Effect of activated carbon particle size on the thermo-foaming of aqueous sucrose resin and properties of the carbon foa
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The carbon foams prepared by the thermo-foaming of dispersions of activated carbon (AC) powder of various average particle sizes (4.9 to 15 lm) in an aqueous sucrose resin were characterized. The stability of the wet foams increased with the decrease in the AC particle size as finer particles preferentially adsorbed on the air–resin interface. The particle agglomeration leading to the foam collapse was observed at lower AC powder to sucrose weight ratios with the finer powders. The cell size (0.33–2.34 mm), foam density (0.1151–0.2281 g/cm3), and compressive strength (0.16–2.77 MPa) of the carbon foams depend on the AC particle size as well as the AC powder to sucrose weight ratio. The thermal conductivity of the carbon foams (0.036–0.049 W m 1 K 1) was much lower than that of the vitreous carbon foams of similar densities. The foams were fire resistant and amenable to machining with the conventional machines and tool.
I. INTRODUCTION
The carbon foam is one of the advanced carbon materials which find a lot of applications in various fields due to its combined properties of carbon and cellular structure.1–11 Due to the environmental concerns and fast depletion of the fossil fuels, there is a robust attraction in the preparation of carbon materials from the natural renewable precursors. The renewable resources like tannin, sucrose, and olive stone have recently gained attention against the current precursors such as synthetic organic polymers, petroleum- and coal tar pitch for the preparation of carbon foams.12–16 Though sucrose is a widely available agricultural product, the carbon foams prepared by foaming aqueous sucrose resin and molten sucrose had low density and compressive strength due to the low carbon yield of sucrose.12,13,16 Recently, we have reported the preparation of carbon foam with improved compressive strength by the thermo-foaming of activated carbon (AC) powder dispersions in an aqueous sucrose resin.17 The AC particles incorporated in the sucrose resin not only increased the carbon content but also retarded the –OH to –OH condensation.13 Further, the AC particles assisted the foaming of low viscous sucrose resins by stabilizing the bubbles by adsorbing on the air– liquid interface.17 The foam stabilization by particles depends on the wetting characteristics of the powder.18–26 It is well known that the wetting of a powder with a liquid depends on the particle size.19,20,22 In the present work,
a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2014.294 46
J. Mater. Res., Vol. 30, No. 1, Jan 14, 2015
http://journals.cambridge.org
Downloaded: 15 Mar 2015
we have investigated the effect of the AC particle size on the foaming characteristics of aqueous sucrose resin and the properties such as density, cell size, compressive strength, thermal conductivity, fire resistance, and machinability of the carbon foams. II. EXPERIMENTAL A. Preparation of carbon foams
Sucrose, nitric acid, AC powder, and acetone used in this study were of analytical reagent grade and pr
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