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Chobam Armour

Chobam armour

Chobham armour is a composite armour developed at the British tank research centre on Chobham Common. Although the exact composition of Chobham armour remains a secret, it appears to be a combination of ceramic layered between armour steel plating, a combination that is excellent at defeating high explosive anti-tank (HEAT) rounds. Possible ceramics for such armours are: boron carbide, silicon carbide, aluminium oxide (sapphire or "alumina"), titanium boride or Syndie, a synthetic diamond composite. Of these boron carbide is the hardest and lightest, but also the most expensive and brittle. Over the years newer composites have been developed, giving about five times the protection value of the original pure ceramics, the best of which were again about five times as effective as a steel plate of equal weight. The ceramic tiles are encased within a metal (today typically titanium) matrix, either by isostatically pressing them into the heated matrix, or by glueing them with an epoxy resin. A more general name is therefore: CMC or Ceramic Matrix Composite. A titanium matrix is extremely expensive to manufacture but the metal is favoured for its lightness, strength and resistance to corrosion, a constant problem with CMC's. The Rank company claims to have invented an alumina matrix for the insertion of boron carbide or silicon carbide tiles. The exact nature of the protection offered by this layering remained a mystery for some time, but it was eventually revealed that Chobham armour works in a manner somewhat similar to reactive armour. When the armour is hit by a HEAT round the ceramic layer shatters under the impact point, forming a dust under high pressure. When the HEAT round "burns through" the outer layers of armour and reaches the ceramic, the dust comes flying back out the hole, slowing the jet of metal. Modern tanks also have to face kinetic energy penetrator rounds of various sorts, which the ceramic layer is not particularly effective against: for the original ceramics the resistance against penetrators was about three times, for the newest composites it is about ten times less than against HEAT-rounds. For this reason many modern designs include additional layers of heavy metals to add more density to the overall armor package. The metal used appears to be either tungsten or, in the case of later M1 Abrams tanks, depleted uranium. Some companies offer titanium carbide modules. These metal modules or rods have many perforations or expansion spaces reducing the weight up to about a third while keeping the protective qualities fairly constant. The effectiveness of Chobham armour was demonstrated in the first Gulf War, where no Coalition tank was destroyed by the obsolete Iraqi armor. In some cases the tanks in question were subject to multiple point-blank hits by both KE-penetrators and HEAT rounds, but the old Russian ammunition used by the Iraqis, in their Polish licence built T-72's, their old T-55's bought from Russia and upgraded with "enigma" type armour, and T-62 tanks left them completely incapable of penetrating coalition armour. It's also worth noting that the Iraqis rarely actually hit the coalition tanks, because of lack of training and inferior optics. To date, only 5-10 Chobham-protected tanks have been defeated by enemy fire in combat, including an M1 that was hit in a weak spot by an RPG-7 in the Second Gulf War. The latest version of Chobham armour is used on the Challenger 2 (called Dorchester armour), and (though the composition most probably differs) the M1 Abrams series of tanks, which according to official sources is presently protected by silicon carbide tiles. Given the publicly stated protection level for the earliest M1: 350 mm steel equivalence against KE-penetrators (APFSDS), it seems to have been equipped with alumina tiles. Though it is often claimed to be otherwise, the Leopard 2 does in fact not use Chobham armour, but pure perforated armour, avoiding the horrendous procurement, maintenance and replacement costs of those ceramic armour systems not based on the cheap but rather ineffective alumina. Ceramic modules will corrode their matrix and gradually fracture during driving and the smallest come at over $100,000. For many modern tanks, such as the French Leclerc and the Italian Ariete, it is yet unknown which type is used. There is a general trend away from ceramic armour towards perforated armour; but even many tanks from the seventies like the Leopard 1A3 and A4, the Italian OF-40 and the French AMX-32 and AMX-40 prototypes used the latter system. Category:Armor Category:Composite materials

Composite armour

Composite Armour is a type of vehicle armour consisting of layers of different material such as metals, plastics, ceramics or air. Most composite armours are lighter than their all-metal equivalent, but instead occupy a larger volume for the same resistance to penetration. It is possible to design composite armour stronger, lighter and less voluminous than traditional armour, but the cost is often prohibitively high, restricting its use to especially vulnerable parts of a vehicle. The most common type of composite armour today is Chobham armour, first developed and used by the British in the experimental FV 4211 tank, which was based on Chieftain tank components. Chobham sandwiches a layer of ceramic between two plates of steel armour, which was shown to dramatically increase the resistance to high explosive anti-tank (HEAT) rounds. HEAT had posed a serious threat to armoured vehicles since its introduction in WWII, and Chobham was such an improvement that it was soon used on the new US M1 Abrams main battle tank (MBT) as well. It is the fabrication of the ceramic in large tiles that gives the Challenger and Abrams their "slab sided" look. Chobham's precise mechanism for defeating HEAT was something of a mystery until the 1980s. High speed photography showed that the ceramic material shatters as the HEAT round penetrates, blowing up to a huge volume which then expands back out the hole and pushes the metal jet of the HEAT with it. The effectiveness of the system was amply demonstrated in Desert Storm, where not a single British Army Challenger tank was lost to enemy tank fire. Chobham-type armor is currently in its third generation and is used on modern western tanks such as the the British Challenger 2E and the American M1A2 SEP Abrams. The first widespread use of a composite armour appears to be on the Soviet T-64. It used an armour known as Combination K, which apparently is glass reinforced plastic sandwiched between inner and outer steel layers. Through a mechanism called thixotropy, the resin changes to a fluid under constant pressure, allowing the armour to be moulded into curved shapes. Later models of the T-64, along with newer designs, used a boron carbide-filled resin aggregate for greatly improved protection. However the quality of the tanks produced during this era varied widely; if the boron carbide was not available in time to meet production quotas, the tank would be shipped with any filler that could be found, and sometimes nothing at all. In order to deal with these problems, the Soviets invested heavily in reactive armour, which allowed them some ability to control quality. The Russian T-90 introduced Kontakt-5, effective both against HEAT warheads and APFSDS. It also carried an appliqué armour pack which is composed of a frontal steel plate about 60 mm thick, backed by an insert of three layers of inert interlayer reactive armour, composed of steel plates and penapolyurethane filler. Composite armour has since been applied to smaller vehicles, right down to jeep-sized. Many of these systems are applied as upgrades to existing armour, which makes them difficult to place around the entire vehicle. Nevertheless they are often surprisingly effective; ceramic upgrades to Canadian M-113s were carried out in the 1990s, after it was realized that it would offer more protection than newly built APCs like the M2 Bradley.

External link

- [http://www.defense-update.com/features/du-1-04/feature-armor-protection.htm Defense Update/Advanced Armor Concepts] Category:Armor

Chobham Common

Chobham Common is large heath area in Surrey, England, formerly a freehold owned by the Earl of Onslow and purchased by Surrey County Council in 1966. Chobham Common is a nature reserve and SSSI (Site of Special Scientific Interest). It is one of the last remaining habitats of the ant Formica rufibarbis, and also is host to such species as the sand lizard and the smooth snake. The Common apparently includes a Bronze Age burial mound (barrow) but its location is no longer clear. A number of other barrows are scattered through the local area. Another apparently Bronze Age work is a series of earthworks known as the Bee Garden, although dating the structure appears difficult. A similar structure with triple embankments, often called the second bee garden, was constructed in the Middle Ages, although its purpose is obscure perhaps a stock enclosure. In the 7th century, the Manor of Chobham was granted to Chertsey Abbey by the Crown and remained in the possession of the Abbey until its surrender to Henry VIII in 1537.John de Rutherwyk, Abbot of Chertsey Abbey during the reign of Edward II created Gracious Pond. This has silted up and is now a wet wood of about 8 ha (20 acres) that is an enclosure in the common. He also enclosed Langshot and he made a moat with running water around Chobham Manor (now Chobham Park). On July 20th 1614 the Manor of Chobham was conveyed to Sir George More, reverting back to the Crown on his death. On November 19th 1620 the Manor was granted to Sir Edward Zouch and again reverted back to the Crown on his death. George II granted the Manor to Walter Abel for a term of 1000 years and Lord Onslow derived his title to the Manor from Walter Abel. The Manor then comprised 1,075 ha (2,658 acres) of arable land and 677 ha (1,672 acres) of grassland. Chobham Common formed part of this lease. Following the Napoleonic Wars, allotments were enclosed for the poor at Jubilee Mount and Burrowhill. In 1853 the Common was used as a large temporary camp for the Army before shipping the troops to the Crimean War. The Monument on the northern part of the Common was built in 1901 to commemorate Queen Victoria's visit in 1853 to review her troops. (According to the Punch magazine of the time, conditions were very unpleasant due to wet weather. For instance, there were cartoons of soldiers with frog's legs, and of soldiers fishing whilst sitting in their tents.) Several curiously alternating banks and depressions just north of the Monument, and on other parts of the Common, are thought to be First World War training entrenchments. In 1952 a stone was erected in Chobham Place Woods by Sir Edward le Marchant, in memory of these troops. During the World War II, The Tank Factory was built on private land near the Common, but extended onto part of the Common. In compensation for the lost land, Chobham Place Woods and Round Pond Woods were added to the Common. Much of the common was used as a driving ground for testing the new tanks and armoured vehicles that were being designed and developed. The damage to the vegetation and erosion caused at that time are still not entirely eradicated, and major portions of the Common had to be ploughed and reseeded after the war. There was also an Italian prisoner of war camp on part of the common now owned by the Sunningdale Golf Club, and an ammunition dump adjoining the common at Childown. Today the Tank Factory is famous for the development of Chobham armour. After the Common was opened to the public, horse riding on the common became popular. However the effect of the horses was fairly detrimental, and there has been ongoing friction between the county and the riders since then.

