What is Praseodymium?
Praseodymium is an element from the lanthanide family of the periodic table of elements with a symbol of Pr and atomic number 59 is categorized among rare earth metals. Praseodymium is a silvery, ductile malleable soft metallic element mostly known for its electrical, optical, chemical and magnetic properties. Based on its high chemical reactivity, it is hard to find praseodymium as a native, unreacted and pure element as it develops its oxidized form when it is exposed to atmospheric oxygen. Therefore, praseodymium occurs along with the other rare earth metals in nature. This metallic element is ranked as the fourth most common rare earth metal and its abundance amounts up to 9.1 ppm in the Earth’s crust. Its discovery goes back to 1841 when a Swedish chemist extracted praseodymium from cerium salts.
Chemically and with regard to its +3 oxidization state stable only in aqueous solutions, it is similar to most rare earth metals and its electronic configuration resembling those of lanthanide family. However, it’s +4 oxidization state occurs in some compounds in solid-state mostly among the lanthanides with its +5 oxidation state in matrix isolation conditions. In aqueous solutions, praseodymium forms yellowish green cations. Based on this property of praseodymium, most applications of this metal in industrial levels is in its ability to filter yellow light from the electromagnetic radiation.
Physical Properties of Praseodymium
Praseodymium ductile metal has a hardness compared to that of silver. Considering its electronic state with the five valence electrons, it can theoretically share all the valence electrons. However, it should be noted that there must be some particular chemical conditions and environments for all the 5 electrons to engage in reactions. Generally, praseodymium shares only its three and hardly ever its four electrons with other elements. Electronic configuration of praseodymium conforms the Aufbau principal predicting that 4f orbitals possess lower energy compared to those of 5D orbitals. It should be noted that this electronic property of praseodymium doesn’t apply to lanthanum and cerium since 4f orbitals sudden contraction take place in the aforementioned elements and that it is not strong enough the avoid 5D orbitals sub-shell occupation 1.
Praseodymium, similar to the elements of lanthanide series, shares only three valence electrons because the ones occupying 4f orbitals are rigidly bound. Even though 4f orbitals penetrate through the inert Xenon core electrons to the nucleus leading to an increase in the ionic charge, it can keep on losing its fourth and fifth valence electrons as the subshell energy is adequately high with the low nuclear charge making the removal of further fourth and fifth electrons possible 2. With regard to this, praseodymium crystalline structure is determined as a double-hexagonal close-packed lattice at room temperature. However, at elevated temperatures of 560°C, it shows a transition to a face-centered cubic structure as well as a body-centered cubic lattice appearing immediately before melting at 935°C. Praseodymium adopts paramagnetic behavior at room temperature similar to metals of lanthanides family with unpaired 4f electrons. Praseodymium is paramagnetic at cryogenic and elevated temperatures 3.
Isotopes of Praseodymium
There is one naturally occurring stable isotope of praseodymium with a mass of 141Pr making it a mononuclidic element. Its standard atomic weight could be determined precisely as it is constant naturally. Praseodymium has 82 neutrons that gives it additional stability. Interestingly, this isotope is generated as a result of fusion in star-forming regions out of the solar system. Other unstable praseodymium isotopes have half-life less than a day and even a minute except for 143Pr with a half-life of 13.6 days. Additionally, praseodymium can be generate as a result of fission of uranium 4.
Abundance and Production of Praseodymium
Praseodymium is generally an abundant element amounting 9.1 mg/kg of the Earth’s crust as well as the fourth most abundant lanthanide metal after cerium, neodymium and lanthanum. The reason why praseodymium is classified among rare earth metals is it scares nature compared to the common earth metals such as magnesia and lime which are basically the very few known minerals that contain praseodymium and making the extraction commercially valuable. As it was mentioned earlier, praseodymium doesn’t occur naturally at all in the minerals and it is always found along with cerium lanthanum and neodymium. It is also extracted and purified using ion-exchange and liquid-liquid extraction. To obtain the metallic praseodymium, fused anhydrous halides are processed through electrolysis and metallometirc reduction of chloride or fluoride with calcium.
Applications of Praseodymium
Based on that physical and chemical properties as well as electronic behavior praseodymium could replace most metals from lanthanides family with no significant change in the properties and function to be used for numerous applications namely fabrication of ferrocerium alloys. If it is combined with metallic neodymium and a number of rare earth metals, praseodymium is used to make magnets with really high power notably long durability. In general, majority of cerium-based alloys and those of based on rare earth metals containing third transition metals lead to considerably stable magnets with applications in small equipment namely loudspeakers, magnetic storage, headphones, printers, watches and motors. Praseodymium is found in combination with rare earth metals of fluoride salts contributing to the formation of carbon arc light core. In order to create metals with high strength with applications in aircraft engines, praseodymium is used in combination with magnesium. In this case, neodymium and yttrium are also alternative substitutes in the fabrication of relevant alloys. Compounds with portions of praseodymium are used in glasses with a yellow color as well as in yellow ceramics. Didymium, glass which is employed to fabricate a particular type of welding and glass blower goggles, contain praseodymium as an important component. In combination with silicate crystals, praseodymium cations have been doped to be applied as slow light pulse. The alloys based on nickel and praseodymium have turned out to adopt a strong magnetocaloric effect to make the sub-zero and cryogenic temperatures accessible for research purposes. Praseodymium doped in fluoride glasses have applications in optical amplifiers with single-mode fibers. In some applications, praseodymium cations as Pr3+ are employed as activators in ultraviolet phosphorus, red, green and blue regions of electromagnetic radiation. Praseodymium is considered to be one of the major components and elements used as permanent magnets in wind turbines in the competition for achieving renewable and sustainable energy source 5.
Praseodymium is a soft metal from lanthanides group capable of being hammered into thin films. It has a melting point of 913°C and the boiling point about 3200°C. Its crystalline structure is temperature-dependent as alpha allotropes converts into its beta allotrope at 800°C. Its reactivity with atmospheric oxygen yields praseodymium oxide (Pr2O3) with a wide range of chemical, magnetic, electrical and optical applications.