Thorium

Thorium is a chemical element, with symbol Th and atomic number 90, of the actinide series. It is found naturally in the minerals monazite, thorite and thorianite. In its pure state it is a soft silver-white metal that oxidizes slowly. If finely ground and heated, it burns and emits white light.

Thorium belongs to the family of radioactive substances, although its half-life is extremely long. Its potential as a nuclear fuel, as a fertile material, is due to the fact that it has a high effective section against slow (thermal) neutrons, resulting in protactinium-233, which rapidly disintegrates into uranium-233, which is a fissile isotope that can sustain a nuclear chain reaction. This app is still under development.

Thorium was discovered in 1828 by Norwegian amateur mineralogist Morten Thrane Esmark and identified by Swedish chemist Jöns Jacob Berzelius, who named it after Thor, the Germanic god of thunder. Its first applications were developed at the end of the XIX century. The radioactivity of thorium was widely recognized during the first decades of the 20th century. In the second half of the century, thorium was superseded in many uses due to concerns about its radioactivity.

Thorium is still used as an alloying element in TIG welding electrodes, but it is slowly being replaced in the field with different compositions. It was also a material in high-end optics and scientific instrumentation, used in some transmission vacuum tubes, and as a gas blanket light source, but these uses have become marginal. It has been suggested as a replacement for uranium as a nuclear fuel in nuclear reactors, and several thorium reactors have been built. Thorium is also used to strengthen magnesium, coat tungsten wire in electrical equipment, control the grain size of tungsten in electric lamps, high-temperature crucibles, and eyewear, including camera lenses and scientific instruments. Other uses for thorium include heat-resistant ceramics, aircraft engines, and in light bulbs. Ocean science has used ²³¹Pa/²³⁰Th ratios of isotopes to understand the ancient ocean.

History

Monacita.

Thorium is named after Thor, the Norse god of lightning and storms. Jöns Jakob Berzelius first isolated it in 1828. In the last decade of the 19th century, researchers Pierre Curie and Marie Curie discovered that this element emitted radioactivity.

Occurrence

Training

²³²Th is a primordial nuclide, having existed in its present form for over ten billion years; it was formed during the r process, which probably occurs in supernovae and kilonovae (neutron star mergers). These violent events spread it throughout the galaxy. The letter "r" stands for 'rapid neutron capture', and occurs in core-collapse supernovae, where heavy seed nuclei like 56Fe rapidly capture neutrons, rising against the neutron drip line, since much more neutrons are captured faster than the resulting nuclides can beta decay toward stability. Neutron capture is the only way stars can synthesize elements beyond iron due to the higher Coulomb barrier that hinders interactions between charged particles at high atomic numbers and the fact that fusion beyond ⁵⁶Fe is an endothermic. Due to the abrupt loss of stability beyond ²⁰⁹Bi, the r process is the only stellar nucleosynthesis process that can create thorium and uranium; all other processes are too slow, and intermediate alpha nuclei decay before capturing enough neutrons to reach these elements.

In the universe, thorium is among the rarest primordial elements, because it is one of two elements that can only be produced in the r process (the other being uranium), and also because it has decayed slowly from the moment it was formed. The only primordial elements rarer than thorium are thulium, lutetium, tantalum, and rhenium, the odd elements just before the third peak of abundances of the r process around the platinum group heavy metals, as well as uranium. In the distant past, thorium and uranium abundances were enriched by the decay of plutonium and curium isotopes, and thorium was enriched relative to uranium by the decay of ²³⁶U to ^{232< /sup> Th and the natural depletion of 235U, but these sources have long since deteriorated and no longer contribute.}

In the Earth's crust, thorium is most abundant: with an abundance of 8.1 parts per million (ppm), it is one of the most abundant heavy elements, almost as abundant as lead (13 ppm) and more abundant than lead. tin (2.1 ppm). This is because thorium is likely to form oxide minerals that do not sink into the core; it is classified as lithophilic (Goldschmidt classification), which means that it is usually found combined with oxygen. Common thorium compounds are also sparingly soluble in water. Thus, although refractory elements have the same relative abundances on Earth as in the Solar System as a whole, there is more accessible thorium than platinum group heavy metals in the crust.

Estimated abundances of the 83 primordial elements of the solar system, drawn on a logarithmic scale. The torium, of atomic number 90, is one of the rarest elements.

On Earth

Thorium is the 41st most abundant element in the earth's crust. Natural thorium is usually nearly pure ²³²Thorium, which is the longest-lived and most stable isotope of thorium, with a half-life comparable to the age of the universe. Its radioactive decay is the single largest contributor to Heat internal of the Earth; the other major contributors are the shorter-lived primordial radionuclides, which are ²³⁸U, ⁴⁰K, and ²³⁵U in descending order of contribution. (At the time of Earth's formation, ⁴⁰K and ²³⁵U contributed much more by virtue of their short half-lives, but they have decayed more rapidly, leaving the contribution of ²³²Th and ²³⁸U predominantly). Its decay accounts for a gradual decrease in the Earth's thorium content: the planet currently has about 85% of the amount present at Earth's formation. The other naturally occurring isotopes of thorium are much shorter. lived; of these, only ²³⁰Th is usually detectable, occurring in secular equilibrium with its parent ²³⁸U, and constituting a maximum of 0.04% of natural thorium.

