Preparation,scratch adhesion and anti-corrosion performance of TiO2-MgO-BHA coating on Ti6Al4V implant by plasma electrolytic oxidation technique

Bovine hydroxyapatite (BHA) (from cortical bone), was selected as the main electrolyte for plasma electrolytic oxidation (PEO) on Ti6Al4V implant. The prepared PEO coatings were examined by X-ray diffraction, field emission scanning electron microscope and energy-dispersive X-ray spectroscopy. The surface roughness, adhesion strength, wettability, surface energy and corrosion behaviour of the film were also investigated. The results show that the oxide layer (26 μm) formation on the Ti6Al4V was rough and porous. The micro-pores were filled with anatase TiO₂, cubic MgO and hexagonal BHA particles. The porous structures and the compound particles were mainly composed of Mg, O, Ca, P, Ti, Na and Al. Unlike previous coatings produced from calcium and phosphorus inorganic solutions, the coating formation from a newly developed bovine bone-derived HA electrolyte revealed an additional MgO phase in the coating layer. Moreover, higher amount of single phase hexagonal crystalline BHA phase with a Ca/P ratio of 1.1 was achieved with a single PEO process. A film-to-substrate adhesion strength of 1862.24 mN and scratch hardness of about 4.1 GPa was achieved from this method. The TiO₂/MgO/BHA film exhibited better wettability, higher surface energy and superior corrosion resistance compared to the bare Ti6Al4V substrate.     

Microstructural evolution and interfacial reactions between Ti and ZrO2/CaTiO3 composites

Various proportions of ZrO₂/CaTiO₃ powders were mixed and hot pressed at 1500°C/30 min for Ti casting. The hot-pressed ZrO₂/CaTiO₃ composites were reacted with pure Ti at 1700°C/10 min in Ar. The interfacial reaction between Ti and ZrO₂/CaTiO₃ composites was investigated through X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The ZrO₂/CaTiO₃ composites with less than 10 vol.%, CaTiO₃, and a minor amount of residual TiO₂ were found. When the content of ZrO₂ was increased to larger than 10 vol.%, two Ca₂Zr₅Ti₂O₁₆ and CaZrTi₂O₇ phases appeared in the composites. The amount of CaTiO₃ and CaZrTi₂O₇ in the composites gradually decreased as the amount of ZrO₂ increased. When Ti came in contact with ZrO₂/CaTiO₃ composites with less than 10 vol.% ZrO₂, the resulting eutectic reaction produced a liquid phase and induced melting. When ZrO₂ was increased to more than 30 vol.% in the composites, Ca₂Zr₅Ti₂O₁₆ and CaZrTi₂O₇ changed completely to CaZrO₃, Ti₂O, CaO, and ZrO₂. With more than 30 vol.% ZrO₂, no other reaction phases occurred in the Ti side after contact with the ZrO₂/CaTiO₃ composites, which is conducive for producing ceramic composites for Ti casting applications.     

Improvement in corrosion resistance of micro-arc oxidation coating on PVD Ti-coated aluminum alloy 7075

Surface treatments are always needed to enhance corrosion-resistant performance of aluminum (Al) alloys when they are used in seawater environments. The paper aimed to prepare the composite oxide ceramic coating on Al alloy 7075 by combining micro-arc oxidation (MAO) and magnetron sputtering technology. The Al substrate was precoated with titanium (Ti) layer by using the magnetron sputtering technology and then treated by MAO in the alkaline aluminate electrolyte, resulting in a composite MAO coating, which is composed of Al₂O₃ and TiO₂ along with the complex oxide (Al₂TiO₅). The potentiodynamic polarization and electrochemical impedance spectroscopy were carried out to evaluate the corrosion performance of the MAO coatings in 3.5 wt% NaCl solution. Better corrosion resistance was observed for composite oxide coating than the reference MAO coating on the bare Al, as evidenced by the higher corrosion potential of −0.664 V versus Ag/AgCl and the lower corrosion current density of 4.41 × 10^-6 A/cm².     

