Evaluation of combustion characteristics for wood specimens coated with metal oxides of different oxidation states in the secondary stage of combustion (II)

Metal oxides were applied to cypress wood typically used as an interior building material. Combustion characteristics were evaluated focusing on the oxidation state of metal ions and char characteristics of the second stage of combustion. The burning properties of the materials were measured using a cone calorimeter (ISO 5660-1). The external heat flux was fixed at 50 kW/m². FeO, Fe₂O₃, SnO and SnO₂ were used as the metal oxides, and sodium silicate was mixed with increasing the flame-retardant effect. SnO₂SS was 1.05 times lower than the 164.76 kW/m² of the uncoated specimen. The other specimens increased 1.03–1.09 times. The peak smoke production rate of the wood specimens coated with flame retardant was 1.2–1.6 times lower than the uncoated specimens. SnO₂SS had the lowest value and showed a synergetic effect with SS. The CO/CO₂ ratio of the test specimens coated with the silicate compound was 1.6–2.3 times lower than that of the uncoated specimen. In SnO₂SS, HRR_{2nd_peak} and SPR_{2nd_peak} decreased because the generated heat was dispersed by convection because of pores in the char. This formed a relatively hard and heat-stable char structure.