   #copyright

Iron

2007 Schools Wikipedia Selection. Related subjects: Chemical elements;
Geology and geophysics


                26                manganese ← iron → cobalt
                 -
                ↑
                Fe
                ↓
                Ru

                                  Periodic Table - Extended Periodic Table

                                                                   General
                                         Name, Symbol, Number iron, Fe, 26
                                         Chemical series transition metals
                                              Group, Period, Block 8, 4, d
                                              Appearance lustrous metallic
                                                      with a grayish tinge
                                              Atomic mass 55.845 (2) g/mol
                                     Electron configuration [Ar] 3d^6 4s^2
                                           Electrons per shell 2, 8, 14, 2
                                                       Physical properties
                                                               Phase solid
                                       Density (near r.t.) 7.86 g·cm^−3
                                    Liquid density at m.p. 6.98 g·cm^−3
                                                     Melting point 1811  K
                                                    (1538 ° C, 2800 ° F)
                                                      Boiling point 3134 K
                                                    (2861 ° C, 5182 ° F)
                                         Heat of fusion 13.81 kJ·mol^−1
                                     Heat of vaporization 340 kJ·mol^−1
                          Heat capacity (25 °C) 25.10 J·mol^−1·K^−1

   CAPTION: Vapor pressure

                                      P/Pa   1    10  100  1 k  10 k 100 k
                                     at T/K 1728 1890 2091 2346 2679 3132

                                                         Atomic properties
                                     Crystal structure body-centered cubic
                                                             a=286.65 pm ;
                                                       face-centered cubic
                                                     between 1185–1667 K
                                               Oxidation states 2, 3, 4, 6
                                                       ( amphoteric oxide)
                                    Electronegativity 1.83 (Pauling scale)
                                                       Ionization energies
                                           ( more) 1st: 762.5 kJ·mol^−1
                                                  2nd: 1561.9 kJ·mol^−1
                                                    3rd: 2957 kJ·mol^−1
                                                      Atomic radius 140 pm
                                              Atomic radius (calc.) 156 pm
                                                    Covalent radius 125 pm
                                                             Miscellaneous
                                           Magnetic ordering ferromagnetic
                               Electrical resistivity (20 °C) 96.1 nΩ·m
                       Thermal conductivity (300 K) 80.4 W·m^−1·K^−1
                       Thermal expansion (25 °C) 11.8 µm·m^−1·K^−1
                          Speed of sound (thin rod) ( r.t.) (electrolytic)
                                                          5120   m·s^−1
                                                   Young's modulus 211 GPa
                                                      Shear modulus 82 GPa
                                                      Bulk modulus 170 GPa
                                                        Poisson ratio 0.29
                                                         Mohs hardness 4.0
                                                  Vickers hardness 608 MPa
                                                  Brinell hardness 490 MPa
                                             CAS registry number 7439-89-6
                                                         Selected isotopes

                   CAPTION: Main article: Isotopes of iron

                       iso    NA    half-life       DM     DE ( MeV)  DP
                      ^54Fe 5.8%   >3.1×10^22 y 2ε capture  ?        ^54Cr
                      ^55Fe syn    2.73 y       ε capture  0.231     ^55Mn
                      ^56Fe 91.72% Fe is stable with 30 neutrons
                      ^57Fe 2.2%   Fe is stable with 31 neutrons
                      ^58Fe 0.28%  Fe is stable with 32 neutrons
                      ^59Fe syn    44.503 d     β          1.565     ^59Co
                      ^60Fe syn    1.5×10^6 y   β^-        3.978     ^60Co

                                                                References

   Iron ( IPA: /ˈʌɪə(r)n/) is a chemical element with the symbol Fe (
   Latin: ferrum) and atomic number 26. Iron is a group 8 and period 4
   metal. Iron and nickel are notable for being the final elements
   produced by stellar nucleosynthesis, and thus the heaviest elements
   which do not require a supernova or similarly cataclysmic event for
   formation. Iron and nickel are therefore the most abundant metals in
   metallic meteorites and in the dense-metal cores of planets such as
   Earth.

Notable characteristics

   It is believed that iron is the tenth most abundant element in the
   universe. Iron makes up 5% of the Earth's crust and is second in
   abundance to aluminium among the metals and fourth in abundance among
   the elements. Iron is also the most abundant element by mass, making up
   35% of the mass of the Earth as a whole. The concentration of iron in
   the various layers of the Earth ranges from very high at the inner core
   to only a few percent in the outer crust.

