International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

Spectroscopic ellipsometry was applied to study the optical properties of Ti–6Al–4V alloy before and after anodization in acetic acid electrolyte. The main findings can be summarized as follows: The ellipsometric spectra of the uncoated alloy were successfully modeled using a multi-Lorentz oscillator approach with MSE values of 20–26, and surface roughness ranging from 17 to 52 nm. Anodized surfaces exhibited distinct interference features, confirming the formation of a transparent oxide layer. The optical modeling revealed increased surface roughness and modified optical constants due to the formation of a TiO₂ -based film with amorphous–anatase character. The applied ellipsometric methodology proved reliable for evaluating the thickness and optical properties of anodic oxide films on titanium alloys. These results form the basis for future quantitative analysis of anodic oxide thickness and refractive index as functions of anodizing parameters, which is important for optimizing the surface properties of titanium alloys in biomedical, protective, and optical applications.

This work presents an overview of sol–gel-derived oxide materials and their relevance to optical, photonic and photovoltaic applications, followed by an experimental study of ZrO₂–Al₂O₃–Sm₂O₃ thin films deposited on glass substrates. Historical developments of the sol–gel process, beginning with early investigations on silica gels in the 19th century, are outlined together with advancements in optical glasses, anti-reflective coatings, and rare-earth-doped systems. Recent progress in functional materials—including boron-, tellurium- and rare-earth-containing glasses, luminescent oxide systems, and sol–gel-derived zirconia-based coatings—is discussed to highlight their structural, optical and radiation-shielding capabilities.
In the present study, multilayer ZrO₂–Al₂O₃–Sm₂O₃ coatings were prepared via the sol–gel method combined with dip-coating, and subsequently thermally treated at 420 °C. Optical characterization (UV–VIS–NIR) revealed changes in transmittance and reflectance linked to film composition and thickness, while X-ray diffraction confirmed their predominantly amorphous structure at the applied heat-treatment temperature. SEM and EDS analyses provided insight into surface morphology and elemental distribution within the films. The results demonstrate that increasing Al₂O₃ content influences coating porosity and thickness, while Sm₂O₃ contributes luminescent functionality and potential reduction of optical reflection in key solar spectral regions. These findings indicate that ZrO₂–Al₂O₃–Sm₂O₃ thin films are promising candidates for protective and functional coatings in photovoltaic applications, where enhanced light harvesting and improved surface properties are essential.

Corrosion remains a major limitation for the long-term use of aluminum alloys such as A356, particularly in chloride-rich environments. Although traditional chromate coatings provide effective protection, their toxicity necessitates environmentally friendly alternatives. In this study, a composite ZrO2–Al2O3–Sm2O3 coating was synthesized via a sol-gel method and deposited on A356 alloy using dip-coating. The precursor system was formulated from zirconyl chloride, samarium oxide, and aluminum oxide, stabilized with acetylacetone and acetic acid at pH 0.5 to ensure homogeneous film formation. The coated samples were thermally treated at 400 °C to obtain dense oxide layers. Corrosion resistance was assessed under neutral salt spray conditions (5% NaCl, 35 °C, 648 h) according to BDS EN ISO 9227:2023. Comparison between uncoated A356, binary Al–Zr (ADZ), and ternary Sm–Al–Zr (SADZ) coatings demonstrated a clear performance improvement with increasing film complexity. While ADZ coatings reduced surface damage relative to the bare alloy, the SADZ films exhibited the lowest amount of corrosion products, minimal surface darkening, and significantly reduced pitting. The enhanced performance is attributed to the synergistic effect of the three oxides: ZrO₂ provides chemical stability, Al2O3 increases layer density, and Sm₂O₃ contributes active corrosion inhibition.
Overall, the ZrO2–Al2O3–Sm2O3 composite film offers a promising non-chromate protective system for improving the long-term corrosion resistance of A356 aluminum alloy.

A survey of the prevailing trends in the field of quartz ceramics has been carried out. The article examines the main technological stages characteristic of the synthesis of quartz ceramics and the production of various product categories. The main technological stages characteristic of the synthesis of quartz ceramics and the production of various categories of products have been presented. The technological conditions applicable to the processing of raw materials, the preparation of suspensions with optimal characteristics, the molding of blanks and the heat treatment of semi-finished products have been examined. The role and influence of various technological factors in the formation of the structural characteristics and operational indicators of the products have been analyzed.

Obtained experimental self-cleaning coatings (based on compositions with the participation of Sm2O3), applied by the sol-gel method on glass slides. This study attempts to improve the overall efficiency of a photovoltaic solar panel by using a Sm2O3 doped ZrO2 (SDZ)-based coating. The optical characterization and phase composition of the obtained experimental samples were investigated using UVVIS- NIR, XRD and XRF methods. The coatings are nanocrystalline according to XRD and XRF analyzes and show transmittance close to that of pure glass when tested with a UV–VIS–NIR spectrophotometer The experimental results represent a prerequisite for the development of a series of additional compositions and a detailed technological regime for obtaining various modifications of resistant, long-lasting selfcleaning coatings, potentially applicable to photovoltaic panels.

