Microstructures and mechanical properties of wear-resistant titanium oxide coatings deposited on Ti-6Al-4V alloy using laser cladding

In this work, a freeze-dried TiO₂ nano-sized powder was used as the coating material and single tracks of TiO_x coating were cladded on Ti-6Al-4V substrates using a diode laser. The microstructure, chemical composition, and mechanical properties of the coatings were characterized and their relationships were explored. Coatings with structural and compositional gradients formed under a laser energy density (LED) of 20 kJ/m, while coatings with a relatively homogeneous microstructure were obtained using a LED of 30 kJ/m. The microstructure evolution was controlled by the molten pool lifetime and the intensity of convective flow during laser processing. The elastic modulus of the graded coating showed a decreasing trend from the top coating surface to the interface while that of the homogeneous coating remained constant. Our results also demonstrated that the hardness and wear resistance of the oxide coatings were up to four and ten times higher than that of the substrate.     

Polyhedral oligomeric silsesquioxanes as titanium dioxide surface modifiers for transparent acrylic UV blocking hybrid coating

Architectural coatings are often recommended to enhance the durability of wood in exterior environment however the coatings itself are not UV stable enough for long term protection. For this reason inorganic UV absorbers like nano TiO₂ in rutile crystal form are of great research interest in last decade. It's advantage is UV reversible absorption activity in polymer composite like coating during weathering [1]. On the other side the TiO₂ surface has limited compatibility with polymers what can result in non-stable dispersion. To achieve a better compatibility between nano-particles and polymer matrix in coating, the use of different inorganic/organic surface modification of TiO₂ rutile nano-particles is recommended.     

Corrosion resistance and photocatalytic activity evaluation of electrophoretically deposited TiO2-rGO nanocomposite on 316L stainless steel substrate

TiO₂-rGO nanocomposite coatings were obtained by electrophoretic deposition (EPD) technique of TiO₂ nanoparticles and graphene oxide (GO) on stainless steel substrate. First, GO particles were synthesized using a modified Hummers' method. GO was reduced electrochemically to form a coating in the presence of nano-sized TiO₂ particles. The influences of different parameters such as GO concentration, coupling co-electro-deposition parameters (electrophoretic duration and voltage) on thickness, surface morphology and, corrosion behavior of the as-synthesized TiO₂-rGO nanocomposite coatings were systematically surveyed. The morphology and microstructure were investigated by field emission scanning electron microscopy (FE-SEM), Raman spectra and X-ray diffraction (XRD) techniques. Atomic force microscopy (AFM) was harnessed to evaluate the topography of the as-prepared GO powder. The bonding characteristics of as-synthesized and as-reduced GO were examined after deposition, by Energy Dispersive Analysis of X-Ray (EDX) and Fourier-transform infrared spectroscopy (FT-IR). Corrosion behavior of coatings and that of the pure TiO₂ layer were evaluated by electrochemical impedance spectroscopy (EIS) and polarization techniques (by applying potentiodynamic polarization spectroscopy (PDS)). Detailed SEM studies showed that increasing EPD voltage brings about a coating with increased porosity and microcracks with higher thickness. In addition to that, the presence of rGO reduced corrosion current density (i_corr) and shifted corrosion potential (E_corr) toward more noble values in 3.5% NaCl at room temperature. Also, Analyses revealed that the optimum electrophoretically synthesized coating was obtained at GO concentration of 1 g/L, 30 V and 30 min at room temperature. The corrosion current density of the corresponding coating was remediated up to 0.2 μA cm⁻², which means an anti-corrosion ability of about 30 times compared to TiO₂-coated and bare 316L stainless steel. The results of impedance spectroscopic studies demonstrated that this coating renders as a barrier layer and resistance increased from 2.95 KΩ cm² for TiO₂-coated layer to 10.49 KΩ cm² for the optimized layer.     

