Mn2+ hyperfine interaction. These spectra suggest a highly ordered environment for the Mn2+ ions (close to octahedral symmetry) in the glass. The EPR spectra of the recrystallized sample exhibit resonances at the same position, suggesting that the Mn2+ ions are located in sites of highly symmetric crystalline field. The increase of the line intensity of the sextet and the decrease of the background line in the thermal treated samples suggest that the Mn2+ ions move to the highly ordered sites which contribute to the sextet structure. The EPR spectra of the Gd3+ doped glasses exhibit the typical U-spectrum of a s-state ion in a low symmetry site in disordered systems. The EPR of the crystallized glasses, in contrast, have shown a strong resonance in g ≈ 2.0, suggesting Gd3+ ions in environment close to cubic symmetry. The 19F NMR spin-lattice relaxation rates were also strongly influenced by the crystallization process that takes over in samples annealed above Tc. For the glass samples (doped or undoped) the 19F magnetization recoveries were found to be adjusted by an exponential function and the spin-lattice relaxation was characterized by a single relaxation time. In contrast, for the samples treated above Tc, the 19F magnetization-recovery becomes non-exponential. A remarkable feature of our results is that the changes in the Cu2+, Mn2+, Gd3+ EPR spectra and NMR relaxation, are always observed for the samples annealed above Tc. © 2006 Elsevier B.V. All rights reserved.

Carbon nanotubes/polyamide 6.6 nanostructured composites crystallization kinetic study

Compared with the traditional composites, the incorporation of carbon nanotubes into polymeric matrices can generate materials with superior properties, especially thermal, electrical and tribological properties. The aim of this study was to study the polyamide 6.6/carbon nanotubes (PA 6.6/CNT) nanostructured composites crystallization kinetics. The solution mixing technique was used to obtain the nanostructured composites studied in this work. PA 6.6 films were produced with amounts of 0.1, 0.5, and 1.0 wt% (weight/weight) CNT. X-ray diffraction analyses were performed in order to determine the crystallographic properties of nanostructured composite. The nanostructured composites crystallization kinetic study was performed using the differential scanning calorimetry under isothermal and nonisothermal (dynamic) conditions. The results have shown addition of CNTs in the PA 6.6 reduces the Avrami exponent, affecting the crystallization process of the composite. © The Author(s) 2012.

Internal standard for amorphous pharmaceuticals products quantification and an application of Parametric Rietveld refinement using time, temperature and relative humidity as 'non-crystallographic' parameters

Pós-graduação em Química - IQ

Systematic analysis of protein-detergent complexes applying dynamic light scattering to optimize solutions for crystallization trials

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Robust isothermal electric control of exchange bias at room temperature

Voltage-controlled spin electronics is crucial for continued progress in information technology. It aims at reduced power consumption, increased integration density and enhanced functionality where non-volatile memory is combined with highspeed logical processing. Promising spintronic device concepts use the electric control of interface and surface magnetization. From the combination of magnetometry, spin-polarized photoemission spectroscopy, symmetry arguments and first-principles calculations, we show that the (0001) surface of magnetoelectric Cr2O3 has a roughness-insensitive, electrically switchable magnetization. Using a ferromagnetic Pd/Co multilayer deposited on the (0001) surface of a Cr2O3 single crystal, we achieve reversible, room-temperature isothermal switching of the exchange-bias field between positive and negative values by reversing the electric field while maintaining a permanent magnetic field. This effect reflects the switching of the bulk antiferromagnetic domain state and the interface magnetization coupled to it. The switchable exchange bias sets in exactly at the bulk Néel temperature.

Influence of spatial constraints in non-crystalline regions on the polymer dynamics in semi-crystalline polyethylene: a solid state NMR study

A broad variety of solid state NMR techniques were used to investigate the chain dynamics in several polyethylene (PE) samples, including ultrahigh molecular weight PEs (UHMW-PEs) and low molecular weight PEs (LMW-PEs). Via changing the processing history, i.e. melt/solution crystallization and drawing processes, these samples gain different morphologies, leading to different molecular dynamics. Due to the long chain nature, the molecular dynamics of polyethylene can be distinguished in local fluctuation and long range motion. With the help of NMR these different kinds of molecular dynamics can be monitored separately. In this work the local chain dynamics in non-crystalline regions of polyethylene samples was investigated via measuring 1H-13C heteronuclear dipolar coupling and 13C chemical shift anisotropy (CSA). By analyzing the motionally averaged 1H-13C heteronuclear dipolar coupling and 13C CSA, the information about the local anisotropy and geometry of motion was obtained. Taking advantage of the big difference of the 13C T1 relaxation time in crystalline and non-crystalline regions of PEs, the 1D 13C MAS exchange experiment was used to investigate the cooperative chain motion between these regions. The different chain organizations in non-crystalline regions were used to explain the relationship between the local fluctuation and the long range motion of the samples. In a simple manner the cooperative chain motion between crystalline and non-crystalline regions of PE results in the experimentally observed diffusive behavior of PE chain. The morphological influences on the diffusion motion have been discussed. The morphological factors include lamellar thickness, chain organization in non-crystalline regions and chain entanglements. Thermodynamics of the diffusion motion in melt and solution crystallized UHMW-PEs is discussed, revealing entropy-controlled features of the chain diffusion in PE. This thermodynamic consideration explains the counterintuitive relationship between the local fluctuation and the long range motion of the samples. Using the chain diffusion coefficient, the rates of jump motion in crystals of the melt crystallized PE have been calculated. A concept of "effective" jump motion has been proposed to explain the difference between the values derived from the chain diffusion coefficients and those in literatures. The observations of this thesis give a clear demonstration of the strong relationship between the sample morphology and chain dynamics. The sample morphologies governed by the processing history lead to different spatial constraints for the molecular chains, leading to different features of the local and long range chain dynamics. The knowledge of the morphological influence on the microscopic chain motion has many implications in our understanding of the alpha-relaxation process in PE and the related phenomena such as crystal thickening, drawability of PE, the easy creep of PE fiber, etc.

