[11/12/2014 20:23] +91 90 86 985450: Hafnium Classification: Hafnium is a transition metal Color: silvery Atomic weight: 178.49 State: solid Melting point: 2230 oC, 2503 K Boiling point: 4600 oC, 4873 K Electrons: 72 Protons: 72 Neutrons in most abundant isotope: 108 Electron shells: 2,8,18,32,10,2 Electron configuration: [Xe] 4f14 5d2 6s2 Density @ 20oC: 13.2 g/cm3 Appearance and Characteristics Harmful effects: Hafnium is considered to be non-toxic. In powdered form it is pyrophoric (can ignite spontaneously). Characteristics: Hafnium is a lustrous, silvery, ductile metal. Chemically it is similar to zirconium. When present in compounds, hafnium exists mostly in the oxidation state IV. Hafnium resists corrosion due to the formation of an oxide film on exposed surfaces. It is unaffected by all acids (apart from hydrogen fluoride) and all alkalis. Hafnium reacts with the halogens to form tetrahalides, and at high temperatures it reacts with carbon, boron, nitrogen, oxygen, silicon and sulfur. Uses of Hafnium Hafnium is used for nuclear reactor control rods because of its ability to absorb neutrons and its good mechanical and corrosion resistance qualities. This is in complete contrast to zirconium, which although is chemically is very similar to hafnium, is very poor at absorbing neutrons. Zirconium is therefore used in the cladding (outer layer) of fuel rods through which it is important that neutrons can travel easily. Hafnium is also used in photographic flash bulbs, light bulb filaments, and in electronic equipment as cathodes and capacitors. Hafnium alloys with several other metals, such as iron, niobium, tantalum and titanium. Hafnium-niobium alloys, for example, are heat resistant and are used in aerospace applications, such as space rocket engines. Hafnium carbide is used to line high temperature furnaces / kilns due to its refractory properties (it does not melt at high temperatures). Hafnium-based compounds are used in gate insulators in the 45 nm generation of integrated circuits for computers. Hafnium oxide-based compounds are being introduced into silicon-based chips to produce smaller, more energy efficient and performance packed processors(4). Abundance and Isotopes Abundance earth’s crust: 3.3 parts per million by weight, 0.4 parts per million by moles Abundance solar system: 1 part per billion by weight, 0.01 parts per billion by moles Cost, pure: $120 per 100g Cost, bulk: $ per 100g Source: Hafnium is not found free in nature but is found in most zirconium minerals at a concentration of between one and five percent. Commercially, hafnium is produced as a by-product of zirconium refining. This is done using the Kroll Process, reducing the tetrachloride with magnesium or with sodium. Isotopes: Hafnium has 32 isotopes whose half-lives are known, with mass numbers 154 to 185. Naturally occurring hafnium is a mixture of six isotopes and they are found in the percentages shown: 174Hf (0.2%), 176Hf (5.3%), 177Hf (18.6%), 178Hf (27.3%), 179Hf (13.6%) and 180Hf (35.1%). The most abundant is 180Hf at 35.1% [12/12/2014 19:30] +91 90 86 985450: Helium Classification: Helium is a noble gas and a nonmetal Color: colorless Atomic weight: 4.00260 State: gas Melting point: -272.2 oC, 0.95 K Boiling point: -268.9 oC, 4.2 K Electrons: 2 Protons: 2 Neutrons in most abundant isotope: 2 Electron shells: 2 Electron configuration: 1s2 Density @ 20oC: 0.0001787 g/cm3 Interesting Facts about Helium Helium is the second most abundant element in the universe. In 1928 helium became available for the first time on the open market. Helium is so light that Earth’s gravity is not strong enough to hold on to it. When helium atoms are released into the atmosphere, they rise until they escape into space. Helium is one of only two natural elements that has never been observed bonding to another element in a compound. The other element is neon. Helium plasma can, however, form temporary excimer molecules with elements including sodium, fluorine and sulfur. At temperatures close to absolute zero, helium condenses to a liquid with amazing properties – the properties of a superfluid, flowing with zero friction up and over the walls of containers. At normal atmospheric pressure, helium does not solidify. At 25 atmospheres of pressure, helium is a solid at 0.95 K. As the pressure rises, the temperature at which solid helium exists also rises. Helium can be made solid at room temperature if the pressure rises to about 114 thousand atmospheres: that is a pressure of 1.67 million psi, or 834 tons per square inch. This is over 100 times greater than the pressure at the oceans’ deepest point, the Challenger Deep, which is almost seven miles deep (10 916 meters). Helium exists in Earth’s atmosphere only because it is constantly resupplied from two sources – decay of radioactive elements on Earth, and cosmic rays, about 9% of which are high energy helium nuclei. The helium we buy in cylinders is produced by the natural radioactive decay of radioactive elements in the earth’s crust – principally thorium and uranium. Radioactive decay of uranium and thorium produces about 3000 metric tons of helium a year. Current world production of helium is over 30 000 metric tons a year. (Helium has been accumulating for many millions of years in a few natural gas fields, therefore we can currently extract more each year than is being created by uranium and thorium decay.) Appearance and Characteristics Harmful effects: Helium is not known to be toxic. Characteristics: Helium is a light, odorless, colorless, inert, monatomic gas. It can form diatomic molecules, but only weakly and at temperatures close to absolute zero. Helium has the lowest melting point of any element and its boiling point is close to absolute zero. Unlike any other element, helium does not solidify but remains a liquid down to absolute zero (0 K) under ordinary pressures. The voice of someone who has inhaled helium temporarily sounds high-pitched. Uses of Helium Magnetic resonance imaging (MRI) is the biggest user of helium. The helium is used to cool MRI scanners’ superconducting magnets. Helium is used for filling balloons (blimps) and for pressurizing liquid fuel rockets. Mixtures of helium and oxygen are used as an artificial ‘air’ for divers and others working under pressure. Helium is used instead of the nitrogen in normal air because, after a long dive, helium leaves the body faster than nitrogen, allowing faster decompression. Helium is used as a gas shield in the vicinity of arc welding preventing, for example, any reaction of hot metal welds with oxygen. The gas is used in the semi-conductor industry to provide an inert atmosphere for growing silicon and germanium crystals. It is also used as a high temperature gas in titanium and zirconium production, and as a carrier gas in in gas chromatography. Abundance and Isotopes Abundance earth’s crust: 8 parts per billion by weight, 43 parts per billion by moles Abundance solar system: 23 % by weight, 7.4 % by moles Cost, pure: $5.2 per 100g Cost, bulk: $ per 100g Source: Nearly all the helium on Earth is the result of radioactive decay. The major sources of helium are from natural gas deposits in wells in Texas, Oklahoma and Kansas. Helium is extracted by fractional distillation of the natural gas, which contains up to 7% helium. Isotopes: Helium has 8 isotopes whose half-lives are known, with mass numbers 3 to 10. Naturally occurring helium is a mixture of its two stable isotopes, 3He and 4He with natural abundances of 0.0001% and 99.999% respectively.
Posted on: Sun, 11 Jan 2015 03:51:32 +0000
Trending Topics
Recently Viewed Topics
© 2015