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{{Infobox musical artist <!-- See Wikipedia:WikiProject Musicians -->
{{for|the hazard|corrosive}}
| Name = SKE48
{{Mechanical failure modes}}
| Img =
'''Corrosion''' means the breaking down of essential properties in a material due to [[chemical reaction]]s with its surroundings. In the most common use of the word, this means a loss of electrons of [[metal]]s reacting with [[water]] and [[oxygen]]. Weakening of [[iron]] due to oxidation of the iron [[atom]]s is a well-known example of [[#Electrochemical theory|electrochemical corrosion]]. This is commonly known as [[rust]]. This type of damage usually affects [[metal]]lic materials, and typically produces [[oxide]](s) and/or [[salt]](s) of the original metal. Corrosion also includes the dissolution of [[ceramic]] materials and can refer to discoloration and weakening of [[polymer]]s by the [[sun]]'s [[ultraviolet]] light.
| Img_size =
| Landscape =
| Background = group_or_band
| Origin = [[Nagoya]], [[Aichi Prefecture|Aichi]], [[Japan]]
| Genre = [[Japanese pop]]
| Years_active = [[2008]] - present
| Label = [[Pitagoras Productions]]
| Associated_acts =
| URL = [http://www.ske48.co.jp SKE48]
| Current_members = [[#Team S|Team S <small>Details</small>]]
| Past_members =
}}
'''SKE48''' is an all-female Japanese theater/idol group produced by [[Yasushi Akimoto]]. The audition was held during the summer and is set to debut in October 2008. SKE48 will perform in the newly built studio in the renewalled Sunshine Sakae in [[Nagoya]], [[Aichi Prefecture]], every Saturday. The first SKE48 stage will be a revival of Team A's Party ga Hajimaru yo. They will start performing at Sunshine Sakae from [[October 15]], [[2008]]. By May 2009, they will perform regularly.


Yasushi Akimoto was offered to start a production in Nagoya along with the renewal of the Sunshin Sakae, when he was thinking of making his "48 project" a nationwide project. He had a couple of offers even from outside of Japan, so he decided to use Nagoya as the place to move on with the project. Akimoto has said that selected members from both AKB48 and SKE48 may release a single, rather than releasing two different singles.<ref>{{citeweb|url=http://www.scramble-egg.com/artist/event08/sunshine_sakae.htm|title=SUNSHINE SAKAEプレス発表会およびSKE48プロジェクト発表|date=2008-06-07|accessdate=2008-06-09|publisher=Scramble Egg|language=Japanese}}</ref>
Most structural [[alloy]]s corrode merely from exposure to moisture in the [[air]], but the process can be strongly affected by exposure to certain substances (see below). Corrosion can be concentrated locally to form a [[Corrosion#Pitting corrosion|pit]] or crack, or it can extend across a wide area to produce general deterioration. While some efforts to reduce corrosion merely redirect the damage into less visible, less predictable forms, controlled corrosion treatments such as [[passivation]] and [[Chromate conversion coating|chromate-conversion]] will increase a material's corrosion resistance.
[[Image:Rust and dirt.jpg|thumb|right|Rust, the most familiar example of corrosion.]]


In AKB48's single "Oogoe Diamond", [[Jurina Matsui]] became the first and only member of SKE48 to be featured on a single cover and in the single itself. Including Jurina Matsui, some members of SKE48 have appeared in the PV marking the first collaboration made by the two groups, so far.
==Electrochemical theory==
{{main|Electrochemistry}}
One way to understand the structure of metals on the basis of particles is to imagine an array of positively-charged [[ions]] sitting in a negatively-charged "[[electron gas|gas]]" of free [[electrons]]. [[Coulombic attraction]] holds these oppositely-charged particles together, but the positively-charged ions are attracted to negatively charged particles outside the metal as well, such as the negative ions ([[anions]]) in an [[electrolyte]]. For a given ion at the surface of a metal, there is a certain amount of energy to be gained or lost by dissolving into the electrolyte or becoming a part of the metal, which reflects an atom-scale tug-of-war between the electron gas and dissolved anions. The quantity of energy then strongly depends on a host of variables, including the types of ions in a solution and their concentrations, and the number of electrons present at the metal's surface. In turn, corrosion processes cause electrochemical changes, meaning that they strongly affect all of these variables. The overall interaction between electrons and ions tends to produce a state of [[local thermodynamic equilibrium]] that can often be described using basic chemistry and a knowledge of initial conditions