Photocatalytic enamel/TiO2 coatings developed by electrophoretic deposition for methyl orange decomposition

The aim of this study was to obtain photocatalytic coatings, capable to decompose organic pollutants, through Electrophoretic Deposition (EPD) of enamels containing respectively 0%, 5%, 10%, 15% (in wt%) of TiO₂ onto carbon steel substrates. High quality and homogeneous coatings were obtained by applying 12.5?V during 10?s, as the best EPD conditions. The layers were subsequently heat treated at 740?°C for 10?min, in order to obtain dense glazes.Rietveld refinement of XRD patterns and Raman results show that, after the heat treatment at 740?°C, TiO₂ mostly exists as anatase, responsible of the photocatalytic effect. Semi-quantitative chemical analysis indicate segregation of TiO₂ on the coatings surface, reaching saturation in the sample with 10?wt% TiO₂. FEG-SEM observations reveal rod-like and spherical Ti-rich phases along the cross section of the coatings; some Ti was also dissolved into the enamel. 3D topographical mapping shows that, by adding TiO₂, surface roughness increases significantly.Photocatalytic tests were carried out using a 2?×?10^?5 M aqueous solution of Methyl Orange (MO) as an organic pollutant. By comparing the decomposition rate of MO achieved with the pure enamel (0% of TiO₂) and with the sample with 10% of TiO₂, it was shown that the addition of 10% of TiO₂ results in 90% photocatalytic efficiency.Moreover, the permeation of organic compounds and their UV degradation were studied by measuring the water contact angle onto the enamel surface directly after dipping into oleic acid and after various UV irradiation times. The longer the UV irradiation time, the lower the contact angle, down to a minimum of 14.54° after 8?h of UV irradiation. This means, the compound was initially adsorbed on the enamel/TiO₂ coating surface (10?wt% TiO₂) but was efficiently decomposed upon UV irradiation.     

Corrosive wear behavior of HVOF-sprayed micro-nano-structured Cr3C2–NiCr cermet coatings under aqueous media

A novel micro-nano-structured Cr₃C₂–NiCr cermet coating was prepared on 316L stainless steel by high-velocity oxygen fuel spraying technology (HVOF). Cermet coatings with different contents of micro-and nano-sized Cr₃C₂ particles as the hard phase and a NiCr alloy matrix as the bonding phase were prepared and characterized in terms of porosity, microhardness, and corrosive wear resistance in a 3.5% NaCl solution and artificial seawater. Compared to nanostructured coatings, micro-nano-structured coatings avoid decarburization and reduce nanoparticle agglomeration during the spray process, and mechanical and electrochemical properties were improved in comparison with those of conventional coatings. The micro-nano-structured Cr₃C₂–NiCr coating rendered low porosity (≤0.34%) and high microhardness (≥1105.0HV_0.3). The coating comprising 50% nano-sized Cr₃C₂ grains exhibited the best corrosive wear resistance owing to its densest microstructure and highest microhardness. Furthermore, compared to static corrosion, the dynamic corrosion of the coatings led to more severe mechanical wear, because corrosion destroyed the coating surface and ions promoted corrosion to invade coatings through the pores during corrosion wear.     

Effects of TiO2 on microstructural,mechanical properties and in-vitro bioactivity of plasma sprayed yttria stabilised zirconia coatings for dental application

One of the most compatible coatings, known as yttria-stabilised zirconia polycrystal (YZP) is deposited on metallic Ti alloys due to its excellent hardness and aesthetic value as well as its low affinity for plaques. However, poor bioactivities of YZP and the existence of micro crack propagations due to the aging of YZP may result in spontaneous implant failure thus limiting its clinical use. In this work, YZP coating reinforced titania (TiO₂), which is formed via a plasma spray technique was investigated in order to enhance the bioactivity and the mechanical properties of YZP coatings for dental implants. Based on microstructural studies performed on the deposited coating, a distinguished lamellar structure comprising YZP and TiO₂ was observed. It was found that the reinforcement of TiO₂ in YZP coating significantly reduced the crack due to the improved densities and the lamellar structure. The mechanical properties were also found to improve with 90% of hardness, 45% of adhesion strength and 54% of Young's Modulus with TiO₂ addition, which is desirable for dental implants. An in-vitro bioactivity test was then conducted by immersing the coatings in a simulated body fluid (SBF). As a result, an apatite formation was found on the YZP/TiO₂ coating surface after 3 days of immersion. Besides, it was verified in an XRD analysis that the crystalline TiO₂ was found in a rutile phase which was highly effective in generating apatite (natural mineral in human bones) on YZP coatings, proving that the bioactivities of the coating were significantly improved. Further studies were also performed on the SBF treatment, which took up to 14 days also demonstrated that only a small decrease in hardness was noted, indicating that YZP/TiO₂ coatings had reached an excellent mechanical stability.     

