Ablation mechanism of polymer layered silicate nanocomposite heat shield

Polymer Engineering Group, Chemical Engineering Department, Faculty of Engineering, Tarbiat Modares University, P.O. Box 14115-143, Tehran, Islamic Republic of Iran.
Journal of hazardous materials (Impact Factor: 4.53). 12/2008; 166(1):445-54. DOI: 10.1016/j.jhazmat.2008.11.061
Source: PubMed


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.

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Available from: A. R. Bahramian, Nov 11, 2015
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    • "Ahmad et al. [12] manufactured Asbestos/phenolic composites with nano clay particles as filler. Oxyacetylene test revealed that the addition of nano clay improved the thermal stability of the filled composites. "
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    ABSTRACT: Cenosphere filled ceramic/phenolic composites were prepared and their thermal, thermo oxidation and ablative behavior were studied by Thermogravimetric Analysis (TGA) and oxyacetylene ablation test. Classical thermal stability parameters, based on initial decomposition temperature and mass loss at various temperatures were calculated before and after subtraction of cenosphere content from the TGA curves. The result shows that the thermal stability of the filled composites seems to be improved and reduction of mass loss was achieved with addition of cenosphere. The characteristic temperature differences (ΔT) were calculated from TGA curves to study the effect of cenosphere on thermo oxidation behavior of the filled composites. Ablation parameters such as linear ablation rate, mass ablation rate and back face temperature profiles were investigated. Ablation results showed that the addition of cenosphere content exhibits the favorable ablation resistance.
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    • "In contrast to conventional composites containing micron-scaled reinforcements, Nanocomposite Rocket Ablative Materials (NRAMs) [11] are nanocomposites particularly designed to work in severe hyperthermal environments. Layered Silicates (LSs) [10] [12] as well as nanosilica [13] [14] [15] have been successfully used in nanostructured ablatives leading to improved ablation resistance. Among the nano-additives, nanosized carbon fillers play an important role in both traditional as well as nanostructured ablative materials: in fact, well before the appearance of the term nanocomposite, carbon black (CB) was widely employed in the production of ablators. "
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    ABSTRACT: In this work, we investigated the ablative properties of two carbon nanofiller-based composites. In particular, carbon black (CB) and multi-walled carbon nanotubes (MWNTs) were used to produce highly loaded (50wt%) phenolic composites. The thermal properties and the ablative response of the composites were studied through the pre and post-burning morphology of the burnt surfaces and an evaluation of the in-depth temperature profiles. When compared to the CB-based counterpart, the MWNT-based composite exhibited a higher thermal diffusivity and an erosion rate that was exactly localized above the flame plume. The CB-based system showed a thin charred region whilst the MWNT-based was characterized by a thick and wide pyrolyzed zone.
    Full-text · Article · Jan 2012 · Composites Part A Applied Science and Manufacturing
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    • "These research results encouraged the examination of these evolving materials as potential ablatives. Bahramian et al. [15] [16], studied the ablative performance and ablation mechanisms of thermoset resin/layered silicate nanocomposites. Vaia et al. [17], discussed the PA6/layered silicate nanocomposites as high performance ablative materials. "
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    ABSTRACT: The ablative properties of hydrogenated nitrile butadiene rubber (HNBR) composites filled with fumed silica, organically modified montmorillonite (OMMT), or expanded graphite (EG) were examined. The HNBR/OMMT composite has the lowest linear ablation rate and the highest mass ablation rate and does not tend to be carbonized. On the other hand, the HNBR/EG composite has the highest linear ablation rate and the lowest mass ablation rate, and is prone to carbonization. The ablative properties of the HNBR/silica composite are between those of HNBR/OMMT and HNBR/EG. From the viewpoint of thermal shielding capability, the HNBR/OMMT has the best ablation resistance. Thermogravimetric analysis (TGA) on different HNBR composites indicated that the filler type has no significant effect on the thermal stability of the composites. To understand the ablation mechanisms, the char layers of different HNBR composites after ablation experiments were characterized by scanning electron microscopy (SEM), energy disperse X-ray spectroscopy (EDS), and wide-angle X-ray diffraction (WAXD). The results showed that the porosity in the char layers of the HNBR/OMMT composite was the highest and the corresponding structure was the loosest of the three composites. The montmorillonite (MMT) dispersed in HNBR experienced phase transition, melting and vaporization when exposed to the flame with the temperature over 2000 °C. Fumed silica only melted at such situation. On the other hand, the EG kept their original crystalline structures after the ablation test. Based on these results, the effect of the filler type on the ablation mechanisms of the HNBR composites was discussed.
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