Preparation of rutile (TiO<Subscript>2</Subscript>) nanostructured materials at low temperature from TiCl<Subscript>4</Subscript> aqueous solution

The synthesis of rutile (TiO₂) nanostructured materials at low temperature from TiCl₄ aqueous solution was described. TiO₂ coatings on polystyrene (PS) particles were prepared by layer-by-layer assembly technique. The samples were characterized by DTA-TG, SEM, XPS, TEM and XRD techniques. The experimental results showed that pure rutile-TiO₂ coatings with nanocrystal structure were synthesized at 100 °C. On the surface of PS particles, sphere-type TiO₂ coatings exhibited uniform shape and a narrow size distribution. The amount of TO₂ (wt%) and shell thickness of particles increased with the adding of coating layers. Hollow TiO₂ spheres were obtained by calcination at 450 °C. TiO₂/PS with 2 coating layers showed higher degradation rate. The photocatalytic activity of hollow TiO₂ spheres was higher than that of TiO₂/PS.     

Effect of Ti<Subscript>3</Subscript>SiC<Subscript>2</Subscript> addition on microwave absorption property of plasma sprayed Ti<Subscript>3</Subscript>SiC<Subscript>2</Subscript>/NASICON coatings

The work attempted to develop a kind of high temperature microwave absorption coating. The Ti₃SiC₂/NASICON composite coatings with different Ti₃SiC₂ concentrations were fabricated by atmospheric plasma spraying. The effect of Ti₃SiC₂ addition on phase, density, microstructure, dielectric property and microwave absorption property of as-sprayed coatings was investigated. Results show that the complex permittivity increases with increasing the content of Ti₃SiC₂ due to the enhanced space charge polarization, decreased porosity and increased conduction loss. When the content of Ti₃SiC₂ increases to 30 wt%, the coating exhibits the optimal microwave absorption property with a bandwidth (below ??5 dB) of 4.01 GHz and lowest reflection loss of ??12.4 dB at 9.63 GHz in 1.4 mm thickness. It indicates that the Ti₃SiC₂/NASICON composite coating can be a potential candidate for microwave absorption.     

Preparation of YSZ/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite coatings via electrophoretic deposition of nanopowders

Using electrophoretic deposition (EPD), we have produced YSZ individual ceramic coatings and YSZ/Al₂O₃ composite coatings for a wide range of applications in modern materials research. YSZ and Al₂O₃ nanopowders were prepared by high-energy physical dispersion techniques, namely, by a laser evaporation–condensation process and electroexplosion of wire, respectively. Stable nonaqueous suspensions for the EPD process have been prepared using YSZ and Al₂O₃ nanopowders with an average particle size of 11 and 22 nm, respectively. The YSZ/Al₂O₃ composite coating produced by sintering at 1200°C has been shown to have higher density in comparison with the YSZ individual coating produced at the same temperature. X-ray diffraction characterization showed that the YSZ/Al₂O₃ composite coating consisted of two crystalline phases: α-Al₂O₃ (corundum) (42 wt %) and cubic ZrO₂〈Y₂O₃〉 (58 wt %). Quantitative analysis of electron micrographs of the surface of the films showed that the YSZ individual coating produced by sintering at 1200°C had a loose structure and contained pores (9%), as distinct from the composite coating, which had a dense, porefree grain structure.     

Direct preparation of CaTi<Subscript>4</Subscript> (PO<Subscript>4</Subscript>)<Subscript>6</Subscript> coatings on the surface of titanium substrate by micro arc oxidation

CaTi₄ (PO₄)₆ coatings was prepared on the surface of CP (commercially pure) Titanium substrate via micro arc oxidation in a newly designed electrolyte system. The preparation method –micro arc oxidation, as well as its discharge characterization was described and studied. The phases, morphology, chemical composition of the coatings were characterized by XRD, EDX and SEM analysis respectively. The results show: the main phase of the prepared coating was CaTi₄ (PO₄)₆ which is a bioactive coating material, the morphology of the coating was rather coarse and not like that of traditional MAO coating which was full of pores. Also the samples prepared in different electrolyte systems were studied and compared.     

