Introduction to Rare Earth Lanthanum

The shiny silvery-white metal lanthanum holds the atomic symbol La and heads the lanthanide rare earth series as number one. However, lanthanum displays atypical abundance for a rare earth element, ranking as the 28th most plentiful element overall. In fact, it constitutes the third most abundant rare earth, despite its position on the series. Yet lanthanum lives up to its categorization with high reactivity second only to lutetium among the lanthanides. This allows lanthanum to readily form various compounds with unique chemical and physical properties. For instance, lanthanum oxide mixed with borosilicate glass increases the refractive index for high-quality optical systems. Overall, lanthanum provides an excellent example of how placement on the periodic table poorly predicts elemental abundance, though the categorization still indicates chemical activity and application potential.

The rare earth element lanthanum, meaning "to lie hidden" in Greek, was first uncovered in 1839 by Swedish chemist Carl Gustaf Mosander. While analyzing cerium nitrate, Mosander detected a new earth oxide he named lanthana. However, elemental lanthanum proved challenging to isolate, remaining concealed until 1923. Fittingly, lanthanum rarely occurs naturally in pure form, instead concentrating within rare mineral deposits like bastnasite and monazite. Today, China actively mines these minerals to extract lanthanum, possessing the world’s largest reserves. After separation from other rare earths, lanthanum gets reduced to a pure reactive silvery metal. With its low density and high reactivity, lanthanum demonstrates why it stayed obscured for many years after initial discovery. Yet its unique properties lead to growing applications from batteries to optics.

Only two lanthanum isotopes occur naturally - 138La and 139La. Of these, 139La overwhelmingly dominates, comprising 99.9% of lanthanum in nature and exhibiting a long half-life. The extremely high prevalence of stable 139La results from lanthanum's position on the light end of rare earth elements. Conversely, most other lanthanum isotopes human-made in nuclear reactors exist as shorter-lived radioactive forms. For instance, the isotope 140La widely used in medical diagnostic testing possesses a short 40-hour half-life. However, 137La stands apart with its exceptional 6,000-year half-life. Overall, lanthanum's natural abundance stems from having two common long-lived isotopes, unlike heavier rare earth elements relying on one or none. This imparts unique nuclear properties, enabling uses from dating rocks to imaging the human body.

Lanthanum Properties

With atomic number 57 and placed in period 6 and the f-block, the properties of the rare earth metal lanthanum stem from its defined position on the periodic table. Lanthanum’s relatively low atomic weight of 138.9 u contributes to a density of just 6.162 g/cm3 in its solid state at room temperature. Additionally, lanthanum forms a highly packed crystalline structure, providing a ductile and malleable texture allowing it to be cut with a knife. When heated, lanthanum melts at 1193 K and boils at 3737 K, with density dropping to 5.94 g/cm3 upon melting. Compared to other lanthanides, lanthanum exhibits low volatility, making it easier to work with.

In addition, lanthanum displays typical magnetic properties for a room temperature rare earth metal, appearing paramagnetic in its ground state. However, its three valence electrons lead lanthanum to readily form compounds in its +3 oxidation state. For example, lanthanum actively oxidizes in air to generate lanthanum(III) oxide. It also reacts with water to yield lanthanum hydroxide. Furthermore, lanthanum compounds dissolve in dilute sulfuric acid, enabling chemical separation.

Overall, with properties dictated by its lighter position amongst the lanthanides, lanthanum demonstrates high reactivity and workability. This allows extensive use in applications ranging from battery electrodes to camera lenses. Although not scarce like heavier rare earths, lanthanum’s unique mix of chemical, physical, and nuclear attributes cements its importance as an indispensable technological material.

With its high reactivity, the rare earth metal lanthanum forms diverse compounds exhibiting unique properties and applications.

One highly utilized lanthanum compound is lanthanum hexaboride (LaB6). This crystalline ionic compound provides thermionic electron emission, allowing LaB6 to replace tungsten filaments in scanning electron microscopes. The lanthanum hexaboride filaments yield finer electron beams at lower temperatures, improving imaging resolution.

Additionally, when lanthanum reacts with fluorine, it produces lanthanum fluoride. Unlike other lanthanum halides, this binary salt does not dissolve readily in water. This inertness allows lanthanum fluoride to serve as an optical coating, thanks to its low refractive index. Optical engineers leverage these antireflective and ultraviolet filtering properties in camera lenses and other systems.

In summary, compounds like versatile LaB6 and optically ideal LaF3 demonstrate how lanthanum’s reactivity produces substances with tailored properties for uses from microscopy to photonics. Although not the most scarce rare earth, lanthanum’s unique chemistry facilitates many essential technological applications.

Lanthanum Applications

Lanthanum has found widespread applications since its initial discovery in 1838. Researchers continue investigating new uses, as lanthanum's unique properties provide value across diverse industries.

Batteries- Used in nickel metal hydride batteries for hybrid vehicles to improve charge capacity and durability. Also used in lithium-ion batteries.

Thin-Film Coating-Lanthanum sputtering targets and Lanthanum evaporation materials are used in deposition processes including semiconductor deposition, chemical vapor deposition (CVD) and physical vapor deposition (PVD).

Catalysts- Lanthanum oxide serves as a catalyst for petroleum refining to produce high-octane fuel. Also used as a catalyst for organic chemical reactions.

Optics- Added to glass to increase the refractive index for camera lenses, optical fibers, and microscope objectives.

Lighting- Lanthanum bromide and cerium bromide are used in carbon arc lamps for studio lighting and projection.

Alloys- Added to steel and other alloys to improve heat resistance and ductility. Also used in nickel superalloys.

Electrics- Due to special magnetic and electric properties, some of the La mixed oxides have various applications in electronic components.

With its combination of abundance and unique properties, lanthanum finds wide-ranging uses from industry to medicine. It offers an impressive example of the versatility of rare earth elements.

Conclusion

As the first element in the lanthanide series, lanthanum serves as the foundation that this entire rare earth group is built upon, even lending its name. With properties typical of the series, lanthanum readily forms useful compounds like LaCl3, LaB6, and La(OH)3. These substances find numerous applications across diverse industries. For example, LaB6's exceptional thermionic emission makes it ideal for electron microscope filaments. Additionally, LaCl3 catalyzes organic chemical reactions, while La(OH)3 helps purify water by removing phosphate. Though not the scarcest lanthanide, lanthanum's unique chemistry enables many key technologies, cementing its significance as the cornerstone rare earth metal.