Análise comparativa das propriedades de óxidos transparentes condutores para aplicação em células solares de filmes finos de CdTe

Este trabalho compara as propriedades de diversos óxidos transparentes condutores para serem utilizadoscomo contatos frontais de células solares de filmes finos de CdTe. Os filmes foram depositados à temperaturaambiente, por pulverização catódica com rádio frequência, sem tratamento térmico posterior, com o objetivode reduzir o número de etapas do processo de fabricação. A relação resistência/transmitância foi avaliadaatravés de uma figura de mérito, de forma a propor os materiais candidatos a atuar como eletrodo frontal dacélula solar. Os óxidos investigados foram divididos em dois grupos: os de baixa resistividade e os de altaresistividade. Eletrodos fabricados com os diversos óxidos foram submetidos a testes de estabilidade térmicanas temperaturas de processamento da célula solar. Os resultados mostraram que os filmes de ZnO e Zn2SnO4são óxidos de alta resistividade ( 0,5 ï—.cm), enquanto que os de SnO2, In2O3, In2O3:Sn, Cd2SnO4 e ZnO:Alsão de baixa resistividade ( 5,0 x 10-3 ï—.cm) e alta transmitância ( 85%). Os filmes de In2O3:Sn e ZnO:Alapresentaram-se como as melhores opções para fabricação dos eletrodos, pois possuem resistividades na faixade 10-3--10-4 ï—.cm e transmitâncias entre 85-92%. No entanto, levando-se em consideração questões decusto e escassez associadas ao índio, filmes de ZnO:Al são os mais adequados para esta aplicação, pois alémde possuírem valores de condutividade e transmitância elevados, apresentaram elevada estabilidade térmicanas temperaturas de processamento da célula

Oxygen Diffusion in Vanadium-Based Alloys

114 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1981.The experimental study of transport and equilibrium properties of oxygen in vanadium-based alloys was made by EMF measurements on solid electrolytic cells over the temperature range of 873-1423(DEGREES)K. The oxygen diffusion in vanadium was not significantly modified by small additions of Ti, Cr, Ni, Nb and Ta. The increase in the activation energy for oxygen diffusion in the V-based alloys containing Cr, Ni, Nb and Ta probably reflects the effect of these substitutional solutes on the activity coefficient of oxygen. The oxygen activity was increased by the addition of 1 at% of Cr, Ni and Nb, and decreased by the addition of Ti and Ta. However, the effects in the alloys containing Nb and Ta are very small.Approximate values for the first order elastic interaction energy between a substitutional solute and oxygen interstitial were computed and compared with the oxygen binding energies to substitutional solutes in niobium. These comparisons together with the present results for the vanadium system suggest that the main contribution to the interactions between substitutional-interstitial solutes arises from chemical effects.The EMF technique was shown capable of monitoring the kinetics of a precipitation process. The oxygen precipitation in vanadium alloys containing Ti, Zr and Hf certainly suggests attractive interactions between oxygen and these solutes.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD

Quantitative X-ray microtomography technique to evaluate high-temperature transient diffusion of Iron diffusants in high alumina-silicate porous refractory media

Diffusion tests were performed with solid diffusants of Iron oxides in contact with porous silico-aluminous refractory castables in high-temperature conditions. A non-destructive X-ray computer microtomography technique with digital 3D reconstruction (3DμCT) was used for spatial monitoring the diffusion into the media. A particle tracking (PT) method was applied to evaluate diffusion through porous materials and to quantify its diffusive properties based on 3D images over time. The influence of temperature was examined in the range from 1100 °C to 1300 °C. Each sample was heat treated for 100 h in the investigated temperature. The normalized concentration of diffusants as a function of the penetration was obtained by 3DμCT images and compared with the concentration profile determined by elementary microanalysis with energy dispersive spectroscopy and surface chemical mapping (MAP/EDS). Thus, the diffusivity of the porous media was quantified from the experimental data. It was observed a variation less than 3.52% between the MAP/EDS and 3DμCT, i.e., between the destructive and non-destructive methods, suggesting that the 3DμCT method may be extended to other media and diffusants. Keywords: High-temperature diffusion, High alumina-silicate refractory, Mechanical properties, X-ray microtomography, Image analysi

On the Intrinsic Limits of the Convolution Method to Obtain the Crystallite Size Distribution from Nanopowders Diffraction

