Sol-gel derived TiO2 coating on plasma nitrided 316L stainless steel

Titania film is coated on plasma nitrided 316L stainless steel by sol-gel method. Crystallization of titania as well as N loss and formation of Fe₂O₃ occurs during the annealing heat treatment. The titania film has short cracks within the grooves of plasma etched grain boundaries. With the increase of annealing temperature and duration, surface hardness of the samples is increased, but the toughness is decreased due to oxidization of the surface layer. The coating sample heat treated at 350 °C for 10 min and 450 °C for 10 min has better corrosion resistance than the nitrided stainless steel tested by the potentiodynamic polarization in 0.9% NaCl solution. Water contact angle of the titania film on the rough nitrided steel substrate decreases with UV irradiation treatment, reaching 17° after 3 h treatment.     

Silicon releasing sol-gel TiO2-SiO230/70 films

TiO₂-SiO₂30/70 mol% sol-gel films were prepared on glass slides by a dip-coating method. The sols were prepared by a two-step hydrolysis process, where either the Si- or Ti-sol was prehydrolyzed before mixing the sols together. The acidity of the prehydrolyzed sol was varied. The surface structure and composition of formed films were characterized by contact angle meter, atomic force microscope and X-ray photoelectron spectroscopy. The silicon dissolution was performed in tris(hydroxymethyl)aminomethane buffer. The films were able to release silicon and the surface chemistry of films was dependent on the preparation method. The prehydrolysis of Si-sol and aging of mixed sol increased surface silica concentration of the formed films. The surface morphology was dependent on the preparation method so that through Si-sol prehydrolysis it was possible to make rougher nanosurfaces with needle-like particles.     

The role of Ag particles deposited on TiO2 or Al2O3 self-organized nanoporous layers in their behavior as SERS-active and biomedical substrates

In this paper, we present recent results of investigations of hybrid materials consisting of nanoporous oxides layers loaded with Ag nanoparticles: Ag/TiO₂-n/Ti and Ag/Al₂O₃-n/Al (where “n-“stands for nanotubes), which could be used as active SERS substrates or as bioactive materials in medicine (implants). Simple electrochemical, chemical and physical methods appear suitable for fabricating such hybrid materials having different functional properties.     

Fabrication of polycrystalline TiO2 nanopatterns by TiO2 sol base imprint lithography

This paper reports a process for fabricating TiO₂ nano-patterns using nanoimprint lithography and a sol–gel method. An ethanol-based TiO₂ sol was prepared using tetrabutylorthotitanate as a precursor and used as an imprint resin. A replicated polydimethylsiloxane (PDMS) mold was used as an imprint stamp. During the imprinting process at 5 atm and 200 °C for 1 h, the TiO₂ sol changed to a TiO₂ gel by absorbing the solvent into the PDMS mold. After imprinting, a TiO₂ gel pattern was formed on an oxidized Si wafer. After subsequent annealing, it confirmed that patterns of the master template were transferred to TiO₂ patterns by Scanning Electron Microscopy. Furthermore, Transmission Electron Microscopy and X-Ray Diffraction showed that the TiO₂ gel patterns had been converted to an inorganic polycrystalline TiO₂ pattern.     

Formation of SrTiO3 from Sr-oxalate and TiO2

SrTiO₃ powder has been prepared from Sr-oxalate and TiO₂ precursors, instead of using titanyl-oxalate. Sr-oxalate was precipitated from nitrate solution onto the surface of suspended TiO₂ powders. Crystallization of SrTiO₃ from the precursor was investigated by TGA, DTA and XRD analysis. It is evident that precursor, upon heating, dehydrates in two stages, may be due to the presence of two different types of Sr-oxalate hydrates. Dehydrated precursor then decomposes into SrCO₃ and TiO₂ mixture. Decomposition of SrCO₃ and simultaneous SrTiO₃ formation occur at much lower temperature, from 800 °C onwards, due to the fine particle size of the SrCO₃ and presence of acidic TiO₂ in the mixture. The precursor completely transforms into SrTiO₃ at 1100 °C. About 90 nm size SrTiO₃ crystallites are produced at 1100 °C/1 h, due to the lower calcination temperature and better homogeneity of the precursor.     

