Chapter 4

Question 1

Diffusion

Answer 1

A process of mass transport that involves the movement of one atomic species into another

Question 2

Diffusion bonding

Answer 2

The process by which two pieces are bonded or joined together by atomic mixing at the interface accomplished by solid state diffusion under conditions of high temperature and pressure

Question 3

Diffusion coefficient

Answer 3

the constant in the equation relating mass flux per unit area to the concentration gradient. It obeys an Arrhenius-type equation and as such is strongly teperature dependent. The diffusion coefficient describes the ease of atomic or ionic motion in the solid state

Question 4

Effective penetration distatance

Answer 4

the distance at which the concentration of a solute in a solid solution reaches a value of approximately the average of the surface concentration and the initial bulk concentration.

Question 5

Fick’s first law

Answer 5

The equation which states that the mass flux per unit area of a diffusing species under steady-state conditions is proportional to the concentration gradient.

Question 6

Fick’s second law

Answer 6

The equation which states that for non-steady-state conditions the rate of change of concentration with respect to time at a given location is proportional to the second derivative of concentration with respect to position.

Question 7

Frenkel Defect

Answer 7

type of defect in an ionic solid consisting of a vacancy/interstitial pair of the same ionic species. Due to size considerations, most Frenkel defects involve cations rather than anions.

Question 8

Hume-Rothery’s rules

Answer 8

set of empirical rules for the formation of substitutional solid solutions. They incorporate relative sizes, bond character, and electronegativity of the atomic species being considered.

Question 9

Impurity

Answer 9

s any atom or ion species that differs from the host or solvent species. While considered to be defects, impurities may confer desirable properties on the solid solution.

Question 10

Impurity Diffusion

Answer 10

is the diffusion of an impurity species implying very low concentrations within the solvent or host material. The low concentration of solute associated with impurities permits the assumption that the diffusion coefficient is independent of composition.

Question 11

Interstitial

Answer 11

is a point defect consisting of an atom or ion that is located in the interstices of the structure under consideration; Interstitials may be either the same or a different species than the solvent.

Question 12

Interstitial solid solutions

Answer 12

are solid solutions in which atoms or ions of a foreign species are located in the interstial positions

Question 13

Point Defect

Answer 13

“Mistake” in the material that involves a single atom, ion, lattice site, or interstitial position. For example, if an atom is missing at a regular lattice site, a point defect is said to have been formed.

Question 14

Schottky defect

Answer 14

is a small cation and anion vacancy cluster that is formed in ionic solids. The cation/anion ratio in these clusters is adjusted to maintain electroneutrality.

Question 15

Self-Diffusion

Answer 15

the mechanism by which a species diffuses in itself.

Question 16

Solute

Answer 16

an atom of ion species that is dissolved in a host or solvent

Question 17

Solvent

Answer 17

the host species for a solute

Question 18

Substitutional solid solution

Answer 18

is a solution formed by substituting species B directly for species A on the lattice sites normally occupied by A. The solution so formed is said to be a substitutional solid solution of B in A.

Question 19

Vacancy

Answer 19

A missing atom or ion at a lattice site that would normally be occupied.