Rust is iron oxide, the red oxide is usually formed by the redox reactions of iron and oxygen in the presence of water or air humidity. Some forms of rust can be distinguished either visually or by spectroscopy, and are formed in different circumstances. Rust consists of hydrated iron (III) oxide Fe 2 O 3 Ã, Â · n H 2 O and iron (III) oxides-hydroxides (FeO (OH), Fe (OH) 3 ).
With enough time, oxygen, and water, every iron mass will eventually turn entirely into rusting and crumbling. The surface of the rust is scaly and brittle, and provides no protection against the underlying iron, unlike the formation of patina on the surface of the copper. Rust is a general term for corrosion of iron and its alloys, such as steel. Many other metals undergo similar corrosion, but the resulting oxide is not commonly called rust.
Other forms of rust exist, such as the reaction between iron and chloride in an oxygen-deprived environment. Rebar used in underwater concrete pillars, which produce green rust, is an example. Although rusty is generally a negative aspect of iron, a certain rusty shape, known as "stable carat," causes the object to have a thin layer of rust on top, and if stored in a relatively low humidity, create a "stable" protective layer for the iron below, but not to the extent of other oxides, such as aluminum.
Video Rust
Reaksi kimia
Rust is another name for iron oxide, which occurs when iron or iron-containing alloys, such as steel, are exposed to oxygen and moisture for long periods of time. Over time, oxygen combines with metal at the atomic level, forming a new compound called oxide and weakening the bonding of the metal itself. Although some people refer to rust in general as "oxidation", the term is much more common; although rust forms when iron undergoes oxidation, not all oxidation forms rust. Only iron or iron-containing alloys can rust, but other metals can corrode in the same way.
The main catalyst for the rusting process is water. The structure of iron or steel may seem solid, but water molecules can penetrate microscopic holes and cracks in any exposed metal. The hydrogen atoms present in the water molecules can join with other elements to form acids, which will eventually lead to more metals exposed. If chloride ions are present, as with salt water, corrosion is likely to occur more rapidly. Meanwhile, the oxygen atoms combine with the metal atoms to form a destructive oxide compound. When atoms are joined, they weaken the metal, making the structure brittle and fragile.
Iron oxidation
When the iron (cast) is not pure in contact with water, oxygen, other strong oxidants, or acids, it rusts. If salt is present, for example in seawater or salt sprays, iron tends to rust more quickly, as a result of electrochemical reactions. Iron metal is relatively unaffected by pure water or by dry oxygen. As with other metals, such as aluminum, the strongly adhered oxide layer, the passivation layer, protects the bulk iron from further oxidation. The conversion of the iron oxide layer of passivation to the carat results from the combined action of two agents, usually oxygen and water.
Other condescending solutions are sulfur dioxide in water and carbon dioxide in water. Under these corrosive conditions, the species of iron hydroxide is formed. Unlike iron oxides, hydroxides do not adhere to bulk metals. When they are formed and peeling off the surface, fresh iron is exposed, and corrosion proceeds until all iron is consumed or all oxygen, water, carbon dioxide, or sulfur dioxide in the system is removed or consumed.
When iron is rusted, oxides take up more volume than the original metal; This expansion can produce large forces, damaging structures made with iron. See economic effects for more details.
