Lanthanum (English: lanthanum), chemical element, element symbol La, Atomic number 57, Atomic mass 138.905,47, belongs to periodic system Ⅲ B group, rare earth element. In 1839, C.G. Mossander of Sweden discovered it from crude Cerium nitrates and named it lanthanum. The word originates from the Greek lanthanein, meaning "hidden", meaning hidden in cerium. The content in the crust is 1.83 × 10% -3% is a relatively abundant rare earth element, mainly present in monazite and bastnaesite. There are two isotopes in nature: the Stable nuclide lanthanum-139 (99.911%) and the radioactive isotope lanthanum-138 (0.089%).

Property: A malleable and malleable silver white metal, soft and easy to cut, with a melting point of 918 ℃, a boiling point of 3464 ℃, and a density of 6.145 g/cm3. Lanthanum has a hexagonal densely packed structure at room temperature. The electronic configuration of lanthanum atom is (Xe) 5d16s2, Oxidation state+3. Chemically active, it is the second most active metal among rare earth elements after europium. The surface will quickly oxidize and lose its luster in dry air, burn in air above 440 ℃, react violently with hot water, and the metal lanthanum must be preserved in mineral oil. The Ionic radius of La3+is the largest among the trivalent rare earth ions, so Lanthanum oxide is the most alkaline among the trivalent rare earth oxides. The important compounds of lanthanum include oxides, halides, nitrates, Oxalate, sulfates, hydrides and nitrides. The compound exhibits diamagnetism.

Preparation method: In industry, high-purity lanthanum is obtained by solvent extraction and ion exchange methods after decomposition of rare earth concentrate. Lanthanum metal is prepared by electrolysis of anhydrous halides or Calciothermic reaction of anhydrous fluoride.

Application: high-purity Lanthanum oxide is widely used to manufacture optical glass with high refractive index and low dispersion index. The Borate glass containing 40% Lanthanum oxide is used to make high-resolution microscopes and telescopes. Lanthanum-nickel alloy LaNi5 is an excellent hydrogen storage material, and Lanthanum hexaboride LaB6 is widely used to make high-power thermionic emission cathode. Lanthanum can also be used as a green luminescent material for producing energy-saving fluorescent lamps, and cerium iron alloys containing 20% to 30% lanthanum can be used as flints.

Over the past decade, China's metal lanthanum and mixed rare earth metals containing lanthanum have made great achievements and development in the application of steel, non-ferrous metals and their alloys, ignition alloys, hydrogen storage materials, and permanent magnet materials. It is expected that greater progress will be made in the future, especially in high-tech rare earth functional materials.

(1) Application in steel and iron.

After adding lanthanum to steel, it can purify the steel liquid (remove O2 and S), refine grains, microalloy, change the morphology and distribution of inclusions (such as changing S in MnS to RES), and resist hydrogen embrittlement and stress corrosion (such as RE absorbing H: generating REH), greatly improving and enhancing the comprehensive performance of the steel.

If 0.03-0.1% RE (La20-29%) is added to the steel, the morphology of inclusions in the steel is changed, resulting in Al: O2, SiOMnS becoming Al, Mn, and Si, while REO reacts with O2 and S to form RE, O, and RES, improving the performance and process performance of the steel; Adding RE0.25% rare earth treated steel (06CuPRE steel) can improve corrosion resistance; For example, 10MnNbRE steel used as pipes can improve low-temperature toughness; 16MnRER steel used for pressure vessels can improve the performance of thick plates; 16Mn steel as an automotive material can improve cold bending and stamping performance; There is also 16Mn steel that can resist hydrogen induced cracking; It has a good effect on 30SiCrMnV low alloy steel.

After adding 0.1% RE to cast steel, it has a good effect on the fluidity, inclusions, microstructure, hot cracking tendency, desulfurization, solidification, porosity, weldability, shrinkage and tempering brittleness of cast steel, thus improving the casting performance and quality. After adding RE treatment to cast steel, O: decreases from 9.50- to 3.99x10-5-5. S decreases from 0.05% to 0.007%, inclusions are also reduced, the fluidity of the steel liquid is improved, and the residual RE content is only 0.004-0.008%.

Adding RE to high alloy stainless steel can improve thermoplastic properties and yield (approximately 15%).

After adding RE into special steel, the liquid steel can be purified, and the Fracture toughness, high temperature strength, hardness and wear resistance can be improved; In addition, it has an inhibitory effect on hydrogen (H2) induced cracking and damage. Practical gear steel (25MnTiBRE), shaft steel (35CrNi, MoVRE), spring steel (55SiMnVBRE), and high-speed steel (W1Ci. VRE) belong to this type of steel.

Adding La0.1% to stainless steel (ZGGCrNiMo) can significantly improve its corrosion resistance and other properties, which is beneficial for practical applications.

After adding 0.3% La (residual La0.01-0.03%) to heat-resistant steel, the oxidation rate can be significantly reduced and the oxidation increment can be doubled. High temperature strength and corrosion resistance have also been greatly improved.

After adding La to iron, it can purify molten iron (deoxygenation, sulfur), change graphite morphology, and prevent interference elements from damaging spheroidization, making the performance of cast iron more excellent and beneficial for practical use. La and RE containing La are good spheroidizing agents. By adding them to iron, the flake graphite in Fe can be transformed into spherical graphite to obtain nodular cast iron. At the same time, it can eliminate anti spheroidized Pb, Bi, Sb, Ti, and Al, ensuring the excellent performance of nodular cast iron.

At present, the manufacturing process of rare earth cast iron is simple, low cost, good performance, and effective. Therefore, it has been widely used in radiators, steel ingot molds, cast iron pipes, and various mechanical castings. It is expected that the production of rare earth treated steel and cast iron in China will develop faster in the future.