==Galvanic corrosion==
== Members ==
=== 1st performance selection members ===
{{main|Galvanic corrosion}}
* [[Aki Deguchi]] ([[March 14]] [[1988]], [[Mie Prefecture|Mie]])
[[Galvanic corrosion]] occurs when two different metals electrically contact each other and are immersed in an [[electrolyte]]. In order for galvanic corrosion to occur, an electrically conductive path and an ionically conductive path are necessary. This effects a [[galvanic cell|galvanic couple]] where the more active metal corrodes at an accelerated rate and the more [[noble metal]] corrodes at a retarded rate. When immersed, neither metal would normally corrode as quickly without the electrically conductive connection (usually via a wire or direct contact). Galvanic corrosion is often utilised in [[sacrificial anode]]s. What type of metal(s) to use is readily determined by following the [[galvanic series]]. For example, zinc is often used as a sacrificial anode for steel structures, such as pipelines or docked naval ships. Galvanic corrosion is of major interest to the marine industry and also anywhere water can contact pipes or metal structures.
* [[Rikako Hirata]] ([[August 7]] [[1989]], [[Aichi Prefecture|Aichi]])
* [[Mizuki Kuwabara]] ([[February 16]] [[1992]], [[Kochi Prefecture|Kochi]])
* [[Jurina Matsui]] ([[March 8]] [[1997]], Aichi)
* [[Rena Matsui]] ([[July 27]] [[1991]], Aichi)
* [[Yui Matsushita]] ([[July 25]] [[1988]], [[Fukuoka Prefecture|Fukuoka]])
* [[Yūka Nakanishi]] ([[January 24]] [[1989]], Aichi)
* [[Haruka Ono]] ([[November 24]] [[1987]], [[Oita Prefecture|Oita]])
* [[Masana Ōya]] ([[November 6]] [[1990]], Aichi)
* [[Mieko Satō]] ([[June 24]] [[1986]], Aichi)
* [[Rina Shinkai]] ([[August 1]] [[1992]], Aichi)
* [[Kirara Suzuki]] ([[July 31]] [[1993]], [[Kanagawa Prefecture|Kanagawa]])
* [[Shiori Takada]] ([[July 19]] [[1990]], Aichi)
* [[Tsukina Takai]] ([[July 6]] [[1995]], Aichi)
* [[Kumi Yagami]] ([[June 13]] [[1994]], Aichi)
* [[Moe Yamashita]] ([[October 27]] [[1992]], Aichi)


=== Research Students ===
Factors such as relative size of anode (smaller is generally less desirable), types of metal, and operating conditions ([[temperature]], [[humidity]], [[salinity]], etc.) will affect galvanic corrosion. The surface area ratio of the anode and cathode will directly affect the corrosion rates of the materials.
* [[Kanako Hiramatsu]] ([[November 14]] [[1991]], Aichi)
* [[Honami Inagaki]] ([[March 25]] [[1989]], Aichi)
* [[Aika Maekawa]] ([[March 11]] [[1997]], Aichi)
* [[Sayuki Mori]] ([[November 3]] [[1996]], Aichi)
* [[Kiharu Ozeki]] ([[December 24]] [[1994]], Aichi)
* [[Seira Satō]] ([[April 30]] [[1992]], Mie)
* [[Aiko Shibaki]] ([[October 18]] [[1990]], Aichi)


===Galvanic series===
== See also ==
*[[AKB48]]
{{main|Galvanic series}}
In a given sea environment (one standard medium is aerated, room-temperature [[seawater]]), one metal will be either more ''[[noble metal|noble]]'' or more ''active'' than the next, based on how strongly its ions are bound to the surface. Two metals in electrical contact share the same electron gas, so that the tug-of-war at each surface is translated into a competition for free electrons between the two materials. The noble metal will tend to take electrons from the active one, while the electrolyte hosts a flow of ions in the same direction. The resulting mass flow or electrical current can be measured to establish a hierarchy of materials in the medium of interest. This hierarchy is called a ''[[galvanic series]]'', and can be a very useful in predicting and understanding corrosion.