Thorium only occurs as a minor constituent of most minerals, and for this reason it had previously been considered a rare element. Soil normally contains about 6 ppm thorium.

In nature, thorium occurs in the +4 oxidation state, along with uranium(IV), zirconium(IV), hafnium(IV), and cerium(IV), and also with scandium, yttrium, and the trivalent lanthanides which possess similar ionic radii. Because of thorium's radioactivity, minerals containing it are often metamyctic (amorphous), their crystal structures having been damaged by alpha radiation produced by thorium. An example extreme is ekanite, (Ca,Fe,Pb)
2(Th,U)If
8O
20, which almost never occurs in the nometamictic form at because of its thorium content.

The radiogenic heat of the 232Th disintegration (violet) is one of the main contributors to the Earth's internal heat balance. Of the four main nucleides that provide this heat, 232Th has grown to provide the greatest amount of heat, as the others fall faster than the torium.

Monazite (mainly phosphates of various rare earth elements) is the most important commercial source of thorium because it is found in large deposits throughout the world, primarily in India, South Africa, Brazil, Australia, and Malaysia. It contains about 2.5% thorium on average, although some deposits may contain as much as 20%. Monazite is a chemically unreactive mineral found as yellow or brown sand; its low reactivity makes it difficult to extract thorium from it. Alanite (largely hydroxide silicates of various metals) can have 0.1 to 2% thorium and zirconium (mainly zirconium silicate, ZrSiO
4) with up to 0.4% thorium,

Thorium dioxide occurs as the rare mineral thorianite. Because it is isotypic with uranium dioxide, these two common actinide dioxides can form solutions in the solid state, and the mineral's name changes depending on the ThO2 content. Thorite (mainly thorium silicate, ThSiO4), also has a high thorium content and is the mineral in which thorium was first discovered. In thorium silicate minerals, Th⁴⁺ ions and SiO_{4⁻⁴ are often replaced with M3+ ions (where M= Sc, Y, or Ln) and phosphate (PO3−4) respectively. Due to the great insolubility of thorium dioxide, thorium it does not usually spread rapidly through the environment when released. The Th⁴⁺ ion is soluble, especially in acid soils, and in such conditions the concentration of thorium can reach 40 ppm.}

Thorium Applications

Apart from its incipient use as a nuclear fuel, metallic thorium or some of its oxides are used in the following areas:

• Incorporation into metallic wolfram to manufacture electrical lamp filaments.
• Applications in high temperature ceramic material.
• Like:

1. Alloy agent in metal structures.
2. Basic component of magnesium technology.
3. Catalyst in organic chemistry.

• Manufacture of:

1. Electronic lamps.
2. High quality lenses for precision instruments. (Torium oxide added to the glass improves its defective properties).
3. Special electrodes for TIG welding (Tungsten Inert Gas), also known as welding GTAW (Gas Tungsten Arc Welding). Alloy with wolframio favors greater emissivity of electrons of the electrode. This facilitates the ignition and allows the wolfram electrode to work at a lower temperature and provides the same performance in the workpiece.

There is a problem that the working temperature of the pure wolfram electrode was approximately the fusion temperature of wolfram: 3 400 °C. By melting, this damaged the electrode profile. This inconvenience is also avoided with electrodes that incorporate other dopants, such as cerium, lantano or circonium.

• Oxygen detector in the electronic industry.^{[chuckles]required]}.

Lately (2018) it has been applied as a radioactive isotope in the detection of fossils greater than carbon 14.^{[citation required]}.

Nuclear decay of thorium

When an atom of thorium 232 (²³²Th) disintegrates, it emits an alpha particle, made up of two protons and two neutrons. The emission of the alpha particle reduces the atomic number of ²³²Th by two units, and the mass number by four, for which it becomes the 228 isotope of another element: radium 228. Subsequent decays complement the thorium series. This process continues until a non-radioactive, and therefore stable, element is finally generated: lead-208, or thorium C.

The half-life of ²³²Th is very long (see table), so over billions of years it releases radioactivity. This in turn means that the amount of radioactivity it emits in a short period (eg one day) is very small.

Thorium can be used as a power source in a Thermal Breeder Reactor (the reaction starts from an initial charge with enriched uranium or plutonium and is sustained by U 233, which is generated from thorium by slow neutron capture until the full use of it, at the same time that energy is obtained with the fission of U 233).^{[citation required]}