Flame molybdenum-containing systems

Molybdenum and zine eontaining compounds have been used as flame and smoke suppressants for a variety of polymers. These metal containing species normally act to assist the build-up of char on the pol mier surface. This ehar is presumed to be the main method of flame retardancy. Halogenated systems form a large proportion of the market for molybdenum and zinc compounds. 

Flame photometric determination cannot be recommended except for solutions containing upwards of 10 p.p.m. of magnesium because the resonance line occurs at 2852 A in the middle of an intense OH molecular band system and correction for this background is difficult even when a recording spectrophotometer is used. A hot flame is required and it has been reported by Knutson that some increase in sensitivity is obtained if an oxy-acetylene flame containing 55 per cent by volume of acetylene is used instead of the stoichiometric level of 29 per cent by volume. The resonance line suffers no serious spectral interference from other elements present in the sample solution but aluminium, chromium and molybdenum cause varying degrees of depression. Silicate, phosphate and sulphur ions depress the emission seriously and other anions less seriously and so standards should be made up to contain the same acids in the same concentrations as the samples. 

---