2. Ion control
(1)Glass surface modification through corona discharge treatment
For higher performance of glass used in the field of information appliances, medicine and energy, it is important to control is not only the bulk composition but also the surface states.
Other than known surface modification methods such as ion exchange, ion injection and various coating methods, a phenomenon called "corona discharge" is applied in this study to control existential states of alkali ions contained in a glass from the outside, and thereby our laboratory tries to explore new functions and characteristics.
The corona discharge is a phenomenon that takes place by gas breakdown at a high-voltage (several kV) applied to the surface of a needle or a wire. When some material is placed on the near-by electrical ground, protons produced from moisture or hydrogen in the gas penetrate into the material without the use of a vacuum or a catalyst.
Using the corona discharge treatment under diverse conditions for alkali-containing glass, this study has examined the details of change in states of the glass surface.
The results have revealed the following.
1) Alkali on the glass surface is replaced with protons, and then it is separated out on the ground side.
2) Replacement of the electric-discharge atmosphere from air into hydrogen improves alkali replacement efficiency severalfold.
3) The template-mediated discharge treatment and etching enable the formation of micro/nano structure.
4) When two plates of glass are superimposed on each other during the discharge process, alkali moves from the upper layer to the lower layer.
The above generic technologies have potential to be applied to the functionalization of a hard-to-treat soda-lime glass surface.
(2)Alkali-proton replacement in a glass using metallic catalyst electrode
The laboratory has studied the process in which DC voltage (several V) is applied to a palladium-filmed glass to introduce protons into the glass. (joint research with Omata laboratory of Osaka University )
Sodium-containing phosphate which showed a high thermal diffusion coefficient of protons in the preceding study. It has been verified that over 95% of sodium can be replaced with protons.
Assessment on the DC polarization characteristics of the obtained material confirmed the stable proton conduction in a hydrogen atmosphere at 350 degree Celsius. Hereafter, an attempt will be made to achieve further characteristical improvement for application of this finding to solid electrolyte in an intermediate-temperature fuel cell from 200 to 500 degree Celsius.