Corrosion 8 Flashcards
cells with two identical electrodes, each in contact with a solution of different composition.
Salt concentration cell
Occurs due to differences in potential between differently Aerated areas.
Differential aeration cell
- A list that describes the arrangement of elements in the order of their increasing electrode potential values.
Electrochemical Series
is an orderly arrangement of the standard potentials for all metals.
Emf Series
- Determines the electrochemical potential and nobility of metals.
Galvanic Cell
Pure mercury is placed at the bottom of the tube, which is covered with a paste of mercury- mercurous
Calomel Reference Electrode
Composed of a silver wire, sometimes coated with a layer of solid silver chloride, immersed in a solution that is saturated with potassium chloride and silver chloride.
Silver-Silver Chloride Reference Electrode
- Consists of metallic copper immersed in saturated copper sulfate.
- The electrode’s precision, though slightly lower than that of calomel or silver chloride electrodes, is still sufficient for most corrosion studies.
Saturated Copper-Copper Sulfate Reference Electrode
of electrolysis relate the current of an electrochemical reaction to the number of moles of the element being reacted and the number of moles of electrons involved.
Faraday’s empirical laws
- current produced in an electrochemical cell during corrosion.
CORROSION CURRENT
It is the speed at which any given metal deteriorates or corrodes in a specific environment.
CORROSION RATE
provides a way to calculate corrosion rate.
Corrosion current
A reduction current that occurs when electrons flow from the electrode surface to a species in solution. For example, oxygen reduction in a fuel cell.
Cathodic current
An oxidation current that occurs when electrons flow into the electrode from a species in solution. For example, hydrogen oxidation in a fuel cell.
Anodic current
Have widespread applications in resisting corrosion but it should be remembered that they do not resist all corrosives.
STAINLESS STEEL
are also more susceptible to localized corrosion than ordinary structural steels.
- less resistant than ordinary structural steel.
- Frequently, the quality of stainless steel is checked with a magnet.
Stainless alloys
The corrosion resistance of a pure metal is usually better than that of one containing impurities or small amounts of other elements. However, pure metals are usually expensive and relatively soft and weak.
METAL PURIFICATION
is achieved by supplying electrons to the metal structure to be protected.
Cathodic protection
This type of CP uses a more reactive metal (the sacrificial anode) that corrodes preferentially to the metal structure (the cathode) that needs to be protected.
GALVANIC OR SACRIFICIAL ANODE METHOD
used for cathodic protection consist of magnesium-base and aluminum-base alloys and, to a lesser extent, zinc.
Sacrificial metals
serve essentially as sources of portable electrical energy. They are useful particularly when electric power is not
Sacrificial anodes
This type of CP uses an external power source (impressed current) to provide the electrons required to cathodically protect the structure.
- An external de power supply is connected to an underground tank. The negative terminal of the power supply is connected to the tank, and the positive to an inert anode such as graphite or Duriron.
IMPRESSED CURRENT METHOD
formation of a protective film on metals by externally applied anodic currents.
- exhibiting an active-passive behavior in order to form a passive film.
- maintaining passive a metal with an active–passive behavior when placed in an aggressive environment.
ANODIC PROTECTION
an electronic device that maintains a metal at a constant potential with respect to a reference electrode to anodically protect a structure.
POTENTIOSTAT
