Preparation and characterization of spherical yttrium iron garnet via coprecipitation

The purpose of this work is to obtain spherical particles yttrium iron garnet (YIG) by coprecipitation technique. The spherical particles were obtained from either nitrate or chloride salt solutions by controlling the precipitation medium. Different agents of dispersion such as PVP and ammonium iron sulfate were used to optimize the shape and size of YIG. Samples were characterized by X-ray diffraction, scanning electron microscopy and vibrating sample magnetometry. The results show that the samples phase transition takes place at 850°C (orthorhombic phase) and at 1200°C (cubic phase). Spherical shape particles, with diameter of around 0.5 μm, present magnetization values close to the bulk value (26 emu g -1). © 2001 Elsevier Science B.V. All rights reserved.

Acid and fermented silage characterization and determination of apparent digestibility coefficient of crude protein for pacu Piaractus mesopotamicus

Three types of raw materials including commercial waste from saltwater (SW), freshwater fish (FW) and tilapia fillet residue (FR) were used to produce fish silage by either acid digestion (2% formic acid and 2% sulfuric acid) or anaerobic fermentation (5% of Lactobacillus plantarum and 15% sugar cane molasses). Six test diets were used in digestibility trials prepared with 70% reference diet and 30% of each experimental silage. These diets were fed to juvenile pacu Piaractus mesopotamicus (146 g average weight) in triplicate. Fish were kept in 500-L tanks and feces collected by manual extrusion. It was observed for both processes that SW waste always had the highest moisture content and lowest fat and ash. Highest crude protein levels were found in silages from commercial fish waste (SW and FW) made from whole fish unfit for human consumption. However, apparent digestibility coefficients did not vary among diets (P > 0.05). Although values did not differ statistically, fermented silage consistently displayed higher digestibility coefficients compared to acid silage. The silages exhibited relatively high protein digestibility (72.5-80.0%), thus suggesting the feasibility of using fish industry by-products in aquaculture feeds.

Rare earth doped HfO2 nanoparticles embedded in SiO2-HfO2 planar waveguides. Preparation, optical, structural and spectroscopic characterization

In this work we present results on the preparation of planar waveguides based on HfO2 and HfO2-SiO2. Stable sols containing europium and erbium doped HfO2 nanoparticles have been prepared and characterized. The nanosized sol was either deposited (spin-coating) on quartz substrates or embedded in (3-glycidoxipropil)trimethoxisilane (GPTS) used as a hybrid host for posterior deposition. The refractive index dispersion and luminescence characteristics were determined for the resulting HfO2 films. The optical parameters of the waveguides such as refractive index, thickness and propagation losses were measured for the hybrid composite. The planar waveguides present thickness of a few micra and support well confined propagating modes.

Comparative study using small-angle x-ray scattering and nitrogen adsorption in the characterization of silica xerogels and aerogels

A comparative study using small-angle x-ray scattering (SAXS) and nitrogen adsorption has been carried out in the structural characterization of silica xerogels and aerogels, obtained from tetraethoxysilane sonohydrolysis. The specific surface and the mean pore size as measured by both the techniques were found to be in notable agreement in all cases for aerogels and xerogels. According to the SAXS data, aerogels at 500 °C exhibit a mass fractal structure with fractal dimension D∼2.4 in the range between the correlation length ξ∼5.3 nm and a∼0.75 nm. An experimental method to probe the mass fractal structure of aerogels from exclusively nitrogen adsorption isotherms has been presented. For aerogels at 500 °C, we have found D∼2.4 in the range between the pore width 2rξ∼33 nm and 2ra∼4.5 nm, which is in notable agreement with the SAXS results (D ∼2.4, ξ∼5.3 nm, a∼0.75 nm) if we assign the pore width 2r probed by the Kelvin equation in the adsorption method to the Bragg distance 2π/q associated to the correlation length 1/q probed by SAXS.

Synthesis and characterization of poly-o-toluidine: Kinetic and structural aspects

Poly(o-methylaniline) (poly-o-toluidine, PTOL) was synthesized by chemical oxidation of o-toluidine with ammonium peroxydisulfate in an aqueous 1.0 mol L -1 HCl solution. The progress of polymerization was followed by measuring the open-circuit potential (OCP) of a Pt electrode immersed in the reaction medium with the polymerization time. The chemical synthesis of PTOL was carried out at different monomer:oxidant (M:O) molar ratios (4:1, 2:1, 1.5:1, 1:1, and 0.66:1), and the products obtained were characterized by infrared spectroscopy, gel permeation chromatography, and X-ray diffraction. The molecular weight and percentage of crystallinity of PTOL are higher for samples synthesized in an excess of the monomer, i.e. at higher M:O ratios. However, the yield of PTOL prepared at higher M:O ratios is considerably low, in particular at a 4:1 M:O ratio, which is the M:O ratio most commonly used in the literature to synthesize polyaniline and its derivatives.

