Alumina fractured surface

FIGURE 7. SEM micrograph showing Nextel 610/monazite/alumina fracture surface. Monazite coatings can be seen on the pulled-out fibers and in the fibertroughs. 

Figure C2.11.5. Scanning electron micrographs showing the microstmcture of an alumina ceramic spark-plug body (a) fracture surface and (b) polished and thennally etched cross section.

Fig. 11. Micrographs of (a) a hot-pressed alumina—TiC ceramic showing a white TiC phase and a dark alumina phase (3) and (b) a fracture surface of an...

FIGURE 5.6 This is a fractured sample of a ceramic composite (alumina with 30 volume-percent silicon carbide whiskers). The lighter regions of circular or cylindrical shape are randomly oriented whiskers protruding from the fractured surface. The rod-like depressions in the surface mark places where whiskers nearly parallel with the fracture were pulled out. Courtesy, Roy W. Rice, W. R. Grace and Company. 

SEM image of the fracture surface of 5.7 vol% SWCNT-Fe-Al203 composite densified by spark plasma sintering (SPS) of a mixture of nanometric alumina and ropes of SWCNTs. Reprint from Nature Materials, No. 2, 2002, pp. 38-42, Zhan G.-D., Kuntz J.D., Wan J. and Mukherjee A.K., Single-wall carbon nanotubes as attractive toughening agents in alumina-based nanocomposites, with the permission of Nature Materials and of the authors (http // www.nature.com/nmat/index.html). 

Fig. 2.1 Fracture surface of an alumina/20 vol.% SiC whisker composite showing microscopically rough surface. Presence of whiskers readily evident due to debonding along the matrix-whisker interface.

Fig. 6.3. Fracture surface of an all alumina multilayer membrane support (SEM picture).

Fig. 6.5. Fracture surface of supported silica membrane (SEM picture). Alumina layer 3 supports alumina layer 4, which supports the silica layer 5.

Fig. 5 Miciostructures of alumina filler loaded preceramic paper left - pulp fiber paper sintered al 1600 °C (porous) right - fracture surface of sintered alumina fibre paper.

FIGURE 1. Fracture surface of SiC whisker reinforced alumina showing very rough surface and tortuous crack propagation. 

FIGURE 2. a) Schematic showing toughening through crack deflection at the fibei/matrix interface, b) SEM micrograph of fracture surface ofNextel 610/monazite/alumina composite tested at 1200°C showing fiber pullout and c) fracture surface ofNextel 610/alumina composite tested under the same conditions. Absence of crack deflection mechanism led to brittle failure in c). 

FIGURE 6. Typical examples of fracture surfaces showing fracture origins for (a) 0 mol% (10-YSZ) (b) 30mol% alumina particulate composite [2]. Bar = 500 p,m. Reprinted with permission of The American Ceramic Society, www.ceramics.org. Copyright [2002]. 

In order to unravel adsorption mechanisms, a detailed knowledge of the composition and reactivity of the adsorption centers on the initial adsorbent is imperative [35-37]. It is well known [37-39] that fractured surfaces can be covered by cations and anions with unoccupied orbitals that act as Lewis acid and Lewis base centers, respectively. After adsorption of water molecules, with the evolution of hydroxyl and hydrogen species, the Lewis centers are transformed into Bronsted centers, which will influence surface properties. In many cases, characterizing the adsorption sites is complicated, and controversy stiU exists in the interpretation of IR spectra of functional groups, even for extensively studied oxides such as silica and alumina [6, 40, 41]. 

Polymer nanocomposites were processed using non-treated alumina (NT-Al Oj) and aminopropyltriethoxysilane treated alumina (APTES-Al Oj) in epoxy matrix [97-98]. The tensile fracture surface is evaluated for analyzing the strengthening and toughening mechanisms. The tensile fracture surfaces of neat epoxy and nanocomposites containing 10 phr-NT- Al O and 10 phr-APTES- Al O are shown in Figure 9.34. 

In poorly bonded NT- Al O /epoxy composites, particles are clearly visible and the crack seems to have propagated aroimd their equator. Ihe fracture surface of nanocomposites consists of hemispherical holes (A), top surface of the debonded particles (B) and particles covered by epoxy matrix (C). The crack may propagate above or below the poles of the particles through the matrix. Interfacial debonding seen in the mirror zone is not seen in the hackle zone for treated alumina-epoxy nanocomposites. Another toughening mechanism noticed in the hackle zone is particle pullout, which is seen in both NT- Al O /epoxy nanocomposites and APTES-Al Oj/epoxy nanocomposites, whereas micro-cracking is noticed only in APTES-Al Oj/epoxy nanocomposites. 

These results are preliminary, and we are not entirely sure why the EE intensity depends on a in this fashion. Optical inspection of the fracture surface indicates that alumina particles are indeed being exposed, although SEM micrographs are far less convincing, so we are still seeking measurements of the degree of interfacial failure that is occurring. Secondly, as a increases, the mechanical... 

Fig. 12. Typical tensile fracture morphology of a pure alumina fibre at high temperature (Fiber FP at 13(X) C). Fracture occurs by the coalescence of microcracks leading to a non-flat fracture surface.

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