Studies of the Physical Aspects of Intumescence Using Advanced Diagnostic Methods

Commercial testing of Intumescent paints can be extremely expensive. There is a need to develop lab scale systems that can cost effectively both study and test intumescent paints under conditions that are closer to commercial and real time fire tests. This research aims to present a strong case for using an impinging flame based rig to test intumescent coatings. The main feature of using flame impingement is the heterogeneous absorption of heat along the wall surface. This property is a great advantage because intumescent paints under complex fire conditions can be simulated more realistically. The heating technique is coupled with advance diagnostics methods to highlight behaviour that has not been observed before. Physical aspects of commercial coatings, under the new setup, are compared to the cone calorimeter – traditional testing setup
The process of intumescence was observed through the use of diagnostic techniques such as Schlieren, thermal and digital imaging. Cross sectional area and surface textures were captured using digital images of fully intumesced char samples that revealed distinct internal structures and surface textures. Temperature of the substrate, Tb, was recorded using a thermocouple attached to the back surface of the panel under different heating conditions.
Schlieren technique, based on the refraction of light phenomenon, has never been use to examine the physical aspects of intumescence. It helped highlight the interaction between the flame and paint surface. The impingement of non-reactive fuel, at low separations was clearly visible and was responsible for influencing mode shape of the resulting char. The expulsions phenomenon observed using this technique has not been visually observed before. It occurred during the pustule appearance phase offering conclusive evidence that invisible gases escape from the surface of the paint. The measurement of char expansion and its rate of growth whilst engulfed in luminous diffusion flames is a methodology developed using this technique. The results revealed that formulations tested had unique expansion behaviours and growth pattern. Furthermore, an expansion activation temperature (EAT) range with respect to substrate temperature was identified for each formulation, which was found to be consistent under a variety of experimental conditions.
The distinctive yellow colour of a diffusion flames engulfs a coating during a test. Due to this, the process of intumescence has not been observed visually. Thermal imaging was used in this study because it allowed the user to bypass the flame and observe intumescence as it occurred.
Using thermal imaging, the physical aspects of intumescence were studied in extensive detail and salient characteristics were identified. The appearance of surface pustules followed by majority of the expansion were characterised as the two distinct phases in the intumescence process. Analysis of the surface temperature revealed that the thermal profile of the surface was non-uniform and highly localized in nature. This was attributed to the higher temperature of the pustules relative to the paint surface. Results from thermal imaging combined well with the Schlieren technique to develop a coherent understanding of the expansion process.
Diagnostic equipment, particularly thermal and digital imaging, were also used on tests conducted in a cone calorimeter. The results between cone heater and impinging flame-based tests were compared. The degree of intumescence, surface temperature profile and various characteristics were found to be different between both methods.
Finally, the use of the techniques was extended to study the process of intumescence and complex char growth patterns on T-shaped panels coated with intumescent formulations. Char growth was observed to be complex and non-linear as compared to flat panel systems. A novel Image processing algorithm using the thermal imaging data from the cone calorimeter was developed marking a further advancement to the use of this technique and gain insight into the growth mechanism when examining a complicated three dimensional system such T-panels.