Preparo de óxido de nióbio suportado em alumina por deposição química em fase vapor: caracterização por espectroscopia vibracional e termogravimetria

Alumina supported niobium oxide was prepared by chemical vapor deposition (CVD) of NbCl5. The alumina was calcined and pretreated at differents temperatures in order to vary the density of OH groups on the surface which was determined by thermogravimetric analysis. A good correlation was found between the amount of anchored niobium and the total number of anionic sites (oxide and hydroxyl groups) on the surface of the alumina. The infrared spectra on the OH stretching region indicate that OH groups coordinated to at least one tetrahedral aluminum were more reactive towards NbCl5.

Comparação de dois tipos de amostragem de chuva: deposição total e deposição apenas úmida em àrea costeira tropical

In a tropical coastal area. During 6 months the composition of rain samples collected simultaneously over 24h with an open collector and with an automatic opened collector (KFA - J¸lich Type) at 500m of the Atlantic coastline of Salvador were compared. All average concentrations were higher for the "total" samples than for the "wet only" samples, except for hydrogen ions, nitrate and ammonium.

Influência da adição de defloculante, ligante e partículas de alumina no comportamento reológico de suspensões a base de frita e caulim

Enamel suspensions were characterized according to their rheological behavior. The suspensions presented a pseudoplastic behavior, yield stress and thixotropy, with or without the presence of deffloculant. Added carboxymethylcellulose increases the apparent viscosity of enamel suspensions and interacts complexly with the deffloculant, here sodium silicate. Addition of crystalline particles of two types of alumina, used to improve the wear resistance of ceramic glazes, also change strongly the rheological behavior of the suspensions. Added high specific area, irregular alumina particles produce a higher increase of the apparent viscosity of enamel suspensions compared to rounded ones.

Partículas nanométricas de ferritas de ítrio

Nanoparticles of yttrium iron garnet (YIG) were obtained by coprecipitation. The particles were prepared by hydrolysis in acid medium with addition of ammonia or urea, for homogeneous nucleation, at 90ºC. Different compositions and spherical morphologies were achieved by changing reactants concentrations and precipitation agent. X-ray diffractometry, transmission electron microscopy, differential thermal analysis and electrophoretic mobility were carried out on these particles to investigate the obtained phase, phase transition temperature, morphology, particle size and zeta potential, respectively.

Estudo das partículas totais em suspensão e metais associados em áreas urbanas

This work aims at the study of the air quality determination regarding the total suspended particles (TSP) and the associated metals in the counties of Charqueadas and Sapucaia do Sul at the state of Rio Grande do Sul. The TSP samples were collected using high volume samplers and the analysis of the metallic elements was accomplished through ICP-AES. The results revealed that the TSP concentrations, found in the two studied regions, have exceded the current air quality patterns established by the Brazilian Legislation. They also revealed high levels of several of the elements being attributed to the presence of anthropogenic sources. The correlation between meteorological data (speed and wind direction) and TSP concentrations were significant and revealed strong influence in particle dispersion.

Estudos da deposição em subtensão de cádmio sobre ouro policristalino na presença de diferentes ânions co-adsorvidos

Cadmium UPD on Au was studied by voltammetric and microgravimetric measurements. In the oxide formation/reduction potential region, a mass increasing/decreasing of 32 ng cm-2 was associated to incorporation/elimination of one oxygen per active site. The modifications promoted in the voltammetric and mass profiles by 10-5 M Cd(ClO4)2 are restricted to potentials more negative than 0.4 V. After a 120 s potential delay at 0.05 V, the positive sweep reveals an anodic peak with charge of 40 muC cm-2 and mass decrease of 22 ng cm-2, associated to Cd ads dissolution. Sulphate or chloride was added to the solution without significant influence, due to the low coverage with Cd or anions.

