Octamolybdates

Molybdenum Oxides. Molybdenum was one of the first elements used to retard the flames of ceUulosics (2). Mote recently it has been used to impart flame resistance and smoke suppression to plastics (26). Molybdic oxide, ammonium octamolybdate, and zinc molybdate ate the most widely used molybdenum flame retardants. Properties ate given in Table 5. These materials ate recommended almost exclusively for poly(vinyl chloride), its alloys, and unsaturated polyesters (qv). 

Mo20 24 2h), and octamolybdate, MogO g) ions. Even larger aggregates may be present in solution and in salts. Both and... 

Antimony trioxide (SbaOj). It is produced from stibnite (antimony sulphide). Some typical properties are density 5.2-5.67 g/cm- pH of water suspension 2-6.5 particle size 0.2-3 p,m specific surface area 2-13 m-/g. Antimony trioxide has been the oxide universally employed as flame retardant, but recently antimony pentoxide (SbaOs) has also been used. Antimony oxides require the presence of a halogen compound to exert their fire-retardant effect. The flame-retarding action is produced in the vapour phase above the burning surface. The halogen and the antimony oxide in a vapour phase (above 315 C) react to form halides and oxyhalides which act as extinguishing moieties. Combination with zinc borate, zinc stannate and ammonium octamolybdate enhances the flame-retarding properties of antimony trioxide. 

Numerous investigations have shown the existence of the heptamolybdate, [Mo7024]6 , and octamolybdate, [Mo8026]4, ions in aqueous solution. Potentiometric measurements with computer treatment of the data proved to be one of the best methods to obtain information about these equilibria. Stability constants are calculated for all species in a particular reaction model, which is supposed to give the best fit between calculated and experimental points. In the calculations the species are identified in terms of their stoichiometric coefficients as described by the following general equation for the various equilibria... 

The a- and y-structures differ from the /3-structure in that the former do not consist only of octahedra the ce-structure has two four-coordinate and the y-structure two five-coordinate molybdenums. The a-octamolybdate consists of a planar ring of six edge-shared Mo06... 

Ammonium ion forms several isopolymolybdates, including ammonium di-, tri-, hepta-, and octamolybdates. Among these, ammonium dimolyhdate, (NH4)2Mo20y [27546-07-2] and ammonium heptamolyhdate,... 

Figure 33 The structures of (a) heptamolybdate, [Mo2024]6, and (b) octamolybdate, [MogO 4- (one Mo06...

Fig. 32. Peak shapes, calculated from crystal structure parameters for the heptamo-lybdate ion, Mo70246", and for two octamolybdates Mo80264 and Mo80288". The separate contributions from Mo—Mo distances (short dashes), Mo—0 distances (dotted lines), and O—0 distances (long dashes) are shown.

Zinc borate is also an effective SS in combination with phosphate ester plasticiser (130). The combination of ammonium octamolybdate and zinc stannate is also beneficial (435). It has been shown that ATH and MDH functional fillers coated with zinc hydroxystannate give significantly increased combustion resistance and lower levels of smoke evolution (386). Copper (I) complexes have been suggested as smoke suppressants (241). Copper oxides have also been investigated with positive results (60). 

Tetra-n-butylammonium octamolybdate, [(C4Hq)4N]4Mo8026. Mol. wt. 2153.39. The amine salt is prepared in 80% yield by reaction of sodium molybdate, Na2Mo04 2H20 (Alfa), with a 40% solution of tetra-n-butylammonium hydroxide in a ciircfully controlled ratio (cf. Klemperer and Shum ). 

Cadmium Octamolybdate, CdMogOgg.THjO, has been described. ... 

Higher molybdates of strontium are not known with certainty. An octamolybdate, of composition 1 SrMog02s.7H20, has, however, been... 

Uranyl Octamolybdate, UOg.SMoOj.lSHjO, is obtained by treating the paramolybdatc mth nitric acid in sunlight, and allowing the solution to evaporate, when it crystallises in prismatic needles. ... 

Zinc Octamolybdate, ZnMOgOas.lSHjO, is obtained as transparent crj stals by allowing a solution containing equivalent quantities of ammonium tetramoh bdate and zinc sulphate to crystallise. 

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