Experimental assessment of environmental decay effects in masonry via non destructive diagnostic techniques and mechanical tests

Environmental decay in porous masonry materials, such as brick and mortar, is a widespread problem concerning both new and historic masonry structures. The decay mechanisms are quite complex dependng upon several interconnected parameters and from the interaction with the specific micro-climate. Materials undergo aesthetical and substantial changes in character but while many studies have been carried out, the mechanical aspect has been largely understudied while it bears true importance from the structural viewpoint. A quantitative assessment of the masonry material degradation and how it affects the load-bearing capacity of masonry structures appears missing. The research work carried out, limiting the attention to brick masonry addresses this issue through an experimental laboratory approach via different integrated testing procedures, both non-destructive and mechanical, together with monitoring methods. Attention was focused on transport of moisture and salts and on the damaging effects caused by the crystallization of two different salts, sodium chloride and sodium sulphate. Many series of masonry specimens, very different in size and purposes were used to track the damage process since its beginning and to monitor its evolution over a number of years Athe same time suitable testing techniques, non-destructive, mini-invasive, analytical, of monitoring, were validated for these purposes. The specimens were exposed to different aggressive agents (in terms of type of salt, of brine concentration, of artificial vs. open-air natural ageing, …), tested by different means (qualitative vs. quantitative, non destructive vs. mechanical testing, punctual vs. wide areas, …), and had different size (1-, 2-, 3-header thick walls, full-scale walls vs. small size specimens, brick columns and triplets vs. small walls, masonry specimens vs. single units of brick and mortar prisms, …). Different advanced testing methods and novel monitoring techniques were applied in an integrated holistic approach, for quantitative assessment of masonry health state.

Detrital Zircon Evidence for Non-Laurentian Provenance, Mesoproterozoic (ca. 1490-1450 Ma) Deposition and Orogenesis in a Reconstructed Orogenic Belt, Northern New Mexico, USA: Defining the Picuris Orogeny

Detrital zircon and igneous zircon U-Pb ages are reported from Proterozoic metamorphic rocks in northern New Mexico. These data give new insight into the provenance and depositional age of a >3-km-thick metasedimentary succession and help resolve the timing of orogenesis within an area of overlapping accretionary orogens and thermal events related to the Proterozoic tectonic evolution of southwest Laurentia. Three samples from the Paleoproterozoic Vadito Group yield narrow, unimodal detrital zircon age spectra with peak ages near 1710 Ma. Igneous rocks that intrude the Vadito Group include the Cerro Alto metadacite, the Picuris Pueblo granite, and the Penasco quartz monzonite and yield crystallization ages of 1710 +/- 10 Ma, 1699 +/- 3 Ma, and 1450 +/- 10 Ma, respectively. Within the overlying Hondo Group, a metamorphosed tuff layer from the Pilar Formation yields an age of 1488 +/- 6 Ma and represents the first direct depositional age constraint on any part of the Proterozoic metasedimentary succession in northern New Mexico. Detrital zircon from the overlying Piedra Lumbre Formation yield a minimum age peak of 1475 Ma, and similar to 60 grains (similar to 25%) yield ages between 1500 Ma and 1600 Ma, possibly representing non-Laurentian detritus originating from Australia and/or Antarctica. Detrital zircons from the basal metaconglomerate and the middle quartzite member of the Marquenas Formation yield minimum age peaks of 1472 Ma and 1471 Ma, consistent with earlier results. We interpret the onset of ca. 1490-1450 Ma deposition followed by tectonic burial, regional Al2SiO5 triple-point metamorphism, and ductile deformation at depths of 12-18 km to reflect a Mesoproterozoic contractional orogenic event, possibly related to the final suturing of the Mazatzal crustal province to the southern margin of Laurentia. We propose to call this event the Picuris orogeny.

Toxicity of eosinophil MBP is repressed by intracellular crystallization and promoted by extracellular aggregation.