Deposição eletrolítica catódica e anódica simultâneas para minimizar interferências de cobre e chumbo na determinação espectrofotométrica de cádmio em água e alimentos via reação com Verde de Malaquita e iodeto

Simultaneous electrolytic deposition is proposed for minimization of Cu2+ and Pb2+ interferences on automated determination of Cd2+ by the Malachite Green-iodide reaction. During electrolysis of sample in a cell with two Pt electrodes and a medium adjusted to 5% (v/v) HNO3 + 0.1% (v/v) H2SO4 + 0.5 mol L-1 NaCl, Cu2+ is deposited as Cu on the cathode, Pb2+ is deposited as PbO2 on the anode while Cd2+ is kept in solution. With 60 s electrolysis time and 0.25 A current, Pb2+ and Cu2+ levels up to 50 and 250 mg L-1 respectively, can be tolerated without interference. With on-line extraction of Cd2+ in anionic resin minicolumn, calibration graph in the 5.00 - 50.0 µg Cd L-1 range is obtained, corresponding to twenty measurements per hour, 0.7 mg Malachite Green and 500 mg KI and 5 mL sample consumed per determination. Results of the determination of Cd in certified reference materials, vegetables and tap water were in agreement with certified values and with those obtained by GFAAS at 95% confidence level. The detection limit is 0.23 µg Cd L-1 and the RSD for typical samples containing 13.0 µg Cd L-1 was 3.85 % (n= 12).

Análises seqüenciais de agrupamentos aplicadas ao estudo de partículas atmosféricas

The present paper has as objective to apply a sequential Cluster Analysis to the atmospheric particles: Hierarchical Cluster Analysis followed by Nonhierarchical Cluster Analysis. The hierarchical cluster analysis results were used as start point for the nonhierarchical cluster analysis as an agglomerative technique. These particles were taken from two areas of the metropolitan region of Porto Alegre, Charqueadas and Sapucaia do Sul., from may /97 to may/98, using a High Volume Sampler (Hi-Vol). Around 10,000 particles were analysed by Scanning Electron Microscope with Energy-Dispersive X-Ray microanalysis (SEM-EDS). The Hierarchical Cluster Analysis allowed the identification of five groups of particles, whose amounts were differentiated according to the summer and the winter campaigns. The abundance of each type of particles inside each group according to the different sections was verified by the Nonhierarchical Cluster Analysis, resulting in information about the emissions sources. The groups of particles of Si/Al and Si and of Fe/Zn and Fe for Charqueadas were more significant in section 2 and 3 (NW and W wind directions) and in section 1 (SE wind direction), evidencing the influence of the coal power plant and steel industry, respectively located in these quadrants. In Sapucaia do Sul the data were more heterogeneous, causing a certain difficulty to identify the source as anthropogenic. Nevertheless the group of particles containing Fe was found in sectors of NW/W wind directions which shows the influence of the steel plant.

Um procedimento simples e barato para a construção de um equipamento "dip-coating" para deposição de filmes em laboratório

In this work we show how to build a piece of equipment for depositing thin films by the dip-coating process, using inexpensive components easily found on the market. This equipment allows us to control the dipping and pulling velocity at which the substrate is put in the film precursor solution, two very important parameters for obtain thin films. This article discusses the construction of the mechanical and electric parts of the equipment, a simple method to interface it to a computer and the development of the software to control the dip-coating parameters.

Caracterización morfológica, textural y composicional de las partículas de oro reveladas en placeres marinos de las playas Mejías y Jiguaní (NE de Cuba Oriental)

En este trabajo se describen los principales rasgos morfológicos, texturales y composicionales de las partículas de oro presentes en los placeres marinos costeros de las playas Mejías y Jiguaní, Cuba. Las partículas de oro estudiadas en ambos depósitos, son muy finas, mostrando formas tabulares predominantes; en ocasiones aparecen muy aplastadas, formando especies de laminillas o hojuelas, observándose, a través de las imágenes de electrones etrodispersados,partículas con texturas internas muy complejas , así como cariado de los granos. Las partículas están compuestas por subgranos de composición diferente,correspondientes a aleaciones naturales de Electrum, oro nativo y oro mercurial en ambos placeres y aleaciones de Au-Cu (tetraauricuprido) en el Placer Jiguaní. Estos subgranos frecuentemente se encuentran alterados en sus bordes. Esta alteración consiste predominantemente en un enriquecimiento en oro con relación a la plata.

