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Macroscopic
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Visible at magnifications to 25x.
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Macrostructure
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The structure of metals as
revealed by macroscopic examination of the etched surface of a
polished specimen.
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Magnetite
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Naturally occurring magnetic oxide
of iron (Fe3O4).
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Martensite
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A generic term for microstructures formed
by diffusionless phase transformation in which the parent and
product phases have a specific crystallographic relationship.
Martensite is characterized by an acicular pattern in the
microstructure in both ferrous and nonferrous alloys. In alloys
where the solute atoms occupy interstitial positions in the
martensitic lattice (such as carbon in iron), the structure is
hard and highly strained; but where the solute atoms occupy
substitutional positions (such as nickel in iron), the martensite
is soft and ductile. The amount of high-temperature phase that
transforms to martensite on cooling depends to a large extent on
the lowest temperature attained, there being a rather distinct
beginning temperature (Ms) and a temperature at which the
transformation is essentially complete (Mf).
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mechanical plating
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Plating wherein fine metal powders
are peened onto the work by tumbling or other means.
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metal dusting
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Accelerated deterioration of metals in
carbonaceous gases at elevated temperatures to form a dust-like
corrosion product; a unique form of high temperature corrosion which forms a
dust-like corrosion product and sometimes develops
hemispherical pits on a susceptible metal surface;
simultaneous carburization is generally observed.
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A galvanic cell caused by a difference in metal ion
concentration at two locations on the same metal surface.
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metallic glass
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An alloy having an amorphous or glassy
structure. See also amorphous solid.
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metallizing
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(1) The application of an electrically
conductive metallic layer to the surface of nonconductors. (2)
The application of metallic coatings by nonelectrolytic
procedures such us spraying of molten metal and deposition from
the vapor phase.
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Perforation of material in outer space resulting from meteor strikes.
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microbial corrosion
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See biological corrosion.
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microscopic
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Visible at magnifications above 25x.
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microstructure
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The structure of a prepared surface of
a metal as revealed by a microscope at a magnification exceeding
25x.
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mill scale
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The heavy oxide layer formed during hot
fabrication or heat treatment of metals.
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mixed potential
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The potential of a specimen (or
specimens in a galvanic couple) when two or more
electrochemical reactions are occurring. Also called galvanic
couple potential.
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molal solution
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Concentration of a solution expressed
in moles of solute divided by 1000 g of solvent.
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molar solution
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Aqueous solution that contains 1 mole
(gram-molecular weight) of solute in 1 L of the solution.
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mole
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One mole is the mass numerically equal (in grams)
to the relative molecular mass of a substance. It is the amount
of substance of a system that contains as many elementary
units (6.023 exp23) as there are atoms of carbon in 0.012 kg of
the pure nuclide C12; the elementary unit must be specified and
may be an atom, molecule, ion, electron, photon, or even a
specified group of such units.
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monomer
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A molecule usually an organic compound, having
the ability to join with a number of identical molecules to form
a polymer.
N
