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Atomically-dispersed metal catalysts (ADMCs) on surfaces have demonstrated high activity and selectivity in many catalytic reactions. However, dispersing and stabilising individual atoms in support materials in an atom/energy-efficient scalable way still presents a significant challenge. Currently, the synthesis of ADMCs involves many steps and further filtration procedures, creating a substantial hurdle to their production at industrial scale. In this work, we develop a new pathway for producing ADMCs in which Pt atoms are stabilised in the nitrogen-interstices of a graphitic carbon nitride (g-C3N4) framework using scalable, solvent-free, one-pot magnetron sputtering deposition. Our approach has the highest reported rate of ADMC production of 4.8 mg h-1 and generates no chemical waste. Deposition of only 0.5 weight percent of Pt onto g-C3N4 led to improved hydrogen production by factor of ca. 3333 ± 450 when compared to bare g-C3N4. PL analysis showed that the deposition of Pt atoms onto g-C3N4 suppressed the charge carrier recombination from the photogenerated electron-hole pairs of Pt/g-C3N4 thereby enhance hydrogen evolution. Scanning transmission electron microscope imaging before and after the hydrogen evolution reaction revealed that the Pt atoms stabilised in g-C3N4 have a high stability, with no agglomeration observed. Herein, it is shown that this scalable and clean approach can produce effective ADMCs with no further synthetic steps required, and that they can be readily used for catalytic reactions.

There are several purposes for investigating hydrotalcite clays and one of them is due to its importance as an anionic adsorbent and ion exchanger, which make them capable of removing various pollutants from water. The most common hydrotalcite structure is based on double lamellar hydroxide of magnesium and aluminum, containing carbonate anions in the interlayer space. However, it is common to investigate the co-substitution of aluminum with other trivalent cations, especially transition metal cations, due to their binding properties. In this work, it was investigate the co-substitution of chromium (III) and aluminum in a sample of magnesium-aluminum carbonated hydrotalcite, comparing it with the same composition without this co-substitution. Thermal stability, crystallinity and morphology were investigated, showing that chromium contributes to the adsorptive capacity at low temperature. As pesquisas com argilas de hidrotalcita têm diversas finalidades e uma delas se deve à sua importância como adsorvente aniônico e trocador de íons, o que as tornam capazes de remover diversos poluentes da água. A estrutura de hidrotalcita mais comum é baseada em hidróxido duplo lamelar de magnésio e alumínio, contendo ânions carbonato no espaço interlamelar. No entanto, é comum investigar a cossubstituição do alumínio por outros cátions trivalentes, especialmente cátions de metais de transição, devido às suas propriedades ligantes. Neste trabalho, foi investigada a cossubstituição do alumínio com cromo (III) em uma amostra de hidrotalcita carbonatada de magnésio-alumínio, comparando-a com a mesma composição sem esta cossubstituição. Estabilidade térmica, cristalinidade e morfologia foram investigadas, mostrando que o cromo contribui para a capacidade adsortiva em baixa temperatura.

Non-stoichiometric glasses (NSG) are much more common than stoichiometric compositions. However, due to inherent difficulties, fundamental studies of crystallization kinetics of NSG are much less frequent. To shed light on the crystal nucleation and growth kinetics of NSG, we adopted a nucleation kinetics model, leaving the interfacial energy and diffusion coefficient as free parameters, to explain experimental nucleation data of glasses of three compositions in the pseudo-binary Li2O·2SiO2–BaO·2SiO2 model system. We show that, as the glass composition approaches the eutectic, the nucleation rates drop drastically, mainly due to an increase in the interfacial energy. This result corroborates the common empirical observation that eutectic compositions tend to show good glass-forming ability. We also found that the structural relaxation times are significantly shorter than the characteristic nucleation times, validating the widely used and scarcely tested assumption that relaxation does not play a noticeable role in crystal nucleation. For a stoichiometric glass the fitted diffusion coefficient determining nucleation, D , is lower than that determining the growth of macro crystals, D U , and this difference significantly increases with decreasing temperature. On the other hand, the diffusion coefficient calculated from viscosity, D η , is close to D U at high temperatures and approaches D in the glass transition range. Finally, after crystallization of the primary phase (lithium disilicate), barium disilicate and more lithium disilicate crystals precipitate in the diffusion zone existing in the residual glass.

