Structure and Properties of TiO2/nanoTiO2 Bimodal Coatings Obtained by a Hybrid PVD/ALD Method on 316L Steel Substrate

This paper presents the synergy of the effect of two surface engineering technologies—magnetron sputtering (MS-PVD) and atomic layer deposition (ALD) on the structure and properties of 316L steel. Recent studies indicate that PVD coatings, despite their thickness of a few micrometers, have many discontinuities and structural defects, which may lead to pitting corrosion after time. Applying an ALD layer to a PVD coating seals its structure and contributes to extending the service life of the coating. Investigations of the structure and morphology of the produced layers were carried out using a scanning electron microscope (SEM) and atomic force microscope (AFM). In addition, the structure of the coatings was investigated on the cross-section using a scanning-transmission electron microscope S/TEM. The tribological properties of the materials studied were determined by the ball-on-disc method. The corrosion resistance of the tested materials was determined by the electrochemical potentiodynamic method by recording the polarization curves of the anodes. Additional information about the electrochemical properties of the tested samples, including the quality, their tightness, and their resistivity, was obtained by electrochemical impedance spectroscopy (EIS). In addition, the main mechanisms of corrosion and tribological wear were determined by SEM observations after corrosion tests and after tribological tests. The study showed that the fabrication of hybrid layers by MS-PVD and ALD techniques allows obtaining coatings with electrochemical properties superior to those of layers fabricated by only one method.     

Performance of MoS2/Zr Composite Coatings at Different Deposition Temperatures

The properties of the MoS₂/Zr coatings can be significantly affected by the deposition temperature. In this study, the MoS₂/Zr composite coatings were fabricated on the cemented carbide surface, utilizing the duplex deposition technology at various deposition temperatures. The effects of deposition temperature on the mechanical and friction properties of the MoS₂/Zr coatings were systematically studied. Results exhibited that as the deposition temperature increased, the adhesion force increased first and then decreased, and the coating thickness and micro-hardness gradually increased. Dry sliding tests against a hardened steel ring showed that the tribological behaviors and wear mechanisms of the MoS₂/Zr coatings varied with deposition temperature, which were due to the changing mechanical properties of coatings caused by the temperature. The coatings deposited at a temperature of 180 °C and 200 °C possessed preferable comprehensive mechanical and tribological properties.     

Thermal Annealing Effect on Optical Properties of Binary TiO2-SiO2 Sol-Gel Coatings

TiO₂-SiO₂ binary coatings were deposited by a sol-gel dip-coating method using tetrabutyl titanate and tetraethyl orthosilicate as precursors. The structure and chemical composition of the coatings annealed at different temperatures were analyzed by Raman spectroscopy and Fourier Transform Infrared (FTIR) spectroscopy. The refractive indices of the coatings were calculated from the measured transmittance and reflectance spectra. An increase in refractive index with the high temperature thermal annealing process was observed. The Raman and FTIR results indicate that the refractive index variation is due to changes in the removal of the organic component, phase separation and the crystal structure of the binary coatings.     

The Effect of Electrophoretic Deposition Parameters on the Microstructure and Adhesion of Zein Coatings to Titanium Substrates

Zein coatings were obtained by electrophoretic deposition (EPD) on commercially pure titanium substrates in an as-received state and after various chemical treatments. The properties of the zein solution, zeta potential and conductivity, at varying pH values were investigated. It was found that the zein content and the ratio of water to ethanol of the solution used for EPD, as well as the process voltage value and time, significantly influence the morphology of coatings. The deposits obtained from the solution containing 150 g/L and 200 g/L of zein and 10 vol % of water and 90 vol % of ethanol, about 4–5 μm thick, were dense and homogeneous. The effect of chemical treatment of the Ti substrate surface prior to EPD on coating adhesion to the substrate was determined. The coatings showed the highest adhesion to the as-received and anodized substrates due to the presence of a thick TiO₂ layer on their surfaces and the presence of specific surface features. Coated titanium substrates showed slightly lower electrochemical corrosion resistance than the uncoated one in Ringer’s solution. The coatings showed a well-developed surface topography compared to the as-received substrate, and they demonstrated hydrophilic nature. The present results provide new insights for the further development of zein-based composite coatings for biomedical engineering applications.     

