La 0.7Ca 0.3MnO 3 / Mn 3O 4 composites: Does an insulating secondary phase always enhance the low field magnetoresistance of manganites

Composites of magnetoresistive La 0.7Ca 0.3MnO 3 (LCMO) with insulating Mn 3O 4 are useful as a model system because no foreign cation is introduced in the LCMO phase by interdiffusion during the heat treatment. Here we report the magnetotransport properties as a function of sintering temperature T sinter for a fixed LCMO/Mn 3O 4 ratio. Decreasing T sinter from 1250 °C to 800 °C causes an increase in low field magnetoresistance (LFMR) that correlates with the decrease in crystallite size (CS) of the LCMO phase. When plotting LFMR at (77 K, 0.5 T) versus 1/CS, we find that the data for the LCMO/Mn 3O 4 composites sintered between 800 °C and 1250 °C follow the same trend line as data from the literature for pure LCMO samples with crystallite size >∼25 nm. This differs from the LFMR enhancement observed by many authors in the usual manganite composites, i.e., composites where the insulating phase contains cations other than La, Ca or Mn. This difference suggests that diffusion of foreign cations into the grain boundary region is a necessary ingredient for the enhanced LFMR. © 2012 American Institute of Physics.

Phase conversion and spectral properties of long lasting phosphor Zn-3 (PO4)(2): Mn2+, Ga3+

A red long lasting phosphor Zn-3(PO4)(2): Mn2+ Ga3+ (ZPMG) was prepared by ceramic method, and phase conversion and spectral properties were investigated. Results indicated that the phase conversion from alpha-Zn-3(PO4), beta-Zn-3(PO4)(2) to gamma-Zn-3(PO4)(2) occurs with different manganese concentration incorporated and sinter process. The structural change induced by the phase transformation results in a remarkable difference in the spectral properties. The possible luminescence mechanism for this red LLP with different forms has been illustrated.

Partial oxidation of methane to syngas over Pt/A(2)O(3) and Pt/CeO2/Al2O3

The catalytic oxidation of methane to syngas has been carried out over Pt/Al2O3 and Pt/CeO2/Al2O3. It was found that the catalysts with ceria exhibit a higher activity and selectivity than those without ceria. The catalysts were characterized by means of TPR, TPD, SEM-EDX and XRD. There is a strong interaction between ceria and platinum under the reaction condition, which increase the dispersion of platinum over catalysts, preventing the sinter of the Pt particles. As a result of the synergistic;effect between Pt and ceria, the activity of Pt/Al2O3 for combustion reaction was suppressed, the activity and selectivity :For partial oxidation were improved greatly. Another role of ceria in the catalyst is the enhancing of the WGSR, which leads to the increase of the selectivity of catalyst for hydrogen and accelerating the equilibrium of the reaction.

