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Molybdenum, Techntium, Rhenium

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Molybdenum, Techntium, Rhenium

  1. 1. molybdenum
  2. 2. History  Discovery Carl Wilhelm Scheele (1778)  First isolation Peter Jacob Hjelm (1781) By 1778 Swedish chemist Carl Wilhelm Scheele stated firmly that molybdena was (indeed) not galena nor graphite. Instead, Scheele went further and correctly proposed that molybdena was an ore of a distinct new element, named molybdenum for the mineral in which it resided, and from which it might be isolated. Peter Jacob Hjelm successfully isolated molybdenum by using carbon and linseed oil in 1781.
  3. 3. Source  the Knaben mine in southern Norway, opened in 1885, was the first dedicated molybdenum mine. It closed from 1973 to 2007, but is now reopened. Large mines in Colorado (such as the Henderson mine and the Climax mine)and in British Columbia yield molybdenite as their primary product, while many porphyry copper deposits such as the Bingham Canyon Mine in Utah and the Chuquicamata mine in northern Chile produce molybdenum as a by product of copper mining.  The Russian Luna 24 mission discovered a molybdenum-bearing grain (1 × 0.6 μm) in a pyroxene fragment taken from Mare Crisium on the Moon. The comparative rarity of molybdenum in the Earth's crust is offset by its concentration in a number of water-insoluble ores, often combined with sulfur, in the same way as copper, with which it is often found. Though molybdenum is found in such minerals as wulfenite (PbMoO4) and powellite (CaMoO4), the main commercial source of molybdenum is molybdenite (MoS2). Molybdenum is mined as a principal ore, and is also recovered as a byproduct of copper and tungsten mining.
  4. 4. How to get  In molybdenite processing, the molybdenite is first heated to a temperature of 700 °C (1,292 °F) and the sulfide is oxidized into molybdenum(VI) oxide by air:  2 MoS2 + 7 O2 → 2 MoO3 + 4 SO2  The oxidized ore is then either heated to 1,100 °C (2,010 °F) to sublimate the oxide, or leached with ammonia, which reacts with the molybdenum(VI) oxide to form water-soluble molybdates:  MoO3 + 2 NH4OH → (NH4)2(MoO4) + H2O  Copper, an impurity in molybdenite, is less soluble in ammonia. To completely remove it from the solution, it is precipitated with hydrogen sulfide.  Pure molybdenum is produced by reduction of the oxide with hydrogen, while the molybdenum for steel production is reduced by the aluminothermic reaction with addition of iron to produce ferromolybdenum. A common form of ferromolybdenum contains 60% molybdenum.
  5. 5. Properties  Phase solid  Melting point 2896 K (2623 °C, 4753 °F)  Boiling point 4912 K (4639 °C, 8382 °F)  Density near r.t. 10.28 g·cm−3  liquid, at m.p. 9.33 g·cm−3  Heat of fusion 37.48 kJ·mol−1  Heat of vaporization 598 kJ·mol−1  Molar heat capacity 24.06 J·mol−1·K−1
  6. 6. Compound  Molybdenum(II) chloride MoCl2 (yellow solid)  Molybdenum(III) chloride MoCl3 (dark red solid)  Molybdenum(IV) chloride MoCl4 (black solid)  Molybdenum(V) chloride MoCl5 (dark green solid)  Molybdenum(VI) chloride MoCl6 (brown solid)  molybdenum(VI) oxide (MoO3)  molybdenum disulfide (MoS2)  molybdates (MoO42−)  heteropolymolybdate P[Mo12O40]3−  molybdenum hexacarbonyl, Mo(CO)6
  7. 7. Reaction  With acids & base : molybdenum does not dissolve in acids or base  With water : At room temperature, molybdenum does not react with water.  With oxygen : 2 Mo + 3 O2 → 2 MoO3  with the halogens : Mo(s) + 3F2(g) → MoF6(l) [colourless] 2Mo(s) + 5Cl2(g) → 2MoCl5(s) [black]
  8. 8. Application  Alloys, estimated fractional global industrial use of molybdenum is structural steel 35%, stainless steel 25%, chemicals 14%, tool & high-speed steels 9%, cast iron 6%, molybdenum elemental metal 6%, and superalloys, 5%.  Molybdenum powder is used as a fertilizer for some plants, such as cauliflower.  Molybdenum anodes replace tungsten in certain low voltage X-ray sources, for specialized uses such as mammography.  Molybdenum disilicide (MoSi2) is an electrically conducting ceramic with primary use in heating elements operating at temperatures above 1500 °C in air.  Molybdenum coated soda lime glass is used for CIGS solar cell fabrication.
  9. 9. Precautions  Molybdenum dusts and fumes, which can be generated by mining or metalworking, can be toxic, especially if ingested (including dust trapped in the sinuses and later swallowed). Low levels of prolonged exposure can cause irritation to the eyes and skin. Direct inhalation or ingestion of molybdenum and its oxides should be avoided. OSHA regulations specify the maximum permissible molybdenum exposure in an 8-hour day as 5 mg/m3. Chronic exposure to 60 to 600 mg/m3 can cause symptoms including fatigue, headaches and joint pains.
