Proceedings of the
9th International Conference of Asian Society for Precision Engineering and Nanotechnology (ASPEN2022)
15 – 18 November 2022, Singapore
doi:10.3850/978-981-18-6021-8_OR-14-0258
Selective Stress Relaxation of Chemically Strengthened Glass for Mechanical Cutting by Reverse Ion-exchange using Electrochemical Discharge (ECD) Processing
1Department of Mechanical Information Engineering, Seoul National University of Science and Technology, 232 Gongreung-ro, Nowong-gu, Seoul, Korea, 139-743
ABSTRACT
Glass can be chemically strengthened by replacing small Na+ ions present on the surface of unstrengthened glass with large K+ ions. Through this process, relatively high compressive stress is generated on the surface while tensile stress is generated inside the glass for counterbalance. Consequently, it is difficult to cut the glass mechanically using the conventional methods such as scribing or grinding once it is strengthened. This limits its wider use for various applications other than display covers. To overcome this difficulty, a novel method for selectively exchanging the K+ ions present on the surface with Na+ ions was developed in this study. This was enabled by immersing the strengthened glass in the electrolyte of sodium hydroxide (NaOH) aqueous solution right below an electrode and generating heat locally by electrochemical-discharge (ECD) sparking. This provides the environment required for the reverse ion-exchange. The ECD system employed a blade-shaped tool electrode rather than a pencil-shaped electrode to reduce the processing time, and equipped with a diamond grinding wheel for mechanically cutting the glass after ECD processing. The preliminary work showed that it is possible to reversely exchange the ions and then cut the glass successfully by grinding even though the treatment is conducted on only one side of the glass without turning it over. For future work, it is necessary to optimize the process conditions for the reverse ion-exchange, which would allow for efficiently cutting chemically strengthened glass just before its use for various applications.
Keywords: Chemically strengthened glass, Mechanical cutting, Stress relaxation, Reverse ion-exchange, Electrochemical-discharge
1Department of Mechanical Information Engineering, Seoul National University of Science and Technology, 232 Gongreung-ro, Nowong-gu, Seoul, Korea, 139-743
ABSTRACT
Glass can be chemically strengthened by replacing small Na+ ions present on the surface of unstrengthened glass with large K+ ions. Through this process, relatively high compressive stress is generated on the surface while tensile stress is generated inside the glass for counterbalance. Consequently, it is difficult to cut the glass mechanically using the conventional methods such as scribing or grinding once it is strengthened. This limits its wider use for various applications other than display covers. To overcome this difficulty, a novel method for selectively exchanging the K+ ions present on the surface with Na+ ions was developed in this study. This was enabled by immersing the strengthened glass in the electrolyte of sodium hydroxide (NaOH) aqueous solution right below an electrode and generating heat locally by electrochemical-discharge (ECD) sparking. This provides the environment required for the reverse ion-exchange. The ECD system employed a blade-shaped tool electrode rather than a pencil-shaped electrode to reduce the processing time, and equipped with a diamond grinding wheel for mechanically cutting the glass after ECD processing. The preliminary work showed that it is possible to reversely exchange the ions and then cut the glass successfully by grinding even though the treatment is conducted on only one side of the glass without turning it over. For future work, it is necessary to optimize the process conditions for the reverse ion-exchange, which would allow for efficiently cutting chemically strengthened glass just before its use for various applications.
Keywords: Chemically strengthened glass, Mechanical cutting, Stress relaxation, Reverse ion-exchange, Electrochemical-discharge