Preparation of K<Subscript>2</Subscript>Ti<Subscript>6</Subscript>O<Subscript>13</Subscript>/TiO<Subscript>2</Subscript> bio-ceramic on titanium substrate by micro-arc oxidation

K₂Ti₆O₁₃/TiO₂ bio-ceramic coatings are prepared successfully by micro-arc oxidation on titanium substrate in pure KOH electrolyte solution. The coating is prepared at various applied current density (150–500 mA/cm²) and in KOH electrolyte with different concentrations (0.5–1.2 mol/L). The composition and surface morphologies of coatings are strongly dependent on the applied current density and the electrolyte concentration. On the condition of lower current density and electrolyte concentration, K₂Ti₆O₁₃ phase almost cannot be formed. The phase is mainly composed of rutile and K₂Ti₆O₁₃ with increasing current density and electrolyte concentration. The surface morphologies are composed of whiskers and porous structures. The ability of K₂Ti₆O₁₃/TiO₂ bio-ceramic films inducing apatite deposition is evaluated by soaking it in biological model fluids. The results show the K₂Ti₆O₁₃/TiO₂ bio-ceramic coatings possess excellent capability of inducing bone-like apatite to deposit.     

Structural State and Properties of Nitride Coatings Based on the Highly Entropic Alloy Ti<Subscript>30</Subscript>Zr<Subscript>25</Subscript>Nb<Subscript>20</Subscript>Hf<Subscript>15</Subscript>Ta<Subscript>10</Subscript>Y<Subscript>5</Subscript>

The regularities of the formations of nitride coatings based on the base of high entropy multicomponent alloy Ti₃₀Zr₂₅Nb₂₀Hf₁₅Ta₁₀Y₅ in the initial state without nitrogen and in nitrogen. The initial material of the alloy is solid solution on the base of the bcc-lattice. At the further sputtering of sample in the atmospheres with different contents of nitrogen the coating forms on the base of fcc-lattice. At the optimal conditions of the sputtering the nitride coating on the base of the highly entopic multicomponent alloy has the hardness at the level of 50 GPa and the reduced elastic modulus 350 GPa.     

Antireflecting coating from Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> and SiO<Subscript>2</Subscript> multilayer films

Sol-gel method is important for depositing antireflective coating that allows control over thickness as well as the index of refraction. Antireflective coatings which are produced from Ta₂O₅ and SiO₂ multi-layer thin films using sol-gel spin coating method are presented. The refractive index and the thickness are controlled by the composition and the concentration of the solution respectively. The thickness, refractive index and extinction coefficient of the films were calculated through transmission and reflection measurement by an NKD analyser. Mechanical properties of the films were checked by the cross tape test and dry sun test at 760 W/m². The result shows that the sample heat treated at 450^∘C for 15 min approaches a reflectance with less than 0.5% at around 840 nm.     

Chemical stability and antimicrobial activity of plasma sprayed bioactive Ca<Subscript>2</Subscript>ZnSi<Subscript>2</Subscript>O<Subscript>7</Subscript> coating

Calcium silicate ceramic coatings have received considerable attention in recent years due to their excellent bioactivity and bonding strength. However, their high dissolution rates limit their practical applications. In this study, zinc incorporated calcium silicate based ceramic Ca₂ZnSi₂O₇ coating was prepared on Ti-6Al-4V substrate via plasma spraying technology aiming to achieve higher chemical stability and additional antibacterial activity. Chemical stability of the coating was assessed by monitoring mass loss and ion release of the coating after immersion in the Tris–HCl buffer solution and examining pH value variation of the solution. Results showed that the chemical stability of zinc incorporated coating was improved significantly. Antimicrobial activity of the Ca₂ZnSi₂O₇ coating was evaluated, and it was found that the coating exhibited 93% antibacterial ratio against Staphylococcus aureus. In addition, in vitro bioactivity and cytocompatibility were confirmed for the Ca₂ZnSi₂O₇ coating by simulated body fluid test, MC3T3-E1 cells adhesion investigation and cytotoxicity assay.     