External links

- [http://www.chobham.org.uk/common.htm Chobham Common] includes a map
- [http://www.surreyheath.gov.uk/surreyheath/events.nsf/webPages/A368144B2DC937A080256D8600351A2A The Military Camp on Chobham Common 1853] Category:Surrey Category:Site of Special Scientific Interest

Ceramic

The word ceramic is derived from the Greek word Κεραμεικος (-keramos- the name of a suburb of Athens). The term covers inorganic non-metallic materials whose formation is due to the action of heat. Up until the 1950s or so, the most important of these were the traditional clays, made into pottery, bricks, tiles and the like, along with cements and glass. The traditional crafts are described in the article on pottery. A composite material of ceramic and metal is known as cermet. The Venus of Dolni Vestonice is the oldest known ceramic in the world. Historically, ceramic products have been hard, porous and brittle. The study of ceramics consists to a large extent of methods to mitigate these problems, and accentuate the strengths of the materials, as well as to offer up unusual uses for these materials.

Classifications of technical ceramics

Technical Ceramics can also be classified into three distinct material categories:
- Oxides: Alumina, zirconia
- Non-oxides: Carbides, borides, nitrides, silicides
- Composites: Particulate reinforced, combinations of oxides and non-oxides. Each one of these classes can develop unique material properties

Examples of ceramic materials

- Barium titanate (often mixed with strontium titanate) displays ferroelectricity, meaning that its mechanical, electrical, and thermal responses are coupled to one another and also history-dependent. It is widely used in electromechanical transducers, ceramic capacitors, and data storage elements. Grain boundary conditions can create PTC effects in heating elements.
- Boron carbide (B₄C), which is used in some helicopter and tank armor.
- Boron_nitride is structurally isoelectronic to carbon and takes on similar physical forms: a graphite-like one used as a lubricant, and a diamond-like one used as an abrasive.
- Bricks (mostly aluminium silicates), used for construction.
- Ferrite (Fe₃O₄), which is ferrimagnetic and is used in the core of electrical transformers and magnetic core memory.
- Lead zirconate titanate is another ferroelectric material.
- Magnesium diboride (Mg B₂), which is an unconventional superconductor.
- Silicon carbide (Si C), which is used as a susceptor in microwave furnaces, a commonly used abrasive, and as a refractory material.
- Silicon nitride (Si₃N₄), which is used as an abrasive powder.
- Steatite is used as an electrical insulator.
- Uranium oxide (UO₂), used as fuel in nuclear reactors.
- Yttrium barium copper oxide (Y Ba₂Cu₃O_7-x), a high temperature superconductor.
- Zinc oxide (Zn O), which is a semiconductor, and used in the construction of varistors.
- Zirconia, which in pure form undergoes many phase changes between room temperature and practical sintering temperatures, can be chemically "stabilized" in several different forms. Its high oxygen ion conductivity recommends it for use in fuel cells. In another variant, metastable structures can impart transformation toughening for mechanical applications; most ceramic knife blades are made of this material.

Properties of ceramics

Mechanical properties

Ceramic materials are usually ionic or covalently-bonded materials, and can be crystalline or amorphous. A material held together by either type of bond will tend to fracture before any plastic deformation takes place, which results in poor toughness in these materials. Additionally, because these materials tend to be porous, the pores and other microscopic imperfections act as stress concentrators, decreasing the toughness further, and reducing the tensile strength. These combine to give catastrophic failures, as opposed to the normally much more gentle failure modes of metals. These materials do show plastic deformation. However, due to the rigid structure of the crystalline materials, there are very few available slip systems for dislocations to move, and so they deform very slowly. With the non-crystalline (glassy) materials, viscous flow is the dominant source of plastic deformation, and is also very slow. It is therefore neglected in many applications of ceramic materials.

Electrical properties

Semiconductivity

There are a number of ceramics that are semiconductors. Most of these are transition metal oxides that are II-VI semiconductors, such as zinc oxide. Whilst there is talk of making blue LEDs from zinc oxide, ceramicists are most interested in the electrical properties that show grain boundary effects. One of the most widely used of these is the varistor. These are devices that exhibit the unusual property of negative resistance. Once the voltage across the device reaches a certain threshold, there is a breakdown of the electrical structure in the vicinity of the grain boundaries, which results in its electrical resistance dropping from several megaohms down to a few hundred ohms. The major advantage of these is that they can dissipate a lot of energy, and they self reset — after the voltage across the device drops below the threshold, its resistance returns to being high. This makes them ideal for surge-protection applications. As there is control over the threshold voltage and energy tolerance, they find use in all sorts of applications. The best demonstration of their ability can be found in electrical substations, where they are employed to protect the infrastructure from lightning strikes. They have rapid response, are low maintenance, and do not appreciably degrade from use, making them virtually ideal devices for this application. Semiconducting ceramics are also employed as gas sensors. When various gases are passed over a polycrystalline ceramic, its electrical resistance changes. With tuning to the possible gas mixtures, very inexpensive devices can be produced.

Superconductivity

Under some conditions, such as extremely low temperature, some ceramics exhibit superconductivity. The exact reason for this is not known, but there are two major families of superconducting ceramics.

Ferroelectricity and subsets

Piezoelectricity, a link between electrical and mechanical response, is exhibited by a large number of ceramic materials, including the quartz resonators used as to measure time watches and other electronics. Such devices use both properties of piezoelectrics, using electricity to produce a mechanical motion (powering the device) and then using this mechanical motion to produce electricity (generating a signal). The unit of time measured is the natural interval required for electricity to be converted into mechanical energy and back again. The piezoelectric effect is generally stronger in materials that also exhibit pyroelectricity, and all pyroelectric materials are also piezoelectric. These materials can be used to interconvert between thermal, mechanical, and/or electrical energy; for instance, after synthesis in a furnace, a pyroelectric crystal allowed to cool under no applied stress generally builds up a static charge of thousands of volts. Such materials are used in motion sensors, where the tiny rise in temperature from a warm body entering the room is enough to produce a measurable voltage in the crystal. In turn, pyroelectricity is seen most strongly in materials which also display the ferroelectric effect, in which a stable electric dipole can be oriented or reversed by applying an electrostatic field. Pyroelectricity is also a necessary consequence of ferroelectricity. This can be used to store information in ferroelectric capacitors, elements of ferroelectric RAM. The most common such materials are lead zirconate titanate and barium titanate. Aside from the uses mentioned above, their strong piezoelectric response is exploited in the design of high-frequency loudspeakers, transducers for sonar, and actuators for atomic force and scanning tunneling microscopes.

Positive thermal coefficient

Increases in temperature can cause grain boundaries to suddenly become insulating in some semiconducting ceramic materials, mostly mixtures of heavy metal titanates. The critical transition temperature can be adjusted over a wide range by variations in chemistry. In such materials, current will pass through the material until joule heating brings it to the transition temperature, at which point the circuit will be broken and current flow will cease. Such ceramics are used as self-controlled heating elements in, for example, the rear-window defrost circuits of most automobiles. At the transition temperature, the material's dielectric response becomes theoretically infinite. While a lack of temperature control would rule out any practical use of the material near its critical temperature, the dielectric effect remains exceptionally strong even at much higher temperatures. Titanates with critical temperatures far below room temperature have become synonymous with "ceramic" in the context of ceramic capacitors for just this reason.

