Lanthanum metal, powder

Bina Selenides. Most biaary selenides are formed by beating selenium ia the presence of the element, reduction of selenites or selenates with carbon or hydrogen, and double decomposition of heavy-metal salts ia aqueous solution or suspension with a soluble selenide salt, eg, Na2Se or (NH 2S [66455-76-3]. Atmospheric oxygen oxidizes the selenides more rapidly than the corresponding sulfides and more slowly than the teUurides. Selenides of the alkah, alkaline-earth metals, and lanthanum elements are water soluble and readily hydrolyzed. Heavy-metal selenides are iasoluble ia water. Polyselenides form when selenium reacts with alkah metals dissolved ia hquid ammonia. Metal (M) hydrogen selenides of the M HSe type are known. Some heavy-metal selenides show important and useful electric, photoelectric, photo-optical, and semiconductor properties. Ferroselenium and nickel selenide are made by sintering a mixture of selenium and metal powder. 

Do you think that lanthanum metal could be made from lanthanum oxide by reaction with aluminum powder (see Section 6-12) ... 

Dissolve the precipitate In about 5 ml of water, add 6 drops of lanthanum solution and 6 drops of the 4 per cent tellurate solution and then about 3 mg of zinc metal powder. When the effervescence ceases, make the solution Just ammonlacal to methyl orange, centrifuge and decant Into another tube. Add 4 drops of 1 per cent potassium Iodide solution and 2 drops of sodium hypochlorite solution. Warm and set aside for 2 minutes. Acidify with about 1 ml of hydrochloric acid, and add about 0.1 g of hydroxylamlne hydrochloride. Boll under a hood until all the Iodine appears to be removed and the volume Is reduced to 5 to 6 ml. Add 2 drops of strontium solution and 2 drops of lanthanum solution and repeat the double barium chloride precipitation and washing, as above. 

Of a series of powdered refractory compounds examined, only lanthanum hexa-boride, hafnium carbide, titanium carbide, zirconium carbide, magnesium nitride, zirconium nitride and tin(II) sulfide were dust explosion hazardous, the 2 latter being comparable with metal dusts. Individual entries are ... 

One method of preparation consists in a modification of the Goldschmidt process. Niobium pentoxide is mixed with an alloy of the rare earths, called mixed metal, obtained in the manufacture of thorium nitrate, and consisting roughly of 45 per cent, of cerium, 20 per cent, of lanthanum, 15 per cent, of didymium, and about 20 per cent, of other rare-earth metals. The reaction is carried out in a magnesia-lined crucible, and is started with a firing mixture of barium peroxide, potassium chlorate, and aluminium powder. Considerable evolution of heat takes place and the reduction is extremely rapid a button of niobium is obtained 4 which, however, is not pure. 

Arsenites of the Rare Earth Metals.—When cerium dioxide is heated with arsenious oxide some oxidation of the latter occurs, but the product appears to be a mixture of oxides.5 Didymium hydrogen orthoarsenite, Di2(HAs03)3, has been obtained6 as a white, granular, insoluble powder by boiling didymium hydroxide with an aqueous solution of arsenious oxide. Lanthanum hydrogen orthoarsenite, La2(HAs03)3, has been prepared in a similar manner. The existence of these compounds needs confirmation, however.7... 

SAFETY PROFILE Poison by intravenous route. Lanthanum and other lanthanoids can cause delayed blood clotting leading to hemorrhages. Has caused liver injury" in experimental animals. The dust is a dangerous fire hazard when exposed to flame can react vigorously with oxidizing materials. Violent reaction with nitric acid, phosphoms (above 400°C), air, halogens. Moderately explosive in the form of dust when exposed to flame or by chemical reaction. Incompatible with H2O, C, N, B, Se, Si, S. See also RARE EARTHS and POWDERED METALS. 

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. 

PZT and PLZT. The development of polycrystalline lead lanthanum zir-conate-titanate (PLZT) electronic ceramic monoliths, which fully transmit incident light, requires methods for controlling stoichiometry, impurity content, porosity, grain size, and so on. Alkoxy-derived PLZT powders were prepared by hydrolytic decomposition of mixed-metal alkoxides [40]. The Zr and Ti alkoxides were synthesized by the ammonia method, and the lanthanum tris-isopropoxide was synthesized by the metal/alcohol reaction method, which were described in the previous section. The Pb alkoxide was prepared by the reaction of anhydrous lead acetate, Pb(C2H302)2, with sodium isoamyloxide, NaOCsHn [40] ... 

The positive electrode, the cathode, is similar to that in nicad cells and consists of a mixture of NiO(OH)/Ni(OH)3 and Ni(OH)2. An alloy that supports hydride formation replaces the cadmium as the negative anode. The alloy most commonly used is derived from LaNis, in which a mixture of other lanthanides replaces the lanthanum, and a nickel-rich alloy replaces the nickel, to give a general formula LnA/5. The anode is composed of an agglomeration of alloy powder. A small amount of potassium hydroxide is added as an electrolyte. The cell voltage is 1.3 V, making these cells suitable for the direct replacement of nicad batteries. The cell construction is identical to that of the nicad cell (Figure 9.10), with the cadmium replaced by metal hydride. The approximate cell reactions are as follows. 

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