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The Many Applications of Antimony Oxide
Antimony trioxide is the main derivative of antimony metal. The metal is mined most often in China, Bolivia, Russia, and South Africa. The oxide derivative can be used in many different industries including the flame retardant industry as a synergist, the plastic manufacturing industry as a catalyst, the glass industry as a clarifying agent, and in porcelain and enamel as an opacifier or white pigment.
When you want to flame retard something the most common additives for doing so is a halogenated compound in combination with a synergist. The halogenated compound alone will provide flammability protection, but the presence of the synergist allows you to use much less halogenated product. You can use approximately half as much halogen if you also use an antimony synergist.
The use of antimony as a flame retardant synergist is very widespread. A wide variety of industries use it including plastics, textiles, paint, rubber, and paper. The most common materials that include a halogenated flame retardant and an antimony synergist are polypropylene (PP), high impact polystyrene (HIPS), polyvinyl chloride (PVC), ethylene propylene diene M-class rubber (EPDM), acrylonitrile butadiene styrene (ABS), polyethylene (PE), polyurethanes, epoxies, and phenolics.
Since halogenated compounds are usually sold in multi-walled paper bags then the antimony trioxide is typically sold that way as well. If you use very large quantities then you can also buy the synergist in large tote bags. If you do not want to deal with powders, some specialty flame retardant companies will provide a liquid dispersion with the halogenated compound and antimony trioxide in the appropriate ratios mixed with whatever liquid is appropriate for your process.
Another large application for trivalent antimony oxide is as a catalyst in the polymerization of polyethylene terephthalate or PET. This process actually requires a higher purity material than flame retardant applications. It is the preferred catalyst for the manufacture of PET because the cost/performance ratio is considered optimal. Other materials are better catalysts in that they result in higher throughputs; but they are cost prohibitive in most cases.
PET is used to make water bottles and other liquid containers. Because these liquids can sit in the bottle for a long time before consumption, there are some concerns about materials in the PET migrating into the PET. There have been some studies that show antimony will migrate into bottled water, but the concentrations are well below the level where we should be concerned. In addition, the toxicity of antimony is very low and its presence will not likely cause much harm.
A third use for antimony is as a clarifying agent for glass. A clarifying agent is just what it sounds like; it clears up glass during the manufacturing process. The antimony trioxide is added during the meltdown phase and will help to remove any bubbles or inclusions as well as ensure clear glass as the final product. Sand has natural impurities when left untreated would give you light blue or green glass. Antimony trioxide is a good choice because some other common clarifying agents will give you clear glass to start with, but will degrade with time. For example, manganese dioxide used to be used frequently, but scientists found that over time the manganese reacts with the ultraviolet light from the sun and turns the glass purple.
Because of its color, white, antimony can also be used as a pigment. One industry that utilizes it this way is the porcelain and enamel industry. Here, the antimony is used as an opacifier in very specific instances. As you can see, the uses of antimony are quite varied and many industries utilize this unique chemical compound.
About the Author Flame retardant additives include antimony trioxide as a synergist. Amspec has been providing plastic additives for over twenty five years.
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