Prediction of ion-exchange process in glass by using multi-component diffusion theory for making of gradient index glasses

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The ion-exchange technique in glass is applied to produce the micro-optic components such as gradient index lens, waveguide, and so on. The key point on the technique is to find out the treated conditions in the ion-exchange process in order to form an intended index distribution, namely concentration distributions in a glass. It is the best way to reliably simulate the concentration profiles during ion-exchange and to find out the conditions by a virtual experiment. Unfortunately, the present stage in the development of gradient index glasses is not as mentioned above.In this study ion-exchange process in glass is described by multi-component diffusion equations, which are derived from the flux densities of mobile cations and the gradient of electrochemical potential, and the numerical solution to obtain the theoretical concentration distributions has been programmed with a finite difference method because the equations are nonlinear. On the other hand, the concentration distributions … More are determined by ion-exchange experiments. The plan is put on the basis which contains a development of glasses with much silver ion and a deal with ion-exchange kinetics among three kinds of mobile cations for practical merits. As the results, bonrphosphate glasses are chosen as the samples which contain Na, K, and Ag ions for mobile ones and have chemical durability. The selfdiffusion coefficients of mobile cations have been determined by means of a radio-isotope tracer technique for the sake of use in the numerical calculation. The theoretical distributions can be rigorously described by using the selfdiffusion coefficients which depend on the composition. The ion-exchange experiments are carried out between glass and molten salt, and glass-glass couples. The experimental distributions after ion-exchange were quantitatively determined by means of an EPMA. When the treated conditions in an ion-exchange experiment were same as the calculation conditions, the simulation profiles coincided closely with the experimental ones. The concentration distributions are transformed into refractive indexes. As we have obtained the convincing condusion that the computer simulation on the diffusion theory is effective, some profiles bompulncl were demonstrated for the purpose of support to the development of gradient index glasses. Less