A study of the physical,chemical and biological properties of TiO2 coatings produced by micro-arc oxidation in a Ca–P-based electrolyte

In this work, a porous and homogeneous titanium dioxide layer was grown on commercially pure titanium substrate using a micro-arc oxidation (MAO) process and Ca–P-based electrolyte. The structure and morphology of the TiO₂ coatings were characterized by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy, and profilometry. The chemical properties were studied using electron dispersive X-ray spectroscopy (SEM–EDS) and X-ray photoelectron spectroscopy. The wettability of the coating was evaluated using contact angle measurements. During the MAO process, Ca and P ions were incorporated into the oxide layer. The TiO₂ coating was composed of a mixture of crystalline and amorphous structures. The crystalline part of the sample consisted of a major anatase phase and a minor rutile phase. A cross-sectional image of the coating–substrate interface reveals the presence of voids elongated along the interface. An osteoblast culture was performed to verify the cytocompatibility of the anodized surface. The results of the cytotoxicity tests show satisfactory cell viability of the titanium dioxide films produced in this study.     

Structural and microstructural study of glasses in the Li2O-TiO2-SiO2 system

Glasses from the Li₂O-TiO₂-SiO₂ system with TiO₂ content ranging between 5 and 20 mol % were prepared. The glasses studied have an opal appearance and when their microstructure is studied through transmission electron microscopy, a strong phase separation in droplet form is observed, with the size of the droplets depending on the TiO₂ and the Li₂O content. X-ray diffraction showed that these glasses are non-crystalline and identified the crystalline phases which take place after the corresponding thermal treatment to enhance liquid immiscibility. A structural study of the samples prepared was carried out through infrared spectroscopy. Titanium oxide is incorporated into glasses as a network modifier, so that titanium atoms place themselves in octahedral positions [TiO₆]. This is attributed to the presence of Li₂O which breaks up the glass network, favouring the hexacoordination of titanium atoms.     

Fabrication of titania coatings on stainless steel via laser-induced deposition of colloidal titanium oxide from sol–gel suspension

A novel processing route that exploits the application of laser energy to induce deposition of colloidal titania (TiO₂) from sol–gel suspension was developed to produce titania coatings onto stainless steel (AISI316) substrate. Various laser parameters were investigated in order to establish the feasibility and to work out the key factors and optimal conditions for effectively fabricating these coatings on the substrate. The SEM, EDS, ATR-FTIR, XRD, and contact angle measurement were employed to analyse surface morphology, phase composition, crystalline structure, and the surface properties of the deposited titania coatings. Results show that the laser energy density plays a key role in controlling the deposition process and the deposited coating's properties, whilst traverse speed is also an effective factor. Higher laser energy density delivered to the specific area leads to thicker coatings and higher crystalline phases in the deposited coatings. At lowest energy density of 4.4 J mm⁻² tested in this work, the deposited coating is mainly amorphous, although a small amount of anatase phase is detectable. More crystalline phases are formed including anatase, rutile, substoichiometric titanium oxides, ilmenite and hematite when the laser energy density is increased to 8.7–17.4 J mm⁻². Further increases in laser energy density to 21.7 J mm⁻² results in an increase in the amount of rutile phase and the disappearance of substoichiometric titanium oxide phase. The coated surfaces show an elemental composition very close to the theoretical atomic ratio of TiO₂ which is significantly different from that of the as-dried coating from the same sol. Laser irradiation over a control solution, which has the same composition as the titania sol, but without the titania precursor, was also carried out and the result showed that no change on the solution composition was detected under all laser conditions, but slight oxidation of the substrate was observed at the higher laser energy density.     

Internal oxidation mechanism for Ta-Ru and Mo-Ru coatings

Ta-Ru and Mo-Ru alloy coatings with phases of intermetallic compounds are often used as protective coatings on die materials. After annealing under an oxygen containing atmosphere, the internal oxidation phenomenon resulted in the preferential oxidation of Ta or Mo in the coatings. This process created a phase separated structure consisting of continuous and alternative oxygen rich and deficient layers with a nano scale period beneath the free surface. The experiments in this study deposited Ta-Ru and Mo-Ru coatings with a Cr interlayer by direct current magnetron co-sputtering at 400 °C. Annealing treatments were conducted at 600 °C for short durations under controlled atmospheres consisting of 50 or 10,000 ppm oxygen with residual nitrogen or argon gas. The internal oxidation behavior in the initial stage was determined by evaluating the variations in crystalline structure, surface morphology and chemical composition. The laminated structure was examined by transmission electron microscopy. Results show distinct oxidation behaviors for Ta₄₇Ru₅₃ and Mo₄₆Ru₅₄ coatings. Internal oxidation phenomena appeared in Ta₄₇Ru₅₃ coatings annealed in both 50 and 10,000 ppm O₂ containing atmospheres. The Mo₄₆Ru₅₄ coatings exhibit external oxidation at 50 ppm O₂ containing atmosphere, and internal oxidation at 10,000 ppm O₂ containing atmosphere. Finally, this study proposes an internal oxidation mechanism for alloy coatings with an orientated structure.     

