Zinc ammonium borate, effect

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. 

It required 5.5 pounds of zinc chloride to reduce flame spread to 35, and 7 pounds to reduce flame spread to 25. Ammonium sulfate and borates were as effective as zinc chloride at retentions of about 4.5 pounds per cubic foot and lower but not as effective at higher retention levels. Boric acid had some effectiveness in reducing flame spread. It was equivalent to zinc chloride, ammonium sulfate, and the borates at a retention of about 2 pounds per cubic foot, but much less effective at high retention levels. 

Samyn, F., Bourbigot, S., Duquesne, S., and Delobel, R. 2007. Effect of zinc borate on the thermal degradation of ammonium polyphosphate. Thermochim. Acta 456 134-144. 

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). 

A1(OH)3 ° In both cases, the reaction is endothermic which contributes a cooling effect to the degrading polymer. Borates degrade at different temperatures depending on their composition (ammonium -120 C, barium metaborate - 200°C, zinc borate - 290°C). ... 

Less than 10% of the polyamide produced is made in a flame retardant version. The best system is composed of a combination of red phosphorus and zinc borate (see table above). The only drawback of this system is its color which is restricted to brick red or black. If other colors are required, ammonium polyphosphate is used either in combination with organic flame retardants or with antimony trioxide. It is possible to manufacture a very wide range of colors in the halogen free system. Some systems make use of the addition of novolac or melamine resins. For intumescent applications, ammonium polyphosphate, in combination with other components, is the most frequently used additive. Figure 13.6 shows that fillers such as calcium carbonate and talc (at certain range of concentrations) improve the effectiveness of ammonium polyphosphate. This is both unusual and important. It is unusual because, in most polymers, the addition of fillers has an opposite influence on the efficiency of ammonium polyphosphate and it is important because ammonium polyphosphate must be used in large concentrations (minimum 20%, typical 30%) in order to perform as a flame retardant. 

In fire retardant applications, a combination of zinc borate with ammonium polyphosphate gives V-0 rating. The use of zinc borate permits a reduction in the amount of ammonium polyphosphate. Red phosphorus alone or in combination with ammonium polyphosphate or melamine phosphate also produced a V-0 rating. The heat release rate can be effectively improved by small additions (1-2 wt%) of silicone powder in combination with other flame retarding additives or at higher concentration (15 wt%) when used by itself. 

There are several fillers and inoiganic/organic additives used in flame retarded materials and these include antimony oxide, aluminum trihydrate, zinc borate, ammonium octamolybdate, and zinc stannate. The details related to the composition required and performance characteristics of inorganic additives can be found in specialized monograph. Some of these compounds are discussed below in relation to their effects on enhancement of performance of phosphate plasticizers. 

Soluble salts of copper, manganese, iron, and zinc are likely to become insoluble when Incorporated in ammonium phosphates or ammoniated mixed fertilizers. The reaction forms one of several metal ammoriiufrr phosphates such as ZnNH4P04. In general, the water solubility decreases with increase in pH of the fertilizer product. Loss of water solubility does not necessarily imply loss of effectiveness but may delay it. Sodium borate when incorporated in ammoniated fertilizers containing calcium may become partially or wholly insoluble presumably because of formation of calcium borate. The boron in calcium borate is insoluble in cold water but soluble in boiling water.) This effect has been noted with nitrophosphate fertilizers and may occur with other formulations. 

It can be used alone as a smoke suppressant with a heat insulation effect but, for some applications, the expanded carbon layers are too unstable and other FRs, such as zinc borate, ammonium polyphosphate, or ethylene diamine phosphate, can be used as stabilizers, giving a good span of properties and applications. 

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