== References ==
==Resistance to corrosion==
{{Reflist}}
Some metals are more intrinsically resistant to corrosion than others, either due to the fundamental nature of the electrochemical processes involved or due to the details of how reaction products form. For some examples, see [[galvanic series]].. If a more susceptible material is used, many techniques can be applied during an item's manufacture and use to protect its materials from damage.


== External links ==
===Intrinsic chemistry===
*[http://www.ske48.co.jp SKE48 official website] {{ja icon}}
[[Image:GoldNuggetUSGOV.jpg|left|thumb|150px|[[Gold]] nuggets do not naturally corrode, even on a geological time scale.]]
The materials most resistant to corrosion are those for which corrosion is [[thermodynamics|thermodynamically]] unfavorable. Any corrosion products of [[gold]] or [[platinum]] tend to decompose spontaneously into pure metal, which is why these elements can be found in metallic form on Earth, and is a large part of their intrinsic value. More common "base" metals can only be protected by more temporary means.


{{SKE48}}
Some metals have naturally slow [[reaction]] [[chemical kinetics|kinetics]], even though their corrosion is thermodynamically favorable. These include such metals as [[zinc]], [[magnesium]], and [[cadmium]]. While corrosion of these metals is continuous and ongoing, it happens at an acceptably slow rate. An extreme example is [[graphite]], which releases large amounts of energy upon [[oxidation]], but has such slow kinetics that it is effectively immune to electrochemical corrosion under normal conditions.

===Passivation===
{{main|Passivation}}
Given the right conditions, a thin film of corrosion products can form on a metal's surface spontaneously, acting as a barrier to further oxidation. When this layer stops growing at less than a micrometre thick under the conditions that a material will be used in, the phenomenon is known as [[passivation]] (rust, for example, usually grows to be much thicker, and so is not considered passivation, because this mixed oxidized layer is not protective). While this effect is in some sense a property of the material, it serves as an indirect kinetic barrier: the reaction is often quite rapid unless and until an impermeable layer forms. Passivation in air and water at moderate [[pH]] is seen in such materials as [[aluminium]], [[stainless steel]], [[titanium]], and [[silicon]].

These conditions required for passivation are specific to the material. The effect of pH is recorded using [[Pourbaix diagram]]s, but many other factors are influential. Some conditions that inhibit passivation include: high [[pH]] for aluminum, low pH or the presence of [[chloride]] ions for stainless steel, high temperature for titanium (in which case the oxide dissolves into the metal, rather than the electrolyte) and [[fluoride]] ions for silicon. On the other hand, sometimes unusual conditions can bring on passivation in materials that are normally unprotected, as the alkaline environment of [[concrete]] does for [[steel]] [[rebar]]. Exposure to a liquid metal such as [[mercury (element)|mercury]] or hot [[solder]] can often circumvent passivation mechanisms.

==Corrosion in passivated materials==
[[Passivation]] is extremely useful in alleviating corrosion damage, but care must be taken not to trust it too thoroughly. Even a high-quality alloy will corrode if its ability to form a passivating film is hindered. Because the resulting modes of corrosion are more exotic and their immediate results are less visible than [[rust]] and other bulk corrosion, they often escape notice and cause problems among those who are not familiar with them.

===Pitting corrosion===
{{main|Pitting corrosion}}
Certain conditions, such as low concentrations of oxygen or high concentrations of species such as [[chloride]] which compete as [[anion]]s, can interfere with a given alloy's ability to re-form a passivating film. In the worst case, almost all of the surface will remain protected, but tiny local fluctuations will degrade the oxide film in a few critical points. Corrosion at these points will be greatly amplified, and can cause ''corrosion pits'' of several types, depending upon conditions. While the corrosion pits only [[nucleation|nucleate]] under fairly extreme circumstances, they can continue to grow even when conditions return to normal, since the interior of a pit is naturally deprived of oxygen and locally the pH decreases to very low values and the corrosion rate increases due to an auto-catalitic process. In extreme cases, the sharp tips of extremely long and narrow can cause [[stress concentration]] to the point that otherwise tough alloys can shatter, or a thin film pierced by an invisibly small hole can hide a thumb sized pit from view. These problems are especially dangerous because they are difficult to detect before a part or structure [[structural failure|fails]]. Pitting remains among the most common and damaging forms of corrosion in passivated alloys, but it can be prevented by control of the alloy's environment, which often includes ensuring that the material is exposed to oxygen uniformly (i.e., eliminating crevices)

