Enhancement of Corrosion Resistance Properties of Electrodeposited Ni/nano-TiC Composite Layers.

This paper presents novel results on the effects of the dispersion of titanium carbide nanoparticles (50 nm mean diameter) into a nickel-plating electrolyte on the corrosion behavior of the nanocomposite layers obtained. The Ni/nano-TiC layers are compared with pure nickel layers obtained at the same electrodeposition parameters with 60 mA·cm-2 current density and 10 min deposition time. The comparative corrosion performances are investigated using a three-electrode electrochemical cell in a solution (mixed boric acid with lithium hydroxide), which simulates the primary water circuit of pressurized water reactors (PWRs). Open circuit potential measurement and electrochemical impedance spectroscopy were employed as the electrochemical methods, using an electrochemical workstation connected to an electrochemical cell, as well as a PC with software to drive the experimental work. The results clearly revealed enhanced corrosion properties for the Ni/nano-TiC hybrid layers as compared to the pure Ni layers. The significantly improved corrosion behavior can be attributed to the TiC nanoparticles embedded into the Ni matrix, which have the effect of insulating centers at the composite layer/corrosive solution interface.

Electro-codeposition of CeO2 nanoparticles into cobalt matrix to improve the tribocorrosion performances of Co/nano CeO2 composite layers in biological solution for medical applications.

Co/nano-CeO2 composite layers were developed by electro-codeposition method from a cobalt electrolyte containing dispersed CeO2 nanoparticles. The tribocorrosion performances of both Co/nano-CeO2 and pure Co layers were comparatively investigated by sliding friction tests under lubricated condition in biological Hank solution. The effect of embedded nano-CeO2 on the corrosion electrochemical response, friction coefficient and wear loss volume is analyzed. The results show that the codeposited of nano-CeO2 particles into cobalt matrix reduce the friction coefficient and wear weight loss as well as the shift of open circuit potential to active state, increasing the polarization resistance and reducing the corrosion damages.

Morphological characterization of as-received and in vivo orthodontic stainless steel archwires.

This study was undertaken to evaluate the material degradation of clinical bracket-archwire-contacting surfaces after in vivo orthodontic use. Twenty-four stainless steel multiloop edgewise archwires with two different cross sections (0.016 x 0.016 and 0.016 x 0.022 inches) were used for at least 6 months in the mouths of 14 patients. The surfaces of both as-received (cross-section of 0.016 x 0.016, 0.016 x 0.022, and 0.017 x 0.025 inches) and the in vivo wires were examined using scanning electron microscopy. The as-received wires exhibited an inhomogeneous surface with different surface irregularities resulting from the manufacturing process. For the in vivo archwires, an increase in the variety, type, and number of surface irregularities were observed. Crevice corrosion occurred not only at surface irregularities formed during manufacturing and orthodontic handling but also at the bracket-archwire-contacting surfaces and at the archwire surfaces coated with plaque and food remnants. This corrosion may be linked to the formation of a micro-environment at these locations. In addition, a limited number of signs of degradation induced during in vivo testing due to wear and friction were observed.

Anticorrosion Performance of the Electrochemically Grown Mixed Porous Oxide Films on Titanium Alloy in Biological Solution.

A thin porous mixed layer of TiO2-ZrO2 was grown on titanium-zirconium alloy surface by electrochemical oxidation. Further comparison of the corrosion behavior in Fusayama-Meyer biological solution was performed. Scanning electron microscopy surface morphology investigations confirm the presence of porous oxide film, while energy-dispersive X-ray spectroscopy analyses provide a high amount of oxygen element in the porous film and a higher amount of Zr element, concluding the mixed nature of oxide film formed, TiO2-ZrO2. For corrosion investigations, electrochemical techniques such as open-circuit potential, electrochemical impedance spectroscopy, and potentiodynamic polarization were applied. The corrosion investigations reveal better behavior of the thin porous mixed oxide layer on titanium alloy compared to the untreated alloy having on their surface the native oxide formed in contact with the air, confirming the possibility to improve the properties of such implant application in saliva solution.

Improved tribocorrosion performance of bio-functionalized TiO2 nanotubes under two-cycle sliding actions in artificial saliva.

