Ablation mechanism of polymer layered silicate nanocomposite heat shield.
ABSTRACT Recent advances in polymer layered silicate nanocomposites especially improve flammability resistance; encourage the examination of this unique class of evolving materials as potential ablatives. Polymer layered silicate nanocomposites show excellent potential as ablative heat shields. Determining the thermal diffusivity together with the mass and energy transfer is an important problem encountered in design of heat shield system which pyrolyses and ablates at high temperature. The aim of this work is to give information on the influence of the experimental conditions to the estimated effective thermal diffusivity of ablative nanocomposite and composite materials. Here, we present the inverse solution to estimate the parameter used to identify the effective thermal diffusivity of resol type phenolic resin-asbestos cloth montmorillonite layered silicate nanocomposite and its composite counterpart. The experimental setup consists of a standard oxyacetylene flame test. The transient temperature measurements, taken from the top surface and through the thickness of the samples, are used in the inverse analysis to estimate the change of the effective thermal diffusivity. The results of this work clarify the mechanism of the ablation and thermal diffusivity of the layered silicate nanocomposite heat shields due to the high temperature degradation in comparison with its composite counterpart.
- SourceAvailable from: onlinelibrary.wiley.com[Show abstract] [Hide abstract]
ABSTRACT: The thermal stability and ablation properties of silicone rubber filled with silica (SiO2), aluminum silicate ceramic fiber (ASF), and acicular wollastonite (AW) were studied in this article. The morphology, composition, and ablation properties of the composite were analyzed after oxyacetylene torch tests. There were three different ceramic layers found in the ablated composite. In the porous ceramic layer, the rubber was decomposed, producing trimers, tetramers, and SiO2. ASF and part of AW still remained and formed a dense layer. The SiO2/SiC filaments in the ceramic layer reduced the permeability of oxygen, improving the ablation properties of the composites. The resultant ceramic layer was the densest, which acted as effective oxygen and heat barriers, and the achieved line ablation rate of the silicone composite were optimum at the proportion of 20 phr/40 phr (ASF/AW). Thermogravimetric analysis (TGA) confirmed that thermal stability of the composites was enhanced by the incorporation of ASF and AW. The formation of the ceramic layer was considered to be responsible for the enhancement of thermal stability and ablation properties. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39700.Journal of Applied Polymer Science 01/2014; 131(1). · 1.40 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: A large number of studies using cone calorimeter have shown that nanoparticles in even small quantities improve flammability resistance by reducing heat release and mass loss rate significantly. In recent years, nanoclay has been increasingly used as an alternative to traditional fire retardants to improve the strength and fire retardancy of polymeric materials. They have distinct advantages over traditional fillers in terms of production, amount of required additive of only 2-10% com-pared to 20-70%. The objectives of this work were the numerical and experimental evaluations of the flammability of the polymeric composite and nanocomposite materials under the external radiation heat flux. The theoretical modelling of mass loss and heat release rate based on conservation equations of mass and energy were then confirmed by the experimental data of cone calorimetry test. Running the computer programme and cone calorimeter, at 8×10 4 W/m 2 external radiation heat flux condition, there were lower heat release rate of 30-50% and a lower mass loss of 20-40% for nanocomposites in comparison with composite counterparts. Nanocomposite samples showed excellent potential as thermal protection system because upon pyrolysis, the organic-inorganic nanostructure in reinforcing the polymer can be converted into a uniform ceramic layer which may lead to significantly higher resistance to oxidation and mechanical erosion compared to simple composites. Formation of this ceramic layer on char formed from the pyrolysis of the nanocomposite at high temperature not only enhances the char mechanical strength, but also acts as secondary protection layer to protect the lower remaining nanocomposite.
- [Show abstract] [Hide abstract]
ABSTRACT: Elastomeric ablative composites for ultrahigh temperature applications were processed and characterized to elucidate the potential of short carbon fibers (SCF) to tailor the thermo-mechanical and ablation characteristics of acrylonitrile butadiene rubber (NBR) composites. SCF was dispersed within NBR using dispersion kneader and two roller mixing mill. Ablation and thermal properties versus back-face temperature elevation during oxy-acetylene flame test, linear/radial ablation rates, percent char yields, insulation index, and thermal conductivity of the fabricated ablatives were measured. Experimental results revealed that the thermo-mechanical and ablation characteristics were significantly improved with increasing SCF concentration in the presence of coupling agent. Improvement in tensile strength, hardness and reduction in elongation at break were obtained with increasing SCF to matrix ratio. The microscopic analysis of the tensile fracture and ablation specimen showed the porosity generation during ablation and uniform dispersion of the impregnated SCF in NBR.Polymer Degradation and Stability 12/2014; 110:195–202. · 2.63 Impact Factor