Nickel Production

JOURNAL

OF MATERIALS

SCIENCE

7 (1972) . LETTERS

solution. We would, however, like to make the following comments on his analysis: (1) He maintains that the flux conservation condition ja/jb = ~//3 applies to all points in the metal matrix. Although for purposes of conservation of stoichiometry the above is plausible at the interfaces, it is not immediately obvious why this should apply everywhere in the bulk: indeed, in this situation, we suggest that the appropriate condition is A jb Ca (bulk) Cb (bulk)

Gibbs-Thompson equation, and which strictly apply to interface phenomena, can be substituted in his equations 4 and 5 which refer to the bulk. Finally, we agree with his misgivings concerning the application of the principle of minimum entropy production in the interpretation of mass transport kinetics in such complex systems, and indeed, this was the reason why we hesitated to analyse our results along these lines.

M. E. D. MCLEAN HONDROS

(2) It is not clear how relations derived from the

National Physical Laboratory Teddington, Middlesex, UK

2 6 ~ by cold rolling. The same techniques were used to improve the mechanical properties of as-cast HS 21 as shown in table I. Orthodox electrochemical measurements [811 The two most popular alloys now used for the such as critical potential, resting potential repair or replacement of damaged bone in human patients are molybdenum-containing versus time, and corrosion current density wrought austenitic stainless steel and preci- versus time at passive potentials were carried sion cast cobalt-chromium-molybdenum-carbon out in isotonic salt solutions and in such of alloys [1]. Unfortunately, neither of the above higher chloride and hydrogen ion content [9]. alloy systems can be regarded as ideally suitable Since such measurements are but of limited implant material. Stainless steel tends to pit usefulness in assessing crevice corrosion resisand crevice corrode in body fluids [2, 3], while tance [10] of...