Processing of ceramic materials

Non-crystalline ceramics, being glasses, tend to be formed from melts. The glass is shaped when either fully molten, by casting, or when in a state of toffee-like viscosity, by methods such as blowing to a mould. If later heat-treatments cause this class to become partly crystalline, the resulting material is known as a glass-ceramic. Crystalline ceramic materials are not amenable to a great range of processing. Methods for dealing with them tend to fall into one of two categories - either make the ceramic in the desired shape, by reaction in situ, or by forming powders into the desired shape, and then sintering to form a solid body. A few methods use a hybrid between the two approaches.

In situ manufacturing

The most common use of this method is in the production of cement and concrete. Here, the dehydrated powders are mixed with water. This starts hydration reactions, which result in long, interlocking crystals forming around the aggregates. Over time, these result in a solid ceramic. The biggest problem with this method is that most reactions are so fast that good mixing is not possible, which tends to prevent large-scale construction. However, small-scale systems can be made by deposition techniques, where the various materials are introduced above a substrate, and react and form the ceramic on the substrate. This borrows techniques from the semiconductor industry, such as chemical vapour deposition, and is very useful for coatings. These tend to produce very dense ceramics, but do so slowly.

Sintering-based methods

The principles of sintering-based methods is simple. Once a roughly held together object (called a "green body") is made, it is baked in a kiln, where diffusion processes cause the green body to shrink. The pores in the object close up, resulting in a denser, stronger product. The firing is done at a temperature below the melting point of the ceramic. There is virtually always some porosity left, but the real advantage of this method is that the green body can be produced in any way imaginable, and still be sintered. This makes it a very versatile route. There are thousands of possible refinements of this process. Some of the most common involve pressing the green body to give the densification a head start and reduce the sintering time needed. Sometimes organic binders such as polyvinyl alcohol are added to hold the green body together; these burn out during the firing (at 200-350°C). Sometimes organic lubricants are added during pressing to increase densification. It is not uncommon to combine these, and add binders and lubricants to a powder, then press. (The formulation of these organic chemical additives is an art in itself. This is particularly important in the manufacture of high performance ceramics such as those used by the billions for electronics, in capacitors, inductors, sensors, etc. The specialized formulations most commonly used in electronics are detailed in the book "Tape Casting," by R.E. Mistler, et al., Amer. Ceramic Soc. [Westerville, Ohio], 2000.) A comprehensive book on the subject, for mechanical as well as electronics applications, is "Organic Additives and Ceramic Processing," by D. J. Shanefield, Kluwer Publishers [Boston], 1996. A slurry can be used in place of a powder, and then cast into a desired shape, dried and then sintered. Indeed, traditional pottery is done with this type of method, using a plastic mixture worked with the hands. If a mixture of different materials is used together in a ceramic, the sintering temperature is sometimes above the melting point of one minor component - a liquid phase sintering. This results in shorter sintering times compared to solid state sintering.

Other applications of ceramics

A couple of decades ago, Toyota researched production of an adiabatic ceramic engine which can run at a temperature of over 6000 °F (3300 °C). Ceramic engines do not require a cooling system and hence allow a major weight reduction and therefore greater fuel efficiency. Fuel efficiency of the engine is also higher at high temperature. In a conventional metallic engine, much of the energy released from the fuel must be dissipated as waste heat in order to prevent a meltdown of the metallic parts. Despite all of these desirable properties, such engines are not in production because the manufacturing of ceramic parts in the requisite precision and durability is difficult. Imperfection in the ceramic leads to cracks, which can lead to potentially dangerous equipment failure. Such engines are possible in laboratory settings, but mass-production is infeasible with current technology. Work is being done in developing ceramic parts for gas turbine engines. Currently, even blades made of advanced metal alloys used in the engines' hot section require cooling and careful limiting of operating temperatures. Turbine engines made with ceramics could operate more efficiently, giving aircraft greater range and payload for a set amount of fuel. Since the late 1990s highly specialized ceramics, usually based on boron carbide, formed into plates and lined with Spectra, have been used in ballistic armored vests to repel large-caliber rifle fire. Such plates are known commonly as small-arms protective inserts (SAPI). Very similar technology is used for armoring of cockpits of some military airplanes, because of the low weight of the material. Recently, there have been advances in ceramics which include bio-ceramics, such as dental implants and synthetic bones. Hydroxyapatite, the natural mineral componet of bone, has been made synthetically from a number of biological and chemical sources and can be formed into ceramic materials. Orthopedic implants made from these materials bond ready to bone and other tissues in the body without rejection or inflammatory reactions. Because of this, they are of great interest for gene delivery and tissue engineering scaffolds. Most Hydroxyapatite ceramics are very porous and lack mechanical strength and are used to coat metal orthopedic devices to aid in forming a bond to bone or as bone fillers. They are also used as fillers for orthopedic plastic screws to aid in reducing the inflammation and increase absorbtion of these plastic materials. Work is being done to make strong-fully dense nano crystalline Hydroxapatite ceramic materials for orthopedic weight bearing devices, replacing foreign metal and plastic orthopedic materials with a synthetic natural bone mineral. Ultimately these ceramic materials may be used as bone replacements or with the incorperation of protein collagens, synthetic bones.

External links

- [http://www.azom.com/details.asp?ArticleID=2123 Advanced Ceramics] – The Evolution, Classification, Properties, Production, Firing, Finishing and Design of Advanced Ceramics Category:Materials Category:Pottery Category:Ceramics ja:セラミックス ms:Seramik th:เซรามิก

Boron carbide

Boron Carbide (chemical formula B₄C) is an extremely hard ceramic material used in tank armor, bulletproof vests, and numerous industrial applications. With a hardness of 9.3 on the mohs scale, it is the fourth hardest material known behind boron nitride, diamond, ultrahard fullerite, and aggregated_diamond_nanorods. Discovered in the 19th Century as a bi-product of reactions involving metal Borides, it was not until the 1930s that the material was studied scientifically. Boron Carbide is now produced industrially by the carbo-thermal reduction of B₂O₃ (boron oxide) in an electric arc furnace.

Applications

- Personal and vehicle anti-ballistic armor plating, small-arms protective inserts.
- Grit blasting nozzles.
- High-pressure water jet cutter nozzles.
- Scratch and wear resistant coatings.
- Cutting tools and dies.
- Abrasives such as used in grinding wheels.
- Neutron absorber in nuclear reactors.

Silicon carbide

Silicon carbide (), also known as moissanite, is a ceramic compound of silicon and carbon. carbon Most silicon carbide is man-made for use as an abrasive (when it is often known by the trademark carborundum), or more recently as a semiconductor and moissanite gemstones. The simplest manufacturing process is to combine sand and carbon at a high temperature, between 1600 °C and 2500 °C. Alpha silicon carbide (α-SiC) is most common, and is formed at temperatures >2000°C. Alpha SiC has the typical hexagonal crystal structure. Beta modification (β-SiC), with a face-centered cubic crystal structure, is formed at temperatures of below 2000°C, but has relatively few commercial uses. The material was discovered by Edward Acheson in 1893, and he not only developed the electric batch furnace by which SiC is still made today, but also formed The Carborundum Company to manufacture it in bulk, initially for use as an abrasive. It is said that Acheson was trying to dissolve carbon in molten corundum (alumina) and discovered the presence of hard, blue-black crystals which he believed to be a compound of carbon and corundum: hence carborundum. The material formed in the Acheson furnace varies in purity, according to its distance from the graphite resistor that is the heat source. Clear, pale yellow and green crystals have the highest purity, and are found closest to the resistor. The colour changes to blue and black at greater distance from the resistor, and these darker crystals are less pure, and usually doped with aluminium, which increases electrical conductivity. Purer product can be made by the more expensive process of chemical vapor deposition. Commercial large single crystal silicon carbide is grown using a physical vapor transport commonly known as modified Lely method. Its high melting point (approximately 2700 °C) makes silicon carbide useful for bearings and furnace parts. It is also highly inert. There is currently much interest in its use as a semiconductor material in electronics, where its high thermal conductivity, high electric field breakdown strength and high maximum current density make it more promising than silicon for high-powered devices. In addition, it has strong coupling to microwave radiation and that, together with its high melting point permits practical use in heating and casting metals. SiC also has very low thermal expansion coefficient and no phase transitions that would cause discontinuities in thermal expansion. Pure SiC is clear. The brown to black color of industrial product is caused by iron impurities. The rainbowish lustre of the crystals is caused by the passivation layer of silicon dioxide that forms on its surface.