Agradecimentos: The authors thank the Brazilian funding agencies CNPq and FAPESP [grant number 16/11261-8], for the financial support of this work. This study was financed in part by the "Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brazil (CAPES)"- Finance Code 001 Abstract: This study investigates and compares the thermal phase transition and crystallization characteristics of a commercial food grade free phytosterol blend (FP) with a stigmasterol analytical standard (SS), the FP behavior in a food model system after its addition to high oleic sunflower oil (HOSO). The properties of the FP:HOSO blends were studied by differential scanning calorimetry, solid content, crystal morphology, and X-ray diffraction (XRD) measurements. The Rietveld method (RM) was applied associated with the XRD measurements to support phase analysis and the study of crystallinity degree. The materials were also characterized by means of chemical composition, such as fatty acids and triacylglycerol profiles, for HOSO, and phytosterol profile, for FP. Regarding phase behavior and crystallinity properties, FP has very similar characteristics to SS. The thermal behavior of FP:HOSO blends has two characteristic peaks, one from FP and the other from HOSO. The similarity reported in the literature between the diffraction pattern of FP and pure phytosterols is a positive characteristic for FP. A high FP concentration resulted in high supersaturation and thus the formation of small crystals. The incorporation of HOSO reduced of the large agglomeration of FP crystals and the dispersion crystalline aggregates (spherulites) of FP crystals. The application of RM in FP:HOSO blends to quantify the crystalline and amorphous phases was successfully used. The application has provided the expected value for these phases, according to the same experimental mass ratio of the blends, thereby validating the applicability of this approach in this type of material COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP Aberto

To meet contemporary industry needs, saline wastewater treatment with zero liquid discharge goals is gaining increasing attention. In this context, evaporative crystallization has been applied to s...

In this work we used two glass stability (GS) parameters, which best correlate with the glass-forming ability (GFA), in an extensive study for analyzing the influence of alkali and alkaline earth modifiers and five glass-formers, in the crystallization resistance of binary oxide glasses. For the good glass formers silica, boria and germania, the addition of small amounts of modifiers rapidly reduces the GS, whereas for the conditional glass formers telluria and alumina, it initially increases the GS. Lower liquidus temperatures are associated with a better GS, and above 50 molar percent of modifier oxide, the liquidus temperature seems to be the main factor controlling GS (except for telluria). Lithium containing glasses show the lowest GS between the alkali systems, while the alkaline earth modifiers show the same effect on the GS. The TeO2 is the only exception, for which the barium tellurites show better GS. The pure oxides rank in the following order of GS: B2O3>SiO2>GeO2>TeO2>Al2O3.

According to the European Union, magnesium is considered as a critical metal, which can also be found in nickel laterite waste processing, where it is a strategic element with nickel, copper, and cobalt. For this reason, the goal of this work was to study the parameters for crystallization of magnesium sulphate under pressure based on nickel laterite leach solution through a reactor designed with separation system where monohydrate crystals were not decomposed. A magnesium monoelementary solution was used for the present study. After the reaction, the solid phase was separated with the reactor still under pressure to avoid crystals decomposition. Magnesium sulphate solubility was determined to complement the data already published in the literature and to define the solubility product from 30 to 230 °C. Pitzer interaction model made possible the Kps values were obtained at high-temperatures. The crystallization of magnesium sulphate reached the equilibrium in 5 h. At pH 5.7 and 230 °C, 81% of the magnesium crystallized. The particles presented a spherical morphology. The reactor here designed allowed the realization of crystallization at high-temperature, without crystals decomposition. The flowchart here proposed represents the novelty since it could be used for critical metals recovery from mining waste.

