Low-temperature synthesis of nanosized bismuth ferrite by the soft chemical method

This paper describes research on a simple low-temperature synthesis route to prepare bismuth ferrite nanopowders by the polymeric precursor method using bismuth and iron nitrates. BiFeO 3 (BFO) nanopowders were characterized by means of X-ray diffraction analyses, (XRD), Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy (Raman), thermogravimnetric analyses (TG-DTA), ultra-violet/vis (UV/Vis) and field emission scanning electron microscopy (FE-SEM). XRD patterns confirmed that a pure perovskite BiFeO 3 structure with a rhombohedral distorted perovskite structure was obtained by heating at 850 °C for 4 hours. Typical FT-IR spectra for BFO powders revealed the formation of a perovskite structure at high temperatures due to a metal-oxygen bond while Raman modes indicated oxygen octahedral tilts induced by structural distortion. A homogeneous size distribution of BFO powders obtained at 850 °C for 4 hours was verified by FE-SEM analyses. © 2012 Elsevier Ltd and Techna Group S.r.l.

Structural and dielectric properties of polyvinyl alcohol/barium zirconium titanate polymer-ceramic composite

The polyvinyl alcohol (PVA)/barium zirconium titanate Ba[Zr0.1Ti0.9]O3 (BZT) polymer-ceramic composites with different volume percentage are obtained from solution mixing and hot-pressing method. Their structural and electrical properties are characterized by X-ray diffraction (XRD), Rietveld refinement, cluster modeling, scanning electron microscope and dielectric study. XRD patterns of PVA/BZT polymer-ceramics composite (with 50% volume fractions) indicate no obvious differences than the XRD patterns of pure BZT which shows that the crystal structure is still stable in the composite. The scanning electron micrograph indicates that the BZT ceramic is dispersed homogeneously in the polymer matrix without agglomeration. The dielectric permittivity (ε r) and the dielectric loss (tan δ) of the composites increase with the increase of the volume fraction of BZT ceramic. Theoretical models are employed to rationalize the dielectric behavior of the polymer composites. The dielectric properties of the composites display good stability within a wide range of temperature and frequency. The excellent dielectric properties of these polymer-ceramic composites indicate that the BZT/PVA composites can be a candidate for embedded capacitors. © 2013 Elsevier B.V.

Effect of yttrium doping in barium zirconium titanate ceramics: A structural, impedance, modulus spectroscopy study

In the current article, we studied the effect of yttrium [Y3+] ions' substitution on the structure and electric behavior of barium zirconate titanate (BZT) ceramics with a general formula [Ba1-x Y 2x/3](Zr0.25Ti0.75)O3 (BYZT) with [x = 0, 0.025, 0.05] which were prepared by the solid-state reaction method. X-ray diffraction patterns indicate that these ceramics have a single phase with a perovskite-type cubic structure. Rietveld refinement data confirmed [BaO 12], [ZrO6], [TiO6], [YO6] clusters in the cubic lattice. The Y3+ ions' effects on the electric conductivity behavior of BZT ceramics as a function of temperature and frequency are described, which are based on impedance spectroscopy analyses. The complex impedance plots display a double semicircle which highlights the influences of grain and grain boundary on the ceramics. Impedance analyses showed that the resistance decreased with the increasing temperature and resulted in a negative temperature coefficient of the resistance property in all compositions. Modulus plots represent a non-Debye-type dielectric relaxation which is related to the grain and grain boundary as well as temperature-dependent electric relaxation phenomenon and an enhancement in the mobility barrier by Y3+ ions. Moreover, the electric conductivity increases with the replacement of Ba 2+ by Y3+ ions may be due to the rise in oxygen vacancies. © 2013 The Minerals, Metals & Materials Society and ASM International.

Determination and fractionation of barium in Brazil nuts

Diversas estratégias para preparo de amostra, determinação e fracionamento, tais como espectrometria de absorção atômica com atomização eletrotérmica em forno de grafite (GF AAS) e espectrometria de emissão óptica com plasma acoplado indutivamente com configuração axial (ICP OES), foram empregadas para o fracionamento de bário em Castanha-do-Pará. Esse alimento é amplamente apreciado tanto pelo valor nutricional, quanto pelo sabor agradável. A análise química de Castanha-do-Pará não é trivial devido à matriz complexa. O fracionamento de bário em Castanha-do-Pará foi estudado devido à toxicidade desse elemento e a correlação entre a forma química e a absorção. Os teores totais de bário nas amostras de Castanha-do-Pará variaram entre 860 e 2084 mg kg^-1. Extrações sequenciais foram feitas com base na solubilidade em diferentes meios e composição química envolvendo lipídios, proteínas e compostos de baixa massa molecular (LMW). Teores mais elevados de bário foram determinados nas frações LMW e insolúvel em água que variaram entre 778-1606 e 551-1520 mg kg^-1, respectivamente. Esses resultados indicaram a indisponibilidade de bário presente nesse alimento ao organismo humano. Baseando-se nos teores de bário e enxofre nas diferentes frações e em cálculos estequiométricos para as possíveis reações envolvidas pode-se inferir que bário se encontra principalmente na forma de BaSO₄. Experimentos termogravimétricos também confirmaram essa suposição.

