ac conductivity and conduction mechanism of NaNbO3 semiconductor antiferroelectric ceramic: A relaxational approach at high temperature

The electric properties of the sodium niobate perovskite ceramic were investigated by impedance spectroscopy in the frequency range from 5 Hz to 13 MHz and from room temperature up to 1073 K, in a thermal cycle. Both capacitance and conductivity exhibit an anomaly at around 600 K as a function of the temperature and frequency. The electric conductivity as a function of angular frequency sigma(omega) follows the relation sigma(omega)=Aomega(s). The values of the exponent s lie in the range 0.15less than or equal tosless than or equal to0.44. These results were discussed considering the conduction mechanism as being a type of polaron hopping. (C) 2003 American Institute of Physics.

Temperature-dependent Raman spectra of K0.2Na0.8NbO3 ceramics

We performed temperature-dependent Raman scattering studies on K0.2Na0.8NbO3 ceramics and compared the results with those for NaNbO3. The wavenumbers associated with NbO6 vibrations suggest the existence of two phase transitions, as occurs with pure NaNbO3 ceramics. Although the disorder on the Na/K site does not change either the room temperature phase of K0.2Na0.8NbO3 or the sequence of phase transitions compared with NaNbO3, it changes the temperature of the lowest phase transition and strongly modifies the temperature of the antiferroelectric --> new phase II phase transition. Additionally, the linewidth analysis shows that the orientational mechanism is the dominant contribution to linewidth, although the anharmonic contribution is increased, when compared with NaNbO3, owing to the random distribution of potassium in the sodium niobate matrix. Copyright (C) 2004 John Wiley Sons, Ltd.

Synthesis and sintering of ultra fine NaNbO3 powder by use of polymeric precursors

Ultra-fine NaNbO3 powder was prepared by the use of polymeric precursors. X-ray diffraction (XRD) results showed that this niobate nucleates from the amorphous precursor, with no intermediate phases, at low temperature (500°C). Studies by XRD and nitrogen adsorption/desorption showed that powders with high crystallinity ( ≈ 100%) and high surface areas (>20 m2/g) are obtained after calcination at 700°C for 5 h. Compacts of calcined powders showed high sinterability reaching 98% of theoretical density when sintered at 1190°C for 3 h.

Particle growth during calcination of polycation oxides synthesized by the polymeric precursors method

The particle-growth kinetics of sodium niobate and zirconium titanate powders that were processed by the polymeric precursors method were studied. The growth kinetics that were studied for the particle, in the final stage of crystallization, showed that the growth process occurs in two different stages. For temperatures <800°C, the particle-growth mechanism is associated with surface diffusion, with an activation energy in the range of 40-80 KJ/mol. For temprratures >800°C, particle growth is controlled by densification of the nanometric particle cluster and by a neck-size-controlled particle-growth mechanism. The results suggest that this behavior was typical of the synthesis method, because two different polycation oxides presented the same behavior.

Síntese de templates para aplicação em piezocerâmicas livre de chumbo

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Structural characterization and Curie temperature determination of a sodium strontium niobate ferroelectric nanostructured powder

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

Dielectric loss and phase transition of sodium potassium niobate ceramic investigated by impedance spectroscopy

The dielectric permittivity of Na0.80K0.20NbO3 ceramic was investigated by impedance spectroscopy. The dielectric characterization was performed from room temperature to 800 degreesC, in the frequency range 5 Hz-13 MHz. The bulk permittivity was derived by the variation of the imaginary part of the impedance as a function of reciprocal angular frequency. The permittivity values as a function of temperature showed two maxima. The first maximum is very similar at 200degreesC and the second one positioned at around 400degreesC, which was associated to Curie's temperature. The evolution of the complex permittivity as a function of frequency and temperature was investigated. At low frequency dispersion was investigated in terms of dielectric loss. The Na0.80K0.20NbO3 showed a dissipation factor between 5 and 40 over a frequency range from 1 to 10(2) kHz. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Determination of potassium and sodium in an ash sample by gamma-ray spectroscopy

Neutron activation analysis and gamma-ray spectroscopy were used to determine the quantity of potassium and sodium in an ash sample of Tabebuia sp bombarded with thermal neutrons. These techniques, widely applied in nuclear physics, can be used in the context of wood science as an alternative for the usual physical chemistry methods applied in this area. The quantity of K and Na in an 8.60 +/- 0.10 mg of ash was determined as being 1.3 +/- 0.3 mg and 11.0 +/- 1.8 mu g, respectively. The ratio of Tabebuia sp converted into ash was also determined as 0.758 +/- 0.004%.

