Materials Science Glossary - N

natural aging. For precipitation hardening, aging at room temperature (see aging).

network polymer. A polymer produced from multifunctional monomers having three or more active covalent bonds, resulting in the formation of three-dimensional molecules.

nodular iron. See ductile iron.

noncrystalline. The solid state wherein there is no long-range atomic order. Sometimes the terms amorphous, glassy, and vitreous are used synonymously.

nonferrous alloy. A metal alloy of which iron is not the prime constituent.

nonsteady-state diffusion. The diffusion condition for which there is some net accumulation or depletion of diffusing species. The diffusion flux is dependent on time.

normalizing. For ferrous alloys, austenitizing above the upper critical temperature, then cooling in air. The objective of this heat treatment is to enhance toughness by refining the grain size.

n-type semiconductor. A semiconductor for which the predominant charge carriers responsible for electrical conduction are electrons. Normally, donor impurity atoms give rise to the excess electrons.

nucleation. The initial stage in a phase transformation. It is evidenced by the formation of small particles (nuclei) of the new phase that are capable of growing.