混合粉体の充てんと反応速度

抄録

(1) Compacting effects on the reaction rate of mixed powders were studied. The effects of the apparent density, shape, specific surface area of compact, and of the particle-size of the starting materials were examined. The reaction employed for the study was the formation of thorium carbide, as follows.
1) Thorium metal+Carbon→Thorium carbide. (Addition reaction)
2) Thorium oxide+Carbon→Thorium carbide. (Exchange reaction with degassing)
(2) The reactants were mixed to less than 0.2wt% standard deviation of C/ThO₂ for the five sampling. Then, “tablet” compacts 1.25cm in diameter and weighing approximately 1.0g were produced under different pressures respectively. Moreover to study the shape effect, the compacts 0.63cm in diameter with different densities were formed.
All the compacts having different densities were placed in a graphite crucible and heated to the specified temperature in a vacuum of 10^-4mmHg. The degree of reaction was measured as the percentage of reacted thorium to total thorium.
(3)-1 The effect of the apparent density: On the addition reaction, the reaction rate increased with the density of the compacts nearly in all of its range. However, this increase in the reaction rate became saturated beyond a certain value in the range. It was considered that the saturation was caused by the disappearance of active points in the compact.
On the other hand, the reaction rate of the exchange reaction with degassing showed a minimum value at a certain value of compacting density.
(3)-2 The shape effect of the compacts: This effect on the reaction rate was also observed. On the exchange reaction, the minimum value of reaction rate shifted to the lower density side for the cylindrical group than that of the tablet group. This was thought to have been caused by the difference of density distribution in the compacts.
(3)-3 The effect of the particle-sizes of the starting materials: This effect on the reaction rate depended on the shape of the particle. The particle having a granular form had a size effect on the reaction rate, but this effect was not observed in the particle with a flaky form, such as graphite powder, possibly due to the layer arrangement of flaky particles in the compact.
(3)-4 The effect of the specific surface area of the compacts: This effect on the reaction rate was observed in the exchange reaction with degassing.
(4) For the study of the chemical kinetics for pressed mixture it was necessary to keep constant the apparent density, shape and size of the compacts. Unless this constancy was maintained it was not possible to obtain accurate activation energy for the reaction.