Characterization of cure of carbon/epoxy prepreg used in aerospace field

Carbon/epoxy 8552 prepreg is a thermoplastic toughened high-performance epoxy being used in the manufacture of advanced army material. Understanding the cure behavior of a thermosetting system is essential in the development and optimization of composite fabrication processes. The cure kinetics and rheological behavior were evaluated using a differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and a rheometer. Values of the kinetic parameters were obtained from dynamic DSC scans using an nth order reaction model. Rheological measurements as a function of temperature and time were made for the prepreg system. The manufacturer's recommended cure cycle was evaluated and considered adequate to consolidated the studied system.

New insights for materials science characterisation using different complementary techniques combined with x-ray absorption spectroscopy

The combination of x-ray absorption spectroscopy (XAS) with UV-Vis and Raman spectroscopies or with Differential Scanning Calorimetry (DSC) has been recently carried out on the D44 beamline of DCI-LURE. The different set-ups used to perform such combinations are described and examples of combined investigations belonging to different field of materials science (coordination chemistry, sol-gel and catalysis) are presented. © Physica Scripta 2005.

Synthesis and characterization of 0.9PMN-0.1PT powders by the use of a modified columbite precursor

The complex perovskite compound 0.9PbMg 1/3Nb 2/3O 3-0.1PbTiO 3 is one of the most promising relaxor ceramic because the addition of lead titanate increases T m, by about 5°C/mol% from intrinsic T m value for pure PMN (near -7 to -15°C). A Ti-modified columbite precursor was used to prepare PMN-PT powders containing single perovskite phase. This variation on columbite route includes Ti insertion in MgNb 2O 6 orthorhombic structure so that individual PT synthesis becomes unnecessary. Furthermore, effects of Li additive on columbite and PMN-PT structures were studied by XRD to verify the phase formation at each processing step. XRD data were also used for the structural refinement by Rietveld method. The additive acts increasing columbite powders crystallinity, and the amount of perovskite phase was insignificantly decreased by lithium addition. By SEM micrographs it was observed that Li presence in PMN-PT powders leads to the formation of rounded primary particles and for lmol% of additive, the grain size is not changed, different from when this concentration is enhanced to 2mol%.

Physical characterization of K-doped 0.9PMN-0.1PT synthesized by an association of the columbite route and the polymeric precursor method

The solid solution 0.9PbMg 1/3Nb 2/3O 3-0.1PbTiO 3 is one of the most widely investigated relaxor ceramic, because of its high dielectric constant and low sintering temperatures. PMN-PT powders containing single perovskite phase were prepared by using a Timodified columbite precursor obtained by the polymeric precursor method. Such precursor reacts directly with stoichiometric amount of PbO to obtain pyrochlore-free PMN-PT powders. The structural effects of K additive included in the columbite precursor and 0.9PMN-0.1PT powders were also studied. The phase formation at each processing step was verified by XRD analysis, being these results used for the structural refinement by the Rietveld method. It was verified the addition of K in the columbite precursor promotes a slight increasing in the powder crystallinity. There was not a decrease in the amount of perovskite phase PMN-PT for 1mol% of K, and the particle and grain size were reduced, making this additive a powerful tool for grain size control.

Structural control of photoluminescence of four poly(urethane-urea-co-1,3,5-triazine)s: Synthesis and characterization

A series of segmented poly(urethane-urea)s containing 1,3,5 triazine in the hard block and hexamethylene spacers in the soft block was prepared. The hard to soft segment ratio was varied systematically, to afford a series of polymers in which the chromophore concentration varied from 4.2% to 18.1%. Although triazine emission is located in the UV region, the films with higher content of the chromophore emitted a visible blue light (425 nm) when excited at the very red-edge of the absorption band. The photophysical properties of the materials were strongly dependent on the relative amount of triazine moieties along the main chain. Isolated moieties emit in copolymers with small amount of triazine groups, indicating that even though in solid state, these moieties tend to be apart. Two photophysical consequences were observed when the amount of triazine increases: there is some energy transfer process involving isolated moieties with consequent decrease of the lifetime and an additional red-edge emission attributed to aggregated lumophores. The mono-exponential decay observed for the isolated form is substituted by a bi-exponential decay of the aggregated species. The materials were not strong emitters, but since the N-containing triazine moieties are good electron transport groups, the polymers have potential application as electron transport enhancers in various applications. © 2006 Elsevier B.V. All rights reserved.