   Iron is a metal extracted from iron ore, and is almost never found in
   the free elemental state. In order to obtain elemental iron, the
   impurities must be removed by chemical reduction. Iron is used in the
   production of steel, an alloy or solid solution of different metals,
   and some non-metals, particularly carbon. The many iron-carbon
   allotropes, which have very different properties, are discussed in the
   article on steel.

   Nuclei of iron have some of the highest binding energies per nucleon,
   surpassed only by the nickel isotope ^62Ni. The universally most
   abundant of the highly stable nucleides is, however, ^56Fe. This is
   formed by nuclear fusion in the stars. Although a further tiny energy
   gain could be extracted by synthesizing ^62Ni, conditions in stars are
   not right for this process to be favoured, and iron abundance on Earth
   greatly favors iron over nickel, and also presumably in supernova
   element production. When a very large star contracts at the end of its
   life, internal pressure and temperature rise, allowing the star to
   produce progressively heavier elements, despite these being less stable
   than the elements around mass number 60, known as the "iron group".
   This leads to a supernova. Some cosmological models with an open
   universe predict that there will be a phase where as a result of slow
   fusion and fission reactions, everything will become iron.

   Iron (as Fe^2+, ferrous ion) is a necessary trace element used by all
   known living organisms. Iron-containing enzymes, usually containing
   heme prosthetic groups, participate in catalysis of oxidation reactions
   in biology, and in transport of a number of soluble gases. See
   hemoglobin, cytochrome, and catalase.

Applications

   Iron is the most used of all the metals, comprising 95% of all the
   metal tonnage produced worldwide. Its combination of low cost and high
   strength make it indispensable, especially in applications like
   automobiles, the hulls of large ships, and structural components for
   buildings. Steel is the best known alloy of iron, and some of the forms
   that iron can take include:
     * Pig iron has 4% – 5% carbon and contains varying amounts of
       contaminants such as sulfur, silicon and phosphorus. Its only
       significance is that of an intermediate step on the way from iron
       ore to cast iron and steel.
     * Cast iron contains 2% – 4.0% carbon , 1% – 6% silicon , and small
       amounts of manganese. Contaminants present in pig iron that
       negatively affect the material properties, such as sulfur and
       phosphorus, have been reduced to an acceptable level. It has a
       melting point in the range of 1420–1470 K, which is lower than
       either of its two main components, and makes it the first product
       to be melted when carbon and iron are heated together. Its
       mechanical properties vary greatly, dependent upon the form carbon
       takes in the alloy. 'White' cast irons contain their carbon in the
       form of cementite, or iron carbide. This hard, brittle compound
       dominates the mechanical properties of white cast irons, rendering
       them hard, but unresistant to shock. The broken surface of a white
       cast iron is full of fine facets of the broken carbide, a very
       pale, silvery, shiny material, hence the appellation. In grey iron,
       the carbon exists free as fine flakes of graphite , and also,
       renders the material brittle due to the stress-raising nature of
       the sharp edged flakes of graphite. A newer variant of grey iron,
       referred to as ductile iron is specially treated with trace amounts
       of magnesium to alter the shape of graphite to sheroids, or
       nodules, vastly increasing the toughness and strength of the
       material.
     * Carbon steel contains between 0.4% and 1.5% carbon, with small
       amounts of manganese, sulfur, phosphorus, and silicon.
     * Wrought iron contains less than 0.2% carbon. It is a tough,
       malleable product, not as fusible as pig iron. It has a very small
       amount of carbon, a few tenths of a percent. If honed to an edge,
       it loses it quickly. Wrought iron is characterised, especially in
       old samples, by the presence of fine 'stringers' or filaments of
       slag entrapped in the metal. Wrought iron does not rust
       particularly quickly when used outdoors. It has largely been
       replaced by mild steel for "wrought iron" gates and blacksmithing.
       Mild steel does not have the same corrosion resistance but is
       cheaper and more widely available.
     * Alloy steels contain varying amounts of carbon as well as other
       metals, such as chromium, vanadium, molybdenum, nickel, tungsten,
       etc. They are used for structural purposes, as their alloy content
       raises their cost and necessitates justification of their use.
       Recent developments in ferrous metallurgy have produced a growing
       range of microalloyed steels, also termed 'HSLA' or high-strength,
       low alloy steels, containing tiny additions to produce high
       strengths and often spectacular toughness at minimal cost.
     * Iron(III) oxides are used in the production of magnetic storage
       media in computers. They are often mixed with other compounds, and
       retain their magnetic properties in solution.

