Antimony trioxides

The combination of antimony trioxide and halogenated FR makes ignition difficult and reduces flame spread rates. Antimony trioxide moderates heat generation by diverting the combustion process into chemical reactions that do not generate heat and preferably absorb it. Antimony also promotes char formation, which insulates the substrate from the heat, and reduces the 

Antimony oxide has disadvantages. It increases the smoke emitted on combustion, and there are serious concerns about its effects on health. There have also been very large fluctuations in price in recent years. These disadvantages have motivated a search for other synergists. 

This white semireinforcing filler is used in flame resistant compounds and sometimes as a colouring agent. 

---

Tartaric acid is noteworthy for a) the excellent way in which the majority of its salts Crystallise, and h) the frequent occurrence of salts having mixed cations. Examples of the latter are sodium potassium tartrate (or Rochelle salt), C4H40 NaK, used for the preparation of Fehling s solution (p. 525), sodium ammonium tartrate, C4H OaNaNH4, used by Pasteur for his early optical resolution experiments, and potassium antimonyl tartrate (or Tartar Emetic), C4H404K(Sb0). The latter is prepared by boiling a solution of potassium hydrogen tartrate (or cream of tartar ) with antimony trioxide,... 

Required Potassium hydrogen tartrate, 5 g. antimony trioxide, 5 g-... 

Add 5 g. of potassium hydrogen tartrate and 5 g. of antimony trioxide (each being finely powdered) to 30 ml. of water contained in a small flask, and boil the mixture under a reflux water-condenser for 15 minutes. Then filter hot, using a Buchner funnel and flask which have been preheated by the filtration of some boiling distilled water. Pour the clear filtrate into a beaker and allow to cool. Potassium antimonyl tartrate separates as colourless crystals. Filter, drain and dry. Yield, 5 g. The product can be recrystallised from hot water, but this is usually not necessary. 

Tartar emetic, as its name indicates, can be used medicinally to cause vomiting. For the preparation of tartar emetic intended for medicinal use, pure antimony trioxide, free (in particular) from traces of arsenic, must of course be employed. 

Sodium Antimonate. Sodium antimonate [15593-75-6] Na SbO, another antimony synergist of commercial importance, has an antimony content of 61—63 wt % and a bulk density of 39.4—46.4 kg/m. Properties are given in Table 2. It is made by oxidizing antimony trioxide using sodium nitrate and caustic. It is a white powder and has a pH of around 9—11 when dissolved in water. 

Sodium antimonate contains less antimony than either antimony trioxide or pentoxide and is thus less effective. However, its unique pH and low refractive index makes the antimonate the most desirable synergist for polymers that hydrolyze when processed with acidic additives or in polymers for which deep color tones are specified. Sodium antimonate costs approximately 3.30—4.40/kg and can be obtained from either Elf Atochem NA under the Thermoguard name or from Anzon Inc. as a Timinox product. 

Toxicity. Antimony has been found not to be a carcinogen or to present any undue risk to the environment (9). However, because antimony compounds also contain minor amounts of arsenic which is a poison and a carcinogen, warning labels are placed on all packages of antimony trioxide. 

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. 

According to the second mechanism the polymer and antimony trioxide form a catalytic complex. The halogen flame retardant then reacts with the complex and expels antimony tribromide. 

Either mechanism can be used to describe how antimony—halogen systems operate in both the condensed and vapor phases. In the condensed phase a chat that is formed during the reaction of the polymer, antimony trioxide, and the halogen reduces the rate of decomposition of the polymer therefore, less fuel is available for the flame (16). 

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. 4. Effect on limiting oxygen index (LOI) of (---) antimony trioxide (---) Flamtard S, and Flamtard H added to (a) the basic unfilled PVC...

Flame Retardants. Flame retardants are added to nylon to eliminate burning drips and to obtain short self-extinguishing times. Halogenated organics, together with catalysts such as antimony trioxide, are commonly used to give free-radical suppression in the vapor phase, thus inhibiting the combustion process. Some common additives are decabromodiphenyl oxide, brominated polystyrene, and chlorinated... 

