Lanthanum sesquioxide

Combustion in air or oxygen produces lanthanum sesquioxide. However, at ambient temperatures, when exposed to moist air, the metal forms a hydrated oxide with a large volume increase. 

Synonyms lanthanum trioxide lanthanum sesquioxide lanthana... 

Oxide. La20, lanlhana, lanthanum sesquioxide, lanthanum trinxidt, almost white, amorphous powder, d 6.51. mp above 2000°. lnsol in water sol in dil mineral adds with formation of salts. Absorbs CO, from the air. 

Dilanthanum oxide Dllanthanum trIoxide EINECS 215-200-5 Lanthana Lanthania (La203> Lanthanum oxide Lanthanum sesquioxide Lanthanum trioxide Lanthanum(3- ) oxide. Used in oaloium lights, optical glass, technical ceramics, cores for carbon-anc electrodes, fluorescent phosphors, refractories. Solid mp = 2315° bp = 4200° d = 6.5100. Atomergic Chemetals Cerac Rhdne-Poulenc Seimi Chem. 

Lanthanum (III) oxide Lanthanum (3+) oxide Lanthanum sesquioxide Lanthanum trioxide. See Lanthanum oxide Lantox 55, 110. See PEG-75 lanolin Lantroi 1673, Lantroi 1674, Lantroi 1675. See Lanolin oil... 

The oxysulphides of lanthanum, cerium and plutonium are found to be iso-structmral with the hexagonal sesquioxides of the lanthanides (63). In these oxysulphides, the central metal atom is seven coordinated and has four oxygens and three sulphur atoms as nearest neighbours (Table 3). 

Europeum metal is prepared from the europium sesquioxide obtained above by the reduction with lanthanum or cerium. The oxide is heated under a vacuum in a tantalum crucible with excess lanthanum turning. Europeum volatilizes and collects as a bright crystalline condensate on the wall of the crucible. It is stored and handled in an inert atmosphere, as the finely divided metal is flammable. 

The principal sources of ytterbium are euxenite, gadolinite, monazite, and xenotime. the latter being the most important. Ytterbium is separated from a mixture of yttrium and the heavy Lanthanides by using the sodium amalgam reduction technique. Ytterbium metal is obtained by heating a mixture of lanthanum metal and ytterbium oxide under high vacuum. The ytterbium sublimes and is collected on condenser plates whereas the lanthanum is oxidized to the sesquioxide. 

A2Pt207, similar to those reported for tin, ruthenium, titanium, and several other tetravalent ions. Trivalent ions which form cubic platinum pyrochlores range from Sc(III) at 0.87 A to Pr(III) at X.14 A. Distorted pyrochlore structures are formed by lanthanum (1.18 A) and by bismuth (1.11 A). Platinum dioxide oxidizes Sb203 to Sb2(>4 at high pressure. The infrared spectra and thermal stability of the rare earth platinates have been reported previously and will not be repeated here, except to point out the rather remarkable thermal stability of these compounds decomposition to the rare earth sesquioxide and platinum requires temperatures in excess of 1200 °C. 

As shown in Table I, lanthanum and lutetium oxides have Sq ground states and consequently their heat capacities should be attributed to lattice vibration. Data on these substances may be used to represent the lattice contribution to a first approximation for neighboring isostructural (and nearly so) sesquioxides. Cubic gadolinium oxide provides a midseries lattice heat capacity approximation at relatively high temperatures... 

Comparison of the predictions of this scheme with the data for the diamagnetic sesquioxides of lanthanum and lutetium (193) suggests that if all of the entropy variation is to be ascribed to the cation, the contributions would have to decrease with increasing mass (or atomic number) from 15.2 for lanthanum to 13.0 for lutetium. As an approximation, the decrease is taken proportional to that of the cationic radius obtained by x-ray diffraction measurements. The following (improved) values then apply ... 

The hydroxides are precipitated by NaOH from Ln solutions and are insoluble in an excess. Apart from the exceptions already mentioned, they are converted into the sesquioxides, 1 303, by heating in air. Lanthanum oxide, a very strong base, slakes like CaO on the addition of water and wil then take up COg. The oxides of the other elements become progressively weaker bases as the size of the Ln + ion diminishes. The lanthanide oxides have particularly high heats of formation ... 

The crystal structure of La202C2 determined from three-dimensional X-ray diffraction on a twin crystal is of monoclinic symmetry, space group C/2m (Seiver and Eick 1976). The lattice parameters are a = 7.069(8) A, b = 3.985(4) A, c = 7.310(9) A and p = 95.70(6)° the calculated density is 5.41 gcm". In this structure, the lanthanum atom has four oxygen and four carbon atoms situated in a distorted bicapped trigonal prismatic arrangement. Interatomic La-O distances range from 2.392(8) to 2.823(9) A and La-C distances from 2.86(1) to 3.11(1) A. The carbon atoms are present as C2 units with an interatomic C-C distance of 1.21(3) A. Oxygen atoms are tetrahedrally coordinated, as in the sesquioxide. 

Leger etal. (1980,1981) have described the preparation, at high pressures, of the metallic monoxides for the elements from lanthanum to samarium and have determined their structure and conductivities. A negative PAV term in the free-energy expression makes it possible to synthesize the monoxides from a mixture of the metal and the sesquioxide under pressure. These monoxides can be maintained at normal pressures after,preparation. The monoxides through NdO are metallic, golden-yellow compounds with the Ln atom being trivalent. SmO is metallic with a valence close to... 

The ytterbium metal was prepared by the reduction-distillation method from a mixture of lanthanum metal and ytterbium sesquioxide, then purified by sublimation at 625°C. The impurities found in the ytterbium (in atppm) were 2570 H, 324 O, 210 Cl, 80 Ca, 62 N, 30 Dy, 29 C, 22 Fe and 20 each Mg and Lu. The lutetium metal... 

Stecura, S., 1965, Crystallographic Modifications and Phase Transformation Rates of Five Rare Earth Sesquioxides Lanthanum Oxide, Neodymium Oxide, Samarium Oxide, Europium Oxide and Gadolinium Oxide, in Bur. of Mines Rept. of Inv. 6616. 

---