Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxide-hydroxide (FeO(OH), Fe(OH)3), and is typically associated with the corrosion of refined iron.
Associated reactions[edit]
The rusting of iron is an electrochemical process that begins with the transfer of electrons from iron to oxygen.[7] The iron is the reducing agent (gives up electrons) while the oxygen is the oxidizing agent (gains electrons). The rate of corrosion is affected by water and accelerated by electrolytes, as illustrated by the effects of road salt on the corrosion of automobiles. The key reaction is the reduction of oxygen:
Because it forms hydroxide ions, this process is strongly affected by the presence of acid. Likewise, the corrosion of most metals by oxygen is accelerated at low pH. Providing the electrons for the above reaction is the oxidation of iron that may be described as follows:
- Fe → Fe2+ + 2 e−
The following redox reaction also occurs in the presence of water and is crucial to the formation of rust:
- 4 Fe2+ + O2 → 4 Fe3+ + 2 O2−
In addition, the following multistep acid–base reactions affect the course of rust formation:
as do the following dehydration equilibria:
From the above equations, it is also seen that the corrosion products are dictated by the availability of water and oxygen. With limited dissolved oxygen, iron(II)-containing materials are favoured, including FeO and black lodestone or magnetite (Fe3O4). High oxygen concentrations favour ferric materials with the nominal formulae Fe(OH)3−xOx⁄2. The nature of rust changes with time, reflecting the slow rates of the reactions of solids.[5]
Furthermore, these complex processes are affected by the presence of other ions, such as Ca2+, which serve as electrolytes which accelerate rust formation, or combine with the hydroxides and oxides of iron to precipitate a variety of Ca, Fe, O, OH species.
The onset of rusting can also be detected in the laboratory with the use of ferroxyl indicator solution. The solution detects both Fe2+ ions and hydroxyl ions. Formation of Fe2+ ions and hydroxyl ions are indicated by blue and pink patches respectively.
Bluing[edit]
Bluing is a technique that can provide limited resistance to rusting for small steel items, such as firearms; for it to be successful, a water-displacing oil is rubbed onto the blued steel and other steel.
Inhibitors[edit]
Corrosion inhibitors, such as gas-phase or volatile inhibitors, can be used to prevent corrosion inside sealed systems. They are not effective when air circulation disperses them, and brings in fresh oxygen and moisture.
Humidity control[edit]
Rust can be avoided by controlling the moisture in the atmosphere.[17] An example of this is the use of silica gel packets to control humidity in equipment shipped by sea.
Rust may be treated with commercial products known as rust converter which contain tannic acid or phosphoric acid which combines with rust; removed with organic acids like citric acid and vinegar or the stronger hydrochloric acid; or removed with chelating agents as in some commercial formulations or even a solution of molasses.[19]
https://en.wikipedia.org/wiki/Rust
Wrought iron is an iron alloy with a very low carbon content (less than 0.08%) in contrast to that of cast iron (2.1% to 4%). It is a semi-fused mass of iron with fibrous slag inclusions (up to 2% by weight), which gives it a "grain" resembling wood that is visible when it is etched, rusted, or bent to the point of failure. Wrought iron is tough, malleable, ductile, corrosion resistant, and easily forge welded, but is more difficult to weld electrically.
Before the development of effective methods of steelmaking and the availability of large quantities of steel, wrought iron was the most common form of malleable iron. It was given the name wrought because it was hammered, rolled or otherwise worked while hot enough to expel molten slag. The modern functional equivalent of wrought iron is mild steel, also called low-carbon steel. Neither wrought iron nor mild steel contains enough carbon to be hardenable by heating and quenching.[1]: 145 [failed verification]
Wrought iron is highly refined, with a small amount of silicate slag forged out into fibres. It consists of around 99.4% iron by mass.[2] The presence of slag can be beneficial for blacksmithing operations, such as forge welding, due to the silicate inclusions being a flux, and gives the material its unique fibrous structure.[3] The silicate filaments of the slag also protect the iron from corrosion and diminish the effect of fatigue caused by shock and vibration.[4]
Historically, a modest amount of wrought iron was refined into steel, which was used mainly to produce swords, cutlery, chisels, axes and other edged tools as well as springs and files. The demand for wrought iron reached its peak in the 1860s, being in high demand for ironclad warships and railway use. However, as properties such as brittleness of mild steel improved with better ferrous metallurgy and as steel became less costly to make thanks to the Bessemer processand the Siemens-Martin process, the use of wrought iron declined.
Many items, before they came to be made of mild steel, were produced from wrought iron, including rivets, nails, wire, chains, rails, railway couplings, water and steam pipes, nuts, bolts, horseshoes, handrails, wagon tires, straps for timber roof trusses, and ornamental ironwork, among many other things.[5][note 1]
Wrought iron is no longer produced on a commercial scale. Many products described as wrought iron, such as guard rails, garden furniture[6] and gates, are actually made of mild steel.[7] They retain that description because they are made to resemble objects which in the past were wrought (worked) by hand by a blacksmith (although many decorative iron objects, including fences and gates, were often cast rather than wrought).[7]
https://en.wikipedia.org/wiki/Wrought_iron
| Photospheric composition (by mass) | |
|---|---|
| Hydrogen | 73.46%[17] |
| Helium | 24.85% |
| Oxygen | 0.77% |
| Carbon | 0.29% |
| Iron | 0.16% |
| Neon | 0.12% |
| Nitrogen | 0.09% |
| Silicon | 0.07% |
| Magnesium | 0.05% |
| Sulphur | 0.04% |
https://en.wikipedia.org/wiki/Sun
https://en.wikipedia.org/wiki/Observable_universe
https://en.wikipedia.org/wiki/Grigory_Mairanovsky
https://en.wikipedia.org/wiki/Soviet_Union
https://en.wikipedia.org/wiki/Federation
https://en.wikipedia.org/wiki/Federation#Federal_governments
https://en.wikipedia.org/wiki/Federalism
https://en.wikipedia.org/wiki/Old_Swiss_Confederacy
https://en.wikipedia.org/wiki/Communism
https://en.wikipedia.org/wiki/Joseph_Stalin
https://en.wikipedia.org/wiki/Communist_Party_of_the_Soviet_Union
No comments:
Post a Comment