Noncrystalline Amorphous Structures Prabhjot Singh Noncrystalline Amorphous Structures

Noncrystalline (Amorphous) Structures §Prabhjot Singh

Noncrystalline (Amorphous) Structures § Many materials are noncrystalline § Water and air have noncrystalline structures § A metal loses its crystalline structure when melted § Important engineering materials have noncrystalline forms in their solid state § Glass § Many plastics § Rubber © 2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Features of Noncrystalline Structures § Two features differentiate noncrystalline (amorphous) from crystalline materials: 1. Absence of long‑range order in molecular structure 2. Differences in melting and thermal expansion characteristics © 2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Arrange? ? ? Noncrystalline (Amorphous) Structures © 2007 John Wiley & Sons, Inc. M

Crystalline versus Noncrystalline Figure 2. 14 Difference in structure between: (a) crystalline and (b) noncrystalline materials. The crystal structure is regular, repeating, and denser; the noncrystalline structure is less tightly packed and random. © 2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Volumetric Effects Figure 2. 15 Characteristic change in volume for a pure metal (a crystalline structure), compared to the same volumetric changes in glass (a noncrystalline structure). © 2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e