Luminescence and excitation spectra of Cr:MgAl2O4 nanoceramics

The effect of the applied sintering pressure on luminescence and excitation spectra of Cr³⁺ doped MgAl₂O₄ nanoceramics was investigated. It was found that the intensity of ²E → ⁴A₂ phosphorescence decreased significantly when pumped directly into ⁴T₁ band. The effect was extremely strong for nanoceramics sintered at higher pressures. Moreover, the intensity of ⁴A₂ → ⁴T₁ band in excitation spectra drastically decreased with sintering pressure compared to ⁴A₂ → ⁴T₂ band. This behavior was related to trigonal distortion of O_h symmetry of Cr³⁺ ion which increases with decreasing the size of nanocrystals resulting in enhancement of the ⁴T₁ → ⁴T₂ nonradiative pathway due to decrease of ΔE (⁴T₁, ⁴T₂) energy gap.     

Electrophoretic deposition of aqueous nano-γ-Al2O3 suspensions

The deposits of nano-sized γ-Al₂O₃ powders were fabricated via a simple electrophoretic deposition process in aqueous suspensions. Bubble-free deposits of nano-γ-Al₂O₃ powders with a uniform microstructure and high green density up to 56.8% were successfully obtained. Some factors that contribute to the deposition characteristics of the EPD in an aqueous suspension are discussed.     

Electrodeposition of biodegradable sol-gel derived silica onto nanoporous TiO2 surface formed on Ti substrate

This paper demonstrates the utility of an electrodeposition technique to deposit a layer of biodegradable sol-gel derived silica on a Ti substrate coated with a nanoporous TiO₂ layer in a controlled manner. The deposition pattern of the silica phase was tailored by controlling the silica sol content in the diluted solution and the deposition time. This allowed the nanopores to be filled with the silica phase, confirmed by energy dispersive spectroscopy and Fourier-transform infrared spectroscopy, whilst preserving the nanoporous surface, particularly when electrodeposition was carried out in a dilute solution with a silica sol content of 30 vol.% for < 30 min at an electric field of 2.5 V/cm.     

Fabrication of TiO2 hollow fibers with surface nanostructure

Polyvinyl alcohol-TiO₂ (PVA-TiO₂) core sheath nanofibers were fabricated by electrospinning an aqueous solution of PVA and introducing the thread-like droplets directly into a titanium tetraisopropoxide (TTIP)/hexane solution. Rod-like and sheet-like structures of lepidocrocite-type layered titanate formed on the surface of the TiO₂ sheath of the nanofibers by alkaline treatment in 1 mol L⁻¹ aqueous NaOH solution at 363 K. The nanofibers were converted to hollow TiO₂ nanofibers with surface nanostructure and anatase crystallinity by acid treatment to remove sodium ions and heat treatment at 773 K. The surface nanostructures enhanced the crystallinity and external surface area of the nanofiber and contributed to the improvement of photocatalytic oxidation activity.     

TiO2-VOx纳米复合膜制备及耐腐蚀性研究

采用溶胶-凝胶法和浸渍提拉技术在316L不锈钢(316Lss)表面构筑纳米TiO2,TiO2/TiO2-VOx/TiO2复合膜,应用AFM和XRD表征膜的形貌及结构,并用光、电化学方法测试复合膜在0.5 mol/L NaCl溶液中暗态或紫外照射下的耐腐蚀性能,结果表明TiO2/TiO2-VOx/TiO2复合膜具有双重保护功能,即在紫外光照下可以起到光生阴极保护的作用,特别是当停止光照后,光生电位仍可维持在较低的电位长达6h以上;作为覆盖层纳米复合膜又可作为良好的阻挡层显著提高金属的耐腐蚀性.     

Effect of PWVA/Sb2O3 complex inhibitor on the corrosion behavior of carbon steel in 55%LiBr solution

The inhibition performance of PWVA/Sb₂O₃ complex inhibitor on carbon steel was studied in 55%LiBr + 0.07 mol L⁻¹ LiOH solution. Results indicated that the complex inhibitor decreased both anodic and cathodic polarization current density and widened the passive potential region of carbon steel in test solution and can be classified as mixed inhibitor. The complex inhibitor exhibited excellent inhibition performance on carbon steel when the concentrations of PWVA and Sb₂O₃ were 300 and 200 mg L⁻¹, respectively. With the solution temperature increasing from 145 to 240 °C, the corrosion rates of carbon steel increased from 4.71 to 120.66 μm y⁻¹. In solution containing the complex inhibitor, the relationship between relative coverage ratio of inhibitor on carbon steel surface and inhibition efficiency at 145 °C was obtained as the equation μ = 0.94η, it was a direct proportion. This result proved that the complex inhibitor inhibited the corrosion of carbon steel by geometric blocking effect. When solution temperature was 160 °C, the adsorption Gibbs free energy of PWVA and Sb₂O₃ on carbon steel were −49.59 and −44.29 kJ mol⁻¹, respectively. It indicated that the adsorption processes of PWVA and Sb₂O₃ on carbon steel surface were spontaneous processes. As a strong oxidant, PWVA facilitated the compact passive film comprising of FeO, Fe₂O₃ and Fe₃O₄ forming on the surface and itself was reduced to heteropoly blue. Sb₂O₃ adsorbed on carbon steel surface formed an adsorption film. PWVA and Sb₂O₃ behaved synergistic effect. The corrosion resistance performance of carbon steel in 55%LiBr + 0.07 mol L⁻¹ LiOH solution was improved by PWVA/Sb₂O₃ complex inhibitor.     

