ZrO2 Coatings Research Articles

Tribological behavior of ZrO2/WS2 coating surfaces with biomimetic shark-skin structure

This study demonstrated the dry friction and wear behavior of sol-gel ZrO2/WS2 coatings with biomimetic shark-skin textured surfaces. The effect of added WS2 on the microstructure and mechanical properties of ZrO2 coatings was examined and the dry sliding wear and friction behaviors against commercial AISI1045 steel balls were investigated. After adding WS2, the micro hardness of ZrO2 coating decreased by ~39% (from 23.7 GPa to 14.5 GPa), and the average steady state friction coefficient was decreased from ~0.43 to ~ 0.2. When the ZrO2/WS2 coating surface was textured biomimetic shark skin, nearly 66% decrease of the average steady state friction coefficient and 82% decrease of ball wear rate were obtained as compared with the pure ZrO2 coatings. The possible frictional mechanism of the biomimetic shark-skin structures was discussed.

Photoluminescence properties of Pr3+ doped ZrO2 formed by plasma electrolytic oxidation

Pr3+ doped ZrO2 coatings were formed by the plasma electrolytic oxidation (PEO) of zirconium in electrolyte containing Pr2O3 powder. The concentration of a uniformly distributed Pr3+ in the coatings increases with time of the PEO process or the concentration of added Pr2O3 powder, causing the stabilization of the tetragonal ZrO2 at the expense of the monoclinic phase. Photoluminescence (PL) emission spectra feature two distinct regions: first attributed to the ZrO2 PL band centered at about 495 nm, while the second region with blue, green, red and NIR PL, is due to the 4f-4f transitions of Pr3+. The most intense PL emission is from 1D2→3H4 transition, however, due to the stabilization of the tetragonal ZrO2, the emissions from the 3P0,1 levels gain in PL intensity with increasing concentration of Pr3+ in the coatings.

Photoluminescence studies of ZrO2:Tm3+/Yb3+ coatings formed by plasma electrolytic oxidation

Zirconia coatings doped with various contents of Tm3+ and Yb3+ were formed by the plasma electrolytic oxidation process of zirconium foils for 15 min in alkaline electrolyte containing Tm2O3 and Yb2O3 powders in different concentrations. The coatings were composed of monoclinic and tetragonal ZrO2 phases, but Tm and Yb incorporated into ZrO2 coatings induces phase transformation from monoclinic phase to tetragonal phase. The excitation photoluminescence (PL) spectra of ZrO2:Tm3+/Yb3+ coatings were featured by a broad band at around 280 nm related to zirconia host, and a peak at around 359 nm corresponding to the 3H6→1D2 transition of Tm3+. The coatings were excited by the 280 nm and 359 nm incident light, resulting in a strong zirconia PL band, and 1D2→3F4 down-conversion luminescence of Tm3+, respectively. With 980 nm excitation and subsequent absorption by Yb3+, an up-conversion PL was observed. Emission at 799 nm is attributed to the 3H4→3H6 transition of Tm3+. PL spectra of samples doped with 8 different combinations of Tm3+ and Yb3+, allow the analysis of the responsible mechanisms and their presentation in the Jablonski diagram. CIE chromaticity coordinates were calculated, revealing dependence of the PL color upon the Tm3+/Yb3+ doping concentration and excitation light wavelength. By 280 nm and 359 nm excitation, the samples emit cyan and purple light, respectively.

Effects of Atomic Layer Deposition of ZrO2 on Infiltrated Mixed Ionic and Electronic Conducting Solid Oxide Cell Electrodes

