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46 Cards in this Set
- Front
- Back
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True or False - Metals will dissolve in a corrosion process
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True
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Show the general equilibrium of a metal electrode in its own solution
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M = M^(z+) + ze^(-)
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True or False - There is a net current flow during equilbrium
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False
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Show the reaction that produces metal ion from metal atoms
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M > M^(z+ + ze-
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Show the reaction where metal ions combine with electron to deposit metal atoms at the surface
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M^(z+) + ze- -> M
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What is a half-cell reaction?
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reactions that need another reaction to either produce or consume electrons
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What type of reaction is an oxidation reaction?
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A reaction that produces electrons. Ionizes metal atoms to ions
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What type of reaction is a reduction reaction
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A reaction that consumes electrons. De-ionization to form metal
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What is a redox reaction?
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M^= M^(z+) + ze-
Contains both the oxidation and reduction half-cell reaction |
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Name one thing oxidation is used in?
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Corrosion
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Name one thing reduction is used in?
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electroplating
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What are the 4 necessary processes to have corrosion take place?
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1) Oxidation half cell reaction
2) Reduction half cell reaction 3) Ion transport 4) Electron transport |
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What is another name for an oxidation reaction?
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anodic reaction
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What is another name for a reduction reaction?
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cathodic reaction
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List five types of reduction reactions
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1. Plating/depository reaction -
M^(z+) + ze- > M 2. Reduction of hydrogen ions in strong, de-aerated acids: 2H+ + 2e- = H2 3. Reduction of oxygen in weak aerated acids to form water. O2 + 4H+ + 4e- = 2H2O 4. Change in ionic state, e.g., Cupric to cuprous ion. Cu2+ + e- = Cu1+ 5. Reduction of oxygen in neutral or basic solutions to form hydroxyl ions. O2 + 2H2O + 4e- = 4(OH-) |
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What is the cathode?
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The location where the cathodic reaction occurs. Only needs to conduct electricity to be a cathode. Does not dissolve
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What is ion transport?
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Medium in which ions can be transported. Conductive medium or electrolte. Sea water, acids and bases work
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What is electron transfer?
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Electron transport between cathode and anode site.
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What is the Exchange Current Density (ECD)?
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The magnitude of the current. Measured in A/cm2. current per unit area exposed. It represents an equilibrium. Corrosion occurs if not at exchange current density
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What is the current flow?
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number of electrons per unit time
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What controls the ECD?
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reaction surface and ions involved
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What are the standard equilibirum conditions?
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1 atm, pure solid, normal ionic solution, 25 C
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What is normalacy?
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number of equivalent per liter
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What is normal ionic strength?
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When 1 gram equivalent dissolve in 1 liter. Example normal solution of HCl is gram molecular weight per liter. For basic solution Oh- used.
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What is the reference scale?
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Electro Motor Force or REDOX potential scale
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What is the usually reference?
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Standard Hydrogen Electrode (SHE). H2 = 2H+ + 2e-. Potential of 0.0 V
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What does a negative EMF mean?
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A negative EMF means it is more likely to corrode.
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Why are some negative EMF resistant to corrosion
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kinetics plays an important role
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What is the Calomel Reference Electrode?
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Hg2Cl2 + 2e- = 2Hg + 2Cl-
Ecal = +0.242 V against SHE for Hg/Hg2Cl2 in saturated KCL |
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Copper/Cupric Sulfate
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copper bar in cupric sulfate
E = 0.34+ |
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What is polarizatin
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The movement away from the redox potential, movement away from equilibrium
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What is the Tafel equation?
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eta - overpotential or voltage movement from Er value, F - Faradays constant
eta = a +/- b logi anodic: a = -ln io(RT/(alpha)zF) b = -(RT/(alpha)zF) cathodic: same as above except (1-alpha) i = current density |
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What do tafel lines do?
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show the effect of anode and redox rate as a function of polarization
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What is the Nernst equation?
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E = Eo + 2.3(RT/zF) ln K
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What is the activity of a dissolved substance?
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a=( Vapor pressure of substance above solution)/ (Vapor pressure of substance in standard state)
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What is the vapor pressure in an ideal system?
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p1 = p1o c1
p10 - vapor pressure in standard state and c1 - concentration in moles. |
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What is the vapor pressure in a non-ideal system?
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p1 = p1o a1
a1 = gamma*10 c1 gamma1o = activity coefficient |
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What is the equation to find the corrosion rate?
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T/t= iEW/(FdA)
T = thickness t = time i = current density EW = equivalent weight = M/z = molecular weight/electrons d = density A = area of surface area F =96,500 coulombs CR = 0.13 (icorr x EW)/d |
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What is Concentration Polarization?
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reactive species cannot transport to or away from electrode fast enough.
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What are the two regions of concentration polarization?
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activation polarization from tafel law, controlled by activation energy.
concentration polarization, reatants limited by transport component. Current density is ilmit ilim = (D z F Co)/x D - diffusion rate of the species, Co - concentration and x - diffusion distance |
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What is faraday's constant?
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F = 96845.34
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how are pourbaix diagrams useful?
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indicate where areas of active corrosion, immunity and passive behavior occurs as a function of potential and pH.
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What is the importance of the oxygen line?
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Below the oxygen line indicates where oxygen will reduce to hydroxyl ions.
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What is the importance of the hydrogen line?
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Area below where hydrogen ions reduce to hydrogen
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What is the MW and density of Al
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29.68 MW, d = 2.7
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What is the MW and density of Fe
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MW = 55.845, d = 7.874
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