|
partial annealing
An imprecise term used to denote a treatment given cold-worked material
to reduce its strength to a controlled level or to effect stress
relief. To be meaningful, the type of material, the degree of cold
work, and the time-temperature schedule must be stated.
parting
The selective attack of one or more components of a solid solution
alloy; eg. dezincification, dealumination etc. See dealloying.
parts per billion
A measure of proportion by weight, equivalent to one unit weight
of a material per billion (109) unit weights of compound.
One part per billion is equivalent to 1 mg/kg.
parts per million
A measure of proportion by weight, equivalent to one unit weight
of a material per million (10sup>6) unit weights of compound.
One part per million is equivalent to l mg/g
passivation
(1) A reduction of the anodic reaction rate of an electrode involved
in corrosion. (2) The process in metal corrosion by which metals
become passive. (3) The changing of a chemically active surface
of a metal to a much less reactive state. Contrast with activation.
passivator
A type of inhibitor that appreciably changes the potential
of u metal to a more noble (positive) value.
passive
(1) A metal corroding under the control of a surface reaction product.
(2) The state of the metal surface characterized by low corrosion
rates in a potential region that is strongly oxidizing for the metal.
(3) The state of a metal when its behavior is much more noble than
its position in the EMF series would predict. This is a surface
phenomena.
passive-active cell
(1) A cell, the emf of which is due to the potential difference
between a metal in an active state and the same metal in a passive
state. (2) A corrosion cell in which the anode is a metal
in the active state and the cathode is the same metal
in the passive state.
passivity
A condition in which a piece of metal, because of an impervious
covering of oxide or other compound, has a potential much
more positive than that at the metal in the active state.
patina
The coating, usually green, that forms on the surface of metals
such as copper and copper alloys exposed to the atmosphere. Also
used to describe the appearance of a weathered surface of any metal.
pearlite
A metastable lamellar aggregate of ferrite and cementite
resulting from the transformation of austenite at temperatures
above the bainite range.
phosphating
Forming an adherent phosphate coating on a metal by immersion in
a suitable aqueous phosphate solution. Also called phosphatizing.
See also conversion coating.
pH
A measure of the acidity or alkalinity of a solution; The negative
logarithm of the hydrogen-ion activity; it denotes the degree of
acidity or basicity of a solution. At 25 ºC (77 ºF), 7.0
is the neutral value. Decreasing values below 7.0 indicate increasing
acidity; increasing values above 7.0, increasing basicity.
physical vapor deposition
A coating process whereby the cleaned and masked component to be
coated is heated and rotated on a spindle above the streaming vapor
generated by melting and evaporating a coating material source bar
with a focused electron beam in an evacuated chamber.
physisorption
The binding of an adsorbate to the surface of a solid by forces
whose energy levels approximate those of condensation. Contrast
with chemisorption.
pickle
A solution or process used to loosen or remove corrosion products
such as scale or tarnish.
pickling
Removing surface oxides from metals by chemical or electrochemical
reaction.
pitting
Localized corrosion of a metal surface, confined to a point
or small area, that takes the form of cavities or pits.
pitting factor
Ratio of the depth of the deepest pit resulting from corrosion divided
by the average penetration as calculated from weight loss.
plane strain
The stress condition in linear elastic fracture mechanics in
which there is zero strain in a direction normal to both the axis
of applied tensile stress and the direction of crack growth (that
is, parallel to the crack front); most nearly achieved in loading
thick plates along a direction parallel to the plate surface. Under
plane-strain conditions, the plane of fracture instability is normal
to the axis of the principal tensile stress.
plane stress
The stress condition in linear elastic fracture mechanics in
which the stress in the thickness direction is zero; most nearly
achieved in loading very thin sheet along a direction parallel to
the surface of the sheet. Under plane-stress conditions, the plane
of fracture instability is inclined 45º to the axis of the
principal tensile stress.
plasma spraying
A thermal spraying process in which the coating material
is melted with heat from a plasma torch that generates a nontransferred
arc: molten coating material is propelled against the base metal
by the hot, ionized gas issuing from the torch.
