HS2440 Week 5 Asyn_ Corrosion of copper alloys during burial

Question 1

How does copper corrode similarly and differently to iron

Answer 1

corrosion in terms of morphology, adherence to the substrate, porosity and layering system.

copper is less readily corroded than iron (positive electrode)

Question 2

Describe the different type of archaeological corrosion profiles of bronze

Answer 2

• describes different patinas of a archaeological copper alloy
• type one is stable and two unstable, based on appearance
• ## chlorides in the structure causes an aggressive harmful corrosion process (type two)

Question 3

Describe formation of Copper oxides in atmosphere

Answer 3

bare metal quickly oxidises when exposed to the atmosphere
- forms cuprite
- depends on burial and atmospheric contexts
- as it forms, slows down corrosion rate.

Question 4

Copper products formed when in the presence of carbon compounds and water

Answer 4

azurite is preferentially formed in acidic environments

Question 5

Copper compounds containing sulphur

Answer 5

cuprite is preferentially formed in oxygen containing environments, so sulphur compounds are quite rare
in reducing environments, sulphur is provided by bacteria
covellite causes pitting

Question 6

All about chloride compounds in copper corrosion

Answer 6

in acidic conditions, ions can dissolve through the cuprite layer, forms next to the metal layer

Question 7

What is Bronze disease, when does it occur

Answer 7

Nantokite, when exposed to the atmosphere triggers the disease
- green, voluminous, rapidly growing, disrupts surface detail and patina
- disruption of layers is extensive
- localised process, starts in pits

Question 8

Four kinds of copper chloride species

Answer 8

forms first/ last according to stability
various shades of green
paratacemite is confused sometimes, but only occurs on alloys

Question 9

The progress of Bronze disease is governed by what two external factors

Answer 9

governed by access to oxygen and atmospheric moisture