Naoto Ohta

Elasto-plastic deformation of glass-like carbons heat-treated at different temperatures

Nano-indentation of glass-like carbons (GCs) heat-treated at different temperatures was carried out with a 3 μm radius spherical tipped indenter. The effect of crystal structure and micro-texture on elastic and elasto-plastic deformation resulting from the indentation was observed. The elastic modulus and yield stress of GCs was found to reduce with elevation of heat treatment temperature (HTT). The power law fitting constant k for the elasto-plastic deformation of the loading stress–strain curves by the indentation and the indentation elasticity index k/E* reduced with development of the graphitic structure of GC, so that ‘elasticity’ of GC decreased with the elevation of HTT of GCs. Hysteresis loops were observed on the indentation force–displacement curve during the loading–unloading cycle. Hysteresis energy loss, which corresponds to the area of the hysteresis loops, increased with the elevation of HTT for the same terminal load. The indentation ductility index D, the ratio of hysteresis energy loss to total indentation energy, was linearly dependent on indentation elasto-plastic deformation strain eep. The indentation elasto-plastic modulus m, which is obtained from the slope of the plots of D versus eep, reduced with the elevation of HTT of GCs. From the reduction of m, it was concluded that ‘plasticity’ (or ‘ductility’) of GC increased with the elevation of HTT of GCs.

Preparation of microporous carbon foams for adsorption/desorption of water vapor in ambient air

Microporous carbon foams were prepared from a fluorinated polyimide using melamine foam as a template. The adsorption/desorption behavior of water vapor in ambient air was examined. The activation of carbon foams at 400℃ for 1h in air was found to be effective in increasing the adsorptivity of water vapor. The amount of water vapor adsorbed after air activation was almost 3 times as large as that before activation, although the micropore volume increase was only 1.5 times. The reversible adsorptivity for water vapor in ambient air showed a linear dependence on micropore volume with an adsorptivity of about 40% mass fraction for a micropore volume of 0.75mL/g.

Water Vapour Adsorption of Microporous Carbon Films Prepared from Fluorinated Aromatic Polyimides

The adsorption of water vapour onto microporous carbon films derived from fluorinated aromatic polyimides was studied at 25°C over the relative pressure range 0–0.95. The carbon films prepared were microporous with a high micropore volume ranging up to 0.44 ml/g and a sharp pore-width distribution at ca. 0.6 nm. The adsorption/desorption isotherm of water vapour onto the carbon films was of type V with slight hysteresis. The carbon films derived from fluorinated polyimides were found to exhibit a much higher water vapour adsorption at low relative pressure regions relative to commercially available activated carbon fibres, with their saturated adsorption capacities being dependent on their micropore volumes. The microporous carbon derived from the polyimide with the highest fluorine content (31.3 mass%) showed the highest saturated adsorption capacity of ca. 465 mg/g, with 90 mass% of the water vapour being adsorbed at a relative pressure below 0.46. Both the high micropore volume and the high water vapour adsorption were maintained even after heat treatment at 1300°C, although the steep uptake of water vapour was shifted to higher relative pressures to some extent.