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METAMORPHOSIS #1005_1/ 2005
(  Satoshi Kinoshita )
| Series: | Paintings: Landscape | | Medium: | "iron rust" on stretched canvas | | Size (inches): | 38 x 32 | | Size (mm): | 965 x 813 | | Catalog #: | PA_086 | | Description: | Signed, titled, date, copyright in magic ink on the reverse.
Iron + oxygen + water = Iron rust.
Rust is the substance formed when iron compounds corrode in the presence of water and oxygen. It is a mixture of iron oxides and hydroxides. Rusting is a common term for corrosion, and usually corrosion of steel.
Iron is found naturally in the ore hematite as iron oxide, and metallic iron tends to return to a similar state when exposed to air, (hydrogen, oxygen, nitrogen, etc) and water. This corrosion is due to the oxidation reaction when iron metal returns to an energetically favourable state. Energy is given off when rust forms. The process of rusting can be summarised as three basic stages: The formation of iron(II) ions from the metal; the formation of hydroxide ions; and their reaction together, with the addition of oxygen, to create rust.
Iron is the main component of steel and the corrosion of steel is observed more frequently, since iron is nearly never used without alloying.
When steel contacts water, an electrochemical process starts. On the surface of the metal, iron is oxidised to iron(II):
Fe -> Fe2+ + 2e-
The electrons released travel to the edges of the water droplet, where there is plenty of dissolved oxygen. They reduce the oxygen and water to hydroxide ions:
4e- + O2 + 2H2O -> 4OH-
The hydroxide ions react with the iron(II) ions and more dissolved oxygen to form iron oxide. The hydration is variable, however in its most general form:
Fe2+ + 2OH- -> Fe(OH)2
4Fe(OH)2 + O2 -> 2(Fe2O3.xH2O) + 2H2O
Hence, rust is hydrated iron(III) oxide. Corrosion tends to progress faster in seawater than fresh water due to higher concentration of sodium chloride ions, making the solution more conductive. Rusting is also accelerated in the presence of acids, but inhibited by alkalis. Rust can often be removed through electrolysis, however the base metal object can not be restored through this method.
Corrosion of aluminum is different from steel or iron, in that aluminum oxide formed on the surface of aluminum metal forms a protective, corrosion resistant, coating.
Hydrated iron oxide is permeable to air and water, meaning that the metal continues to corrode after rust has formed. The iron mass eventually converts entirely to rust, and disintegrates. There are several methods available to control corrosion and prevent the formation of rust. Galvanising consists of coating metal with a thin layer of another metal, such as zinc. The electrochemical potential of zinc is more negative than steel (or iron) and will provide cathodic protection to the underlying steel. Typically, zinc is applied by either hot-dip galvanizing or electrogalvanizing. A nice thing about galvanising is that a scratch on a galvanised piece of iron will not lead to rust at the scratch. The zinc layer acts as a galvanic anode.
Cathodic protection is a method to control corrosion and the formation of rust using electrochemical techniques.
Corrosion control can be done using a coating to isolate the metal from the environment.
Covering steel with concrete provides protection to steel by the high pH environment at the steel-concrete interface. However, if concrete covered steel does corrode, the rust formed can cause the concrete to spall and fall apart, this will create structural problems.
-www.arthistoryclub.com/art_history/Rust
LESSON 23 Rusting of Metals: Brown Village Roofs, Grade Level: 7-10.
1. Grades 7-10
2. Overview Rusting is a chemical process that, can take place in metals exposed to the atmosphere. Not all metals however rust. Rusting is common with the metal, iron. Certain conditions in the air around a metal have to be present for iron to rust. Iron rust which, generally appears brown, is itself a chemical compound quite different from the iron itself. The rusting of iron can be prevented. In towns and large cities where iron sheets are used for roofing houses, rusting can also take place if the iron sheets are not protected from rusting.
3. Purpose When an iron sheet rusts, it forms a new coating around the iron itself. The purpose of this lesson is to show that the brown corrugated iron roofs in some villages is as a result of the rusting of the iron in the sheets. Rusting can be prevented.
4. Objectives Students will be able to:
i. Identify what is iron rust.
ii. Demonstrate how a piece of iron can be made to rust
iii. Show that rusting in iron can be prevented.
5. Resources/materials
* Strips of different metals-iron, copper, aluminium, tin
* Test tubes, iron nails
* World map showing iron ore deposits
* Wall charts showing iron and its uses.
6. Activities and Procedures Iron and its allied product, steel are important in the development of many countries. Iron ore, the raw material for the manufacture of iron is found as mineral deposit in some countries of the world. Here the teacher should guide the students to search and study the iron mineral deposits in the world.
When metals are exposed to the atmosphere over a long period, they change their appearance. Some get duller and less bright while some like iron develop a coating over its surface. The words tarnish and rust are then applied. Iron is known to rust while a metal like aluminium tarnishes. This lesson should help to explain the following:
* What is iron rust?
* How is iron rust formed?
* Is iron rust useful?
* How can iron rust be prevented?
This lesson offers good opportunity for the students to carry out simple experiments on rusting with simple materials. This study of rusting will involve some bit of chemistry. Iron rust is a compound of iron. It is formed when iron reacts with the oxygen of the air in the presence of moisture (water) to form a brown substance known as iron oxide. The process is a chemical reaction, which takes place over a period of time. It should be noted that oxygen and water are necessarily present for iron to rust.
Iron + oxygen + water ====== Iron rust.
The conditions for iron to rust can then be easily deduced. The rusting of iron is at times referred to as slow burning. Why?
Rusting of iron affects the quality of the iron. It is like the decay of the iron. Rusting costs the community a great deal of money. It has to be prevented otherwise articles made of iron will decay away. The students should then be guided to search for cases of iron rusting in their environment. What materials rust and where are they found. An abandoned car on the road side over a long time get covered with a brown substance-rust. The students should explain this. That discussion can lead to the observation of old brownish iron roofs found in many villages and towns.
The teacher should now perform the simple experiments with the iron nails. Then the methods applied for preventing rusting should be discussed-painting, greasing, electroplating and galvanising should be studied.
7. Tying it all together Rusting is a term appropriately applied to the behaviour of iron under certain conditions. When iron rusts, a new substance is formed. The rusting of iron affects the iron and it could be costly. So it has to be prevented.
8. Assessment The students should deduce how iron can be distinguished from other metals.
9. Author(s) S. T. Bajah
10. References STAN (1998) Nigerian Integrated Science Project. Book Two. Ibadan: Heinemann Educational Books (Nigeria) Limited.
-library.unesco-iicba.org/English/SECONDARY_SCIENCE_SERIES/
science_lessons/23_rusting_of_metals.htm
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