Weighable amounts of berkelium-249 (half-life 314 days) make it possible to determine some of its properties using macroscopic quantities. As of 2004 it had not been isolated in its elemental form, but it is predicted to be a silvery metal that would easily oxidize in air at elevated temperatures and would be soluble in dilute mineral acids. X-ray diffraction techniques have been used to identify various berkelium compounds such as berkelium dioxide (BkO2), berkelium fluoride (BkF3), berkelium oxychloride (BkOCl) ...

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The value of Avogadro's number depends on the definition of the mole, which depends on the definition of the kilogram. Both definitions, especially that of the kilogram, are arbitrary: the kilogram system is currently based on the mass of a particular "standard" bar of metal in France. This means that the particular value of Avogadro's number is the result of convention; there is no physical reason for it. Hence, Avogadro's number is not a fundamental constant. Avogadro's number can be regarded as a conversion factor between the micro ...

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Vanadium is a soft and ductile, gray-white metal. It has good resistance to corrosion by alkalis, sulfuric and hydrochloric acid. It oxidizes readily at about 933 K. Vanadium has good structural strength and a low fission neutron cross section, making it useful in nuclear applications. Although definitely a metal, it shares with Chromium and Manganese the property of having valency oxides with acid properties. Common oxidation states of vanadium include +2, +3, +4 and +5. A popular experiment with ammonium vanadate (NH4VOSee also:

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Chromium is a steel-gray, lustrous, hard metal that takes a high polish, melts with difficulty, and tarnishes. The most common oxidation states of chromium are +2, +3, and +6, with +3 being the most stable. +4 and +5 are rare. Chromium compounds of oxidation state 6 are powerful oxidants. Chromium(0) is unstable in oxygen, immediately producing a thin oxide layer that is impermeable to oxygen and protects the metal below. ...

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Weighable amounts of californium make it possible to determine some of its properties using macroscopic quantities. Californium-252 (2.6 year half-life) is a very strong neutron emitter and is thus extremely radioactive and harmful (one microgram spontaneously emits 170 million neutrons per minute). The decay of californium-254 (55-day half-life) may have been detected through telescopes in supernovae remnants. Californium-249 is formed from the beta decay of berkelium-249 and most other californium isotopes are made by subjecting berke ...

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Xylitol - Dental care. Xylitol is a toothfriendly sugar substitute. In addition to discouraging tooth decay by replacing dietary sugars, xylitol may actively aid in repairing minor cavities caused by dental caries. Recent research confirms a plaque-reducing effect and suggests that the compound, having some chemical properties similar to table sugar, attracts and then "starves" harmful micro-organisms, allowing the mouth to remineralize damaged teeth with less interruption. (However, this same effect also interfe ...

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Naturally occurring cobalt is composed of 1 stable isotope, 59-Co (59Co). 22 radioisotopes have been characterized with the most stable being 60Co with a half-life of 5.2714 years, 57-Co (57Co) with a half-life of 271.79 days, and 56-Co (56Co) with a half-life of 77.27 days, and 58-Co (58Co) with a half life of 70.86 days. All of the remaining radioactive isotopes have half-lifes that are less than 18 hours and the majority of these have half lives that are less than 1 second. This element also has 4 meta states, all of which ha ...

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Cobalt is a hard ferromagnetic silver-white element. The Curie temperature is of 1388 K with 1.6~1.7 Bohr magnetons per atom. It is frequently associated with nickel, and both are characteristic ingredients of meteoric iron. Mammals require small amounts of cobalt salts. Cobalt-60, an artificially produced radioactive isotope of cobalt, is an important radioactive tracer and cancer-treatment agent. Cobalt has a relative permeability two thirds that of iron. Metallic cobalt commonly presents a mixture of two crystallographic structures hcp and fcc with a transition temperature hcp→fcc of 722 K. Common oxidation states of ...

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Powdered cobalt in metal form is a fire hazard. Cobalt compounds should be handled with care due to cobalt's slight toxicity. Cobalt-60 is a powerful gamma ray emitter and exposure to 60Co is therefore a cancer risk. Ingestion of 60Co will lead to incorporation of some cobalt into tissues, which is released very slowly. Cobalt-60 is a risk factor in a nuclear confrontation because neutron emissions will convert iron into this isotope. Some nuclear weapon designs could intentionally increase the amount of Cobalt-6 ...

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The bulk of the nickel mined comes from two types of ore deposits. The first are laterites where the principal ore minerals are nickeliferous limonite: (Fe,Ni)O(OH) and garnierite (a hydrous nickel silicate): (Ni,Mg)3Si2O5(OH). The second are magmatic sulfide deposits where the principal ore mineral is pentlandite: (Ni,Fe)9S8. see Ore genesis In terms of supply, the Sudbury region of Ontario, Canada, produces about 30 percent of the world's supply of nickel. Th ...

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Many but not all hydrogenases contain nickel in addition to iron-sulfur clusters. Nickel centres are a common element in those hydrogenases whose function is to oxidise rather than evolve hydrogen. The nickel centre appears to undergo changes in oxidation state, and evidence has been presented that the nickel centre might be the active site of these enzymes. A nickel-tetrapyrrole coenzyme, Co-F430, is present in the methyl CoM reductase and in methanogenic bacteria. The tetrapyrrole is intermediate in structure between porphyrin and corrin. Changes in redox state, as well as changes in nickel ...