Evidence of magnetoelectric coupling on calcium doped bismuth ferrite thin films grown by chemical solution deposition

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Second Phase Precipitation in Ultrafine-grained Ferrite Steel

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

Rapid calcination of ferrite Ni0.75Zn0.25Fe2O4 by microwave energy

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Structural and functional characterization of barium zirconium titanate/epoxy composites

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

A novel synthesis of perovskite bismuth ferrite nanoparticles

Abstract. Biochar is the solid by-product of biomass pyrolysis. It is a promising soil conditioner and can be a material with high aggregate economic value, since its performance can improve plant’s nutrient utilization and reduce the usage of conventional fertilizers. Biochar can be used in the formulation of new types of fertilizers as polymeric microbeads. These microbeads can be enriched with biochar and nutrients in its matrix to form fertilizers of slow release of nutrients. Thus, as a promising agricultural material, it is important to assess the environmental hazards caused by the implementation of these microbeads. In this context, seeds were sown in a soil-less Petri dish with microbeads produced with biochar from sugarcane enriched with or without phosphate. The seeds germination and its vitality were evaluated by the first germination count (FGC) and the germination speed index (GSI). The short-term effects showed that the microbeads, in general, assessed by the means of FGC, GSI and mass gain showed the best performance, suggesting that the environment created by these materials provided the best chemical and physical interaction with the embryonic axes.

Effects of the addition of ions barium on the structural and electrical properties of PZT ceramic

Lead zirconate titanate, with Zr/Ti ratio of 53/47 was prepared by the polymeric precursor method. It was investigated the barium (II) modification at 0.0, 0.2, 0.4 and 0.6 mol% in substitution to the lead (II) cation in A site of perovskite structure. The powder samples were characterized by XRD and the diffraction patterns were used to Rietveld refinement. The percentages of tetragonal and rhombohedral phases and a systematic study of the effect of barium (II) on the morphology and the dielectric properties of PZT were carried out. The results showed that the tetragonal phase is favored and the ceramic density is improved with the barium (II) insertion. The Curie temperature (Tc) is increased besides the slight reduction of dielectric constant (Kc).

Determination of labile barium in petroleum-produced formation water using paper-based DGT samplers

A polyacrylamide hydrogel containing the Chelex-100 resin has traditionally been used as the binding agent for the diffusion gradients in thin films (DGT) technique. The Chelex-100 resin, although important for the determination of various transition metals, is unsatisfactory for the determination of alkaline earth metals, particularly Ba. In this paper, a cellulose membrane, treated with phosphate (P81 membrane), was evaluated as a binding agent for DGT devices for the determination of Ba in produced formation water (PEW) samples. In addition, diffusive layers of filter paper (cellulose) were tested to diffuse Ba through the DGT devices. Experiments to evaluate the key variables of the technique (pH, deployment time, and ionic strength/salinity) were performed. The Ba sampled by these DGT devices was measured using inductively coupled plasma optical emission spectrometry. Aiming to generate information (related to bioavailability of Ba) on the reuse of PEW for irrigation, the determination of Ba in onshore and offshore samples was performed. The new approach was effective for determination of Ba in onshore samples. To determine Ba in offshore samples, it was necessary to use an alternative calibration procedure due to the high NaCl concentration in these samples. (C) 2012 Elsevier B.V. All rights reserved.

