Exposure of hydrocarbon intumescent coatings to the UL1709 heating curve and furnace rheology: Effects of zinc borate on char properties

Hydrocarbon intumescent coatings are an efficient means to passive fire protection of steel structures in high-risk environments such as petrochemical plants and offshore platforms. In the present study, the effects of zinc borate on the performance of hydrocarbon intumescent coatings were investigated. The analyses include steel temperature-time relationships and char expansion, as well as structural investigations and compositional profiles of the char. Furthermore, transient rheological coating behaviors and thermal degradation of the coatings were measured and analyzed. Results of furnace experiments, conducted under a standard hydrocarbon fire curve (UL1709), showed that a formulation containing 15 wt.% zinc borate gave the best performance. Fully expanded char measurements and the associated rheological recordings, evidenced that adjusting the zinc borate content from 0 to 20 wt.% increased the dynamic viscosity minimum of the incipient char from 6.2 to 5671.4 Pa·s. The increased dynamic viscosity resulted in a more uniform, but less expanded char layer. Compositional profiles of intumescent chars, measured using X-ray Diffraction, showed an increasing phosphate (especially BPO4) content with increasing levels of zinc borate in the intumescent coatings. Finally, the thermogravimetric analyses revealed that zinc borate can help to reduce epoxy binder degradation and oxidation of the carbon-inorganic residue. Due to the health risks associated with borate and its compounds, there is a requirement to find alternatives. The present work has mapped out some of the beneficial properties of zinc borate, and the results may provide some insight as to how to formulate without these compounds in the future.