Abstract
We investigated the humidity control capacity of charcoals from wood carbonized at 500, 700 and 900°C. As an index of the capacity, we adopted the slope (B) of the linear equation approximating the relationship between logarithm of relative humidity and temperature in a closed steel box (volume : V = 0.0197 m3) containing charcoal (weight : W kg). The value of B of charcoal blocks was affected by the period of temperature change, while that of charcoal grains (5.5∼8.0 mm) was independent of the period and comparable to that of activated carbon or wood powder. There was no significant difference in the capacity between charcoals carbonized at 500 and 700°C. However, the capacity of charcoals carbonized at 900°C was slightly inferior to that of charcoals carbonized at 500 and 700°C. Charcoal capacity was much inferior to that of silica gels when used for humidity conditioning in repositories of museums below a W/V value of 0.5 kg/m3 as recommended by the silica gel maker. However, above a W/V value of 1.0 kg/m3, there is only a small difference in capacity between charcoal and silica gel. In silica gels, differences in wave shape of temperature changes had no recognizable effect on the value of B. The quantity of absorbed or desorbed moisture per unit weight of material was abruptly increased by decreasing W/V, especially in silica gels. However, at W/V greater than 1.5 kg/m3, it showed almost the same value of 1∼2 g/kg regardless of the material.