Infiltration of mixed ionic and electronic conducting (MIEC) nanoparticles into ionic or MIEC scaffolds has been employed to improve the performance of solid oxide cells (SOCs) designed to operate at relatively low temperatures (<600°C). However, the high MIEC specific surface area also hastens sintering and coarsening processes that can lead to a high rate of performance degradation for the electrodes over time. Atomic layer deposited (ALD) coatings have been investigated as a means of curbing the degradation of nano-scale MIEC electrodes. ALD is desirable for coating porous electrodes because of its self-limiting layer-growth characteristic — fully conformal coating can ideally be achieved throughout the depth of a porous electrode, including the most electrochemically active region near the electrolyte. However, results reported to date have yielded mixed results: in some cases, the ALD coating suppresses degradation, whereas in others the coating actually degrades electrode performance. Successful performance improvement seems to be dependent on a combination of factors from choice of electrode substrate and its architecture, to the coating species, its thickness throughout an electrode, and the experimental procedures for coating. This presentation seeks to better elucidate the nature of these dependencies via a study of Sr0.5Sm0.5CoO3-δ (SSC) infiltrated Gd-doped ceria (GDC) electrodes with ALD-ZrO2 coating. Life tests were carried out with degradation accelerated by using a relatively high ageing temperature of 750°C, with impedance spectroscopy measured periodically at 600°C. Rises in polarization resistance with time were substantially mitigated by 30 ALD deposition cycles, and to a lesser extent by 60 cycles, relative to uncoated samples. The overall 0-hour performance is virtually the same across the coated and uncoated samples after a short break-in period, with the benefit from ALD being entirely in the increased sustained performance. The mechanistic benefit of ALD-ZrO2 on these electrodes is parsed with the aid of microstructural and chemical characterization. Scanning electron microscopy with energy dispersive spectroscopy of cross-sections of the coated samples reveals a substantial gradient in the ZrO2 coating thickness, with several nm thickness near the free surface decreasing to sub-monolayer thickness near the electrode/electrolyte interface. This is sensible because thicker ZrO2 coatings on SSC powders were found by powder x-ray diffraction to react extensively, forming Sr- and Sm-zirconates and cobalt oxide species. The results suggest that sub-monolayer ALD-ZrO2 coatings form a very thin layer of reactants that do not cover electrochemically-active surface sites but can help suppress particle coarsening. Based on this mechanism, a coarsening model previously developed for infiltrated SSC-GDC electrodes is shown to fit the polarization resistance versus time data by assuming that the ALD layer decreases the cation diffusion. The ideal thickness is that which balances the negative effect of the reaction of active SSC material with the positive effect of a reduced effective diffusion coefficient. This thickness is sensitive to the number of ALD cycles deposited as well as the aspect ratio of the pores the ALD precursors must traverse within the electrode. The results will be contrasted to those obtained from ALD-ZrO2 on conventional La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) electrodes, which do not degrade by coarsening due to the larger feature sizes. In this case, there is no benefit from monolayer-thickness ALD-ZrO2, and thicker layers substantially degrade the performance. Figure 1

Structural and microstructural studies on SiC-SiO2 ceramic composites

In this study, SiC ceramic substrates were prepared with 99.5% silicon carbide powders which were came from waste silicon mud during the manufacturing process of solar cells. It is found that a SiO2 layer with 50 nm in thickness is present on the SiC surface by TEM analysis. The relative density of the SiC samples is too low after sintering to 1550 °C, which is only 60% of the relative density. It will cause a poor mechanical strength at lower relative density of samples. To improve the density of SiC samples, an amorphous SiO2 was introduced as a sintering aid. Different amounts of amorphous SiO2 from 1 wt% to 5 wt% were then added into SiC powders and made into discs. We call this modified-SiC. These samples were sintered at high temperatures from 1350 °C to 1500 °C. The SiO2 addition and sintering temperature effects on the density, phase evolution, microstructure and mechanical properties of modified-SiC were investigated. A Y-ZrO2 layer was then coated onto the SiC disc. Sintering temperature can be efficiently decreased and the mismatch between ZrO2 coatings and SiC disc can be reduced when SiO2 is added into SiC. It is found that SiC powders with 3 wt% SiO2 addition shows the most optimum outcome with higher density and stronger mechanical properties.

Electrochemical Performance Enhancement of Na0.7MnO2 for Sodium-Ion Batteries By Doping and Conformal Surface Coating

Sodium-ion batteries (SIBs), which have similar working mechanism to that of Li-ion batteries (LIBs), have attracted great attention as new power sources for large-scale energy storage because of the abundant of Na reserves. However, there is still a huge challenge for the development of SIBs due to the low rate capacity and poor cycle stability of cathode materials. Different approaches of element doping and surface modifications have been widely applied to improve the electrochemical performance of those cathode materials. Herein, doping of Ti4+ and Zr4+ and coating of TiO2 and ZrO2 have been achieved by atomic layer deposition (ALD). The rate capability and cycling stability of the modified material were improved and the enhancement mechanism was studied. The TiO2 and ZrO2 coatings act as a stable interfacial layer to enhance the cycle stability of NMO by suppressing side reactions between the electrode and electrolyte. The doping of transition metal ions reduces the bond length of Mn-O and increases its bond energy, which further enhances the stability of the layered structure. In addition, the doping of transition metal ions can also enhance the intrinsic electronic conductivity by enlarging the Na-O bond length and lowering the Na+ migration barrier, thereby increasing the rate capacity.

