Antimonious Oxide

Kaiser B, Bernhardt T M, Kinne M, Rademann K and Fleidenreich A 1999 Formation, stability, and structures of antimony oxide cluster ions J. Chem. Phys. 110 1437... 

Although acrylonitrile manufacture from propylene and ammonia was first patented in 1949 (30), it was not until 1959, when Sohio developed a catalyst capable of producing acrylonitrile with high selectivity, that commercial manufacture from propylene became economically viable (1). Production improvements over the past 30 years have stemmed largely from development of several generations of increasingly more efficient catalysts. These catalysts are multicomponent mixed metal oxides mostly based on bismuth—molybdenum oxide. Other types of catalysts that have been used commercially are based on iron—antimony oxide, uranium—antimony oxide, and tellurium-molybdenum oxide. 

Acryhc and modacryhc fibers are sold mainly as staple and tow products with small amounts of continuous filament fiber sold in Europe and Japan. Staple lengths may vary from 25 to 150 mm, depending on the end use. Eiber deniers may vary from 1.3 to 17 dtex (1.2 to 15 den) 3.2 dtex (3.0 den) is the standard form. The appearance of acryhcs under microscopical examination may differ from that of modacryhcs in two respects. Eirst, the cross sections (Eig. 1) of acryhcs are generally round, bean-shaped, or dogbone-shaped. The modacryhcs, on the other hand, vary from irregularly round to ribbon-like. The modacryhcs may also contain pigment-like particles of antimony oxide to enhance their flame-retardant properties. 

Fig. 1. Paiticle size distribution of the antimony oxides A, Thermoguard UF B, Thermoguard S C, Thermoguard L.

Antimony Oxide as a Primary Flame Retardant. Antimony oxide behaves as a condensed-phase flame retardant in cellulosic materials (2). It can be appHed by impregnating a fabric with a soluble antimony salt followed by a second treatment that precipitates antimony oxide in the fibers. When the treated fabric is exposed to a flame, the oxide reacts with the hydroxyl groups of the cellulose (qv) causing them to decompose endothermically. The decomposition products, water and char, cool the flame reactions while slowing the production and volatilization of flammable decomposition products (see Flaa retardants for textiles). 

Mixed Metal Antimony Synergists Worldwide scarcities of antimony have prompted manufacturers to develop synergists that contain less antimony. Other metals have been found to work in concert with antimony to form a synergist that is as effective as antimony alone. Thermoguard CPA from Elf Atochem NA, which contains zinc in addition to antimony, can be used instead of antimony oxide in flexible poly(vinyl chloride) (PVC) as well as some polyolefin appHcations. The Oncor and AZ products which contain siUcon, zinc, and phosphoms from Anzon Inc. can be used in a similar manner. The mixed metal synergists are 10 to 20% less expensive than antimony trioxide. 

Ammonium Fluoroborate. Ammonium fluoroborate [13826-83-0] NH BF, is unique in that when it is exposed to a flame, it generates both a halogen and a boron flame retardant (20). Antimony oxide is usually recommended as a co-synergist. 

Antimony Oxide. The effect of antimony trioxide on the oxygen index of flexible poly(vinyl chloride) containing from 20 to 50 parts of plasticizer is shown in Figure 2. The flame resistance as measured by the oxygen index increases with the addition of antimony oxide until the oxygen index appears to reach a maximum at about 8 parts of Sb202. Further addition of antimony oxide does not have any increased beneficial effect. 

Fig. 2. The effect of antimony oxide on the oxygen index of poly(vinyl chloride) plasticized with dioctyl phthalate (DOP), (—...

Zinc Borate. Zinc borate is also effective in enhancing the flame-inhibiting powers of chlorine. Although zinc borate increases flame resistance, it is not as effective as antimony oxide, as is illustrated in Figure 3. However, zinc borate can be used in combination with antimony oxide to obtain equivalent and in some instances enhanced effects over what can be obtained using either of the two synergists alone (Table 9). 

Fig. 3. A comparison of the effect of antimony oxide (-) and Firebrake ZB (---) on the oxygen index of PVC containing 50 phr DOP.

Molybdenum Oxide. Molybdenum compounds incorporated into flexible PVC not only increase flame resistance, but also decrease smoke evolution. In Table 10 the effect of molybdenum oxide on the oxygen index of a flexible PVC containing 50 parts of a plasticizer is compared with antimony oxide. Antimony oxide is the superior synergist for flame retardancy but has Httle or no effect on smoke evolution. However, combinations of molybdenum oxide and antimony oxide may be used to reduce the total inorganic flame-retardant additive package, and obtain improved flame resistance and reduced smoke. 

Table 10. Effect of Flame Retardancy of Molybdenum Oxide and Antimony Oxide ...

Zinc Sta.nna.tes, The zinc staimates are also effective synergists for flexible PVC however, as shown in Figure 4a, antimony oxide is more effective. If more chlorine such as in a chlorinated paraffin such as Cereclor is added, then the staimates become more effective and eventually outperform antimony oxide (Fig. 4b). 

Alumina Trihydrate. Alumina trihydrate is usually used as a secondary flame retardant in flexible PVC because of the high concentration needed to be effective. As a general rule the oxygen index of flexible poly(vinyl chloride) increases 1% for every 10% of alumina trihydrate added. The effect of alumina trihydrate on a flexible poly(vinyl chloride) formulation containing antimony oxide is shown in Figure 5. 

Synergists. The effect of antimony oxide on the flammabiUty of unsaturated polyesters that contain chlorine is shown in Table 11. A similar effect on the flammabiUty of unsaturated polyester containing 2inc stannates and bromine instead of chlorine is given in Table 12. 

Table 11. Effect of Chlorine and Antimony Oxide on the Oxygen Index of Unsaturated Polyesters...

Antimony oxide and 2inc borate are also used as synergists for unsaturated polyesters. Their combined effect on the flame spread index (25) is ... 

Polymer UL-94 rating at 3.2 mm Flame retardant, wt % Antimony oxide, wt %... 

Cblorina.ted Pa.ra.ffins, The term chlotinated paraffins covers a variety of compositions. The prime variables are molecular weight of the starting paraffin and the chlorine content of the final product. Typical products contain from 12—24 carbons and from 40—70 wt % chlorine. Liquid chlotinated paraffins are used as plasticizers (qv) and flame retardants ia paint (qv) and PVC formulations. The soHd materials are used as additive flame retardants ia a variety of thermoplastics. In this use, they are combiaed with antimony oxide which acts as a synergist. Thermal stabilizers, such as those used ia PVC (see vinyl polymers), must be used to overcome the inherent thermal iastabiUty. 

M. J. Drews, C. W. Jarvis, and G. C. Lickfield, Temay Reactions AmongPolymer Substrate—Organohalogen—Antimony Oxides Under Pyrolytic, Oxidative and Flaming Conditions, NIST-GCR-89-558, U.S. Department of Commerce, Gaithersburg, Md., 1989. 

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