Effects of powder size and metallic bonding layer on corrosion behaviour of plasma-sprayed Al2O3-13% TiO2 coated mild steel in fresh tropical seawater

This study focuses on the effects of powder size and Ni–Al bonding layer on the electrochemical behaviour of plasma-sprayed Al₂O₃-13% TiO₂ coating in fresh tropical seawater. The presence of the metallic bonding layer reduces the coating porosity and increases the surface roughness for both microparticle and nanoparticle coatings. The nanoparticle exhibits better corrosion rate of 1.9×10⁻⁶ mmpy compared to the microparticle coating, with a corrosion rate of 3.05×10⁻⁶ mmpy. However, the presence of the metallic bonding layer increases the corrosion rate for both micro and nanoparticle coatings. The corrosion mechanism for the coating with and without the metallic bonding layer is discussed in detail.     

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.     

Surface coating performance of TiO<Subscript>2</Subscript> nanoparticle-modified veneered panels and their influence on formaldehyde emission

The physical and mechanical properties of wood and wood-based panels can be effectively improved by modification with nanoparticles. This paper focuses on effects of modifying veneer with titanium dioxide (TiO₂) nanoparticles on the performance of a waterborne coating and formaldehyde emission. Commercial waterborne varnish was used to apply a surface finish on the modified veneered panels. Changes caused by TiO₂ nanoparticle treatment that could affect the finishing performance were measured. The results showed slight increases in the weight and contact angle of the veneers treated with TiO₂ nanoparticles, whereas the modified veneered panels after surface finishing presented improved hardness at high nanoparticle loadings. Modification of the veneers by nanoparticles had a minor negative influence on the coating glossiness and adhesion due to a blocking effect between the coating film and the modified veneers. Formaldehyde emissions were considerably reduced due to degradation by the TiO₂ particles under UV-light irritation.     

Corrosion behavior of titania films coated by liquid‐phase deposition on AISI304 stainless steel substrates

Fouling deposition and localized corrosion on the heat‐transfer surfaces of the stainless steel equipments often simultaneously exist, which can introduce additional thermal resistance to heat‐transfer and damage heat‐transfer surfaces. It is a good anticorrosion way to coat a barrier layer of certain materials on the metal surface. In this article, the TiO₂ coatings with nanoscale thicknesses were obtained by liquid‐phase deposition method on the substrates of AISI304 stainless steel (ASS). The coating thickness, surface roughness, surface morphology, crystal phase, and chemical element were characterized with the film thickness measuring instrument, roughmeter, atomic force microscopy, field emission scanning electron microscopy, X‐ray diffraction, and energy‐dispersive X‐ray spectroscopy analyzer, respectively. Corrosion behavior of the TiO₂ coatings was evaluated by potentiodynamic polarization, cyclic voltammograms scanning, and electrochemical impedance spectroscopy tests with the mixed corrosion solution composed of 3.5 wt. % NaCl and 0.05 M NaOH. It is shown that the TiO₂ coating is composed of the nanoparticles with smooth, crack‐free, dense, and uniform surface topography; the roughness of coating surface increases slightly compared with that of the polished ASS substrate. The anatase‐phase TiO₂ coatings are obtained when sintering temperature being varied from 573.15 to 923.15 K and exhibit better anticorrosion behavior compared with ASS surfaces. The corrosion current density decreases and the polarization resistance increases with the increase of the coating thickness. The corrosion resistance of the TiO₂ coatings deteriorates with the increase of the corrosion time. The capacitance and the resistance of the corrosion product layer between the interface of the ASS substrate and the TiO₂ coating are found after the corrosion time of 240 h. A corrosion model was introduced, and a possible new explanation on the anticorrosion mechanisms of the TiO₂ coating was also analyzed. The corrosion mechanism of the TiO₂ coating might comply with the multistage corrosion process. © 2011 American Institute of Chemical Engineers AIChE J, 58: 1907–1920, 2012     

A novel hybrid composite coating of poly-3-amino-5-mercapto-1,2,4-triazole/TiO<Subscript>2</Subscript> on copper for corrosion protection