Optical Constants of Crystallized TiO2 Coatings Prepared by Sol-Gel Process

Titanium oxide coatings have been deposited by the sol-gel dip-coating method. Crystallization of titanium oxide coatings was then achieved through thermal annealing at temperatures above 400 °C. The structural properties and surface morphology of the crystallized coatings were studied by micro-Raman spectroscopy and atomic force microscopy, respectively. Characterization technique, based on least-square fitting to the measured reflectance and transmittance spectra, is used to determine the refractive indices of the crystallized TiO₂ coatings. The stability of the synthesized sol was also investigated by dynamic light scattering particle size analyzer. The influence of the thermal annealing on the optical properties was then discussed. The increase in refractive index with high temperature thermal annealing process was observed, obtaining refractive index values from 1.98 to 2.57 at He-Ne laser wavelength of 633 nm. The Raman spectroscopy and atomic force microscopy studies indicate that the index variation is due to the changes in crystalline phase, density, and morphology during thermal annealing.     

Electrophoretically Deposited Chitosan/Eudragit E 100/AgNPs Composite Coatings on Titanium Substrate as a Silver Release System

Due to the possibility of bacterial infections occurring around peri-implant tissues, it is necessary to provide implant coatings that release antibacterial substances. The scientific goal of this paper was to produce by electrophoretic deposition (EPD) a smart, chitosan/Eudragit E 100/silver nanoparticles (chit/EE100/AgNPs) composite coating on the surface of titanium grade 2 using different deposition parameters, such as the content of AgNPs, applied voltage, and time of deposition. The morphology, surface roughness, thickness, chemical and phase composition, wettability, mechanical properties, electrochemical properties, and silver release rate at different pH were investigated. Using lower values of deposition parameters, coatings with more homogeneous morphology were obtained. The prepared coatings were sensitive to the reduced pH environment.     

Intrinsic Properties of Multi-Layer TiO2/V2O5/TiO2 Coatings Prepared via E-Beam Evaporation

Nanocomposite multi-layer TiO₂/V₂O₅/TiO₂ thin films were prepared via electron-beam evaporation using high-purity targets (TiO₂ and V₂O₅ purity > 99.9%) at substrate temperatures of 270 °C (TiO₂) and 25 °C (V₂O₅) under a partial pressure of oxygen of 2 × 10⁻⁴ mbar to maintain the stoichiometry. Rutherford backscattering spectrometry was used to confirm the layer structure and the optimal stoichiometry of the thin films, with a particle size of 20 to 40 nm. The thin films showed an optical transmittance of ~78% in the visible region and a reflectance of ~90% in the infrared. A decrease in transmittance was observed due to the greater cumulative thickness of the three layers and multiple reflections at the interface of the layers. The optical bandgap of the TiO₂ mono-layer was ~3.49 eV, whereas that of the multi-layer TiO₂/V₂O₅/TiO₂ reached ~3.51 eV. The increase in the optical bandgap was due to the inter-diffusion of the layers at an elevated substrate temperature during the deposition. The intrinsic, structural, and morphological features of the TiO₂/V₂O₅/TiO₂ thin films suggest their efficient use as a solar water heater system.     

