Thermoplastic polymers have secondary bonds between

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: o high electrical conductivities and ductile behavior for most metals. Regardless of the type of primary bond formed between two atoms or ions, there is a competition between the atomic forces of attraction and repulsion. The separation distance for which the total force between the atoms or ions is zero is defined to be the equilibrium separation distance, or bond length. The bond-energy curve, which is the integral of the bond-force curve, may be used to explain several important macroscopic properties of a solid, including the bond length, the modulus (or stiffness) of the material, the bond strength, and the linear coefficient of thermal expansion. The coordination number (CN) of an atom represents its number of nearest neighbors. In covalently bonded materials CN is determined by the valence of the atoms involved. The CN in ionic and metallic solids is determined from simple geometrical considerations (i.e., the radius ratio). Secondary bonds occur as a result of the formation of an electric dipole within certain atoms or molecules. The dipole can be temporary, induced, or permanent. Some solids have primary bonds with mixed properties. For example, many ceramics exhibit mixed ionic and covalent characteristics. Other materials display properties typical of a mixture of primary and secondary bonding. Thermoplastic polymers have secondary bonds between chains, and thermosetting polymers have a three-dimensional covalent bond network. As a result, thermoplastic polymers can be repeatedly reheated and reshaped, while thermosetting polymers retain their original shape and degrade rather than melt when they are reheated. KEY TERMS ........................................................................................................................................................................... amorphous material coordination number ground state polymers Arrhenius equation core electrons hydrogen bond quantum number atomic scale structure coulombic force ionic bond short-range order bond angles covale...
View Full Document

This note was uploaded on 02/25/2013 for the course PHYS 2202 taught by Professor Sowell during the Spring '10 term at Georgia Tech.

Ask a homework question - tutors are online