Relation between generation rate and specific surface area of ultrafine metal particles produced by the Ar-H-2 arc plasma method

The relation between the generation rate and specific surface area of ultra fine particles (UFPs) was investigated to examine the possibility of partic le size control of UFPs produced using the Ar-H-2 are plasma method. UFPs of Ni and Cu were produced in an are with a voltage of 25-40 V, a curr ent of 90-220 A, and an Ar-H-2 mixed gas of atmospheric pressure. The specific surface area of UFPs, A, decreased with increasing generation rate, R-g, and the relation between those was described with a power law, A = k(g)R(g)(-n). The value of exponent n was 0.55-0.57 with Ni and 0.36 wit h Cu when UFPs were produced with a constant torch gas flow rate. When the torch gas flow rate was changed from 0 to 20 L/min, the value of n was 0.8- 0.9 with Ni and 1.4 with Cu. The relation between the generation rate and specific surface area of UFPs was discussed based on the theory of Brownian coagulation and the theoretic al value of n was derived as 0.4. The growth of UFPs produced using the are plasma method is described well with the Brownian coagulation theory becau se the experimental value of,I agrees with the theoretical value under the condition of constant torch gas flow rate. The increase in n when the torch gas flow rate was changed, is described qualitatively as the change of rea ction time and generation rate with the change of flow rate. The average particle size of UFPs can be controlled by controlling the gene ration rate or the electric power.