Zirconium Incorporation into CaTiO3 Perovskite Prepared from Xerogels and Implication for the Fate of (Ca,Sr)TiO3 Nuclear Waste Ceramics

CaTiO₃ perovskite has been proposed as a ceramic waste form for immobilization of ⁹⁰Sr. Nonradioactive coprecipitated xerogel powders with nominal atomic ratios of Ca:Zr:Ti = 0.75:0.25:1.00 were synthesized to mimic the fate of (Ca_0.75⁹⁰Sr_0.25)TiO₃ solid solution after complete decay of the Sr and its intermediate product Y to stable Zr when an excess B⁴⁺ (Ti and ⁹⁰Zr) cations will present. Ca:Ti = 1.00:1.00 samples were used as a reference. The powders were heated to various conditions to explore the thermodynamic stability of its oxides. The heated Ca:Zr:Ti = 0.75:0.25:1.00 samples formed a major orthorhombic Ca(Zr_1?xTi_x)O₃ perovskite phase. The Ti/(Ti + Zr) ratio of the perovskite preserves its nominal ratio at 600°C. The Zr rejects from the Ca(Zr_1?xTi_x)O₃ with further increasing the temperature, following the formation of Ca–Ti–Zr–O secondary phases. This study indicates a tendency of the Zr to segregate from an original (Ca,Sr)TiO₃ waste form when the stoichiometry is controlled by the conversion of Sr to Zr (in normal oxidation states).     

Synthesis of CaTiO3 and CaTiO3/TiO2 nanoparticulate compounds through Ca2+/TiO2 colloidal sols: Structural and photocatalytic characterization

CaTiO₃ and CaTiO₃/TiO₂ nanocompounds have been synthesized through a colloidal sol-gel route using Ca²⁺/TiO₂ nanoparticulate sols. The peptization time was determined so that as higher is the Ca²⁺ concentration, shorter is the peptization time. The obtained cryogels from the respective sols were calcined at different temperatures (300–900 °C) and the structural and morphological changes were characterized mainly by X-ray diffraction and transmission electron microscopy. In all cases, the formation of the CaTiO₃ phase was observed after calcination at temperatures as low as 500 °C. Mesoporous cryogels with nanoparticles with sizes below 50 nm were obtained and their photocatalytic activity changes as a function of the calcination temperature and the applied wavelength were determined. Quantum yield values revealed that either CaTiO₃ or the CaTiO₃/TiO₂ (0.4 M ratio) compound can be chosen as the most efficient photocatalyst at higher calcination temperatures and longer wavelengths, while TiO₂ is more effective at low calcination temperatures and shorter wavelengths.     

Surface,Biocompatible and Hemocompatible Properties of Meta‐Amorphous Titanium Oxide Film

This study involved modification of the surface of Ti by micro‐arc oxidation (MAO). A rough and porous oxide film with good wettability was formed on the Ti surface. This MAO‐treated film exhibited a meta‐amorphous structure comprising crystalline anatase and rutile TiO₂ as well as amorphous phases. In addition, the incorporation of Ca and P in the MAO‐treated film was induced by micro‐arc discharge. The biological responses of the MAO‐treated surfaces were evaluated by observing the adhesion of MG63 osteoblast‐like cells and platelets. The MAO‐treated Ti had a considerably better biocompatibility and blood compatibility than untreated Ti.     

Effects of primer and annealing treatments on the shear strength between anodized Ti6Al4V and epoxy

The effects of primer and annealing treatments on the shear strength between anodized Ti6Al4V and epoxy were investigated. Primer coating improved the shear strength between anodized Ti alloy and epoxy by up to 81.3% using concurrent curing compared with that of control specimens. After annealing of anodized Ti alloy and applying primer, the shear strength of the specimen was further increased by 6.4% due to the formation of stable TiO₂ transferred from TiO in the anodization process. SEM analysis revealed the specimen without primer and annealing treatments showed adhesive failure between epoxy–alloy interface and discontinuous cohesive failure of epoxy. Primer coating initiated a new interfacial failure mode between the oxide layer and alloy due to the improved bonding strength between epoxy and oxide layer. In addition, annealing and primer treatments generated large tracts of epoxy continuous cohesive failure, showing good agreement with its higher shear strength and work of fracture.     

