Question

Describe the “closest approach” Adam diameter and explain how it determines metallic lattice size and bond length in a polymer

Answer 1

For a semi crystalline polymer ,for instance ,100% crystallinity is never obtained by this definition since there are large interfacial regions where some degree of disorder is present .Perfect 3D order means that the structure repeats in all directions so that by describing the structure locally the entire structure can be uniquely described .

Nomenclature

Point Lattice= An array of points in space so arranges that each point has identical surroundings .

Unit cell= a collection of 3 vectors along crystallographic axes each of which is described by a magnitute or length and an angle from the origin.These 6 parameters (3 magnitute and 3 direction) are the Lattice parameters.

There are several ways to categorize crystals .One involves the 7 crystal systems described on pp .35 of the text.The crystal systems are described in terms of the Lattice parameters .

Cubic a=b=c=g=90 deg S ,FC,BC

Tetragonal a=b a=b=g=90 deg S,BC

Orthorhombic a=b=g=90 deg S ,FC,BC,BaseC

Rhombohedral (Trigonal) a=b=c a=b=g=Not 90 deg S

Hexagonal a=b a=b=90 deg g=120 deg S

Monoclinic 1-b=90 deg S ,BaseC

Triclinic S