Zero liquid discharge strategies for industrial wastewater treatment have become prominent in recent years. When evaporative simultaneous crystallization is applied, knowledge about the particle crystallization mechanisms and morphology are important to ease solids downstream handling and for recovery of their valuable components. In this work, batch simultaneous crystallization of sodium chloride (NaCl) and calcium sulphate hemihydrate (CaSO4.0.5H2O) from aqueous solution was studied. It was found that CaSO4.0.5H2O is not an effective substrate for NaCl heterogeneous nucleation, but agglomerates with NaCl particles instead. CaSO4.0.5H2O particles on the surface of NaCl crystals sterically hamper agglomeration of NaCl particles with each other and, for a sufficiently high CaSO4.0.5H2O seed load, cover the NaCl crystals so that NaCl supersaturation rises, inducing NaCl primary nucleation. Simultaneous crystallization of CaSO4.0.5H2O and NaCl yields a satisfactory product for downstream handling even for high CaSO4.0.5H2O content in the crystallizer. However, seeding with CaSO4.0.5H2O is not recommended as it reduces the mean size and increases product size dispersion. NaCl seeding may be considered if it is desirable to separate CaSO4.0.5H2O from NaCl downstream the crystallizer by size classification, as it favors CaSO4.0.5H2O to build up in product sizes of 200 μm and below.

Several scientific investigations have focused on providing new strategies for supporting the development of low saturated and zero trans lipid materials, as healthier fat alternatives for food application. This work evaluated the consistency, crystallization behavior, microstructure and polymorphism of six blends composed of palm and canola oils at different concentrations (100:0, 80:20, 60:40, 40:60, 20:80 and 0:100, in w/w%) added with 5.0% of fully hydrogenated palm oil (FHPO) or with a mixture of 2.5% of FHPO and 2.5% of sorbitan monostearate (SMS). The results were compared with the non-structured blends (standard samples). Through microstructure images, the formation of a more homogeneous and denser packed crystal network was observed for samples added with both crystallization modifiers (FHPO/SMS) compared to the corresponding standard samples, after stabilization at 25 °C during 3 h. In particular, enhanced crystallization modifications were observed for the 40:60 blend, in which the crystal form β′ emerged after the addition of FHPO/SMS. Moreover, the 40:60 blend structured with FHPO/SMS showed increased consistency (from 30 to 658 g(F)/cm(2)) and induced onset crystallization in a higher temperature (from 13.1 to 23.9 °C) compared with the non-structured one, due to the specific crystallization effects provided by both added structurants. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s13197-017-3026-5) contains supplementary material, which is available to authorized users.

In this study, we report on the synthesis of a bioactive glass powder with the original 45S5 composition (Bioglass®) by means of an acetic acid-assisted sol–gel route. A glassy material was obtained after the gels underwent a thermal stabilization treatment at 600 °C for 3 h. Above this temperature, the heat-treated gels crystallized partially, forming a sodium-calcium-silicate Na2CaSi2O6 phase. Even after crystallization, this material showed in vitro bioactivity in simulated body fluid after 12 h, when the formation of hydroxycarbonate apatite on the material surface was identified by X-ray diffraction. Not surprisingly, microbiological assays revealed that these gel-derived materials appear to have an antibacterial effect against Pseudomonas aeruginosa (ATCC 27853)—a Gram-negative bacterium that is noted for its environmental survival versatility, ability to produce biofilm and resistance to some antibiotics. Thus, using common precursors that are widely available, relatively cheap, simple to use, and which result in gels with low stabilization temperature, it was possible to explore the versatility of sol–gel processing to obtain the golden standard 45S5 bioglass.