Anti-corrosion mechanism of epoxy-resin and different content Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> coatings on magnesium alloy

In this study, anti-corrosion coatings were prepared and coated successfully on magnesium alloy substrates by mixing nanopowders, solvent, curing agent with epoxy resin. The effect of the amount of iron trioxide (Fe₂O₃) on the adhesion strength and corrosion resistance on magnesium alloy was investigated with standard protocols, and electrochemical measurements were also made in 3.5 wt.% NaCl solutions. The surface morphology and corrosion mechanism after corrosion tests was characterized using FESEM analysis. Nanoparticles in matrix acted as filler, and interstitial cross-linked spaces and other coating artifacts regions (micro cracks and voids) would all affect the anti-corrosion properties of coating. The results showed the proper powder content not only provided adhesion strength to these coatings but also improved obviously their anticorrosion. Hydrogen bound to the amine nitrogen (¹N) could take part in the curing process rather than hydrogen of the amide site due to the smaller ΔG and the more stable configuration.     

Study of wear resistance and nanostructure of tertiary Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Y<Subscript>2</Subscript>O<Subscript>3</Subscript>/CNT pulsed electrodeposited ni-based nanocomposite

We study the electrodeposition of tertiary Alumina/Yitria/carbon nanotube (Al₂O₃/Y2O₃/CNT) nanocomposite by using pulsed currents. The process of coating is performed in a nickel-sulfate bath and the nanostructure of the obtained compound layer is examined with the help of high-precision figure analysis of SEM nanographs. The effects of process variables, i.e., the Y₂O₃ concentration, treatment time, current density, and the temperature of electrolyte are experimentally investigated. Statistical methods are used to achieve the minimum wear rate and average size of nanoparticles. Finally, the percentage contributions of different effective factors are revealed, and the confirmation run showed the validity of the obtained results. It is also revealed that the wear properties of the coatings undergo significant changes if the sizes of nanoparticles change. The atomic-force microscopy (AFM) and transmissionelectron microscopy (TEM) analyses confirm the smooth surfaces and average sizes of nanoparticles in the optimal coating.     

Enhanced electrochemical performance of Na<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>F<Subscript>3</Subscript> for Na-ion batteries with nanostructure and carbon coating

Carbon-coating Na₃V₂(PO₄)₂F₃ nanoparticles (NVPF@C NP) were prepared by a hydrothermal assisted sol–gel method and applied as cathode materials for Na-ion batteries. The as-prepared nanocomposites were composed of Na₃V₂(PO₄)₂F₃ nanoparticles with a typical size of ~?100 nm and an amorphous carbon layer with the thickness of ~?5 nm. Cyclic voltammetry, rate and cycling, and electrochemical impedance spectroscopy tests were used to discuss the effect of carbon coating and nanostructure. Results display that the as-prepared NVPF@C NP demonstrates a higher rate capability and better long cycling performance compared with bare Na₃V₂(PO₄)₂F₃ bulk (72 mA h g^?1 at 10 C vs 39 mA h g^?1 at 10 and 1 C capacity retention of 95% vs 88% after 50 cycles). The remarking electrode performance was attributed to the combination of nanostructure and carbon coating, which can provide short Na-ion diffusion distance and rapid electron migration.     

Thermal stability of CrN<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> nanometric coatings deposited on stainless steel

Thin CrN _x coatings are often used as protective coatings for steel. In these applications, coated parts might be subjected to high temperatures that can alter the coatings structural and mechanical properties. In this work, the properties of nanometric CrN _x coatings deposited by reactive magnetron sputtering on AISI 304L stainless steel were studied by transmission electron microscopy, glazing incident X-ray diffraction, Atomic Force Microscopy, and nanoindentation. The effect of annealing, both in air and vacuum, on the coating crystal structure, surface morphology and hardness were also investigated. It was found that annealing in vacuum-induced phase transformation from CrN to Cr₂N, while after annealing in air only Cr₂O₃ phase was present. Surface roughness did not increase for annealing in vacuum. CrN _x coatings with higher Cr₂N phase content showed lower roughness increase for annealing in air. Measured hardness was >10 GPa for as-deposited CrN _x samples. An increase in hardness up to >20 GPa was found for vacuum-annealed samples.     