===Weld decay and knifeline attack===
{{main|Intergranular corrosion}}
[[Stainless steel]] can pose special corrosion challenges, since its passivating behavior relies on the presence of a minor alloying component ([[Chromium]], typically only 18%). Due to the elevated temperatures of [[welding]] or during improper [[heat treatment]], chromium [[carbide]]s can form in the [[crystallite|grain boundaries]] of stainless alloys. This chemical reaction robs the material of chromium in the zone near the grain boundary, making those areas much less resistant to corrosion. This creates a [[electrochemistry|galvanic couple]] with the well-protected alloy nearby, which leads to ''weld decay'' (corrosion of the grain boundaries near [[welding|welds]]) in highly corrosive environments. Special alloys, either with low carbon content or with added carbon "[[getter]]s" such as [[titanium]] and [[niobium]] (in types 321 and 347, respectively), can prevent this effect, but the latter require special heat treatment after welding to prevent the similar phenomenon of ''knifeline attack''. As its name applies, this is limited to a small zone, often only a few micrometres across, which causes it to proceed more rapidly. This zone is very near the weld, making it even less noticeable<sup>1</sup>.

===Crevice corrosion===
{{main|Crevice corrosion}}
Crevice corrosion is a localized form of corrosion occurring in spaces to which the access of the working fluid from the environment is limited and a concentration cell, areas with different oxygen concentration, will take place with conseguent high corrosion rate . These spaces are generally called crevices. Examples of crevices are gaps and contact areas between parts, under gaskets or seals, inside cracks and seams, spaces filled with deposits and under sludge piles.

==Microbial corrosion==
[[Image:Titanic-bow seen from MIR I submersible.jpeg|thumb|''[[RMS Titanic|Titanic]]''<nowiki>'s</nowiki> bow exhibiting microbial corrosion damage in the form of 'rusticles']]
{{main|Microbial corrosion}}
[[Microbial corrosion]], or bacterial corrosion, is a corrosion caused or promoted by [[microorganism]]s, usually [[chemoautotroph]]s. It can apply to both metals and non-metallic materials, in both the presence and lack of [[oxygen]]. [[Sulfate-reducing bacteria]] are common in lack of oxygen; they produce [[hydrogen sulfide]], causing [[sulfide stress cracking]]. In presence of oxygen, some bacteria directly oxidize iron to iron oxides and hydroxides, other bacteria oxidize sulfur and produce sulfuric acid causing [[biogenic sulfide corrosion]]. [[Concentration cell]]s can form in the deposits of corrosion products, causing and enhancing [[galvanic corrosion]].

==High temperature corrosion==
High temperature corrosion is chemical deterioration of a material (typically a metal) under very high temperature conditions. This non-galvanic form of corrosion can occur when a metal is subject to a high temperature atmosphere containing oxygen, sulfur or other compounds capable of oxidising (or assisting the oxidation of) the material concerned. For example, materials used in aerospace, power generation and even in car engines have to resist sustained periods at high temperature in which they may be exposed to an atmosphere containing potentially highly corrosive products of combustion.

The products of high temperature corrosion can potentially be turned to the advantage of the engineer. The formation of oxides on stainless steels, for example, can provide a protective layer preventing further atmospheric attack, allowing for a material to be used for sustained periods at both room and high temperature in hostile conditions. Such high temperature corrosion products in the form of [[compacted oxide layer glaze]]s have also been shown to prevent or reduce wear during high temperature sliding contact of metallic (or metallic and ceramic) surfaces.
===Surface treatments===
[[Image:Galvanized surface.jpg|thumb|180px|right|[[Galvanization|Galvanized]] surface]]

====Applied coatings====
{{main|Galvanization}}
[[Plating]], [[paint]]ing, and the application of [[vitreous enamel|enamel]] are the most common anti-corrosion treatments. They work by providing a barrier of corrosion-resistant material between the damaging environment and the (often cheaper, tougher, and/or easier-to-process) structural material. Aside from cosmetic and manufacturing issues, there are tradeoffs in mechanical flexibility versus resistance to abrasion and high temperature. Platings usually fail only in small sections, and if the plating is more noble than the substrate (for example, [[chromium]] on [[steel]]), a galvanic couple will cause any exposed area to corrode much more rapidly than an unplated surface would. For this reason, it is often wise to plate with a more active metal such as zinc or cadmium.