Titania/hydroxyapatite bi-layer coating on Ti metal by electrophoretic deposition: Characterization and corrosion studies

Titania–hydroxyapatite (HAp) bi-layer coating on Ti metal substrate with improved adhesion strength is fabricated by a simple two step processes: electrodeposition of Ti sol and electrophoretic deposition of HAp powder, followed by heat treatment at 800 °C. At optimized process parameters, the bi-layer developed consists of dense, thin and crystalline titania interlayer with porous, thick and crystalline HAp top layer. The heat treatment of bi-layer coating allows elemental intermixing at the interface of TiO₂ and HAp, as determined by energy dispersive X-ray spectroscopy (EDX) and Raman spectra analysis. Compared to monolithic HAp coating, the TiO₂/HAp bi-layer coating shows significant enhancement in the adhesion strength (48 MPa) as well as corrosion resistance without compromising its biocompatibility. The steep increase in adhesion strength is believed to be due to mechanical interlocking and diffusion bonding at the interface. Presence of dense titania interlayer in the bi-layer coating reduces the corrosion current in Ringer's solution to a negligible value (～100 nA).     

Improvement of the luminescence properties of CaTiO3:Pr obtained by modified solid-state reaction

Using tetra-n-butyl titanate and nitrates as starting materials, the red persistent phosphor CaTiO₃:Pr has been successfully synthesized by modified solid-state reaction. In order to improve the luminescent properties of the phosphor, boric acid as flux regent and aluminum ion as charge compensator were added in, and the influences of partially replacing Ca²⁺ in CaTiO₃ with Zn²⁺ or Mg²⁺ on the long persistent properties were studied. The results of luminescence spectrometer (PL), X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed that a certain quantity of boric acid, Al³⁺, Mg²⁺ or Zn²⁺ was effective in improving the photoluminescence intensity of CaTiO₃:Pr phosphor particles, and the optimum molar ratios of Al³⁺ and boric acid to Ca²⁺ were about 0.1% and 30%, respectively. The photoluminescence brightness and decay curves showed that the sample of Ca_0.8Zn_0.2TiO₃:Pr with 0.l% Al³⁺ and 30% H₃BO₃ obtained at the sintering temperature of 900 °C exhibited the optimal luminescent properties.     

Bioactive HA/TiO2 coating on magnesium alloy for biomedical applications

Magnesium alloys are new class of biodegradable alloys having many favourable properties to overcome the limitations of currently used biomedical alloys. Recently, several coatings have been developed to overcome their higher degradation rate. In this regard, a new attempt has been made to develop Hydroxyapatite and Hydroxyapatite/TiO₂ coatings on magnesium alloys to increase the biocompatibility and reduce the corrosion rate. The coated surfaces were characterized by Fourier-Transform Infrared Spectroscopy (FT-IR), X-ray Diffraction Analysis (XRD), Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray (EDX) Spectroscopy, Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM). Contact angle measurements proved higher hydrophilic nature of HA/TiO₂ coating compared to HA coating. In-vitro studies showed that HA–TiO₂ coated alloy exhibited higher osteoinduction compared to HA coated alloy. Hydrogen evolution studies and corrosion studies confirmed greater reduction in degradation rate of HA/TiO₂ coated alloy. Vickers microhardness test also showed enhancement in mechanical strength of the composite coated alloy compared to HA coated alloy. Three point bend test depicted better adherence of the HA/TiO₂ coating compared to HA coating on the substrate. Cell culture studies proved higher cell attachment and proliferation on composite coated alloy by controlling the release of magnesium ions into the surrounding body tissue.     

Characteristics of in-situ synthesized Hydroxyapatite on TiO2 ceramic via plasma electrolytic oxidation

The biocompatibility properties of Ti scaffolds can be improved significantly by hydroxyapatite (HA) composite coating. We successfully coated the surface of the Ti substrates by in-situ formation of HA nanocrystals on TiO₂ sublayer under calcium acetate and trisodium phosphate electrolytes through the plasma electrolytic oxidation (PEO) process. The effects of the process parameters and passivation on the characteristics of the coated substrates were studied using X–ray diffraction, Fourier-transform infrared spectroscopy, Field emission scanning electron microscopy, and Energy–dispersive X–ray spectroscopy. The systematically controlled experimental studies indicated that using the higher calcium/phosphorous ratio in the electrolyte enhances the micro arcs power and consequently, thickens the synthesized HA layer. The HA nanocrystals were tailored on the walls and edges of the discharge channels due to the locally concentrated heating zones, which consequently resulted in noticeable amounts of Ca and P dopants in porous TiO₂.     

