Magnesium Hydroxide endothermic decomposition

One of the emerging technologies that is showing great promise is the use of hydrated mineral fillers such as aluminium and magnesium hydroxides, as such materials can provide high levels of flame retardancy without the formation of smoke or corrosive and potentially toxic fumes. The use of fillers as flame retardants has recently been reviewed by Rothon [23]. Essentially the key features are an endothermic decomposition to reduce the temperature, the release of an inert gas to dilute the combustion gases and the formation of an oxide layer to insulate the polymer and to trap and oxidise soot precursors. 

Flame-retardants are used as additives in the preparation of fire retardant paints. They are decomposed by heat to produce nonflammable components, which are able to blanket the flames. Both inorganic and organic types of flame-retardants are available in the market. The most widely used inorganic flame-retardants are aluminum trihydroxide, magnesium hydroxide, boric acid, and their derivatives. These substances have a flame-retardant action mainly because of their endothermic decomposition reaction and their dilution effect. The disadvantage of these solids is that they are effective in very high filler loads (normally above 60 percent). 

The flame-retardant effect of magnesium hydroxide and ATH is based on the endothermic decomposition to magnesium or aluminum oxide, see reactions (11.1) and (11.2). This decomposition effectively acts as a heat sink cooling the surface of the polymer. 

Metal hydroxides, particularly aluminum trihydrate and magnesium hydroxide, contribute to several fire-retardant actions. They first decompose endothermically and release water. The endothermic decomposition serves to remove heat from the surroundings of the flame and, thus, cool the flame. This is often referred to as the heat sink phenomenon. Pyrolysis decreases in the condensed phase as a result of... 

Endothermic processes inherent to additives such as aluminum trihydrate (AI2O3 3H2O, also known as aluminum hydroxide, Al(OH)3) and magnesium hydroxide, Mg(0H)2, cool the substrate to temperatures below those required to sustain combustion. Water vapor evolved in their endothermic decomposition... 

Metal hydroxides, in particular aluminium trihydroxide (ATH), which is a low-cost filler, and magnesium dihydroxide (MDH). The endothermic decomposition of Al(OH)3 occurs between 180 and 200°C and leads to the release of water and the formation of an insulating ceramic layer of alumina (AI2O3). The use of ATH also reduces the HRR peak aud the smoke production. Mg(OH)2 acts in a similar way but its endothermic degradation occurs at a higher temperature (over 300°C) and a protective layer of MgO is formed at the composite surface. 

First there are additives which act to remove heat by endothermic decomposition and/or the generation of copious quantities of inert gases to dilute the combustible polymer degradation products. Materials such as alumina trihydrate (ATH) and magnesium hydroxide, which in toimage terms are by far the most widely used halogen-free flame retardants, work in this way. These additives are more fully described in the section Flame retardants inorganic oxide and hydroxide systems. ... 

Keywords endothermic decomposition, alumina trihydrate, magnesium hydroxide, phosphorus, organophosphorus, intumescent flame retardants, melamine. 

Magnesium hydroxide decomposes at 300-330 °C also as a result of an endothermic reaction with the evaporation of 31% of water in the form of steam [Ij. Endothermic effect for this reaction is valued between 1244 and 1450 J/g according to various sources [1, 2, 4, 5]. The high decomposition temperature of magnesium hydroxide makes it more suitable for polymers which require high temperatures of processing. According to Hornsby, the effectiveness of hydroxide as a fire retardant means is caused by [6-8]... 

Tmaxa) attributed to thermal decomposition of magnesium hydroxide due to endothermic water release. 

Endothermic Endothermic additives can sublime or absorb heat in their decomposition, evolving inert gases (usually water) to dilute the fuel and/or lower the temperature of the flame front. Hydrated mineral fillers such as alumina trihydrate (aluminum trihydrate, ATH) or magnesium hydroxide (Mg(OH)2) and melamine or its salts (phosphates, cyanurates, etc.) are examples of this methodology. Use of ATH is discussed in Section 16.3 and magnesium compounds in Section 16.4. 

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