<div><p>The present work briefly reviews the convolution of crystallite shape functions and discusses its experimental limitations. The diffraction from a theoretical spherical shape powder is used to exemplify the limits of the convolution procedure. Mean lattice distortions were not considered since the discussed limitations are inherent to the convolution method using Fourier transforms. The diffraction pattern and the convolution were calculated using appropriate macros for the Topas program. It is shown that very small crystallites require a large 2θ convolution span and the smallest subdivision for the distribution will depend on this convolution span. To show the importance of the convolution limits and its application, the nanocrystalline CeO2 round-robin diffraction pattern was evaluated. The chord frequency distribution by XRD showed conformity with the chord distribution calculated from a grain size histogram obtained by transmission electron microscopy for this sample.</p></div

Evaluation via multivariate techniques of scale factor variability in the rietveld method applied to quantitative phase analysis with X ray powder diffraction

The present work uses multivariate statistical analysis as a form of establishing the main sources of error in the Quantitative Phase Analysis (QPA) using the Rietveld method. The quantitative determination of crystalline phases using x ray powder diffraction is a complex measurement process whose results are influenced by several factors. Ternary mixtures of Al2O3, MgO and NiO were prepared under controlled conditions and the diffractions were obtained using the Bragg-Brentano geometric arrangement. It was possible to establish four sources of critical variations: the experimental absorption and the scale factor of NiO, which is the phase with the greatest linear absorption coefficient of the ternary mixture; the instrumental characteristics represented by mechanical errors of the goniometer and sample displacement; the other two phases (Al2O3 and MgO); and the temperature and relative humidity of the air in the laboratory. The error sources excessively impair the QPA with the Rietveld method. Therefore it becomes necessary to control them during the measurement procedure

Cold-rolled multiphase boron steels: microstructure and mechanical properties

The influence of the boron concentration on phase transformation characteristics, microstructure and mechanical properties of multiphase steels was investigated using computational thermodynamics (Thermo-Calc®), dilatometry, quantitative metallography and tensile tests. Pilot scale 50 kg steel ingots were prepared in an induction furnace operating under an argon gas atmosphere with boron contents between 0 and 47 ppm. The ingots were cut into 35 mm thick blocks, which were reheated to 1250 °C for 1 h and hot rolled for seven passes to attain a thickness of 7.0 mm. The hot-rolled sheets were machined and then cold rolled to a final thickness of 1.2 mm. Continuous annealing cycles were performed in a Bähr dilatomer and in a Gleeble machine. Continuous annealing laboratory simulations showed that boron did not significantly influence the amount of austenite formed during heating and soaking steps. However, boron influenced austenite transformation during the cooling step, which reduced the amount of ferrite and increased the amount of bainite. Regarding the mechanical properties, adding boron increased strength and decreased ductility of the product. The steels with boron concentrations up to 27 ppm exhibited the greatest effect. The amount of austenite, which was calculated using Thermo-Calc®, was slightly overestimated compared with that obtained by dilatometry and metallography, particularly for soaking temperatures lower than 800 °C

Microstructural Evidence of beta Co(2)Si- phase Stability in the Co-Si System

The aim of this work was to verify the stability of the beta Co(2)Si phase in the Co-Si system. The samples were produced via arc-melting and characterized through Scanning Electron Microscopy (SEM) and Differential Thermal Analysis (DTA). The results have confirmed the stability of the beta Co(2)Si phase, however, a modification of the shape of beta CoSi phase field is proposed in order to fully explain the results

Development of Bulk Bi2+xSr3-yCa yCu 2O8+delta Superconductors by Partial-Melting Route for Fault Current Limiters Application

The production of bulk Bi2+xSr3-yCa yCu 2O8+delta (Bi-2212) superconductors for fault current limiter application was developed via a partial-melting route. Aiming high Ic (critical current), which is the essential superconducting characteristic for application of this material in the construction of Fault Current Limiters (FCL), the produced blocks have predominance of Bi-2212 phase (83 wt%), which characterizes with high values of zero and onset transport critical temperature of 92K and 97.5K, respectively. A relatively low transition width, deltaT, from the superconducting to the normal state of 5.5K, revealed a good intergrain connectivity. Consequently, current measurements on the blocks of Bi-2212 show promising Ic values of 230A and 850A for direct and alternate current, respectively. It is expected that further increases in the Ic values will depend on the elimination of an observed amorphous phase and further reduction of amount and grain sizes of secondary phases, still present in the blocks obtained by the proposed partial-melting route. This may be achieved by a further optimization of the partial-melting processing parameters