After insertion into bone, dental implants may be subjected to tribocorrosive conditions resulting in the release of metallic ions and solid wear debris, which can induce to peri-implant inflammatory reactions accompanied by bone loss, and ultimately implant loosening. Despite the promising ability of TiO2 nanotubes (NTs) to improve osseointegration and avoid infection-related failures, the understanding of their degradation under the simultaneous action of wear and corrosion (tribocorrosion) is still very limited. This study aims, for the first time, to study the tribocorrosion behavior of bio-functionalized TiO2 NTs submitted to two-cycle sliding actions, and compare it with conventional TiO2 NTs. TiO2 NTs grown by anodization were doped with bioactive elements, namely calcium (Ca), phosphorous (P), and zinc (Zn), through reverse polarization anodization treatments. Characterization techniques such as scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and scanning transmission electron microscopy (STEM), were used to characterize the films. Tribocorrosion tests were carried out in artificial saliva (AS) by applying two cycles of reciprocating sliding actions. The open circuit potential (OCP) was monitored before, during, and after both cycles of sliding, during which the coefficient of friction (COF) was calculated. The resulting wear scars were analyzed by SEM and EDS, and wear volume measurements were performed by 2D profilometry. Finally, the mechanical features of TiO2 NTs were accessed by nanoindentation. The results show that bio-functionalized TiO2 NTs display an enhanced tribocorrosion performance, ascribed to the growth of a nano-thick oxide film at Ti/TiO2 NTs interface, which significantly increased their adhesion strength to the substrate and consequently their hardness. Furthermore, it was discovered that during tribo-electrochemical solicitations, the formation of a P-rich tribofilm takes place, which grants both electrochemical protection and resistance to mechanical wear. This study provides fundamental and new insights for the development of multifunctional TiO2 NTs with long-term biomechanical stability and improved clinical outcomes.

Tribological behaviour of orthodontic archwires under dry and wet sliding conditions in-vitro. I--Frictional behaviour.

OBJECTIVE: To evaluate the frictional behaviour of orthodontic archwires in dry and wet conditions in-vitro. METHODS: Two types of archwire materials were investigated: stainless steel and NiTi. A fretting wear tribometer fitted with an alumina ball was operated at 23 degrees C in three different environments: ambient air with 50 per cent relative humidity, 0.9 wt. per cent sodium chloride solution, and deionised water. RESULTS: NiTi archwires sliding against alumina exhibited high coefficients of friction (about 0.6) in the three environments. Stainless steel archwires sliding against alumina had relatively low coefficients of friction (0.3) in the solutions, but high coefficients (0.8) in air. CONCLUSION: The low frictional forces of the stainless steel wires sliding against alumina in the solutions were due to a lubricating effect of the solutions and corrosion-wear debris. The high frictional forces between the NiTi wires and alumina are attributed to an abrasive interfacial transfer film between the wires and alumina.

Tribological behaviour of orthodontic archwires under dry and wet sliding conditions in-vitro. II--Wear patterns.

OBJECTIVE: To evaluate the wear patterns of orthodontic archwires in dry and wet conditions in-vitro. METHODS: The patterns of wear of stainless steel and NiTi orthodontic archwires were investigated with a fretting wear tribometer fitted with an alumina ball. The tribometer was operated at 23 degrees C in three different environments: ambient air with 50 per cent relative humidity (RH), 0.9 wt. per cent sodium chloride solution and deionised water. Differences in the wear characteristics of the archwires were investigated by scanning electron microscopy. Energy Dispersive X-ray Analysis and Inductively Coupled Plasma Analysis were used to investigate the surface composition of the wires, the wear debris generated during fretting and the corrosion products in the test solutions. RESULTS: Both archwire materials were degraded by oxidational wear in ambient air. The NiTi wires were more resistant to wear than the stainless steel wires. In the aqueous media the stainless steel wires were degraded by abrasive wear, while the NiTi wires were degraded by adhesive wear. CONCLUSION: In ambient air with 50 per cent RH, NiTi wires were more resistant to wear than stainless steel wires. Both archwire materials exhibited higher wear rates in the solutions than in air, indicating some synergism between the wear and corrosion processes. In the solutions the stainless steel archwires had a much lower corrosion-wear resistance than the NiTi archwires.

Effect of Nano-TiC Dispersed Particles and Electro-Codeposition Parameters on Morphology and Structure of Hybrid Ni/TiC Nanocomposite Layers.

This research work describes the effect of dispersed titanium carbide (TiC) nanoparticles into nickel plating bath on Ni/TiC nanostructured composite layers obtained by electro-codeposition. The surface morphology of Ni/TiC nanostructured composite layers was characterized by scanning electron microscopy (SEM). The composition of coatings and the incorporation percentage of TiC nanoparticles into Ni matrix were studied and estimated by using energy dispersive X-ray analysis (EDX). X-ray diffractometer (XRD) has been applied in order to investigate the phase structure as well as the corresponding relative texture coefficients of the composite layers. The results show that the concentration of nano-TiC particles added in the nickel electrolyte affects the inclusion percentage of TiC into Ni/TiC nano strucured layers, as well as the corresponding morphology, relative texture coefficients and thickness indicating an increasing tendency with the increasing concentration of nano-TiC concentration. By increasing the amount of TiC nanoparticles in the electrolyte, their incorporation into nickel matrix also increases. The hybrid Ni/nano-TiC composite layers obtained revealed a higher roughness and higher hardness; therefore, these layers are promising superhydrophobic surfaces for special application and could be more resistant to wear than the pure Ni layers.

