We use the surface integral technique for calculation of the extinction spectra of small metal particles of different shapes. We consider in detail different nonellipsoidal geometries in the electrostatic limit, including cylinders and a variety of capped cylinders. It is shown that different capping geometries have pronounced effects on the energy and intensity of the longitudinal surface plasmon mode. In addition, we propose that atomic scale surface roughness may also be an important determinant of the surface plasmon peak energy. A surface roughness of 0.10, equivalent to around two atomic layers, can generate redshifts in surface plasmon modes similar in magnitude to the redshifts induced by changes in the end-cap geometry.

A light scattering model under the Rayleigh-Gans-Debye approximation has been developed for polycristalline alumina. The model states that transmittance of dense alumina ceramics basically depends not only on the maximum grain size but also on the preferential orientation of their c-axis, or texture. The effect of texture in transparency has been experimentally measured on several dense alumina samples with different grain size and compared to that obtained from x-ray Rietveld refinements with a very good agreement. The Rayleigh-Gans-Debye approximation also allows to represent optical data in a very simple way (logarithm of transmittance vs. the inverse of the wavelength square). Using these variables, a straight line is obtained for the Rayleigh-Gans-Debye approximation, its slope being proportional to the maximum grain size and textural parameter. Deviation from this law implies the presence of pores or grain of extremely large size.

The behavior of SiC ceramic joints brazed with commercially available Incusil ABA (Ag‐32.25Cu‐12.5In‐1.25Ti, in wt.%) was characterized especially with respect to the mechanical performance at temperatures up to 550°C using four‐point bending and torsional shear tests. The failure mechanisms with changing temperature were investigated with the aid of fractography. Additionally, the microstructure of brazed specimens was characterized in detail by high resolution scanning electron microscopy. The test geometry and setup for the high temperature torsional shear test is presented. The change in mechanical behavior of the joints as a function of temperature is shown and discussed. The brazed joints interestingly showed that flexural bending strength was maintained with only a small decrease up to 300°C. Above 300°C, the bending strength decreased much faster. For the first time, this joint system was characterized in torsional shear test at temperatures up to 550°C to achieve the intrinsic shear strength values. Very strong joints were achieved, resulting in failure through the ceramic base materials up to (torsional shear) testing temperatures of 400°C. The results indicate that SiC joints brazed with Incusil ABA exhibit excellent mechanical performance for applications up to 300°C.

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Al 2 O 3 -CeO 2 ceramics were found to be transparent in the IR range and high-traslucent in the visible range. The surface of nanometric α-alumina particles was modified by deposition-precipitation of small fractions of ceria nanoparticles. The powders were sintered using Spark Plasma Sintering. Values of Real In-line Transmittance up to 70% in the IR-Vis range have been measured. Transparency enhancement has been attributed to Cerium oxide nanoparticles located at the grain boundaries and triple points. These particles are hindering alumina grain growth during SPS at a temperature as high as 1430°C. This effect is found to be effective under SPS low vacuum conditions and short dwell times. The optimum ceria content was found to be 0.7 wt.%. Diffusion in Al 2 O 3 -*Manuscript 2 CeO 2 as a function of the atmosphere has been studied in diffusion couples. The results obtained by the proposed route are discussed considering the data reported in the literature for SPS ed transparent alumina.

It is well known that obtaining transparent alumina is of special interest for applications that require the combination of optical and mechanical properties. Sapphire and polycrystalline alumina are being used in industrial and military applications, such as armour parts, discharge lamps, airborne infrared sensors and lasers. [1] In addition, the high cost of the production of transparent sapphire crystals and the difficulties of carrying out the synthesis process for large-sized alumina monocrystals has focused attention on the development of polycrystalline transparent alumina materials (PTAMs). [2] Obtaining PTAMs requires that two main challenges be dealt with: i) the porosity in the final material must be lower than 0.05 vol.-% to avoid scattering effects and so to achieve transparency, [3] and, ii) the birefringence character of alumina grains, which is inherent to the material and seems to be more critical for larger grains, must be balanced. In this context, the key factor to achieve PTAMs seems to be the control of the grain growth in order to decrease the flaw size (< 100 nm) and, therefore, the volume of porosity, as well as to minimize the influence of birefringence in the optical properties of alumina.Several authors have reported that the presence of second phases, such as MgO, Y 2 O 3 , SiO 2 TiO 2, CaO, etc., modifies the grain growth rate of alumina when sintering. [4][5][6] Nevertheless, this is not enough to reach transparency due to the anisotropic character of alumina. Moreover, the effect of these elements on decreasing porosity is not well understood currently.The influence of oxides (such as MgO, TiO 2 , CaO, etc.) on the transparency of polycrystalline alumina compacts are widely studied in the literature. In this work, a completely different approach is developed, consisting of precipitating 0.5 wt.-% CeO 2 nanoparticles (< 5 nm) on the surface of the starting alumina nanopowder (d 50 approximately 170 nm) using cerium(III) acetate as precursor. It is shown that the ceria nanoparticles strongly enhance the transparency of the spark plasma sintered compacts due to: i) the ceria nanoparticles acting as powder lubricant, increasing by around 15% the initial density of the powder in the SPS die, and, ii) the CeO 2 nanoparticles, having a very low solid solubility in the alumina grains, locating at grain boundaries, hindering alumina grain growth by pinning during SPS sintering at 1 430 8C, 80 MPa for 2 min. This effect is found to be effective only under SPS vacuum conditions. In order to explain the light scattering behavior in the near-infrared and visible range, a light scattering model under the Rayleigh-Gans-Debye approximation for polycrystalline alumina is used. This model offers an additional and simple tool for a completed bulk evaluation of the SPS compacts microstructure. 1154 wileyonlinelibrary.com ß

Development of new electrodes is the key element for the improvement of the high rate Resistive Plate Chambers (RPC). In the particular case of resistive electrodes, the fabrication of these devices is a challenging problem from a material science point of view. The combination of resistivity, permittivity and stability requirements is really hard to satisfy for any known material. Respecting this, several materials have been found to be suitable for fabrication of resistive plates. In this work, we have carried out electrical characterizations of some of these materials that are currently used in RPCs or are solid candidates to be used as resistive plates for high rate RPCs. As a result, we have found strong evidences that ion conduction processes under moderate to high electric fields are able to drift high amounts of charge which are crucial to understand the degradation nature of the involved processes.