Poly-3-amino-5-mercapto-1,2,4-triazole/TiO₂ (p-AMTA/TiO₂) composite was effectively synthesized over the copper surface by cyclic voltammetric technique and used as a protective coating against corrosion. The resulting polymeric composite was characterized using Fourier transform infrared spectroscopy. The presence of TiO₂ particles in the polymer matrix was substantiated from X-ray diffraction pattern and energy-dispersive X-ray spectrum. The uniform dispersion of TiO₂ particles in the polymeric matrix was confirmed by the scanning electron microscope images. The protective effect of composite coating was evaluated by electrochemical impedance spectroscopy and potentiodynamic polarization methods in 3.5 % NaCl medium. Impedance measurements showed that charge transfer resistance (R _ct) values increased for polymeric composites which suggested the enhanced corrosion protection of copper. Further, the decrease in corrosion current density (i _corr) values and shifting of corrosion potential (E_corr) toward the cathodic direction confirmed the anticorrosive behavior of the polymeric composite. The reason for the higher protection of polymeric composite may be due to the well-dispersed TiO₂ particles in the polymer matrix exhibiting the enhanced barrier properties to protect copper surface from corrosion. The defects in the coatings can be reduced by embedded TiO₂ particles in the pores of the polymeric films to enhance the corrosion protection, consequently.     

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.     

The effect of TiO2 as a pigment in a polyurethane/polysiloxane hybrid coating/aluminum interface based on damage evolution

The effect of titanium oxide as an additive on the performance of a polyurethane/polysiloxane hybrid coating was characterized by an electrochemical approach. The performance evolution was quantified by exposing the hybrid coating on an aluminum substrate to NaCl solution at pH 5 over time. Real-time measurements were performed to quantify and correlate the mechanisms that occur at the coating/substrate interface. Electrochemical impedance spectroscopy (EIS) quantified the hybrid coating/substrate interface performance over the course of the 263 days of exposure, and electrically passive elements described and characterized the degradation/performance stages upon exposure to the acidic NaCl solution.The addition of TiO₂ produced hydrophobicity functionality, and TiO₂ acted as a physical barrier layer that influenced the initial damage stage. Different exposure times were associated the different stages of damage evolution for the hybrid coating and coating/substrate interfaces. Electrochemical testing with high-resolution techniques such as AFM (atomic force microscope) and IFM (infinite focus microscope) characterized the coating surface and the interface performance and resolved the surface and defect formation observed with different levels of TiO₂ content. Of the systems tested, the system with 10 wt% TiO₂ provided the best corrosion inhibition.     

In situ polymerizations of thiophene on TiO2 films using the semiconductors as initiators

In this work, we prepare the TiO₂ nanoparticle film and anatase TiO₂ nanoarray film, and we achieve the polymerizations of thiophene using the photoexcited TiO₂ film as the initiators. It is measured that the in situ polymerizations of thiophene take place on the surfaces of the two films. The growth of polythiophene (PTh) on the TiO₂ nanoarray is monitored using Fourier‐transform Raman spectroscopy. The TiO₂ nanoarray is found to strongly interact with the PTh polymers. It is observed using scanning electron microscope that the microspores in the nanoarray are filled by the polymers after the reaction of 3 h, and the nanoarray is fully covered by the polymer layer when the polymerization lasts for 5 h. The PTh–TiO₂ nanoarray composite films are measured for the transient photocurrents and photocurrent‐voltage characteristics. The dependence of the photocurrents on the reaction time is revealed and discussed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40187.     

Synthesis of nitrogen-doped carbon coated TiO2 microspheres and its application as metal support in cinnamaldehyde hydrogenation

N-doped carbon coated TiO₂ microspheres (CNx/TiO₂) were synthesized by the carbonization of the polypyrrole (PPy) coating on the surface of TiO₂ microspheres and used as support to disperse Pt and PtCo nanoparticles for investing the selective hydrogenation of cinnamaldehyde. The support and catalysts have been characterized in terms of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscope (TEM), scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS). The hydrogenation results showed the conversion increased with an increase of CNx amount until the CNx coated TiO₂ microspheres completely.     

