Surface study of vitreous carbon obtained from glassy carbon powder

This work presents a surface study of monolithic vitreous (or glassy) carbon - MVC - obtained from vitreous carbon powder. Defective MVC pieces are crushed in a ball mill and size classified by sifting. The MVC powder is mixed with furfuryl-alcohol resin and compacted in a mould using a hydraulic press. Samples with different powder granulometries are produced in this way and carbonized in a furnace under nitrogen atmosphere. Complete carbonization of the powder is achieved in only one day and losses due to breakage of the pieces is less than 5%. These results compare very favorably with respect to traditional MVC production methods where full carbonization may require up to seven days and losses due to breakage can be as high as 70%. After carbonization, samples are sanded and polished. Surface roughness and microstructure are characterized by light microscopy. Porosity is quantified from micrographs using ImageJ software and nanometric height variations are measured by atomic force microscopy. © 2012 Materials Research Society.

Physicochemical analysis of Ti-Si-B powder aalloys

Titanium alloys of Ti-Si-B system were manufactured by blended elemental powder method using Ti, Si and B powders as starting materials. It was found that uniaxial and isostatic pressing followed by hot pressing at around 1000°C, for 20 minutes, provided good densification of such alloys. The physicochemical studies were performed by means of scanning electron microscopy, X-ray diffraction, atomic force microscopy and microindentation/wear tests. The investigations revealed a multiphase microstructure formed mainly by α-titanium, Ti6Si2B, Ti5Si3, TiB and Ti3Si phases. The phase transformations after pressureless sintering at 1200°C was also studied by X-ray diffraction for the Ti-18Si-6B composition. As stated in some other researches, these intermetallics in the α-titanium matrix provide high wear resistance and hardness, with the best wear rate of 0.2 mm3/N.m and the highest hardness of around 1300 HV. © (2012) Trans Tech Publications, Switzerland.

Photoluminescence of core-shell nanoparticles made from yttrium stabilized zirconia powder grain coated with alumina

A YSZ@Al2O3 nanocomposite was obtained by Al 2O3 coating on the surface of yttrium stabilized zirconia via a polymeric precursor method. The resulting core-shell structures were characterized by X-ray diffraction, scanning electron microscopy, transmission electronic microscopy and PL spectra. The TEM micrographs clearly show a homogeneous Al2O3 shell around the ZrO2 core. The observed PL is related to surface-interface defects. Such novel technologies can, in principle, explore materials which are not available in the bulk single crystal form but their figure-of-merit is dramatically dependent on the surface-interface defect states. © 2013 This journal isThe Royal Society of Chemistry.

Fabricação e caracterização de fios supercondutores do sistema BSCCO pelo método Powder-In-Tube (PIT)

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Desenvolvimento e aplicação de um software cristalográfico com protocolo de acesso a um banco de dados distribuído

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Reassessment of the potential applications of Eu3+-doped Y2O3 photoluminescent material in ceramic powder form

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

High activity photocatalyst powder formed by three ceramic oxides

A Photocatalyst ceramic powder that presented high photoactivity based on TiO2 modified with 25% molar of SnO2 and up to 5% molar of Ag2O was obtained in the present work. The aforementioned ceramic powder was obtained using all commercial oxides as well as the oxides mixture technique. The powders were ground in high energy mill for one hour with subsequent thermal treatment at 400°C for four hours. They were, furthermore, characterized using surface area of around 6m2/g, where the X-Ray diffraction results provided evidence for the presence of anatase and rutile phases, known to be typical characteristics of both the TiO2 and SnO2 used. During the thermal treatment, Ag2O was reduced to metallic silver. The photodegradation rehearsals were carried out using a 0.01 mmol/L Rhodamine B solution in a 100mg/L photocatalyst suspension in a 500ml beaker, which was irradiated with 4W germicide Ultraviolet light of 254nm. In addition, samples were removed after duration of about 10 minutes to an hour, where they were analyzed thoroughly in UV-vis spectrophotometer. The analysis of the results indicated that for the compositions up to 2.5% molar of Ag2O, the photoactivity was found to be greater than that of Degussa P25 photocatalyst powder, and as such it was then used as a reference. Taking into account 90% degradation of Rhodamine B, a duration period of 11 minutes was obtained for the developed photocatalyst powder compared to the 38 minutes observed for the Degussa P25. FEG-SEM micrographies enabled the verification of the morphology as well as the interaction of the oxide particles with the metallic silver, which led us to propose a model for the increase in photoactivity observed in the photocatalyst powder under investigation.