====Reactive coatings====
If the environment is controlled (especially in recirculating systems), [[corrosion inhibitor]]s can often be added to it. These form an electrically insulating and/or chemically impermeable coating on exposed metal surfaces, to suppress electrochemical reactions. Such methods obviously make the system less sensitive to scratches or defects in the coating, since extra inhibitors can be made available wherever metal becomes exposed. Chemicals that inhibit corrosion include some of the salts in [[hard water]] (Roman water systems are famous for their [[Eifel Aqueduct#The aqueduct as a stone quarry|mineral deposits]]), [[chromate]]s, [[phosphate]]s, and a wide range of specially-designed chemicals that resemble [[surfactant]]s (i.e. long-chain organic molecules with ionic end groups).

[[Image:Belaying8.jpg|thumb|left|This figure-8 descender is annodized with a yellow finish. [[Climbing equipment]] is available in a wide range of anodized colors.]]

====Anodization====
{{main|Anodising}}
Aluminium alloys often undergo a surface treatment. Electrochemical conditions in the bath are carefully adjusted so that uniform pores several [[nanometer]]s wide appear in the metal's oxide film. These pores allow the oxide to grow much thicker than [[passivation|passivating]] conditions would allow. At the end of the treatment, the pores are allowed to seal, forming a harder-than-usual surface layer. If this coating is scratched, normal passivation processes take over to protect the damaged area.

=== Controlled Permeability Formwork ===
{{main|Controlled Permeability Formwork}}
Controlled Permeability Formwork (CPF) is a method of preventing the corrosion of [[reinforcement]] by naturally enhancing the durability of the [[cover]] during concrete placement, . CPF has been used in environments to combat the effects of [[Carbonation]], [[chloride]]s, [[frost]] and abrasion.

=== Cathodic protection ===
{{main|Cathodic protection}}
Cathodic protection (CP) is a technique to control the corrosion of a metal surface by making that surface the [[cathode]] of an [[electrochemical cell]].

It is a method used to protect metal structures from corrosion. Cathodic protection systems are most commonly used to protect [[steel]], water, and fuel [[pipeline transport|pipelines]] and tanks; steel pier [[Deep foundation|piles]], ships, and offshore [[oil platform]]s.

For effective CP, the potential of the steel surface is polarized (pushed) more negative until the metal surface has a uniform potential. With a uniform potential, the driving force for the corrosion reaction is halted. For galvanic CP systems, the anode material corrodes under the influence of the steel, and eventually it must be replaced. The polarization is caused by the current flow from the anode to the cathode, driven by the difference in electrochemical potential between the anode and the cathode.

For larger structures, galvanic anodes cannot economically deliver enough current to provide complete protection. [[Cathodic protection#Impressed Current CP|Impressed Current Cathodic Protection]] (ICCP) systems use anodes connected to a [[direct current|DC]] power source (a [[cathodic protection rectifier]]). Anodes for ICCP systems are tubular and solid rod shapes of various specialized materials. These include high [[silicon]] [[cast iron]], [[graphite]], mixed [[metal]] [[oxide]] or [[platinum]] coated titanium or [[niobium]] coated rod and wires.