The aim of this work was to evaluate the crystal size distribution (CSD) and microscopy of the crystalline phase in isothermal lactose crystallization, using a high seeding concentration (dense phase). In-line monitoring was carried out using Focused Beam Reflectance Measurement (FBRM) and Particle Vision Measurement (PVM) probes in a stainless steel trunk-conical shaped jacketed crystallizer. The vibratory shaking system consisted of two perforated discs coupled to a movable axle. A conventional crystallization unit, with a three-blade propeller attached to a stainless steel shaft, was used for comparison. Concentrated cheese whey, purified with an organic coagulant, and commercial lactose solutions were used. Crystallization was improved in the high-purity solutions. Microparticles and/or aggregates appeared before seeding, mainly in the purified cheese whey solution, in which there are impurities. Secondary nucleation was present in both the vibratory agitation and conventional rotary agitation systems, being intensified by increases in agitation. Crystallization in a vibratory system should be carried out with a vibration frequency of 250 rpm, since an increase to 400 rpm reduced the amount of larger crystals. Resumo O estudo visa avaliar a distribuição de tamanho cristalino e a microscopia da fase cristalina na cristalização isotérmica de lactose, usando alta concentração de sementes (fase densa). O monitoramento in-line foi realizado utilizando as sondas de medição de reflexão de feixe focalizado (FBRM) e de medição de visão de partículas (PVM), um cristalizador de aço inoxidável encamisado, em formato tronco-cônico. O sistema de agitação vibratório foi composto por dois discos perfurados, acoplados a um eixo móvel. Uma unidade de cristalização convencional, com três pás do tipo hélice conectadas a um eixo de aço inoxidável, foi utilizada como comparação. Utilizou-se soro de queijo concentrado, purificado com um coagulante orgânico, e soluções de lactose comercial. O rendimento da cristalização foi aumentado em soluções de alta pureza. Houve presença de aglomerados e/ou agregados antes da semeadura, principalmente nas soluções de soro purificado, nas quais há impurezas. A nucleação secundária esteve presente nos experimentos, tanto no sistema com agitação por vibração quanto no sistema de agitação convencional por rotação, sendo intensificada pelo aumento da agitação. A cristalização em leito vibrado deve ser realizada com uma frequência de vibração de 250 rpm, porque um incremento a 400 rpm reduz o número de cristais maiores.

The synthesis of mixed-metal spinels based on substituted &gamma, Ga2O3 is reported using metal acetylacetonate precursors in solvothermal reactions with alcohols as solvents at 240 &deg, C. New oxides of Cr, Mn and Fe have been produced, all of which are formed as nanocrystalline powders, as seen by high-resolution transmission electron microscopy (HR-TEM). The first chromium-gallium mixed oxide is thus formed, with composition 0.33Ga1.87Cr0.8O4 ( = vacant site). X-ray absorption near-edge spectroscopy (XANES) at the chromium K-edge shows the presence of solely octahedral Cr3+, which in turn implies a mixture of tetrahedral and octahedral Ga3+, and the material is stable on annealing to at least 850 &deg, C. An analogous manganese material with average chemical composition close to MnGa2O4 is shown to contain octahedral Mn2+, along with some Mn3+, but a different inversion factor to materials reported by conventional solid-state synthesis in the literature, which are known to have a significant proportion of tetrahedral Mn2+. In the case of iron, higher amounts of the transition metal can be included to give an Fe:Ga ratio of 1:1. Elemental mapping using energy dispersive X-ray spectroscopy on the TEM, however, reveals inhomogeneity in the distribution of the two metals. This is consistent with variable temperature 57Fe M&ouml, ssbauer spectroscopy that shows the presence of Fe2+ and Fe3+ in more than one phase in the sample. Variable temperature magnetisation and electron paramagnetic resonance (EPR) indicate the presence of superparamagnetism at room temperature in the iron-gallium oxides.

