Molybdates types

Mechanisms There is a derth of knowledge about the mechanisms operative in selective oxidation reactions. The only exceptions are the reactions of ethylene to ethylene oxide on supported silver catalysts and of propylene to acrolein on bismuth molybdate type catalysts. For the latter, it is well established through isotopic labeling experiments that a symmetric allyl radical is an intermediate in the reaction and that its formation is rate-determining. Many studies simply extrapolate the results substantiated for this case to other reactions. New ideas on mechanisms are presented by Oyama, et oL, Parmaliana, et aL, and Laszlo. 

This process is performed very successfully on an industrial scale using either macrocrystalline silver or an iron molybdate type of catalyst. The... 

Ni(N03)2 on the Al203-surface. It may thus be predicted that by appropriate choice of the conditions Co- and Ni-promoted catalysts such as molybdate-type materials can also be prepared by this "dry" technique. 

X-ray diffraction was used as a complementary technique and evidenced the formation of a crystallized phase for the regeneration at higher temperatures. The peaks can be attributed to a mixed oxide of molybdenum and nickel with the following formula x (NiO), (M0O3), z (H2O). So the metals partially sinter during regeneration into a bulky phase, which is no longer active. The appearance of this nickel - molybdate type phase, expressed as the area of... 

Bismuth vanadate (q.v.) and vanadate molybdate-type pigments are also yellow in colour modem paints labelled bismuth yellow will be of this type. This is listed by the Colour Index (1971) as Cl Pigment Yellow 184. 

The carbonates, sulfates, nitrates, and haUdes of lead (except the yeUow iodide) are colodess. Bivalent lead forms a soluble nitrate, chlorate, and acetate a slightly soluble chloride and an insoluble sulfate, carbonate, chromate, phosphate, molybdate, and sulfide. Highly crystalline basic lead salts of both anhydrous and hydrated types are readily formed. Tetrabasic lead sulfate [52732-72-6] 4PbO PbSO, and the hydrated tribasic salt [12397-06-7] ... 

Technical molybdic oxide can be reduced by reaction of ferrosiUcon in a thermite-type reaction. The resulting product contains about 60% molybdenum and 40% iron. Foundries generally use ferromolybdenum for adding molybdenum to cast iron and steel, and steel mills may prefer ferromolybdenum to technical molybdic oxide for some types of steels. 

Absorption-type refrigerators operating with strong lithium bromide solutions can also be inhibited by a number of chemicals. Thus, a mixture of lithium hydroxide -I- BTA -I- sodium molybdate has been reported . 

The primary types of corrosion inhibitor treatments employed are generally based on inorganic chemicals such as sodium nitrite (together with combinations of borate, silicate, molybdate, and phosphate) and the addition of even 2 to 3 pints (0.95-1.4 liters) to a boiler can immediately raise the TDS in the BW to a level at which priming can occur. Secondary problems include an associated rise in the level of BW suspended solids and sludge. 

Although azoles are commonly thought of as only yellow metal inhibitors, they are, in fact, used for corrosion inhibition in a wider range of metals such as steel and aluminum. They also are often incorporated in molybdate-based programs to both provide some synergism and reduce the level of molybdate required. Azoles also are employed in many types of organic-based formulations, where they improve the overall protection of steel and reduce the risk of corrosion of yellow metals due to the corrosive action of some common phosphonates. 

As a consequence, it is not possible to devise a single class of anodic inhibitor formulation that satisfies all water treatment requirements. Rather, there several types of formulations, and some formulators may offer each of these products in different strengths, with or without oxygen scavengers and indicator dyes in their blends. As examples, a nitrite/sUicate formulation and a molybdate/nitrite formulation are provided here ... 

The most extensively studied rate processes in this group are those which yield spinels [1] (ferrites, chromites, etc.), molybdates and tungstates, and complex iodides. These types are conveniently exemplified by the representative systems... 

This type of pigment is the precipitate formed when molybdic oxide is dissolved in aqueous sodium hydroxide with the addition of sodium chromate. The resulting mixture is reacted with a solution of lead nitrate. The precipitate formed is further processed through filtration, washing, drying, milling, and packaging. 

An excellent example of this type of analysis involves the determination of phosphate in soil extracts. Soil is extracted with an appropriate extractant and added to a solution of acid molybdate, with which the phosphate reacts to produce a purple- or blue-colored solution of phosphomolybdate. Standard phosphate solutions are prepared, reacted with acid molybdate, and the intensity of the phosphomolybdate color produced is measured. A standard curve (also called a calibration curve) is prepared (see Section 14.10) from which the intensity of the color is directly related to the concentration of phosphate in the extract. 

P.R.48 4, the manganese salt, affords red shades, which are noticeably on the bluish side of P.R.48 3 and yellower than P.R.48 2. The pigment is used in a variety of applications, especially in paints. In order to produce opaque shades of red, P.R.48 4 is frequently combined with Molybdate Orange. The pigment is considerably more lightfast and durable than other P.R.48 types, especially in full shades. 

With 4o/44Ca- and 92/ioojio- data the differentiation of the translational and librational modes was obtained for the molybdates and tungstates with scheelite structure 98, 100, 101). Tables 29 and 30 reproduce these results. In contrast to early findings, the lower frequency bands were found to be librations and not translations. Furthermore, the band associated with Vi for CaMo04 and CaW04 cannot be expressed as a pure deformational vibration of the MOl group, but this mode is coupled with the translational vibrations, as indicated in Table 29. The relationship between the translational vibration, E, and the square root of the mass of the cation for compounds of the type AMO 4 (A = Ca, Sr, Ba, Pb M = Mo, W) was determined to be linear (100). 

The interpretation of the lattice vibrations for scheeUte type molybdates or tungstates with relatively light cations, Ca or Sr, has indicated that the lowest translational vibrations are produced by Mo—Mo or W—W motions respectively, while those at higher frequency are from cation-cation motions 98). This has not been found, however, in the case of the barium or lead compounds. The librational frequencies have been found to decrease hnearly with the ionic radius of the cation for AMO4 type compounds, where A = Ca, Sr, Ba, or Pb and M =Mo or W 98). 

Normal isopoly- and peroxymolydates of ammonium and several metals are known. The normal or orthomolybdates may be considered as salts of molybdic acid having formulas H2Mo04 xH20 or M20 Mo03 xH20. They are either of monoclinic or scheelite type crystal structure and obtained as hydrated salts. 

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