Imaging of oxide dielectrics by near-field microwave microscopy

Scanning near-field microwave microscopy was used to image LaAlO₃ and TiO₂ single crystals and bulk yttria-stabilized zirconia (YSZ) polycrystalline ceramic microstructures. The effect of microstructural features including grain boundaries, twins, surface roughness, and oxygen content variations on the local dielectric constant, and the resulting microscope image quality are discussed.     

Extended hydrophobicity and self-cleaning performance of waterborne PDMS/TiO<Subscript>2</Subscript> nanocomposite coatings under accelerated laboratory and outdoor exposure testing

It has been shown that incorporation of TiO₂ nanoparticles into hydrophobic coatings can show self-cleaning performance. Accelerated laboratory testing indicated that the coats retain their hydrophobic nature for an extended time period. In this paper, hydrophobic polydimethylsiloxane (PDMS)/TiO₂ nanocomposite coatings with a TiO₂ content of 0–40% were fabricated by simple blending of a PDMS dispersion with an aqueous TiO₂ nanoparticle dispersion. Their long-term hydrophobicity and self-cleaning performance were investigated both in laboratory and real-world outdoor testing. As expected, TiO₂ nanoparticle-based coatings exhibited better self-cleaning relative to the TiO₂-free PDMS control coating as measured by methylene blue degradation testing. Excellent long-term hydrophobicity was observed in accelerated weathering testing when they contained the appropriate levels of TiO₂ nanoparticles (i.e., 0–30%). However, the same PDMS/TiO₂ coatings did not show self-cleaning performance, and instead, exhibited improved dirt pickup resistance, in outdoor exposure testing. Sustained hydrophobicity was observed in outdoor exposure testing for the clear films except when TiO₂ levels were at 40%. The hysteresis of water contact angle (HWCA) significantly increased for the PDMS control coating, and water beading was lost as the film surface picked up dirt. In contrast, the TiO₂-based coatings with appropriate TiO₂ levels maintained a relatively low HWCA after outdoor exposure and no water sheeting on rainy days was observed. This result demonstrates that while photocatalytic TiO₂ nanoparticles can maintain coating hydrophobicity upon outdoor exposure, long-term self-cleaning performance in polluted environments has not yet been achieved with this type of coating under real-world conditions.     

Effect of Fe3+ and F− on black micro-arc oxidation ceramic coating of magnesium alloy

This study focuses on a black micro-arc oxidation ceramic coating prepared on the surface of magnesium alloy by the technology of micro-arc oxidation in the electrolyte containing F^– and Fe³⁺ as well as its mechanism of F^– and Fe³⁺. It needs coatings to experience detail analyses on their thickness, roughness, corrosion resistance, thermal control property, valence states of elements, phase composition, and morphology of coatings, respectively, through coating thickness gauge, roughness tester, electrochemical workstation, AE radiometer, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscope (SEM), and energy-dispersive X-ray spectroscopy (EDS). Results showed that with the help of F^– in electrolyte, Fe³⁺ can be complexed and MgF₂ can be obtained in the coating, which reduces the pores on the surface of micro-arc oxidation coating. In addition, Fe³⁺ in the electrolyte contributes to the preparation of Fe₂O₃ and Fe₃O₄ in the coating, which can blacken the surface of the coating. Both F^– and Fe³⁺ benefit to improve the corrosion resistance and thermal control performance of micro-arc oxidation coating. There is higher iron oxide in the outer layer but higher fluoride in the inner layer of the coating.     

An evaluation of plasma-sprayed coatings based on Al2O3 and Al2O3–13 wt.% TiO2 with bond coat on pure titanium substrate

In this study, the effects of bond coat on the properties of Al₂O₃ and Al₂O₃–13 wt.% TiO₂ coatings, which is plasma sprayed onto a commercial pure titanium substrate with and without Ni–5 wt.% Al (METCO 450 NS) as bond coating layer were investigated in terms of microhardness, bonding strength and surface roughness. Optical and scanning electron microscopy (SEM) examinations revealed that there is a uniform coating layer with no spalling and delamination. However, there is a little amount of porosity. The results indicated that the application of bond coat layer in the plasma spraying of Al₂O₃ and Al₂O₃–13 wt.% TiO₂ on pure titanium substrate has increased the hardness and bonding strength of coatings. While the adhesive bonding is dominant without bond coat, the cohesive bonding is dominant with the application of the bond coating layer. It has been observed that percentage of cohesion strength was about three times higher than that of adhesion strength.     