Synthesis and Characterization of Anti-fungus,Anti-corrosion and Self-cleaning Hybrid Nanocomposite Coatings Based on Sol–Gel Process

Anti-corrosion, anti-fungus, and self-cleaning properties of coatings containing ZnO–TiO₂, SiO₂–TiO₂ and SiO₂/TiO₂/ZnO nanoparticles synthesized based on sol–gel precursors using tetra methoxysilane, 3-glycidoxypropyl trimethoxysilane, tetra (n-butyl orthotitanate) and zinc acetate dihydrate were investigated by FESEM, EDAX and TEM analyses. Results indicated uniform dispersion of inorganic nanoparticles in the range of 20–40 nm in size. Anti-corrosion property of the hybrid coating was characterized by EIS measurements and parametrically analyzed in an equivalent circuit when the coating was exposed to salt solution. Results showed that, ZnO and TiO₂ nanoparticles enhance anti-corrosion property of the hybrid coatings. Anti-fungus and anti-bacterial properties of the coatings were determined by diameter of inhibition zone and inhabitation of bacterial growth, respectively. The coating containing ZnO and TiO₂ nanoparticles showed anti-fungus and anti-bacterial properties which were related to their photocatalytic properties. Degradation of methylene blue in aqueous solution was determined by UV–Visible tests which indicated self-cleaning property of the coatings containing ZnO and TiO₂ nanoparticles.     

UV-protective treatment for Vectran® fibers with hybrid coatings of TiO2/organic UV absorbers

The high performance of Vectran^® fiber makes its application as an envelope material for airship feasible. The ultraviolet (UV) resistance of this fiber, however, is poor, and UV irradiation in the stratospheric environment causes rapid fiber aging. To protect Vectran^® fibers from UV irradiation, we prepared TiO₂ nanosols via a sol–gel method and added benzotriazole UV-1130, triazine Tinuvin^® 477, and hindered amine Tinuvin^® 123 to them to form organic/inorganic hybrid coatings. Fiber specimens were subjected to accelerated aging using a xenon arc weatherometer. Mechanical measurements as well as surface morphology and chemical composition analyses were performed to evaluate the UV-protective performance of different coatings. Hybrid coatings performed better than TiO₂ coatings in protecting fibers from UV. Among the hybrid coatings obtained, UV-1130 especially reinforced the UV-protective ability of the TiO₂ coating because of its strong UV absorbance. Although the performances of Tinuvin^® 477 and Tinuvin^® 123 were below optimal when combined with TiO₂ alone, both hybrids exhibited excellent synergistic effects when used together with UV-1130 and improved the UV-protective ability of the resultant hybrid coatings.     

Photostabilization of cationic UV-cured coatings in the presence of nanoTiO2

The effect of TiO₂ nanoparticles for sun-weathering protection of UV-cured coatings is investigated. TiO₂ is either introduced in the form of nanoparticles in the photocurable formulations or generated in situ via sol–gel process. Cured films containing comparable amounts of TiO₂ were weathered for 800 h under UV irradiation and compared with free-TiO₂ coating. The TiO₂ presence induces a clear lower mass loss decrease during weathering as well as a lower gel content decrease. The TiO₂ screen effect is also confirmed by a lower alkyl-band reduction monitored by FT-IR during weathering. The TiO₂ generated in situ via sol–gel gives rise to transparent coatings without interfering with photopolymerization process and therefore without compromising UV-cured film properties.     

