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.

Structural and functional characterization of barium zirconium titanate/epoxy composites

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

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).

Rectal atresia in a newborn donkey

P>A case of a type I rectal atresia (also known as membranous rectal atresia) in a newborn donkey is reported. Clinical examination, survey radiographs and barium enema radiographs suggested rectal atresia. An exploratory laparotomy was performed; however, surgical correction of the defect was not possible due to the narrow pelvic cavity. Euthanasia was performed. At necropsy, it was possible to observe a fibrous cord connecting the small colon to a residual rectal ampulla, which opened to a normal anus. The radiographic and anatomical characteristics enabled the classification of the defect as type I rectal atresia, which is a rare congenital anomaly that is difficult to correct through surgery. This report contributes to the study of rectal atresia in newborn equids, alerts for the occurrence in donkeys and is, to our knowledge, the first to be reported in this species in Brazil.

Bário, cádmio, cromo e chumbo em plantas de milho e em latossolo após onze aplicações anuais de lodo de esgoto

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

Electronic structure and optical properties of BaMoO4 powders

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Influence of Tungsten Dopant on Sintering and Curie Temperatures of Ba(Zr0.10Ti0.90)O-3 Ceramics

Ba(Zr0.10Ti0.90)O3 (BZT10) and W+ 6 substituted BZT ceramics (BZT10:W) were prepared by mixed oxide method. The effect of W+ 6 addition in the BZT was evaluated by X-ray diffraction (XRD), dilatometer analysis, microstructural and dielectrical properties. When tungsten is introduced in the BZT lattice, a decrease in the grain size and shift on Curie temperature to lower value besides broadening of dielectric permittivity is evident. This is due repulsion between tungsten and their nearest neighbors leading to a structure which is tetragonal distorted. The sintering temperature is reduced when tungsten is introduced in the BZT lattice.

Mesoscopic structure evidenced by AC dielectric nonlinearities in Sr(0.75)Ba(0.25)Nb(2)O(6) relaxor ferroelectric thin films

The AC electric field and temperature dependences of the dielectric permittivity for strontium barium niobate (Sr(0.75)Ba(0.25)Nb(2)O(6)) relaxor ferroelectric thin films have been investigated. The results indicate the existence of a true mesoscopic structure evidenced by the nonlinear dielectric response of these films, which is similar to those observed for bulk relaxor ferroelectrics. A tendency for a temperature dependent crossover from a linear to a quadratic behaviour of the dielectric nonlinearity was observed, indicating an evolution from paraelectric to glass-like behaviour on cooling the samples towards the freezing temperature transition.

Rhodamine 6G encapsuled mesoporous silica channels

We report the effect of solvent on the rhodamine 6G encapsuled into channels of mesoporous silica, synthesized by two-step process that gives intermediary stable hybrid micelles. Mesoporous materials have been obtained by the method that involves surfactant micelles (mainly cationic) and inorganic precursor of the structure to be obtained. MSU-X type mesoporous silica has been synthesized with polyethylene oxide surfactant as the directing-structure agent and tetraethyl orthosilicate Si(OEt)(4) as the silica source. The influence of the solvent on the encapsulation of rhodamine dye was systematically explored, specially its influence on the luminescence properties. Rhodamine 6G encapsuled into mesoporous silica channel was characterized by UV-Vis and luminescence spectroscopies, scanning electron microscopy, small angle x ray scattering and N(2) sorption-desorption. The pore size and the solvent effects into luminescence dye encapsuled into mesoporous silica channels are observed in the visible absorption and emission spectra of rhodamine 6G. The intense photo luminescence band of rhodamine 6G dye is in 500 to 600 nm region. The observed shift of the absorption and emission bands can be assigned to the effect of the solvents dielectric constant and pore size of mesoporous silica.

Investigation of nonlinear dielectric properties in Sr0.75Ba0.25Nb2O6 relaxor ferroelectric thin films

The ac and dc driving fields dependence of the dielectric permittivity for the strontium barium niobate relaxor ferroelectric thin films has been investigated. The nonlinear dielectric properties were obtained by using the measurements of the dielectric permittivity of the material as a function of the ac and dc "bias" electric field amplitude in wide frequency (100 Hz-10 MHz) and temperature (50-450 K) intervals. The results hint the existence of a true mesoscopic dielectric relaxor response in the ferroelectric thin film, which is very similar to those observed in bulk relaxor ferroelectrics. An anomalous behavior of the NL dielectric response was observed when submitted to moderate dc electric fields levels,,indicating a crossover from paraelectric to a glasslike behavior on cooling the sample toward the freezing transition. The obtained results were analyzed within the framework of the models proposed in the current literature.