This work investigates the modification, resulting from fs-laser irradiation (150 fs, 775 nm and 1 kHz), on the structure and surface morphology of hydrogenated amorphous silicon (a-Si:H) thin films. The sample morphology was studied by performing a statistical analyzes of atomic force microscopy images, using a specially developed software that identifies and characterizes the domains (spikes) produced by the laser irradiation. For a fluence of 3.1 MJ/m2, we observed formation of spikes with smaller average height distribution, centered at around 15 nm, while for fluencies higher than 3.7 MJ/m2 aggregation of the produced spikes dominates the sample morphology. On the other hand, Raman spectroscopy revealed that a higher crystalline fraction (73%) is obtained for higher fluences (> 3.1 MJ/m2), which is accompanied by a decrease in the size of the produced crystals. Therefore, such results indicate that there is a trade-off between the spike distribution, crystallization fraction and size of the nanocrystals attained by laser irradiation, which has to be taken into account when using such approach for the development of devices.

Os principais fatores que afetam a textura em um fondant são: formulação, relacionada com a existência de outros ingredientes além da sacarose; temperatura de cristalização; geometria do cristalizador, e velocidade de cristalização. Neste estudo, procurou-se avaliar a influência de parâmetros de processo sobre as características texturais e de atividade de água de um fondant produzido com xarope de glicose obtido pela hidrólise da fécula de mandioca, utilizando-se um protótipo de cristalização contínuo com capacidade para 1 a 2 kg.h-1. Este equipamento foi projetado e construído baseado em modelo de equipamento contínuo para a produção industrial de fondant, sendo configurado com um sistema de rosca sem fim, encamisada para circulação de água fria. Selecionaram-se, para seu dimensionamento, parâmetros, como tamanho da rosca (comprimento, diâmetro e passo) e espaçamento (gap) entre a rosca e o tubo externo; para permitir variações na velocidade de rotação da rosca, optou-se pela instalação de um inversor de frequência acoplado ao motor. Amostras de fondant foram produzidas a partir de misturas de sacarose e xarope de fécula de mandioca 42DE, estudando-se a influência das variáveis temperatura de cristalização e velocidade de rotação sobre sua textura, e a atividade de água, utilizando-se delineamento estatístico Composto Central Rotacional com base na Metodologia de Superfície de Resposta (MSR). Com o uso do protótipo dotado de rosca de 250 mm de comprimento e 27,2 mm de diâmetro, e considerando-se as repostas de atividade de água e textura, concluiu-se que para obter as melhores características no fondant, com textura adequada e maior estabilidade microbiológica, deve-se trabalhar com teores de xarope de glicose de, no mínimo, 20% (mínima atividade de água), velocidade de rotação entre 105 e 110 rpm, e temperatura inicial de cristalização ao redor de 60 °C.

The microstructural behavior of industrial standardized cocoa butter samples and cocoa butter samples from three different Brazilian states is compared. The cocoa butters were characterized by their microstructural patterns, crystallization kinetics and polymorphic habits. The evaluation of these parameters aided in establishing relationships between the chemical compositions and crystallization behavior of the samples, as well as differentiating them in terms of technological and industrial potential for use in tropical regions.En este trabajo se presenta el comportamiento de la microestructura y la cristalización de mantecas de cacao representativas de las mezclas industriales, y de la manteca de cacao original de tres regiones geográficas diferentes de Brasil. Las muestras se evaluaron de acuerdo a la microestructura, la cinética de cristalización y el comportamiento polimórfico. La evaluación de estos parámetros nos permite establecer relaciones entre la composición química y el comportamiento de la cristalización de las muestras, así como las diferencias sobre la adecuación del potencial tecnológico e industrial para su aplicación en las regiones tropicales.

The glass forming ability was investigated in the codoped Er3+/Yb3+ ternary system NaPO3-WO3-PbF2 with increasing amounts of PbF2. It has been found that glass samples can be obtained for PbF2 contents ranging from 0 mole% to 50 mole% for the codoped samples and an undoped sample containing 60% of lead fluoride could also be vitrified. Thermal properties of the most PbF2 concentrated glasses exhibit strong dependence of the composition with a decrease of the glass transition temperatures and thermal stabilities against devitrification with increasing the lead fluoride content. These glass samples were heat-treated near the crystallization peaks and the X-ray diffraction measurements pointed out that the dominant phase which precipitates from the glass samples containing 40% and 50% of PbF2 is the lead fluorophosphate phase Pb5F(PO4)3 whereas the sample containing 60% of PbF2 exhibits a preferential bulk crystallization of cubic lead fluoride β-PbF2.

