Hafnium is a chemical element with the symbol Hf and atomic number A lustrous , silvery gray, tetravalent transition metal , hafnium chemically resembles zirconium and is found in many zirconium minerals. Its existence was predicted by Dmitri Mendeleev in , though it was not identified until , by Coster and Hevesy, making it the last stable element to be discovered. Hafnium is named after Hafnia , the Latin name for Copenhagen , where it was discovered. Hafnium is used in filaments and electrodes. Some superalloys used for special applications contain hafnium in combination with niobium , titanium , or tungsten.
CH104: Chemistry and the Environment
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A nuclear reactor , formerly known as an atomic pile , is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat from nuclear fission is passed to a working fluid water or gas , which in turn runs through steam turbines. These either drive a ship's propellers or turn electrical generators ' shafts.
Calcium – Periodic Table
By: Marshall Brain. For example, when the Enterprise approaches a star on " Star Trek ," a member of the crew might warn about an increase in radiation levels. In Tom Clancy's book "The Hunt for Red October," a Russian submarine has a nuclear reactor accident with radiation leakage that forces the crew to abandon ship. At Three Mile Island and Chernobyl , nuclear power plants released radioactive substances into the atmosphere during nuclear accidents.
Nuclear half-life expresses the time required for half of a sample to undergo radioactive decay. Exponential decay can be expressed mathematically like this:. So, if a problem asks you to calculate an element's half-life, it must provide information about the initial mass, the quantity left after radioactive decay, and the time it took that sample to reach its post-decay value. Let's say you have a radioactive isotope that undergoes radioactive decay. It started from a mass of