Uses

Semiconductor

Pure α-SiC is an intrinsic semiconductor with a band gap of 1.90 ±10 eV. Silicon carbide is used for blue LEDs, ultrafast Schottky diodes and MESFETs. Due to its high thermal conductivity, SiC is also used as substrate for other semiconductor materials such as gallium nitride[http://www.qinetiq.com/home/commercial/information_communication_and_electronics/Electronics/optronics/quantum_electronics.html]. It is also used as an ultraviolet detector. Nikola Tesla, around the turn of the 20th century, performed a variety of experiments with carborundum. Electroluminescence of silicon carbide was observed by Captain Henry Joseph Round in 1907 and by O.V. Lossev in the Soviet Union in 1923 [http://www.indiana.edu/~hightech/fpd/papers/ELDs.html]. Due to its wide band gap, SiC-based parts are capable of operating at high temperature (over 350 °C), which together with good thermal conductivity of SiC reduces problems with cooling of power parts. They also possess increased tolerance to radiation damage, making it a material desired for defense and aerospace applications. Its main competitor is gallium nitride. Pure SiC is a bad electrical conductor. Addition of suitable dopants significantly enhances its conductivity. Such material has positive temperature coefficient, making it suitable material for heating elements.

Structural material

In the 1980s and 1990s, silicon carbide was studied on several research programs for high-temperature gas turbines in the United States, Japan, and Europe. The components were intended to replace nickel superalloy turbine blades or nozzle vanes. However, none of these projects resulted in a production quantity, mainly because of its low impact resistance and its low fracture toughness.

Astronomy

Silicon carbide's hardness and rigidity make it a desirable mirror material for astronomical work, although they also make manufacturing and figuring such mirrors quite difficult. Silicon carbide may be a major component of the mantles of as-yet hypothetical diamond planets.

Grit

Silicon carbide is a popular product in modern lapidary due to the durablility and low cost of the material. It is also used in "super fine" grit sandpapers.

Disc brake

Silicon-infiltrated carbon-carbon composite is used for high performance brake discs as it is able to withstand extreme temperatures. The silicon reacts with the graphite in the carbon-carbon composite to become silicon carbide. These discs are used on some sports cars, including the Porsche Carrera GT.

Cutting Tools

In 1982 at the Oak Ridge National Laboratories, George Wei, Terry Tiegs, and Paul Becher discovered a composite of aluminum oxide and silicon carbide whiskers. This material proved to be exceptionally strong. Development of this laboratory-produced composite to a commercial product took only three years. In 1985, the first commercial cutting tools made from this aluminium and silicon carbide whisker-reinforced composite were introduced by the Advanced Composite Materials Corporation (ACMC) and Greenleaf Corporation.

Culture

In 2001: A Space Odyssey and the related series of books and movies (by Arthur C. Clarke and Stanley Kubrick, among others) the monoliths (or at least their exteriors) were made of silicon carbide.

Patents and Trademarks

Edward Goodrich Acheson (1856–1931) patented the method for making silicon carbide powder on February 28, 1893. On May 19, 1896, he was also issued a patent for an electrical furnace used to produce silicon carbide.
- -- Production of artificial crystalline carbonaceous material Carborundum is a trademark of Saint-Gobain Abrasives.

External links

- [http://www.nature.com/news/2004/040823/full/040823-9.html Computer chips get tough] (news@nature.com)
- [http://www.grc.nasa.gov/WWW/SiC/SiC.html NASA Glenn High Temperature Integrated Electronics and Sensors Team]
- [http://engr-118-02.eleg.uark.edu/sic/current_projects.htm University of Arkansas Silicon Carbide Device Modeling Team]
- [http://physchem.ox.ac.uk/MSDS/SI/silicon_carbide.html Material Safety Data Sheet] for Silicon Carbide
- [http://www.ms.ornl.gov/researchgroups/process/cpg/sic.htm] SiC Whisker-Reinforced Ceramic Composites Category:Carbides Category:Silicon compounds Category:Semiconductor materials Category:Superhard materials Category:Ceramics ja:炭化ケイ素

Aluminium oxide

Aluminium oxide or aluminum oxide is a chemical compound of aluminium and oxygen with the chemical formula ₂₃. It is also commonly referred to as alumina in the mining, ceramic, and materials science communities. Alumina is generally available in two concentrations: 99.5% and 96%. Aluminium oxide is responsible for metallic aluminium's resistance to weathering. Metallic aluminium is very reactive with atmospheric oxygen, and a thin layer of aluminium oxide quickly forms on any exposed aluminium surface. This layer protects the metal from further oxidation. The thickness and properties of this oxide layer can be enhanced using a process called anodising. A number of alloys, such as aluminum bronzes, exploit this property by including a proportion of aluminum in the alloy to enhance corrosion resistance. Aluminium oxide is an excellent thermal and electrical insulator. In its crystalline form, called corundum, its hardness makes it suitable for use as an abrasive and as a component in cutting tools. Powdered aluminium oxide is frequently used as a medium for chromatography. The gems ruby and sapphire are mostly aluminium oxide, given their characteristic colors by trace impurities. In August 2004, scientists in the United States working for 3M developed a technique for making an alloy of alumina and rare earth elements to produce a strong glass called transparent alumina. Aluminium oxide was taken off the EPA's chemicals lists in 1988.

Industrial Fabrication Process

Aluminium oxide is the main component of bauxite, the principal ore of aluminium. Industrially, bauxite is purified to aluminium oxide via the Bayer process, and then converted to aluminium metal in the Hall-Heroult process. The bauxite ore is made up of impure Al₂O₃ + Fe₂O₃ + SiO₂. This is then purified by the Bayer Process: Al₂O₃ + 3H₂O + 2NaOH --(heated)--> 2NaAl(OH)₄. The Fe₂O₃ does not dissolve in the base. The SiO₂ dissolves as silicate Si(OH)₆^-6. Upon filtering, Fe₂O₃ is removed. With the addition of an acid, Al(OH)₃ precipitates. The silicate remains in solution. Then, Al(OH)₃ --(heated)--> Al₂O₃ + 3H₂O. The Al₂O₃ is of course, alumina.

External links

- [http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc03/icsc0351.htm International Chemical Safety Card 0351]
- [http://physicsweb.org/article/news/8/8/9 PhysicsWeb article on Transparent alumina] Category:Aluminium compounds Category:Oxides ja:酸化アルミニウム th:อะลูมิเนียม ออกไซด์

Titanium boride

Titanium Diboride (chemical formula TiB₂) is an extremely hard ceramic material (33GPa) with excellent corrosion resistance at high temperatures and very good wear resistance which does not occur naturally in earth. Many TiB₂ applications are inhibited by economic factors, particularly the costs of densifying a high melting point material. Current use of this material appears to be limited to specialized applications in such areas as impact resistant armor, cutting tools, crucibles and wear resistant coatings. It is also used as an inoculant to refine the grain size when casting aluminium alloys. Thin layers of TiB₂ have a wide range of potential industrial applications due to the wear and corrosion resistance properties that TiB₂ can provide to a cheap and/or tough substrate. The electroplating of TiB₂ layers possess two main advantages compared with plasma (PVD, CVD) methods: the growing rate of the layer is 200 times higher (up to 5μms⁻¹) and the inconveniences of covering complex shaped products are dramatically reduced. Category:Borides Category:Titanium compounds Category:Ceramics

Composite material

Composite materials (or composites for short) are engineered materials made from two or more constituent materials that remain separate and distinct on a macroscopic level while forming a single component. There are two categories of constituent materials: matrix and reinforcement. At least one portion (fraction) of each type is required. The matrix material surrounds and supports the reinforcement materials by maintaining their relative positions. The reinforcements impart their special mechanical, electrical and physical properties to enhance the matrix properties. A synergism produces material properties unavailable from naturally occurring materials. Due to the wide variety of matrix and reinforcement materials available, the design potentials are incredible. The most primitive composite materials comprised straw and mud in the form of bricks for building construction. The most advanced examples perform routinely on spacecraft in demanding environments. The most visible applications pave our roadways in the form of either steel and aggregate reinforced portland cement or asphalt concrete. Those composites closest to our personal hygiene form our shower stalls and bath tubs made of fiberglass. Solid surface, imitation granite and cultured marble sinks and countertops are widely used to enhance our living experiences. There are the so-called natural composites like bone and wood. Both of these are constructed by the processes of nature and beyond the scope of this text. Engineered composite materials must be formed to shape. This involves strategically placing the reinforcements while manipulating the matrix properties to achieve a melding event at or near the beginning of the component life cycle. A variety of methods are used according to the end item design requirements, and they are commonly named molding or casting processes, as appropriate. The principle factors impacting the methodology are the natures of the chosen matrix and reinforcement materials. Another important factor is the gross quantity of material to be produced. Large quantities can be used to justify high capital expenditures for rapid and automated manufacturing technology. Small production quantities are accommodated with lower capital expenditures but higher labor and tooling costs at a correspondingly slower rate. Most commercially produced composites use a polymer matrix material often called a resin or resin solution. There are many different polymers available depending upon the starting raw ingredients. There are several broad categories, each with numerous variations. The most common categories are known as polyester, vinyl ester, epoxy, phenolic, polyimide, polyamide, and others. The reinforcement materials are often fibers but also commonly ground minerals. Fibers are often transormed into a textile material such as a felt, fabric, knit or stitched construction. Advanced composite materials constitute a category comprising carbon fiber reinforcement and epoxy or polyimide matrix materials. These are the aerospace grade composites and typically involve laminate molding at high temperature and pressure to achieve high reinforcement volume fractions. One component is often a strong fibre such as fiberglass, quartz, kevlar, Dyneema or carbon fibre that gives the material its tensile strength, while another component (called a matrix) is often a resin such as polyester, or epoxy that binds the fibres together, transferring load from broken fibers to unbroken ones and between fibers that are not oriented along lines of tension. Also, unless the matrix chosen is especially flexible, it prevents the fibers from buckling in compression. Some composites use an aggregate instead of, or in addition to, fibers. In terms of stress, any fibers serve to resist tension, the matrix serves to resist shear, and all materials present serve to resist compression, including any aggregate. Composite materials can be divided into two main categories normally referred to as short fiber reinforced materials and continous fiber reinforced materials. Continuous reinforced materials will often constitute a layered or laminated structure. Shocks, impact, loadings or repeated cyclic stresses can cause the laminate to separate at the interface between two layers, a condition known as delamination. Individual fibers can separate from the matrix e.g. fiber pull-out.