中国北方表沙无机碳储量及次生碳酸盐固碳潜力研究

This paper selected the Taklamakan Desert and the Badain Jaran Desert as the research areas, tested the carbonate content of surface-sand samples of dunes using Eijkelkamp carbonate goniophotometer, and analyzed the spatial-distribution characteristics of carbonate and estimated the carbonate-stock and secondary carbonate-stock in 1m depth of surface sand in the Taklamakan Desert and the Badain Jaran Desert. In addition, the paper test XRD, SEM, TDA, stable carbon isotope and radioactive strontium isotope of lacustrine deposits in the Taklamakan Desert and carbonates, such as kunkar, root canal, lacustrine deposits, sinter and calcrete, in the Badain Jaran Desert. Resting on the achievements by our predecessors, it analyzed the mineral-composition differences of the carbonates, calculated the contents of secondary carbonate and, furthermore, evaluated their potential of sequestration of CO2 in the atmosphere. The overall goal of this study was to increase our understanding of soil carbonate in the context of carbon sequestration in the arid region in China. That is, to advance our understanding about whether or not secondary carbonate in desert is a sink for atmospheric CO2. The following viewpoints were obtained: 1 Carbonate contents of surface-sand samples decend from the south to the north of the Taklamakan Desert. The minimum lies in the south and the maxmum in the mid. Carbonate content of surface-sand of megadunes in the Badain Jaran Desert has low value generally in the dune-crest and the base of slope, and large value in the mid. The average of Carbonate contents of all sorts of collected samples in the same area of the Taklamakan Desert has small diffetences. The average is about 9%. 2 Using carbonate contents as key parameters, calculate the carbon-stock of carbonates in 1m depth of surface sand in the Taklamakan Desert and the Badain Jaran Deser.They are 1.13Pg and 0.19 Pg respectively. There are 0.53Pg and 0.088Pg carbon-stock of secondary-carbonates in 1m depth of surface sand in the Taklamakan Desert and the Badain Jaran Desert. 3 Through testing data from XRD （X-ray diffraction）and TAD ( Thermal Analysis Data), the most significant conclusion derived from is that the main mineral ingredient is calcite in different carbonate substances in arid regions, From the SEM(Scanning electron microscopy ) images, can obtains the information about the micro environment of different carbonate forms in which they can grow. 4 Selected gas by termal cracking and traditional phosphoric acid method, their δ13C show that δ13C is a good parameter to indicate the micro environment in which different secondary carbonate forms. From the δ13C of the same type samples, if the redeposit degree is hard, theδ13C is light, the redeposit degree is weak, the δ13C is heave. and the δ13C of the different type samples, δ13C is mainly controlled by the micro environment in which secondary formed. if the procedure is characterized by redeposit and dissolve of marine facies carbonate, δ13C is heavy, it is characterized by CO2 which produced by plant respiration,δ13C is light. 5 From the δ13C of lacustrine deposit in the different grain size, there exsit certain differences in their micro environment and secondary degree among different grain size in the same grade. 6 The secondary carbonate content of lacustrine deposits in Taklimakan Desert is 47.26%. And those of root canal, sinter, calcrete, kunkar, lacustrine deposit and surface sand in Badain Jaran Desert are 91.74%, 78.46%, 76.26%, 87.87%, 85.37%and 46.49%, respectively. Of different grain size samples, the secondary carbonate contents of coarse fraction (20-63μm), sub-coarse fraction (5-20μm) and fine fraction (<5μm) are 80.10%, 47.2%and 50.07%, respectively. 7 There is no obvious relevance betweenδ13C of secondary carbonate and the content of secondary carbonate,theδ13C of secondary carbonate mainly reflects the parameters of secondary process, the content of secondary carbonate reflects difference of secondary degree.. 8 Silicates potentially supply 3.4 pencent calcium source during forming process of lacustrine deposits in Taklimakan Desert. If calcium source is mainly supplied by goundwater, it can be calculated that about 5.18 %, 6.13%, 5.68%, 5.64 % and 6.82% silicates supply calcium source respectively for root canal, kunkar, lacustrine deposit, calcrete and sinter, during the forming process of different kinds of carbonates in Badain Jaran Desert.

L’expérience des intervenants dans l’accompagnement vers le rétablissement des personnes vivant dans les milieux de soins de longue durée en psychiatrie

Cette étude qualitative porte sur l’expérience des intervenants dans l’accompagnement au rétablissement dans les unités d’hébergement et de soins de longue durée en psychiatrie de l’Institut universitaire en santé mentale de Québec, avec un intérêt particulier pour les difficultés et les éléments facilitant cette expérience. Neufs intervenants de différentes professions (infirmiers, professionnels, éducateurs spécialisés) ont été rencontrés entre février et juin 2014. Chacun a participé à une entrevue semi-dirigée et complété le Recovery Attitude Questionnaire, version à 7 items (RAQ-7). Les entrevues ont fait l’objet d’une analyse de contenu thématique, complétée par une analyse des pointages provenant du RAQ-7. Résultats : Trois composantes de l’expérience d’accompagnement sont inter-reliées et s’inter-influencent : l’espoir (croire), l’implication et l’attachement envers la personne aidée. Une attitude positive envers le rétablissement, la compréhension de ce concept comme processus personnel et le fait de côtoyer des collègues qui croient en la possibilité d’un rétablissement influencent positivement l’expérience. En parallèle, le fait d’être confronté à des usagers-résidents présentant des symptômes importants, une culture d’intervention orientée vers la stabilisation des symptômes et un vécu d’intervention marqué par l’échec influencent négativement l’expérience. Conclusions et implications : L’expérience d’accompagnement au rétablissement est donc influencée par différents facteurs individuels et environnementaux (voir : environnement organisationnel). La connaissance de ces facteurs peut favoriser une implantation réussie de modes d’intervention favorables au rétablissement des usagers dans les milieux d’hébergement et de soins de longue durée en psychiatrie. Mots clés : rétablissement, maladie mentale sévère, Centre d’hébergement et de soins de longue durée, vécu des intervenants, intervenants, interventions, pratiques orientées vers le rétablissement.

