Behavioral responses SICS

A mixed ion conductor, BaSnO, has also been tested as a contact layer on a Schottky sensor [90]. The BaSnOj/SiC sensor showed a response to oxygen and this was most pronounced at 400°C. The sensor was tested from 200°C to 700°C. Operated at 700°C, the sensor showed a negative resistance peak at a bias of 2V (Figure 2.8). This peak was accounted for by the tunneling or Esaki effect [91]. Up to an operation temperature of 400°C, thermionic emission was proposed to explain its behavior. At higher temperatures, a resistance connected in series with a Schottky diode can model the device [5, 73]. At temperatures of 500-600°C, the BaSn03 shows a mixed behavior of electronic and ion conduction, and the Nernst potential [92] can be added to the model. The complete proposed model is given in (2.9). 

As may be noted, water vapor speeds up device response to hydrogen. Figure lib gives V-p (where V-pn is the turn on voltage for transport down the channel created by the stored charge) versus time for a MOSFET based on the Pd/Si02/Si structure. These data are for an exposure to 180 ppm H2 in air at 150°C. In this case, both response and recovery behavior are shown. Figure 12 clearly shows that Pd/SiC>2/... 

Fig. 5.2 Comparison of creep behavior and time-dependent change in fiber and matrix stress predicted using a 1-D concentric cylinder model (ROM model) (solid lines) and a 2-D finite element analysis (dashed lines). In both approaches it was assumed that a unidirectional creep specimen was instantaneously loaded parallel to the fibers to a constant creep stress. The analyses, which assumed a creep temperature of 1200°C, were conducted assuming 40 vol.% SCS-6 SiC fibers in a hot-pressed SijN4 matrix. The constituents were assumed to undergo steady-state creep only, with perfect interfacial bonding. For the FEM analysis, Poisson s ratio was 0.17 for the fibers and 0.27 for the matrix, (a) Total composite strain (axial), (b) composite creep rate, and (c) transient redistribution in axial stress in the fibers and matrix (the initial loading transient has been ignored). Although the fibers and matrix were assumed to exhibit only steady-state creep behavior, the transient redistribution in stress gives rise to the transient creep response shown in parts (a) and (b). After Wu et al 1...

Fig. 6.2 Room temperature stress-strain behavior of a woven 0°/90° Q/SiC composite. Because of processing-related matrix cracking and progressive fracture near the crossover points of fiber bundles, Stage II behavior (non-linear stress-strain response) is observed from the onset of loading. Above a strain of approximately 0.5% the composite exhibits Stage III (linear) behavior.

In 2D CVI SiC/SiC composites Em ( 410 GPa) > Ef ( s200 GPa). The 2D SiC/SiC composites exhibit an elastic damageable behavior (figure 3). This means that the response of the damaged material is elastic as indicated by the linear portion of the curves on reloading. Figure 4 shows the dependence of elastic modulus on damage. 

The tensile behavior of minicomposites was correlated with microstructure features. Trends for Hi-Nicalon S fiber reinforced minicomposites are similar to those observed with earlier generations of SiC fibers (namely Nicalon and Hi-Nicalon) weak interfaces, limited matrix cracking and ultimate failure controlled by tows. A different trend was observed on the SA3 fiber reinforced minicomposites stronger interfaces, premature failure attributed to non uniform fiber/matrix bonding, and ultimate failure is not controlled by tows. This behavior was changed after heat treatments which caused fiber/matrix bond release, leading to a composite response with ultimate failure controlled by tows. 

The electrical conductivity of Si-C fibers with low oxygen content increases sharply at first when the pyrolysis temperature is increased from 1200 to 1400°C, and then more slowly. Initially, most of the residual hydrogen is released and the carbon is formed. Subsequently the SiC crystals grow and an intervening carbon network is formed. The thin carbon layer (or sheath) on the surface of Si-C fibers is not alone responsible for the observed gain in electrical conductivity since its removal by a brief oxidation treatment at 600°C does not markedly affect its electrical behavior [29]. 

The objective of the current work was to compare FOD behavior between the SiC/SiC and the oxide/oxide CMCs in terms of impact morphologies and strength degradation, based on the previous work [1-2], In addition, the response to static indentation of the two composites with respect to deformation was also characterized using the same steel balls that were employed in the previous FOD testing. The static indentation results were then used in order to make an attempt of quasi-static prediction of impact force as a function of impact velocity involved in the FOD testing. 

The present studies are mainly devoted to silicon carbide (SiC)-based materials in the form of isolated clusters, nanopartides, or several architectures, which exhibit various original features. The interests in SiC is motivated by the large offered possibihties from structural aspects as well as physical responses such as electronic, optics, photovoltaic or dielectric properties. Additionally, beyond good thermal stability and mechanical hardness, the SiC is versatile from structural aspect (more than 170 polytypes), electronic behavior (a variable energy gap from 2.4 to 3.3 eV) as well as photorefractive properties (Vonsovici et al. 2000). As matter of fact, the nanocrystalline size modulates all the intrinsic parameters involved in the parent bulk materials. When nanopartides are associated with suitable matrixes, promising new potentialities... 

The linear electro-optical (EO) behavior, i.e., the Pockels effect, constitutes a manifestation of nonlinear optical features of anisotropic and non-centro-symmetric media. Functional architectures based on host polymer matrixes and guest SiC nanoparticles (nc-SiC) as active chromophores were realized. The intrinsic dipole moments of the chromophore combined with the eventual polarization at the interfaces with the host matrix constitute the physical origin of the electro-optical responses. The experiments were carried out in hybrid materials based on SiC nanocrystals and matrixes such as PVK, PMMA, or PC. 

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