Influência dos parâmetros de processo na deposição de nitreto de titânio por plasma em gaiola catódica

Titanium nitride films were grown on glass using the Cathodic Cage Plasma Deposition technique in order to verify the influence of process parameters in optical and structural properties of the films. The plasma atmosphere used was a mixture of Ar, N2 and H2, setting the Ar and N2 gas flows at 4 and 3 sccm, respectively and H2 gas flow varied from 0, 1 to 2 sccm. The deposition process was monitored by Optical Emission Spectroscopy (OES) to investigate the influence of the active species in plasma. It was observed that increasing the H2 gas flow into the plasma the luminescent intensities associated to the species changed. In this case, the luminescence of N2 (391,4nm) species was not proportional to the increasing of the H2 gas into the reactor. Other parameters investigated were diameter and number of holes in the cage. The analysis by Grazing Incidence X-Ray Diffraction (GIXRD) confirmed that the obtained films are composed by TiN and they may have variations in the nitrogen amount into the crystal and in the crystallite size. The optical microscopy images provided information about the homogeneity of the films. The atomic force microscopy (AFM) results revealed some microstructural characteristics and surface roughness. The thickness was measured by ellipsometry. The optical properties such as transmittance and reflectance (they were measured by spectrophotometry) are very sensitive to changes in the crystal lattice of the material, chemical composition and film thicknesses. Therefore, such properties are appropriate tools for verification of this process control. In general, films obtained at 0 sccm of H2 gas flow present a higher transmittance. It can be attributed to the smaller crystalline size due to a higher amount of nitrogen in the TiN lattice. The films obtained at 1 and 2 sccm of H2 gas flow have a golden appearance and XRD pattern showed peaks characteristics of TiN with higher intensity and smaller FWHM (Full Width at Half Maximum) parameter. It suggests that the hydrogen presence in the plasma makes the films more stoichiometric and becomes it more crystalline. It was observed that with higher number of holes in the lid of the cage, close to the region between the lid and the sample and the smaller diameter of the hole, the deposited film is thicker, which is justified by the most probability of plasma species reach effectively the sample and it promotes the growth of the filmCoordenação de Aperfeiçoamento de Pessoal de Nível SuperiorFilmes finos de nitreto de titânio foram crescidos sobre vidro utilizando a técnica de deposição por descarga em gaiola catódica a fim de averiguar a influência das variáveis de processo nas propriedades ópticas e estruturais do filme. Como atmosfera do plasma foi utilizada a mistura de gases Ar, N2 e H2, fixando o fluxo de Ar e N2 em 4 e 3 sccm, respectivamente, e usando fluxos de 0, 1 e 2 sccm de H2. O processo de deposição foi monitorado por Espectroscopia de Emissão Óptica (OES) para investigação das espécies ativas no plasma. Observou-se que com o aumento fluxo de H2 as intensidades das espécies luminescentes no plasma sofrem alterações e que a espécie N2 (391,4 nm) não teve um crescimento proporcional ao fluxo de H2. Outros parâmetros investigados foram o diâmetro e o número de furos da gaiola. As análises de difração de raios X com ângulo de incidência rasante (GIXRD) comprovaram que os filmes obtidos são compostos por TiN, podendo ter variações quanto a quantidade de nitrogênio na rede e o tamanho de cristalito; a microscopia óptica forneceu dados sobre a homogeneidade, a partir da microscopia de força atômica (AFM) observou-se algumas características microestruturais do filme e a rugosidade. A espessura foi quantificada através das análises de elipsometria. As propriedades ópticas como refletância e transmitância (medidas por espectrofotometria) são bastante sensíveis a alterações na rede cristalina do material, composição química e espessura, sendo, portanto, uma boa ferramenta para verificação do controle do processo. De maneira geral, os filmes obtidos com fluxo de 0 sccm de H2 possuem uma maior transmitância atribuída ao menor cristalinidade decorrente da maior quantidade de nitrogênio na rede cristalina do TiN. Os filmes obtidos nos fluxos de 1 e 2 sccm de H2 obtiveram um aspecto dourado e o difratograma apresentou picos característicos do TiN com maior intensidade e menor largura a meia altura, sugerindo que com a presença de hidrogênio na atmosfera do plasma os filmes são mais estequiométricos e com maior cristalinidade. Quanto à configuração da gaiola observou-se que com maior quantidade de furos na tampa, maior a proximidade da tampa com a amostra e menor o diâmetro do furo, maior é a espessura do filme, o que é justificado pela maior probabilidade das espécies do plasma atingirem efetivamente o substrato e promoverem o crescimento do film

Porous Transport Layers Made of Niobium/Steel Composites for Water Electrolysis

In future energy concepts, water splitting by polymer electrolyte membrane (PEM) electrolysis is a key technology for converting regenerative energy from wind or sun into hydrogen. In this study, a novel porous transport layer for PEM electrolysis units was developed, which is based on a stainless steel substrate coated with a porous Nb layer. Nb layer is expected to improve the electrochemical performance and lifetime of electrolysis cells due to formation of a stable passivation layer with good electrical conductivity. Scalable powder metallurgical techniques like tape casting, screen printing and field assisted sintering/spark plasma sintering FAST/SPS were used for manufacturing this composite structure. The porous transport layer was characterized with respect to microstructure. FAST/SPS was found to be promising to decrease interdiffusion at the interface. Finally, first electrochemical tests were conducted on laboratory scale demonstrating the potential of the composite to replace state-of-the-art titanium-based transport layers

Manufacturing of highly porous titanium by metal injection molding in combination with plasma treatment

Highly-porous titanium was produced by metal injection molding (MIM) of feedstock containing potassium chloride particles as a space holder. Macroporosity was generated by dissolving the potassium chloride particles in water. Challenges for MIM of highly-porous parts include shape retention during debinding and sintering and achieving open surface porosity. This study demonstrates that plasma treatment can remedy both these effects for highly-porous titanium. Plasma treatment of unsintered MIM samples enables attaining porosities of up to 64% in combination with good dimensional accuracy. The effect of plasma treatment on the uptake of interstitial impurities, dimensional accuracy, sintered microstructure and porosity, as well as the interaction of the plasma with partially-debinded MIM samples, was investigated. Highly-porous titanium produced by MIM and plasma treatment is attractive for biomedical implants due to its low impurity content, good dimensional accuracy and shape stability in combination with enhanced open porosity, the latter contributing to bone ingrowth and implant fixation