==Economic impact==
The US [[Federal Highway Administration]] released a study, entitled ''Corrosion Costs and Preventive Strategies in the United States,'' in 2002 on the direct costs associated with metallic corrosion in nearly every U.S. industry sector. The study showed that for 1998 the total annual estimated direct cost of corrosion in the U.S. was approximately $276 billion (approximately 3.1% of the US [[gross domestic product]]). FHWA Report Number:FHWA-RD-01-156. The [[NACE International]] [http://www.nace.org website] has a [http://www.nace.org/nace/content/publicaffairs/cost_corr_pres/cost_corrosion_files/frame.htm summary] slideshow of the report findings. Jones<sup>1</sup> writes that electrochemical corrosion causes between $8 billion and $128 billion in economic damage per year in the United States alone, degrading structures, machines, and containers.
[[Image:Silver Bridge collapsed, Ohio side.jpg|thumb|right|The collapsed Silver Bridge, as seen from the Ohio side]]
Rust is one of the most common causes of bridge accidents for example. As rust has a much higher volume than the originating mass of iron, its build-up can also cause failure by forcing apart adjacent parts. It was the cause of the collapse of the [[Mianus river bridge]] in 1983, when the bearings rusted internally and pushed one corner of the road slab off its support. Three drivers on the roadway at the time died as the slab fell into the river below. The following [[NTSB]] investigation showed that a drain in the road had been blocked for road re-surfacing, and had not been unblocked so that runoff water penetrated the support hangers. It was also difficult for maintenance engineers to see the bearings from the inspection walkway. Rust was also an important factor in the [[Silver Bridge]] disaster of 1967 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.

Similarly corrosion of concrete-covered steel and iron can cause the concrete to [[spall]], creating severe structural problems. It is one of the most common failure modes of [[reinforced concrete]] [[bridge]]s.

==Corrosion in nonmetals==
Most [[ceramic]] materials are almost entirely immune to corrosion. The strong ionic and/or covalent bonds that hold them together leave very little free chemical energy in the structure; they can be thought of as already corroded. When corrosion does occur, it is almost always a simple dissolution of the material or chemical reaction, rather than an electrochemical process. A common example of corrosion protection in ceramics is the [[Calcium oxide|lime]] added to soda-lime [[glass]] to reduce its solubility in water; though it is not nearly as soluble as pure [[sodium silicate]], normal glass does form sub-microscopic flaws when exposed to moisture. Due to its [[brittle]]ness, such flaws cause a dramatic reduction in the strength of a glass object during its first few hours at room temperature.

[[Polymer degradation]] is due to a wide array of complex and often poorly-understood physiochemical processes. These are strikingly different from the other processes discussed here, and so the term "corrosion" is only applied to them in a loose sense of the word. Because of their large molecular weight, very little [[entropy]] can be gained by mixing a given mass of polymer with another substance, making them generally quite difficult to dissolve. While dissolution is a problem in some polymer applications, it is relatively simple to design against. A more common and related problem is ''swelling'', where small molecules infiltrate the structure, reducing strength and stiffness and causing a volume change. Conversely, many polymers (notably flexible [[polyvinyl chloride|vinyl]]) are intentionally swelled with [[plasticizer]]s, which can be leached out of the structure, causing brittleness or other undesirable changes. The most common form of degradation, however, is a decrease in polymer chain length. Mechanisms which break polymer chains are familiar to biologists because of their effect on [[DNA]]: [[ionizing radiation]] (most commonly [[ultraviolet]] light), [[Radical (chemistry)|free radical]]s, and [[redox|oxidizer]]s such as [[oxygen]], [[ozone]], and [[chlorine]]. [[Additive]]s can slow these process very effectively, and can be as simple as a UV-absorbing [[pigment]] (i.e., [[titanium dioxide]] or [[carbon black]]). [[Plastic shopping bag]]s often do not include these additives so that they break down more easily as [[litter]].

== Corrosion of glasses ==
The corrosion of silicate glasses in aqueous solutions is governed by two mechanisms: [[diffusion]]-controlled leaching (ion exchange) and glass network hydrolytic dissolution<ref>A.K. Varshneya. ''Fundamentals of inorganic glasses''. Society of Glass Technology, Sheffield, 682pp. (2006).</ref>. Both corrosion mechanisms strongly depend on the [[pH]] of contacting solution: the rate of ion exchange decreases with pH as 10<sup>-0.5pH</sup> whereas the rate of hydrolytic dissolution increases with pH as 10<sup>0.5pH</sup> <ref>M.I. Ojovan, W.E. Lee. ''New Developments in Glassy Nuclear Wasteforms''. Nova Science Publishers, New York, 136pp. (2007).</ref>

