macro cell corrosion—corrosion of a metal embedded in porous media (e.g., concrete or soil) caused by concentration or galvanic cells that exist on a scale at least as large as the smallest major dimension of the corroding item (e.g., the diameter of a bar or pipe).
malleable cast iron—white cast iron that is thermally treated to convert most or all of the cementite to graphite (temper carbon).
martensite—a hard,body-centered cubic phase of iron supersaturated with carbon, usually produced by rapid cooling.
martensitic steel—steel in which a micro structure of martensite can be attained by quenching at a cooling rate fast enough to avoid the formation of other micro structures.
mastic—(1) aromatic resin of the mastic tree,commonly used in lacquers and varnishes. (2)a material of relatively viscous, paste-like consistency that can be poured when heated but often requires mechanical manipulation (e.g., using a trowel)to apply, which dries or cures to form a thick protective coating. (Mastics usually contain fillers, such as powdered lime or graded mineral aggregate, to produce the desired consistency.)
metal dusting—accelerated deterioration of a metal or alloy exposed to a carbonaceous or nitrogenous gas at elevated temperatures that forms a dust-like corrosion product.
metallizing—the coating ofa surface with a thin metal layer by thermal spraying, hot dipping, or vacuum deposition.
microbiologically influenced corrosion—corrosion affected by the presence or activity,or both, of microorganisms.
mill scale—the oxide layer formed during hot fabrication or heat treatment of metals.
mist coat—a thin tack coat, applied as a mist of spray, used to improve adhesion of a new coat to an existing partially cured coat or to displace air in a porous substrate.
mixed potential—a potential resulting from two or more electro-chemical reactions occurring simultaneously on one metal surface.
modulus of elasticity—a measure of the stiffness or rigidity of a material. It is actually the ratio of stress to strain in the elastic region of a material if determined by a tension or compression test. [also called Young’s Modulus or coefficient of elasticity]
mud zone—that portion of a structure that is located below the interface of a water body with its respective sea-, lake-, or riverbed and is covered by mostly solid material.