CHAPTER 5

IMPERFECTIONS IN SOLIDS

LEARNING OBJECTIVES

  1. Describe both vacancy and self-interstitial crystalline defects.
  1. Given the density and atomic weight for some material, as well as Avogadro's number, compute the number of atomic sites per cubic meter.
  1. For some material, given the number of atomic sites per cubic meter, the energy required for vacancy formation, and, in addition, the value for the gas constant, compute the equilibrium number of vacancies at some specified temperature.
  1. Name and describe eight different ionic point defects that are found in ceramic compounds (including Schottky and Frenkel defects).
  1. Define the term electroneutrality, and note what part it plays in the formation of ionic point defects in ceramic materials.
  1. Define stoichiometric, and cite one example of a nonstoichiometric material.
  1. Note two ways in which an ionic compound can be made to be nonstoichiometric.
  1. (a) For some ceramic material, given the number of atomic sites per cubic meter, the energy required for the formation of Frenkel defects, and, in addition, the value for the gas constant, compute the equilibrium number of Frenkel defects at some specified temperature.

(b) Carry out the same computation for Schottky defects.

  1. (a) Given a substitutional impurity ion, determine whether or not it will render an ionic compound nonstoichiometric.

(b) If the host material does become nonstoichiometric, ascertain what kind(s) of defect(s) form, and how many form for every substitutional impurity ion.

  1. Define what is meant by the term alloy.
  1. Name the two types of solid solutions, and provide a brief written definition and/or schematic diagram of each.
  1. State the criteria for the formation of each of substitutional and interstitial solid solutions.
  1. Given the atomic radii of host and impurity atoms, as well as their crystal structures, electronegativities, and valences, determine if solid solutions that form are

(a) substitutional with appreciable solubility,

(b) substitutional with limited solubility, or

(c) interstitial.

  1. Note three requirements that must be met in order for there to be significant solid solubility of one ionic compound in another.
  1. Given the masses and atomic weights of two or more elements in a metal alloy, compute the weight percent and atomic percent of each element.
  1. (a) Given the composition (in weight percent) and atomic weights for two elements in an alloy, determine the composition in atom percent.

(b) Make a composition conversion from atom percent to weight percent.

  1. Given the atomic weights and densities for two elements in an alloy:

(a)Determine the average density when the composition is specified in weight percent.

(b)Determine the average density when the composition is specified in atom percent.

  1. Given the atomic weight for each of two elements in an alloy:

(a)Determine the average atomic weight when the composition is specified in weight percent.

(b)Determine the average atomic weight when the composition is specified in atom percent.

  1. For each of edge, screw, and mixed dislocations:

(a)describe and make a drawing of the dislocation;

(b)note the location of the dislocation line; and

(c)indicate the direction along which the dislocation line extends.

  1. (a) Describe the atomic structure within the vicinity of a grain boundary.

(b) Make a distinction between high- and small-angle grain boundaries.

(c) Explain how a small-angle tilt boundary is formed by an array of edge dislocations.

  1. Describe the arrangement of atoms in the vicinity of a twin boundary.
  1. Note the role of surface defects in the operation of automobile catalytic converters, which reduce polluting exhaust emissions.
  1. Define the terms microstructure and microscopy.
  1. Explain what preparations are necessary for observation of the grain structure of a polycrystalline material with an optical microscope.
  1. Name and briefly describe the operation of each of the two types of electron microscopes.
  1. In general terms briefly explain how scanning probe microscopes operate.
  1. Given a photomicrograph of a polycrystalline material, as well as the magnification, determine the grain size using intercept and ASTM methods.