The efficiency of photovoltaic (PV) systems is significantly influenced by surface contamination, which can reduce light transmission and energy conversion performance. In this study, self-cleaning nanostructured coatings based on titanium dioxide (TiO₂ ), zirconium dioxide (ZrO₂ ), and their doped and composite variants (with Y₂ O₃ and Eu₂ O₃ ) were synthesized using the sol-gel method and applied to photovoltaic glass substrates. The coatings were characterized in terms of their optical transmittance, surface morphology (AFM), wettability (contact angle), and crystallographic properties (XRD). Results indicate that TiO₂ coatings offer superior superhydrophilic behavior, while stabilized ZrO₂ -based composites show excellent transparency, surface homogeneity, and long-term durability. Eu₂ O₃ -doped coatings exhibit additional luminescent functionalities, potentially useful for photonic enhancement. These findings highlight the potential of sol-gel coatings in improving PV panel performance via integrated passive cleaning mechanisms and multifunctional surface engineering.

Thin coatings of aluminum oxide (Al2O3), zirconium oxide (ZrO2) and samarium oxide (Sm2O3) on aluminum alloy Al7SiMg (A356) were prepared by sol-gel method and immersion technique. The materials were characterized in detail by X-ray diffraction. The luminescent properties at room temperature were also investigated. Luminescence analysis showed that the Al2O3 coating containing ZrO2 exhibits broad excitation and emission bands, peaking at 328 nm and 392 nm, respectively. Photoluminescence data for the Al2O3 coating containing ZrO2 and Sm2O3 indicated effective excitation at 404 nm and strong broadband emission, which is due to the co-emission of ZrO2 and Sm2O3. Chromaticity coordinate analysis revealed that Al2O3 coating containing ZrO2 and Al2O3 coating containing ZrO2 and Sm₂ O₃ emit in the blue-purple and pale pink regions, respectively.The chromaticity coordinates, color purity and CIE (Commission Internationale de L’Eclairage) color-correlated temperature were determined.

The technological possibilities for the synthesis of barium-titanate phases were investigated by applying mechanochemical activation (from 30 min. to 2 h) of the starting charges and thermal treatment of the compositions up to 900°C (with an isothermal delay of 1 h). The applied laboratory regime for the preparation of the experimental samples is in accordance with the preliminary thermodynamic calculations. The identification of the obtained phases was carried out by X-ray phase analysis (XRD). Based on the experimental results, the necessary technological conditions for the synthesis of titanate monophasic product by heat treatment at lower temperature values than those typical for standard classical synthesis have been established. The potential possibilities of application of the synthesized phases for the deposition of thin layers on metal surfaces and the preparation of various coatings with different functional purposes are considered.

Thin coatings of zirconia oxide (ZrO2) and samarium oxide (Sm2O3) on glass have been prepared by using sol-gel method and dip coating technique. Materials were characterized in detail by X-ray diffraction. The luminescent properties at room temperature were also investigated. Excitation and emission spectra of ZrO2 coating consists of broad bands with maximums at 318 and 365 nm respectively.
The photoluminescence measurements of samarium coating suggest that can be efficiently excited with 700 nm and consist of emission bands centered at 567, 603, 639 and 707 nm, consistent with characteristic Sm3+ transitions. The CIE (Commission Internationale de L’Eclairage) chromatic coordinates, color purity and color correlated temperature were determined.

Obtained experimental self-cleaning coatings (based on compositions with the participation of Eu2O3), applied by the solgel method on glass slides. This study attempts to improve the overall efficiency of a photovoltaic solar panel by using a ZrO2-based coating, with Y2O3 and addition of Eu2O3. The optical characterization and phase composition of the obtained experimental samples were investigated using UV-VIS-NIR, XRD and XRF methods. The coatings are nanocrystalline according to XRD and XRF analyzes and show transmittance close to that of pure glass when tested with a UV–VIS–NIR spectrophotometer The experimental results represent a prerequisite for the development of a series of additional compositions and a detailed technological regime for obtaining various modifications of resistant, long-lasting self-cleaning coatings, potentially applicable to photovoltaic panels.

Chromium coatings were obtained from spent (waste) chromium electrolyte with the addition of nanosized aluminum oxide. The recovery of the waste chromium electrolyte is carried out by the activation of the chromium ions using the addition of Al2O3 nanoparticles. Electrochemically thin chromium films were deposited directly on S235 steel. The recovered chromium electrolyte has a concentration of nanoparticles of Al2O3 up to 10 g/l, which particles act as intensifiers of the electrochemical process. Analysis was performed with a “Polyvar Met” metallographic microscope and a Bruker D8 Advance powder X-ray diffractometer (XRD). The microstructure of the layer and the matrix were examined and the main phases were determined. SEM-EDS analysis of the chromium layer and the steel matrix was performed. The thickness of the obtained chrome coating with aluminum oxide nanoparticles was determined, which varies between 5 – 10μm.

Experimental vitreous samples with the presence of self-cleaning coatings applied by the sol-gel method were selected, which were tested in a real environment under cyclic atmospheric conditions in different TPPs / TPP-Sofia and TPP-Republika, Pernik/. The resulting thin films were studied by UV-NIS – VIR spectroscopy, AFM, contact angle, etc. The experimental samples are potentially applicable in the operation of photovoltaic panels with increased efficiency and sustainability in the conditions of an industrial environment and under the influence of various meteorological factors.