Examples of composite materials:

- Fibre reinforced plastics:
- Classified by type of fiber:
- Wood (cellulose fibers in a lignin and hemicellulose matrix)
- Carbon-fibre reinforced plastic or CRP
- Glass-fibre reinforced plastic or GRP (informally, "fiberglass")
- Classified by matrix:
- Thermoplastic Composites
- long fiber thermoplastics or long fiber reinforced thermoplastics
- glass mat thermoplastics
- Thermoset Composites
- Metal matrix composites or MMCs:
- White cast iron
- Hardmetal (carbide in metal matrix)
- Metal-intermetallic laminate
- Ceramic matrix composites:
- Cermet (ceramic and metal)
- concrete
- Reinforced carbon-carbon (carbon fibre in a graphite matrix)
- Bone (hydroxyapatite reinforced with collagen fibers)
- Organic matrix/ceramic aggregate composites
- Mother of Pearl
- Syntactic foam
- Asphalt concrete
- Chobham armour (see composite armour)
- Engineered wood
- Plywood
- Oriented strand board
- Wood plastic composite (recycled wood fiber in polyethylene matrix)
- Pycrete (sawdust in ice matrix) ms:Bahan komposit th:วัสดุผสม

Reactive armour

Reactive armor is a type of vehicle armour that reacts in some way to the impact of a weapon to reduce the damage done to the vehicle being protected. The most common type of reactive armor is by far Explosive Reactive Armor (ERA), but other types include Self-Limiting Explosive Reactive Armor (SLERA), Non-Energetic Reactive Armor (NERA), Non-Explosive Reactive Armor (NxRA), and electric reactive armor. Unlike ERA and SLERA, NERA and NxRA modules can withstand multiple hits, but a second hit in exactly the same location will still penetrate. Reactive armour can be defeated with multiple hits in the same place, employed in tandem-charge weapons, which use two or more shaped charge explosions in rapid succession. Lacking these weapons, emulating this effect is difficult as it requires either precision artillery, luck, or close-quarter use of shoulder-launched anti-tank weapons.

Explosive Reactive Armor

luck Explosive reacting armor is constructed of "bricks" or "tiles" of explosive sandwiched between two plates, almost always metal, called the reactive or dynamic elements. Essentially all anti-tank munitions work by piercing the armor and killing the crew inside. Explosive reactive armor's protective mechanism against shaped charge warheads involves producing an explosion when it is impacted by a weapon, moving the reactive elements and thus disrupting the jet of metal the warhead produces, significantly reducing its penetration capability. The disruption happens by two mechanisms. First, the moving plates change the effective velocity and angle of impact of the shaped charge jet, reducing the angle of incidence and increasing the effective jet velocity versus the plate element. Second, since the plates are angled compared to the usual impact direction of shaped charge warheads, as the plates move outwards the impact point on the plate moves over time, making the jet have to cut through fresh plate material. This second effect increases the effective plate thickness during the impact significantly. Most ERA is not of much use against kinetic energy projectiles, which are much thicker and heavier than the plates are, but the thicker moving plates of "heavy ERA" such as the Russian Kontakt-5 can break apart a penetrating rod that is longer than the ERA is deep, again significantly reducing penetration capability. The effects on shaped charge warheads was discovered in 1967–68 by a German researcher, Manfred Held, working in Israel. He and his team were using the large quantities of wrecked tanks from the Six Day War to test shells. They accidentally discovered that tanks that still contained live ordnance could disrupt a shaped charge by the explosion of the shells, the basis of ERA. The concept was patented in 1970. Explosive reactive armour has been held in great favor by the former Soviet Union and its now-independent component states since the 1980s, and almost every tank in eastern military inventory today has either been manufactured to use ERA or had ERA tiles added to it, even the very old T-55 and T-62 tanks from forty and fifty years ago, used today by reserve units. ERA tiles are used as add-on armour to the most vulnerable portions of an armoured fighting vehicle, typically the front of the hull and the front and sides of the turret. They require fairly heavy armour on the vehicle itself, since the exploding ERA would otherwise damage the vehicle and injure or kill the personnel inside. Usually, ERA is not mounted on the sides or rear of a vehicle, since the underlying armour is not as heavy on those parts. Exploding ERA also poses a danger to friendly troops in close proximity to the vehicle. Though it was once quite common for a dozen or so infantrymen to ride on the outside of a tank's hull, this is not done with ERA-plated vehicles—for obvious reasons.

Non-Explosive and Non-Energetic Reactive Armor

NERA and NxRA operate similarly to explosive reactive armor, but without the explosive liner. Two metal face plates sandwich an inert liner, such as rubber. When struck by a shaped charge metal jet, some of the impact energy is dissipated into the inert liner layer, and that causes a localized bending or bulging of the face plates in the area of the impact. As the plates bulge, the point of jet impact shifts with the plate bulging, increasing the effective thickness of the armor. This is almost the same mechanism as the second mechanism that explosive reactive armor uses, but it uses energy from the shaped charge jet rather than an explosive layer in the armor. Since the inner liner is not explosive itself, the bulging is less energetic than on explosive reactive armor. However, NERA and NxRA are lighter and completely safe to handle (and safe for nearby infantry), and can be packaged in multiple spaced-out layers if necessary.

Electric reactive armour

A new technology of Electric Reactive Armour is in development, where the armour is made up of two or more conductive plates separated by an insulator, creating a high-power capacitor. In operation, a high-voltage power source charges the armor. When an incoming body penetrates the plates and closes the circuit, the capacitor discharges, dumping a great deal of energy into the penetrator, which may vaporize it or even turn it into a plasma, significantly diffusing the attack. It is not public knowledge whether this is supposed to function against both KE-penetrators and shaped charge jets, or only the latter. This technology has not been introduced on any operational platform.

External links

- [http://www.defense-update.com/features/du-1-04/reactive-armor.htm Defense Update: Reactive Armor Suits]
- [http://www.defense-update.com/features/du-1-04/feature-armor-protection.htm Defense Update: Advanced Protection for Modern Armored Vehicles] Category:Armor Category:Explosives ja:爆発反応装甲

Heavy metals

For other meanings, see heavy metal The term heavy metal may have various more general or more specific meanings. According to one definition, the heavy metals are a group of elements between copper and lead on the periodic table of the elements -- having atomic weights between 63.546 and 200.590 and specific gravities greater than 4.0. Living organisms require trace amounts of some heavy metals, including cobalt, copper, manganese, molybdenum, vanadium, strontium, and zinc, but excessive levels can be detrimental to the organism. Other heavy metals such as mercury, lead and cadmium have no known vital or beneficial effect on organisms, and their accumulation over time in the bodies of mammals can cause serious illness. A stricter definition restricts the term to those metals heavier than the rare earth metals, at the bottom of the periodic table. None of these are essential elements in biological systems; all of the more well-known elements with the exception of bismuth and gold are horribly toxic. Thorium and uranium are sometimes included as well, but they are more often called simply "radioactive metals". In medical usage, the definition is considerably looser, and "heavy metal poisoning" can include excessive amounts of iron, manganese, aluminium, or beryllium (the second-lightest metal) as well as the true heavy metals. Also, often the elements beyond mercury, e.g. the actinides such as uranium and plutonium, are not excluded from the heavy metals. In the context of nuclear power plants, tHM means tons of heavy metal.

