Abstract
Flame-retardant coatings have drawn much attention in recent years. In this study, an inorganic sodium silicate-based intumescent flame-resistance coating with an excellent flameproof properties is developed by mainly utilizing sodium silicate as the ceramizable binder, via hydrolysis and self-condensation reaction. Fly ash, metakaoline, and wollastonite behave as supplement cementing materials. Major formulation encompasses the combination of the ammonium polyphosphate and pentaerythritol as the flame-retardant additives, and aluminum hydroxide or expandable graphite as the intumescence-improving filler agents. Expandable graphite was found to play an important role in the eventual performance of flame-resistance testing. The results showed that solid interaction forces can be formed between metakaoline and sodium silicate, resulting in a similar material to geopolymer with excellent physical properties. After high-temperature flame testing, a densely complex protective layer of carbon-char created on top of the robust silicon dioxide networks offers notable flame resistance. An optimal ratio in this inorganic intumescent coating contains sodium silicate—metakaoline (weight ratio = 9:1)—ammonium polyphosphate and pentaerythritol, aluminum hydroxide (3, 3, 10 wt.%)—expandable graphite (1 wt.%), which can create 4.7 times higher expansion ratio compared with neat sodium silicate matrix. The results of flame testing demonstrate only 387.1 °C and 506.3 °C on the back surface of steel substrate after one and three hours flaming (>1000 °C) on the other surface, respectively, which could meet the requirements according to the level of fire rating.
Highlights
As notable progress has been made in flame-retarding abilities in recent years, four types of flame-retarding materials or approaches have been developed, including flame quencher, heat absorber [1], intumescent flame retardance [2] and synergist [3,4]
Intumescent sodium silicate-based materials play a major role by improving the expansion ratio to inhibit thermal conduction and follow flaming, which is one of the key mechanisms for flame resistance
The flame-resistant abilities can be enhanced by the inorganic intumescent coating containing sodium silicate, metakaolin, ammonium polyphosphate, pentaerythritol, aluminum hydroxide and expandable graphite, which play individual roles as a ceramizable matrix, flame-retardant filler, heat-absorber and intumescence-improver, respectively
Summary
As notable progress has been made in flame-retarding abilities in recent years, four types of flame-retarding materials or approaches have been developed, including flame quencher, heat absorber [1], intumescent flame retardance [2] and synergist [3,4]. Intumescent flame retardance is one of the promising ways and effective methods of protecting substrate from fire damage. A number of organic intumescent materials related to flame retardancies [5,6,7,8,9,10,11] have been published. Inorganic counterparts are still rarely adopted as the flame-retarding materials, owing to the lack of understanding of the expansion properties of inorganic binder. Inorganic intumescent coatings [13], especially for silicate-based, have gradually emerged as a potential alternative discipline. Sodium silicate-based composite is broadly used in building construction, and can be synthesized through hydrolysis and condensation reactions to build ceramic
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