Corrosion Properties of S-Phase/Cr2N Composite Coatings Deposited on Austenitic Stainless Steel

In order to study the suitability of the S-phase layers as the interlayer for Cr₂N chromium nitride coatings, a number of composite coatings were deposited by the reactive magnetron sputtering (RMS) method on austenitic steel substrates with various initial surface conditions (as delivered and polished) and their corrosion resistance was assessed. Coatings with S-phase interlayer were deposited at three different nitrogen contents in the working atmosphere (15%, 30%, and 50%), which influenced the nitrogen concentration in the S-phase. Coatings with chromium, as a traditional interlayer to improve adhesion, and uncoated austenitic stainless steel were used as reference materials. Detailed microstructural and phase composition studies of the coatings were carried out by means of scanning electron microscopy (SEM), optical microscopy (LM), and X-ray diffraction (XRD) and were discussed in the context of results of corrosion tests carried out with the use of the potentiodynamic polarization method conducted in a 3% aqueous solution of sodium chloride (NaCl). The performed tests showed that the electrochemical potential of the S-phase/Cr₂N composite coatings is similar to that of Cr/Cr₂N coatings. It was also observed that the increase in the nitrogen content in the S-phase interlayer causes an increase in the polarization resistance of the S-phase/Cr₂N composite coating. Moreover, with a higher nitrogen content in the S-phase interlayer, the polarization resistance of the S-phase/Cr₂N coating is higher than for the Cr/Cr₂N reference coating. All the produced composite coatings showed better corrosion properties in relation to the uncoated austenitic stainless steel.     

Deposition of Aluminide Coatings onto AISI 304L Steel for High Temperature Applications

The nickel aluminides are commonly employed as a bond coat material in thermal barrier coating systems for the components of aeroengines operated at very high temperatures. However, their lifetime is limited due to several factors, such as outward diffusion of substrate elements, surface roughness at high temperatures, morphological changes of the oxide layer, etc. For this reason, inter-diffusion migrations were studied in the presence and absence of nickel coating. In addition, a hot corrosion study was also carried out. Thus, on one set of substrates, nickel electrodeposition was carried out, followed by a high activity pack aluminizing process, while another set of substrates were directly aluminized. The microstructural, mechanical, and oxidation properties were examined using different characterization techniques, such as SEM-EDS, optical microscopy, XRD, optical emission spectroscopy, surface roughness (Ra), and adhesion tests. In addition, the variable oxidation temperatures were employed to better understand their influence on the roughness, degree of spallation (DoS), and morphology. The results show that AISI 304L substrates do not respond to aluminizing treatment, i.e., no aluminide coating was formed; rather, a nearly pure aluminum (or alloy) was observed on the substrate. On the contrary, successful formation of an aluminide coating was observed on the nickel-electrodeposited substrates. In particular, a minimum amount of migrations were noted, which is attributed to nickel coating. Moreover, the scratch test at 10 N load revealed neither cracking nor peeling off, thereby indicating good adhesion of the aluminide coating before oxidation. The as-aluminized samples were oxidized between 700 °C to 1100 °C in air for 8 h each. The degree of spallation showed an incremental trend as temperatures increased. Likewise, oxide morphologies showed temperature dependence. On the other hand, average surface roughness (from Ra = 2.3 µm to 5.8 µm) was also increased as temperatures rose. Likewise, the mass gain showed linearity as temperatures increased during oxidation. The hot corrosion responses of electrodeposited-aluminized samples were superior among all specimens. An extensive discussion is presented based on the observations noted above.     

Electrophoretic Deposition of Biocompatible and Bioactive Hydroxyapatite-Based Coatings on Titanium

Current trends in biomaterials science address the issue of integrating artificial materials as orthopedic or dental implants with biological materials, e.g., patients’ bone tissue. Problems arise due to the simple fact that any surface that promotes biointegration and facilitates osteointegration may also provide a good platform for the rapid growth of bacterial colonies. Infected implant surfaces easily lead to biofilm formation that poses a major healthcare concern since it could have destructive effects and ultimately endanger the patients’ life. As of late, research has centered on designing coatings that would eliminate possible infection but neglected to aid bone mineralization. Other strategies yielded surfaces that could promote osseointegration but failed to prevent microbial susceptibility. Needless to say, in order to assure prolonged implant functionality, both coating functions are indispensable and should be addressed simultaneously. This review summarizes progress in designing multifunctional implant coatings that serve as carriers of antibacterial agents with the primary intention of inhibiting bacterial growth on the implant-tissue interface, while still promoting osseointegration.     

