Molybdate method structure

The silicate anion structures of C-S-H(I) preparations appear to be affected by how long the material remains in contact with its mother liquor and by how strongly it is subsequently dried. Experiments using the molybdate method showed that the anions in precipitates made from CaCl, and sodium silicate solutions at 0 "C were mainly those present in the silicate solution, and thus monomeric if the latter is sufficiently dilute (S45). By allowing such products to stand in contact with their mother liquors at O C. and drying at — 10°C, preparations with Ca/Si ratios of 1.2-1.5 were obtained that contained only dimeric silicate anions. 

Crystal structures of the bismuth molybdate and of the mixed iron and cobalt solid solution molybdate samples were controlled by X-ray diffraction (10). The chemical compositions of the samples were determined by atomic absorption and their surface areas measured by nitrogen adsorption using the BET method. 

LoJacono et al. (108) also utilized X-ray diffraction methods to study the structural and phase transformations which occurred in the Bi-Fe-Mo oxide system. They detected two ternary compounds containing bismuth, molybdenum, and iron. One of the compounds formed when the atomic ratio Bi/Fe/Mo = 1 1 1 the other formed when the atomic ratio Bi/Fe/Mo = 3 1 2. The X-ray data indicated a close structural relationship of the bismuth iron molybdate compounds with the scheelite structure of a-phase bismuth molybdate. Moreover, their structures were similar to compound X. The structure of the Bi/Fe/Mo = 3 1 2 compound was identical to the compound reported by Sleight and Jeitschko (107). The authors proposed that the structures of both of the compounds could be viewed as resulting from the substitution of Fe3+ in the a-phase lattice. In the Bi/Fe/Mo = 1 1 1 compound, 1 Mo6+ ion is replaced by 2 Fe3+ ions one Fe3+ ion occupies a Mo6+ site the other Fe3+ ion occupies one of the vacant bismuth sites. In the Bi/Fe/Mo = 3 1 2 compound, the Fe3+ ion replaces one Mo6+ ion while the additional Bi3+ ion occupies one of the vacant bismuth sites. 

In addition to the 12-molybdocerate complexes described in Section 2.1, and the Peacock-Weakley analogs listed in Table 4, there have been other attempts to synthesize rare-earth complexes of molybdates. In view of the inadequacies of 95Mo-NMR caused by low sensitivity and quadrupolar relaxation, and the ambiguities of other spectroscopic methods, it has so far been impossible to confirm whether those compounds that reveal discrete polyoxoanions in crystal structure analysis yield solutions that retain the same structures. 

Because C-S-H gel is nearly amorphous. X-ray diffraction has given only very general indications of its structure. The nature of the silicate anions has been determined from the kinetics of the reaction with molybdate (S43), and, in greater detail, by trimethylsilylation (TMS) and Si NMR. In TMS methods, the sample is treated with a reagent that converts the silicate anions into the corresponding silicic acids, which then react further with replacement of SiOH by SiOSi(CH3)3. The resulting TMS derivatives can be identified and semiquantitatively determined by various procedures, of which the most widely used have been differential evaporation to isolate the... 

Lead molybdate, PbMo04, has the scheelite structure typified by calcium tungstate. Discussions of the growth and physical properties of PbMo04 are included in papers on CaW04 (Ranon and Volterra, 1964). The ion in PbMo04 replaces the Pb ion, and some method of charge compensation must... 

Using a one-pot reaction design, an intercalated compound of polyaniline into M0O3 was prepared by Shao et al. [60]. This particular method of synthesis uses a coprecipitation route to fabricate the layered structure. An excess of aniline was acidified to a pH of 0.5, to which was added ammonium molybdate [(NH4)gMo7024.7H20] and FeCl3. The powder pattern of the isolated product revealed the formation of an intercalated phase of polyanihne into M0O3. The identity of the entrapped polymer was confirmed by FTIR... 

It is logical to assume that the rate of depolymerization or dissolution of colloidal silica particles would be proportional to the specific surface area. Thus different solvents such as dilute hydrofluoric acid, molybdic acid, or dilute alkali, all of which convert the monomeric silica permanently to other silicon compounds, may therefore be employed to measure surface area. The difficulty, however, is that the types of silica particles studied have been so varied and ill-defined that this approach has not been of any value until recently, when sols of uniform discrete solid particles have become available. Even then the value of the method is in doubt unless one can be sure that the samples of silica under study all have the same composition and structure. Variables in the rate of dissolution per unit of surface area include the following ... 

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