Antimony oxide halides

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. 

Antagonism between antimony oxide and phosphorus flame retardants has been reported in several polymer systems, and has been explained on Ihe basis of phosphorus interfering with the formation or volatilization of antimony halides, perhaps by forming antimony phosphate. 

The first reaction would produce allylic cations whose initiating capability must be very limited, as shown by Kennedy . The second one is an electron transfer which, as we have already pointed out, is possible with antimony (V) halides under special conditions 91,420) but unlikely with elements which do not possess lower oxidation states. 

Antimony has a great affinity for charged sulfur ligands which include thiolates, xanthates (R0CS2 ), dithiocarbamates (R2NCS2 ), and dithiophosphates ((RO)2PS2 ). In contrast to arsenic, where this chemistry is limited to oxidation state III, antimony forms compounds in oxidation states III and V. The xanthate, dithiocarbamate, and dithiophosphate complexes are mostly made by reaction of antimony(III) halides or organohalides with Na, NH4, or Ag salts of the acids. Complexes... 

For the polymerization to proceed at a reasonable rate, the use of a transesterification catalyst is needed. Compounds which are usually used as a catalyst for the preparation of polyesters through transesterification can be used here. These include lithium, sodium, zinc, magnesium, calcium, titanium, maganese, cobalt, tin, antimony, etc. in the form of a hydride, hydroxide, oxide, halide, alcoholate, or phenolate or in the form of salts of organic or mineral acids, complex salts, or mixed salts.(10) In this study, tetrabutyl titanate (TBT) in the amount of 1000 ppm was used normally. 

Reaction of phosgene with antimony halides and oxide halides... 

Many theories attempt to explain the mechanism of flame retardancy. The flame retarding action is thought to take place in the vapor phase above the burning surface. For antimony oxide to work, the halogen and antimony oxide must be found in a vapor phase which will occur at temperatures above 315°C. At these temperatures, antimony halides and oxyhalides are formed and act as flame extinguishing moieties by quenching radicals as they form. 

Earlier in this chapter, it was indicated that the presence of halide ions (e.g., Cl and Br ) is undesirable because they tend to promote the corrosion of parts of the IC. Low-flammability requirements for these encapsulants are realized through the use of brominated epoxy resins in combination with antimony oxide (Sb203). For some time the brominated epoxies have been suspected as a possible source of Br ions. Since it is difficult to achieve low flammability for these encapsulants without the bromine-containing species, efforts have been made to arrive at bromine-containing flame retardants of greater hydrolytic stability so that the flame retardant does not inadvertently diminish the corrosion protection these encapsulants are expected to provide. 

The antimony oxide-alkyl (aryl) halide system functions on heating according to the following mechanism (shown for chloride) ... 

It has been suggested that when antimony oxide is used as a synergist with organic halogen compounds, it is first converted to antimony trihalide by hydrogen halide. The antimony is then decomposed in the combustion zone giving a fine fog of antimony oxide dust, the flame-retardant effect being partly due to the dust effect [16]. 

Antimony oxide is nniqne in its activity as a synergist with halogen compounds. This may be due to the ease with which it reacts with hydrogen halides to form volatile halides, which can pass throngh a number of decompositions and re-combinations (some of which are endothermic) and finally decompose at higher temperatures to give the oxide and release the halogens. 

Halogen-containing flame-retardants such as chlorinated parafBns, poly-bromodiphenyl oxides, and polybromodiphenyls are used in conjunction with antimony oxide. On exposure to fire, the halogen gases liberated by decomposition of the resin component of the paint film react with the antimony oxide to produce a vapor of antimony halide that blankets the flame. 

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