   The main drawback to iron and steel is that pure iron, and most of its
   alloys, suffer badly from rust if not protected in some way. Painting,
   galvanization, plastic coating and bluing are some techniques used to
   protect iron from rust by excluding water and oxygen or by sacrificial
   protection.

History

   The first signs of use of iron come from the Sumerians and the
   Egyptians, where around 4000 BCE [citation needed], a few items, such
   as the tips of spears, daggers and ornaments, were being fashioned from
   iron recovered from meteorites [citation needed]. Because meteorites
   fall from the sky, some linguists have conjectured that the English
   word iron (OE īsern), which has cognates in many northern and western
   European languages, derives from the Etruscan aisar which means "the
   gods". Even if this is not the case, the word is likely a loan into
   pre- Proto-Germanic from Celtic or Italic (Krahe IF 46:184f. compares
   Old Irish, Illyrian, Venetic and Messapic forms). The meteoric origin
   of Iron in its first use by humans is also alluded to in the Quran :
   "and We sent down Iron in which is incredible strength and many
   benefits for mankind" (57:25 page:541)[linguistic citations needed; no
   mention of Proto-Boreal, Nostratic terms or Afro-Asiatic terms].

   Ancient Greeks considered the Halybes to be "the inventors of iron"
   [citation needed; "the Greeks" are not a homogeneous group of people
   publishing one idea]. The people of the Caucasian Isthmus, Khaldi
   people (or Khalib/Halyb and Halisones by Strabo) were one of the oldest
   west-Georgian tribes (4th to 2nd millennia BC). The word "Halybes" may
   refer to people in Anatolia or in the Caucasus, and it is also possible
   that by the time the Greeks knew of iron, it was associated with
   Chaldea, where it was produced in large quantities (but not where it
   was invented).

   By 2500 BCE to 2000 BCE, increasing numbers of smelted iron objects
   (distinguishable from meteoric iron by the lack of nickel in the
   product) appear in Mesopotamia, Anatolia, and Egypt[citation needed].
   However, their use appears to be ceremonial, and iron was an expensive
   metal, more expensive than gold[citation needed, especially as regards
   to pricing concerning gold, as the word is often confused with "bronz"
   in ancient texts]. In the Iliad, weaponry is mostly bronze, but iron
   ingots are used for trade [an actual iron macehead was located at Troy
   in 1902; citation for either of these facts needed]. Some resources
   (see the reference What Caused the Iron Age? below) suggest that iron
   was being created then as a by-product of copper refining, as sponge
   iron, and was not reducible by the metallurgy of the time. By 1600 BCE
   to 1200 BCE, iron was used increasingly in the Middle East, but did not
   supplant the dominant use of bronze[citation needed; same story told
   about off-products of gold producing unusable iron].
   Axe of iron from Swedish Iron Age, found at Gotland, Sweden.
   Enlarge
   Axe of iron from Swedish Iron Age, found at Gotland, Sweden.

   In the period from the 12th to 10th century BCE, there was a rapid
   transition in the Middle East from bronze to iron tools and weapons.
   The critical factor in this transition does not appear to be the sudden
   onset of a superior iron working technology, but instead the disruption
   of the supply of tin. This period of transition, which occurred at
   different times in different parts of the world, is the ushering in of
   an age of civilization called the Iron Age. Classical authors ascribe
   the first invention of ironsmithing to peoples of the Caucasus and
   eastern Anatolia, such as the Khaldi (Chaldei) and the Khalib
   (Chalybes)[very likely the same people mentioned above - but
   erroneously located in Georgia, instead! the Khaldi are either in
   Georgia or Anatolia - but if both, then some major disambiguation needs
   to occur here]. If local customs regarding the importation of other
   metal-working techniques prevailed in the case of iron, then it would
   have been customary for people from the ironworking region (in this
   case, in Anatolia - since there are many agreements on that source), to
   establish self-named ethnic enclaves or new towns near the places where
   they wished to market their goods. Fierce defense of trade secrets had
   already made this the typical plan, whether with pottery, copper
   working, jewelry making or bronze making. The inventors moved closer to
   the markets, but kept themselves distinct and protected their secrets
   carefully. It is possible that other people came to these new
   metalworking towns to learn trade secrets, but probably had to pay a
   price of some kind (Abram and Lot may have been two such, coming to the
   new place, Ur of the Chaldees, which was a new Ur, not the old Ur,
   designed for metal production).
   The common alchemical symbol for iron, the metal of weapons, is that of
   Mars, the god of war.
   Enlarge
   The common alchemical symbol for iron, the metal of weapons, is that of
   Mars, the god of war.