Related reactions
Ironing is an electrochemical process that begins with the transfer of electrons from iron to oxygen. Iron is a reducing agent (releasing electrons) while oxygen is an oxidizing agent (electron gain). The level of corrosion is affected by water and accelerated by electrolytes, as illustrated by the effect of road salt on car corrosion. The main reaction is oxygen reduction:
- O 2 4Ã, e - 2Ã, H 2 O -> 4Ã, OH -
Because it forms hydroxide ions, this process is strongly influenced by the presence of acids. Indeed, corrosion of most metals with oxygen accelerates at low pH. Providing electrons for the above reactions is the iron oxidation which can be described as follows:
- Fe -> Fe 2 2Ã, e -
The following redox reactions also occur in the presence of water and are essential for the formation of rust:
- 4Ã, Fe 2 O 2 -> 4Ã, Fe 3 2Ã, 2 -
In addition, the following multistepic acid-base reactions affect the course of rust formation:
- Fe 2 2Ã, H 2 O? Fe (OH) 2 2Ã, H
- Fe 3 3Ã, H 2 O? Fe (OH) 3 3Ã, H
seperti halnya equilibria dehidrasi berikut:
- Fe (OH) 2 ? FeO H 2 O
- Fe (OH) 3 ? FeO (OH) H 2 O
- 2Â FeO (OH)? Fe 2 O 3 H 2 O
From the above equation, it is also seen that the corrosion product is determined by the availability of water and oxygen. With limited dissolved oxygen, iron (II) -contains the preferred material, including FeO and black stone or magnetite (Fe 3 O 4 ). The high oxygen concentration supports the iron material with the nominal formula of Fe (OH) 3- x O x / 2 . The nature of the rust changes over time, reflecting the slow reaction rates of solids.
Furthermore, this complex process is affected by the presence of other ions, such as Ca 2 , which acts as an electrolyte that accelerates the formation of rust, or combines with hydroxides and iron oxides to precipitate various Ca, Fe, O, OH.
The commencement of rusting can also be detected in the laboratory by using a ferroxyl indicator solution. The solution detects Fe 2 and hydroxyl ions. The formation of Fe 2 ion and hydroxyl ions are indicated by blue and pink patches respectively.
Maps Rust
Prevention
Due to the widespread use and importance of iron and steel products, the prevention or retardation of rust is the basis of major economic activity in a number of specialized technologies. A brief overview of the method is presented here; for detailed coverage, see cross-reference articles.
Rust is permeable to air and water, therefore the metallic interior iron under the rust layer continues to corrode. Therefore, rust prevention requires coatings that block the formation of rust.
Stainless alloy
Stainless steel forms a passive layer of chrome (III) oxide. Similar passive behavior occurs with magnesium, titanium, zinc, zinc oxide, aluminum, polyaniline, and other electroactive conductive polymers.
Special "weathering steel" alloys such as Cor-Ten rust at a much slower rate than usual, because the rust attached to the metal surface in the protective layer. The design using this material should include measures that avoid the worst exposure, as the material still continues to rust slowly even under near ideal conditions.
Galvanization
Galvanization consists of applications on objects that must be protected from metallic zinc coatings by either galvanizing or electroplating. Zinc is traditionally used because it is cheap, adheres well to steel, and provides cathodic protection to the steel surface in case of damage to the zinc coating. In a more corrosive environment (such as brine), cadmium coating is preferred. Galvanization often fails at sutures, holes, and joints where there is a gap in the lining. In this case, the coating still provides partial cathodic protection for iron, acting as the galvanic anode and corrosion itself instead of the underlying protected metal. The protective zinc layer is consumed by this action, and thus galvanizing provides protection only for a limited period of time.
A more modern layer adds aluminum to the layer as zinc-alume ; aluminum will migrate to cover scratches and thus provide protection for longer periods. This approach relies on aluminum and zinc oxide that protect once-etched surfaces, not oxidation as sacrificial anodes as in traditional galvanic coatings. In some cases, such as a very aggressive environment or long design life, both zinc and coating are applied to provide enhanced corrosion protection.
Typical galvanization of steel products subject to normal daily weathering in an external environment comprises a heat-treated zinc layer of 85 μm. Under normal weather conditions, this will deteriorate at a rate of 1 Ã,Âμm per year, giving about 85 years of protection.
Cathodic protection
Cathodic protection is a technique used to inhibit corrosion of submerged or immersed structures by supplying an electrical charge suppressing an electrochemical reaction. If applied correctly, corrosion can be completely stopped. In its simplest form, this is achieved by attaching the sacrificial anode, thereby making the cathode iron or steel in the cell form. The sacrificial anode must be made of something with a more negative electrode potential than iron or steel, generally zinc, aluminum, or magnesium. The victim's anode will eventually rust, stop its protective action unless it is replaced in a timely manner.
