Electrical Conductivity Of Grains Research Articles

Electrophysical and Morphological Properties of a Hydrothermally Synthesized CuFe2O4 and CuFe2O4 / Reduced Graphene Oxide Composite

The aim of this paper is to compare the structural, morphological and electrical properties of the CuFe2O4 and CuFe2O4 / reduced graphene oxide composite. XRD and Mossbauer studies have shown that joint hydrothermal synthesis of cubic copper ferrite and reduction of graphene oxide leads to a decrease in ferrite particles from 14 to 8 nm. Based on the impedance spectroscopy data, a model of the obtained composite material has been prepared as a system consisting of contacting spinel particles covered with rGO clusters and separated by porous rGO. For CuFe2O4 / rGO composite material, the predominance of hopping charge transfer mechanisms has been shown, and the activation energies of electrical conductivity of grains and grain boundaries have been calculated.

Structural, morphological and electrical properties of alumina/YAG composites as solid electrolyte for IT - SOFC

Alumina/YAG composites (AYX_t) with high relative density (99.2 %TD) were successfully obtained by mixing commercial alumina powder with different volume fractions of yttrium aluminium garnet (Y3Al5O12-YAG; 7, 14, 21 and 28). YAG was synthetized by nitrate glycine reaction in the form of precursor powder. Polycrystalline YAG powder was obtained by calcination at 950?C for 2 h. Additionally, obtained compositions were characterized by XRD, SEM, EDX and electrochemical impedance spectroscopy. By XRPD analysis was found that the particle size of YAG powders lies in the nanometric range (being lower than 35 nm). By SEM microphotographs of composites were confirmed the formation of a conductive path consisting from mutually interconnected YAG particles. This was confirmed by the electrochemical impedance spectroscopy. The highest electrical conductivity of grain (?g) and grain boundary (?gb) at 700?C amounted to 2.22?10-2 ?-1cm-1and 9.44?10-3 ?-1cm-1, respectively, was measured in the composite containing 21 vol% of YAG.

Electrical conductivity and ethanol sensing of a new perovskite NiSnO3 sprayed thin film

This work deals with the sensitivity performance of NiSnO3 sprayed thin films against ethanol vapor. First, this film shows a polycrystalline nature by means of AFM observations with a crystallite size close to 50 nm. Also, TEM technique shows uniform in shape and particle size of as prepared NiSnO3. Second, the electrical conductivity was studied using impedance spectroscopy technique in the frequency range 10 Hz−13 MHz at various temperatures (175°C–225 °C). The electrical conductivity appears as the sum of both contribution of the electrical conductivity of grain and grain boundary. Finally, the ethanol sensing performance of the films has been investigated at various concentrations in air at operating temperatures varying from 175 °C to 250 °C. A noticeably sensitivity to ethanol vapor concentration of C = 0.1% is found at T = 225 °C.

Desempenho de estratégias de aeração de milho armazenado: Fungos e condutividade elétrica

Objetivou-se, com o presente trabalho, avaliar e comparar o desempenho de três estratégias de aeração de milho armazenado quanto à ocorrência de fungos e à condutividade elétrica dos grãos. As estratégias avaliadas foram: aeração contínua; aeração noturna e aeração em condições de umidade de equilíbrio entre os grãos e o ar ambiente. Realizaram-se dois ensaios de aeração com grãos de milho secos (11% b.u.) e úmidos (17% b.u.). Amostras de grãos foram retiradas durante os ensaios para contagem de fungos e medida da condutividade elétrica dos grãos. Grãos armazenados úmidos apresentaram maior ocorrência de fungos do que grãos armazenados secos. Observou-se que o Fusarium spp. apresentou contagens mais elevadas, o Penicillium spp. manifestou desenvolvimento e o Aspergillus spp. ocorreu com menor frequência. As estratégias de aeração empregadas não interferiram na condutividade elétrica dos grãos de milho armazenados, visto que não houve diferença significativa dos valores de condutividade elétrica entre os grãos submetidos a aeração e os grãos armazenados sem aeração.