Eosinophils are white blood cells that function in innate immunity and participate in the pathogenesis of various inflammatory and neoplastic disorders. Their secretory granules contain four cytotoxic proteins, including the eosinophil major basic protein (MBP-1). How MBP-1 toxicity is controlled within the eosinophil itself and activated upon extracellular release is unknown. Here we show how intragranular MBP-1 nanocrystals restrain toxicity, enabling its safe storage, and characterize them with an X-ray-free electron laser. Following eosinophil activation, MBP-1 toxicity is triggered by granule acidification, followed by extracellular aggregation, which mediates the damage to pathogens and host cells. Larger non-toxic amyloid plaques are also present in tissues of eosinophilic patients in a feedback mechanism that likely limits tissue damage under pathological conditions of MBP-1 oversecretion. Our results suggest that MBP-1 aggregation is important for innate immunity and immunopathology mediated by eosinophils and clarify how its polymorphic self-association pathways regulate toxicity intra- and extracellularly.

Transition from isentropic to isothermal expansion in laser produced plasma

The transition that the expansion flow of laser-produced plasmas experiences when one moves from long, low intensity pulses (temperature vanishing at the isentropic plasma-vacuum front,lying at finite distance) to short, intense ones (non-zero, uniform temperature at the plasma-vacuum front, lying at infinity) is studied. For plznar geometry and lqge ion number Z, the transition occurs for dq5/dt=0.14(27/8)k712Z’1zn$/m4f, 12nK,,; mi, and K are laser intensity, critical density,ion mass, and Spitzer’s heat conduction coefficient. This result remains valid for finite Zit,h ough the numerical factor in d$/dt is different. Shorter wavelength lasers and higher 4 plasmas allow faster rising pulses below transition.

Experimental and numerical study of cw green laser crystallization of a-Si:H thin films

Crystallization and grain growth technique of thin film silicon are among the most promising methods for improving efficiency and lowering cost of solar cells. A major advantage of laser crystallization and annealing over conventional heating methods is its ability to limit rapid heating and cooling to thin surface layers. Laser energy is used to heat the amorphous silicon thin film, melting it and changing the microstructure to polycrystalline silicon (poly-Si) as it cools. Depending on the laser density, the vaporization temperature can be reached at the center of the irradiated area. In these cases ablation effects are expected and the annealing process becomes ineffective. The heating process in the a-Si thin film is governed by the general heat transfer equation. The two dimensional non-linear heat transfer equation with a moving heat source is solve numerically using the finite element method (FEM), particularly COMSOL Multiphysics. The numerical model help to establish the density and the process speed range needed to assure the melting and crystallization without damage or ablation of the silicon surface. The samples of a-Si obtained by physical vapour deposition were irradiated with a cw-green laser source (Millennia Prime from Newport-Spectra) that delivers up to 15 W of average power. The morphology of the irradiated area was characterized by confocal laser scanning microscopy (Leica DCM3D) and Scanning Electron Microscopy (SEM Hitachi 3000N). The structural properties were studied by micro-Raman spectroscopy (Renishaw, inVia Raman microscope).

In situ observation of bainite growth during isothermal holding

The mechanism of bainite growth has been investigated using in situ transmission electron microscopy observations. It was found that, in a number of alloys studied, a bainitic embryo is made of basic transformation units. These units are either a group of stacking faults or, in two dimensions, a series of parallelograms of different sizes. Thickening/widening of the bainite embryo takes place through shear along the stacking fault planes or twining planes. The bainite embryo is elongated by the formation of new transformation units at both tips of the bainite plate. The three-dimensional morphology of bainite is a convex tens-like lath. It is believed that the bainite embryo grows by shearing, which is controlled by the diffusion of solute atoms during the transformation. As the growth rate is much lower than that of martensite, it is therefore detectable. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Isothermal fatigue of an aluminide-coated single-crystal superalloy:Part II. Effects of brittle precracking

The effect of brittle coating precracking on the fatigue behavior of a high-activity aluminide-coated single-crystal nickel-base superalloy has been studied using hollow cylindrical specimens at test temperatures of 600 °C, 800 °C, and 1000 °C. Three types of precrack were studied: narrow precracks formed at room temperature, wide precracks formed at room temperature, and narrow precracks formed at elevated temperature. The effect of precracking on fatigue life at 600 °C was found to depend strongly on the type of precrack. No failure was observed for specimens with narrow room-temperature precracks because of crack arrest via an oxidation-induced crack closure mechanism, while the behavior of wide precracks and precracks formed at elevated temperature mirrored the non-precracked behavior. Crack retardation also occurred for narrow room-temperature precracks tested at 800 °C - in this case, fatigue cracks leading to failure initiated in a layer of recrystallized grains on the inside surface of the specimen. A significant reduction in fatigue life at 800 °C relative to non-precracked specimens was observed for wide precracks and elevated temperature precracks. The presence of precracks bypassed the initiation and growth of coating fatigue cracks necessary for failure in non-precracked material. No effect of precracking was observed at 1000 °C.