Rheological Properties of a Sodium Bentonite and Lactose Aqueous Dispersion

Aim of this paper is show the viscosity measure of a sodium bentonite-water-lactose mixture and your rheological behaviour. This analysis showed the formation of tridimensional structure type and formation of stratified silicate/lactose, this occurred due to different concentrations of organic products into mixture and due to a difference of rotation during viscosity measument. Formation of networks is a consequence of the attraction between the silicate layers in water-lactose mixture. In the present work aqueous solutions of lactose with concentration of 7%, 5%, 3%, 1% and 0% (wt %) were used.

Sodium chloride added to transport water and physiological responses of Matrinxã Brycon amazonicus (Teleost: Characidae)

A adição de sal à água tem sido utilizada para a mitigação de estresse e aumento da taxa de sobrevivência em peixes. O presente estudo avaliou o efeito do cloreto de sódio (0,0; 1,0; 3,0 e 6.0 g/l) nas concentrações de cortisol plasmático, glicemia, triglicerídios, proteínas total plasmática, hematócrito, hemoglobina, número de eritrócitos, glicogênio e lipídio hepáticos, e lipídio muscular em matrinxã Brycon amazonicum adultos após quatro horas de transporte e durante período de recuperação de 96 h. Amostras foram coletadas antes e depois do transporte, bem como 24 e 96 h após a chegada. O nível de cortisol plasmático estava mais elevado logo após o transporte quando comparado à condição inicial (pré-transporte), exceto para os peixes transportados com sal nas concentrações 3,0 e 6,0 g/l. Comportamento semelhante foi observado para a glicemia, porém os peixes dos tratamentos 0,0, 1,0 e 3,0 g/l necessitaram de período superior a 24 h para recuperar a condição inicial. Foram registrados níveis mais baixos de glicogênio hepático em peixes do tratamento controle (0,0 g/l). Os parâmetros hemoglobina, número de eritrócitos, proteína plasmática total e lipídio hepático não apresentaram alterações durante o período experimental. Os valores de hematócrito diminuíram logo após o transporte em todos os tratamentos, retornando aos níveis iniciais após 24 h. Todos os tratamentos apresentaram redução nos níveis de lipídio muscular e triglicerídios durante o período de recuperação. Os resultados sugerem que a adição de 6,0 g/l de sal na água de transporte reduz as alterações fisiológicas de estresse e que é necessário período de 96 h após o transporte para a recuperação da condição inicial de matrinxãs transportados sem a adição de sal.

ACUTE TOXICITY of SODIUM SELENITE and SODIUM SELENATE TO TILAPIA, Oreochromis niloticus, FINGERLINGS

Selenium is an essential nutrient for many organisms, including fish. It can be released in the water by natural processes of dissolving rocks and minerals, and by the wastewater from industries and agricultural activities, which can increase its concentration in the environment, leading to toxic effects to the aquatic biota. Median Lethal Concentrations (LC(50-96h)) of two forms of selenium were estimated to fingerlings of Nile tilapia Oreochromis niloticus, focusing on estimating indicators for future environmental risk assessments in aquatic ecosystems contaminated with those elements, particularly for evaluate sources of water quality suitable for rearing tilapia. The results were: LC(50-96h) of sodium selenite (Na(2)SeO(3)) = 4.42 mg Se(4+) L(-1), and LC(50-96h) of sodium selenate (Na(2)SeO(4)) = 14,67 mg Se(6+) L(-1). According to those data, it was possible to classify sodium selenite as highly toxic and sodium selenate as moderately toxic to fingerlings of tilapia.

Controle de plantas daninhas através da palha de cana-de-açúcar associada à mistura dos herbicidas trifloxysulfuron sodium + ametrina

O objetivo deste trabalho foi avaliar os efeitos da palha de cana-de-açúcar resultante da colheita sem queima e da mistura comercial dos herbicidas trifloxysulfuron sodium + ametrina, na emergência e no acúmulo de biomassa seca de nove espécies de plantas daninhas. Os tratamentos foram distribuídos em esquema fatorial 3 x 3, sendo três quantidades de palha resultantes da colheita da cana-de-açúcar sem queima (0, 10 e 15 t ha-1), e três doses da mistura formulada dos herbicidas trifloxysulfuron sodium + ametrina (0, 1,75 e 2,00 kg ha-1), aplicados em condições de pós-emergência das plantas daninhas. As densidades das plantas daninhas foram avaliadas aos 15, 60 e 90 dias após a aplicação (DAA) da mistura dos herbicidas, e a biomassa seca das plantas daninhas, aos 90 DAA. A presença de palha sobre o solo suprimiu as densidades das populações de Brachiaria plantaginea, Digitaria horizontalis, Panicum maximum, Sida glaziovii e Amaranthus hybridus a níveis de infestação considerados satisfatórios de controle. A palhada também reduziu as populações de Senna obtusifolia, Ipomoea hederifolia, I. grandifolia e I. nil, porém em níveis insatisfatórios de controle. A mistura de herbicidas nas doses estudadas controlou todas as espécies de plantas daninhas avaliadas. Na presença da palha, o controle das plantas de S. obtusifolia, I. nil, I. hederifolia e I. grandifolia somente foi satisfatório quando foi aplicada a mistura de herbicidas. Para o controle de P. maximum, houve vantagem na integração dos dois métodos de controle, em relação à aplicação isolada da menor quantidade de palha estudada ou à aplicação da mistura de herbicidas.

