This preview shows page 1. Sign up to view the full content.
Unformatted text preview: with the typically lower
CNs for these structures (CN 4), can result in groups of atoms (molecules) that have
fulﬁlled their primary bond requirements without the establishment of a 3-D primary
bond network. In these materials, secondary bonds play a dominant role in determining
the engineering properties. It is important to note that the strongest and stiffest directions
in covalent solids are ones in which a continuous primary bond structure exists. In these
directions covalent solids are every bit as strong and stiff as metallic and ionic solids. It
is only in the directions in which primary bonds are absent that the properties are
controlled by secondary bonds. The directional dependence of properties in covalent
materials is utilized effectively in producing ﬁbers that are very strong along their length
direction (i.e., covalent bond direction) from polymeric materials. The high strength and
stiffness along the ﬁber axis are obtained, however, at the expense of properties in the
perpendicular directions. 2.8 MIXED BONDING | v v As mentioned previously, the type of primary bond formed in a compound depends on the
electronegativities of the atoms involved. In compounds involving more than one element,
ionic bonds are favored when the difference in electronegativities, EN, is large, and
covalent bonds are favored when EN is small. The transition from pure ionic to pure
covalent bonding is gradual, and many compounds display a bond with mixed ionic/ | e-Text Main Menu | Textbook Table of Contents 1-27-98 plm/iq 3-21-98 MP1 51 result from surface deposits of contaminants occurring in
ae occurring in some steels.
stagnant pools of electrolyte located on horizontal
position pof austenite.
g052 [V] G2 7-27060 / IRWIN / Schaffer
js 1-27-98 plm 3-21-98
sections of metal.
%RA) The change in area
planar density The number of atoms or ions centered
(expressed in percent) of a
on a crystallographic plane per unit area of the plane.
Part I Fundamentals
en fractured. 52
plastic deformation Deformation that is permanent;
ansformation, during cooling, [R] G15 7-27060 / IRWIN / Schaffer
covalentfor example, a...
View Full Document