PRECISE PURITY-EVALUATION OF HIGH-PURITY COPPER BY RESIDUAL RESISTIVITY RATIO

To evaluate the purity of high-purity copper with high accuracy by the residual resistivity ratio (RRR), the optimum annealing condition bef ore the RRR measurement and the diameter dependence (size effect) of R RR for high-purity copper (5N and 6N grade copper) wires, 0.2-2 mm in diameter, annealed under the optimum condition have been investigated. The most suitable annealing temperature and period were determined to be 923 K and more than 14.4 ks (4 h), respectively. For the size effe ct on RRR, the relationship between RRRW (RRR measured for a copper wi re with diameter d), RRRB (RRR of the bulk copper) and the specimen di ameter d (mm) was found as follows: RRRW-1=RRRB-1+(3.8x10(-5)).d(-1) T he product of rho.lambda=6.5x10(-16)Ohm m(2) for copper was also obtai ned from the slope of the above equation. Furthermore, it became clear that the difference in RRRW is dependent on the specimen diameter and increases with purity of the specimen. Therefore, the influence of th e size dependence on RRR must be considered carefully whenever to eval uate and to compare the purity of high-purity metals by RRR.