Thorium dioxide
Thorium dioxide also called thorium(IV) oxide is a white, crystalline powder. It was formerly known as thoria or thorina. It is produced mainly as a by-product of lanthanide
The lanthanide or lanthanoid series comprises the fifteen metallic chemical elements with atomic numbers 57 through 71, from lanthanum through lutetium...

 and uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...

Thorianite is a rare mineral, originally discovered by Ananda Coomaraswamy in 1904 as uraninite, but recognized as a new species by Wyndham R. Dunstan. It was so named on account of its high percentage of thorium ; it also contains the oxides of uranium, lanthanum, cerium and didymium...

 is the name of the mineralogical form of thorium dioxide. It is moderately rare and crystallizes in isometric system.


The compound is radioactive due to the radioactivity of thorium
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....

. Thorium dioxide can be used as a nuclear
Nuclear reaction
In nuclear physics and nuclear chemistry, a nuclear reaction is semantically considered to be the process in which two nuclei, or else a nucleus of an atom and a subatomic particle from outside the atom, collide to produce products different from the initial particles...

 fuel. (Refer to the article of thorium
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....

 for more information on this application.)
The high thermal stability
Thermal stability
Thermal stability is the stability of a molecule at high temperatures; i.e. a molecule with more stability has more resistance to decomposition at high temperatures....

 of thorium dioxide allows applications in flame spraying and high temperature ceramics. Thorium dioxide was the primary ingredient in the X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...

 contrast medium Thorotrast
Thorotrast is a suspension containing particles of the radioactive compound thorium dioxide, ThO2, used as a contrast medium in X-ray diagnostics in the 1930s and 40s ....

. Use of Thorotrast was abandoned when it was found to be a carcinogen
A carcinogen is any substance, radionuclide, or radiation that is an agent directly involved in causing cancer. This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes...

, sometimes causing cholangiocarcinoma
Cholangiocarcinoma is a cancer of the bile ducts which drain bile from the liver into the small intestine. Other biliary tract cancers include pancreatic cancer, gallbladder cancer, and cancer of the ampulla of Vater...

. Today, barium sulfate
Barium sulfate
Barium sulfate is the inorganic compound with the chemical formula BaSO4. It is a white crystalline solid that is odorless and insoluble in water. It occurs as the mineral barite, which is the main commercial source of barium and materials prepared from it...

 is the standard X-ray contrast agent.
Thoria has the fluorite
Fluorite is a halide mineral composed of calcium fluoride, CaF2. It is an isometric mineral with a cubic habit, though octahedral and more complex isometric forms are not uncommon...

 crystal structure. Few other binary dioxides have this structure: uranium dioxide
Uranium dioxide
Uranium dioxide or uranium oxide , also known as urania or uranous oxide, is an oxide of uranium, and is a black, radioactive, crystalline powder that naturally occurs in the mineral uraninite. It is used in nuclear fuel rods in nuclear reactors. A mixture of uranium and plutonium dioxides is used...

, hafnium dioxide and cerium dioxide, not to mention plutonium dioxide
Plutonium dioxide
Plutonium oxide is the chemical compound with the formula PuO2. This high melting point solid is a principal compound of plutonium. It can vary in color from yellow to olive green, depending on the particle size, temperature and method of production....

. The band gap
Band gap
In solid state physics, a band gap, also called an energy gap or bandgap, is an energy range in a solid where no electron states can exist. In graphs of the electronic band structure of solids, the band gap generally refers to the energy difference between the top of the valence band and the...

 of thoria is about 6 eV
In physics, the electron volt is a unit of energy equal to approximately joule . By definition, it is equal to the amount of kinetic energy gained by a single unbound electron when it accelerates through an electric potential difference of one volt...