Black Talc-Based TiO2/ZnO Composite for Enhanced UV-Vis Photocatalysis Performance

Herein, using black talc as a carrier, a ternary black talc-TiO₂/ZnO composite photocatalyst was prepared by the sol-gel method, and the effect of the black talc on the hetero-structure properties of the TiO₂ and ZnO was systematically studied. The prepared composite photocatalyst showed an excellent degradation performance of the pollutant, where black talc plays an important role in promoting the interface interaction by enhancing the contact area between the TiO₂ and ZnO. Moreover, the free carbon element doping in black talc favors the formation of more oxygen vacancies, thereby improving the response as a photocatalyst in visible light. In addition, the carbon in the black talc can also adsorb organic pollutants and enrich the surroundings of the photocatalyst with pollutants, so it further improves the catalytic efficiency of the photocatalyst. Under UV irradiation, the degradation rate of Rhodamine B on black talc-TiO₂/ZnO was found 3.3 times higher than that of black talc-TiO₂ with good stability.     

One-Step Formation of WO3-Loaded TiO2 Nanotubes Composite Film for High Photocatalytic Performance

High aspect ratio of WO₃-loaded TiO₂ nanotube arrays have been successfully synthesized using the electrochemical anodization method in an ethylene glycol electrolyte containing 0.5 wt% ammonium fluoride in a range of applied voltage of 10–40 V for 30 min. The novelty of this research works in the one-step formation of WO₃-loaded TiO₂ nanotube arrays composite film by using tungsten as the cathode material instead of the conventionally used platinum electrode. As compared with platinum, tungsten metal has lower stability, forming dissolved ions (W⁶⁺) in the electrolyte. The W⁶⁺ ions then move towards the titanium foil and form a coherent deposit on titanium foil. By controlling the oxidation rate and chemical dissolution rate of TiO₂ during the electrochemical anodization, the nanotubular structure of TiO₂ film could be achieved. In the present study, nanotube arrays were characterized using FESEM, EDAX, XRD, as well as Raman spectroscopy. Based on the results obtained, nanotube arrays with average pore diameter of up to 74 nm and length of 1.6 µm were produced. EDAX confirmed the presence of tungsten element within the nanotube arrays which varied in content from 1.06 at% to 3.29 at%. The photocatalytic activity of the nanotube arrays was then investigated using methyl orange degradation under TUV 96W UV-B Germicidal light irradiation. The nanotube with the highest aspect ratio, geometric surface area factor and at% of tungsten exhibited the highest photocatalytic activity due to more photo-induced electron-hole pairs generated by the larger surface area and because WO₃ improves charge separation, reduces charge carrier recombination and increases charge carrier lifetime via accumulation of electrons and holes in the two different metal oxide semiconductor components.     

Enhanced Surface Plasmon by Clusters in TiO2-Ag Composite

The surface plasmon in the composite composed of the noble metals and the semiconductors is interesting because of the various charges and the potential applications in many fields. Based on a highly ordered 2D polystyrene spheres array, the ordered composite nanocap arrays composed of TiO₂ and Ag were prepared by the co-sputtering technique, and the surface morphology was tuned by changing TiO₂ sputtering power. When TiO₂ sputtering power was 60 W and Ag sputtering power was 10 W, the composite unit arrays showed the nanocap shapes decorated by many composite clusters around. The composite clusters led to the additional local coupling of the electromagnetic fields and significant Surface-Enhanced Raman Scattering (SERS) observations, which was also confirmed by the finite-different time-domain simulation. The SERS-active substrate composed of the composite nanocaps decorated by clusters realized the accurate detection of the thiram with concentrations down to 10⁻⁹ M.     

