Alumina Trihydrate and Magnesium Hydroxide are the most commonly used inorganic flame retardant. Alumina trihydrate (ATH, also read Aluminum Hydroxide) is by far the most widely used flame retardant. It is of low cost, but usually requires a maximum loading of more than 65% in the polymer. Its flame retardancy effect is based on the release of water, which cools the polymer and dilutes the flame zone. Magnesium hydroxide (MDH) is used for higher processing temperature polymers because it is decomposed at temperatures up to 310°C.
Aluminum hydroxide flame retardant, processing temperature up to about 210°C, used for wire and cable, electronic and electrical components based on thermosetting resin, building materials, public transportation, paint and varnish, paper
Magnesium hydroxide flame retardant can be used to treat wires and cables, electronic and electrical components based on polyamide resin, and the maximum temperature of building materials is about 310°C.
There are other minerals with flame retardant properties that can be used for commercial purposes. Most of them are used as synergists, that is, they can enhance the performance of other flame retardants, or for specific effects, such as suppressing the formation of smoke and increasing coke formation. For example, borate is used as a mixture of boric acid and borax, a flame retardant for cellulose (cotton), and a zinc borate flame retardant for polyvinyl chloride and other plastics (such as polyolefin, elastomer, polyimide, or epoxy resin). In halogen-containing systems, zinc borate is used in combination with antimony oxide (mainly to reduce costs), while in halogen-free systems, zinc borate is usually used in combination with ATH, MDH, or red phosphorus. In some specific applications, zinc borate can be used alone. The boron-containing compound works by gradually releasing water and forming a glass-like coating that protects the surface.
Zinc borate was originally developed as a smoke suppressant for PVC. It was later discovered that they also act as flame retardants in certain plastics, mainly by promoting the formation of carbon. Other inorganic fillers such as talcum powder or chalk powder (calcium carbonate) are sometimes also called flame retardants, and their mode of action is only by dilution, that is, they reduce the polymer content, thereby reducing the fire load.
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