Phase relations in the oxygen rich region of the CrWO ternary system

The phases occurring in the ternary CrWO system at 1370 K have been determined using x-ray diffraction and electron and optical microscopy. It was found that at this temperature no Cr enters WO₃ or the other tungsten oxides and no ternary CS phases appear to form. Instead, the Cr reacts to form one or two ternary rutile phases and equilibrium lies between them and the appropriate binary tungsten oxide. The compositions of these ternary oxides are Cr₂WO₆ and a previously unreported phase CrWO₄. No extended homogeneity ranges have been detected for these oxides. A phase diagram summarises the results which are also considered in the light of the formation of crystallographic shear phases in tungsten oxides.     

Influence of the aluminum incorporation on the structure of sputtered ZrNx films deposited at low temperatures

We have studied the influence of the Al incorporation in the crystalline structure of ZrN thin films deposited by dc magnetron sputtering processes at low temperature. The incorporation of the aluminum in the films depends directly on the Ar/N₂ ratio in the gas mixture and the power applied to the aluminum cathode during the deposition. The chemical composition and the crystalline structure of the films were analyzed by Energy Dispersive X-ray (EDX) spectroscopy and X-ray Diffraction (XRD), respectively. When Al atoms are incorporated into the ZrN coatings, the strong ZrN (200) preferred orientation is modified to a combination of phases related to (111) ZrN with a contribution of cubic (111) AlN and possibly (211) Zr₃N_4, which are detected by XRD for high aluminum concentrations. Fourier Transform Infrared (FTIR)spectroscopy allowed us to complete the identification of the nitrides and oxides incorporated into the deposited films. The effect of a bias voltage applied to the substrate has also been investigated and related to the changes in the microstructure and in the nanohardness values of the ZrAlN films.     

Preparation of alkaline earth carbonates and oxides by the EDTA-gel process

The ethylene-diamine-tetra-acetic acid (EDTA)-gel process has been used to produce carbonates and oxides of the alkaline earth elements Ba, Sr and Ca and their solid solutions. These materials have a range of potential applications including electron emission and catalysis. Gels of composition Ba-EDTA, Sr-EDTA, [Ba_0.5Sr_0.5]-EDTA, [Ba_0.5Sr_0.45Ca_0.05]-EDTA were prepared at pH 6 from aqueous solutions of the alkaline earth nitrates and EDTA and their thermal decomposition studied by TGA/DSC. The gels and the products derived from calcination of these gels at different temperatures have been characterised by FTIR, XRD and SEM, and shown to have high chemical homogeneity and fine particle size. Decomposition of the gels to the carbonate form occurred below 300°C with subsequent formation of the oxide occuring on heat treatment at temperatures ranging from approximately 800°C to > 1000°C depending upon gel composition. The process route is suitable for the production of particulate materials or porous coatings.     

Growth of nano-particles of Al2O3, AlN and iron oxide with different crystalline phases in a thermal plasma reactor

The paper presents the experimental results showing that the crystalline phase of the nano-particles, synthesized in a DC transferred arc thermal plasma reactor, critically depend on the operating pressure in the reaction zone. The paper reports about the changes in crystalline phases of three different compounds namely: aluminium oxide (Al₂O₃), aluminium nitride (AlN) and iron oxide (Fe_xO_y) synthesized at 760 Torr and 500 Torr of operating pressures. The major outcome of the present work is that the phases having higher defect densities are more probable to form at the sub-atmospheric operating pressures. The variations in the crystalline structures are discussed on the basis of the change in the temperature during the nucleation process, prevailing at the boundary of the plasma, on account of the ambient pressures. The as-synthesized nano-particles were examined by X-ray diffraction analysis and transmission electron microscopy. In addition, the confirmatory analysis of the crystalline phases of iron oxides was carried out with the help of Mössbauer spectroscopy.     

