Gadolinium: The coldest metal in the world

Gadolinium, element 64 of the periodic table.

Lanthanide in the periodic table are a large family, and their chemical properties are very similar to each other, so it is difficult to separate them. In 1789, Finnish chemist John Gadolin obtained a metal oxide and discovered the first rare earth oxide – Yttrium(III) oxide through analysis, opening the discovery history of rare earth elements. In 1880, Swedish scientist Demeriak discovered two new elements, one of which was later confirmed to be samarium, and the other was officially identified as a new element, gadolinium, after being purified by French chemist Debuwa Bodeland.

Gadolinium element originates from silicon beryllium gadolinium ore, which is cheap, soft in texture, good in ductility, magnetic at room temperature, and is a relatively active rare earth element. It is relatively stable in dry air, but loses its luster in humidity, forming loose and easily detached flake like white oxides. When burned in air, it can generate white oxides. Gadolinium reacts slowly with water and can dissolve in acid to form colorless salts. Its chemical properties are very similar to other Lanthanide, but its optical and magnetic properties are slightly different. Gadolinium is Paramagnetism at room temperature and ferromagnetic after cooling. Its characteristics can be used to improve permanent magnets.

Using the Paramagnetism of gadolinium, the gadolinium agent produced has become a good contrast agent for NMR. The self research of nuclear magnetic resonance imaging technology has been initiated, and there have been 6 Nobel Prizes related to it. Nuclear magnetic resonance is mainly caused by the spin motion of atomic nuclei, and the spin motion of different atomic nuclei varies. Based on the electromagnetic waves emitted by different attenuation in different structural environments, the position and type of atomic nuclei that make up this object can be determined, and the internal structural image of the object can be drawn. Under the action of a magnetic field, the signal of nuclear magnetic resonance imaging technology comes from the spin of certain atomic nuclei, such as hydrogen nuclei in water. However, these spin capable nuclei are heated in the RF field of magnetic resonance, similar to a microwave oven, which typically weakens the signal of magnetic resonance imaging technology. Gadolinium ion not only has a very strong Spin magnetic moment, which helps the spin of the atomic nucleus, improves the recognition probability of diseased tissue, but also miraculously keeps cool. However, gadolinium has certain toxicity, and in medicine, chelating ligands are used to encapsulate gadolinium ions to prevent them from entering human tissues.

Gadolinium has a strong magnetocaloric effect at room temperature, and its temperature varies with the intensity of the magnetic field, which brings up an interesting application – magnetic refrigeration. During the refrigeration process, due to the orientation of the magnetic dipole, the magnetic material will heat up under a certain external magnetic field. When the magnetic field is removed and insulated, the material temperature decreases. This kind of magnetic cooling can reduce the use of refrigerants such as Freon and cool down rapidly. At present, the world is trying to develop the application of gadolinium and its alloys in this field, and produce a small and efficient magnetic cooler. Under the use of gadolinium, ultra-low temperatures can be achieved, so gadolinium is also known as the “coldest metal in the world”.

Gadolinium isotopes Gd-155 and Gd-157 have the largest thermal neutron Absorption cross section among all Natural isotopes, and can use a small amount of gadolinium to control the normal operation of nuclear reactors. Thus, gadolinium based light water reactors and gadolinium Control rod were born, which can improve the safety of nuclear reactors while reducing costs.

Gadolinium also has excellent optical properties and can be used to make optical isolators, similar to diodes in circuits, also known as light-emitting diodes. This type of light-emitting diode not only allows light to pass in one direction, but also blocks the reflection of echoes in the optical fiber, ensuring the purity of optical signal transmission and improving the transmission efficiency of light waves. Gadolinium gallium garnet is one of the best substrate materials for making optical isolators.