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Organisationseinheit der BAM
Revealing the inner secrets of intumescent chars by advanced small scale tests combined with µ-CT
(2015)
Testing of intumescent coatings for Steel is usually done in intermediate scale or even full scale experiments and is hence quite expensive. We developed two complementary small scale tests, simulating fully developed Tire. First is a strongly modified electrical muffle furnace, which is now able to follow the Standard temperature-time curve (according EN 1363-1) for 90 min in a very accurate manner. Düring the experiment backside temperatures are recorded and the growth of the char is observed with a custom made high temperature endoscope. Second is a testing apparatus based on a propane-oxygen-bumer for direct severe flame impingement of coated samples, reaching temperatures far above 1500 °C.
Our small scale samples are coated Steel plates of a size of 75 x 75 x 2 mm3. The structure-propertyrelation between additives, thermal properties and morphology of the char were examined using a well determined series of samples consisting of basic composition mixed with different additives. With the burner-testing-apparatus we studied the behavior of a high performance coating, which shows a transformation of the carbonaceous char into a ceramic foam at temperatures as high as 1600 °C. Nondestructive micro-computed tomography was used to characterize the morphology of the char. According to the structure of the foams we used different analytic methods like cell-detection or wallthickness-analysis. Additional scanning electron and optical microscopy were performed. The combination of the CT-data with the measured backside temperatures of the different samples provides us a deep understanding of the interaction between isolating properties and morphology of intumescent chars.
The pyrolysis and the fire behaviour of PC/ABS containing various aryl phosphates and their combinations with aluminium hydroxide oxide, talc and zinc borate were investigated. Main interest was focused on the flame retardant effect and mechanism of aryl phosphates (e.g. BDP) in PC/ABS, especially in combination with the other additives. Therefore the thermal and thermo oxidative decomposition was characterised by the means of thermogravimetry analysis and thermogravimetry coupled with infrared Fourier transform spectroscopy (TG-FTIR). The results were verified with further methods, e.g. pyrolysis-gaschromatography/mass spectroscopy (Py-GC/MS). Kinetic analysis and evolved gas analysis were used to study the pyrolysis mechanisms and to expose existent synergisms in the combined systems. The fire behaviour was investigated by cone calorimeter. The flammability was determined by LOI and UL 94. The chemical compositions of the residues were also examined.
The exploration of condensed phase mechanisms such as charring and intumescence has been pushed forward in the last decades, since it is believed that focusing on these concepts will bring materials closer to an efficient and ecologically friendly fire retardancy. They promise to concentrate efficient fire retardancy at the key position between pyrolysis zone and gas phase. Examples of residue/char forming and intumescent materials are used to illustrate the influence of mass and heat barrier effects on the fire behavior of materials and general results are presented. A comprehensive understanding of the mechanisms and structure-property relationships in fire retardancy is presented.