Dielectric relaxation and relaxor behavior in bilayered perovskites

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Prevalência, classificação e características do refluxo cecoileal diagnosticado pelo enema opaco

OBJETIVO: Verificar, retrospectivamente, a prevalência do refluxo cecoileal diagnosticado pelo enema opaco, caracterizar sua distribuição etária e sexual e classificá-lo conforme o grau de intensidade. MATERIAIS E MÉTODOS: Foram revistos 715 enemas opacos, incluindo 268 homens e 447 mulheres com idade média de 54 anos. RESULTADOS: Dos 715 casos examinados, 46,5% apresentaram refluxo cecoileal, sendo 45% do tipo leve, 37,5% do tipo moderado e 17,5% do tipo severo. Refluxo cecoileal esteve presente em 48,3% das mulheres e em 43,6% dos homens. A distribuição percentual do refluxo cecoileal por faixa etária mostrou 46,1% nos indivíduos com menos de 21 anos, 42,1% nos indivíduos entre 21-40 anos, 49,8% nos indivíduos entre 41-60 anos e 44,7% nos indivíduos com mais de 60 anos. CONCLUSÃO: Refluxo cecoileal foi achado relativamente freqüente em nosso material, correspondendo os graus moderado e severo a 25% do material examinado. Aparentemente, não há associação entre seu surgimento e sexo ou idade. A etiopatogenia e conseqüências do refluxo cecoileal são ainda pouco conhecidas. Alguns estudos sugerem que o comprometimento de componentes da junção ileocecal, como os ligamentos, pode favorecer seu aparecimento. Entre as conseqüências prováveis, incluem-se a contaminação e alteração motora ileais, resultantes do material refluído do ceco.

Genotoxicity in primary human peripheral lymphocytes after exposure to radiopacifiers in vitro

Taking into consideration that DNA damage plays an important role in carcinogenesis, the purpose of this study was to evaluate whether some radiopacifiers widely used in clinical practice are able to induce genetic damage in primary human cells in vitro. Human peripheral lymphocytes obtained from 10 healthy volunteers were exposed to barium sulphate (BaSO(4)), zirconium oxide (ZnO(2)) and bismuth oxide (Bi(2)O(3)) at final concentrations ranging from 1 to 1000 mu g/mL for 1 h at 37 degrees C. The negative control group was treated with vehicle control (phosphate buffer solution) for 1 h at 37 degrees C and the positive control group was treated with hydrogen peroxide (at 100 mu M) for 5 min on ice. Results were analyzed by the Friedman non-parametric test. The results pointed all compounds tested out did not induce DNA breakage in human peripheral lymphocytes as depicted by the mean tail moment and tail intensity in all concentrations tested. In summary, our results indicate that exposure to these radiopacifiers may not be a factor that increases the level of DNA lesions in human peripheral lymphocytes as detected by single cell gel (comet) assay.

Effect of Chemical Disinfection and Accelerated Aging on Color Stability of Maxillofacial Silicone with Opacifiers

Purpose: The purpose of this study was to evaluate the color stability of MDX4-4210 maxillofacial elastomer with opacifier addition submitted to chemical disinfection and accelerated aging.Materials and Methods: Ninety specimens were obtained from Silastic MDX4-4210 silicone. The specimens were divided into three groups (n = 30): Group I: colorless, Group II: barium sulfate opacifier, Group III: titanium dioxide opacifier. Specimens of each group (n = 10) were disinfected with effervescent tablets, neutral soap, or 4% chlorhexidine gluconate. Disinfection was conducted three times a week for 2 months. Afterward, the specimens were submitted to different periods of accelerated aging. Color evaluation was carried out after 60 days (disinfection period) and after 252, 504, and 1008 hours of accelerated aging, using a reflection spectrophotometer. Color alterations were calculated by the CIE L*a*b* system. Data were analyzed by three-way ANOVA and Tukey test (alpha = 0.05).Results: Group II exhibited the lowest color change, whereas Group III the highest (p < 0.05), regardless of the chemical disinfection and accelerated aging periods.Conclusion: Opacifier addition, chemical disinfection, and accelerated aging procedures affected the color stability of the maxillofacial silicone.