Characteristics of the Dye-Sensitized Solar Cells Using TiO2 Nanotubes Treated with TiCl4

The replacement of oxide semiconducting TiO₂ nano particles with one dimensional TiO₂ nanotubes (TNTs) has been used for improving the electron transport in the dye-sensitized solar cells (DSSCs). Although use of one dimensional structure provides the enhanced photoelectrical performance, it tends to reduce the adsorption of dye on the TiO₂ surface due to decrease of surface area. To overcome this problem, we investigate the effects of TiCl₄ treatment on DSSCs which were constructed with composite films made of TiO₂ nanoparticles and TNTs. To find optimum condition of TNTs concentration in TiO₂ composites film, series of DSSCs with different TNTs concentration were made. In this optimum condition (DSSCs with 10 wt% of TNT), the effects of post treatment are compared for different TiCl₄ concentrations. The results show that the DSSCs using a TiCl₄ (90 mM) post treatment shows a maximum conversion efficiency of 7.83% due to effective electron transport and enhanced adsorption of dye on TiO₂ surface.     

Base Plate Preheating Effect on Microstructure of 316L Stainless Steel Single Track Deposition by Directed Energy Deposition

The microstructural morphology in additive manufacturing (AM) has a significant influence on the building structure. High-energy concentric heat source scanning leads to rapid heating and cooling during material deposition. This results in a unique microstructure. The size and morphology of the microstructure have a strong directionality, which depends on laser power, scanning rate, melt pool fluid dynamics, and material thermal properties, etc. The grain structure significantly affects its resistance to solidification cracking and mechanical properties. Microstructure control is challenging for AM considering multiple process parameters. A preheating base plate has a significant influence on residual stress, defect-free AM structure, and it also minimizes thermal mismatch during the deposition. In the present work, a simple single track deposition experiment was designed to analyze base plate preheating on microstructure. The microstructural evolution at different preheating temperatures was studied in detail, keeping process parameters constant. The base plate was heated uniformly from an external heating source and set the stable desired temperature on the surface of the base plate before deposition. A single track was deposited on the base plate at room temperature and preheating temperatures of 200 °C, 300 °C, 400 °C, and 500 °C. Subsequently, the resulting microstructural morphologies were analyzed and compared. The microstructure was evaluated using electron backscattered diffraction (EBSD) imaging in the transverse and longitudinal sections. An increase in grain size area fraction was observed as the preheating temperature increased. Base plate preheating did not show influence on grain boundary misorientation. An increase in the deposition depth was noticed for higher base plate preheating temperatures. The results were convincing that grain morphology and columnar grain orientation can be tailored by base plate preheating.     

Influence of Carrier Gas Composition on the Stress of Al2O3 Coatings Prepared by the Aerosol Deposition Method

Al₂O₃ films were prepared by the aerosol deposition method at room temperature using different carrier gas compositions. The layers were deposited on alumina substrates and the film stress of the layer was calculated by measuring the deformation of the substrate. It was shown that the film stress can be halved by using oxygen instead of nitrogen or helium as the carrier gas. The substrates were annealed at different temperature steps to gain information about the temperature dependence of the reduction of the implemented stress. Total relaxation of the stress can already be achieved at 300 °C. The XRD pattern shows crystallite growth and reduction of microstrain while annealing.     

Degradation of 2,4-Dichlorophenoxyacetic Acid (2,4-D) by Novel Photocatalytic Material of Tourmaline-Coated TiO2 Nanoparticles: Kinetic Study and Model

The novel complex photocatalytic material was prepared by coating TiO₂ nanoparticles on tourmaline using the sol-gel method, and used in the degradation of the herbicide 2,4-D. The results indicated that coating TiO₂ with tourmaline enhanced the photocatalytic activity significantly. Based on the research of a simplified model for the average light intensity in the photoreactor, the influence of the concentration of photocatalyst, and the initial concentration of 2,4-D, a model for the degradation of 2,4-D by the tourmaline-coated TiO₂ nanoparticles was established. Further tests showed that results calculated from this model were close to those obtained in the actual experiments.     