Expérience subjective et différences individuelles dans l'intégration d'informations visuelle et kinesthésique

L’expérience subjective accompagnant un mouvement se construit a posteriori en intégrant différentes sources d’informations qui s’inter-influencent à différents moments tant avant qu’après le mouvement. Cette expérience subjective est interprétée par un modèle d’attribution bayésien afin de créer une expérience d’agentivité et de contrôle sur les mouvements de son propre corps. Afin de déterminer l’apport de l’interaction entre les paramètres considérés par le modèle d’attribution et d’investiguer la présence de disparités inter-individuelles dans la formation de l’expérience subjective du mouvement, une série de 90 pulsations simples de stimulation magnétique transcrânienne (SMT) sur le cortex moteur primaire (M1) suivi de multiples questions sur l’expérience subjective reliée au mouvement provoqué a été effectuée chez 20 participants normaux. Les données objectives du mouvement ont été recueillies par électromyographie (EMG) et capture du mouvement. Un modèle de régression a entre autres été effectué pour chaque participant afin de voir quelle proportion du jugement subjectif pouvait être expliqué par des indices objectifs et cette proportion variait grandement entre les participants. Les résultats de la présente étude indiquent la présence d’une capacité individuelle à se former des jugements subjectifs reflétant adéquatement la réalité comme en témoigne la cohérence entre les différentes mesures d’acuité et plusieurs variables mesurant l’expérience subjective.

Desenvolvimento e caracterização de filtros cerâmicos para aplicações a altas temperaturas

Ceramic filters are cellular structures that can be produced by various techniques, among which we highlight the replication method, or method of polymeric sponge. This method consists of impregnating polymeric foam with ceramic slurry, followed by heat treatment, where will occur decomposition of organic material and the sinter of the ceramic material, resulting in a ceramic whose structure is a replica of the impregnated sponge. Ceramic filters have specific properties that make this type of material very versatile, used in various technological applications such as filters for molten metals and burners, make these materials attractive candidates for high temperature applications. In this work we studied the systems Al2O3-LZSA ceramic filters processed in the laboratory, and commercial Al2O3-SiC ceramics filters, both obtained by the replica method, this work proposes the thermal and mechanical characterization. The sponge used in the processing of filters made in the laboratory was characterized by thermogravimetric analysis. The ceramic filters were characterized by compressive strength, flexural strength at high temperatures, thermal shock, permeability and physical characterization (density and porosity) and microstructural (MEV and X-rays). From the results obtained, the analysis was made of the mechanical behavior of these materials, comparing the model proposed by Gibson and Ashby model and modified the effective area and the tension adjusted, where the modified model adapted itself better to the experimental results, representing better the mechanical behavior of ceramic filters obtained by the replica method

Comportamento da adição do carbeto de nióbio (nBC) na matriz metálica do aço ferrítico 15kH2mfa

