The purpose of scientific thought is to predict what will happen in given experimental circumstances. All the philosophical discussion is an evasion of the point. – Feynman The purpose of scientific thought is to predict what will happen in given experimental circumstances. All the philosophical discussion is an evasion of the point. – Feynman

Last class - More corrosion - micro cells Welding HAZ Sensitization Ol' Harold's story Last class - More corrosion - micro cells Welding HAZ Sensitization Ol' Harold's story Today - Suppressing corrosion Corrosion examples Today - Suppressing corrosion Corrosion examples

Suppressing corrosion Components of a cell: anode cathode electrolyte connection Components of a cell: anode cathode electrolyte connection

Suppressing corrosion Occlude electrolyte - coatings asphalt greases, oils paints polymers ceramic coatings "noble" metals asphalt greases, oils paints polymers ceramic coatings "noble" metals

Suppressing corrosion Occlude electrolyte - coatings "noble" metals: unless scratch heals, a galvanic cell is set up "noble" metals: unless scratch heals, a galvanic cell is set up

Suppressing corrosion Cathodic protection galvanizing: Zn coating applied by hot-dipping electroplating galvanizing: Zn coating applied by hot-dipping electroplating

Suppressing corrosion Cathodic protection galvanizing: presence of scratch does not promote corrosion of protected metal galvanizing: presence of scratch does not promote corrosion of protected metal but steel helps Zn corrode

Suppressing corrosion Cathodic protection set up cell by adding metal which is more anodic than metal or alloy to be protected set up cell by adding metal which is more anodic than metal or alloy to be protected

Suppressing corrosion Cathodic protection example: protecting ship plate example: protecting ship plate

Suppressing corrosion Cathodic protection example: protecting hot water heater tanks example: protecting hot water heater tanks

Suppressing corrosion Cathodic protection Problem: steel fermentation tank in brewery Problem: steel fermentation tank in brewery sacrificial anodes add metallic ions to electrolyte

Suppressing corrosion Cathodic protection Different approach: Impose a voltage across cell formed by tank (cathode) and an inert anode Different approach: Impose a voltage across cell formed by tank (cathode) and an inert anode choice of anode material: very inert material like Pt choice of anode material: very inert material like Pt but oxygen gas produced at anode

Suppressing corrosion Cathodic protection Different approach: Impose a voltage across cell formed by tank (cathode) and an inert anode Different approach: Impose a voltage across cell formed by tank (cathode) and an inert anode choice of anode material: use carbon - inert C + O 2  CO 2 choice of anode material: use carbon - inert C + O 2  CO 2

Suppressing corrosion Cathodic protection "….. join in a planned discussion of whether it is best to use copper tubing coils or stainless steel tubing coils inside of a stainless steel beer fermenter, the coils being used as a chiller? There has been a discussion in another brewing forum about competing concerns between the two, i.e., copper conducts heat better and is easier to bend, versus copper will slowly dissolve in the acidic environment of beer"

Suppressing corrosion Use passivated materials Ni - NiO Ti - TiO 2 Al - Al 2 O 3 Ni - NiO Ti - TiO 2 Al - Al 2 O 3 COR-TEN: 0.19% C 0.30% Cu 0.40% Ni 0.50% Cr 0.05% V COR-TEN: 0.19% C 0.30% Cu 0.40% Ni 0.50% Cr 0.05% V

Suppressing corrosion Anodizing Al & other materials can be anodized very thick oxide coating formed (8-50 microns) Al & other materials can be anodized very thick oxide coating formed (8-50 microns)

Suppressing corrosion Thinking again of noble metal coatings, what about Cr plating? Cr plating usually filled w/ microcracks due to stresses in plating 540x 2300x

Suppressing corrosion Cr plating frequently a series of layers

Corrosion examples in shuttle mat'ls 1x 60x 235x 1180x

Corrosion examples in shuttle mat'ls

Corrosion area effect Area effect: large cathode & small anode - corrosion accelerated Area effect: large cathode & small anode - corrosion accelerated electrochemical cell current density high try to keep potential anodic areas large relative to cathode

Polymers - the nightmare begins I am inclined to think that the development of polymerization is, perhaps, the biggest thing that chemistry has done, where it has the biggest effect on everyday life I am inclined to think that the development of polymerization is, perhaps, the biggest thing that chemistry has done, where it has the biggest effect on everyday life LORD TODD President of the Royal Society of London LORD TODD President of the Royal Society of London

What are polymers? Why important ? What are polymers? Why important ? Long chain molecules Extraordinary range of physical properties Many (not all) are cheap Low densities Long chain molecules Extraordinary range of physical properties Many (not all) are cheap Low densities

Assignment: Review today's classnotes a. coatings b. cathodic protection c. passivation d. anodizing e. Cr plating f. corrosion examples g. area effect h. what is a polymer? Read: pp , , chapter 14 Assignment: Review today's classnotes a. coatings b. cathodic protection c. passivation d. anodizing e. Cr plating f. corrosion examples g. area effect h. what is a polymer? Read: pp , , chapter 14