Investigating the role of surface treated titanium dioxide nanoparticles on self-cleaning behavior of an acrylic facade coating

In this study, the addition of silane treated TiO₂ nanoparticles on the self-cleaning properties of an acrylic facade coating was evaluated. Tetraethoxyorthosilicate, TEOS, was used for surface treatment of TiO₂ nanoparticles. The silica grafting on the TiO₂ nanoparticles was characterized via Fourier Transform Infrared spectroscopy, specific surface area measurement, pore size distribution, and real density measurements. The effect of surface treatment and content of nanoparticles on the photocatalytic activity of acrylic coating and self-cleaning properties was studied. For this purpose, the photodegradation of Rhodamine B (Rh.B) dyestuff, as a colorant model, was investigated by colorimetric technique, while the coating samples were exposed to UVA irradiation. Performance of the acrylic coating films was evaluated by gloss change during accelerated weathering conditions. Also, the surface morphology of the coating films was studied using SEM analysis. The results showed that the addition of both treated and untreated TiO₂ nanoparticles provides self-cleaning property to the acrylic coatings. However, silica surface treatment of TiO₂ nanoparticles reduces the coating degradation caused by TiO₂. This is more evident when higher concentrations of the treated TiO₂ nanoparticles are used.     

Synthesis,characterization and demonstration of self-cleaning TiO2 coatings on glass and glazed ceramic tiles

An effort was made not only to demonstrate the performance of the self-cleaning coatings on building materials such as ceramic glazed tiles and glass windows, but also to understand the fundamental issues that are still alive in the field of self-cleaning surfaces based on photocatalysis. Nano TiO₂ transparent thin films were generated by dip, spray and flow coating method. The present results indicate that the inconsistent results in the self-cleaning studies may be due to the effect of aggregation of model pollutant (methylene blue) dye on TiO₂ surface. The effect of aliovalent metal ion (Ni²⁺, Fe³⁺, Nb⁵⁺) doping on phase formation, polymorphic transition, visible light absorbance and optical transparency of TiO₂ film were investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV visible absorption spectroscopy. The improved visible light activity of doped TiO₂ thin film was correlated to the Ti(Ni/Fe)O₃ phase formation, UV and visible light absorbance, variation in the optical energy band gap and the probable light scattering associated with grain size.     

Photocatalytic performance of plasma sprayed Pt-modified TiO2 coatings under visible light irradiation

Plasma sprayed Pt/TiO₂ coatings were prepared by Atmospheric Plasma Spraying process. As-sprayed coatings were characterized by TEM, XRD and XPS. The photocatalytic performance was evaluated through the photo mineralization of methylene blue. All the Pt modified titanium dioxide coatings show significant absorption in the visible light range, while the pure titania coating reflects almost all the visible light. The photocatalytic efficiencies of as-sprayed pure TiO₂ coating and Pt/TiO₂ coatings are almost same under the irradiation of visible light. However, the efficiencies of all Pt/TiO₂ coating are greatly improved comparing with that of pure TiO₂ coating by applying 15 V external bias under the irradiation of visible light.     

UV‐curable coatings with nano‐TiO2

Nano‐TiO₂ particles were first milled into butyl acetate or trimethylolpropane triacrylate (TMPTA) to obtain TSB and TST slurries, then embedded into epoxy acrylate to obtain UV‐curable coating. The influence of nano‐TiO₂ particles on the photopolymerization kinetics, tack free time, thermal and optical properties of UV‐curable coatings was investigated. It was found that TST‐based coating had a decreasing but TSB‐based coating had an increasing UV cured rate in comparison with the pristine epoxy acrylate. Nevertheless, the TST‐based coating occupied shorter tack free time, good thermal property and UV absorbance than their corresponding TSB‐based coating. POLYM. ENG. SCI. 46:1402–1410, 2006. © 2006 Society of Plastics Engineers.     

Preparation and antibacterial activity of Ag/TiO2-functionalized ceramic tiles

An Ag/TiO₂ coating was deposited onto glazed ceramic tiles by a sol-gel and spraying method at high temperatures. The coating was characterized by X-ray diffraction, scanning electron microscopy, and atomic force microscopy. The results showed that silver was present in rutile-TiO₂, and the temperature did not change the phase composition of the samples. The Ag/TiO₂ coating had a higher roughness than the TiO₂ coating. The tape test (D 3359–08) showed that the coatings prepared at 950 °C and 1000 °C had good adhesion to the ceramic tile substrate. The antibacterial activity of the coating was tested by photocatalytic sterilization experiments. The results showed that the Ag/TiO₂ coating had a higher antibacterial activity than the TiO₂ coating, and the sterilization efficiency of Escherichia coli, Staphylococcus aureus, Shigella, and Salmonella exceeded 99.655% under 2 h of visible light irradiation. This research provides a method to create Ag/TiO₂ coatings with good thermal resistance, adhesion, and antibacterial activity. This improves the low photocatalytic activity caused by the anatase-to-rutile transformation of TiO₂ at high temperatures and the poor adhesion at low temperatures.     