Improving the stability and bioactivity of micro-arc oxidized calcium phosphate/titania porous coatings by high energy shot peening pretreatment

Micro-arc oxidation (MAO) is one of the conventional methods for surface modification of titanium (Ti)-based dental materials. However, in the process of MAO, the surface porous titania (TiO₂) coating is prone to micro-crack, which affects the stability of coating and the long-term service life of the implant. In this work, high-energy shot peening (HESP) pretreatment would be used to improve the stability and bioactivity of the MAO coatings and increase the effective doping of calcium and phosphorus (Ca & P) elements in surfaces. We verified that the MAO specimens pretreated by HESP (S-MAO) had larger pore size (~ 4.0 μm), coating thickness (~ 8.5 μm) and critical load (~ 11.1 N) than the samples without pretreatment (MAO, ~ 3.1 μm, 6.2 μm & 6.2 N); and the content of Ca and P in S-MAO group (Ca: ~ 6.3 wt%; P: ~ 9.4 wt%) was higher than that of MAO group (Ca: ~ 5.8 wt%; P: ~ 6.7 wt%. Meanwhile, it was also proved that compared with Ti and MAO groups, MC3T3-E1 cells on S-MAO substrates had better spreading, viability, ALP activity, and osteogenic gene expression. All the above results indicate that the HESP pretreatment has excellent potential to improve the coating stability and bioactivity of MAO-treated substrates.     

Improving the adhesive,mechanical, tribological properties and corrosion resistance of reactive sputtered tantalum oxide coating on Ti6Al4V alloy via introducing multiple interlayers

Tantalum oxide film has become an investigation focus for surface modification materials in the biomedical field owing to its outstanding biocompatibility, anti-corrosion, and anti-wear performances. However, tantalum oxide films exhibit poor adhesion because of the mismatch between the properties of the film and the substrate. In this study, a novel multilayer tantalum oxide coating of Ta_mO_n/Ta_mO_n-TiO₂/TiO₂/Ti (code M-Ta_mO_n) was deposited on Ti6Al4V by magnetron sputtering with Ta_mO_n single-layer coating as control. The purpose of this work is to evaluate the influence of the introduced Ta_mO_n-TiO₂/TiO₂/Ti multi-interlayer on the microstructure, adhesive, mechanical, and anti-corrosion properties of reactive sputtered tantalum oxide coatings. The outcomes show that the Ta_mO_n-TiO₂/TiO₂/Ti intermediate layer improves the bonding strength between the Ta_mO_n layer and Ti6Al4V matrix from 17.83 N to over 50 N and enables the Ta_mO_n coating to have an increased H/E and H³/E² ratio, decreased friction coefficient and wear rate, raised potential, and reduced corrosion current density. The improved properties of the multilayer system are attributed to the positive effects of the inserted multiple interlayers in reducing the residual stress in the coating, coupling the mechanical performance between the layer and the substrate, blocking the continuous growth of penetrating defects in a film with columnar structure. These experimental results provide a workable route for improving the properties of the tantalum oxide coating on Ti6Al4V alloy for medical applications.     

Ca-containing additives in PTC-BaTiO3 ceramics: effects on the microstructural evolution

Two series of Ca²⁺-modified BaTiO₃ ceramics have been prepared of the gross composition La_0.002Ba_0.998–xCa_xTi_1.01O_3.02 (0<x<0.24). In the first series, CaCO₃, BaCO₃, TiO₂ and La₂(C₂O₄)₃·9H₂O were used as starting materials. The calcination of mixtures with x⩽0.08 resulted in the formation of the corresponding titanate solid solution (Ba_1–xCa_x)TiO₃. With values of x higher than 0.08, CaTiO₃ was observed as an additional phase. In the second series, a La_0.002Ba_0.998TiO₃ starting powder was hydrothermally recrystallized in Ca(NO₃)₂ solution. High resolution imaging and analytical methods revealed that the BaTiO₃ grains are surrounded by small CaTiO₃ crystallites, which influence the evolution of the microstructure of the ceramic in the sintering process strongly by acting as seeds during the recrystallization of the matrix material. Thus, it was possible to optimize the microstructural and electrical characteristics of a ceramic of the second series by adding only 4 mol% Ca, while in case of the first series 16 mol% Ca are necessary.     

