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Highly Porous Expanded Graphite: Thermal Shock vs. Programmable Heating.

ABSTRACT: Highly porous expanded graphite was synthesized by the programmable heating technique using heating with a constant rate (20 °C/min) from room temperature to 400-700 °C. The samples obtained were analyzed by scanning electron microscopy, energy-dispersive spectroscopy, low-temperature nitrogen adsorption, X-ray photoelectron spectroscopy, Raman spectroscopy, thermogravimetry, and differential scanning calorimetry. A comparison between programmable heating and thermal shock as methods of producing expanded graphite showed efficiency of the first one at a temperature 400 °C, and the surface area reached 699 and 184 m2/g, respectively. The proposed technique made it possible to obtain a relatively higher yield of expanded graphite (78-90%) from intercalated graphite. The experiments showed the advantages of programmable heating in terms of its flexibility and the possibility to manage the textural properties, yield, disorder degree, and bulk density of expanded graphite.

SUBMITTER: Bannov AG

PROVIDER: S-EPMC8708924 | biostudies-literature | 2021 Dec

REPOSITORIES: biostudies-literature

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Highly Porous Expanded Graphite: Thermal Shock vs. Programmable Heating.

Bannov Alexander G AG Ukhina Arina V AV Maksimovskii Evgenii A EA Prosanov Igor Yu IY Shestakov Artyom A AA Lapekin Nikita I NI Lazarenko Nikita S NS Kurmashov Pavel B PB Popov Maksim V MV

Materials (Basel, Switzerland) 20211213 24

Highly porous expanded graphite was synthesized by the programmable heating technique using heating with a constant rate (20 °C/min) from room temperature to 400-700 °C. The samples obtained were analyzed by scanning electron microscopy, energy-dispersive spectroscopy, low-temperature nitrogen adsorption, X-ray photoelectron spectroscopy, Raman spectroscopy, thermogravimetry, and differential scanning calorimetry. A comparison between programmable heating and thermal shock as methods of producin ...[more]

PMID: 34947281

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Project description:This article introduces an innovative approach to the investigation of the conductive-radiative heat transfer mechanism in expanded polystyrene (EPS) thermal insulation at negligible convection. Closed-cell EPS foam (bulk density 14-17 kg·m-3) in the form of panels (of thickness 0.02-0.18 m) was tested with 1-15 µm graphite microparticles (GMP) at two different industrial concentrations (up to 4.3% of the EPS mass). A heat flow meter (HFM) was found to be precise enough to observe all thermal effects under study: the dependence of the total thermal conductivity on thickness, density, and GMP content, as well as the thermal resistance relative gain. An alternative explanation of the total thermal conductivity "thickness effect" is proposed. The conductive-radiative components of the total thermal conductivity were separated, by comparing measured (with and without Al-foil) and simulated (i.e., calculated based on data reported in the literature) results. This helps to elucidate why a small addition of GMP (below 4.3%) forces such an evident drop in total thermal conductivity, down to 0.03 W·m-1·K-1. As proposed, a physical cause is related to the change in mechanism of the heat transfer by conduction and radiation. The main accomplishment is discovering that the change forced by GMP in the polymer matrix thermal conduction may dominate the radiation change. Hence, the matrix conduction component change is considered to be the major cause of the observed drop in total thermal conductivity of EPS insulation. At the microscopic level of the molecules or chains (e.g., in polymers), significant differences observed in the intensity of Raman spectra and in the glass transition temperature increase on differential scanning calorimetry(DSC) thermograms, when comparing EPS foam with and without GMP, complementarily support the above statement. An additional practical achievement is finding the maximum thickness at which one may reduce the "grey" EPS insulating layer, with respect to "dotted" EPS at a required level of thermal resistance. In the case of the thickest (0.30 m) panels for a passive building, above 18% of thickness reduction is found to be possible.

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Highly Porous Expanded Graphite: Thermal Shock vs. Programmable Heating.

Publications

Highly Porous Expanded Graphite: Thermal Shock vs. Programmable Heating.

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