External link

- [http://www.iupac.org/publications/pac/2002/pdf/7405x0793.pdf Survey of meanings of the term] (pdf)
- [http://www.food-info.net/uk/metal/intro.htm Overview of heavy metals in food and their health effects] Category:Chemical element groups category:Toxicology Category:Periodic table ko:중금속 ja:重金属

M1 Abrams

The M1 Abrams main battle tank is the principal combat tank of the United States Army and the United States Marine Corps, with three main versions being deployed starting in 1980: the M1, M1A1, and M1A2. The latest versions of the M1A2 have a new armor and electronics package. It is named after General Creighton Abrams, former Army Chief of Staff and commander of the Army's 37th Armored Battalion. The M1 Abrams replaced the M60 Patton in US service.

Production history

The M1 Abrams was designed by Chrysler Defense (In 1982, General Dynamics Land Systems Division purchased Chrysler Defense Division) and is currently produced by General Dynamics Corporation and first entered US Army service in 1980. An improved version of the M1, the M1A1, was introduced in 1985. The M1A1 has the L44 120 mm smoothbore gun developed by Rheinmetall AG of Germany for the Leopard 2, improved armor, and an NBC protection system. The M1A2 is a further improvement of the M1A1 with a commander's thermal viewer and weapon station, position navigation equipment, digital data bus and a radio interface unit. Further upgrades include depleted uranium armor for all variants, a system overhaul that returns all A1's to zero hours (M1A1 AIM), a digital enhancement package for the A1 (M1A1D), a commonality program to standardize parts between the US Army and the Marine Corps (M1A1HC), and an electronic upgrade for the A2 (M1A2 SEP). In this article, "Abrams" is used to refer to all variants of the tank, while the specific variants are referred to as the M1, M1IP, M1A1, and M1A2. NBC to develop an M1 prototype.]] During Operations Desert Shield and Desert Storm and for Bosnia, some M1A1s were modified with armor upgrades. The M1 can be equipped with mine plow and mine roller attachments if needed. The M1 chassis also serves as a basis for the Grizzly combat engineering vehicle and the M104 Wolverine heavy assault bridge. Over 8,800 M1 and M1A1 tanks have been produced. Export variants, with the export armor package and different options (such as multi-fuel diesel engines) of the M1 Abrams are also used by the defence forces of:
- Australia (59 M1A1)
- Egypt (777 M1A1)
- Saudi Arabia (315 M1A2)
- Kuwait (218 M1A2)
- Also tested but not adopted by Sweden, Greece and a number of other nations.

Combat history

Greece The Abrams remained untested in combat until the Gulf War in 1991. A total of 1,848 M1A1s were deployed to Saudi Arabia. The M1A1 was superior to Iraq's Soviet-era T-55 and T-62 tanks, as well as degraded Russian T-72s which lack night vision and any modern range finders and locally-produced copies (Asad Babil tank). Only 18 M1A1s were taken out of service due to battle damage and none of these losses resulted in crew casualties. The M1A1 was capable of making kills at ranges in excess of 4000 m. Further combat was seen during 2003 when US forces invaded Iraq and deposed the Iraqi leader Saddam Hussein. The campaign saw very similar performance from the tank with no Abrams crew member being lost to hostile fire during the battle in Iraq. However, on October 29, 2003, two soldiers were killed and a third wounded when their tank was disabled by an anti-tank mine, which may have been combined with other explosives to increase its effect. This marked the first time deaths resulted from a hostile-fire assault on the M1 tank. On November 27, 2004 an Abrams tank was completely destroyed and its driver killed from shrapnel wounds when an extremely powerful improvised explosive device consisting of three L15 155 mm shells with a total explosive weight of 34.5 kg detonated next to the tank. The other three crew members were able to escape, a testament to the armor of the M1A2. During the major combat operations in Iraq, Abrams crew members were lost when one tank with the US Army's 3rd Infantry Division, and US Marine Corps troops, drove onto a bridge. The bridge failed, dropping the tank into the Euphrates River, where one soldier drowned. No Abrams tank has ever been destroyed as a result of fire from an enemy tank, though a number have been disabled in ambushes employing short-range antitank rockets like the Russian RPG-7. Also, during the Operation Desert Storm four Abrams were disabled in a friendly fire incident by Hellfire missiles fired from AH-64 Apache attack helicopters.

Armor

AH-64 Apache The Abrams is protected by a type of composite armor (derived from the British Chobham armour) formed by multiple layers of steel and ceramics. It may also be fitted with reactive armor if needed; however, this modification has never actually been done. Fuel and ammunition are in armored compartments to protect the crew and reduce the risk of cooking off if the tank is damaged. Protection against spalling is provided by a kevlar liner. Beginning in 1988, M1A1 tanks received improved armor packages that incorporated depleted uranium reinforcing rods in their armor at the front of the turret and the front of the hull. Armor thus reinforced offers significantly better resistance towards all types of anti-tank weaponry, but at the expense of adding considerable weight to the tank. The first M1A1 tanks to receive this upgrade were tanks stationed in Germany, since they were the first line of defense against the Soviet Union. US tankers participated in Operation Desert Storm received an emergency program to upgrade their tanks with depleted uranium armor immediately before the onset of the campaign. The newer M1A2 tanks uniformly incorporate depleted uranium armor, and the majority of the M1A1 tanks in active service have been upgraded to this standard as well. depleted uranium

Armament

Main armament

M68A1 rifled gun

The main armament of the original model M1 was the M68A1 105 mm rifled tank gun firing a variety of APFSDS, HEAT, high explosive, white phosphorus (smoke), and a highly efficient and lethal anti-personnel (flechette) round.

M256 smoothbore gun

flechette]] The main armament of the M1A1 and M1A2 is the M256 120 mm smoothbore gun, designed by Rheinmetall AG of Germany and manufactured under license in the US by General Dynamics Land Systems Division in their plant in Lima, Ohio. It fires depleted uranium armor-piercing, fin-stabilized, discarding-sabot long-rod penetrator (APFSDS) rounds like the M829A3 and high explosive anti-tank HEAT shaped charge rounds like M830, the latest versions of which (M830A1) incorporate a sophisticated multi-mode electronic sensing fuze which allow them to be used effectively against both armored vehicles and personnel, or even (at least in theory) low-flying aircraft. The new M1028 120 mm anti-personnel canister cartridge has been brought into service early for use in the 2003 occupation of Iraq. It contains 1,150 ten-millimetre tungsten shot projectiles which spread from the muzzle to produce a shotgun effect lethal out to 500 m. The tungsten balls can be used to clear enemy dismounts, break up hasty ambush sites in urban areas, clear defiles, stop infantry attacks and counter-attacks, and support friendly infantry assaults by providing cover-by-fire. In addition to this the new MRM-KE (Mid-Range-Munition), otherwise known as X-Rod, is also in development. Essentially a cannon fired guided round, it has a range of roughly 12km, and uses a KE warhead which is rocket assisted in its final phase of flight.

Secondary armament

X-Rod The Abrams tank has three machine guns: # A .50 cal (12.7 mm) M2 machine gun in front of the commander's hatch. On the M1,M1IP and M1A1, this gun is on a powered mount and can be fired using a 3× magnification sight, while the vehicle is buttoned up. On the M1A2, M1A2SEP, the M2 is on a flex mount. # A 7.62 mm M240 machine gun in front of the loader's hatch on a skate mount. # A 7.62 mm M240 machine gun in a coaxial mount. The coaxial MG is aimed and fired with the computer fire control system. The turret is fitted with two six-barreled smoke grenade launchers. These can create a thick smoke that blocks both vision and thermal imaging. The engine is also equipped with a smoke generator.

Aiming

The Abrams is equipped with a fire control computer that uses data from a variety of sources, including the Gunner's Primary Sight or "GPS" (thermal or daylight), a laser rangefinder, a wind sensor, a cant sensor, and data on the ammunition type, and computes a firing solution. Either the commander or gunner can fire the main gun.