Out-of-plane and primarily in-plane lattice strain distributions, along the two perpendicular crystallographic directions on the subsurface of a silicon layer with embedded FeSi2nanoparticles, were analyzed and resolved as a function of the synchrotron X-ray beam energy by using ω:φ mappings of the ({\overline 1}11) and (111) Bragg-surface diffraction peaks. The nanoparticles, synthesized by ion-beam-induced epitaxial crystallization of Fe+-implanted Si(001), were observed to have different orientations and morphologies (sphere- and plate-like nanoparticles) within the implanted/recrystallized region. The results show that the shape of the synthesized material singularly affects the surrounding Si lattice. The lattice strain distribution elucidated by the nonconventional X-ray Bragg-surface diffraction technique clearly exhibits an anisotropic effect, predominantly caused by plate-shaped nanoparticles. This type of refined detection reflects a key application of the method, which could be used to allow discrimination of strains in distorted semiconductor substrate layers.

Using molecular dynamic simulations we study a waterlike model confined between two fixed hydrophobic plates. The system is tested for density, diffusion and structural anomalous behavior and compared with the bulk results. Within the range of confining distances we had explored we observe that in the pressure-temperature phase diagram the temperature of maximum density (TMD line), the temperature of maximum and minimum diffusion occur at lower temperatures when compared with the bulk values. For distances between the two layers below a certain threshold ,$d\le d_c$, only two layers of particles are formed, for $d\ge d_c$ three or more layers are formed. In the case of three layers the central layer stays liquid while the contact layers crystallize. This result is in agreement with simulations for atomistic models.

The crystallization of laser glasses in the system (B2O3)0.6{(Al2O3)0.4−y(Y2O3)y} (0.1 ≤ y ≤ 0.25) doped with different levels of ytterbium oxide has been investigated by X-ray powder diffraction, differential thermal analysis, and various solid-state NMR techniques. The homogeneous glasses undergo major phase segregation processes resulting in crystalline YBO3, crystalline YAl3(BO3)4, and residual glassy B2O3 as the major products. This process can be analyzed in a quantitative fashion by solid-state 11B, 27Al, and 89Y NMR spectroscopies as well as 11B{27Al} rotational echo double resonance (REDOR) experiments. The Yb dopants end up in both of the crystalline components, producing increased line widths of the corresponding 11B, 27Al, and 89Y NMR resonances that depend linearly on the Yb/Y substitution ratio. A preliminary analysis of the composition dependence suggests that the Yb3+ dopant is not perfectly equipartitioned between both crystalline phases, suggesting a moderate preference of Yb to substitu...

