Synergistic effects of tubular halloysite clay and zirconium phosphate on thermal behavior of intumescent coating for structural steel

Zirconium phosphate (ZrP) recently introduced in intumescent fire protective coating has shown improvement in developing ceramic layer. The tubular halloysite clay (THC) due to its unique molecular structure can be combined with ZrP to enhance fire resistance by developing a strong silica network on the char surface. This study is aimed to investigate the synergistic effects of tubular halloysite clay and zirconium phosphate fillers to improve the thermal performance of the intumescent coating. The control coating formulation and a range of coating formulations using a combination of weight percentage of THC and ZrP were developed to study the influences of fillers on fire performance. The char expansion and fire resistance tests of the coatings were conducted using furnace fire test and Lab scale fire jet. Thermal stability of the coating was determined by TGA and char was characterized by FESEM, XRD, FTIR and XPS. Water-resistance test of the coating was performed according to ASTM D-870. Results showed that the reinforcement of THC-ZrP showed promising improvement on the performance of IFC and substrate temperature was far below the critical temperature, 550 °C. Sample HZ 5 showed the least backside steel substrate temperature of 219 °C. Expansion rate of char was found reduced with the addition of THC but improved the char compactness. The addition of THC and ZrP in IFC improved 18% fire resistance performance and 5% residual wt. Of char. Char morphology showed silica network, XRD and FTIR confirmed the presence of silicon. Water absorption test showed 95% less water absorption (HZ-5) compared to control coating. Post water immersion, fire test showed 7% increase in substrate temperature which is 18% less than control coating after water immersion fire test.