Enhancement of hydroxyapatite formation on anodic TiO2 nanotubular arrays via precalcification

Hydroxyapatite (HA) depositions on metallic biomedical implants have been widely applied to generate bioactive surfaces in simulated biological environments. Meanwhile, highly ordered TiO₂ nanotubular arrays obtained via anodization have attracted increasing interest for biomedical applications. However, capability to grow HA coating on TiO₂ nanotubular arrays at room temperature remains problematic. In this study, we applied a precalcification treatment on anodic TiO₂ nanotubular arrays to examine the formation of HA coating in simulated biological fluid. The as-formed TiO₂ nanotubular arrays on titanium were immersed in boiling saturated Ca(OH)₂ solutions for up to 40 min. The specimens readily grew HA once immersed in the simulated biological fluid (SBF) after 4 days immersion. The carbonated HA coating was formed with more than 5 μm thickness after 12 days of immersion while only a few calcium phosphate particles were observed on annealing TiO₂ nanotubular arrays immersed in the same solution for the same duration. This treatment dramatically improved efficiency for promoting HA formation on anodic TiO₂ nanotubular arrays without high temperature treatment.     

Bond strength of hybrid sol–gel coatings with different additives

The hybrid sol–gel coating on Al 2024-T3 was modified by adding polyaniline, TiO₂, or γ-Al₂O₃ nanoparticles in the formulation separately. The coating was then used as an adhesive to bond Al 2024-T3 alloys, forming a single lap joint. The bond strength of the sol–gel coating was investigated using a universal tensile test machine. The lap shear strength of the original sol–gel coating was about 1.38 MPa and it was increased up to 2.26 MPa after the modification by adding 0.05 wt% PANI microparticles in the sol–gel coating. The small increase in strength was attributed to an improvement in its adhesive flexibility because of incorporation of the long-chain organic polymer in its structure. Furthermore, the addition of different amounts of TiO₂ nanoparticles in the unmodified sol–gel coating also led to an increase in shear strength compared to the undoped sol–gel coating. Typically, a sol–gel coating containing 2.0 wt% of TiO₂ recorded the highest adhesive strength of about 4.0 MPa. A similar increase in strength was observed when doping γ-Al₂O₃ nanoparticles into the original hybrid sol–gel coating. Adding 0.5 wt% of γ-Al₂O₃ in the sol–gel coating increased the adhesive bonding strength up to 4.48 MPa. The fracture surface of the specimen was separately observed by SEM and Optical Microscopy in order to examine potential evidences of mechanism and nature of failure. The reason why the adhesive strength increased after the modification of the sol–gel coating is discussed in this article.     

Synthesis and characterization of a bi-functional hydroxyapatite/Cu-doped TiO2 composite coating

In the present work, a two-layer hydroxyapatite (HA)/Cu-doped TiO₂ composite coating was prepared via one-step micro-arc oxidation in an aqueous electrolyte containing calcium acetate, sodium di-hydrogen phosphate and ethylene diamine tetraacetic acid cupric disodium (CuNa₂-EDTA) at a constant current density of 100?mA/cm². After micro-arc oxidation for 20?min, Cu species incorporate into the TiO₂ as CuO and Cu₂O, resulting in the formation of Cu-doped TiO₂-based coating. In addition, spherical-shaped HA phase of nanometre scale is also present on the Cu-doped TiO₂-based coating. With HA phase boosting osseointegration and Cu species killing pathogenic microbes, a bi-functional coating fabricated by one-step micro-arc oxidation is of promising potential application in the bio-medical field.     

