pH response and mechanical properties of Fe2O3–TeO2-based glass/stainless steel enamel electrodes for pH sensors

Glass pH sensors are unsuitable for in vivo biomedical, clinical, or food applications because of the brittleness of glass and the difficulty in measuring small volumes. Enamel structures such as glass/stainless steel are candidates for glass-based pH electrodes. In this study, new enamel electrodes for pH sensors using Fe2O3–TeO2-based glass/stainless steel were developed. The effect of NiO addition to Fe2O3–TeO2 glass on the pH sensitivity and the three-point bending strength of enamels were investigated. The effect of NiO addition to Fe2O3–TeO2 glass/stainless steel on the pH sensitivity was negligible. Fe2O3–TeO2-based glass/stainless steel showed pH sensitivity appropriate to a working electrode. Enameling at a lower temperature under an air atmosphere was desirable for narrowing the gap between pH 4–7 and pH 7–9 sensitivities. The NiO addition to Fe2O3–TeO2 glass/stainless steel decreased the three-point bending strength. Therefore, NiO did not serve as an adhesion oxide in the Fe2O3–TeO2 glass. Fe2O3–TeO2 glass/stainless steel possessed the highest three-point bending strength among all samples when prepared at 670 °C under an air atmosphere. Therefore, no NiO addition and enameling at a lower temperature under an air atmosphere are desirable for obtaining more robust Fe2O3–TeO2 glass/stainless steel than Li2O–SiO2-based glass electrodes for pH sensors.