Effect of Boron Doping on the Wear Behavior of the Growth and Nucleation Surfaces of Micro- and Nanocrystalline Diamond Films.

B-doped diamond has become the ultimate material for applications in the field of microelectromechanical systems (MEMS), which require both highly wear resistant and electrically conductive diamond films and microstructures. Despite the extensive research of the tribological properties of undoped diamond, to date there is very limited knowledge of the wear properties of highly B-doped diamond. Therefore, in this work a comprehensive investigation of the wear behavior of highly B-doped diamond is presented. Reciprocating sliding tests are performed on micro- and nanocrystalline diamond (MCD, NCD) films with varying B-doping levels and thicknesses. We demonstrate a linear dependency of the wear rate of the different diamond films with the B-doping level. Specifically, the wear rate increases by a factor of 3 between NCD films with 0.6 and 2.8 at. % B-doping levels. This increase in the wear rate can be linked to a 50% decrease in both hardness and elastic modulus of the highly B-doped NCD films, as determined by nanoindentation measurements. Moreover, we show that fine-grained diamond films are more prone to wear. Particularly, NCD films with a 3× smaller grain size but similar B-doping levels exhibit a double wear rate, indicating the crucial role of the grain size on the diamond film wear behavior. On the other hand, MCD films are the most wear-resistant films due to their larger grains and lower B-doping levels. We propose a graphical scheme of the wear behavior which involves planarization and mechanochemically driven amorphization of the surface to describe the wear mechanism of B-doped diamond films. Finally, the wear behavior of the nucleation surface of NCD films is investigated for the first time. In particular, the nucleation surface is shown to be susceptible to higher wear compared to the growth surface due to its higher grain boundary line density.

How do titanium and Ti6Al4V corrode in fluoridated medium as found in the oral cavity? An in vitro study.

The purpose of this work was to evaluate the corrosion of commercially pure (CP) titanium and Ti6Al4V in vitro at different F(-) concentrations regularly found in the oral cavity by using different electrochemical tests and surface analysis techniques. electrochemical impedance spectroscopy (EIS), open circuit potential (OCP) and potentiodynamic polarization tests were associated to advanced characterization techniques such as SEM, EDS, AFM, ICP-MS and XPS. OCP tests revealed a higher reactivity of both CP titanium and Ti6Al4V at 12,300 ppm F(-) concentration than that recorded at 227 ppm F(-). Also, a significant decrease of the corrosion resistance of both materials was noticed by EIS in fluoride solutions. Material loss caused by corrosion was noticed on titanium surfaces by SEM and AFM in the presence of high F(-) concentration. CP titanium degraded by pitting corrosion while Ti6Al4V suffered from general corrosion showing micro-cracks on surface. Furthermore, a high release of metallic ions from the test samples after immersion at high F(-) concentrations was detected by ICP-MS, that can be potentially toxic to oral tissues.

Mechanical and chemical analyses across dental porcelain fused to CP titanium or Ti6Al4V.

The aim of this study was to evaluate the evolution of mechanical properties and chemical variation across veneering dental porcelain fused to different titanium-based substrates. Test samples were synthesized by fusing dental feldspar-based porcelain onto commercially pure titanium grade II or Ti6Al4V alloy. Samples were cross-sectioned at angles of 10 and 90° to the interface plane. Afterwards, nanoindentation tests and Scanning Electron Microscopy (SEM) imaging coupled to an Energy Dispersive Spectroscopy (EDS) system were carried out across interfaces extending from the metal towards the porcelain area. Elemental diffusion profiles across the porcelain-to-metal interfaces were also obtained by EDS analysis. The mismatch in mechanical properties found in porcelain-to-Ti6Al4V interfaces was lower than that of porcelain-to-CP titanium. Cracking was noticed at low-thickness veneering dental porcelain regions after the nanoindentation tests of samples cross-sectioned at low angles to the interface plane. A wide reaction zone between titanium and porcelain as well as higher incidence of defects was noticed at the porcelain-to-CP titanium interfaces. This study confirmed Ti6Al4V as an improved alternative to CP-titanium as it showed to establish a better interface with the veneering dental porcelain considering the slight chemical interaction and the lower mechanical properties mismatch. The elastic modulus of porcelain-to-Ti6Al4V samples showed to be less sensitive to porcelain thickness variations.

