HS2440 Archaeological iron_Corrosion exemplar.pdf Flashcards
Kinetic and environmental influences on iron corrosion
Complexity of iron corrosion
- layers, the altered layer, DPL (dense product layer) and the metal
- x rays pass through less dense material
- corrosion is differential
- galvanic corrosion, silver acting as a cathode for the iron corrosion
Variations in corrosion of iron
range of colours tells us about the oxides
image of potential- PH diagrams
these graphs tell us what corrosion product is stable
- potential is the energy in the environment, as you move up, areas in environments where theres more oxygen available, as you move down towards negative, they are more reducing environments, less oxygen available
- X axis is PH measure
How to use PH graphs for calculations
- predictive charts
- horizontal, movement of ions
- vertical is solubility
Simplified Pourbaix chart, what does it inform us of?
Natural environments likely to find in burial environments
measured redox potential and PH
image of the range of iron oxides
greek letters mean different structure
Chart showing iron in water and corrosion predictions
Burial environments- what corrosion products can we expect to find on iron?
Microanalysis identifying iron compounds in cross sections of archaeological iron
electrolytes like chlorides cause corrosion
Diagram of corrosion in a carbonated environment
Archaeological iron contains a lot of chlorides
Chloride during burial environments in iron- what forms can it be in?
Structure of akagneite, problematic in corrosion
chloride is made a part of its crystal structure and is absorbed into its tunnels
- the chloride sits on the surface and can be absorbed by water, producing a corrosion causing electrolyte
How corrosion pitting occurs
chloride is solvated in the pit
- pits are acidic environments which support corrosion
Chloride on iron at the point of excavation
analysis looking at % of chlorides on iron using EDS X-ray
Post- excavation corrosion in iron objects
akagneite- iron oxide with high volume, eg compared to a dense structure like magnetite
Conditions fro formation of akagneite post excavation of iron
Sulphur in a burial environment- impact on iron corrosion
Graph- Does beta- FeOOH cause corrosion of iron?
Layering of rust due to low oxygen in water, wet/ dry cycles
Table of different iron minerals and oxides
