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A water-based fire resistive nano-coating was prepared via adding CaAlCO 3 -layered double hydroxides (CaAlCO 3 -LDHs) as an inorganic filler to intumescent fire retardant coating. The influence of CaAlCO 3 -LDHs on the coatings properties was investigated by thermogravimetry (TG), differential thermal analysis (DTA), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), cone calorimeter (CONE) and fire performance test. The results showed that CaAlCO 3 -LDHs could improve the quality of the residual char layer, increase the degree of the cross-linking and the carbon accumulation, and enhance the oxidation resistance of the char layer. The addition of 5 mass% CaAlCO 3 -LDHs to the coating could reduce the fire hazards of the coating itself, lower the rate of flame propagation and thermal degradation, and improve the char structure and fire resistance of the coating, which was attributed to the synergistic effect of CaAlCO 3 -LDHs and the intumescent fire retardant (APP/PER/MEL). [ABSTRACT FROM AUTHOR]

Development of effective methods for quantificationally characterizing the thermal resistance of the intumescent char layer of fired fire-retardant coating is of interest in many academic researches and industrial applications. In this work, a novel approach is proposed to calculate the thermal resistance of the intumescent char layer produced after the ultra-thin fire-retardant coating exposed to fire. A correlation was established based on the relative thermal resistance of the char layer to that of steel plate and the surface temperature at the back of the coated steel plate under steady-state heat transfer. The thermal resistance of the steel plate was obtained about 0.009 K·m2·W−1 by calculating the heat flux based on the radiation heat exchange involving three-surface enclosure model (flame, steel, and wall). The thermal resistances of the char layers without and with the layered double hydroxide (LDH) were 0.011 K·m2·W−1 and 0.013 K·m2·W−1, respectively. The results show that the external roughness and internal honeycomb structure can increase both the conductivity and the convective thermal resistances of the char layer to protect the steel structures. The porosity of the char layer is between 0.15 and 0.18, and its thermal conductivity is between 0.4 and 0.8 W·m−1·K−1 in the process of fire. Unlabelled Image • A novel method is proposed to calculate thermal resistance of intumescent char layer. • Thermal resistance is used to evaluate heat-shielding performance of char layer. • LDH improves external roughness and internal honeycomb structure of char layer. • Porosity of char layers is obtained to be 0.15–0.18 via SEM images processing. • Thermal conductivity of char layers is 0.4–0.8 W·m−1·K−1 in the process fire. [ABSTRACT FROM AUTHOR]

• Addition of MgAlCO 3 -LDHs and CaAlCO 3 -LDHs improved thermal insulation of IFR coating. • Metal ions from LDHs were chelated with carbon materials to form 3D reticular char. • LDHs can delay oxidation and improve degradation performance of char layers. MgAlCO 3 -layered double hydroxides (LDHs) and CaAlCO 3 -LDHs were respectively added as a synergistic agent to intumescent fire retardant (IFR) coatings. The 2.4 wt% of MgAlCO 3 -LDHs and the 6.7 wt% of CaAlCO 3 -LDHs were found to possess the best thermal insulation according to the fire performance tests. Further characterization by a cone calorimeter shows that the MgAlCO 3 -LDHs are superior to decreasing the specific extinction area of IFR coating, and the CaAlCO 3 -LDHs are advantageous in some other properties such as heat release rate, effective heat combustion and total heat release. Moreover, the X-ray diffraction (XRD) results infer that the flame retardant of char layer is primarily dependent on the amorphous structure formed after exposure to fire, the X-ray photoelectron spectroscopy (XPS) measurements of O 1s , C 1s , P 2p and N 1s reveal that the LDHs fillers suppress the oxidation of the IFR coating, and the Fourier transform infrared spectroscopy (FTIR) tests demonstrate that the LDHs protect the bridge frame structures. It is concluded that the LDHs can prevent the degradation and improve the thermal insulation of IFR coatings. [ABSTRACT FROM AUTHOR]

• An analysis method for SEM images of intumescent fire retardant char layers is proposed. • Foams in an intumescent fire retardant char layer are characterized quantificationally. • Appropriate addition of CaAlCO 3 -LDHs makes the char layer compact and uniform. • Unsatisfactory result image after color transformation is returned to object segmentation. A new characterization method is proposed to investigate the microscopic morphology of intumescent fire retardant (IFR) char layer observed under a scanning electron microscope (SEM). The method consists of object segmentation extracting the object, color transformation improving the recognition of subtle details, and statistical analysis obtaining the features (area, average, and standard deviation) of the object in the SEM images. There is a descending trend in the standard deviation of the foams with the increase of CaAlCO 3 -LDHs (layered double hydroxides) added to the coatings. Specifically, the number of the foams in the IFR coating with 5 wt% of CaAlCO 3 -LDHs addition is increased from 102 (that of the char layer without CaAlCO 3 -LDHs) to 123. Meanwhile, the standard deviation of the foams in the char layer is decreased from 6383.6 to 4304.5, demonstrating that an appropriate addition of CaAlCO 3 -LDHs can improve the foam quality of the IFR coating by making it more compact and uniform, and enhance the thermal insulation of the char layer covered on the substrate surface. [ABSTRACT FROM AUTHOR]