Triple-grain junction

Dihedral angle of liquid on triple grain junction... 

Figure 8.15 Energy-dispersive X-ray spectra collected from glass pockets at triple grain junctions in two samples with additives of 6.25 wt% Y2O3-1.0wt% AI2O3 and 4.0wt% Y203-2.8wt% AUO3. The Al concentration was...

Fig. 3 A conventional scanning electron micrograph (a), a PM image (b), and a hyperspectral wavelength-shift image of the band-gap emission (c) at a triple-grain junction in polycrystalline BaTiOs. Micrograph and maps were taken at the same location.

Figure 5.34 presents various situations, from the case of a (amorphous) second phase which wets extremely well (Figs. 5.34f and 5.33c) to its absolute opposite (Fig. 5.34a), the complete separation of the second phase into the triple-grain junction. While the surface tension is accessible from wetting experiments (see Eq. (5.76)), the grain boundary tension can be determined by measuring the grooving angle of the grain boimdary trench (see Fig. 5.35). The relevant relationship follows from...

Fig. 5.33a Three copper grains, sintered at 1300 K for 8h, on the way to an ideal triple grain junction [161]. From Ref. [162].

Fig. 5.34 The morphology of an inclusion as a function of the interfacial tension between the grain phase and the phase in the triple-grain junction. It can be characterized by rnesms of the dihedral angle. This is defined by the internal angle of the tangents to the a-0 boimdaries at the point of intersection and varies between 180 and 0 (cf also Fig. 5.33c). Diagrams a to f illustrate the characteristic morphologies corresponding to angles of 180 (a), 135° (b), 90° (c), 60° (d), 30 (e) and 0° (f). Prom Ref [165].

Fig. 5.85 By cation adsorption the insulating A particles induce highly conducting boundary layers in the ionic conductor MX. In (a) the A-grain is isolated (e.g. in the triple-grain junction), and the overall effect is negligible. In (b) coherent paths are formed between the MX grains [249].

The diffusion coefficients of the process controlling superplasticity may be enhanced or retarded by the addition of impurities or solute atoms or by the addition of secondary phases, normally used as sintering aids, which distribute along the grain boundaries and triple-point junctions of the grains. 

An EDX spectrum typical of thin-film analysis in TEM/(S)TEM is shown in Eig. 4.26. It was obtained from a polycrystalline TiC/Zr02 ceramic by use of an Si(Li) detector at 100 keV primary electron energy. Eor spectrum recording the electron probe of approximately 1 nm in diameter was focused on the triple junction between the grains in the STEM mode (Eig. 4.26a). Besides the elements expected for the material under investigation, viz. Ti and Zr, Si, Ee, and Co were also detected, hinting at the presence of a (Ee, Co) silicide as an impurity. Eor ceramic materials it is known that... 

Solution. As shown in Fig. 15.17, for side grains and corner grains the number of triple junctions is one less than the number of neighboring grains, TV. For the side grains, the inclination of the boundary normal changes by 7r from one end to the other ... 

Microstructures are generally too complex for exact models. In a polycrystalline microstructure, grain-boundary tractions will be distributed with respect to an applied load. Microstructures of porous bodies include isolated pores as well as pores attached to grain boundaries and triple junctions. Nevertheless, there are several simple representative geometries that illustrate general coupled phenomena and serve as good models for subsets of more complex structures. 

TEM micrograph of a Cu-Al203 nanocomposite. The Cu particles are elongated and located at grain boundaries and triple junctions. 

---