The 15Kh2MFA steel is a kind of Cr-Mo-V family steels and can be used in turbines for energy generation, pressure vessels, nuclear reactors or applications where the range of temperature that the material works is between 250 to 450°C. To improve the properties of these steels increasing the service temperature and the thermal stability is add a second particle phase. These particles can be oxides, carbides, nitrites or even solid solution of some chemical elements. On this way, this work aim to study the effect of addition of 3wt% of niobium carbide in the metallic matrix of 15Kh2MFA steel. Powder metallurgy was the route employed to produce this metallic matrix composite. Two different milling conditions were performed. Condition 1: milling of pure 15Kh2MFA steel and condition 2: milling of 15Kh2MFA steel with addition of niobium carbide. A high energy milling was carried out during 5 hours. Then, these two powders were sintered in a vacuum furnace (10-4torr) at 1150 and 1250°C during 60 minutes. After sintering the samples were normalized at 950°C per 3 minutes followed by air cooling to obtain a desired microstructure. Results show that the addition of niobium carbide helps to mill faster the particles during the milling when compared with that steel without carbide. At the sintering, the niobium carbide helps to sinter increasing the density of the samples reaching a maximum density of 7.86g/cm³, better than the melted steel as received that was 7,81g/cm³. In spite this good densification, after normalizing, the niobium carbide don t contributed to increase the microhardness. The best microhardness obtained to the steel with niobium carbide was 156HV and to pure 15Kh2MFA steel was 212HV. It happened due when the niobium carbide is added to the steel a pearlitic structure was formed, and the steel without niobium carbide submitted to the same conditions reached a bainitic structure

Estudo de titanatos nanoestruturados obtidos por tratamento hidrotérmico de óxido de titânio em meio alcalino

TiTanate NanoTubes (TTNT) were synthesized by hydrothermal alkali treatment of TiO2 anatase followed by repeated washings with distinct degrees of proton exchange. TTNT samples with different sodium contents were characterized, as synthesized and after heattreatment (200-800ºC), by X-ray diffraction, scanning and transmission electron microscopy, electron diffraction, thermal analysis, nitrogen adsorption and spectroscopic techniques like FTIR and UV-Vis diffuse reflectance. It was demonstrated that TTNTs consist of trititanate structure with general formula NaxH2−xTi3O7·nH2O, retaining interlayer water in its multiwalled structure. The removal of sodium reduces the amount of water and contracts the interlayer space leading, combined with other factors, to increased specific surface area and mesopore volume. TTNTs are mesoporous materials with two main contributions: pores smaller than 10 nm due to the inner volume of nanotubes and larger pores within 5-60 nm attributed to the interparticles space. Chemical composition and crystal structure of TTNTs do not depend on the average crystal size of the precursor TiO2-anatase, but this parameter affects significantly the morphology and textural properties of the nanostructured product. Such dependence has been rationalized using a dissolution-recrystallization mechanism, which takes into account the dissolution rate of the starting anatase and its influence on the relative rates of growth and curving of intermediate nanosheets. The thermal stability of TTNT is defined by the sodium content and in a lower extent by the crystallinity of the starting anatase. It has been demonstrated that after losing interlayer water within the range 100-200ºC, TTNT transforms, at least partially, into an intermediate hexatitanate NaxH2−xTi6O13 still retaining the nanotubular morphology. Further thermal transformation of the nanostructured tri- and hexatitanates occurs at higher or lower temperature and follows different routes depending on the sodium content in the structure. At high sodium load (water washed samples) they sinter and grow towards bigger crystals of Na2Ti3O7 and Na2Ti6O13 in the form of rods and ribbons. In contrast, protonated TTNTs evolve to nanotubes of TiO2(B), which easily convert to anatase nanorods above 400ºC. Besides hydroxyls and Lewis acidity typical of titanium oxides, TTNTs show a small contribution of protonic acidity capable of coordinating with pyridine at 150ºC, which is lost after calcination and conversion into anatase. The isoeletric point of TTNTs was measured within the range 2.5-4.0, indicating behavior of a weak acid. Despite displaying semiconductor characteristics exhibiting typical absorption in the UV-Vis spectrum with estimated bandgap energy slightly higher than that of its TiO2 precursor, TTNTs showed very low performance in the photocatalytic degradation of cationic and anionic dyes. It was concluded that the basic reason resides in its layered titanate structure, which in comparison with the TiO2 form would be more prone to the so undesired electron-hole pair recombination, thus inhibiting the photooxidation reactions. After calcination of the protonated TTNT into anatase nanorods, the photocatalytic activity improved but not to the same level as that exhibited by its precursor anatase

