Lanthanum metal preparation

Europium is now prepared by mixing EU2O3 with a 10%-excess of lanthanum metal and heating the mixture in a tantalum crucible under high vacuum. The element is collected as a silvery-white metallic deposit on the walls of the crucible. 

Americium, californium, and einsteinium oxides have been reduced by lanthanum metal, whereas thorium has been used as the reductant metal to prepare actinium, plutonium, and curium metals from their respective oxides. Berkelimn metal could also be prepared by Th reduction of Bk02 or Bk203, but the quantity of berkelium oxide available for reduction at one time has not been large enough to produce other than thin foils by this technique. Such a form of product metal can be very difficult to handle in subsequent experimentation. The rate and yield of Am from the reduction at 1525 K of americium dioxide with lanthanum metal are given in Fig. 2. 

The Pu-242 obtained in the nuclear reaction is separated by chemical extraction. Americium metal can be prepared from its dioxide by reducing with lanthanum metal at high temperature in a vacuum. 

Lanthanum chloride is used to prepare other lanthanum salts. The anhydrous chloride is employed to produce lanthanum metal. 

It has been found that in the preparation of pure europium the starting materials need not be extremely pure. The common impurity viz. samarium is completely eliminated in the above process because samarium is less volatile than europium, and the reduction of Sn Os to the metal requires a higher temperature than the EU2O3 reduction. Commeri-cal lanthanum turnings can also be used for the reduction in place of more expensive very pure lanthanum metal. Extreme care should be taken to ensure that the reactants contain no calcium as it appears as an impurity in the final product if present in the charge. 

EvO. — This lower oxide of europium was prepared by the reduction of EuaOs with lanthanum metal at 1300 —1500° C by Eick et al. [319]. EuO has a NaCl type structure with a = 5.1439 0.0005 A. Gaston and Hukln [320] attempted the preparation of EuO by controlled oxidation of europium metal at 350° C with a stoichiometric addition of oxygen and obtained the oxide in fairly pure state. They also tried the thermal decomposition of EuCOs, Eu(HCOO)2 and Eu(OH)2. Only Eu(OH)2 proved to be advantegeous and gave a sample of EuO of reasonable purity. 

Later berkelium metal samples of up to 0.5 mg each have been prepared via the same chemical procedure (120). Elemental berkelium can also be prepared by reduction of BkF4 with lithium metal and by reduction of Bk02 with either thorium or lanthanum metal. The latter reduction process is better suited to the preparation of thin metal foils unless multimilligram quantities of berkelium are available. 

Europium is prepared by heating its oxide with lanthanum metal ... 

It took scientists more than 60 years to sort out these elements and separate them from each other. It was not until 1923 that a pure sample of lanthanum metal was even prepared. Still, Mosander is given credit for the discovery of lanthanum. 

Another interesting development using intermetallics has been described in the patent literature (ref. 20). Alloys of copper and oxidisable rare earth metals such as cerium and lanthanum were prepared by melting mixtures of the powders of the pure metals. Additives such as aluminium and palladium were investigated. The alloys were crushed and screened to obtain 0.6 to 0.85 mm particles that were suitable for laboratory testing under typical methanol synthesis conditions. Typical results obtained are presented in Table 2. 

Fig. 287. Preparation of lanthanum metal, a graphite crucible h corundum crucible c molyb-deniun electrode d iron rod e corundum protective tube /thermocouple.

The major breakthrough occurred in 1953 when the Ames Laboratory team (Daane et al. 1953) reported the preparation of samarium, europium and ytterbium in high purity and high yields by the reduction of their oxides with lanthanum metal in a vacuum. With the preparation of samarium metal, finally, 126 years after the first rare earth element was reduced to its metallic state, all of the naturally occurring rare earths were now available in their elemental state in sufficient quantity and purity to measure their physical and chemical properties. The success of this reaction is due to the low vapor pressure of lanthanum and the extremely high vapor pressures of samarium, europium and ytterbium (Daane 1951, 1961, Habermann and Daane 1961). It is interesting to note that this same technique has been the method of choice for the preparation of some transplutonium metals (Cunningham 1964). 

Metal purity also had an effect on the reported values, especially for metals prepared before World War II. One of the early reports for the melting point of lanthanum gave a value of 805°C which is more than 110"C below the currently accepted value of 918°C. Work on the La-C phase diagram by Spedding et al. (1959) offers a reasonable explanation for this low value. These authors found that the La-C eutectic melts at 806°C, and since most of the early light lanthanide metals were prepared by electrolysis using graphite electrodes it is quite likely that their metal was contaminated by carbon. About 0.5 wt.% C would be sufficient for some of the metal (or better yet, alloy) to melt at 806 C. 