Estudo do efeito do tratamento superficial por moagem sobre as propriedades das partículas de uma liga de hidreto metálico

This work reports results of studies on the electrochemical and structural properties of a Ti/Zr-based metal hydride alloy covered by Ni and LaNi4,7Sn0,3 powder additives by ball milling. The effect of this treatment is investigated for the activation time, hydrogen storage capacity and equilibrium pressure, cycling stability and the hydration/dehydration kinetics. Charge and discharge cycles show a significant decrease of the activation time due to an increase of the active area caused by the milling treatment, independent of the additive. However, other results have evidenced little effect of the milling surface treatment on the charge storage capacity, hydrogen equilibrium pressure, and hydration/dehydration kinetics, for both the Ni and LaNi4,7Sn0,3 covered materials.

Biomateriais: deposição de hidroxiapatita sobre superfície de Ti-cp modificada por aspersão térmica

The osseointegrated titanium implants are reliable and safe alternatives to treatments for long periods of time. For surface modification, thermal aspersion of TiO2 was used. The samples with and without TiO2 were treated with NaOH and SBF in order to obtain a layer of HA. Characterization was done by SEM and FTIR. The images of HA obtained by SEM show a uniform morphology and a porous structure with spherical particles. The IR spectra show that the surface of Ticp/ TiO2 is more favorable for the HA deposit, as can be seen by the increase of the crystalline structure and the very intense and defined bands of the OH group of HA that is verified about 3571 and 630 cm-1. Thus the Ticp/ TiO2 surface presents a satisfactory nucleation of HA when compared to Ticp.

Hidrogenação eletrocatalítica de substratos orgânicos utilizando eletrodos modificados poliméricos contendo partículas de Ni/Pd e Ni/Pt

Novel modified electrodes bearing dispersed Pd and Pt particles have been prepared from poly (allyl ether of the p-benzenesulfonic acid) films with incorporated nickel particles making use of galvanic displacement reactions. The SEM analysis of the new modified electrodes revealed efficient deposition of Pd but weak up-take of Pt. Electrocatalytic hydrogenation of several classes of organic substrates were carried out using the MEs Ni, Ni/Pd and Ni/Pt. The Ni/Pd ME showed to be the best of them for the hydrogenation of double, triple and carbonyl bonds. The complete hydrogenation of the aromatic rings for the well-adsorbed substrates acetophenone and benzophenone is noteworthy.

Sistema RTP: uma técnica poderosa para o monitoramento da formação de nanotubos de carbono durante o processo por deposição de vapor químico

In this work, a TPR (Temperature Programmed Reduction) system is used as a powerful tool to monitor carbon nanotubes production during CVD (Chemical Vapour Deposition), The experiments were carried out using catalyst precursors based on Fe-Mo supported on Al2O3 and methane as carbon source. As methane reacts on the Fe metal surface, carbon is deposited and H2 is produced. TPR is very sensitive to the presence of H2 and affords information on the temperature where catalyst is active to form different forms of carbon, the reaction kinetics, the catalyst deactivation and carbon yields.

Produção de substratos sers eficientes através da deposição de ouro sobre um molde de microesferas de poliestireno

This work reports on the SERS activity of a nanostructured substrate that was obtained by electrodepositing gold over a template consisting of polystyrene microspheres. This substrate displayed superior SERS performance for the detection of 4-merctaptopyridine as compared to a conventional roughened Au electrode. In order to investigate the substrate capability for the detection at low concentration limits, a series of Rhodamine 6G (1 nM) spectra were registered. Our spectral dynamics data is in agreement with single-molecule behavior, showing that the control over the substrate morphology is crucial to enable the production of highly reproducible and sensitive SERS substrates.