Chosen thermal properties of polymer ablative composites
Wojciech Kucharczyk, Tadeusz Opara, Przemysław Kula
Quarterly No. 2, 2009 pages 170-174
DOI:
keywords: ablative shields and coats, polymer composites, high-melting fillers, thermo-protective materials
abstract The term „ablation” refers to the transport of heat and mass on surface of a body by thermochemical and mechanical processes. There are many applications involving ablation. At present polymer ablative composites are more and more often used to create thermo-protective systems in various applications. They should be used due the fire protection of modern build-ing constructions, in tunnelling designing and as thermo protective systems of electronic, optic and magnetic memories of digi-tal data. The ablative composites have the better thermo-protective properties when the components have: high specific heat cp(t), high density , and small thermal conductivity (t), so small thermal diffusivity (t) too. This paper reports results of studies on chosen thermal and ablative properties of polymer shields made of phenolic- of formaldehyde matrix or coats with epoxy matrix with high-melting and high-density powder fillers. Silicate carbon SiC, aluminium oxide Al2O3, solid solution WCTiC and tungsten powders W were used to prepare composite specimens. There were presented typical ablative properties of polymer composite under intensive heat flow: average rate of ablation va, the mass waste Ua and the back side temperature of specimen ts, as well as the research results of thermal stability analysed by thermo gravimetric analysis TG and thermal degradation of composite structure by differential thermal analysis DTA. One represented also the results of measurements in Perkin Elmer microcalorimeter of specific heat cp(t) as a function of tempera-ture. Phenolic- of formaldehyde composites have worse typical thermo-protective ablation properties: bigger average linear rate of ablation va and higher back side temperature of specimen ts, but they have smaller mass waste Ua than epoxies. F-F8 composites also has lower specific heat cp(t) than epoxy E8 (in dependence from temperature - from 36 to 52%). However it F-F8 has better thermal stability expressed: 3 times narrower range of changes of specific heat cp(t); over 3 times higher tempera-ture of thermal degradation, as well as over 3.5 times smaller mass waste during degradation processes, and those with con-necting of small mass waste Ua are essential guilds in the case of autonomous shields.