Silicone functionalized pigment to enhance coating performance

The present study reports chemical treatment of pigment titanium dioxide (TiO₂) with silicone to give surface functionalized TiO₂. The surface functionalization was confirmed by Fourier Transform Infra Red Spectroscopy, Scanning Electron Microscopy, Transition Electron Microscopy and Dynamic Light Scattering analysis. Coatings were formulated by incorporation of these functionalized TiO₂ into the epoxy polymer matrix and compared for coating properties with untreated TiO₂. The effect of the functionalized TiO₂ on various coating properties with respect to physico-mechanical properties, anticorrosion efficiencies, UV resistance and chemical resistance was studied in detail. The results revealed remarkable enhancement of coating properties with functionalized TiO₂ when compared with the coatings formulated with untreated TiO₂.     

Plasma-sprayed TiO2 coatings: Hydrophobicity enhanced by ZnO additions

Titanium dioxide (TiO₂) powder mixed individually with 10 and 30 weight percentage (wt%) ZnO was thermally sprayed onto a grade B API 5 L carbon steel substrate by atmospheric plasma spraying. The effect of the addition of ZnO (10 wt% and 30 wt%) on the microstructures and wettability properties of the TiO₂/ZnO coatings was investigated. The characterization of the coatings was carried out using scanning electron microscopy, X-ray diffraction (XRD), laser confocal microscope, and sessile droplet system. The XRD analysis of the coating revealed that the anatase phase of TiO₂ in the powder state transformed into rutile phases for the produced TiO₂/ZnO coatings. Surface microstructure analysis revealed that the coatings had typical micro-roughened surfaces of plasma spraying products. The coating with 30 wt% ZnO produced a coating with remarkable pores and microcracks compared with the TiO₂ coating and coating with 10 wt% ZnO. Additionally, the increase in the wt% of ZnO increased the surface roughness value of the produced coatings and substantially changed the wettability properties of the TiO₂ coating from hydrophilic to hydrophobic.     

Uniform coating of TiO2 nanoparticles using biotemplates for photocatalytic wastewater treatment

Immobilization of TiO₂ particles over substrates like glass can facilitate the separation after photocatalytic runs. Photocatalytic activity of TiO₂ coatings is related to its morphology, crystallography, optical properties and adherence of the coating. Biotemplates, including animal-based and herbal-based templates are inexpensive, biocompatible and abundant and can control the quality of TiO₂ coating. In this study the effects of biotemplates such as agar, gelatin, and starch on the physiochemical properties of TiO₂ coatings were investigated. Synthesized coatings were characterized by XRD, BET, FESEM, TEM, FTIR, EDX, and UV-Vis DRS analyses. The results showed that using biotemplates reduces the TiO₂ crystallite size. Template-free TiO₂ had 30 nm crystallite size, but using templates like agar decreased the size to 18 nm. Moreover, the addition of biotemplates decreased the thickness of TiO₂ coatings compared to template free coating. And the use of biotemplates also limits the pore size distribution and increases BET surface area. According to EDX, TiO₂ coating with agar indicated a uniform Ti distribution and crack-free homogenous morphology. TEM analysis of agar-templated TiO₂ film showed a uniform morphology of TiO₂ particles with average particle size of 20 nm. The UV-Vis DRS also confirmed a reduction in the band gap of TiO₂ after the introduction of biotemplates. The study of the photocatalytic performance of samples showed that agar-templated TiO₂ coating was able to remove 62.4% of methylene blue, while the coatings synthesized with gelatin and starch were just able to remove 42.77% and 35%, respectively. The TiO₂ coating with agar was studied at different pH values and different initial methylene blue concentrations as well. The stability test of agar-templated TiO₂ coating after four runs indicated just 5% of activity lost.     

