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In this paper, we employed plasma electrolytic oxidation (PEO) of aluminum in a water solution of sodium tungstate (Na2WO4∙2H2O) with the addition of the pure and Ce-loaded zeolites clinoptilolite and 13 X for the preparation of oxide coatings. The obtained coatings were characterized with respect to their morphologies and chemical and phase compositions using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, atomic force microscopy, and X-ray diffraction. The prepared coatings contained γ-alumina, WO3, and metallic tungsten. The surface morphologies of the obtained coatings strongly depended on the PEO processing time, the roughness of all coatings increased with PEO time, while porosity decreased with PEO processing time as a result of microdischarge coalescence and growth. All coatings contained elements originating from the substrate and from the electrolytes. Coatings containing zeolites with Ce showed higher photoactivity than those with immobilized pure zeolites. The highest photocatalytic activity levels were observed for coatings containing immobilized Ce-exchanged clinoptilolite processed for 10 min. It was observed that both clinoptilolite and 13X zeolites improved the features of the PEO coatings in a similar manner, making natural and abundant clinoptilolite an excellent candidate for various applications.

Plasma electrolytic oxidation (PEO) process of Al–Zn–Si alloy in water solution containing 4 g L-1 sodium metasilicate at constant current den­sity of 400 mA cm-2 was investigated. The species present in PEO micro- -discharges and their ionization stages were identified using optical emission spectroscopy tech­nique. The obtained PEO spectrum consists of atomic/ionic lines originating from the elements present both in the substrate (Al, Zn) and the electrolyte (Na, O, H). Apart from atomic and ionic lines, AlO band at 484.2 nm was also det­ected. Plasma electron number density diagnostics was performed from the Hb line shape. The electron temperature of 4000±400 K was estimated by measuring the relative line intensities of zinc atomic lines at 481.05 and 636.23 nm. In addi­tion, surface morphology, chemical and phase composition of oxide coatings were investigated by SEM-EDS and XRD. Oxide coating morphology is strongly dependent of PEO time. The elemental components of PEO coatings are Al, Zn, O and Si. The oxide coatings are partly crystallized and mainly composed of gamma phase of Al2O3.