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Nickel can be recovered using extractive metallurgy. Oxy-hydroxide ores are treated using hydrometallurgy, and from sulfide mineral concentrates using pyrometallurgical or hydrometallurgical techniques. Sulfide mineral concentrates are produced by applying the froth flotation process. Nickel is extracted from its ores by conventional roasting and reduction processes which yield a metal of >95% purity. Final purification to >99.99% purity is performed by reacting nickel and carbon monoxide to form nickel carbonyl. This gas is pas ...

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During World War II, nylon replaced Asian silk in parachutes. It was also used to make tires, tents, ropes, ponchos, and other military supplies. It was even used in the production of a high-grade paper for U.S. currency. At the outset of the war, cotton accounted for more than 80% of all fibers used, and manufactured and wool fibers accounted for the remaining 20%. By August, 1945, manufactured fibers had taken a ma ...

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Nickel use is ancient, and can be traced back as far as 3500 BCE. Bronzes from what is now Syria had a nickel content of up to two percent. Further, there are Chinese manuscripts suggesting that "white copper" (e.g. baitung) was used in the Orient between 1400 and 1700 BC. However, because the ores of nickel were easily mistaken for ores of silver, any understanding of this metal and its use dates to more contemporary times. Minerals containing nickel (e.g. kupfernickel, or false copper) were of value for colouring glass green. In 175 ...

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Above their melting temperatures, Tm, thermoplastics like nylon are amorphous solids or viscous fluids in which the chains approximate random coils. Below Tm, amorphous regions alternate with regions which are lamellar crystals.[1] The amorphous regions contribute elasticity and the crystalline regions contribute strength and rigidity. The planar amide (-CO-NH-) groups are very polar, so nylon forms multiple hydrogen bonds among adjacent strands. Because the nylon backbone is so regular and symmetrical, es ...

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Exposure to nickel metal and soluble compounds should not exceed 0.05 mg/cm³ in nickel equivalents per 40-hour work week. Nickel sulfide fume and dust is believed to be carcinogenic, and various other nickel compounds may be as well. Nickel carbonyl, [Ni(CO)4], is an extremely toxic gas. The toxicity of metal carbonyls is a function of both the toxicity of a metal as well as the carbonyl's ability to give off highly toxic carbon monoxide gas, and this one is ...

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Naturally occurring nickel is composed of 5 stable isotopes; 58-Ni, 60-Ni, 61-Ni, 62-Ni and 64-Ni with 58-Ni being the most abundant (68.077% natural abundance). 18 radioisotopes have been characterised with the most stable being 59-Ni with a half-life of 76,000 years, 63-Ni with a half-life of 100.1 years, and 56-Ni with a half-life of 6.077 days. All of the remaining radioactive isotopes have half-lifes that are less than 60 hours and the majority of these have half lifes that are less than 30 seconds. ...

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At present it is not technologically feasible to count the exact number of atoms in 12 g of carbon-12, so the precise value of Avogadro's number is unknown. The 2002 CODATA recommended value for Avogadro's number is where the number in parentheses represents the one standard deviation uncertainty in the last digits of the value. A number of methods can be used to measure Avogadro's number. One modern method is to calculate Avogadro's number from the density of a crystal, the relative atomic mass, and the un ...

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Naturally occurring chromium is composed of 3 stable isotopes; 52-Cr, 53-Cr, and 54-Cr with 52-Cr being the most abundant (83.789% natural abundance). 19 radioisotopes have been characterized with the most stable being 50-Cr with a half-life of (more than) 1.8E17 years, and 51-Cr with a half-life of 27.7025 days. All of the remaining radioactive isotopes have half-lifes that are less than 24 hours and the majority of these have half lifes that are less than 1 minute. ...

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Chromium is notable for its ability to form quintuple covalent bonds. Writing in Science, Tailuan Nguyen and coworkers of the University of California describe how they synthesized a compound (which does not appear to have a common name) of chromium and a hydrocarbon radical; X-ray diffraction showed unambiguously that the compound had a quintuple bond joining the two central chromium atoms. The compound had chemical formula Ar − Cr − Cr − Ar where Ar is the aryl group ...

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Cobalt was known in ancient times through its compounds, which would color glass a rich blue. George Brandt (1694-1768) is credited with the discovery of cobalt. The date of discovery varies depending on the source, but is between 1730 and 1737. He was able to show that cobalt was the source of the blue color in glasses, which previously had been attributed to the bismuth found with cobalt. During the 19th century, cobalt blue was produced at the Norwegian Blaafarveværket (70-80 % of world production), led by the Prussian industrialist Benjamin Wegner. In 1938, John Livingood and G ...

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Potassium dichromate is a powerful oxidizing agent and is the preferred compound for cleaning laboratory glassware of any possible organics. Chrome green is the green oxide of chromium, Cr2O3, used in enamel painting, and glass staining. Chrome yellow is a brilliant yellow pigment, PbCrO4, used by painters. Chromic acid has the hypothetical structure H2CrO4. Neither chromic nor dichromic acid is found in nature, but their anions are found in a variety of compounds. Chromium trioxide, CrO3, the acid anhydride of chromic acid, i ...

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