Critical-current anisotropy in superconducting Nb<Subscript>3</Subscript>Sn coatings produced by electrocodeposition of Nb and Sn

We report the critical current of superconducting Nb₃Sn coatings produced by electrocodeposition from molten salts and its anisotropy in transverse magnetic fields. The anisotropy is quantified by the ratio of the critical currents measured in magnetic fields parallel and normal to the coating surface, k. The effect of doping with tantalum and nitrogen on the microstructure, critical current, and anisotropy factor k of Nb3Sn coatings is examined. The k of the undoped and tantalum-doped coatings ranges from 0.4 to 1.0, and that of the nitrogen-doped coatings, from 0.4 to 1.4. The critical current anisotropy is interpreted in terms of the microstructure of the coatings.     

Influence of high velocity oxy-fuel parameters on properties of nanostructured TiO<Subscript>2</Subscript> coatings

A liquid fuel high velocity oxy-fuel (HVOF) thermal spray process has been used to deposit TiO₂ nanostructured coatings utilizing a commercially available nanopowder as the feedstock. The coatings were characterized by means of X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and transmission electron microscope (TEM), respectively. Photocatalytic activity was evaluated as a rate constant of decomposition reaction of methylene blue (MB) determined from the changes of relative concentration of MB with UV irradiation time. The results indicate that the sprayed TiO₂ coatings were composed of both TiO₂ phases viz. anatase and rutile, with different phase contents and crystallite sizes. A high anatase content of 80% by volume was achieved at 0·00015, fuel-to-oxygen ratio with nanostructure coating by grain size smaller than feedstock powder. Photocatalytic activity evaluation results indicated that all the TiO₂ coatings are effective to degradation MB under UV radiation and their activities differ in different spray conditions. It is found that fuel flow rate strongly influenced on phase transformation of anatase to rutile and by optimizing the rate which can promote structural transformation and grain coarsening in coating and improving photocatalytic activity.     

Electrochemical properties of Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>/C and Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>/C/Ag nanomaterials

We have prepared and characterized lithium titanate-based anode materials, Li₄Ti₅O₁₂/C and Li₄Ti₅O₁₂/C/Ag, using polyvinylidene fluoride as a carbon source. The formation of such materials has been shown to be accompanied by fluorination of the lithium titanate surface and the formation of a highly conductive carbon coating. The highest electrochemical capacity (175 mAh/g at a current density of 20 mA/g) is offered by the Li₄Ti₅O₁₂-based anode materials prepared using 5% polyvinylidene fluoride. The addition of silver nanoparticles ensures a further increase in electrical conductivity and better cycling stability of the materials at high current densities.     

Liquid-phase epitaxy of NdAl<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> and Yb-doped YAl<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript>

Epitaxial layers of NaAl₃(BO₃)₄ (NAB) and YAl₃(BO₃)₄〈Yb〉 (YAB〈Yb〉) containing up to 10 at % Yb have been grown by liquid-phase epitaxy on YAB substrates. Their growth kinetics have been studied at relative supersaturations of the high-temperature solution from 2 × 10^?2 to 16 × 10^?2. The ytterbium concentration in YAB〈Yb〉 has been shown to vary little during the epitaxial process. Near the edges of the substrate, the surface morphology of the layers is complicated by vicinals, which have a spiral form in the case of YAB〈Yb〉. On \(\{ 10\overline 1 1\} \) YAB substrates, homogeneous single-crystal NAB films have been grown.     