Anelastic characterization and superconducting properties of RuSr2GdCu2O8+δ

Since the discovery of the high Tc superconductors, many researches have been carried out on the different properties of these materials, especially on the transition temperature into the superconducting state. The rutheno-cuprates belong to a new class of composites, which were synthesized for the first time by Bauernfeind in 1995. Bernhard and collaborators discovered, in 1999, the coexistence of the ferromagnetism and the superconductivity in this phase, which is known as antagonistic phenomenon in the electromagnetism due to spin-charge interactions established in these states. However, the physical nature of the superconducting and magnetic states is still very obscure. The non-stoichiometric (interstitial) oxygen is considered as a possible cause for the non-uniformity of the sample properties. In this paper, results of mechanical spectroscopy in Ru-1212 samples are presented showing complex anelastic spectra, which were attributed to the mobility of the interstitial oxygen atoms in the Ru-1212 lattice.

Characterization of Zn0. 95Mn0.05O synthesized by polymeric precursors

This paper discusses the preparation and characterization of Zn 0.95Mn0.05O phase obtained by the polymeric precursor method for DMS applications. The as-obtained powders were calcined between 500 to 800°C and characterized by XRD, SEM and BET. The XRD analysis of the powder showed a crystalline material containing second phase. The crystallite sizes ranged from 20 to 51 nm. The micrographs showed that the powders consisted of soft and homogeneous agglomerations. The nitrogen adsorption/desorption curves of the Zn0.95Mn0.05O phases were type II curves, which is characteristic of mesoporous materials.

The use of slot filter in piezocone tests for site characterization of tropical soils

The use of piezocone tests with a slot filter filled with automotive grease for site characterization of tropical soils is assessed. Laboratory tests using the slot filter filled with automotive grease as well as the conventional porous piezo-element saturated with glycerin were carried out to evaluate the pore pressure (u 2) transducer response. CPTu tests using piezo-elements saturated with glycerin and the slot filter filled with grease were pushed side by side in different research sites in Brazil. Estimates of mechanical and hydraulic soil parameters were made based on pore pressure dissipation curves from using both techniques. Laboratory test results indicate that the pore pressure response using the slot filter with grease was delayed when compared to the piezo-element saturated with glycerin, since grease has a higher viscosity. For tropical soils, the records of u2 in piezocone tests using slot filter with grease presented larger peaks than with porous element saturated with glycerin. Records of u2 using the slot filter above the groundwater table suggest the increase of the degree of saturation in unsaturated zone, where porous filter can be desaturated by suction. The slot filter can be used to help the interpretation of the soil profile with deep groundwater level as well as to help detecting its position for some studied soils. The results shown high repeatability for all study sites. This technique is much easier to handle, especially for tropical soils, where the groundwater table is usually deep and pre-drilling is expensive and time consuming. © 2009 IOS Press.

Ultrasonic material characterization using diffraction-free PVDF receivers

This work describes the use of a large aperture PVDF receiver in the measurement of density of liquids and elastic constants of composite materials. The density measurement of several liquids is obtained with the accuracy of less than 0.2% using a conventional NDT emitter transducer and a 70-mm diameter, 52-μm P(VDF-TrFE) membrane with gold electrodes. The determination of the elastic constants of composite materials is based in the measurement of phase velocity. It is shown that the diffraction can lead to errors around 1% in the velocity measurement when using a pair of ultrasonic transducers (1MHz and 19mm diameter) operating in transmission-reception mode separated by a distance of 100 mm. This effect is negligible when using a pair of 10-MHz transducers. On the other hand, the dispersion at 10 MHz can result in errors of about 0.5%, measuring the velocity in composite materials. The use of an 80-mm diameter, 52-μm thick PVDF membrane receiver allows measuring the phase velocity without the diffraction effects.

Characterization and in vitro cytocompatibility of an acid-etched titanium surface

The aims of this study were to characterize the microstructure of a commercially pure titanium (cpTi) surface etched with HCl/H 2SO 4 (AE-cpTi) and to investigate its in vitro cytocompatibility compared to turned cpTi (T-cpTi). T-cpTi showed a grooved surface and AE-cpTi revealed a surface characterized by the presence of micropits. Surface parameters indicated that the AE-cpTi surface is more isotropic and present a greater area compared to T-cpTi. The oxide film thickness was similar between both surfaces; however, AE-cpTi presented more Ti and O and less C. Osteoblastic cell proliferation, alkaline phosphatase activity, and bone-like nodule formation were greater on T-cpTi than on AE-cpTi. These results show that acid etching treatment produced a surface with different topographical and chemical features compared to the turned one, and such surface modification affected negatively the in vitro cytocompatibility of cpTi as demonstrated by decreasing culture growth and expression of osteoblastic phenotype.