plastic deformation
The permanent (inelastic) distortion of metals under applied stresses
that strain the material beyond its elastic limit.
|
plasticity
The property that enables a material to undergo permanent deformation
without rupture.
polarization
(1) The change from the open-circuit electrode potential as the result
of the passage of current. (2) A change in the potential of
an electrode during electrolysis, such that the potential of an anode
becomes more noble, and that of a cathode more active,
than their respective reversible potentials. Often accomplished by
formation of a film on the electrode surface.
polarization admittance
The reciprocal of polarization resistance (di/dE).
polarization curve
A plot of r urrent density versus electrode potential for
a specific electrode-electrolyte combination.
polarization resistance
The slope (dE/di) at the corrosion potential of a potential
(E)/current density (i) curve. Also used to describe the method of
measuring corrosion rates using this slope.
polyester
Resin formed by condensation of polybasic and monobasic acids with
polyhydric alcohols.
polymer
A chain of organic molecules produced by the joining of primary units
called monomers.
potential
Any of various functions from which intensity or velocity at any point
in a field may be calculated. The driving influence of an electrochemical
reaction. See also active potential, chemical potential, corrosion
potential, critical pitting potential, decomposition potential, electrochemical
potential, electrode potential, electrokinetic potential, equilibrium
(reversible) potential, free corrosion potential, noble potential,
open-circuit potential, protective potential, redox potential, and
standard electrode potential.
potential-pH diagram
See Pourbaix (potential-pH) diagram.
potentiodynamic (potentiokinetic)
The technique for varying the potential of an electrode in
a continuous manner at a preset rate.
potentiostat
An instrument for automatically maintaining an electrode in an electrolyte
at a constant potential or controlled potentials with respect to a
suitable reference electrode.
potentiostatic
The technique for maintaining a constant electrode potential.
poultice corrosion
A term used in the automotive industry to describe the corrosion of
vehicle body parts due to the collection of road salts and debris
on ledges and in pockets that are kept moist by weather and washing.
Also called deposit corrosion or attack.
Pourbaix (potential-pH) diagram
A plot of the redox potential of a corroding system versus
the pH of the system, compiled using thermodynamic data and the Nernst
equation. The diagram shows regions within which the metal itself
or some of its compounds are stable.
powder metallurgy
The art of producing metal powders and utilizing metal powders for
production of massive materials and shaped objects.
precious metal
One of the relatively scarce and valuable metals: gold, silver, and
the platinum-group metals. Also called noble metal(s).
precipitation hardening
Hardening caused by the precipitation of a constituent from a supersaturated
solid solution. See also age hardening and aging.
precipitation heat treatment
Artificial aging in which a constituent precipitated from a
supersaturated solid solution.
precracked specimen
A specimen that is notched and subjected to alternating stresses until
a crack has developed at the root of the notch.
primary current distribution
The current distribution in an electrolytic cell that is free
of polarization.
primary passive potential (passivation potential)
The potential corresponding to the maximum active current density
(critical anodic current density) of an electrode that exhibits active-passive
corrosion behavior.
primer (prime coat)
The
first
coat of paint applied to a surface. Formulated to have good bonding
and wetting characteristics; may or may not contain inhibiting pigments.
principal stress (normal)
The maximum or minimum value at the normal stress at a point
in a plane considered with respect to all possible orientations of
the considered plane. On such principal planes the shear stress is
zero. There are three principal stresses on three mutually perpendicular
planes. The state of stress at a point may be (1) uniaxial, a state
of stress in which two of the three principal stresses are zero, (2)
biaxial, a state of stress in which only one of the three principal
stresses is zero, and (3) triaxial, a state of stress in which none
of the principal stresses is zero. Multiaxial stress refers to either
biaxial or triaxial stress.
profile
Anchor pattern on a surface produced by abrasive blasting or acid
treatment.
protective potential
The threshold value of the corrosion potential that has to
be reached to enter a protective potential range. The term used
in cathodic protection to refer to the minimum potential required
to supress corrosion.
protective potential range
A range of corrosion potential values in which unacceptable
corrosion resistance is achieved for a particular purpose. |