Alumina grain boundary

Susnitzky, D.W. and Carter, C.B., (1990), Structure of alumina grain boundaries prepared with and without a thin amorphous intergranular film , J. Am. Ceram. Soc., 73 (8), 2485-2493. 

The addition of yttrium and other oversized isovalent cations to alumina has also been shown to enhance creep strength (Figure 5-3) (French et al., 1994). The oversized ions segregate to the alumina grain boundaries (Figure 5-4). One... 

The effect of the addition of zirconia on the high-temperature mechanical behaviour is to delay the onset of plasticity to 1100°C and to decrease the strain rates in creep (Pysher and Tressler, 1992 Lavaste et al., 1995). The mechanisms proposed have been the pinning of the grain boundaries by the intergranular zirconia particles and more recently the modification of the AP+ diffusion rates at the alumina/alumina grain boundaries by the presence of Zr + and Y + ions. However, these mechanisms are less... 

A similar strategy was used by Lim and co-workers [27-28] to synthesise CNTs/alumina composites to investigate the effect of CNT composition and distribution on the tribological properties of the composite. A significant improvement was obtained when CNTs were localised at alumina grain boundaries [28]. The resulting properties will be discussed later in this review. 

One of the first studies on SWCNT/ceramic composites was reported by Zhan et al. [39] who used the SPS technique to produce fully dense alumina composites containing 10 vol% SWCNTs. By using the SPS method, they achieved almost 100% relative density as well as incorporation of undamaged CNTs at the alumina grain boundaries, resulting in an impressive improvement of the fracture toughness as discussed in the next paragraph. 

Fracture toughness of the obtained CNFs/alumina composites increased with a decrease in average alumina grain size [5]. This result was explained by bridging and/or pull-out of CNFs bended along alumina grain boundaries. 

Marker experiments made with lead to the determination of oxygen diffusion coefficients via alumina grain boundaries and via the oxide bulk. Taking into consideration the plots of In [ 0] = f(x), the first part of the curve corresponds to the apparent diffusion of oxygen. From the three diffusion regimes, the B regime is usually chosen for the study of intergranular diffusion... 

The diffusion experiments performed on both synthetic and thermally grown alumina have shown that aluminium diffusion predominates over oxygen diffusion in the alumina grain boundaries, but the values calculated in the case of synthetic alumina are largely different from the values determined in thermally grown scales. The chemistry (especially the impurity level or dopant concentration evolution) and/or microstructure (grain size, transient alumina formation, etc.) of the two types of alumina could explain these differences [99,100], thus it appears very difficult to compare diffusion experiments on synthetic and thermally grown alumina. 

Illustration of the segregation of yttrium and zirconium at the alumina grain boundaries and at the metal-oxide interface in the case of an FeCrAI-Y-Zr alloy oxidised for 50 h at 1100°C (a) bright field image (b) EDX analyses of the indicated zones (1 interior of the grain, 2 grain boundary, 3 triple point at the metal-oxide interface). 

The segregation of RE at alumina grain boundaries leads to the decrease of the oxygen diffusion coefficient, as indicated in Fig. 10.13, even if the results appear sometimes contradictory. Once more, the comparison of oxygen... 

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