Numerically, corrosion rates of glasses are characterised by normalised corrosion rates of elements NR<sub>i</sub> (g/cm<sup>2</sup> d) which are determined as the ratio of total amount of released species into the water M<sub>i</sub> (g) to the water-contacting surface area S (cm<sup>2</sup>), time of contact t (days) and weight fraction content of the element in the glass f<sub>i</sub>:

NR<sub>i</sub>=M<sub>i</sub>/S·f<sub>i</sub>·t

The overall corrosion rate is a sum of contributions from both mechanisms (leaching + dissolution) NR<sub>i</sub>=Nrx<sub>i</sub>+NRh.
Diffusion-controlled leaching (ion exchange) is characteristic of the initial phase of corrosion and involves replacement of alkali ions in the glass by a hydronium (H<sub>3</sub>O<sup>+</sup>) ion from the solution. It causes an ion-selective depletion of near surface layers of glasses and gives an inverse square root dependence of corrosion rate with exposure time. The diffusion controlled normalised leaching rate of cations from glasses (g/cm<sup>2</sup> d) is given by:

NRx<sub>i</sub>=2·ρ·(D<sub>i</sub>/π·t)<sup>1/2</sup>

where t is time, D<sub>i</sub> is the i-th cation effective diffusion coefficient (cm<sup>2</sup>/d), which depends on pH of contacting water as D<sub>i</sub> = D<sub>i0</sub>·10<sup>-pH</sup>, and ρ is the density of the glass (g/cm<sup>3</sup>).
Glass network dissolution is characteristic of the later phases of corrosion and causes a congruent release of ions into the water solution at a time-independent rate in dilute solutions (g/cm<sup>2</sup> d):

NRh=ρr<sub>h</sub>,

where r<sub>h</sub> is the stationary [[hydrolysis]] (dissolution) rate of the glass (cm/d).
In closed systems the consumption of protons from the aqueous phase increases the pH and causes a fast transition to hydrolysis<ref> ''Corrosion of Glass, Ceramics and Ceramic Superconductors''. Edited by: D.E. Clark, B.K. Zoitos, William Andrew Publishing/Noyes, 672pp. (1992).</ref>. However further silica saturation of solution impedes hydrolysis and causes the glass to return to an ion-exchange, e.g. diffusion-controlled regime of corrosion.

In typical natural conditions normalised corrosion rates of silicate glasses are very low and are of the order of 10<sup>-7</sup> - 10<sup>-5</sup> g/cm<sup>2</sup> d. The very high durability of silicate glasses in water makes them suitable for hazardous and nuclear waste immobilisation.

===Glass corrosion tests===
[[Image:Spidergraph ChemDurab.png|thumb|Influences of selected glass component additions on the chemical durability against water corrosion of a specific base glass (corrosion test ISO 719).<ref> [http://glassproperties.com/chemical_durability/ Calculation of the Chemical Durability (Hydrolytic Class) of Glasses]</ref>]]
There exist numerous standardized procedures for measuring the corrosion (also called '''chemical durability''') of glasses in [[pH|neutral]], [[pH|basic]], and [[pH|acidic]] environments, under simulated environmental conditions, in simulated body fluid, at high temperature and pressure<ref>[http://www.vscht.cz/sil/english/chemtech_ag/vht.htm Vapor Hydration Testing (VHT)]</ref>, and under other conditions.

In the standard procedure ISO 719<ref>[http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=4948 International Organization for Standardization, Procedure 719 (1985)]</ref> a test of the extraction of water soluble basic compounds under neutral conditions is described: 2 g glass, particle size 300-500 μm, is kept for 60 min in 50 ml de-ionized water of grade 2 at 98°C. 25 ml of the obtained solution is titrated against 0.01 mol/l [[Hydrochloric acid|HCl]] solution. The volume of HCl needed for neutralization is recorded and classified following the values in the table below.

