Crystal grains

The density of dislocations is usually stated in terms of the number of dislocation lines intersecting unit area in the crystal it ranges from 10 cm for good crystals to 10 cm" in cold-worked metals. Thus, dislocations are separated by 10 -10 A, or every crystal grain larger than about 100 A will have dislocations on its surface one surface atom in a thousand is apt to be near a dislocation. By elastic theory, the increased potential energy of the lattice near... 

A separate study was the improvement of magnetic permeability in soft alloys such as are used in transformers and motors by lining up the orientations of individual crystal grains, also known as a preferred orientation this became an important subspeciality in the design of transformer laminations made of dilute Fe-Si alloys, introduced more than 100 years ago and still widely used. 

Grain growth and other microstructural changes. When a deformed metal is heated, it will recrysiallise, that is to say, a new population of crystal grains will... 

When particle impacts with a solid surface, the atoms of the surface layer undergo crystal lattice deformation, and then form an atom pileup on the outlet of the impacted region. With the increase of the collision time, more craters present on the solid surface, and amorphous transition of silicon and a few crystal grains can be found in the subsurface. 

The macrostructure of the boron nitride obtained here is porous with pores 2 pm in diameter. There is no evidence for microporosity and the BET surface area 1s 35 m2 g-1. Transmission electron micrographs (Figure 4) show regions of well developed crystallinity. The crystalling grains are 5—10 nm on a side and 30-40 nm long. The BN (002) lattice fringes are clearly visible. 

The question is When is it epitaxy Does the deposit have to have the same unit cell, or does it just have to be commensurate, in register with the substrate structure What size single crystal grains need to form to call it epitaxy Is it only nonepitaxial when the deposit is incommensurate with the substrate, or when it is amorphous ... 

In comparison to skeletal nickel, skeletal copper has a significantly larger crystallite size of about 10-100 nm [32,46,92,96,100,101], Fasman and coworkers [46,100,101] examined the crystal structure more closely and found that it consisted of copper crystals that had agglomerated into granules or precipitated onto oxides. The copper crystal grains and subgrains were of about 10-13 nm in size, while the copper agglomerates were 50-80 nm. 

Lateral and vertical growth rate of the crystal grains. 

As sketched for spheres and films, the processes involve either a totally reacted external region and a totally umeacted core or a spatially uniform solid in which the transformation occurs microscopically (perhaps in each single crystal grain) such that macroscopicaUy the solid appears to be spatially uniform at any degree of conversion. 

Possible solid composition profiles of a partially reacted solid film or pellet are shown in Figure 9-9. It is evident that there are multiple possible fluid concentration profiles within the fikn or pellet such as within pores (where diSusivities are high), down grain boundaries where some solutes have high diffusivities, and within single crystal grains where diSiision... 

Bubble Nucleation in a Liquid Phase The above classical nucleation theory can be easily extended to melt nucleation in another melt. It can also be extended to melt nucleation in a crystal but with one exception. Crystal grains are usually small with surfaces or grain boundaries. Melt nucleation in crystals most likely starts on the surface or grain boundaries, which is similar to heterogeneous nucleation discussed below. Homogeneous nucleation of bubbles in a melt can be treated similarly using the above procedures. Because of special property of gases, the equations are different from those for the nucleation of a condensed phase, and are hence summarized below for convenience. 

Fig. 5.4 Grain boundaries in a tungsten tip. One of them runs nearly parallel to the tip axis across the central section of the tip, as indicated by black arrows. One is near the upper left-hand corner, which is more difficult to visualize. The lattice match of the crystal grains is excellent. The tip has been carefully annealed, thus the grain boundaries are thermally well equilibrated.

---