Impedance spectroscopy of Ba<Subscript>3</Subscript>Sr<Subscript>2</Subscript>DyTi<Subscript>3</Subscript>V<Subscript>7</Subscript>O<Subscript>30</Subscript> ceramic

Polycrystalline sample of Ba₃Sr₂DyTi₃V₇O₃₀ was prepared at 950°C using a high-temperature solid-state reaction technique. X-ray structural analysis indicated the formation of a single-phase orthorhombic structure with lattice parameters: a = 12·2719 (39) Å, b = 8·9715(39) Å and c = 19·7812(39) Å. Microstructural study showed densely packed uniform distribution of grains over the surface of the sample. The a.c. impedance plots were used as tools to analyse the electrical response of the sample as a function of frequency at different temperatures (30–500°C). These plots revealed the presence of grain boundary effect, from 200·C onwards. Complex impedance analysis showed non-Debye type of dielectric relaxation. The Nyquist plots showed the negative temperature coefficient of resistance character of Ba₃Sr₂DyTi₃V₇O₃₀. A hopping mechanism of electrical transport processes in the system is evident from the modulus analysis. The activation energy of the compound (calculated both from loss and modulus spectrum) is the same, and hence the relaxation process may be attributed to the same type of charge carrier.     

Plasma sprayed cerium oxide coating inhibits H<Subscript>2</Subscript>O<Subscript>2</Subscript>-induced oxidative stress and supports cell viability

Oxidative stress is a risk factor in the pathogenesis of osteoporosis, and plays a major role in bone regeneration of osteoporotic patients. Cerium oxide (CeO₂) ceramics have the unique ability to protect various types of cells from oxidative damage, making them attractive for biomedical applications. In this study, we developed a plasma sprayed CeO₂ coating with a hierarchical topography where ceria nanoparticles were superimposed in the micro-rough coating surface. The protective effects of the CeO₂ coating on the response of osteoblasts to H₂O₂-induced oxidative stress have been demonstrated in terms of cell viability, apoptosis and differentiation. The CeO₂ coating reversed the reduced superoxide dismutase activity, decreased reactive oxygen species production and suppressed malondialdehyde formation in H₂O₂-treated osteoblasts. It indicated that the CeO₂ coating can preserve the intracellular antioxidant defense system. The cytocompatibility of the CeO₂ coating was further assessed in vitro by cell viability assay and scanning electron microscopy analysis. Taken together, the CeO₂ coating could provide an opportunity to be utilized as a potential candidate for bone regeneration under oxidative stress.     

An extended spectrum bactericidal titanium dioxide (TiO<Subscript>2</Subscript>) coating for metallic implants: in vitro effectiveness against MRSA and mechanical properties

Implant infections remain feared and severe complications after total joint arthroplasty. The incidence of multi-resistant pathogens, causing such infections, is rising continuously, and orthopaedic surgeons are confronted with an ever-changing resistance pattern. Anti-infectious surface coatings aim for a high local effective concentration and a low systemic toxicity at the same time. Antibacterial efficacy and biomechanical stability of a novel broad-spectrum anti-infectious coating is assessed in the present study. Antibacterial efficacy of a sol–gel derived titanium dioxide (TiO₂) coating for metal implants with and without integrated copper ions as antibiotic agent was assessed against methicillin resistant Staphylococcus aureus (MRSA 27065). Both bacterial surface adhesion and growth of planktonic bacteria were assessed with bare and various TiO₂-coated Ti6Al4V metal discs. Furthermore, bonding strength of the TiO₂ surface coating, using standard testing procedures, as well as surface roughness were determined. We found a significant reduction of the bacterial growth rate for the coatings with integrated copper ions, with highest reduction rates observed for a fourfold copper TiO₂-coating. Pure TiO₂ without integrated copper ions did not reduce bacterial growth compared to uncoated Ti6Al4V. The coating was not detached from the substrate by standard adhesive failure testing, which indicated an excellent durability of the implant coating. The TiO₂ coating with integrated copper ions could offer a new strategy for preventing implant-associated infections, with antibacterial properties not only against the most common bacteria causing implant infections but also against multiresistant strains such as MRSA.     

Antireflective coatings based on SiO<Subscript>2</Subscript> nanoparticles

Single-layer antireflective coatings, produced by sol-gel method on soda-lime glass substrates, were studied. Optimal parameters of the silica sols synthesis and coating procedure of the antireflective coatings based on SiO₂ nanoparticles on soda-lime glasses for producing composite glasses with high optical transmittance within the visible range of wavelengths were obtained.