{| class="wikitable"
|-
! 0.01M HCl needed to neutralize<br>extracted basic oxides, ml
! Extracted [[Sodium oxide|Na<sub>2</sub>O]]<br>equivalent, μg
! Hydrolytic<br>class
|-
| to 0.1
| to 31
| 1
|-
| above 0.1 to 0.2
| above 31 to 62
| 2
|-
| above 0.2 to 0.85
| above 62 to 264
| 3
|-
| above 0.85 to 2.0
| above 264 to 620
| 4
|-
| above 2.0 to 3.5
| above 620 to 1085
| 5
|-
| above 3.5
| above 1085
| >5
|}

==References==
{{reflist}}
* {{cite book
| title = Principles and Prevention of Corrosion
| edition = 2nd edition
| last = Jones
| first = Denny
| authorlink = Denny A. Jones
| publisher = [[Prentice Hall]]
| location = [[Upper Saddle River, New Jersey]]
| year = [[1996]]
| id = ISBN 0-13-359993-0 }}
* [http://www.llnl.gov/es_and_h/hsm/doc_14.08/doc14-08.html Working Safely with Corrosive Chemicals]

== See also ==
<div style="-moz-column-count:3; column-count:3;">
* [[Cathodic protection]]
* [[Corrosion inhibitor]]
* [[Chemical hazard label]]
* [[Controlled Permeability Formwork]]
* [[Copper band]] corrosion.
* [[Electronegativity]]
* [[Environmental stress fracture]]
* [[Forensic engineering]]
* [[Galvanization]]
* [[Hydrogen analyzer]]
* [[Oxidation]]
* [[Periodic table]]
* [[Rust]]ing
* [[Salt spray test]]
* [[STLE|Society of Tribologists and Lubrication Engineers]]
* [[Stress corrosion cracking]]
* [[Zinc pest]]
</div>

== External links ==
{{Commons|Category:Corrosion|Corrosion}}
*[http://www.nace.org/ NACE International] -Professional society for corrosion engineers ( [[NACE International|NACE]] )
*[http://www.corrosion-doctors.org/ corrosion-doctors.org] - Site dedicated to corrosion of all forms
*[http://www.efcweb.org/Member_Societies.html efcweb.org] - European Federation of Corrosion
*[http://www.corrosionist.com/Corrosion_Fundamental.htm Metal Corrosion] - Corrosion Theory
*[http://www.worldstainless.org/About+stainless/What+is/Corrosion/ worldstainless.org] Corrosion Properties of Stainless Steel
*[http://openlearn.open.ac.uk/mod/resource/view.php?id=233628 corrosion case studies] Analysis of corrosion
*[http://www.composite-agency.com/materials-forum.htm forum composite community]Community for surface corrosion & chemical degradation of composite materials
*[http://electrochem.cwru.edu/ed/encycl/art-c02-corrosion.htm Electrochemistry of corrosion]
* A comprehensive 3.4-Mb pdf handbook "Corrosion Prevention and Control", 2006, 296 pages, US DoD, [http://ammtiac.alionscience.com/pdf/Corrosion_Hdbk_S2.pdf here]


[[Category:Corrosion| ]]
[[Category:Girl groups]]
[[Category:Glass engineering and science]]
[[Category:Japanese musical groups]]
[[Category:Sony Music Japan artists]]


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Revision as of 15:37, 10 October 2008

SKE48

SKE48 is an all-female Japanese theater/idol group produced by Yasushi Akimoto. The audition was held during the summer and is set to debut in October 2008. SKE48 will perform in the newly built studio in the renewalled Sunshine Sakae in Nagoya, Aichi Prefecture, every Saturday. The first SKE48 stage will be a revival of Team A's Party ga Hajimaru yo. They will start performing at Sunshine Sakae from October 15, 2008. By May 2009, they will perform regularly.

Yasushi Akimoto was offered to start a production in Nagoya along with the renewal of the Sunshin Sakae, when he was thinking of making his "48 project" a nationwide project. He had a couple of offers even from outside of Japan, so he decided to use Nagoya as the place to move on with the project. Akimoto has said that selected members from both AKB48 and SKE48 may release a single, rather than releasing two different singles.[1]

In AKB48's single "Oogoe Diamond", Jurina Matsui became the first and only member of SKE48 to be featured on a single cover and in the single itself. Including Jurina Matsui, some members of SKE48 have appeared in the PV marking the first collaboration made by the two groups, so far.

Members

1st performance selection members

Research Students

See also

References

  1. ^ "SUNSHINE SAKAEプレス発表会およびSKE48プロジェクト発表" (in Japanese). Scramble Egg. 2008-06-07. Retrieved 2008-06-09.

External links

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