Thorium dioxide is used as a stabilizer in tungsten
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...

 electrodes in TIG welding, electron tubes, and aircraft engines. As an alloy, thoriated tungsten metal is not easily deformed because the high fusion material thoria augments the high temperature mechanical properties, and thorium helps stimulate the emission of electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...

s (thermions). It is the most popular oxide additive because of its low cost, but is being phased out in favor of non-radioactive elements such as cerium
Cerium is a chemical element with the symbol Ce and atomic number 58. It is a soft, silvery, ductile metal which easily oxidizes in air. Cerium was named after the dwarf planet . Cerium is the most abundant of the rare earth elements, making up about 0.0046% of the Earth's crust by weight...

, lanthanum
Lanthanum is a chemical element with the symbol La and atomic number 57.Lanthanum is a silvery white metallic element that belongs to group 3 of the periodic table and is the first element of the lanthanide series. It is found in some rare-earth minerals, usually in combination with cerium and...

 and zirconium
Zirconium is a chemical element with the symbol Zr and atomic number 40. The name of zirconium is taken from the mineral zircon. Its atomic mass is 91.224. It is a lustrous, grey-white, strong transition metal that resembles titanium...


A major use in the past was in gas mantle
Gas mantle
An incandescent gas mantle, gas mantle, or Welsbach mantle is a device for generating bright white light when heated by a flame. The name refers to its original heat source, existing gas lights, which filled the streets of Europe and North America in the late 19th century, mantle referring to the...

s of lanterns, which were frequently composed of 99 percent ThO2 and 1% cerium(IV) oxide
Cerium(IV) oxide
Cerium oxide, also known as ceric oxide, ceria, cerium oxide or cerium dioxide, is an oxide of the rare earth metal cerium...

. Even as late as the 1980s it was estimated that about half of all ThO2 produced (several hundred tonnes per year) was used for this purpose. Some mantles still use thorium, but yttrium oxide (or sometimes zirconium oxide) is used increasingly as a replacement.

Thorium dioxide was formerly added to glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...

es during manufacture to increase their refractive index
Refractive index
In optics the refractive index or index of refraction of a substance or medium is a measure of the speed of light in that medium. It is expressed as a ratio of the speed of light in vacuum relative to that in the considered medium....

, producing thoriated glass with up to 40% ThO2 content. These glasses were used in the construction of high-quality photographic lens
Photographic lens
A camera lens is an optical lens or assembly of lenses used in conjunction with a camera body and mechanism to make images of objects either on photographic film or on other media capable of storing an image chemically or electronically.While in principle a simple convex lens will suffice, in...

es. However, the radioactivity of the thorium caused both a safety and pollution hazard and self-degradation of the glass (turning it yellow or brown over time). Lanthanum oxide has replaced thorium dioxide in almost all modern high-index glasses.

The melting point of thorium oxide is 3300°C - the highest of all known oxides. Only a few elements (including tungsten
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...

 and carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

) and a few compounds (including tantalum carbide
Tantalum carbide
Tantalum carbides form a family of binary chemical compounds of tantalum and carbon with the empirical formula TaCx, where x usually varies between 0.4 and 1. They are extremely hard, brittle, refractory ceramic materials with metallic electrical conductivity. They appear as brown-gray powders...

) have higher melting points.).

Thorium dioxide is a Welsbach material. It has been suggested that these chemicals could be sprayed into the upper atmosphere to reflect sunlight and thus lower the global temperature.

Thorium dioxide is a catalyst in many chemical reactions, including the Ruzicka large ring synthesis
Ruzicka large ring synthesis
The Ruzicka large ring synthesis or Ruzicka reaction or Ruzicka cyclization is an organic reaction in which a dicarboxylic acid is converted to a cyclic ketone at high temperature and a suitable catalyst such as thorium oxide...

, petroleum cracking
Cracking (chemistry)
In petroleum geology and chemistry, cracking is the process whereby complex organic molecules such as kerogens or heavy hydrocarbons are broken down into simpler molecules such as light hydrocarbons, by the breaking of carbon-carbon bonds in the precursors. The rate of cracking and the end products...

, conversion of ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

 to nitric acid
Nitric acid
Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming...

 and preparation of sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...


Thoria dispersed nickel finds its applications in various high temperature operations like combustion engines because it is a good creep resistant material. It can also be used for hydrogen trapping.
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.