Mikrostruktur und Eigenschaften HVOF‐gespritzter Schichten im System TiO2 – Cr2O3

Microstructure and properties of HVOF‐sprayed coatings of the TiO₂ – Cr₂O₃ system Thermally sprayed titanium oxide coatings are known for their good tribological properties and their electrical conductivity. The latter is due to oxygen deficiency from the stoichiometric composition TiO₂. These lattice defects can be ordered and are called crystallograhic shear planes. These structures are known as Magnéli phases. At high temperature in oxygen‐containing atmospheres the material forms isolating TiO₂, therefore the application under such conditions is restricted. At the titania‐rich side of the system TiO₂‐Cr₂O₃ also compounds with the structure of Magnéli‐phases are formed. According to information from the literature, these phases are stable in oxygen‐containing atmospheres and are therefore promising for corresponding coating applications at elevated temperatures. In this paper first results of systematic studies of microstructure and properties of HVOF‐sprayed coatings are presented.     

Properties of colored oxide films formed electrochemically on titanium in green electrolytes under ultrasonic stirring

Titanium anodization was successfully carried out in green electrolytes such as acetic acid and sodium bicarbonate solutions, yielding uniformly colored oxide films as passive coatings. Oxide formation was carried out galvanostatically at 9.7 mA cm^?2 up to various cell potential values (in the 20–140 V range), in ultrasonic-stirred electrolyte at room temperature. The anodization rate values varied in the range of 1.8–2.0 nm V^?1 for sodium bicarbonate solutions and 2.3–2.7 nm V^?1 for acetic acid solutions. Micro-Raman spectroscopy allowed the identification of the anatase crystalline phase in the oxides grown up to the highest potentials; under these conditions, the micrographs obtained by scanning electron microscopy revealed oxides with rough and porous surfaces. A variety of colors were obtained for the titanium oxide films (yellow, blue, brown, purple, pink, and green, and different tones of each of them), depending on the final formation potential and the electrolyte nature and concentration; chromatic coordinates measurements exactly defined the color of the films.     

Ion-plated aluminium/aluminium oxide coatings using a pulsed oxygen process

Pulsed oxygen was utilized in a thermionically assisted triode ion plating process to produce dense, hard and highly adherent aluminium/aluminium oxide coatings on steel substrates. The coatings were deposited in a 0.1 Pa argon discharge while oxygen gas was injected at various pulse rates into the chamber. The influence of the oxygen flow rates, the pulse rates and the substrate bias on the structure and crystal phase of the coating were investigated using scanning and transmission electron microscopy, X-ray diffraction and Rutherford backscattering techniques. The analysis showed that the resultant coating structure consist of a mixed state of crystalline and non-crystalline phases depending on the oxygen flow rate and on the substrate bias at a constant oxygen pulse rate. Analysis showed that the non-crystalline phase approached stoichiometry for Al₂O₃ at oxygen flow rates of 7.5 Torr l s^-1 and a substrate bias of 2 kV and that there was a substantial increase in hardness.     

Niobium oxides and niobates physical properties: Review and prospects

For the last 75 years several studies have been reporting on the physical properties of niobium oxides, but there is still many contradictory, inconsistent and insufficient information on these metal oxides. This review will begin by describing the niobium oxygen system and the different stoichiometric and non-stoichiometric phases, specifically Nb, NbO, NbO₂, Nb₂O₅ and Nb₂O_5−δ. The crystalline phases and polymorphs of these materials are often inconsistently identified in different works and thus, a clarification of the nomenclature of the several niobium oxides polymorph and their crystalline structure is also presented. Due to their interesting physical properties, many applications of these materials have been suggested such as solid electrolytic capacitors, catalysis, photochromic devices, transparent conductive oxides or memristors, becoming obvious that a good understanding of niobium oxides physical properties and their control is essential and urgent. Additionally, a short review on different types of niobates, namely alkali niobates, columbite niobates and rare earth niobates and the relation of the properties of these materials with niobium oxides will be presented.     

Titanium-oxide interface structures formed by degassing and anodization processes