  10. 10. Technetium
  11. 11. History Discovery and first isolation Carlo Perrier and Emilio Segrè (1937) From the 1860s through 1871, early forms of the periodic table proposed by Dimitri Mendeleev contained a gap between molybdenum (element 42) and ruthenium (element 44). The discovery of element 43 was finally confirmed in a December 1936 experiment at the University of Palermo in Sicily conducted by Carlo Perrier and Emilio Segrè. Prediction by Dmitri Mendeleev (1871)
  12. 12. Source  In 1952, astronomer Paul W. Merrill in California detected the spectral signature of technetium (in particular, light with wavelength of 403.1 nm, 423.8 nm, 426.2 nm, and 429.7 nm) in light from S-type red giants. The stars were near the end of their lives, yet were rich in this short-lived element, meaning nuclear reactions within the stars must be producing it. This evidence was used to bolster the then-unproven theory that stars are where nucleosynthesis of the heavier elements occurs. More recently, such observations provided evidence that elements were being formed by neutron capture in the s-process.  Since its discovery, there have been many searches in terrestrial materials for natural sources of technetium. In 1962, technetium-99 was isolated and identified in pitchblende from the Belgian Congo in extremely small quantities (about 0.2 ng/kg); there it originates as a spontaneous fission product of uranium-238. There is also evidence that the Oklo natural nuclear fission reactor produced significant amounts of technetium-99, which has since decayed into ruthenium-99.
  13. 13. How to get  The metastable isotope technetium-99m is continuously produced as a fission product from the fission of uranium or plutonium in nuclear reactors. Because used fuel is allowed to stand for several years before reprocessing, all molybdenum-99 and technetium-99m will have decayed by the time that the fission products are separated from the major actinides in conventional nuclear reprocessing. The liquid left after plutonium–uranium extraction (PUREX) contains a high concentration of technetium as TcO−4 but almost all of this is technetium-99, not technetium-99m.  The vast majority of the technetium-99m used in medical work is produced by irradiating dedicated highly enriched uranium targets in a reactor, extracting molybdenum-99 from the targets in reprocessing facilities, and recovering at the diagnostic center the technetium-99m that is produced upon decay of molybdenum-99. Molybdenum-99 in the form of molybdate MoO−4 is adsorbed onto acid alumina (AlO) in a shielded column 2 23chromatograph inside a technetium-99m generator ("technetium cow", also occasionally called a "molybdenum cow"). Molybdenum-99 has a half-life of 67 hours, so short-lived technetium-99m (half-life: 6 hours), which results from its decay, is being constantly produced. The soluble pertechnetate TcO−4 can then be chemically extracted by elution using a saline solution.
  14. 14. Properties  Phase solid  Melting point 2430 K (2157 °C, 3915 °F)  Boiling point 4538 K (4265 °C, 7709 °F)  Density near r.t. 11 g·cm−3  Heat of fusion 33.29 kJ·mol−1  Heat of vaporization 585.2 kJ·mol−1  Molar heat capacity 24.27 J·mol−1·K−1
  15. 15. Compound  pertechnetate TcO−4  sodium pertechnetate NaTcO4  Pertechnetic acid (HTcO4)  Technetium heptoxide Tc2O7  technetium heptasulfide Tc2S7
  16. 16. Reaction  With base : Tc2O7 + 2 NaOH → 2 NaTcO4 + H2O  With water : Technetium does not react with water under normal conditions.  With oxygen : 4 Tc + 7 O2 → 2 Tc2O7  with the halogens : Tc(s) + 3F2(g) → TcF6(s) 2Tc(s) + 7F2(g) → 2TcF7(s)  with acids : technetium is insoluble in hydrochloric acid (HCl) and hydrofluoric acid (HF). It does dissolve in nitric acid, HNO3, or concentrated sulphuric acid, H2SO4, both of which are oxidizing, to form solutions of pertechnetic acid, HTcO4.
  17. 17. Application  Nuclear medicine and biology 1. Technetium-99m is used in radioactive isotope medical tests, for example as the radioactive part of a radioactive tracer that medical equipment can detect in the human body. 2. The longer-lived isotope technetium-95m, with a half-life of 61 days, is used as a radioactive tracer to study the movement of technetium in the environment and in plant and animal systems.  Industrial and chemical 1. National Institute of Standards and Technology (NIST) standard beta emitter, and is therefore used for equipment calibration. Technetium-99 has also been proposed for use in optoelectronic devices and nanoscale nuclear batteries. 2. technetium can serve as a catalyst. For some reactions, for example the dehydrogenation of isopropyl alcohol, it is a far more effective catalyst than either rhenium or palladium.
