Aluminum Trihydrate: A Powerful Additive for Track and Flame Retardancy of Reinforced Plastics

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Abstract
The role of aluminum trihydrate as an arc suppressant has long been recognized in the plastic industry. As early as 1953 an application by Jones and Wilkinson [29] was received at the U.S. Patent office for an arc-suppressing device. This consisted of a shield made up of an organic-type binder such as phenolic, urea, melamine, silicone, or polyester. With these binders were included asbestos along with aluminum, magnesium oxide, or hydrate as a filler. The study of Jones and Wilkinson showed that hydrates are more effective arc-suppressing substances than were oxides. Similar behavior was observed by Kessel and Norman [30] in electrical equipment subjected to contaminating atmospheric conditions such as moisture, dust, fog, and salt. This scrubbing action of aluminum trihydrate was described by Norman and Kessel as the most important function of this type of filler electrical application [31]. This use of aluminum trihydrate as an arc suppressant involves the release of the chemically combined water at a temperature of ∼250°C. All grades of aluminum trihydrate contain 3 moles of combined water per mole of alumina. When this water of hydration is released, the surface temperature is lowered, thereby reducing the tendency of the substance to carbonize and form a conductive path.

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