Thorium
Element Name: Thorium
Atomic Number: 90
Atomic Mass: 232.0377
Atomic Symbol: Th
Melting Point: 1750° C
Boiling Point: 4788° C
Thorium is a bright silvery-white metal of the actinide series. Over several months it will tarnish in air to the black oxide. Pure thorium is hard to make since it becomes an oxide so readily, and its properties can very widely depending on how much oxide is in the sample. Pure thorium is ductile and can be rolled, swaged, and drawn. When ground into a fine powder thorium is pyrophoric (ignites spontaneously). Thorium has two allotropes which it changes between at the breakpoint of 1306°C, and another allotrope when under extreme pressures. In total 30 isotopes of Thorium exist, all of which are radioactive. The majority of natural thorium is 232Th, which makes up almost 100% of thorium found in the crust. However, the decay chains of several radioactive isotopes cause 230Th, 229Th, 228Th, 234Th, and 227Th to be found in trace amounts. Thorium is usually found in the +4 oxidation state, but +3, +2, and +1 are known. This makes it more like the transition metals zirconium and hafnium than the lanthanide above it, cerium.
Interesting Facts:
Thorium has the largest liquid range of any element, spanning over 3000 degrees. Thorium dioxide has the highest melting point of any oxide at 3300°C. Carl Auer von Welsbach found the first commercial use of thorium in gas lighting. By mixing 99 parts thorium oxide and 1 part cerium oxide. This made a satisfactorily bright white light when heated with gas (and since thorium oxide’s melting point was so high it would produce this light without deforming). By measuring the ratio of the trace isotopes of thorium in a radioactive sample it’s possible to use radiometric dating. During the Second World War, the allied forces were concerned that the Germans had been stockpiling thorium from Paris. Thorium was necessary to make nuclear bombs, and the allied intelligence services thought the Germans must’ve been close to finishing their own bomb. This scare was not true – the group who’d taken the thorium planned to make thoriated toothpaste once the ware was done.
Sources:
Thorium is not found in its elemental form in nature. Typically, it’s found in minerals and alluvial sands. It can be found in the minerals thorianite, monazite, thorite, and bastnasite, as well as a few others in near-negligible amounts. Monazite is the most economically important source of thorium since large deposits can be found worldwide in places like India, South Africa, Brazil, Australia, and Malaysia. Such deposits of monazite can have between 2.5% and 20% thorium content. Thorium makes up 6 parts per million of the earth’s crust by weight, making about three times as common as uranium.
Industrial Uses:
Thorium has few applications now, but its potential as a nuclear power source makes it a great interest to industry and scientists alike. It is being researched for use in thorium-cycle converter-reactor systems that abuse thorium’s decay chain. Thorium is much more abundant, and what’s more the most abundant isotope of thorium is suitable for this process. In the case of uranium only 0.7% of the ore mined has the isotopes suitable for reaction. The waste of thorium would also be substantially safer, losing most of its radioactivity after a few hundred years instead of a many thousands. Other uses of thorium are limited due to its radioactivity. Coating tungsten with thorium makes it have better properties at high temperatures. Gas tungsten arc welding uses small amounts of it for this purpose, along with tungsten filaments in lightbulbs. High quality glasses may have thorium oxide because it has a high refractive index and decreases dispersion. Heat resistant ceramics may also use small amounts of thorium oxide.
References:
“Thorium.” Chemicool Periodic Table. Chemicool.com, 18 Oct. 2012. Web. 26 July
2016.
“Thorium.” Wikipedia. Wikimedia Foundation, n.d. Web. 26 July 2016.
“Facts About Thorium.” Livescience. Livescience.com, 16 Sept. 2013. Web. 26 July 2016.
Gray, Theodore W., and Nick Mann. The Elements: A Visual Exploration of Every
Known Atom in the Universe. New York: Black Dog & Leventhal, 2009. Print.
Aldersey-Williams, Hugh. Periodic Tales: A Cultural History of the Elements, from
Arsenic to Zinc. New York: Ecco, 2011. Print.