Molybdenum sesquioxide

The red solutions obtained by dissolving molybdenum sesquioxide or dioxide in aqueous hydrogen iodide were examined by Berzelius, but insufficiently to obtain definite conclusions. 

Molybdenum and rhenium are particularly interesting. Exhaustive efforts to obtain paramagnetic supported molybdenum dioxide have all failed. These unsuccessful efforts included impregnation of the alumina with molybdenum carbonyl in benzene solution. On the other hand, a dilute three-dimensional solid solution of molybdena in alumina shows definite paramagnetism, and supported molybdenum sesquioxide gives some evidence of paramagnetism. 

Titanium Sesc uioxide. Ti202 has the comndum stmcture. At room temperature it behaves as a semiconductor having a small (0.2 eV) band gap. At higher temperatures, however, it becomes metallic. This is associated with marked change in the mean Ti—Ti distance. As with TiO, titanium sesquioxide, Ti202, may be made by heating a stoichiometric mixture of titanium metal and titanium dioxide powders at 1600°C under vacuum in an aluminum or molybdenum capsule. 

The melting-point of tungsten is higher than that of any other known metal. The metals are stable in air at ordinary temperatures, but when heated they exhibit a remarkable difference in behaviour. Uranium burns briskly at 170° C., producing uranous oxide UO2 molybdenum at a red heat yields the trioxide M0O3 chromium only burns at 2000° C. and forms the sesquioxide CrjOg tungsten is not oxidised at any temperature, except in the vapour form. 

Molybdous Oxide.—The black precipitate obtained by addition of caustic soda to a solution of molybdenum diehloride or dibromide, originally thought to be hydrated molybdous oxide, has been show actually to be the sesquioxide. 

Nitrates of molybdenum are not kno-wn. Bj digesting dilute nitric acid with excess of molybdenum, or -with the hydrate of molybdenum dioxide or sesquioxide, a dark bro-wn solution is obtained, wliich on further evaporation yields oxides of nitrogen and moiybdic acid. 

Electrolytic Methods.—3Iolvbdenum mav be accurately deter-mined in solutions of molybdates by means of electrolysis. In presence of free sulphuric acid the metal is completely precipitated on the cathode as the hydrated sesquioxide, HyChoehlorie acid may be used instead of sulphuric acid to accelerate the deposition. The precipitate after washing may be converted by gentle ignition to molybdenum trioxide, and weighed as such. 

The metal oxides thus far considered belong, in general, to the class of those which are reducible at moderately high temperatures in the presence of water or of alcohol. To the class of the so-called irreducible oxides of the metals and non-metals belong those of zinc, aluminum, molybdenum, silicon, and vanadium and chromium sesquioxide. The last has been described by Sabatier and Mailhe 06 as affording an excellent... 

Molybdenum deficiency in tropical and subtropical soils is more widespread than elsewhere because soils in the tropics are highly weathered. In fact, many soils in the tropics are so highly weathered that little remains except sesquioxides and some 1 1 layer silicates (Pasricha and Fox, 1993). The acidic nature of many of these soils with a dominant content of sesquioxides is the major cause of Mo deficiency. In some cases there can be ample amounts of Mo04 present in the adsorbed form in these sesquioxide-rich low-pH soils, but the solubility of Mo and its concentration in the soil solution are the important factors from the point of view of the availability of Mo to crop plants and natural herbage growing on such soils, and those conditions of high sesquioxide content and low soil pH result in a low concentration of Mo in the soil solution. 

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