Mobility

firing solution The M1 Abrams is powered by a 1500 hp (1119 kW) Honeywell AGT1500 (originally made by Lycoming) gas turbine, and a 4-forward/2-reverse speed transmission, giving it a governed top speed of 45 mph (72 km/h) on roads, 30 mph (48 km/h) cross-country. With the engine governor removed, speeds of around 60 mph (100 km/h) are possible on an improved surface; however, damage to the drivetrain (especially to the tracks) can occur at speeds above 45 mph. The tank can be fueled diesel fuel, kerosene, JP-4, any grade of MOGAS (motor gasoline), or JP-8 jet fuel; the U.S. Army uses diesel fuel in order to simplify logistics. The Abrams can be carried by the C-5 Galaxy and C-17 Globemaster III. The limited capacity (one combat-ready tank or two transport-ready tanks in a C-5, one combat-ready tank in a C-17) caused serious logistical problems when deploying the tanks for the first Gulf War, though there was enough time for 1,848 tanks to be transported by ship. Tanks shipped in the transport-ready configuration require depot-level maintenance to install a number of sections of armor, and need to be fueled and loaded with ammunition. Tanks shipped in the combat-ready configuration can enter combat immediately.

Tank Urban Survival Kit for M1A2

first Gulf War The Tank Urban Survival Kit, or TUSK, is a series of improvements to the M1A2 Abrams intended to improve fighting ability in urban environments. Historically, urban and other close battlefields have been the worst place for tanks to fight -- a tank's front armor is much stronger than that on the sides, top, or rear, and in an urban environment, attacks can come from any direction, and attackers can get close enough to reliably hit weak points in the tank's armor, or get sufficient elevation to hit the top armor square on. Armor upgrades include reactive armor on the sides of the tank and slat armor (similar to that on the Stryker) on the rear to protect against rocket-propelled grenades and other shaped charge warheads. A gun shield and a thermal sight system are added to the loader's top-mounted 7.62 mm machine gun, and the mount for commander's .50-caliber heavy machine gun is modified to allow the weapon to be operated from within the turret with the hatch closed (the original M1 and M1A1 had this capability, but it was lost on the M1A2 due to the reconfiguration of several turret systems). An exterior telephone allows supporting infantry to communicate with the tank commander. The TUSK system is a field-installable kit that allows tanks to be upgraded without needing to be recalled to a maintenance depot.

Variants & Kits

- M1 Original version Production started in 1980 and continued to 1985
- M1 IP (IPM1) Produced briefly in 1985 before production shifted to the M1A1
- M1A1Production started in 1986 and continued to 1992. Gun upgraded to M256 120mm gun
- M1A1AIM Production overhall of existing inventory
- M1A1D Digital upgrade replacing control systems to M1A1 [http://www.fas.org/man/dod-101/sys/land/m1.htm]
- M1A2 Production began in 1992.
- M1A2SEP
- M1 Grizzly Engineer Vehicle [http://www.globalsecurity.org/military/systems/ground/grizzly.htm]
- M1 Panther II Remote controlled mine clearing vehicle [http://www.globalsecurity.org/military/systems/ground/panther.htm]
- M104 Wolverine Heavy assault bridge [http://www.globalsecurity.org/military/systems/ground/wolverine.htm]
- M1 Mine Clearing Blade System
- M1 Mine Clearing Roller System
- Tank Urban Survival Kit

Specifications of variants

References

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-

External links

- [http://www.army-technology.com/projects/abrams/index.html M1A1/A2 Abrams Main Battle Tank Information]
- [http://www.armytimes.com/story.php?f=1-292925-2348567.php Army Times - Two soldiers die in attack on Abrams tank, October 29, 2003]
- [http://www.enemyforces.com/tanks/m1a1abrams.htm Main Battle Tank M1A1 Abrams]
- [http://www.army-guide.com/eng/product.php?prodID=429 M1A1 Abrams], [http://www.army-guide.com/eng/product.php?prodID=1779 M1A2 Abrams], [http://www.army-guide.com/eng/product.php?prodID=2936 M1A2 SEP Abrams] at army-guide.com Category:Main battle tanks Category:American tanks Category:Cold War American tanks Category:Modern tanks ja:M1エイブラムス

Depleted uranium

__TOC__

Depleted uranium (DU) is uranium which contains a reduced proportion of the fissile isotope U-235 and (usually) the highly radioactive but rare isotope U-234, compared to natural uranium.

Uranium enrichment process

Natural uranium contains nominally 0.71% U-235 (+/-0.1%), 99.28% U-238, and about 0.0054% U-234, while depleted uranium contains only 0.2 to 0.4 weight-percent U-235. The U-235 is concentrated into enriched uranium through the process of isotope separation for use in nuclear reactors and nuclear weapons. The enrichment process does not create U-235 but merely separates the different isotopes of uranium. Therefore the process leaves large amounts of depleted uranium as a waste product. For example producing 1 kg of 5% enriched uranium requires 11.8 kg of natural uranium, leaving about 10.8 kg of depleted uranium with 0.3% U-235.
- Nuclear marine propulsion reactors usually use uranium containing 90% or more of U-235
- Commercial light water nuclear reactor fuel is usually enriched up to a maximum of 5% (the 5% limit is set by the currently licensed transport containers — in the future the 5% limit may be increased up to 7% for improved fuel economy).
- Research reactor fuel is today limited to maximum 20% (most older research reactors have been or will be converted down to this lower enrichment level).
- The use of U-235 in nuclear weapons has has been superseded by plutonium fueled devices. However the production of plutonium itself requires enriched uranium as a feedstock.

US stockpiles

The United States Department of Energy currently has an inventory of 704,000 tons of depleted uranium hexafluoride (stored in 58,000 metal cylinders), corresponding to 476,000 tonnes of uranium [http://web.ead.anl.gov/uranium/]. It encourages the use of DU as a means of disposing of the stock, and plans to eventually convert the remaining inventory to a less toxic form, probably either uranium metal or oxide.

Uses and availability

As a product otherwise requiring long term storage as low level radioactive waste, depleted uranium can be obtained cheaply. It is useful for its extremely high density, which is only slightly less than that of tungsten. As well as a lower initial cost, depleted uranium is easier to roll, machine and cast than tungsten. However, it has extremely poor corrosion properties, can burn, spalls easily, and since it is toxic and radioactive the facilities for processing it need to monitor and filter dust and airborne particles. One disadvantage of DU is that it needs to be correctly handled when an object containing it is scrapped. The uranium is normally leased from the manufacturer and subsequently returned at the end of the object's life.

Nuclear applications

Depleted uranium [DU] is natural uranium that is somewhat depleted in the isotope U-235 and is not normally usable directly as nuclear fuel. Depleted uranium can be used as a source material for creating the element plutonium. Breeder reactors carry out a process of transmutation to convert "fertile" isotopes such as U-238 into fissile material, It has been estimated that there is anywhere from 10,000 to five billion years worth of Uranium-238 for use in these power plants [http://www-formal.stanford.edu/jmc/progress/cohen.html]. Breeder technology has been used in several reactors [http://www.world-nuclear.org/info/inf08.htm]. Currently (December 2005), the only breeder reactor producing power is BN-600 [http://eng.rosatom.ru/?razdel=160] in Beloyarsk, Russia. (The electricity output of BN-600 is 600 MW - Russia has planned to build another unit, BN-800, at Beloyarsk nuclear power plant.) Also, Japan's Monju reactor is planned for restart (having been shut down since 1995), and both China and India intend to build breeder reactors. DU is also used as a radiation shield — its alpha radiation is easily stopped by the non-radioactive casing of the shielding and the uranium's high atomic weight and high number of electrons is highly effective in absorbing gamma radiation and x-rays.

Military applications

Projectile weapons

One use of DU is for kinetic energy penetrators for the anti-tank role. Kinetic energy penetrator rounds consist of a long, relatively thin flechette surrounded by a discarding sabot. Two materials lend themselves to flechette construction: tungsten and depleted uranium, the latter in designated alloys known as staballoys. Depleted uranium is favoured for flechette construction due to two particular properties: being self-sharpening and pyrophoric. On impact with a hard target, such as an armoured vehicle, the nose of the flechette rod fractures in such a way that it remains sharp. Further, the impact and subsequent release of heat energy causes it to disintegrate to dust and combust when it reaches air (compare to ferrocerium). Against an armoured vehicle this is devastating, piercing the hull to create an extremely hot ball of dust and gas in the interior, killing or injuring the crew and igniting fuel and ammunition. Depleted uranium also has the advantage of being easy to melt and cast into shape; a difficult and costly process for tungsten. Depleted uranium is also very dense: at 19050 kg/m³, it is 70% denser than lead. Thus a given weight of it has a smaller diameter than an equivalent lead projectile, with less aerodynamic drag and better penetration due to a higher pressure at point of impact. The US Army uses the DU in an alloy with around 3.5% titanium. It is used by the US Army in 120 mm or 105 mm calibre by the M1 Abrams and M60A3 tanks and in 25 mm calibre by the M242 mounted on the M2 Bradley. The US Navy used it in its 20 mm Phalanx CIWS guns (though it has now switched to armor-piercing tungsten alloys for this application, primarily because multiple stray DU rounds hit friendly ships; those that strike metal often burn, so the incindary effect of uranium presented an easily avoidable danger. Tungsten costs 5-10x that of depleted uranium rounds, and its shrapnel is also chemically toxic, causing cancer but not birth defects.) The Air Force uses the 30 mm PGU-14/B amour-piercing round in the GAU-8 Avenger cannon of the A-10 Thunderbolt II. The Marine Corps uses DU in the 25 mm PGU-20 round fired by the GAU-12 Equalizer cannon of the AV-8B Harrier, and also in the 20 mm M197 gun mounted on AH-1 helicopter gunships. The Russian military has used DU munitions in tank main gun ammunition since the late 1970s, mostly for the 110 mm guns in the T-62 tank and the 125 mm guns in the T-64, T-72, T-80, and T-90 tanks. DU munitions (in the form of tank and naval artillery rounds) are also deployed by the armed forces of the UK, Israel, France, China, Russia, Pakistan, and many more. DU rounds are manufactured in 18 countries. DU is also used to make body armour piercing bullets.