High-resolution electron microscopy was used to investigate two types of titanium-oxide interface structures. The first type was generated by thermal oxidation during the degassing process, which is one step in the process of porcelain-fused-to-metal systems. The thermal oxidation was performed for 1 min at a temperature of 1073 K in a porcelain furnace under a reduced pressure at 27 hPa. Columnar and granular rutile oxide formed on the titanium, and the surface oxide layer was almost 1 μ m thick. On an atomic scale, the crystal size of the rutile adjacent to the interface decreased about 10 nm. In addition, a very thin transitional layer 2–3 nm thick formed at the titanium-oxide interface. The crystal structure of the thin layer seemed to be the T{i}O phase with a NaCl-type structure. The interface between the hcp titanium and T{i}O phases was coherent through the close-packed planes ((0 0 0 2)_hcp and (1 1 1)_TiO). Partial coherency was observed at the interface between the T{i}O and T{i}O₂ phases. The second type of titanium-oxide interface was generated by anodization on a screw-type titanium implant. The morphology of the surface suggested that the titanium implant had been treated by spark anodization. The surface oxide, which was estimated to be about 10 μ m thick, was a mixture of the anatase-type T{i}O₂ phase and the amorphous phase. The crystal size of the anatase varied from less than 10 nm to more than 100 nm. A phosphate anion was concentrated in the amorphous phase. Between the surface oxide and the titanium base, macroscopic defects like cracks and voids were observed. Microscopic observation could not confirm the formation of a clear interface and lattice coherency between the titanium and oxide as a result of the degassing process.     

Studies of calcium-precipitating oral bacterial adhesion on TiN,TiO2 single layer,and TiN/TiO2 multilayer-coated 316L SS

Titanium nitride (TiN), titanium oxide (TiO₂) single layer, and TiN/TiO₂ multilayer coatings were deposited on a 316L stainless steel substrate using reactive magnetron sputtering process with the aim of preventing bacterial adhesion. The crystal structures of as-prepared coatings were evaluated using X-ray diffraction analysis. The cubic structure of TiN, anatase, and rutile structure of TiO₂ was noticed. Atomic force microscopy images exhibited a relatively smooth surface for all coatings. The surface wettability studies confirmed that the coatings were hydrophilic in nature. The rate of bacterial adhesion was evaluated using scanning electron microscopy and epifluorescence microscopy. These results demonstrated that the coated substrates could help to effectively reduce the bacterial adhesion and biofilm formations.     

Preparation and properties of composite particles made by nano zinc oxide coated with titanium dioxide

In this paper, composite particles of nano zinc oxide coated with titanium dioxide were prepared and characterized by TEM, XRD, XPS and FT-IR, and the properties of the composite particles for photo catalysis and light absorption were studied. Tetrabutyl titanate (TBT) was hydrolyzed in an alcoholic suspension of nano zinc oxide with diethanolamine (DEA) as an additive, resulting in a film with a thickness of 20–30 nm being coated on the surface of nano zinc oxide, and the composite particles contained ZnTiO₃ after drying and calcination. Photocatalysis capabilities of the composite particles for the degradation of phenol in an aqueous solution were greatly improved as compared with nano zinc oxide particles before coating, with pure nano ZnO and nano TiO₂ with similar average sizes, or with the mixture of nano ZnO and TiO₂ with the similar composition as the composite particles. The light absorption scope of the composite particles was enlarged when compared to nano titanium dioxide with same average size.     

Structural analysis and corrosion studies on an ISO 5832-9 biomedical alloy with TiO2 sol–gel layers

The aim of this study was to demonstrate the relationship between the structural and corrosion properties of an ISO 5832-9 biomedical alloy modified with titanium dioxide (TiO₂) layers. These layers were obtained via the sol–gel method by acid-catalyzed hydrolysis of titanium isopropoxide in isopropanol solution. To obtain TiO₂ layers with different structural properties, the coated samples were annealed at temperatures of 200, 300, 400, 450, 500, 600 and 800 °C for 2 h. For all the prepared samples, accelerated corrosion measurements were performed in Tyrode’s physiological solution using electrochemical methods. The most important corrosion parameters were determined: corrosion potential, polarization resistance, corrosion rate, breakdown and repassivation potentials. Corrosion damage was analyzed using scanning electron microscopy. Structural analysis was carried out for selected TiO₂ coatings annealed at 200, 400, 600 and 800 °C. In addition, the morphology, chemical composition, crystallinity, thickness and density of the deposited TiO₂ layers were determined using suitable electron and X-ray measurement methods. It was shown that the structure and character of interactions between substrate and deposited TiO₂ layers depended on annealing temperature. All the obtained TiO₂ coatings exhibit anticorrosion properties, but these properties are related to the crystalline structure and character of substrate–layer interaction. From the point of view of corrosion, the best TiO₂ sol–gel coatings for stainless steel intended for biomedical applications seem to be those obtained at 400 °C.     

