Electrode effects in the sweeping of alpha quartz

摘要

Experimental observations are described in the air-sweeping of alpha-quartz that reveal the introduction of hydrogen. Porous electrodes facilitate the indiffusion of hydrogen. By contrast, the use of thick, nonporous, strongly adherent Au/Cr electrodes causes a color-center front to advance from anode to cathode. Evidence is presented that indicates that: (1) color centers form beneath nonporous portions of the anode that correlate with the formation of Cr/sub 2/O/sub 3/ on the metal surface and Cr-silicides at the metal-quartz interface, and (2) large-diameter clear striae form along the c-axis that correlate with small openings in the anode. These observations suggest that: (1) openings in the anode metallization are required for hydrogen introduction; (2) the electrochemical charge-transfer reaction, leading to hydrogen introduction, occurs at the gas-electrode-quartz boundary and spreads laterally by interfacial diffusion of hydrogen species; and (3) color centers form through the suppression of interfacial H-diffusion. Additionally, electrode-surface damage and high electric fields can result in undesirable electrode-metal indiffusion.