Rules of Grain Growth
Grain growth has long been studied primarily by the examination of sectioned, polished and etched samples under the optical microscope. Although such methods enabled the collection of a great deal of empirical evidence, particular with regard to factors such as temperature or composition, the lack of crystallographic information limited the development of an understanding of the fundamental physics. Nevertheless, the following became well-established features of grain growth:
- Grain growth occurs by the movement of grain boundaries and not by coalescence (i.e. like water droplets)
- Boundary movement is discontinuous and the direction of motion may change suddenly.
- One grain may grow into another grain whilst being consumed from the other side
- The rate of consumption often increases when the grain is nearly consumed
- A curved boundary typically migrates towards its centre of curvature
- When grain boundaries in a single phase meet at angles other than 120 degrees, the grain included by the more acute angle will be consumed so that the angles approach 120 degrees.
Read more about this topic: Grain Growth
Famous quotes containing the words rules of, rules, grain and/or growth:
“There are ... two minimum conditions necessary and sufficient for the existence of a legal system. On the one hand those rules of behavior which are valid according to the system’s ultimate criteria of validity must be generally obeyed, and on the other hand, its rules of recognition specifying the criteria of legal validity and its rules of change and adjudication must be effectively accepted as common public standards of official behavior by its officials.”
—H.L.A. (Herbert Lionel Adolphus)
“The duce of any other rule have I to govern myself by in this affair—and if I had one ... I would twist it and tear it to pieces, and throw it into the fire when I had done—Am I warm? I am, and the cause demands it—a pretty story! is a man to follow rules—or rules to follow him?”
—Laurence Sterne (1713–1768)
“A true politeness does not result from any hasty and artificial polishing, it is true, but grows naturally in characters of the right grain and quality, through a long fronting of men and events, and rubbing on good and bad fortune.”
—Henry David Thoreau (1817–1862)
“But parents can be understanding and accept the more difficult stages as necessary times of growth for the child. Parents can appreciate the fact that these phases are not easy for the child to live through either; rapid growth times are hard on a child. Perhaps it’s a small comfort to know that the harder-to-live-with stages do alternate with the calmer times,so parents can count on getting periodic breaks.”
—Saf Lerman (20th century)