MODULE 2: 1-6 Flashcards
The relationship between chemical reactions and electricity
ELECTROCHEMISTRY
movement of electrons
ELECTRICITY
involve movement of electrons
CHEMICAL REACTIONS
X loses electrons
Reducing agent
A process in which one substance or molecule is reduced & another is oxidized
REDOX REACTION
Devices that use a chemical reaction to create electricity
GALVANIC CELL OR VOLTAIC CELL
Example of Galvanic/Voltaic Cell
Battery
positive electrode
anode
negative electrode
cathode
Metals that are usually solid
Neutral Metals
Metals that dissolve in water
DISSOCIATED METALS
Decrease in cell potential caused by the operation of the cell (current flow)
POLARIZATION
2 Forms of Polarization
- Concentration polarization
- Activation polarization/Hydrogen polarization/Cathodic Polarization
Decrease in cell potential, which results from changes in concentrations of the ions in the electrolytic solutions
Concentration Polarization
The rate of redox reaction (electron movement) _____ as it reaches saturation.
decreases
The layer of adsorbed atomic hydrogen is said to polarize the cell.
ACTIVATION/HYDROGEN/CATHODIC POLARIZATION
Both concentration and activation polarization ____ the net oxidation-reduction (REDOX) reaction rate.
decrease
In corrosion processes, ______ usually has the greater effect.
activation polarization
All metals (except for ___, ____, and ____)
exist naturally in combined forms as ___, non-metals, semi-metals.
gold, platinum, palladium, metal
Metals in combined form are called as ___
MINERALS
Combined forms
OCCSS
- Oxides
- Carbonates
- Chlorides
- Sulfides
- Sulfates
____ as a process is exactly the reverse of the extraction materials.
Corrosion
___is the deterioration or degradation of a material due to interaction with its environment.
Corrosion
Loss of useful properties due to corrosion
*weakening of metallic material
*metal becomes brittle (lesser malleable, lesser ductile)
*decaying of surface
Types of metal corrosion
- Dry or Chemical Corrosion
- Wet or Electrochemical Corrosion
Oxidation of metal by oxygen or by other gases
Dry or Chemical Corrosion
Oxidation of metal exposed to an aqueous environment
Wet or Electrochemical Corrosion
The ___ of metals is the oxidation step of the overall redox reaction.
wet corrosion
During oxidation half-step, the cations or dissociated metals may:
- Dissolve into solution
- Combine with available anions or water to form IONIC COMPOUNDS/HYDRATED OXIDES
The more ___ the electrode potential is, the ___ is the tendency for the pure metals to oxidize.
negative, higher
___ is the process whereby the surface of a metal undergoes a SLOW, relatively uniform, removal of material
GENERAL CORROSION
2 required conditions for Gen. Corrosion to occur
- Metal is exposed to a moisture/aqueous environment.
- Chemical reaction bet. metal and aqueous solution to form an oxide
compound containing oxygen
OXIDE
Water is an _____
ampholyte
Capable of reacting chemically as either acid or base. Said to be amphoteric.
AMPHOLYTE
____ and ____ lead to preferential removal of metal from certain parts of the surface.
Impurities, imperfections
The corrosion cells, changing as surface and solution differences change, cause ____.
GENERAL OVERALL CORROSION
rare iron oxide, BLACK-colored powder, confused with RUST, consists of hydrated iron oxide
Iron (II) Oxide or FERROUS OXIDE (FeO)
DARK RED, called as rust. Builds up on FeO layer
Iron (III) Oxide or Ferric Oxide (Fe2O3)
HEMATITE
plus 3 oxidation state
FERRIC IRON (Fe3+)
plus 2 oxidation state
FERROUS IRON (Fe2+)
contains O2-, Fe2+, Fe3+, BLACK powder
Iron (II, III) Oxide OR Ferroferric Oxide (Fe3O4)
MAGNETITE
metal does not become active in the corrosion reaction
PASSIVITY
most desirable oxide layer, adheres best on the metal
FE3O4
Metals that form thin, tenacious oxide films when exposed to atmosphere
ZIRCONIUM, CHROMIUM, ALUMINUM, STAINLESS STEEL
Factors affecting General Corrosion Rate
- Temperature
- Water velocity
- Oxygen
- pH
- Metal surface condition and composition
- Dissolved solids
Substances (like O2) that remove the adsorbed atomic hydrogen
DEPOLARIZERS
FeO is SOLUBLE, oxide dissolves as it is formed. Metal is in direct contact w/ acid solution
pH < 4.0
Corrosion rate is relatively independent of pH of the solution
pH 4 - 10
corrosion rate is observed to fall as pH is INCREASED
pH > 10
@ high temp,
corrosion rate is HIGH, pH goes LOWER
pH < 4.0
@ high temp, corrosion rate is lower as pH value increases
pH bet. 4 and 12
@ high temp, corrosion rate increases
pH beyond 12
Plant pH to prevent corrosion
pH 9 and 11
another factor affecting General corrosion rate
exposure TIME of metals to corrosive environment