Fabrication of superhydrophilic self-cleaning SiO2–TiO2 coating and its photocatalytic performance

Generally, superhydrophilic self-cleaning coatings are prepared from semiconductors with photocatalytic properties. Organic pollutants attached to the coating surface can be degraded by its photocatalytic performance realizing a self-cleaning goal. Herein, SiO₂–TiO₂ composite particles were fabricated by the hydrolysis and precipitation of TiOSO₄, and SiO₂ microspheres were chosen as carriers, which are inexpensive and environmentally friendly. Then, superhydrophilic self-cleaning SiO₂–TiO₂ coatings were fabricated by spraying the composites on the surfaces of substrates. The morphology, structure and self-cleaning performance of the SiO₂–TiO₂ coating were characterized and tested. The results revealed that nano-TiO₂ was loaded on the surfaces of SiO₂ microspheres uniformly forming a hierarchical micro/nanostructure. The SiO₂–TiO₂ composite particles exhibited excellent photocatalytic degradation performance, and the degradation rate of methyl orange (10 ppm) was more than 98% under UV irradiation for 40 min. Furthermore, the coating prepared with the SiO₂–TiO₂ composite particles exhibited superhydrophilicity. A water droplet spreads completely on the coating surface in 0.35 s, and the contact angle reaches 0°. In addition, rhodamine B (RhB) and methylene blue (MB) on the coating surface can be degraded efficiently under sunlight irradiation. The SiO₂–TiO₂ composite particles can be sprayed directly on the surfaces of concrete, brick, wood, and glass slides. Therefore, the particles showed good adaptability to different substrates. The superhydrophilic property was due to the hydrophilicity of SiO₂ and TiO₂, the hierarchical micro/nanostructure of the SiO₂–TiO₂ composites, and the photoinduced superhydrophilicity of TiO₂. The above experimental results show that the as-prepared superhydrophilic self-cleaning SiO₂–TiO₂ coating has a large application potential.     

Wet film application techniques and their effects on the stability of RuO2–TiO2 coated titanium anodes

The effect of wet film application techniques on the physical and electrochemical properties and operational stability of RuO₂–TiO₂ coated titanium anodes was evaluated. Four compositions of RuO₂–TiO₂ coatings were applied to Ti substrates by three different wet coating methods—brush, dip and spin. Changing the coating technique resulted in different morphologies. Electrochemically active surface area of the coatings was related to the morphology. A shift in Ru(III)/Ru(IV) oxidation potential occurred upon changing the application technique. For lower ruthenium content coatings, this shift was related to coating lifetime. Anode stability in accelerated lifetesting showed that dip coated samples lasted up to three times longer than brush coated samples for lower ruthenium content.     

Solar reflectance,surface adhesion,and thermal conductivity of wood/natural rubber composite sheet with Tio2/polyurethane topcoat for roofing applications

Effects of titanium dioxide (TiO₂) dosage in polyurethane (PU) coating and PU coating thickness on solar reflectance, surface adhesion, crack resistance to bending, and thermal conductivity of wood/(natural rubber) (WNR) composite sheet were studied before and after prolonged UV aging. The TiO₂ powder content added to the PU coating was varied from 0 to 15 parts per hundred parts of PU. The average PU coating thickness on the WNR composite sheet was altered from 127 ± 10 to 315 ± 10 μm. The experimental results suggested that the solar reflectance slightly increased with increasing TiO₂ powder but did not change upon varying the PU coating thicknesses. The presence of TiO₂ in the PU coating caused a slight decrease in thermal conductivity because of porosities occurring due to the presence of voids, but increasing the TiO₂ powder content in the coating resulted in a progressive increase in thermal conductivity of the composite sheet. In a UV‐accelerated weathering tester (UVB 313 nm), the lightness of the PU coating slightly increased owing to PU discoloration, whereas the solar reflectance, PU/WNR layer adhesion, and crack resistance to bending remained unaffected with increasing UV aging time. J. VINYL ADDIT. TECHNOL., 18:184–191, 2012. © 2012 Society of Plastics Engineers