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radiation
damage
A general term for the alteration of properties of a
material arising from exposure to ionizing radiation (penetrating
radiation), such as x-rays, gamma rays. neutrons, heavy-particle radiation,
or fission fragments in nuclear fuel material.
rare
earth metal
One of the group of l5 chemically similar metals with
atomic numbers 57 through 7l, commonly referred to as the lanthanides.
reactive
metal
A metal that readily combines with oxygen at elevated
temperatures to form very stable oxides, for example, titanium, zirconium,
and beryllium. Reactive metals may also become embrittled by the
interstitial absorption of oxygen, hydrogen, and nitrogen.
recrystallization
(1) Formation of a new, strain free grain structure
from that existing in cold worked metal, usually accomplished by heating.
(2) The change from one crystal structure to another, as occurs on heating
or cooling through a critical temperature.
redox
potential
The potential of a reversible
oxidation-reduction electrode measured with respect to a reference electrode,
corrected to the hydrogen electrode, in a given electrolyte.
reducing
agent
A compound that causes reduction, thereby
itself becoming oxidized.
reduction
A reaction in which there is a decrease in valence
resulting from a gain in electrons. Contrast with oxidation.
reference
electrode
A nonpolarizable electrode with a known and
highly reproducible potential used for potentiometric and
voltammetric analyses. See also calomel electrode.
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refractory
metal
A metal having an extremely high melting point, for
example, tungsten, molybdenum, tantalum, niobium, chromium, vanadium, and
rhenium. In the broad sense, this term refers to metals having melting
points above the range for iron, cobalt, and nickel.
relative
humidity
The ratio, expressed as a percentage, of the amount of
water vapor present in a given volume of air at a given temperature to the
amount required to saturate the air at that temperature.
residual
stress
Stresses that remain within a body as a result of plastic
deformation.
resistance
The opposition that a device or material offers to the
flow of direct current, equal to the voltage drop across the element
divided by the current through the element. Also called electrical
resistance.
resistivity
See electrical resistivity.
rest
potential
See corrosion potential and open-circuit
potential.
ringworm
corrosion
Localized corrosion frequently observed in oilwell
tubing in which a circumfrential attack is observed near a region of metal
"upset".
riser
(1) That section of pipeline extending from the ocean
floor up the platform. Also, the vertical tube in a steam generator
convection bank that circulates water and steam upward. (2) A reservoir of
molten metal connected to a casting to provide additional metal to the
casting, required as the result of shrinkage before and during
solidification.
rust
A visible corrosion product consisting of hydrated
oxides of iron. Applied only to ferrous alloys. See also white rust.
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