   Concurrent with the transition from bronze to iron was the discovery of
   carburization, which was the process of adding carbon to the irons of
   the time. Iron was recovered as sponge iron, a mix of iron and slag
   with some carbon and/or carbide, which was then repeatedly hammered and
   folded over to free the mass of slag and oxidise out carbon content, so
   creating the product wrought iron. Wrought iron was very low in carbon
   content and was not easily hardened by quenching. The people of the
   Middle East found that a much harder product could be created by the
   long term heating of a wrought iron object in a bed of charcoal, which
   was then quenched in water or oil. The resulting product, which had a
   surface of steel, was harder and less brittle than the bronze it began
   to replace.

   In China the first irons used were also meteoric iron, with
   archaeological evidence for items made of wrought iron appearing in the
   northwest, near Xinjiang, in the 8th century BCE. These items were made
   of wrought iron, created by the same processes used in the Middle East
   and Europe, and were thought to be imported by non-Chinese people.

   In the later years of the Zhou Dynasty (ca 550 BCE), a new iron
   manufacturing capability began because of a highly developed kiln
   technology. Producing blast furnaces capable of temperatures exceeding
   1300 K, the Chinese developed the manufacture of cast, or pig iron.

   Iron was used in India as early as 250 BCE. The famous iron pillar in
   the Qutb complex in Delhi is made of very pure iron (98%) and has not
   rusted or eroded till this day.
   This blast furnace in eastern Missouri consumed up to 11,000 tons of
   ore and 16,000 cords (58,000 m³) of wood annually from 1827 to 1891.
   Enlarge
   This blast furnace in eastern Missouri consumed up to 11,000 tons of
   ore and 16,000 cords (58,000 m³) of wood annually from 1827 to 1891.

   If iron ores are heated with carbon to 1420–1470 K, a molten liquid is
   formed, an alloy of about 96.5% iron and 3.5% carbon. This product is
   strong, can be cast into intricate shapes, but is too brittle to be
   worked, unless the product is decarburized to remove most of the
   carbon. The vast majority of Chinese iron manufacture, from the Zhou
   dynasty onward, was of cast iron. Iron, however, remained a pedestrian
   product, used by farmers for hundreds of years, and did not really
   affect the nobility of China until the Qin dynasty (ca 221 BCE).

   Cast iron development lagged in Europe, as the smelters could only
   achieve temperatures of about 1000 C; or perhaps they did not want
   hotter temperatures, as they were seeking to produce blooms as a
   precursor of wrought iron, not cast iron. Through a good portion of the
   Middle Ages, in Western Europe, iron was thus still being made by the
   working of iron blooms into wrought iron. Some of the earliest casting
   of iron in Europe occurred in Sweden, in two sites, Lapphyttan and
   Vinarhyttan, between 1150 and 1350 CE. Cast iron was then made into
   wrought iron by the osmond process. Some scholars have speculated the
   practice followed the Mongols across Russia to these sites, but there
   is no clear proof of this hypothesis. In any event, by the late
   fourteenth century, a market for cast iron goods began to form, as a
   demand developed for cast iron cannonballs.

   Early iron smelting used charcoal as both the heat source and the
   reducing agent. In 18th century England, wood supplies became
   inadequate to enable the industry to expand and coke, a fossil fuel,
   began to be used an alternative. This innovation is associated with
   Abraham Darby at Coalbrookdale in 1709, but it was only later in the
   century that economically viable means of converting pig iron to bar
   iron were devised. The most successful such process was Henry Cort's
   puddling process, patented in 1784. Those processes permitted the great
   expansion in the production of iron that constitutes the Industrial
   Revolution for that industry.

