01-1A-509-1 Ch3 Flashcards
Corrosion Theory
What is the s the chemical
or electrochemical deterioration of a material?
Corrosion
What type of corrosion product does Aluminum and magnesium form?
white oxides or hydroxides
What is the most common type of corrosion and the one that can be treated effectively by maintenance personnel?
Electrochemical corrosion
Can corrosion occur in the absence of water?
Yes but only at high temperatures found in gas turbine
engines.
What is the smallest unit of an element, made up of positively charged nucleus surrounded by a system of negatively charged electrons?
Atom
What is a negatively charged subatomic particle?
Electron
What is an atom or group of atoms or molecules which have acquired a net electric charge by gaining or losing electrons?
ION
If an ION gains electrons, is it positive or negative?
It is a negative ION
If an ION loses electrons, is it a positive or negative ION?
It is a positive ION.
Ions are forced to move through liquid solutions, what can ions not move through?
metal conductors
What is a liquid (usually water) solution containing ions?
Electrolyte
In the theory of corrosion, when a metal corrodes, the atoms ______ electrons and become _______ charged?
lose, positively
How many conditions are necessary for metal corrosion to occur?
4
a. a metal which has tendency to corrode must be present
b. a dissimilar conductive material must be present
c. a conductive liquid (electrolyte) must connect the anode and cathode
d. electrical contact between the anode and cathode must exist
What is the corroding metal called?
anode
Filiform corrosion can be prevented by storing equipment and aircraft in an environment with a relative humidity below ___%, by using coating systems having a low rate of diffusion for oxygen and water vapors, and maintaining coatings in good condition, and applying corrosion preventive compounds(CPCs) when coating is damaged.
65%
Filiform corrosion is a form or ____ corrosion.
Crevice corrosion
Methods to minimize crevice corrosion include closing the crevice by welding, sealant, or soldering, and use of ______.
nonabsorbent gaskets (such as Teflon)
Crevice corrosion may occur in?
In any crevice where a stagnant solution has pooled. Crevices are usually found at gasket surfaces, lap joints, and under bolt or rivet heads.
Exfoliation Corrosion is an advanced form of what type of corrosion?
intergranular corrosion
What is intergranular corrosion?
Is an attack on the grain boundaries of the metal
Pitting corrosion failures are common in ____ electrolytes.
electrolytes containing chloride or chlorine containing ions such as sea water
______ corrosion is a form of extremely localized attack that results in holes in the metal.
Pitting corrosion
Galvanic occurs when ______ are in contact with each other and an electrolyte such as sea water.
different metals
What is the most common type of corrosion?
Uniform surface corrosion.
What is uniform surface corrosion?
it is a direct chemical attack on a metal surface that proceeds uniformly over the entire exposed surface
What type of corrosion it this: the surface becomes rough and possibly frosted in appearance. Magnesium and low alloy steels are most susceptible to this type of corrosion.
Uniform surface corrosion
Which corrosion type is : due to impingement or cavitation can be accelerated due to the action of a corrosive fluid against the metal surface.
Erosion Corrosion
How is erosion corrosion characterized?
by grooves, gullies, waves, rounded holes, and or valleys in the metal surface.
What is the difference between hydrogen embrittlement and Stress Corrosion Cracking(SCC)?
Hydrogen embrittlement is very similar to SCC. They are distinguished by the interaction of an applied electrical current with the base metal.
-if the current makes the metal more anodic and cracking is accelerated the failure mechanism is SCC.
-If the current makes the metal more cathodic, which accelerates hydrogen generation, the failure is hydrogen embrittlement.
What is corrosion fatigue?
is the cracking of metals caused by the combined effects of cyclic stress and corrosion.
Since pure aluminum is more corrosion resistant that most alloys, aluminum alloys are often covered with a thin layer of what?
a thin layer of nearly pure aluminum called cladding or Alclad.