Deposition behavior and characteristics of hydroxyapatite coatings on Al2O3, Ti,and Ti6Al4V formed by a chemical bath method

A simple chemical bath method was used to deposit hydroxyapatite (HA) coatings on Al₂O₃, Ti, and Ti6Al4V substrates at ambient pressure by heating to 65–95 °C in an aqueous solution prepared with Ca(NO₃)₂·4H₂O, KH₂PO₄, KOH, and EDTA. The deposition behavior, morphology, thickness, and phase of the coatings were investigated using scanning electron microscopy and X-ray diffractometry. The bonding strength of the coatings was measured using an epoxy resin method. The HA coatings deposited on the three kinds of substrates were fairly dense and uniform and exhibited good crystallinity without any additional heat treatment. A coating thickness of 1–1.8 μm was obtained for the samples coated once. By repeating the coating process three times, the thickness could be increased to 4.5 μm on the Al₂O₃ substrate. The bonding strength of these coatings was 18 MPa.     

Microstructures,mechanical properties and corrosion resistance of sprayed Ca–P coating for micropatterning carbon/carbon substrate surface

Carbon/carbon (C/C) surface micropatterning is a method of modifying the surface into the complete and regular geometry. In this work, we introduce a positive effect on bonding strength between sprayed Ca–P coating and surface micropatterning C/C substrate. Interestingly, C/C substrate coated by Ca–P coating provides textured surface for a new bone ingrowth. The sprayed Ca–P coating is then subjected to microwave-hydrothermal (MH) treatment with the aim of eliminating surface defects and obtaining a uniform purity phase. These objectives were achieved in our previous study by the MH method. The molar ratio of Ca/P in the coatings is nearly close to 1, which is far below that of Ca/P for hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, HA, 1.67). The purpose of this article is to transform the phases in the sprayed Ca–P coating, which owns the better bioactivity and high corrosion resistance. In order to raise the molar ratio of Ca/P, the coatings are treated under high-temperature (around 700 °C). They are analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and a fourier transform infrared spectra (FTIR). The bonding strength (coating/substrate), biological activity and corrosion resistance of the coatings are investigated. The resulting coatings own the different microstructures and phase compositions from the original sprayed Ca–P coating. Especially, results show that the shear strength of the sprayed Ca–P coating deposited on surface micropatterning C/C substrate increases by 61% which is more than that of the coating on non-surface micropatterning C/C substrate. Additionally, high-temperature treated coating presents a good biological activity and an excellent corrosion resistance of current density (1.3078 × 10^-6 A/cm²) and potential (−0.17 V_SCE).     

Infusion of Ag‐Ion from Aqueous Solution into Solid Calcium Phosphate of Hydroxyapatite (HA) Crystal Structure

In contrast to extensive literature concerning Ag incorporation in hydroxyapatite, HA, while the phosphate approximated to stoichiometry of Ca₁₀(PO₄)₆(OH)₂, with added Ag has been precipitating from an aqueous solution, the paper presents Ag incorporation through Ag ion infusion from AgNO₃ solution into solid HA pressed in pellet and ignited at 800°C. After Ag ions infused into the HA‐solid (crossed the interfacial solution‐solid boundary), they diffused across the crystal structure to a depth of time‐dependent several mm. The path of Ag diffusion in the solid HA was recorded using SEM‐EDS point analyses of Ag, Ca, P, EDS‐linear analyses of those elements, and elemental mapping. Time‐dependent concentrations of Ag⁺, Ca²⁺, and PO₄^3? in AgNO₃ solutions were also analyzed. The appearance of Ag in the crystalline HA with simultaneous local depletion in Ca and phosphate recorded as P, observed by EDS with simultaneous appearance of Ca²⁺ and PO₄^3? ions and a decrease in Ag⁺ concentration in AgNO₃ solution led the authors to a conclusion that Ag⁺ for Ca²⁺ substitution supported by PO₄^3? charge balancing in the crystalline HA was in process. The HA particles in the section of the pellet without Ag had a uniform shape and size approximated to 300–400 nm. SEM image of the HA solid section, where Ag ions appeared was characterized by irregular aggregates of smaller crystals with sporadically present large, shaped in prism blocks identified by the XRD as Ag₃PO₄.