Submitted by Guilherme Lemeszenski (guilherme@nead.unesp.br) on 2013-08-22T19:02:42Z No. of bitstreams: 1 S0366-69132007000300018.pdf: 1816818 bytes, checksum: 8b2cd62383fc852a42f2907d9ab1bf12 (MD5) Made available in DSpace on 2013-08-22T19:02:42Z (GMT). No. of bitstreams: 1 S0366-69132007000300018.pdf: 1816818 bytes, checksum: 8b2cd62383fc852a42f2907d9ab1bf12 (MD5) Previous issue date: 2007-09-01 Made available in DSpace on 2013-09-30T20:03:55Z (GMT). No. of bitstreams: 2 S0366-69132007000300018.pdf: 1816818 bytes, checksum: 8b2cd62383fc852a42f2907d9ab1bf12 (MD5) S0366-69132007000300018.pdf.txt: 37766 bytes, checksum: 14b6158c22bbaba2bd6a401034c9f807 (MD5) Previous issue date: 2007-09-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T13:29:41Z No. of bitstreams: 2 S0366-69132007000300018.pdf: 1816818 bytes, checksum: 8b2cd62383fc852a42f2907d9ab1bf12 (MD5) S0366-69132007000300018.pdf.txt: 37766 bytes, checksum: 14b6158c22bbaba2bd6a401034c9f807 (MD5) Made available in DSpace on 2014-05-20T13:29:41Z (GMT). No. of bitstreams: 2 S0366-69132007000300018.pdf: 1816818 bytes, checksum: 8b2cd62383fc852a42f2907d9ab1bf12 (MD5) S0366-69132007000300018.pdf.txt: 37766 bytes, checksum: 14b6158c22bbaba2bd6a401034c9f807 (MD5) Previous issue date: 2007-09-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) O presente trabalho reporta estudos sobre a cristalização em vidros teluretos 20Li2O-80TeO2 induzida a partir de tratamentos térmicos realizados sobre vidros com tamanho de partículas entre 38 µm e 75 µm. Estes estudos foram conduzidos em duas matrizes vítreas tratadas e não tratadas termicamente para aliviar as tensões após o quenching, utilizando-se de forma combinada às técnicas de difração de raios X, calorimetria diferencial de varredura e espectroscopia no infravermelho. Os resultados revelaram a presença de três fases cristalinas distintas durante o processo de cristalização e apontaram para uma hierarquia tal que as fases alfa-TeO2 e gama-TeO2 cristalizam-se antecipadamente à fase Li2Te2O5 no vidro 20Li2O-80TeO2 sujeito a tensões mecânicas induzidas durante a síntese. No vidro 20Li2O-80TeO2, livre de tensões mecânicas, não foi possível discriminar esta hierarquia de cristalização. This work report crystallization studies on tellurite 20Li2O-80TeO2 glasses induced from heat thermal annealing on glasses with particle size between 38 µm and 75 µm. These studies were conducted on two glass matrix heat thermal annealed and non-annealed to remove the stress after the quenching, by using the X-Ray diffraction analysis, Fourier transform infrared spectroscopy and differential scanning calorimetry techniques. The results shown the presence of three distinct crystalline alpha-TeO2, gamma-TeO2 and Li2Te2O5 phases during the crystallization process, suggesting a crystallization hierarchy on the glass matrix under stress, since the gamma-TeO2 and alpha-TeO2 phases crystallization occurs before the Li2Te2O5 phase. on the glass stress free, this crystallization hierarchy was not clearly determined. Universidade Estadual Paulista Departamento de Física e Química Universidade Estadual Paulista Departamento de Física e Química