Surface wettability of macroporous anodized aluminum oxide.

The correlation between the structural characteristics and the wetting of anodized aluminum oxide (AAO) surfaces with large pore sizes (>100 nm) is discussed. The roughness-induced wettability is systematically examined for oxide films grown by a two-step, high-field anodization in phosphoric acid of three different concentrations using a commercial aluminum alloy. This is done for the as-synthesized AAO layers, after various degrees of pore widening by a wet chemical etching in phosphoric acid solution, and upon surface modification by either Lauric acid or a silane. The as-grown AAO films feature structurally disordered pore architectures with average pore openings in the range 140-190 nm but with similar interpore distances of about 405 nm. The formation of such AAO structures induces a transition from slightly hydrophilic to moderately hydrophobic surfaces up to film thicknesses of about 6 µm. Increased hydrophobicity is obtained by pore opening and a maximum value of the water contact angle (WCA) of about 128° is measured for AAO arrays with a surface porosity close to 60%. Higher surface porosity by prolonged wet chemical etching leads to a rapid decrease in the WCA as a result of the limited pore wall thickness and partial collapse of the dead-end pore structures. Modification of the AAO surfaces by Lauric acid results in 5-30° higher WCA's, whereas near-superhydrophobicity (WCA ~146°) is realized through silane coating. The "rose petal effect" of strongly hydrophobic wetting with high adhesive force on the produced AAO surfaces is explained by a partial penetration of water through capillary action into the dead-end pore cavities which leads to a wetting state in-between the Wenzel and Cassie states. Moreover, practical guidelines for the synthesis of rough, highly porous AAO structures with controlled wettability are provided and the possibility of forming superhydrophobic surfaces is evaluated.

Correlating in vitro scratch test with in vivo contact free occlusal area wear of contemporary dental composites.

OBJECTIVES: The aims of this study are to determine the extent to which the ranking order for clinical Contact-Free-Occlusal-Area (CFOA) wear performance of composites correlates with the ranking based on in vitro scratch hardness, and to analyze the extent to which the microstructure influences the overall trend. MATERIALS AND METHODS: The patient data and CFOA wear measurements of 16 Tetric-C, 17 Tetric-EC, 16 Gradia-DP, 18 Filtek Supreme, 19 Z100 restorations in 31 subjects (8 males, 23 females) of two randomized clinical trials were fitted in a mixed-effect model. The in vivo performance of the restoratives was summarized by ranking the estimated material-related coefficients in the model. Scratch tests on two specimens per composite were run at a constant speed of 0.05 mm/s under indenter with normal loads of 15, 25, and 35 mN. Scratch width, depth and hardness calculated by imaging the scratch tracks were summarized in a model, the material-related coefficients were ranked and correlated with that of in vivo ranking order. RESULTS: The best in vivo model included as significant factors (p<0.0001) the variables material, time/month, cavity type, and jaw type. The CFOA wear ranking order - Filtek Supreme, Z100>Tetric-C, Tetric-EC>Gradia-DP-correlated closely (R(2)=0.991) with the order of scratch hardness - Z100>Filtek Supreme>Tetric-C, Tetric-EC>Gradia-DP. SIGNIFICANCE: Scratch tests could roughly categorize a new material as to whether it will probably exhibit a high or low in vitro scratch resistance and/or clinical CFOA wear rate.

Corrosion behaviour of titanium in the presence of Streptococcus mutans.

OBJECTIVE: The main aim of this in vitro study was to evaluate the influence of Streptococcus mutans on the corrosion of titanium. METHODS: S. mutans biofilms were formed on commercially pure titanium (CP-Ti) square samples (10mm×10mm×1mm) using a culture medium enriched with sucrose. Open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) measurements were used to evaluate the corrosion behaviour of CP-Ti in the presence of S. mutans in Fusayama's artificial saliva. The corrosion of biofilm-free CP-Ti samples was also evaluated in artificial saliva. Biofilms biomass was measured by spectrophotometry, using crystal violet staining, after 1, 2 and 7 days. RESULTS: The OCP values recorded on CP-Ti in the presence of S. mutans (-0.3±0.02V vs. SCE) was lower than those on biofilm-free CP-Ti (-0.1±0.01V vs. SCE) after 2h of immersion in artificial saliva (p<0.05). That reveals a high reactivity of titanium in presence of S. mutans. Impedance spectra revealed the formation of a compact passive film on titanium in artificial saliva or in the presence of a 2 days old S. mutans biofilm even though the corrosion resistance of CP-Ti has decreased in presence of a S. mutans biofilm. CONCLUSION: The presence of bacterial colonies, such as S. mutans, negatively affected the corrosion resistance of the titanium.