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Vacancies and oxygen
ELSEVIER El
Materials Chemistry and Physics 50 ( 1997) 116
Vacancies and oxygen J.S. Koehler 101 W WindsorA~vnue. Apt #4114, Urbana, IL 61802, USA
In the beginning life was simple. Bauerle [ I] quenched pure gold and got reasonable results. Then Doyama [2] tried to quench pure silver. That proved much more difficult. I believe that the presence of oxygen in silver makes the study of lattice vacancies in silver more difficult. I believe that vacancies in copper are also complicated by the presence of oxygen. Let me try a theory. A lattice vacancy in these metals behaves like a screened negative charge. Oxygen behaves like a screened double positive charge. Hence the two entities attract one another. At low temperature the two can combine to form vacancy oxygen complexes. The number of complexes will depend on the solubility of oxygen and on the concentration of lattice vacancies. If B is the binding energy of a complex then the equilibrium concentration of complexes is: Cc = CvCo exp(B /kT) where Cc is the concentration of complexes, Cv is the concentration of lattice vacancies, and Co is the concentration of oxygen atoms. A complication arises because the above equation assumes thermal equilibrium which may not be the case. For example if one quenches silver from near its melting point to room temperature one starts at the high temperature with high concentrations of lattice vacancies and oxygen atoms, but few complexes. During cooling one loses vacancies and forms complexes. One also loses oxygen atoms. Exactly what happens depends on the diffusion constants of vacancies, of oxygen, and of the complexes. It also depends on B, the binding energy of the complexes. In addition the oxygen atoms may combine to form oxygen molecules. It seems clear that to decide what occurs during quenching and annealing one needs much additional information.
References [l] J.E. Bauerle and J.S. Koehkr, Phys. Reo., 107 (1957) 1493. 123 M. Doyama and J.S. Koehler, Whys.Reu., 127 (1962) 21.
0254.0584/97/$17.00 0 1997 Elsevier Science S.A. All rights reserved PIISO254-0584(97)01923-8
Materials Chemistry and Physics 50 ( 1997) 116
Vacancies and oxygen J.S. Koehler 101 W WindsorA~vnue. Apt #4114, Urbana, IL 61802, USA
In the beginning life was simple. Bauerle [ I] quenched pure gold and got reasonable results. Then Doyama [2] tried to quench pure silver. That proved much more difficult. I believe that the presence of oxygen in silver makes the study of lattice vacancies in silver more difficult. I believe that vacancies in copper are also complicated by the presence of oxygen. Let me try a theory. A lattice vacancy in these metals behaves like a screened negative charge. Oxygen behaves like a screened double positive charge. Hence the two entities attract one another. At low temperature the two can combine to form vacancy oxygen complexes. The number of complexes will depend on the solubility of oxygen and on the concentration of lattice vacancies. If B is the binding energy of a complex then the equilibrium concentration of complexes is: Cc = CvCo exp(B /kT) where Cc is the concentration of complexes, Cv is the concentration of lattice vacancies, and Co is the concentration of oxygen atoms. A complication arises because the above equation assumes thermal equilibrium which may not be the case. For example if one quenches silver from near its melting point to room temperature one starts at the high temperature with high concentrations of lattice vacancies and oxygen atoms, but few complexes. During cooling one loses vacancies and forms complexes. One also loses oxygen atoms. Exactly what happens depends on the diffusion constants of vacancies, of oxygen, and of the complexes. It also depends on B, the binding energy of the complexes. In addition the oxygen atoms may combine to form oxygen molecules. It seems clear that to decide what occurs during quenching and annealing one needs much additional information.
References [l] J.E. Bauerle and J.S. Koehkr, Phys. Reo., 107 (1957) 1493. 123 M. Doyama and J.S. Koehler, Whys.Reu., 127 (1962) 21.
0254.0584/97/$17.00 0 1997 Elsevier Science S.A. All rights reserved PIISO254-0584(97)01923-8