Review of Crystal Physics

Review of Crystal Physics

Learning Objectives

While reading and after studying this chapter, you will be able to:

● Understand the difference between crystalline and amorphous solids.

● Review the various terms and definitions associated with crystallography.

● Know the names and definitions of seven crystal systems.

● Develop the concept of unit cells and sketch the unit cells of the SC, BCC, FCC, and HCP structures.

● Appreciate how atoms are packed with- in planes and how the differing crystal systems are produced by the stacking of planes of atoms.

● Understand Miller notation and visual- ize crystal directions and planes from the Miller indices.

● Identify the various crystal imperfec- tions and their significances.

● Describe the effect of grain size and familiarize with ASTM grain size number.

UNIT-0

Review of Crystal Physics

Optimist: The glass is half full.

Pessimist: The glass is half empty.

Re-engineering consultant: That glass is twice as large as it needs to be.

- The Economic Press, US.

INTRODUCTION

The matter is usually found to exist in solids and fluids (i.e., liquids and gases). All these materials consist of atoms and molecules. We know some solids are brittle, some are ductile, some are malleable, some are strong, some are weak, some are good conductors of heat and electricity, some are bad conductors of heat and electricity, some are magnetic, some are non-magnetic and so on. The reasons for these different properties of the solids are due to their structure. The behaviour of the solid materials is closely related to the structure of the materials. Thus the study of crystal geometry helps us understand the diverse behaviour of solids in their mechanical, metallurgical, electrical, magnetic and optical properties.

The solids can be either crystalline or noncrystalline. The crystallography is the science of study of the geometric form and other physical properties of crystalline solids by using X-rays, electron beams and neutron beams etc. In order to appreciate and study the crystalline solid state, a knowledge of this science is essential.

This unit reviews the elementary concepts of crystal geometry, structure of important crystalline solids, imperfections in crystals followed by a brief about grain size.