  18. 18. Rhenium
  19. 19. History  Rhenium (Latin: Rhenus meaning: "Rhine") was the last element to be discovered having a stable isotope (other new radioactive elements have been discovered in nature since then, such as neptunium and plutonium). The existence of a yet undiscovered element at this position in the periodic table had been first predicted by Dmitry Mendeleev. Other calculated information was obtained by Henry Moseley in 1914.[5] It is generally considered to have been discovered by Walter Noddack, Ida Tacke, and Otto Berg in Germany. In 1925 they reported that they detected the element in platinum ore and in the mineral columbite. They also found rhenium in gadolinite and molybdenite.[6] In 1928 they were able to extract 1 g of the element by processing 660 kg of molybdenite.[7] It was estimated in 1968 that 75% of the rhenium metal in the United States was used for research and the development of refractory metal alloys. It took several years from that point on before the super alloys became widely used.  In 1908, Japanese chemist Masataka Ogawa announced that he discovered the 43rd element and named it nipponium (Np) after Japan (Nippon in Japanese). However, later analysis indicated the presence of rhenium (element 75), not element 43.[10] The symbol Np was later used for the element neptunium.
  20. 20. Source Rhenium is one of the rarest elements in Earth's crust with an average concentration of 1 ppb other sources quote the number of 0.5 ppb making it the 77th most abundant element in Earth's crust.[28] Rhenium is probably not found free in nature (its possible natural occurrence is uncertain), but occurs in amounts up to 0.2% in the mineral molybdenite (which is primarily molybdenum disulfide), the major commercial source, although single molybdenite samples with up to 1.88% have been found. Chile has the world's largest rhenium reserves, part of the copper ore deposits, and was the leading producer as of 2005. It was only recently that the first rhenium mineral was found and described (in 1994), a rhenium sulfide mineral (ReS2) condensing from a fumarole on Russia's Kudriavy volcano, Iturup island, in the Kurile Islands. Kudryavy discharges up to 20–60 kg rhenium per year mostly in the form of rhenium disulfide. Named rheniite, this rare mineral commands high prices among collectors.
  21. 21. How to get  Commercial rhenium is extracted from molybdenum roaster-flue gas obtained from copper-sulfide ores. Some molybdenum ores contain 0.001% to 0.2% rhenium. Rhenium(VII) oxide and perrhenic acid readily dissolve in water; they are leached from flue dusts and gasses and extracted by precipitating with potassium or ammonium chloride as the perrhenate salts, and purified by recrystallization.  Total world production is between 40 and 50 tons/year; the main producers are in Chile, the United States, Peru, and Poland. Recycling of used Pt-Re catalyst and special alloys allow the recovery of another 10 tons per year. Prices for the metal rose rapidly in early 2008, from $1000–$2000 per kg in 2003–2006 to over $10,000 in February 2008.  The metal form is prepared by reducing ammonium perrhenate with hydrogen at high temperatures: 2 NH4ReO4 + 7 H2 → 2 Re + 8 H2O + 2 NH3
  22. 22. Properties  Phase solid  Melting point 3459 K (3186 °C, 5767 °F)  Boiling point 5869 K (5596 °C, 10105 °F)  Density near r.t. 21.02 g·cm−3  liquid, at m.p. 18.9 g·cm−3  Heat of fusion 60.43 kJ·mol−1  Heat of vaporization 704 kJ·mol−1  Molar heat capacity 25.48 J·mol−1·K−1
  23. 23. Compound  rhenium chlorides are ReCl6, ReCl5, ReCl4, and ReCl3  The oxychlorides are most common, and include ReOCl4, ReO3Cl.  oxides include Re2O5, ReO2, and Re2O3.  The sulfides are ReS2 and Re2S7.  Rhenium diboride (ReB2)  bromopentacarbonylrhenium(I) Re(CO)5Br  Pentacarbonylhydridorhenium Re(CO)5H
  24. 24. Reaction  With base : Not react  With water : Rhenium does not react with water under normal conditions.  With oxygen : 4Re(s) + 7O2(g) → 2Re2O7(s)  with the halogens : Re(s) + 3F2(g) → ReF6(s) 2Re(s) + 7F2(g) → 2ReF7(s)  with acids : rhenium is insoluble in hydrochloric acid (HCl) and hydrofluoric acid (HF). It does dissolve in nitric acid, HNO3, or concentrated sulphuric acid, H2SO4, both of which are oxidizing, to form solutions of perrhenic acid, HReO4.
  25. 25. Application The Pratt & Whitney F-100 engine uses rhenium-containing second-generation superalloys CFM International CFM56 jet engine still with blades made with 3% rhenium Catalysts Rhenium in the form of rhenium-platinum alloy is used as catalyst for catalytic reforming, which is a chemical process to convert petroleum refinery naphthas with low octane ratings into high-octane liquid products. Other uses The isotopes 188Re and 186Re are radioactive and are used for treatment of liver cancer. 188Re is also being used experimentally in a novel treatment of pancreatic cancer where it is delivered by means of the bacterium Listeria monocytogenes.

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