Comparison of the coatings deposited using Ti and B4C powder by reactive plasma spraying in air and low pressure

The coatings were deposited by reactive plasma spraying (RPS) in air and low-pressure plasma spraying (LPPS) based on the reaction between Ti and B₄C powder, respectively. The thermal spray powder of Ti and B₄C added with powder Cr (metallic binder) in air is compared with that without powder Cr addition in the low pressure. (Prior to deposition, the powder was screened and separated for RPS whereas spray drying, sintering and sieving were done for LPPS.) The phase composition and the microstructure of coatings were studied by X-ray diffractometer (XRD) and scanning electron microscopy (SEM). The anti-corrosion property of coatings was also investigated. It is found that the coating prepared by RPS, which is more densification, is composed of TiN, TiB₂, and a small phase fraction of titanium oxides. The composition of the coating deposited by reactive LPPS is TiB₂, Ti(C, N), Ti₄N_3−x and impurity phase of Ti₅Si₃. There is no appearance of titanium oxides in low pressure. The coatings have the typical lamellar structure and adhere to the bond coating well. The mean Vickers microhardness value of the coating deposited by RPS is higher than that of the coating deposited by LPPS. Furthermore, the corrosion resistance of the coating deposited by RPS is superior to that of the coating prepared by LPPS in near neutral 3.5 wt% NaCl electrolyte.     

Sol-gel preparation and characterisation of mixed metal tin oxide thin films

Mixed metal oxide stannates were prepared by sol-gel methods and coated onto solid titanium substrates as thin films using spin and dip coating methods. Metal oxides such as Sb₂O₅, ZrO₂, CuO, MnO_x and PdO were introduced into a SnO₂ host matrix using sol-gel technology. The mixed metal tin oxide materials prepared via the sol-gel route were extensively characterised in terms of surface characterisation and chemical composition. Thermogravimetric analysis was performed to confirm that at 600 °C (the calcination temperature) no further structural changes due to mass loss occur. UV spectroscopy of the liquid gels allowed the determination of the band gap energy. The surface morphology of the thin film electrodes were characterised by atomic force microscopy and scanning electron microscopy and the effect of the coating method employed i.e. spin or dip coating could be clearly seen in the estimated values of surface roughness. These techniques were also able to confirm the thickness of the films in the nano range. Combined nuclear beam techniques such as Rutherford backscattering spectroscopy and particle induced X-ray emission provided some insight into the chemical composition of the mixed metal tin oxides and confirmed the presence of the dopant element in the SnO₂ host material.     

Effect of Ti or TiN codeposition on the performance of MoS2-based composite coatings

Properties of MoS₂ coatings can be improved by the codeposition of a small amount of titanium (Ti). In this study, MoS₂-based composite coatings, which consisted of Ti or titanium nitride (TiN) and molybdenum disulfide, are synthesized by unbalanced plasma plating. Two forms of MoS₂-based composite coatings have been developed: TiN-MoS₂/Ti and TiN-MoS₂/TiN coatings. The effect of Ti or TiN and processing parameters on properties of such coatings are investigated. Scanning electron microscopy (SEM), dry drilling and turning tests are used to determine the structure, composition and tribological performance of MoS₂-based coatings. Experimental results indicate that these MoS₂-based composite coatings are considerably more wear-resistant and are less sensitive to atmospheric water vapor than pure MoS₂ coatings. These coatings show excellent results when tested for a wide range of industrial turning and drilling applications.     

Industrially-styled room-temperature pulsed laser deposition of titanium-based coatings

Titanium-based compounds are widely used as coating materials for mechanical, tribological, electrical, optical, catalytic, sensoric, micro-electronical applications due to their exceptionally physical and chemical properties. Recently, the trend of using temperature-sensitive materials like polymers and tool steels with the highest hardness demands new low-temperature coating techniques for protective surface finishing as well as for surface functionalization, but up to now there is lack of industrially scaled vacuum coating techniques at temperatures below 50 °C. An alternative for overcoming this problem is the pulsed laser deposition (PLD) technique, which was up-scaled for industrial demands at Laser Center Leoben of JOANNEUM RESEARCH Forschungsgesellschaft mbH.The current paper summarizes the application of the industrially-scaled PLD technique on the deposition of the presently most important Ti-based coatings: metallic titanium, titanium nitride (TiN), titanium oxide (TiO₂) and titanium carbonitride (TiCN). PLD coating allows, even at room temperature, the formation of film structures of Zone-T type of Thornton's structure zone model, both on substrates aligned normal and parallel to the incident vapor flux. The high-energetic deposition conditions are revealed by the occurrence of (2 2 0) textures for the fcc TiN-based films. The dense grown structure affects advantageously the tribological behavior—generally, low wear rates and (for TiCN) very low friction coefficients were found. For TiO₂ coatings, growing as a mixture of β-TiO₂ and amorphous phases, the easily reproducible change of deposition parameters in the room-temperature PLD allows large differences in the optical transmission and electrical resistance.