Characterization and investigation of in vitro properties of antibacterial copper deposited on bioactive ZrO2 coatings on zirconium

In this study, porous and rough bioceramic structures were coated on commercial pure Zr by PEO (plasma electrolytic oxidation). Then, Cu was deposited onto the PEO surfaces without any morphological changing by TE (thermal evaporation). Mainly, meta-stable Ca0.15Zr0.85O1.85 (calcium zirconium oxide), cubic-ZrO2 (zirconia) and perovskite-CaZrO3 (calcium zirconate) were observed on the surfaces by powder-XRD (powder X-ray diffraction) and TF-XRD (thin film XRD) analyses as the phases of Zr and Cu2(P2O7) (copper pyrophosphate) were detected as a trace amount on the Cu-deposited PEO surface. The average thicknesses of the PEO coating and TE layer were measured as approximately 21.8 ± 2.4 μm and 20 nm, respectively. The Cu-deposited PEO surfaces indicated superhydrophobic character while the PEO surface exhibited hydrophilic behavior. The apatite-forming abilities on both coatings were evaluated by surface and cross-sectional SEM (scanning electron microscopy) and surface EDS (energy dispersive X-ray spectroscopy)-mapping analyses at post-soaking in SBF (simulated body fluid) up to 10 days. However, apatite formed on the Cu-deposited PEO surfaces was thicker and more homogenous than the PEO surface. Thus, in vitro bioactivity was considerably improved by Cu-deposition on the PEO. In vitro microbial adhesion test of both surfaces was investigated by bacterial adhesions for Gram positive and Gram negative bacteria. The bacterial adhesions on the Cu-deposited PEO surfaces were lower compared to the PEO surfaces for all bacteria types.

Understanding the thermodynamic properties of 20% CeO2 stabilized ZrO2 coatings with atomistic modeling and simulations

To understand the improved stability and reduced thermal conductivity of 20% CeO2 stabilized ZrO2 coatings compared to pure zirconia, different Ce doped ZrO2 systems are modeled. The Ce insertion in ZrO2 lattice elongates the lattice parameters and the elongation is proportional to the Ce doping concentration. Moreover, the cell volume linearly increases with the Ce doping level. X-ray diffraction analysis confirmed the Zr0.84Ce0.16O2 phase, describing the substitutional Ce doped at Zr sites. Ce doping modified the electronic band structure of ZrO2 without creating any isolated states in the band gap. The Ce4Zr12O32 modeled system with Ce doping concentration of 8.33% provided the stable phonon density of states curves compared to the pure and doped systems. Ce doping reduced the thermal conductivity of ZrO2. Increasing Ce doping level further reduced the thermal conductivity reaching the maximum reduction at 8.33% doping concentration. Further increase in the Ce level has no effective reduction in the thermal conductivity values. The reduced thermal conductivity is attributed to the enhanced phonon scattering due to the substitutional Ce4+ dopant and optimal doping concentration. The experimental observation could be satisfactorily explained by the calculations results.

Thermal control coatings based on pigments modified with Al2O3 nanoparticles

The effect of modification with aluminum oxide nanopowders on reflectivity in the range of 0.25–2.5 μm and the radiation stability of white ZnO, TiO2, and ZrO2 pigments and coatings based on them was studied. It has been shown that the effectiveness of the modification to increase the radiation stability after irradiation with electrons (Е = 30 keV, F = (1–9) ∙ 1016 cm−2) depends on the type of pigment. The effectiveness does not exceed 26% for coatings based on ZnO and TiO2 pigments, while for the coating ZrO2 pigment it is 50%. The types of defects, the mechanisms of radiation defect formation in the initial and modified pigments and their influence on the reflection spectra have been considered.

Porous nanostructured ZrO2 coatings prepared by plasma spraying

Porous nanostructured ZrO2 coatings were prepared on the surface of TC4 titanium alloy by plasma spraying. The porosity of the coatings was improved by adding MDPE and PEEK as pore-forming agents in the ZrO2 powder. The results indicate that the addition of pore-forming agents significantly increased the porosity of the ZrO2 coatings, and the porosity of the ZrO2 coatings increased with increasing the content of the pore-forming agents. PEEK pore-forming agent was superior to MDPE concerning the pore-forming ability in the present preparation condition. The porosity of the ZrO2 coatings was further increased by subsequent heat treatment. The porosity of ZrO2–15% PEEK coating after heat treatment reached 20.6%. The microhardness of the porous nanostructured ZrO2 coatings were about HV0.11000, which decreased little with the increase of the porosity of the coatings.