Influence of temperature and hydrodynamic conditions on the corrosion behavior of AISI 316L stainless steel in pure and polluted H3PO4: Application of the response surface methodology

Phosphoric acid is mainly produced by the wet acid process, where corrosion problems could be intensified due to the presence of impurities in the phosphate ores. Operating temperatures and flowing conditions aggravate the aforementioned problems. This work studies the influence of temperature (25–60 °C) and hydrodynamic conditions (Reynolds numbers from 1456 to 5066) on the corrosion of AISI 316L stainless steel in pure and polluted phosphoric acid solutions, by means of cyclic potentiodynamic polarization curves in a hydrodynamic circuit. The effect of temperature is the same as that caused by impurities, that is, higher corrosion rates and hindered passivation and repassivation resistance of the alloy. Statistical analysis by means of surface response methodology proved that the effect of temperature on the corrosion parameters of AISI 316L is more influential than the Reynolds number effect. The Reynolds number seems to have no significant influence on the corrosion behavior of stainless steel. Furthermore, the influence of temperature on the corrosion rate is much higher than on the rest of the corrosion parameters analyzed, especially in polluted phosphoric acid solutions. AISI 316L stainless steel has a clear interest for the phosphoric acid industry as a component material of some equipment due to its good corrosion properties at the different temperatures and Reynolds numbers studied even in polluted media.     

Fabrication, structure, and enhanced photocatalytic properties of hierarchical CeO2 nanostructures/TiO2 nanofibers heterostructures

Combining the versatility of electrospinning technique and hydrothermal growth of nanostructures enabled the fabrication of hierarchical CeO₂/TiO₂ nanofibrous mat. The as-prepared hierarchical heterostructure consisted of CeO₂ nanostructures growing on the primary TiO₂ nanofibers. Interestingly, not only were secondary CeO₂ nanostructures successfully grown on TiO₂ nanofibers substrates, but also the CeO₂ nanostructures were uniformly distributed without aggregation on TiO₂ nanofibers. By selecting different alkaline source, CeO₂/TiO₂ heterostructures with CeO₂ nanowalls or nanoparticles were facilely fabricated. The photocatalytic studies suggested that the CeO₂/TiO₂ heterostructures showed enhanced photocatalytic efficiency of photodegradation of dye pollutants compared with bare TiO₂ nanofibers under UV light irradiation.     

Photoactive and self-cleaning TiO2-SiO2 thin films on 316L stainless steel

In this study, TiO₂-SiO₂ nanocomposite films with different amounts of SiO₂ were prepared by sol-gel process and were coated onto stainless steel 316L. The effect of addition of various amount of SiO₂ in the precursor solution on the photocatalysis, photo-generated hydrophilicity and self-cleaning property of TiO₂ thin films was investigated by X-ray diffraction, Fourier transform infrared spectroscopy, water contact angle measurements and UV spectroscopy. In the tested ranges of SiO₂ content and sintering temperature, the highest photocatalytic activity and self-cleaning property were observed in the 15 mol% SiO₂ sample sintered at 750 °C. Addition of less than 30 mol% SiO₂ had a suppressive effect on the transformation of anatase to rutile and on the crystal growth of anatase in the sintering heat treatment. Phase separation occurred in the composite films for SiO₂ content of 30 mol% or more.     

Effect of nano-TiO2 particles size on the corrosion resistance of alkyd coating

The coating system containing various sizes (∼10, 50, 100, 150 nm) of nano-TiO₂ were prepared and investigated for corrosion protection of carbon steel in 1.0 M H₂SO₄ using polarization, EIS and transmission electron microscopy (TEM) techniques. It was found that nano-TiO₂ particles improved the corrosion resistance of alkyd coatings. The corrosion resistance occurs via physical adhesion on the metal surface. O₂ and H₂O permeability of coating decreased with decrease in the nano-TiO₂ size. The inhibition efficiency was found to increase with decreasing the size of nano-TiO₂ and with decreasing the temperature.     