The first indications of the existence of organometallic compounds of the lanthanoides was furnished in the observation that methyl radicals do react with lanthanum metal (l). The publication of the successful syntheses of Sc(C2Hs)3 and Y(C2H5)3 (2), the first supposed alkyl derivatives of the rare earth metals, however, proved to be wrong (3). Also, all attempts to prepare the first phenyl derivatives of lanthanum, carried out by Gilman and coworkers in connection with the separation of... 

Lundin (1970), in an investigation of the formation of samarium-type structure in intra rare earth binary alloys included six compositions in the lanthanum-scandium system ranging from 10 to 85at% La. Lundin prepared his alloys using 99.8(wt )% pure lanthanum metal (major impurities, 330 ppm other rare earths, 510 ppm O, 50 ppm each Si, Mg and Zn) and 99 -F (wt )% pure scandium for which there were no details given on the impurities. Lundin found two-phase inuniscibility at low temperatures in the lanthanum-scandium system and, since no samarium-type structure was found, he concluded that scandium behaves more like the neighboring transition elements than it does as a rare earth metal. 

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... 

Americium metal has been prepared by the following methods (1) reduction of AmF3 with barium (or lithium) metal (2) reduction of Am02 with lanthanum metal (3) bomb reduction of AmF4 with calcium metal (4) thermal decomposition of Pts Am. Lanthanum reduction of Am02 in tantalum equipment and subsequent distillation of the americium metal from the reaction mixture yields americium of very high (>99.9%) purity. There is about 10 -fold difference in americium-lanthanum volatility. Extensive application of this technique by the Euratom group has led to important new measurements of the physical properties and thermodynamic properties of americium metal [81,342], Rocky Flats workers have reported similar success with vacuum distillation [333]. 

Gr. aktis, aktinos, beam or ray). Discovered by Andre Debierne in 1899 and independently by F. Giesel in 1902. Occurs naturally in association with uranium minerals. Actinium-227, a decay product of uranium-235, is a beta emitter with a 21.6-year half-life. Its principal decay products are thorium-227 (18.5-day half-life), radium-223 (11.4-day half-life), and a number of short-lived products including radon, bismuth, polonium, and lead isotopes. In equilibrium with its decay products, it is a powerful source of alpha rays. Actinium metal has been prepared by the reduction of actinium fluoride with lithium vapor at about 1100 to 1300-degrees G. The chemical behavior of actinium is similar to that of the rare earths, particularly lanthanum. Purified actinium comes into equilibrium with its decay products at the end of 185 days, and then decays according to its 21.6-year half-life. It is about 150 times as active as radium, making it of value in the production of neutrons. 

Catalysts used for preparing amines from alcohols iaclude cobalt promoted with tirconium, lanthanum, cerium, or uranium (52) the metals and oxides of nickel, cobalt, and/or copper (53,54,56,60,61) metal oxides of antimony, tin, and manganese on alumina support (55) copper, nickel, and a metal belonging to the platinum group 8—10 (57) copper formate (58) nickel promoted with chromium and/or iron on alumina support (53,59) and cobalt, copper, and either iron, 2iac, or zirconium (62). 

Sihca is reduced to siUcon at 1300—1400°C by hydrogen, carbon, and a variety of metallic elements. Gaseous siUcon monoxide is also formed. At pressures of >40 MPa (400 atm), in the presence of aluminum and aluminum haUdes, siUca can be converted to silane in high yields by reaction with hydrogen (15). SiUcon itself is not hydrogenated under these conditions. The formation of siUcon by reduction of siUca with carbon is important in the technical preparation of the element and its alloys and in the preparation of siUcon carbide in the electric furnace. Reduction with lithium and sodium occurs at 200—250°C, with the formation of metal oxide and siUcate. At 800—900°C, siUca is reduced by calcium, magnesium, and aluminum. Other metals reported to reduce siUca to the element include manganese, iron, niobium, uranium, lanthanum, cerium, and neodymium (16). 

Polyisoprenes of 94—98% as-1,4 content were obtained with lanthanum, cerium, praseodymium, neodymium, and other rare-earth metal ions (eg, LnCl ) with trialkyl aluminum (R3AI) (34). Also, a NdCl 2THF(C2H3)3A1 catalyst has been used to prepare 95% <7j -l,4-polyisoprene (35). <7j -l,4-Polyisoprene of 98% as-1,4 and 2% 3,4 content was obtained with organoalurninum—lanthariide catalysts, NdCl where L is an electron-donor ligand such as ethyl alcohol or butyl alcohol, or a long-chain alcohol, and is 1 to 4 (36). 

---