Down- and up-conversion photoluminescence of ZrO2:Ho3+ and ZrO2:Ho3+/Yb3+ coatings formed by plasma electrolytic oxidation

This paper discusses ZrO2:Ho3+ and ZrO2:Ho3+/Yb3+ coating formation by the plasma electrolytic oxidation (PEO) of zirconium in alkaline electrolyte containing Ho2O3 and Ho2O3/Yb2O3 particles, respectively. The morphology, chemical and phase composition, as well as down- and up-conversion photoluminescence (PL) of the coatings, were investigated. Down-conversion PL emission spectra of ZrO2:Ho3+ excited by 280 nm radiation are composed of broad PL band associated with ZrO2 host and bands corresponding to f–f transitions of Ho3+. The main PL emission bands of Ho3+ at around 540 nm and 550 nm are assigned to 5F4→5I8 and 5S2→5I8 transitions, respectively. The down-conversion PL intensity of ZrO2:Ho3+ excited by 450 nm radiation (transition 5I8→5G6) strongly depends on the concentration of Ho3+ incorporated into ZrO2 coatings. That is, it depends on the duration of the PEO process and concentration of Ho2O3 particles in electrolyte. PL intensity increases with rising Ho3+ concentration in ZrO2 coatings, reaching a maximum Ho:Zr ratio of about 18⋅10−3 and shows concentration quenching for higher values. Excitation of ZrO2:Ho3+/Yb3+ coatings by 980 nm laser diode results in the appearance of a strong green (5F4,5S2→5I8), weaker red (5F5→5I8), and NIR (5F4,5S2→5I7) up-conversion emissions. An increase of the PL intensity with increasing Yb3+ concentration indicates an efficient transfer of energy from excited Yb3+ ions to Ho3+ ions.

Enhanced electrochemical performance of Li-rich layered oxide, Li1.2Mn0.54Co0.13Ni0.13O2, by surface modification derived from a MOF-assisted treatment

We developed a promising cathode material prepared by effective surface modification of Li-rich layered oxide (LLO) materials, using a Zr-based MOF (UIO-66-F4), as a precursor to produce in-situ MOF-derived ZrO2 (MDZ) coatings. A new method for F doping on LLO was also proposed. The MOF-assisted treatment renders a uniform nanoscale coating of ZrO2 and a porous structure of Li1.2Mn0.54Co0.13Ni0.13O2 hierarchical secondary microsphere. The rate capability, cycling stability, and first coulombic efficiency of LLO were significantly improved by the MOF-assisted treatment. The discharge capacity of the MOF-derived ZrO2 coated LLO (MDZ@LLO) material was 279 and 110.0 mAh g−1 at 0.1 C and 5 C, respectively. The capacity retention increased from 71.1% to 83.8% after 200 cycles at 1 C while the coulombic efficiency increased from 62% to 72% during the first cycle.

ToF-SIMS Characterization of Nanostructured ZrO2 Coatings Applied to Near Equiatomic Ni-Ti Alloy

The ToF-SIMS technique was applied to analyze thin ZrO2 coatings deposited on the surface of a Ni-Ti alloy. Due to its nanostructured nature, these films are difficult to characterize by conventional techniques. ZrO2 coatings were deposited on near equiatomic Ni-Ti wires by pulse electrodeposition. Part of the samples was electrolytically polished before the coating process. The coated samples were then analyzed by ToF-SIMS to evaluate the influence of the deposition time and previous surface electropolishing on the structure of the deposited coating. The results indicate that thicker coatings were produced on the electropolished samples, in comparison with the as-received ones. The best uniformity in thickness was achieved when Ni-Ti samples were previously electropolished followed by ZrO2 electrodeposition for 1200 seconds. Moreover, it was possible to observe by this technique that the inclusions in the Ni-Ti matrix were not entirely covered by the coating.

