corrosion II basic corrosion Flashcards
what are the three categories of corriosion?
electrochemical, galvanic, and electrolytic
what 4 things must be involved to create corrosion?
anode, cathode, metallic path, electrolyte
what two elements are always involved with corrosion?
oxygen and hydrogen
what is a positive electrode called?
cathode
where will positive ions flow tward?
toward the negative anode
what is electrochemical corrosion?
a single piece of metal in contact with electrolyte. this can occur in the atmosphere or under immersion. It is often a slow process
what is Galvanic corrosion?
two or more dissimilar metals, connected by a metallic path, in electrolyte
what is electrolytic corrosion?
two dissimilar metals, in the same electrolyte, and an electrical current from an outside source flowing between the two metals.
what is electrochemistry?
chemical reactions that produce electric currents and the chemical reactions that are caused by those currents in an electrolyte
what are qualities of less noble metals?
they are the most active
considered anodic
electrically more negative
what are qualities of more noble metals?
they are more passive chemically
they are less negative electrically
these metals are catotic and more resistant to corrosion
do electrons flow toward the least noble metal or the most noble metal?
most noble metal
what are two major things that happen during all corrosion in seawater?
- metal atoms are lost by the anode
- ions are formed in the seawater. these can either be a protective coating on the cathode or produce alkalis that attack wood
what does every anode reaction involve?
the loss of two atoms of solid metal
what is the white powder coating on aluminum and the pink coating on bronze?
hydroxyl ions. a cathodic protective coating that occurs as a reaction from the anode loosing its atoms onto the cathodic metal. this happens on most metals except iron or mild steel.