Compacidade do suporte cerâmico cru versus propriedades do revestimento cerâmico cozido

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

Methods to estimate the number of surface nucleation sites on glass particles

Based on the Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory, we propose two new models to describe the crystallisation kinetics of glass particles and use them to determine the density of nucleation sites, N(s), on glass powders. We tested these models with sintered compacts of diopside glass particles using sinter-crystallisation treatments at 825 degrees C (T(g)similar to 727 degrees C), that covered from null to almost 100% crystallised volume time fraction. We measured and compared the evolution of the crystallised volume fractions by optical microscopy and x-ray diffraction. Then we fit our expressions to experimental data using Ns and R (the average particle radius) as adjustable parameters. For comparison, we also fit to our data existing expressions that describe the crystallised volume fraction in glass powders. We demonstrate that all the methods allow one to estimate N(s) with reasonable accuracy. For our ground and water washed diopside glass powder, N(s) is between 10(10)-10(11) sites.m(-2). The reasonable agreement between experimental and adjusted R confirms the consistency of all five models tested. However, one of our equations does not require taking into account the change of crystallisation mode from 3-dimensional to 1-dimensional, and this is advantageous.

Sintering of tin oxide processed by slip casting

Sintering of SnO 2 compacts, obtained through slip casting, was studied by means of dilatometry, Hg porosimetry, scanning electron microscopy, and density measurement (Archimedes method). Sintering is strongly influenced by the green microstructure. Moreover, the sintering mechanisms are not dependent on the slurries' solid content up to 50% of solids in volume. Above this value, agglomerates are formed, leading to differential sintering inside and among the agglomerates. Another important point is the reduction of the temperature of maximum shrinkage rate when compared to tin oxide processed by isostatic pressing. This reduction is more accentuated when ammonium hydroxide is added to the suspension. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.

Viabilidade de aplicação das coberturas argilosas da região de Alfenas na indústra cerâmica

The region of Alfenas, in the state of Minas Gerais, Brazil, is predominantly constituted of Pre-Cambrian rocks with well developed alteration profiles in association with colluvial and alluvial sediments. No study to date has examined in detail its potential use in the ceramic industry. The scarce knowledge of its mineralogical and technological properties limits its value and consequently its industrial use. Until now, these clay materials have been used in a rudimental manner, in small scale in the fabrication of red tiles. The present study aimed at analyzing these clays mineralogically (X-ray diffraction), chemically (major and minor elements by X-ray fluorescence and organic carbon analysis) and technologically (pressing granulometric distribution; mechanical resistence; water absorption, apparent porosity; linear firing shrinkage; color of firing and others) in order to better understand the raw material and develop adequate technological applications. The best results of ceramic properties were the samples with higher organic content (more plastic clays) and higher values of Al2O3 (kaolinite and gibbsite) and Fe2O3 as well lower SiO2 content and finer grain size which contribute to a better sinterization.

Zirconia-Porcelain Bonding: Effect of Multiple Firings on Microtensile Bond Strength

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

Densification and enhancement of the grain boundary conductivity of gadolinium-doped barium cerate by ultra fast flash grain welding

Doped barium cerate is a promising solid electrolyte for intermediate temperature fuel cells as a protonic conductor. However, it is difficult to sinter it to high density at a reasonable temperature. Moreover, it presents a high grain boundary resistivity at intermediate temperatures. Flash grain welding was applied to compacted samples, starting from a temperature of 910 degrees C and applying, for a short time, an ac electric polarization of 40 V, 1000 Hz. At that frequency, the resulting current flows through the grain boundaries promoting a welding via a local Joule heating. A large decrease of the grain boundary resistivity was observed by impedance spectroscopy. Scanning electron microscopy observations of polished and etched surfaces revealed highly sintered regions. Attempts were also made to combine flash grain welding with conventional sintering. (C) 2012 Elsevier Ltd. All rights reserved.