Cathodic protection may also be provided by means of special purpose electric devices to precisely induce electrical charges.
Coating and painting
The formation of rust can be controlled by coatings, such as paints, varnishes, varnishes, or wax bands that isolate iron from the environment. Large structures with closed-box sections, such as modern ships and cars, often have wax-based products (technically "sprinkler oil") injected into this section. Such treatments usually also contain rust inhibitors. Closing steel with concrete can provide protection against steel because of the pH environment of the base at the concrete-steel interface. But the rusting of steel in concrete can still be a problem, because the expanding rust can break or slowly "explode" the concrete from the inside.
As a closely related example, iron bars are used to reinforce stone from the Parthenon in Athens, Greece, but cause extensive damage by rust, swelling, and destruction of building marble components.
When only temporary protection is required for storage or transportation, thin films of oil, fat, or special blends such as Cosmoline can be applied to the surface of the iron. Such care is widely used when "mothballing" steel vessels, cars, or other equipment for long-term storage.
Special antisei lubricant blends are available, and applied to metallic yarns and other precision machining surfaces to protect them from rust. These compounds usually contain fat mixed with copper, zinc, or aluminum powder, and other proprietary materials.
Bluing
Bluing is a technique that can provide limited resistance to rusting for small steel items, such as firearms; In order to succeed, oils that replace the water are rinsed into blued steel and other steels.
Inhibitor
Corrosion inhibitors, such as gas phases or volatile inhibitors, may be used to prevent corrosion within the sealed system. They are ineffective when the air circulation spreads, and carries oxygen and fresh moisture.
Humidity control
Rust can be avoided by controlling moisture in the atmosphere. An example of this is the use of silica gel packets to control the moisture in equipment sent by sea.
Treatment
Removal of rust from small iron or steel objects by electrolysis can be done at home workshop using simple materials such as plastic bucket, tap water, rebar length, washing soda, wire baling, and battery charger.
Rust may be treated with commercial products known as rust converters containing tannic acid or phosphoric acid that combine with rust; removed with an organic acid such as citric acid and vinegar or a stronger hydrochloric acid; or removed with a chelating agent as in some commercial formulations or even a molasses solution.
Economic effects
Rust is associated with degradation of tools and iron-based structures. Since rust has a much higher volume than the starting mass of iron, its buildup can also cause failure by forcing adjacent separate parts - a phenomenon sometimes known as "rust packing." It was the cause of the collapse of the Mianus river bridge in 1983, when the cushioning rusted internally and pushed one corner of the path from its support.
Rust was an important factor in the 1967 Silver Bridge disaster in West Virginia, when a steel suspension bridge collapsed in less than a minute, killing 46 drivers and passengers on the bridge at the time. The Kinzua Bridge in Pennsylvania was destroyed by a tornado in 2003, largely because the central base bolt that holds the structure to the ground has rusted, leaving the bridge moored only by gravity.
Reinforced concrete is also susceptible to rust damage. Internal pressure caused by widespread corrosion of steel and concrete-covered iron can cause the concrete to spill, creating severe structural problems. This is one of the most common modes of failure of bridges and reinforced concrete buildings.
- Structural failure caused by rust
Cultural symbolism
Rust is a common metaphor used for slow decay due to negligence, as it gradually turns strong iron and steel into a soft powder. The vast portion of the Central American and North American industrial zones, once dominated by smelting steel, the automotive industry, and other manufacturers, has undergone severe economic cuts that have led to the region being dubbed the "Rust Belt".
In music, literature, and art, carats are associated with images of faded glory, neglect, decay, and destruction.
Gallery
References
Further reading
- Waldman, J. (2015): Karat - the longest war. Simon & amp; Schuster, New York. ISBN 978-1-4516-9159-7
External links
- corrosion case study Corrosion analysis
- Doctor Corrosion Strengthen the article
Source of the article : Wikipedia
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