Densificação, tamanho de grãos e condutividade elétrica da céria-samária

A céria contendo 20% mol samária é um eletrólito sólido proposto para uso em células a combustível de óxido sólido que operam em temperaturas intermediárias (~500 a 700 ºC), devido sua alta condutividade iônica. Um dos fatores limitantes para isto é sua relativamente baixa sinterabilidade. Neste trabalho foram utilizados dois métodos alternativos de sinterização com a finalidade de obter amostras densas, microestrutura homogênea e tamanho de grãos controlado. Outro objetivo foi relacionar os efeitos observados na microestrutura e na densificação com a condutividade elétrica das amostras sinterizadas. Para isto foi utilizada a Ce0,8Sm0,2O1,9 comercial, conformada uniaxial e isostaticamente, e sinterizada ao ar. As amostras sinterizadas foram analisadas por diversas técnicas. Resultados de medidas da densidade aparente revelaram que ambos os métodos são eficazes para a obtenção de cerâmicas com densidade relativa superior a 92%. A condutividade elétrica dos grãos e dos contornos de grão são também similares nas diversas amostras estudadas, apesar dos tamanhos dos grãos serem diferentes.

Electrical conductivity of yttria-stabilized zirconia with cobalt addition

Yttria-stabilized zirconia is the most developed solid electrolyte for use in high-temperature solid oxide fuel cells. Commercial yttria-stabilized zirconia powders reach high densification at temperatures higher than that of the usual anode materials. Reduction of the sintering temperature of the solid electrolyte could allow for co-firing of both ceramic components, thereby reducing production costs. The main purpose of this work was to study the effect of small cobalt additions on densification and on electrical conductivity of 8 mol% yttria-stabilized zirconia. Linear shrinkage results show that the onset temperature for shrinkage decreases with increasing cobalt content. Impedance spectroscopy measurements reveal that the electrical conductivity depends on the sintering profile. For specimens sintered at 1400 °C for 0.1 h the electrical conductivity of grains and grain boundaries are almost unchanged with that of 8YSZ. In contrast, for specimens sintered at the same temperature but for 0.5 h of soaking time, the electrical conductivity is higher in 0.025 mol% samples and is lower for 1 mol% Co doped 8YSZ. Degradation of the microstructure by increased porosity was obtained for high additive contents.

Interaction of yttria stabilized zirconia electrolyte with Fe2O3 and Cr2O3

Yttria stabilized zirconia electrolytes were sintered with addition of iron oxide or chromium oxide. The phase composition of the composites, sintering properties and DC and AC electrical properties are evaluated and compared with available data. Results show, that after sintering there is only single-phase material found in the XRD patterns. Iron can be considered as a sintering promoter while chromium decreases the apparently sintering process. Addition of either oxide decreases total electrical conductivity in comparison to pure samples. Based on impedance spectra it can be concluded that chromium mainly influences electrical conductivity of grain boundary, while iron influences electrical conductivity of both grain and grain boundary, with a solubility limit at grain boundaries estimated at about 2 mol% Fe.

Effect of solvent on physical properties of samaria-doped ceria prepared by homogeneous precipitation

Samaria-doped ceria solid solutions were prepared by homogeneous precipitation with hexamethylenetetramine using water and mixtures of alcohol/water as solvent. The mixed solvent influences several physical properties of the synthesized material when compared to those of samples prepared in water. The solid solution is formed, at least partially, during precipitation as demonstrated by Raman spectroscopy data. The dried precipitate is crystalline and single phase with fluorite-type structure, and consists of a mixture of anhydrous and hydrated cerium oxide with average sizes in the 5–8 nm range. Thermal decomposition of the as-synthesized material occurs at 400 °C. High densification was obtained at low temperatures (∼1200 °C). The electrical conductivity of grains and grain boundaries is improved for synthesized samples when compared to specimens prepared by mixing of starting oxides. These improved characteristics of synthesized powders are attributed to the interaction among the solvent and hydroxyl and water species on the surface of nanoparticles. The strength of this interaction is related to the carbon content in the alcohol chain.