Study of Combustion Characteristics on Single Cylinder Direct Injection Diesel Engine with Plasma and HVOF Coated Ceramic Powders on Piston Crown

Abstract Wear resistive and thermal barrier ceramic coating plays a vital role in the combustion and performance of diesel engines. The biodiesel extract from jatropha with methyl ester blends, were tested for their alternate resource in diesel engines. This paper is a study on the combustion characteristics, of a single cylinder direct injection diesel engine with the partially stabilized ZrO2 and Cr3C2 coatings over the piston crown for thermal performance and wear resistance. Biodiesel extract from jatrophais is used as blends to study on the combustion and performance characteristics of the diesel Engine. Experimental investigation on combustion characteristics, such as, heat release, peak pressure, ignition delay and brake thermal efficiency, is studied for varying loads 0%, 25%, 50%, 75%, 100% for both coated and uncoated piston. The biodiesel blends prepared from jatropha is prepared through esterification process (10-20 % by volume). From the combustion study, the results reveal that, combustion parameters (peak pressure and heat release) is improved by 10 % on a compression ratio, of 17.5 for the coated piston with jatropha biodiesel blends. In the comparison of varying volume % of jatropha and diesel the cylinder, pressure inceases at 20% JME blend for the coated piston in comparison to the uncoated piston, for the optimal compression ratio 17.5. The wear resistance characteristics proves, that the coated piston has a difference in wear depth 47 % of and total wear volume of 35% than the uncoated improving the tribological characterization of the piston.

Microstructure Formation Properties of ZrO2 Coating by Powder, Suspension and Liquid Precursor Plasma Spraying

The research provides a brief analysis of the requirements for the plasma sprayed zirconia for obtaining thermal barrier coatings and solid oxide electrochemical devices. We present the results of depositing 7-8% YSZ coatings by powder spraying (APS) in the regimes of low and high velocity plasma flow as well as the results of liquid materials plasma spraying, namely of suspension and precursor solution (SPS and LPPS). The studies of the coatings microstructure are executed by analyzing SEM images. APS powder coatings are characterized by high porosity of 20-30% with coarse microstructure, LPPS coating has a porosity of 12% and columnar structure, and the SPS coating has a low porosity of 1.4 % and a gas-tight structure.

Photoluminescence properties of Er3+/Yb3+ doped ZrO2 coatings formed by plasma electrolytic oxidation

In the present work, down- and up-conversion photoluminescence properties of Er3+/Yb3+ doped ZrO2 coatings formed by plasma electrolytic oxidation of zirconium in electrolyte containing Er2O3 and Yb2O3 particles were investigated. Down-conversion PL analysis shows that emission spectra of ZrO2:Er3+/Yb3+ coatings excited with 280 nm radiation are composed of broad PL band related to ZrO2 host and bands assigned to f-f transitions of Er3+. The main PL emission bands of Er3+ at around 548 nm and 560 nm are related to 4S3/2→4I15/2 transition. PL excitation spectra monitored at 548 nm feature broad band in the region from 250 nm to 350 nm which is associated with the electron transfer transition from 2p orbital of O2− to 4f orbital of Er3+ and transitions of ZrO2. On the other hand, bands in PL excitation spectra ranging from 350 nm to 535 nm are related to 4f transitions of the Er3+ from the ground state 4I15/2 to higher energy levels. Down-conversion PL intensity decreases with increasing concentration of Yb3+ in coating due to energy transfer from Er3+ to Yb3+. ZrO2:Er3+/Yb3+ coatings show intense green (4S3/2→4I15/2) and red (4F9/2→4I15/2) up-conversion PL emission under the excitation with a 980 nm diode laser. With increasing Yb3+ concentration red up-conversion PL intensity increases more rapidly with respect to green emission, because red up-conversion PL intensity strongly depends on Yb3+ concentration, i.e. 4F9/2 state of Er3+ is directly excited by energy transfer from excited Yb3+.

Comparison of Corrosion Resistance and Cytocompatibility of MgO and ZrO2 Coatings on AZ31 Magnesium Alloy Formed via Plasma Electrolytic Oxidation

In this work, one coating is comprised of ZrO2 and the other consists of MgO as main phase composition was produced on AZ31 magnesium alloy using one-step plasma electrolytic oxidation (PEO). The purpose of this work was to study the corrosion resistance and cytocompatibility of the above-coated AZ31 magnesium alloys in order to provide a basis for AZ31 Mg alloy’s clinical applications of biomedical use. The morphology and phase composition of the coatings were studied using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The corrosion properties were examined using electrochemical testing, hydrogen evolution measurements, and immersion tests in a simulated body fluid (SBF). Compared with bare magnesium and the MgO coating, the ZrO2-containing coating exhibited an improved corrosion resistance. Cell proliferation assays and cell morphology observations showed that the ZrO2-containing coating was not toxic to the L-929 cells. The ZrO2 coating was much denser and more homogeneous than the MgO coating, hence the corrosion resistance of the ZrO2-coated AZ31 Mg alloy was superior and more stable than the MgO-coated AZ31 Mg alloy, and ZrO2/AZ31 did not induce a cytotoxic reaction to L-929 cells and promote cell growth.

