Question

how will you differ HCP and CCP?

Answer 1

The face centered cubic and hexagonal close packed structures both have a packing factor of 0.74, consist of closely packed planes of atoms, and have a coordination number of 12. The difference between the fcc and hcp is the stacking sequence. The hcp layers cycle among the two equivalent shifted positions whereas the fcc layers cycle between three positions. As can be seen in the image, the hcp structure contains only two types of planes with an alternating ABAB arrangement. Notice how the atoms of the third plane are in exactly the same position as the atoms in the first plane. However, the fcc structure contains three types of planes with a ABCABC arrangement. Notice how the atoms in rows A and C are no longer aligned. Remember that cubic lattice structures allow slippage to occur more easily than non-cubic lattices, so hcp metals are not as ductile as the fcc metals.



The table below shows the stable room temperature crystal structures for several elemental metals.

Metal

Crystal Structure

Atomic Radius (nm)

Aluminum

FCC

0.1431

Cadmium

HCP

0.1490

Chromium

BCC

0.1249

Cobalt

HCP

0.1253

Copper

FCC

0.1278

Gold

FCC

0.1442

Iron (Alpha)

BCC

0.1241

Lead

FCC

0.1750

Magnesium

HCP

0.1599

Molybdenum

BCC

0.1363

Nickel

FCC

0.1246

Platinum

FCC

0.1387

Silver

FCC

0.1445

Tantalum

BCC

0.1430

Titanium (Alpha)

HCP

0.1445

Tungsten

BCC

0.1371

Zinc

HCP

0.1332

A nanometer (nm) equals 10-9 meter or 10 Angstrom units

Answer 2

The atom binding proceses in the solid substances has different types, according to their atom packing method differences.

HCP:In the HCP package or the hexagonal closest packed ,the atom distribution is described as the a-b-a-b-a-b.

On the other hand,

CCP: In the CCP package or the cubic closed packing,the atom distribution is described as individual cubic lattices.