Lanthanum, The, Atomic number 57

General

Lanthanum [lanta ː n] is a chemical element with the element symbol La and atomic number 57. It is one of the transition metals and the rare earth metals, in the periodic table it is in the 6. Period and the 3. Subgroup (group 3) or scandium. Usually it is also numbered among the lanthanides, even if the f-shell of the element is unoccupied.

Lanthanum (Greek. err, lanthanein, "Be hidden") was 1839 by the Swedish chemist Carl Gustav and surgeon discovered Mosander. For a supposedly pure cerium nitrate, he won by fractional crystallization of lanthanum.

Lanthanum is of course only in chemical compounds present accompanied by other lanthanides in various minerals. Mainly, these are:

Monazite ((This, The, Th, Nd, And)PO4)
Bastnäsit ((This, The, And)CO3F)

Extraction

After extensive separation of the other Lanthanbegleiter, the oxide with hydrogen fluoride to lanthanum fluoride reacted. Subsequently, this reduced with calcium to form calcium fluoride to lanthanum. The removal of residual calcium residues and contaminants carried in an additional remelting in vacuum.

Special features

The silver-white lustrous metal is malleable and ductile. There are three metallic modifications.

Lanthanum is ignoble. It covers on the air quickly with a white oxide, which continues to react in moist air to the hydroxide.

At temperatures above 440 ° C to burn lanthanum lanthanum (La2O3). Causes the formation of hydrogen in cold water, a slow, in warm water for a rapid response to Hydroxid.In dilute acids lanthanum dissolves with evolution of hydrogen auf.Mit many elements it reacts directly in the heat, with halogens at room temperature. Lanthanum and hydrogen form a black, water-sensitive hydride unstöchiometrisches.

Use

Lanthanum is a component in the mixed metal. Pyrophoric materials contained flints for 25 to 45 Weight percent lanthanum. In addition, it is used as a reducing agent in metallurgy. As a cast iron addition, it supports the formation of spheroidal graphite, as an alloying addition, it improves the oxidation resistance. Lanthanbeimengungen reduce the hardness and temperature sensitivity of molybdenum.

High-quality cathodes for the generation of free electrons are made of lanthanum hexaboride as a replacement for tungsten filament. High-purity lanthanum oxide is z in the glass industry to produce high quality glasses with high refractive index on the optical. B. used for camera lenses.

mit Cobalt:

The cobalt-lanthanum alloy LaCo5 is a magnetic material, lanthandotiertes barium titanate for the production of thermistors (temperature-dependent resistors) used. In conjunction with cobalt, Require, Mangan, Strontium u. a. it serves as a cathode for high temperature fuel cell (SOFC). "Contaminated" lanthanum-nickel (LaNi5) is used as hydrogen storage in nickel-metal hydride batteries used. As an extra, it comes in carbon arc lamps for studio lighting and Filmvorführanlagen (historical application?) before.

mit Titan:

A metal alloy material with compositions of lanthanum and titanium is attributed to the effect, that span is reduced visual processing, the chip length. This is intended to facilitate the processing of the metal.

In the medical field are made of the metal alloy corrosion resistant and readily sterilizable instruments. This metal alloy with titanium to be suitable for tools and equipment for surgical procedures particularly well, because the allergy tendency to be low when using such metal alloy with titanium in comparison with other alloys to.

Als Lanthanoxid

Preparation of glasses (Lanthanglas) with comparatively high refractive index, which in turn changes only slightly with the wavelength (Dispersion geringe), for cameras, Telescopic lenses and eyeglasses
Production of crystal glass and porcelain glazes. It replaces more toxic lead compounds with the simultaneous improvement of chemical resistance (Improvement of alkali resistance, "Dishwasher safe")
Addition of a catalyst in fluid catalytic cracking on zeolites in petroleum refinery for processing
Production of ceramic capacitor materials and silicate-free glasses
Component of glass polishing agents
Manufacture of thermionic cathodes for electronic tubes (also Lanthanboride)

Als Lanthancarbonat

Drug to reduce phosphate levels in dialysis patients (suction. Phosphate binder)

Lanthanum is considered less toxic than. A toxic dose is unknown. Nevertheless, when lanthanum powder as a highly corrosive, because it very easily by e.g.. Skin moisture responds to basic lanthanum (similar to the elements calcium and strontium). The lethal dose in rats 720 mg.

General
Name, Symbol, Number Lanthanum, The, 57
Series Transition metals
group, Period, Block 3, 6, d
Appearance silvery white
CAS-Nummer 7439-91-0
Mass fraction of element 17 ppm
Atomic
Atomic mass 138,9055 you
Atomradius 195 pm
Kovalenter Radius 207 pm
Elektronenkonf. [Car] 5d(1) 6s2
1. Ionization 538,1 KJ / mol
2. Ionization 1067 KJ / mol
3. Ionization 1850 KJ / mol
Physically
Physical State fixed
Crystal structure hexagonal
Density 6,17 g/cm3 (20 ° C)
Magnetism paramagnetisch (χm = 5,4 * 10(-5))
Melting point 1193 K (920 C)
Boiling point 3743 K (3470 C)
Molar Volume 22,39 * 10(-6)m(3)/mol
Heat of vaporization 400 KJ / mol
Schmelzwärme 6,2 KJ / mol
Electrical conductivity 1,626*10(6) A/(V * m)
Thermal conductivity 13 W /(m*K)
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