The tracer diffusion of O in silicate melts, at temperatures of between 1450 and 1550C, was studied for SiO2 contents which ranged from 30 to 45mol% (figure 22). The measurements were performed by using a capillary reservoir method and a specially designed capillary which was intended to avoid convection. The 18O diffusion profiles were obtained by secondary ion mass spectrometric analysis, the effective diffusivities were obtained by fitting these profiles to appropriate solutions of Fick’s second law. The effective O diffusivity was found to be lower than that of Co, but higher than that of Si. It was found that the compositional dependence of the activation energy for O diffusion was different to that of Si or Co. The variation in the activation energy as a function of composition was less in the case of O. The experimentally determined diffusion profiles were compared with computer simulations that were based upon a kinetic model. The agreement between the shapes of the experimental and simulated concentration profiles, and a similarity of the compositional dependences of the experimental and simulated effective O diffusivities was considered to be evidence for a strong tendency to polycondensation in the present melts.

T.F.Young, J.Kieffer, G.Borchardt: Journal of Physics - Condensed Matter, 1994, 6[46], 9825-34

Table 52

O Tracer Diffusion in CoO