Fundamentals of Materials Science and Engineering: An Integrated Approach, 3e

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5.6 Specification of Composition • 137

Screw dislocation

(ramp continues

to spiral upward)

Branch

Chain

ends

Loose

chain

Noncrystalline

region

Dangling

chain

Crystallite

boundary

Edge dislocation (extra plane)

Vacancy

Impurity

Figure 5.7

Schematic

representation of

defects in polymer

crystallites.

contains two hypothetical atoms denoted by 1 and 2, the concentration of 1 in wt%,

C 1 , is defined as

C 1 =

m 1

m 1 +m 2

× 100 (5.6)

Computation of

weight percent (for a

two-element alloy)

wherem 1 andm 2 represent the weight (or mass) of elements 1 and 2, respectively.

The concentration of 2 would be computed in an analogous manner.

atom percent The basis foratom percent(at%) calculations is the number of moles of an

element in relation to the total moles of the elements in the alloy. The number of

moles in some specified mass of a hypothetical element 1,nm 1 , may be computed as

follows:

nm 1 =

m 1 ′

A 1

(5.7)

Here,m′ 1 andA 1 denote the mass (in grams) and atomic weight, respectively, for

element 1.

Concentration in terms of atom percent of element 1 in an alloy containing 1

and 2 atoms,C′ 1 is defined by^4

C 1 ′=

nm 1

nm 1 +nm 2

× 100 (5.8)

Computation of

atom percent (for a

two-element alloy)

In like manner, the atom percent of 2 may be determined.

(^4) In order to avoid confusion in notations and symbols used in this section, we should point
out that the prime (as inC′ 1 andm 1 ′) is used to designate both composition, in atom percent,
and mass of material in units of grams.