The preparation and property analysis of B4C modified inorganic amorphous aluminum phosphates-based intumescent flame retardant coating

[Display omitted] •An inorganic amorphous aluminum phosphate emulsion was applied as intumescent coating matrix.•The addition of B4C effectively improve the porous structure and increase the ablation resistance.•The backside temperature was controlled below 140℃ in 1 h, 33.4 % lower than blank coating.•The smoke density was only 64.73 %, 36.3 % lower than that of blank coating.•After combustion, the thickness of coating expanded about 5.8 times. In response to high environmental requirements, an incombustible inorganic intumescent flame retardant coating was prepared from amorphous aluminum phosphate emulsion as the matrix, with boron carbide as the modifier. The influence of boron carbide (B4C)on the fire resistance performance and physic-chemical properties of coatings were studied by means of large panel combustion method, smoke density test, Fourier transformed infra-red analysis (FTIR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), specific surface area (BET method) and pore size analysis. With the addition of 0.75 wt% B4C, the backside temperature of APB3 coating (aluminum phosphate-based coating modified with 0.75 wt% B4C) after an hour was only 140 ℃, 33.4 % lower than that of blank APB0 coating. And the smoke density (Ds) of APB3 was only 64.73 %, 36.3 % lower than that of blank APB0. The foaming expansion caused by decomposition reactions, the structural improvement caused by boron carbide oxidation, and the formation of ablative resistant ceramics and glass were the main reasons for excellent flame retardant and thermal insulation performance. Remarkably, the melting B2O3 generated from the oxidation of B4C could repair cracks, modify pore structure, improve the integrity of closed pores, increase the specific surface area of porous structure, and promote the formation of borosilicate glass. Due to the structural integrity of the outermost coating surface caused by the oxidation of B4C and the construction of borosilicate glass, much gas was shielded inside the coating, making the coating more eco-friendly. Besides, APB3 coating has good water resistance. After immersion in water for 360 h, the reduction rate of fire resistance performance of the coating was only 17.1 %. This work provides theoretical guidance for broadening the types of intumescent coatings and promotes the development of inorganic green coatings.