Submitted by Guilherme Lemeszenski (guilherme@nead.unesp.br) on 2013-08-22T19:02:39Z No. of bitstreams: 1 S0366-69132003000100013.pdf: 614907 bytes, checksum: b0ff2a91c7380306b82dc32fb61fa110 (MD5) Made available in DSpace on 2013-08-22T19:02:39Z (GMT). No. of bitstreams: 1 S0366-69132003000100013.pdf: 614907 bytes, checksum: b0ff2a91c7380306b82dc32fb61fa110 (MD5) Previous issue date: 2003-03-01 Made available in DSpace on 2013-09-30T20:03:45Z (GMT). No. of bitstreams: 2 S0366-69132003000100013.pdf: 614907 bytes, checksum: b0ff2a91c7380306b82dc32fb61fa110 (MD5) S0366-69132003000100013.pdf.txt: 16189 bytes, checksum: 00ee22a473ba10fe24f4302cbaa9515f (MD5) Previous issue date: 2003-03-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T15:16:21Z No. of bitstreams: 2 S0366-69132003000100013.pdf: 614907 bytes, checksum: b0ff2a91c7380306b82dc32fb61fa110 (MD5) S0366-69132003000100013.pdf.txt: 16189 bytes, checksum: 00ee22a473ba10fe24f4302cbaa9515f (MD5) Made available in DSpace on 2014-05-20T15:16:21Z (GMT). No. of bitstreams: 2 S0366-69132003000100013.pdf: 614907 bytes, checksum: b0ff2a91c7380306b82dc32fb61fa110 (MD5) S0366-69132003000100013.pdf.txt: 16189 bytes, checksum: 00ee22a473ba10fe24f4302cbaa9515f (MD5) Previous issue date: 2003-03-01 Filmes finos de SrBi2Ta2O9 foram depositados em substratos de Pt/Ti/SiO2/Si e, pela primeira vez, sinterizados em forno microondas doméstico. Os padrões de difração de raios X mostraram que os filmes são policristalinos. O processamento por microondas permite utilizar baixa temperatura na síntese e obter filmes com boas propriedades elétricas. Ensaios de microscopia eletrônica de varredura (MEV) e de Força Atômica (MFA) revelam boa aderência entre filme e substrato, com microestrutura de superfície apresentando grãos finos e esféricos e rugosidade de 4,7 nm. A constante dielétrica e o fator de dissipação, para freqüência de 100 KHz, à temperatura ambiente, foram de 77 e 0,04, respectivamente. A polarização remanescente (2Pr) e o campo coercitivo (Ec) foram 1,04 miC/cm² e 33 kV/cm. O comportamento da densidade de corrente de fuga revela três mecanismos de condução: linear, ôhmico e outro mecanismo que pode ser atribuído à corrente de Schottky. Dos padrões de DRX, análises das imagens por MEV e topografia de superfície por MFA observa-se que 10 min de tratamento térmico a 550 ºC, em forno microondas, é tempo suficiente para se obter a cristalização do filme. SrBi2Ta2O9 thin films were deposited on Pt/Ti/SiO2/Si substrates and, for the first time, sintered in a domestic microwave oven. The X-ray diffraction patterns showed that the films are polycrystalline. The microwave processing allows to use a low temperature for the synthesis, obtaining films with good electrical properties. Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) results reveal good adherence between film and substrate and a surface microstructure presenting thin and spherical grains and roughness of 4.7 nm. The dielectric constant and the dissipation factor, for a frequency of 100 KHz at room temperature, were 77 and 0.04, respectively. The remaining polarization (2Pr) and the coercive field (Ec) were 1.04 C/cm² and 33 kV/cm, respectively. The behavior of the drift current density reveals three electric conduction mechanisms: linear, ohmic and another mechanism that can be attributed to the Schottky current. From the XRD patterns, analyses of the SEM images and AFM surface topography it was noticed that 10 min of thermal treatment at 550 ºC, in a microwave oven, is enough time to obtain the crystallization of the films. Universidade Estadual Paulista Instituto de Química Universidade Federal de São Carlos (UFSCar) Departamento de Química Universidade Federal de São Carlos (UFSCar) Departamento de Eletroeletrônica Centro Federal de Educação Federal do Maranhão Departamento de Química Universidade Estadual Paulista Instituto de Química

The dynamics and mechanism of migration of a vacancy point defect in a two-dimensional (2D) colloidal crystal are studied using numerical simulations. We find that the migration of a vacancy is always realized by topology switching between its different configurations. From the temperature dependence of the topology switch frequencies, we obtain the activation energies for possible topology transitions associated with the vacancy diffusion in the 2D crystal.

The physicochemical, structural, and mechanical properties of silicon nitride films deposited by radio frequency reactive magnetron sputtering were investigated before and after thermal annealing in 18O2. As-deposited films were essentially amorphous, stoichiometric, and free from contaminants for a wide range of deposition parameters, with hardness figures ranging from 16.5–22 GPa, depending mainly on the deposition temperature. After 18O2 annealing at 1000 °C, films hardness converged to 21 GPa, independently of the deposition temperature, which is explained based on the crystallization of the films at this annealing temperature. Moreover, oxygen is incorporated only in 7.5 nm of the Si3N4, forming silicon oxynitride at the top surface of the film, indicating a good oxidation resistance at high temperature. Finally, the elastic strain to failure (H³ /E²) , which mimics the wear resistance of the film, doubles after the 1000 °C annealing. These observations show the great potential of silicon nitride as a hard coating for high temperature applications.