Sodium levels for Japanese quail at initial phases

The aim of this research was to determine the nutritional requirements of sodium for Japanese quail (Coturnix coturnix Japonica) during the periods of 1 to 21 d and 22 to 40 d of age, as well as to evaluate the residual effect on egg production and densitometry bone traits from 41 to 63 d. Two experiments were developed. Experiment 1: 360 Japanese quail were used, from 1 to 21 d of age. Treatments consisted of 5 sodium levels (0.06, 0.12, 0.18, 0.24, and 0.30%). Experiment 2: 240 Japanese quail were used, from 22 to 40 d. Treatments consisted of 5 sodium levels (0.04, 0.12, 0.20, 0.28, and 0.36%). In both experiments, weight gain, final weight, and feed conversion presented a quadratic trend, whereas water intake presented a linear trend. Treatments did not affect the densitometry of bone traits, although they presented a quadratic influence on tibia ash, calcium, and calcium: phosphorus ratio. Therefore, the nutritional requirement of sodium for Japanese quail from 1 to 21 d and from 22 to 40 d is 0.222% and 0.253%, respectively.

Feed restriction on performance and blood parameters of broilers fed diets with different sodium levels

The experiment was conducted to evaluate the effect of feed restriction and different sodium levels in the diet on the performance and hematological values (erythrocyte, hemoglobin, hematocrit, mean cell volume, mean cell hemoglobin, mean cell hemoglobin concentration and white blood cell) of broilers from 22 to 42 days of age. A completely randomized design was used in a 4 x 2 x 2 factorial (levels of sodium: 0.16%, 0.19%, 0.22% and 0.25%; with or without feed restriction; male and female), and two replicates of thirty broilers each. Sodium levels did not affect performance (p>0.05). Feed restriction resulted in increased feed intake and affected weight gain and feed conversion negatively (p<0.05). Better weight gain and feed conversion (p<0.05) were seen in male broilers. Hematological values were not affected by sodium levels, feed restriction or sex (p>0.05).

Eficiência e seletividade dos herbicidas trifloxysulfuron-sodium + ametryne e hexazinone + diuron em função da tecnologia de aplicação e do manejo mecânico da palha de cana-de-açúcar na linha de plantio

Com objetivo de otimizar a utilização de trifloxysulfuron-sodium + ametryne e hexazinone + diuron em função da adoção de diferentes pontas de pulverização e manejo mecânico da palha de cana-de-açúcar na linha de plantio, dois experimentos foram conduzidos na Destilaria Parálcool S/A, localizada em Paraguaçu Paulista/SP. No experimento 1, 12 tratamentos foram estudados em esquema fatorial 2 x 2 x 3, com quatro repetições, contrastando a presença e ausência de palha da cana na linha de plantio; dos herbicidas trifloxysulfuron sodium + ametryne (37 + 1.463 g i.a. ha-1 e 0,2% v/v de Aterbane®) e hexazinone + diuron (330 + 1.170 g i.a. ha-1 e 0,2% v/v de Aterbane®) e das pontas de pulverização XR11002-VS (128 L ha-1), AI11002-VS (200 L ha-1) e TF-VP5 (310 L ha-1). No experimento 2, a deposição da calda de pulverização nas plantas de cana-de-açúcar e Digitaria horizontalis, gerada pelas interações entre herbicidas e pontas, foi monitorada utilizando-se solução traçadora constituída por corante FDC-1 + herbicida. Os resultados sugerem que a presença da palhada da cultura proporcionou controle excelente das espécies infestantes mesmo na ausência do tratamento herbicida. O controle químico de D. horizontalis (6 folhas até 1-2 perfilhos) e Brachiaria decumbens (2 a 6 folhas) apresentou-se eficiente (> 91%) nas linhas sem palha a partir dos 14 DAA (dias após aplicação) para os herbicidas e pontas de pulverização estudados. D. horizontalis foi mais rapidamente controlada aos 7 DAA pelo trifloxysulfuron-sodium + ametryne com a ponta AI11002-VS. Houve toxicidade até os 21 DAA, sendo esta mais intensa para os tratamentos com hexazinone + diuron associado com as pontas AI11002-VS e TF-VP5, em decorrência da maior deposição do herbicida nas folhas da cultura.