Synchrotron X-ray diffraction characterization of healthy and fluorotic human dental enamel

With the introduction of fluoride as the main anticaries agent used in preventive dentistry, and perhaps an increase in fluoride in our food chain, dental fluorosis has become an increasing world-wide problem. Visible signs of fluorosis begin to become obvious on the enamel surface as opacities, implying some porosity in the tissue. The mechanisms that conduct the formation of fluorotic enamel are unknown, but should involve modifications in the basic physical-chemistry reactions of demineralization and remineralisation of the enamel of the teeth, which is the same reaction of formation of the enamel's hydroxyapatite (HAp) in the maturation phase. The increase of the amount of fluoride inside of the apatite will result in gradual increase of the lattice parameters. The aim of this work is to characterize the healthy and fluorotic enamel in human tooth using Synchrotron X-ray diffraction. All the scattering profile measurements were carried out at the X-ray diffraction beamline (XRD1) at the Brazilian Synchrotron Light Laboratory-LNLS, Campinas, Brazil. X-ray diffraction experiments were performed both in powder samples and polished surfaces. The powder samples were analyzed to obtain the characterization of a typical healthy enamel pattern. The polished surfaces were analyzed in specific areas that have been identified as fluorotic ones. X-ray diffraction data were obtained for all samples and these data were compared with the control samples and also with the literature data. (c) 2012 Elsevier Ltd. All rights reserved.

Photoluminescence of core-shell nanoparticles made from yttrium stabilized zirconia powder grain coated with alumina

A YSZ@Al2O3 nanocomposite was obtained by Al2O3 coating on the surface of yttrium stabilized zirconia via a polymeric precursor method. The resulting core–shell structures were characterized by X-ray diffraction, scanning electron microscopy, transmission electronic microscopy and PL spectra. The TEM micrographs clearly show a homogeneous Al2O3 shell around the ZrO2 core. The observed PL is related to surface–interface defects. Such novel technologies can, in principle, explore materials which are not available in the bulk single crystal form but their figure-of-merit is dramatically dependent on the surface–interface defect states.

Technique to measure heats of reaction of Ti-B, Al-Ti-B, and Al-Ti-B4C powder blends

In this research, a modification to initiation aid ignition in bomb calorimetry that involves systemically blending levels of boron and potassium nitrate initiation aids with a bulk structural energetic elemental power blend is developed. A regression is used to estimate the nominal heat of reaction for the primary reaction. The technique is first applied to the synthesis of TiB2 as a validation study to see if close proximity to literature values can be achieved. The technique is then applied to two systems of interest, Al-Ti-B, and Al-Ti-B4C. In all three investigations, x-ray diffraction is used to characterize the product phases of the reactions to determine the extent and identity of the product phases and any by-products that may have formed as a result of adding the initiation aid. The experimental data indicates the technique approximates the heat of reaction value for the synthesis of TiB2 from Ti-B powder blends and the formation of TiB2 is supported by volume fraction analysis by x-ray diffraction. Application to the Al-Ti-B and Al-Ti-B4C blends show some correlation with variation of the initiation aid, with x-ray diffraction showing the formation of equilibrium products. However, these blends require further investigation to resolve more complex interactions and rule out extraneous variables.

Mineralogical assemblage in sediment core GeoB12309-5 and in area samples from the Makran subduction zone

In order to study late Holocene changes in sediment supply into the northern Arabian Sea, a 5.3 m long gravity core was investigated by high-resolution geochemical and mineralogical techniques. The sediment core was recovered at a water depth of 956 m from the continental slope off Pakistan and covers a time span of 5 kyr. During the late Holocene source areas delivering material to the sampling site did, however, not change and were active throughout the year.