Effect of surface textures and electrohydrodynamically atomized WS2 films on the friction and wear properties of ZrO2 coatings

The combination of WS2 films and surface textures were investigated for improving the friction and wear properties of sol-gel ZrO2 coatings. Grid-like grooves with different groove pitch were fabricated by laser surface texturing technology. All the textured coatings showed improved hydrophilicity (the contact angle of ZrO2 coatings decreased by ~ 3.5–22.8% after texturing). WS2 films were deposited on the ZrO2 coatings by electrohydrodynamic atomization technology. The dry sliding friction and wear properties of samples with surface textures or/and WS2 films additive were evaluated. Both the coefficient of friction of ZrO2 coatings and steel ball wear rate were affected by laser surface texturing and WS2 films additive. The textured samples with the texture coverage of 0.679 showed the lowest friction coefficient and lowest steel ball wear rate, decreasing by ~ 16% and ~ 70%, respectively, when comparing with those of the untextured samples. The further improved antifriction and antiwear properties were obtained by the synergistic combination of surface textures and deposited WS2 films. Additionally, laser surface micro-texturing could contribute to prolong the WS2 films wear life and magnify its lubricating effect.

Reduced thermal conductivity of solid solution of 20% CeO2 + ZrO2 and 8% Y2O3 + ZrO2 prepared by atmospheric plasma spray technique

To reduce the thermal conductivity and improve the durability of ZrO2 based materials, coatings from different contents of 20% CeO2 + ZrO2 and 8% Y2O3 + ZrO2 are deposited by atmospheric plasma spray technique. The obtained coatings are characterized by X-ray diffraction, scanning electron microscopy and the thermal diffusivity/conductivity is calculated. Substitutional point defects are created in the coating which improves the phonon scattering thereby influencing the thermal conductivity. Pores and cracks are identified in the microstructure and quantitatively analyzed. Samples with higher concentration of defects provided minimum thermal conductivity which might be due to the enhanced phonon scattering. Among the prepared coatings, samples with 25% of 20% CeO2 + ZrO2 and 75% of 8% Y2O3 + ZrO2 provided minimum thermal conductivity in the temperature range 25–1200 °C. The prepared coatings are compared with the pure 8% Y2O3 + ZrO2 coatings. The solid solution of 20% CeO2 + ZrO2 and 8% Y2O3 + ZrO2 demonstrated lower thermal conductivity than the 8YSZ. The reduced thermal conductivity is attributed to the higher concentration of defects which improve the phonons scattering.

Self-cleaning properties of zirconium dioxide thin films

Here we focused on the fundamental study of self-cleaning properties of zirconium dioxide films, including photoinduced alteration of surface hydrophilicity, photocatalytic and photoinduced bactericidal activities. The accent was made on the factors influencing the photoinduced hydrophilic conversion such as surface acidity and spectral composition of light for the surface photoexcitation. The studies on photoinduced hydrophilic conversion of the ZrO2 thin film were carried out using the contact angle measurements and XPS method. The experimental data demonstrate the very different hydrophilic behavior of the hydrated surface depending on the spectral region of photoexcitation corresponding to intrinsic or extrinsic ZrO2 absorption. This is explained by the difference in the concentration of photoelectrons and photoholes which participate in the photo-induced surface processes. It is suggested that hole-trapping species such as surface hydroxyl groups and adsorbed water molecules play a crucial role in the photoinduced superhydrophilic transition. The effect of the electron-acceptor and electron-donor gas atmospheres on the aging of the surface superhydrophilicity is found to be in agreement with this conclusion. The photochemical activity of ZrO2 coatings was tested by photodegradation of stearic acid. The antibacterial properties are investigated against Escherichia coli. The ZrO2 thin films reveal self-cleaning properties and can be successfully used as biomedical or construction material.