With the exception of the soHd methoxide [19727-40-3], the lower antimony trialkoxides are colorless or slightly colored distillable Hquids, easily hydroly2ed. Thermally these alkoxides are rather stable. The lower antimony trialkoxides are manufactured from antimony trichloride, the higher from antimony trioxide, both on a small scale. They are used in polyester manufacture, in fireproofing, as catalysts, and for coatings. For further information about antimony trialkoxides, see references 21, 65, 98. 

Some of the chemicals mentioned above and others, such as chlorinated mbber or paraffin, antimony trioxide, calcium carbonate, calcium borate, pentaerythrithol, alumina trihydrate, titanium dioxide, and urea—melamine—formaldehyde resin, may be used to formulate fire retardant coatings. Many of these coatings are formulated in such a way that the films intumesce (expand) when exposed to fire, thus insulating the wood surface from further thermal exposure. Fire retardant coatings are mostly used for existing constmction. 

Antimony Compounds. The greatest use of antimony compounds is in flame retardants (qv) for plastics, paints, textiles, and mbber. Antimony compounds used in flame retardants are antimony pentoxide, sodium antimonate [15593-75-6] Na[Sb(OH) ], and, most importantly, antimony trioxide. These compounds, when used alone, are poor flame retardants however, when combined with halogen compounds, they produce mixtures that are effective. 

Antimony trioxide and sodium antimonate are added to specialty glasses as decolorizing and fining agents, and are used as opacifiers in porcelain enamels. Antimony oxides are used as white pigments in paints, whereas antimony trisulfide and pentasulfide yield black, vermilHon, yeUow, and orange... 

Antimony Trioxide. Antimony(III) oxide (antimony sesquioxide) [1309-64-4] Sb203, is dimorphic, existing in an orthorhombic modification valentinite [1317-98-2] is colorless (sp gr 5.67) and exists in a cubic form and senarmontite [12412-52-17, Sb O, is also colorless (sp gr 5.2). The cubic modification is stable at temperatures below 570°C and consists of discrete Sb O molecules. The molecule is similar to that of P40 and As O and consists of a bowed tetrahedron having antimony atoms at each corner united by oxygen atoms lying in front of the edges. This solid crystallizes in a diamond lattice with an Sb O molecule at each carbon position. 

At higher temperatures the stable form is valentinite, which consists of infinite double chains. The orthorhombic modification is metastable below 570 °C however, it is sufficientiy stable to exist as a mineral. Antimony trioxide melts in the absence of oxygen at 656°C and partially sublimes before reaching the boiling temperature, 1425°C. The vapor at 1500°C consists largely of Sb O molecules, but these dissociate at higher temperatures to form Sb202 molecules. 

Antimony trioxide is insoluble in organic solvents and only very slightly soluble in water. The compound does form a number of hydrates of indefinite composition which are related to the hypothetical antimonic(III) acid (antimonous acid). In acidic solution antimony trioxide dissolves to form a complex series of polyantimonic(III) acids freshly precipitated antimony trioxide dissolves in strongly basic solutions with the formation of the antimonate ion [29872-00-2] Sb(OH) , as well as more complex species. Addition of suitable metal ions to these solutions permits formation of salts. Other derivatives are made by heating antimony trioxide with appropriate metal oxides or carbonates. 

Antimony trioxide has numerous practical applications (1). Its principal use is as a flame retardant in textiles and plastics (see Flame RETARDANTS Flame retardants in textiles). It is also used as a stabilizer for plastics, as a catalyst, and as an opacifier in glass (qv), ceramics (qv), and vitreous enamels... 

Na[Sb(OH)g], respectively. The latter compound is one of the least soluble sodium salts known and is useful in sodium analysis. Numerous polyantimonate(V) derivatives are prepared by heat treatment of mixtures of antimony trioxide and other metal oxides or carbonates. Of these, K Sb O [12056-59-6] and K Sb O [52015-49-3] have been characterized by x-ray. These consist of three-dimensional networks of SbO in which corners and edges are shared with K" ions located in tunnels through the network (23). Simple species such as SbO and Sb20 2, analogous to orthophosphate and pyrophosphate, apparendy do not exist. 

---