Influence of TiO2 incorporation in HfO2 and Al2O3 based capacitor dielectrics

Atomic layer deposition was applied to fabricate metal oxide films on planar substrates and also in deep trenches with appreciable step coverage. Atomic layer deposition of Ru electrodes was realized on planar substrates. Electrical and structural behaviour of HfO₂-TiO₂ and Al₂O₃-TiO₂ nanolaminates and mixtures as well as Al₂O₃ films were evaluated. The lowest leakage current densities with the lowest equivalent oxide thickness were achieved in mixed Al₂O₃-TiO₂ films annealed at 700 °C, compared to all other films in as-deposited state as well as annealed at 900 °C. The highest permittivities in this study were measured on HfO₂-TiO₂ nanolaminates.     

Thermo-responsive copolymer coated MnFe2O4 magnetic nanoparticles for hyperthermia therapy and controlled drug delivery

This study is about multifunctional magnetic nanoparticles surface-modified with bilayer oleic acid, and coated with a thermo-responsive copolymer poly(N-isopropylacrylamide-co-acrylamide) by emulsion polymerization, for controlled drug delivery and magnetic hyperthermia applications. Nanoparticles were loaded with anticancer drug doxorubicin into the copolymer chains at 25 °C. Composite nanoparticles (hydrated) of average diameter 45 nm were of core–shell structure having magnetic core of about 18 nm and shell was composed of organic compounds and water. Magnetic core was superparamagnetic lacking coercive force and remanance due to the pseudo-single domain nanostructure. Lower critical solution temperature (LCST) of the thermo-responsive copolymer was observed to be around 39 °C. Below this temperature, copolymer was hydrophilic, hydrated and swelled. But above LCST, copolymer became hydrophobic, dehydrated and shrank in volume. UV visible spectrophotometer was used to investigate the drug loading and releasing profile at different temperatures as well as under magnetic heating. There was almost absence of drug release at around 37 °C (normal body temperature). Drug was released at temperatures above LCST, which is significant for controlled drug delivery. Magnetic heat-generation was studied by exposing the magnetic fluid to alternating magnetic field of 7.2 kA m⁻¹ having frequency 70 kHz. A simple magnetic capturing system (simulating a blood vessel) was used to analyze the capturing of magnetic nanoparticles under various applied fields for drug targeting purpose.     

Photoelectrochemical property of ZnFe2O4/TiO2 double-layered films

ZnFe₂O₄/TiO₂ double-layered films on indium-tin oxide (ITO) substrate were prepared by a dip-coating method, and the optical absorption and photocurrent of the as-prepared films were measured. In the double-layered films, the onset of fundamental absorption edge shifts to a longer wavelength, and even shifts to a longer wavelength than that of ZnFe₂O₄-only film as the ZnFe₂O₄ layer thickness increases. Application of the coupled photoanodes double-layered films composed of ZnFe₂O₄ and TiO₂ can obviously increase the photocurrent. It was found that the photocurrent density of ZnFe₂O₄/TiO₂ double-layered films first increased and then decreased with increasing the ZnFe₂O₄ layer thickness. A five-fold increase in the photocurrent density was obtained compared with TiO₂-only films under optimum condition.     

Solid phase preparation of submicron-sized SrTiO3 crystallites from SrO2 nanoparticles and TiO2 powders

Submicron-sized SrTiO₃ crystallites were prepared by a low temperature solid state method. The proposed preparation method involved two simple steps: firstly, SrO₂ nanoparticles of 35–90 nm were precipitated from the reaction of Sr(NO₃)₂ and H₂O₂ in an alkalescent aqueous solution (pH = 8) under the ambient condition; secondly, perovskite phase SrTiO₃ with a minor amount of SrCO₃ impurity were produced by heating the mixture of excessive SrO₂ nanoparticles and commercial TiO₂ powders in air at 700 °C for 10 h, which could be easily washed with 1 mol/l HNO₃ aqueous solution and distilled water to yield pure SrTiO₃ crystallites with the size of about 125–320 nm. The phase, purity and size of the as-obtained product were characterized by means of powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy (FESEM).     

Fabrication and characterization of mesoporous TiO2/polypyrrole-based nanocomposite for electrorheological fluid

Mesoporous TiO₂/polypyrrole (PPy)-based nanocomposite for electrorheological fluid was synthesized through one-pot method. By exploiting the combination conductivity of PPy and high dielectric constant of TiO₂, the ER fluid exhibited an enhanced effect. The shear stress was 3.3 times as high as that of mesoporous TiO₂. Powder X-ray diffraction (XRD), TEM and Fourier transform infrared (FT-IR) spectroscopy were employed to characterize the as-made samples. Using a modified rotational viscometer, the electrorheological effect was measured. Dielectric spectra were also given to explain the mechanism.