Predicting Delta Ferrite Content in Stainless Steel Castings

The distribution of delta ferrite fraction was measured with the magnetic method in specimens of different stainless steel compositions cast by the investment casting (lost wax) process. Ferrite fraction measurements published in the literature for stainless steel cast samples were added to the present work data, enabling an extensive analysis about practical methods to calculate delta ferrite fractions in stainless steel castings. Nineteen different versions of practical methods were formed using Schaeffler, DeLong, and Siewert diagrams and the nickel and chromium equivalent indexes suggested by several authors. These methods were evaluated by a detailed statistical analysis, showing that the Siewert diagram, including its equivalent indexes and iso-ferrite lines, gives the lowest relative errors between calculated and measured delta ferrite fractions. Although originally created for stainless steel welds, this diagram gives relative errors lower than those for the current ASTM standard method (800/A 800M-01), developed to predict ferrite fractions in stainless steel castings. Practical methods originated from a combination of different chromium/nickel equivalent indexes and the iso-ferrite lines from Schaeffler diagram give the lowest relative errors when compared with combinations using other iso-ferrite line diagrams. For the samples cast in the present work, an increase in cooling rate from 0.78 to 2.7 K/s caused a decrease in the delta ferrite fraction, but a statistical hypothesis test revealed that this effect is significant in only 50% of the samples that have ferrite in their microstructures.

Subdivision of Hysteresis Loss in Mn-Zn Ferrite Toroidal Cores

The hysteresis loss subdivision method proved to be a strong tool to help in the analysis of different energy dissipation mechanisms along the quasi-static hysteresis loop measured on electrical steels. This paper used the samemethod to discuss the mechanisms involving the energy loss dissipation in Mn-Zn ferrite toroidal cores. The samples, sintered under controlled atmosphere in industrial conditions, were measured under triangular waveform excitation at very low frequency (5 mHz) and peak flux densities varying from 0.05 T to 0.45 T. The results show a different behavior between the low inductions hysteresis loss (WLI) and the high induction hysteresis loss (WHI) which proves the existence of different energy dissipation mechanisms affecting these loss components.

Field dependent transition to the non-linear regime in magnetic hyperthermia experiments: Comparison between maghemite, copper, zinc, nickel and cobalt ferrite nanoparticles of similar sizes

Further advances in magnetic hyperthermia might be limited by biological constraints, such as using sufficiently low frequencies and low field amplitudes to inhibit harmful eddy currents inside the patient's body. These incite the need to optimize the heating efficiency of the nanoparticles, referred to as the specific absorption rate (SAR). Among the several properties currently under research, one of particular importance is the transition from the linear to the non-linear regime that takes place as the field amplitude is increased, an aspect where the magnetic anisotropy is expected to play a fundamental role. In this paper we investigate the heating properties of cobalt ferrite and maghemite nanoparticles under the influence of a 500 kHz sinusoidal magnetic field with varying amplitude, up to 134 Oe. The particles were characterized by TEM, XRD, FMR and VSM, from which most relevant morphological, structural and magnetic properties were inferred. Both materials have similar size distributions and saturation magnetization, but strikingly different magnetic anisotropies. From magnetic hyperthermia experiments we found that, while at low fields maghemite is the best nanomaterial for hyperthermia applications, above a critical field, close to the transition from the linear to the non-linear regime, cobalt ferrite becomes more efficient. The results were also analyzed with respect to the energy conversion efficiency and compared with dynamic hysteresis simulations. Additional analysis with nickel, zinc and copper-ferrite nanoparticles of similar sizes confirmed the importance of the magnetic anisotropy and the damping factor. Further, the analysis of the characterization parameters suggested core-shell nanostructures, probably due to a surface passivation process during the nanoparticle synthesis. Finally, we discussed the effect of particle-particle interactions and its consequences, in particular regarding discrepancies between estimated parameters and expected theoretical predictions. Copyright 2012 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. [http://dx.doi. org/10.1063/1.4739533]

Preparation and Structural Characterization of Vulcanized Natural Rubber Nanocomposites Containing Nickel-Zinc Ferrite Nanopowders

Single-phase polycrystalline mixed nickel-zinc ferrites belonging to Ni0.5Zn0.5Fe2O4 were prepared on a nanometric scale (mean crystallite size equal to 14.7 nm) by chemical synthesis named the modified poliol method. Ferrite nanopowder was then incorporated into a natural rubber matrix producing nanocomposites. The samples were investigated by means of infrared spectroscopy, X-ray diffraction, scanning electron microscopy and magnetic measurements. The obtained results suggest that the base concentration of nickel-zinc ferrite nanoparticles inside the polymer matrix volume greatly influences the magnetic properties of nanoconnposites. A small quantity of nanoparticles, less than 10 phr, in the nanocomposite is sufficient to produce a small alteration in the semi-crystallinity of nanocomposites observed by X-ray diffraction analysis and it produces a flexible magnetic composite material with a saturation magnetization, a coercivity field and an initial magnetic permeability equal to 3.08 emu/g, 99.22 Oe and 9.42 X 10(-5) respectively.