Occurrence

   The red appearance of this water is due to iron in the rocks.
   Enlarge
   The red appearance of this water is due to iron in the rocks.

   Iron is one of the most common elements on Earth, making up about 5% of
   the Earth's crust. Most of this iron is found in various iron oxides,
   such as the minerals hematite, magnetite, and taconite. The earth's
   core is believed to consist largely of a metallic iron-nickel alloy.
   About 5% of the meteorites similarly consist of iron-nickel alloy.
   Although rare, these are the major form of natural metallic iron on the
   earth's surface.

Production of iron from iron ore

   How Iron was extracted in the 19th century
   Enlarge
   How Iron was extracted in the 19th century
   This heap of iron ore pellets will be used in steel production.
   Enlarge
   This heap of iron ore pellets will be used in steel production.

   Industrially, iron is produced starting from iron ores, principally
   hematite (nominally Fe[2]O[3]) and magnetite (Fe[3]O[4]) by a
   carbothermic reaction (reduction with carbon) in a blast furnace at
   temperatures of about 2000 °C. In a blast furnace, iron ore, carbon in
   the form of coke, and a flux such as limestone are fed into the top of
   the furnace, while a blast of heated air is forced into the furnace at
   the bottom.

   In the furnace, the coke reacts with oxygen in the air blast to produce
   carbon monoxide:

          6 C + 3 O[2] → 6 CO

   The carbon monoxide reduces the iron ore (in the chemical equation
   below, hematite) to molten iron, becoming carbon dioxide in the
   process:

          6 CO + 2 Fe[2]O[3] → 4 Fe + 6 CO[2]

   The flux is present to melt impurities in the ore, principally silicon
   dioxide sand and other silicates. Common fluxes include limestone
   (principally calcium carbonate) and dolomite ( magnesium carbonate).
   Other fluxes may be used depending on the impurities that need to be
   removed from the ore. In the heat of the furnace the limestone flux
   decomposes to calcium oxide (quicklime):

          CaCO[3] → CaO + CO[2]

   Then calcium oxide combines with silicon dioxide to form a slag.

          CaO + SiO[2] → CaSiO[3]

   The slag melts in the heat of the furnace, which silicon dioxide would
   not have. In the bottom of the furnace, the molten slag floats on top
   of the more dense molten iron, and spouts in the side of the furnace
   may be opened to drain off either the iron or the slag. The iron once
   cooled, is called pig iron, while the slag can be used as a material in
   road construction or to improve mineral-poor soils for agriculture. Pig
   iron is later reduced to steel using convertors.

   Approximately 1100Mt (million tons) of iron ore was produced in the
   world in 2000, with a gross market value of approximately 25 billion US
   dollars. While ore production occurs in 48 countries, the five largest
   producers were China, Brazil, Australia, Russia and India, accounting
   for 70% of world iron ore production. The 1100Mt of iron ore was used
   to produce approximately 572Mt of pig iron.

Isotopes

   Naturally occurring iron consists of four isotopes: 5.845% of
   radioactive ^54Fe (half-life: >3.1×10^22 years), 91.754% of stable
   ^56Fe, 2.119% of stable ^57Fe and 0.282% of stable ^58Fe. ^60Fe is an
   extinct radionuclide of long half-life (1.5 million years). Much of the
   past work on measuring the isotopic composition of Fe has centered on
   determining ^60Fe variations due to processes accompanying
   nucleosynthesis (i.e., meteorite studies) and ore formation.

   The isotope ^56Fe is of particular interest to nuclear scientists. A
   common misconception is that this isotope represents the most stable
   nucleus possible, and that it thus would be impossible to perform
   fission or fusion on ^56Fe and still liberate energy. This is not true,
   as both ^62Ni and ^58Fe are more stable.

   In phases of the meteorites Semarkona and Chervony Kut a correlation
   between the concentration of ^60Ni, the daughter product of ^60Fe, and
   the abundance of the stable iron isotopes could be found which is
   evidence for the existence of ^60Fe at the time of formation of the
   solar system. Possibly the energy released by the decay of ^60Fe
   contributed, together with the energy released by decay of the
   radionuclide ^26Al, to the remelting and differentiation of asteroids
   after their formation 4.6 billion years ago. The abundance of ^60Ni
   present in extraterrestrial material may also provide further insight
   into the origin of the solar system and its early history. Of the
   stable isotopes, only ^57Fe has a nuclear spin (−1/2).