A Novel Approach to Well‐Aligned TiO2 Nanotube Arrays and Their Enhanced Photocatalytic Performances

A simple route has been developed to prepare well‐aligned TiO₂ nanotube arrays, which is based on outward coating of TiO₂ and inward etching of Cu(OH)₂ nanorod templates. Effects of annealing temperature and time on the crystal size and crystallinity of TiO₂ nanotube arrays and photocatalytic activities of TiO₂ nanotube arrays for degradation of Rhodamine B in aqueous solution have been investigated. The results indicate that the TiO₂ nanotube arrays annealed at 500°C for 2 h possessed an enhanced photocatalytic activity in comparison with the TiO₂ nanotube arrays without post heating and commercial anatase TiO₂ nanoparticle film and presented a good life cycle performance. Scale‐up of the process has also been demonstrated. Our work opens a new avenue to fabricate free‐standing TiO₂ nanotube arrays and demonstrates an excellent photocatalytic performance of the anatase TiO₂ nanotube arrays for wastewater treatment. © 2012 American Institute of Chemical Engineers AIChE J, 59: 2134–2144, 2013     

TiO<Subscript>2</Subscript>/Ni Inverse-Catalysts Prepared by Atomic Layer Deposition (ALD)

Abstract  

Atomic layer deposition (ALD) was used to deposit TiO₂ on Ni particles, and the catalytic activity of Ni for CO₂ reforming of methane (CRM) was evaluated. In the presence of TiO₂ islands on Ni surfaces, the onset temperature of the CRM reaction was lower than that of bare Ni. During the CRM reaction, carbon was deposited on the surface of bare Ni, which reduced the catalytic activity of the surface with time, and TiO₂ islands were able to remove carbon deposits from the surface. When the Ni surface was completely covered with TiO₂, the catalytic activity disappeared, demonstrating that tuning of the TiO₂ coverage on Ni is important to maximize the activity of the CRM reaction.     

Optimizing Graphene Oxide Encapsulated TiO2 and Hydroxyapatite; Structure and Biological Response

Nanocomposites based on hydroxyapatite (HAP) are fabricated with/without combining titanium oxide (TiO₂) and graphene oxide. Structure investigation was done for all compositions using X-ray diffraction (XRD), Fourier-transform infrared in addition to X-ray photoelectron to study the chemical compositions of the obtained nanocomposites. The surface morphology investigation was done with the scanning electron microscope and transmission electron microscope. In this regard, TiO₂ nanoparticles were exhibited in spherical shapes, while HAP was detected as nanorods. The dimensions of HAP have been decreased from 53 and 18 to 27 and 10 nm for length and diameter, respectively. The crystallite sizes obtained from XRD data are around 15 and 33 nm for HAP and TiO₂ respectively. Moreover, the diameter of TiO₂ reached 80 nm. Further, the average roughness parameter (R_a) improved from 9.2 to 11.1 nm from HAP to TNC. Besides, the root mean square (R_q), maximum height of the roughness (R_t), and maximum roughness valley depth (R_v) increased to 14.7, 104, and 55.9 nm, respectively. Furthermore, cell viability enhanced from 96.3?±?3 to 102.4?±?3%. Besides, the antibacterial behavior improved to be 15.3?±?1.3 and 14.2?±?0.9 mm for TNC against E. coli and S. aureus respectively.

