Abstract. In this study, starting mixed wet powders were uniaxially compressed at 200 MPa for 40 min and simultaneously heated at 200 °C to form hardened bodies. Three different starting slurries composed of 100 g of fly ash powders with particles of different sizes after grinding treatment, 15 g of reagent-grade sodium, and 33.3 g of fresh water were considered. In this time, the uniaxial pressure was fixed at 200 MPa. This method is called the warm press method because the heating temperature is not as high as that in the conventional hot press sintering method used for ceramics. When ground fly ash with a diameter of 6.8 μm was used, the average compressive strength of the hardened bodies reached approximately 120 MPa. As the heating temperature and duration were increased at the fixed uniaxial pressure of 200 MPa, the compressive strength of the geopolymers increased. When ground fly ash with a diameter of 6.8 μm was used and the heating temperature and duration were 280 °C and 60 min, respectively, the compressive strength of the geopolymers reached approximately 150 MPa.

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An experimental system was developed for the physisorption study of hydrogen at substrate temperatures between 1.8 K and 10 K and at pressures down to 10-10 Pa. The vaccum system was separated into two rooms by a bulkhead ; the upper chamber contained a cryostat equipped with a 4 K mechanical refrigerator and the lower one a substrate kept in an extremely high vacuum. Helium was liquefied at the refrigerator in the upper chamber and was stored in a pot in the lower one. The substrate was directly attached to the helium pot. The substrate temperature was controlled with an accuracy of 0.1 K by a heater located in the helium pot. The adsorption density of hydrogen physisorbed on the copper surface was measured with use of the electron stimulated desorption method. The mean residence time of hydrogen was directly determined by applying this technique to the transient state of adsorption. The adsorption isotherms were obtained by monitoring the hydrogen ion yield as a function of the pressure in the adsorption equilibrium state.