Iron in biology

   Structure of Heme b
   Enlarge
   Structure of Heme b

   Iron is essential to all known organisms. It is mostly stably
   incorporated in the inside of metalloproteins, because in exposed or in
   free form it causes production of free radicals that are generally
   toxic to cells. To say that iron is free doesn't mean that it is free
   floating in the bodily fluids. Iron binds avidly to virtually all
   biomolecules so it will adhere nonspecifically to cell membranes,
   nucleic acids, proteins etc.

   Many animals incorporate iron into the heme complex, an essential
   component of cytochromes, which are proteins involved in redox
   reactions (including but not limited to cellular respiration), and of
   oxygen carrying proteins hemoglobin and myoglobin. Inorganic iron
   involved in redox reactions is also found in the iron-sulfur clusters
   of many enzymes, such as nitrogenase (involved in the synthesis of
   ammonia from nitrogen and hydrogen) and hydrogenase. A class of
   non-heme iron proteins is responsible for a wide range of functions
   within several life forms, such as enzymes methane monooxygenase
   (oxidizes methane to methanol), ribonucleotide reductase (reduces
   ribose to deoxyribose; DNA biosynthesis), hemerythrins (oxygen
   transport and fixation in marine invertebrates) and purple acid
   phosphatase ( hydrolysis of phosphate esters). When the body is
   fighting a bacterial infection, the body sequesters iron inside of
   cells (mostly stored in the storage molecule ferritin) so that it
   cannot be used by bacteria.

   Iron distribution is heavily regulated in mammals, both as a defense
   against bacterial infection and because of the potential biological
   toxicity of iron. The iron absorbed from the duodenum binds to
   transferrin, and is carried by blood to different cells. There it gets
   incorporated, by an as yet unknown mechanism, into target proteins.. A
   lengthier article on the system of human iron regulation can be found
   in the article on human iron metabolism.

Iron in organic synthesis

   The usage of iron metal filings in organic synthesis is mainly for the
   reduction of nitro compounds. Additionally, iron has been used for
   desulfurizations, reduction of aldehydes, and the deoxygenation of
   amine oxides.

Precautions

   Excessive iron is toxic to humans, because excess ferrous iron reacts
   with peroxides in the body, producing free radicals. Iron becomes toxic
   when it exceeds the amount of transferrin needed to bind free iron. In
   excess, uncontrollable quantities of free radicals are produced.

   Iron uptake is tightly regulated by the human body, which has no
   physiologic means of excreting iron and regulates iron solely by
   regulating uptake. However, too much ingested iron can damage the cells
   of the gastrointestinal tract directly, and may enter the bloodstream
   by damaging the cells that would otherwise regulate its entry. Once
   there, it causes damage to cells in the heart, liver and elsewhere.
   This can cause serious problems, including the potential of death from
   overdose, and long-term organ damage in survivors.

   Humans experience iron toxicity above 20 milligrams of iron for every
   kilogram of weight, and 60 milligrams per kilogram is a lethal dose.
   Over-consumption of iron, often the result of children eating large
   quantitities of ferrous sulfate tablets intended for adult consumption,
   is the most common toxicological cause of death in children under six.
   The DRI lists the Tolerable Upper Intake Level (UL) for adults as 45
   mg/day. For children under fourteen years old the UL is 40 mg/day.

   If iron intake is excessive iron overload disorders can sometimes
   result, such as hemochromatosis. Iron overload disorders require a
   genetic inability to regulate iron uptake; however, many people have a
   genetic susceptibility to iron overload without realizing it and
   without knowing a family history of the problem. For this reason,
   people should not take iron supplements unless they suffer from iron
   deficiency and have consulted a doctor. Blood donors are at special
   risk of low iron levels and are often recommended to supplement their
   iron intake.

   The medical management of iron toxicity is complex. One element of the
   medical approach is a specific chelating agent called deferoxamine,
   used to bind and expel excess iron from the body in case of iron
   toxicity.
   Retrieved from " http://en.wikipedia.org/wiki/Iron"
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