Characteristics of Doped TiO2 Nanoparticle Photocatalysts Prepared by the Rotten Egg White

In this study, expired egg white was used as a template, and a sol–gel method was employed to prepare pure-phase TiO₂ nano-powder and mixed-phase powders doped with NaF and NaI. The influences of different calcination temperatures, doping elements, and doping amounts during the preparation process on the photocatalytic performance and activity of the prepared TiO₂ powders were studied. The results of the experiments showed that the F-doped TiO₂ had the highest photocatalytic activity when the doping amount was 1.2%, as examined by EDS, where the sintering temperature was 500 °C. F-doped TiO₂ nanoparticles were also synthesized by the sol–gel method using tetrabutyl titanate and NaF mixed with expired egg white protein as the precursor. The F-TiO₂ photocatalyst was characterized using FE-SEM, HR-TEM, EDS, XPS, and UV-Vis, and the photocatalytic activity was evaluated by photodegradation of methylene blue under visible light. The results showed that doping with F reduced the energy band gap (3.04 eV) of TiO₂, thereby increasing the photocatalytic activity in the visible-light region. The visible-light wavelength range and photocatalytic activity of the catalyst were also affected by the doping amount.     

Tuning the Defects of Two-Dimensional Layered Carbon/TiO2 Superlattice Composite for a Fast Lithium-Ion Storage

Defect engineering is one of the effective ways to improve the electrochemical property of electrode materials for lithium-ion batteries (LIB). Herein, an organic functional molecule of p-phenylenediamine is embedded into two-dimensional (2D) layered TiO₂ as the electrode for LIB. Then, the 2D carbon/TiO₂ composites with the tuning defects are prepared by precise control of the polymerization and carbothermal atmospheres. Low valence titanium in metal oxide and nitrogen-doped carbon nanosheets can be obtained in the carbon/TiO₂ composite under a carbonization treatment atmosphere of N₂/H₂ gas, which can not only increase the electronic conductivity of the material but also provide sufficient electrochemical active sites, thus producing an excellent rate capability and long-term cycle stability. The prepared composite can provide a high capacity of 396.0 mAh g⁻¹ at a current density of 0.1 A g⁻¹ with a high capacitive capacity ratio. Moreover, a high specific capacity of 80.0 mAh g⁻¹ with retention rate of 85% remains after 10,000 cycles at 3.0 A g⁻¹ as well as the Coulomb efficiency close to 100%. The good rate-capability and cycle-sustainability of the layered materials are ascribed to the increase of conductivity, the lithium-ion transport channel, and interfacial capacitance due to the multi-defect sites in the layered composite.     

Effect of Bimetallic Dimer-Embedded TiO2(101) Surface on CO2 Reduction: The First-Principles Calculation

The first-principles calculation was used to explore the effect of a bimetallic dimer-embedded anatase TiO₂(101) surface on CO₂ reduction behaviors. For the dimer-embedded anatase TiO₂(101) surface, Zn-Cu, Zn-Pt, and Zn-Pd dimer interstitials could stably stay on the TiO₂(101) surface with a binding energy of about −2.36 eV, as well as the electronic states’ results. Meanwhile, the results of adsorption energy, structure parameters, and electronic states indicated that CO₂ was first physically and then chemically adsorbed much more stably on these three kinds of dimer-embedded TiO₂(101) substrate with a small barrier energy of 0.03 eV, 0.23 eV, and 0.12 eV. Regarding the reduction process, the highest-energy barriers of the CO₂ molecule on the Zn-Cu dimer-embedded TiO₂(101) substrate was 0.31 eV, which largely benefited the CO₂-reduction reaction (CO₂RR) activity and was much lower than that of the other two kinds of Zn-Pt and Cu-Pt dimer-TiO₂ systems. Simultaneously, the products CO* and *O* of CO₂ reduction were firmly adsorbed on the dimer-embedded TiO₂(101) surface. Our results indicated that a non-noble Zn-Cu dimer might be a more suitable and economical choice, which might theoretically promote the designation of high CO₂RR performance on TiO₂ catalysts.