Armour plate

Because of its high density, depleted uranium can also be used in tank armour, sandwiched between sheets of steel armor plate. For instance, some late-production M1A1HA and M1A2 Abrams tanks built after 1998 have DU reinforcement as part of its armour plating in the front of the hull and the front of the turret and there is a program to upgrade the rest.

Nuclear weapons

Most modern Nuclear weapons utilize depleted uranium as a "tamper" material (see Nuclear weapon design). A tamper which surrounds a fissile core works to reflect neutrons and add inertia to the compression of the core. As such, it increases the efficiency of the weapon and reduces the amount of critical mass required. This feature is common to the primary of the Teller-Ulam design as well.

Thermonuclear weapons

Thermonuclear warheads often have a layer of DU surrounding the main charge of fusion fuel. Initially, this serves as a reaction mass to allow more forceful compression (see inertial confinement fusion) during detonation and allow more complete fusion to occur. The high flux of very energetic neutrons from the resulting fusion reaction causes the U-238 to fission and adds energy to the yield of the weapon. Such weapons are referred to as fission-fusion-fission weapons after the three consecutive stages of the explosion. The larger portion of the total explosive yield in this design, comes from the final fission stage fueled by DU, producing enormous amounts of radioactive fission products. For example, 77% of the 10.4 megaton yield of the Ivy Mike thermonuclear test in 1952 came from fast fission of the DU tamper. Because DU has no critical mass, it can be added to thermonuclear bombs in almost unlimited quantity. The 1961 Soviet test of Tsar Bomba produced "only" 50 megatons, over 90% from fusion, because the DU final stage was replaced with lead. Had DU been used, the yield would have been 100 megatons, and would have produced fallout equivalent to one third of the global current total since the invention of nuclear weapons.

Civilian applications

Depleted uranium is also used in a number of civilian applications, generally where a high density weight is needed. Such applications include sailboat keels, as counterweights and sinker bars in oil drills, gyroscope rotors, and in other places where there is a need to place a weight that occupies as little space as possible. Tungsten could be used instead, but it is much more expensive. Aircraft may also contain depleted uranium trim weights (a Boeing 747 may contain 400 to 1,500 kg). However there is some controversy about its use in this application because of concern about the uranium entering the environment should the aircraft crash, since the metal can oxidise to a fine powder in a fire. This was highlighted by the collision of two Boeing 747s at Tenerife Airport in 1977 when the resulting fire consumed 3000 kg of the material. (Another well-known crash with DU release was the Bijlmermeer disaster in 1992 in Amsterdam.) Consequently its use has been phased out in many newer aircraft, for example both Boeing and McDonnell-Douglas discontinued using DU counterweights in the 1980s. An unexpected application is in Formula 1 racing cars. The rules state a minimum weight of 600 kg, but builders strive to get the weight as low as possible and then bring it up to the 600 kg mark by placing depleted uranium where needed to achieve a better balance.

Health concerns

Early scientific studies usually found no link between depleted uranium and cancer, and sometimes found no link with increases in the rate of birth defects, but newer studies have found the latter [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11738513&dopt=Abstract] and offered explaination of such links. Some have raised concerns about the use of this material, particularly in munitions, because of its proven mutagenicity[http://toxsci.oxfordjournals.org/cgi/content/abstract/89/1/287], teratogenicity[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12539863&dopt=Abstract],[http://www.ehjournal.net/content/4/1/17], and neurotoxicity[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15681127], and its suspected carcinogenic potential, because it remains radioactive for an exceedingly long time with a half-life of approximately 4.5 billion years (about the age of the Earth); and because it is also toxic in a manner similar to lead and other heavy metals. The long half-life indicates that depleted uranium is only weakly radioactive, but, all isotopes of uranium are chemical toxicants. Please see Gulf War Syndrome. Such issues are of concern to those attacked with DU weapons, those firing DU weapons, those protected by DU armour-plating, civilians and troops operating in a theatre where DU is used, and to people who will live at any time after in such areas or breathing air or drinking water from these areas. Studies showing detrimental health effects have claimed the following:
- Pre-1993 military DU studies mainly evaluated external exposure, but other studies take inhalation risk into consideration. These studies indicate that DU passes into humans more easily than previously thought after battlefield use. (Teratogenic and radioactive particles absorbed into the body are far more harmful than a similar background radiation level outside the body, due to their immediate proximity to delicate structures such as DNA, bone marrow and the like.) [http://www.triumf.ca/safety/rpt/rpt_2/node22.html][http://toxsci.oxfordjournals.org/cgi/content/abstract/89/1/287]
- DU can disperse into the air and water, as mentioned in a United Nations Environment Programme (UNEP) study [http://www.unep.org/pdf/iraq_ds_lowres.pdf]: : "The most important concern is the potential for future groundwater contamination by corroding penetrators (ammunition tips made out of DU). The munition tips recovered by the UNEP team had already decreased in mass by 10-15% in this way. This rapid corrosion speed underlines the importance of monitoring the water quality at the DU sites on an annual basis."
- According to the IAEA, if depleted uranium is ingested or inhaled it can be harmful because of its chemical toxicity. High concentrations can cause kidney damage.[http://www.iaea.org/NewsCenter/Features/DU/faq_depleted_uranium.shtml] The US military watchdog group Federation of American Scientists came to similar conclusions prior to 2000. The IAEA claims that there is no link between DU exposure and increases in human cancers.
- A 1997 report by [http://www.euradcom.org The European Committee on Radiation Risk (ECRR)] suggested that DU posed serious health risks. At that time, other studies had shown that DU ammunition had no measurable detrimental health effects in the short term. Most other teratogens cause more cancer in proportion to increased birth defects than was measured in U.S. and U.K. troops.

Legal status of military use

In 1996 and 1997, the United Nations Human Rights Commission in Geneva, passed a resolution to ban the use of depleted uranium weapons. The Subcommission adopted resolutions which include depleted uranium weaponry amongst "weapons of mass and indiscriminate destruction, ... incompatible with international humanitarian or human rights law." (Secretary General's Report, 24 June 1997, E/CN. 4/Sub.2/1997/27) A UN report of 2002 states that DU weapons also potentially breach each of the following laws: The Universal Declaration of Human Rights; the Charter of the United Nations; the Genocide Convention; the Convention Against Torture; the four Geneva Conventions of 1949; the Conventional Weapons Convention of 1980; and the Hague Conventions of 1899 and 1907. All of these laws are designed to spare civilians from unwarranted suffering in or after armed conflicts. According to the UN, the resolutions in 1996-97 were passed because DU breaches several international laws concerning inhumane weapons: it is not limited in time or space to the legal field of battle, or to military targets; it continues to act after the war; it is "inhumane" by virtue of its ability to cause prolonged or long term death by cancer and other serious health issues, it causes harm to future civilians and passers by (including unborn children and those breathing the air or drinking water); and it has an "unduly negative" and long term effect on the natural environment and food chain. In detail: # Weapons may only be used in the legal field of battle, defined as legal military targets of the enemy in war. Weapons may not have an adverse effect off the legal field of battle. DU shells burn into fine particles which remain in the air or the environment. So they affect others over a wide range, and future passers-by, with uranium poisoning. # Weapons can only be used for the duration of an armed conflict. A weapon that is used or continues to act after the war is over violates this criterion. # Weapons may not be unduly inhumane. Weapons that cause cancer and illness long after the war are widely considered to be legally "inhumane". Health issues to unborn children and civilians may also be crimes against humanity under international law. # Weapons may not have an "unduly negative" effect on the natural environment. The dust from DU impact becomes widespread in the environm

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