     

Study of morphology and gas separation properties of polysulfone/titanium dioxide mixed matrix membranes

Polysulfone (PSf)‐based mixed matrix membranes (MMMs) with the incorporation of titanium dioxide (TiO₂) nanoparticles were prepared. Distribution and agglomeration of TiO₂ in polymer matrix and also surface of membranes were observed by scanning electron microscopy, transmission electron microscopy, and energy dispersive X‐ray. Variation in surface roughness of MMMs with different TiO₂ loadings was analyzed by atomic force microscopy. Physical properties of membranes before and after cross‐linking were identified through thermal gravimetric analysis. At low TiO₂ loadings (≤3 wt%), both CO₂ and CH₄ permeabilities decreased and consequently gas selectivity improved and reached to 36.5 at 3 bar pressure. Interestingly, PSf/TiO₂ 3 wt% membrane did not allow to CH₄ molecules to pass through the membrane and this sample just had CO₂ permeability at 1 bar pressure. Gas permeability increased considerably at high filler contents (≥5 wt%) and CO₂ permeance reached to 37.7 GPU for PSf/TiO₂ 7 wt% at 7 bar pressure. It was detected that, critical nanoparticle aggregation has occurred at higher filler loadings (≥5 wt%), which contributed to formation of macrovoids and defects in MMMs. Accordingly, MMMs with higher gas permeance and lower gas selectivity were prepared in higher TiO₂ contents (≥5 wt%). POLYM. ENG. SCI., 55:367–374, 2015. © 2014 Society of Plastics Engineers     

Biocompatibility,corrosion resistance and antibacterial activity of TiO2/CuO coating on titanium

In this work, TiO₂/CuO coating was prepared on titanium (Ti) by combination of magnetron sputtering and annealing treatment. The microstructure, biocompatibility, corrosion resistance and antibacterial property of TiO₂/CuO coating were investigated in comparison with pure Ti and TiO₂ coating. The results show that TiO₂/CuO coating is mainly composed of TiO₂ and CuO. In vitro cytocompatibility evaluation suggests that no obvious toxicity appears on the TiO₂/CuO coating, and the coating stimulates the osteoblast spreading and proliferation. Compared with Ti and TiO₂ coating, TiO₂/CuO coating exhibits improved corrosion resistance and antibacterial ability against S.aureus. This study is the first attempt to apply the combination of magnetron sputtering and annealing treatment to introduce the Cu into TiO₂ coating for surface modification of Ti-based implant materials, which may provide a research foundation for further development of bioactive multifunctional coatings to meet the better clinical demand.     

Structures and properties of the polyester nonwovens coated with titanium dioxide by reactive sputtering

Nanoscale titanium dioxide (TiO₂) films were deposited on the surface of polyester nonwovens by using direct current (DC) reactive magnetron sputtering. The effect of coating thickness on the surface structures and properties of TiO₂ coated fabrics was investigated by atomic force microscope (AFM), X-ray diffraction (XRD), energy dispersive X-ray analysis system (EDX), scanning electron microscope (SEM), and antistatic test in this article. The results indicated that the grain sizes of the sputtered clusters increased and the coating layer became more compact as film thickness was increased, but the crystal structure did not have any significant change. At the same time, the film mechanical properties and antistatic performance in general depended strongly on the film thickness which could lead to the optimum thickness for a particular application.     

Gel-sol synthesis of surface-treated TiO2 nanoparticles and incorporation with waterborne acrylic resin systems for clear UV protective coatings

Visible transparent UV protective coatings were developed by incorporating nano-TiO₂ into waterborne acrylic systems to provide UV protection for UV-sensitive color cool roofing. Water-based high crystalline TiO₂ nanoparticle suspension was prepared via a gel-sol method at a basic pH. The TiO₂ nanoparticles have an average size of 20 nm and are stable against agglomeration. As-prepared TiO₂ nanosuspension is ready to be well dispersed in commercial waterborne acrylic resin system without extra-surface modification. The fabricated TiO₂/acrylic nanocomposite coating achieved a UV cut-off below 350 nm with a visible transmission greater than 85% at 700 nm. It is also demonstrated by using Rhodamine 6G that surface modification of nano-TiO₂ with a SiO₂ insulation layer would suppress the catalytic activity of nano-TiO₂ and improve the UV protection for UV and photocatalysis sensitive dyes.