Plasma electrolytic synthesis and characterization of pH-sensitive TiO2-ZrO2-ZrTiO4-CeOx films on titanium

The Ti/TiO2 + ZrO2, Ti/TiO2 + CeOx, and Ti/TiO2 + CeOx + ZrO2 composites, including Y-doped ones, have been fabricated by one-stage plasma electrolytic oxidation (PEO) of titanium in aqueous electrolytes based on Zr(SO4)(2) and/or Ce-2(SO4)(3) with and without additives of Y(CH3COO)(2) at effective anodic current density of 0.05 A/cm(2) for 10 min. SEM, XRD, and EDX methods have been used for investigation of the composition of the coatings. The resulting PEO coatings contain crystalline TiO2 in rutile and anatase modifications. PEO coatings formed in 0.1 M Zr(SO4)(2) electrolyte additionally include TiZrO4 and m-ZrO2. The introduction of yttrium acetate or cerium sulfate into this electrolyte leads to the formation of t-ZrO2 instead of m-ZrO2 in the composition of PEO coatings. The pH sensitivity of obtained composites depends on the composition and morphology of their surface. The Ti/TiO2 + CeOx + ZrO2 composite revealed the highest electrode function slope equal to 51 +/- 1 mV/pH and excellent performance for end-point indication potentiometric acid-base titration similar to the conventionally used glass electrode. The Ti/Ce + Zr electrodes have shown excellent performance for determining the alkalinity of both technogenic waters and seawater. These composites are promising for use as wear- and corrosion-resistant pH solid-state sensors for long-term monitoring of highly saline waters, including seawater.