Fabrication of highly porous titanium (Ti) scaffolds with two interlaced periodic pores

This paper reports a novel type of porous titanium (Ti) scaffolds with two interlaced periodic pores that were produced by coating the surfaces of a dual-channeled hydroxyapatite (HA) scaffold, as a supporting framework, with a titanium hydride (TiH₂) slurry followed by heat-treatment at 1200 °C for 3 h in a vacuum to convert TiH₂ to Ti metal. This method allowed the porous Ti scaffolds to mimic the original pore structure of the dual-channeled HA scaffold in a tightly controlled manner. It was observed that the Ti layer was strongly adhered to the HA layer, owing to the diffusion of P ions into the Ti layer. The fabricated sample showed a high compressive strength of 6.0 ± 0.77 MPa and a porosity of 78 vol.% due to its unique pore structure, as well as perfect interconnections between the pores.     

Nanoporous TiO2 thin film based conductometric H2 sensor

Nanoporous titanium dioxide (TiO₂) based conductometric sensors have been fabricated and their sensitivity to hydrogen (H₂) gas has been investigated. A filtered cathodic vacuum arc (FCVA) system was used to deposit ultra-smooth Ti thin films on a transducer having patterned inter-digital gold electrodes (IDTs). Nanoporous TiO₂ films were obtained by anodization of the titanium (Ti) thin films using a neutral 0.5% (wt) NH₄F in ethylene glycol solution at 5 V for 1 h. After anodization, the films were annealed at 600 °C for 8 h to convert the remaining Ti into TiO₂. The scanning electron microscopy (SEM) images revealed that the average diameters of the nanopores are in the range of 20 to 25 nm. The sensor was exposed to different concentrations of H₂ in synthetic air at operating temperatures between 100 °C and 300 °C. The sensor responded with a highest sensitivity of 1.24 to 1% of H₂ gas at 225 °C.     

Fabrication of porous titanium scaffolds with high compressive strength using camphene-based freeze casting

We herein report the fabrication of highly porous titanium (Ti) scaffolds with unusually high compressive strength by freezing a titanium hydride (TiH₂)/camphene slurries at 42 °C. As the freezing time was increased from 1 to 7 days, the pore size obtained was increased significantly from 143 to 271 μm due to the continual overgrowth of camphene dendrites. However, interestingly, the formation of the micro-pores inside the Ti walls was suppressed at longer freezing time. This resulted in a significant increase in compressive strength up to 110 ± 17 MPa with a porosity of 64%. It is believed that this unusually high compressive strength with large interconnected pores makes this material suitable for applications as load-bearing parts.     

Fabrication of titanium scaffolds with porosity and pore size gradients by sequential freeze casting

This paper reports a novel method for producing porous Ti scaffolds with a gradient in porosity and pore size using the freeze casting method, in which TiH₂/camphene slurries with various TiH₂ contents (40, 25, and 10 vol.%) were cast sequentially into a mold, followed by freeze drying and heat-treatment in a vacuum at 1300 °C for 3 h. This simple sequential freeze casting method produced good bonding between the layers with different porosities of 35, 53, and 75 vol.% obtained using the TiH₂ contents of 40, 25 and 10 vol.%, respectively. In addition, the pore size could be increased significantly by increasing the freezing time. The pore sizes obtained in the regions produced using 40, 25, and 10 vol.% TiH₂ after freezing for 7 days were 96, 166, and 270 μm, respectively.     

Development of highly porous titanium scaffolds by selective laser melting

The selective laser melting (SLM) of the TiH₂-Ti blended powder was performed in the present work. Porous titanium scaffolds characterized by high porosity (∼ 70%), interconnected Ti walls and open porous structures with macroscopic pores (in a range of ∼ 200 to ∼ 500 μm) were successfully prepared at a laser power of 1000 W and a scan speed of 0.02 m/s. The effects of componential and processing conditions in terms of TiH₂ content and scan speed on the microstructural development of porous titanium (porosity and pores size) were investigated. Reasonable mechanisms for pores formation during SLM apart from microstructural evolutions were proposed.     

Freeze casting of porous Ni-YSZ cermets

Dual-phase porous Ni-YSZ cermets were fabricated via the freeze casting of a ceramic/camphene slurry. After removing the frozen camphene via sublimation at room temperature, the green samples were sintered for 3 h in air at various temperatures, ranging from 1100 to 1350 °C, and then reduced in an Ar-5% H₂ atmosphere at 700 °C for 3 h. The fabricated Ni-YSZ cermets showed 3-D pore channels formed by the replication of the entangled camphene dendrite network and small pores in the Ni-YSZ walls produced by partial sintering of the NiO-YSZ composite. Furthermore, the fabricated samples were found to possess reasonable electrical conductivities, thus rendering them suitable for use as the basic components of planar solid oxide fuel cells (SOFCs).     

Growth, structure and friction behavior of titanium doped tungsten disulphide (Ti-WS2) nanocomposite thin films

This study describes the synthesis, structure and friction behavior of titanium doped tungsten disulphide (Ti-WS₂) nanocomposite solid lubricant thin films grown by cosputtering at room and 300 °C in situ substrate temperatures. The films were studied by focused ion beam (FIB) prepared cross-sectional scanning and transmission electron microscopies and X-ray diffraction (XRD) to determine the thin film structure and crystallinity as a function of varying titanium atomic percent and sputtering power. XRD confirmed that the pure WS₂ thin films grown at room temperature (RT) and 300 °C were crystalline with hexagonal texture. Basal planes with c-axis orientated parallel to the substrate surface [(100) and (101) texture] were predominantly observed in all thin films. Co-sputtering at RT with any amount of Ti induced a dramatic change in the microstructure, i.e., Ti prevented the formation of crystalline WS₂, making it amorphous with well-dispersed nanocrystalline (1-3 nm) precipitates. For RT friction tests, longer thin film lifetimes were exhibited when the thin films were doped with low amounts of Ti (∼ 5-14 at.%) in comparison to pure WS₂ but there was no change in friction coefficient (∼ 0.1). For high temperature (500 °C) friction tests, slightly higher friction coefficients (0.2) but longer lifetimes were observed for the low at.% Ti doped thin films. Mechanisms of solid lubrication were studied by FIB prepared cross-sectional specimens and Raman spectroscopy wear maps inside the wear tracks to determine the sub-surface deformation behavior and formation of tribochemical products, respectively. It was determined that WS₂ oxidized to form relatively low shear strength WO₃ during wear (tribo-oxidation) and heating at 500 °C (thermal oxidation) as determined by Raman spectroscopy in the wear track and transfer film (third body) on the counterface.     

Field emission from the structure of well-aligned TiO2/Ti nanotube arrays

Well-aligned TiO₂/Ti nanotube arrays were synthesized by anodic oxidation of titanium foil in 0.5 wt.% HF in various anodization voltages. The images of filed emission scanning electron microscopy indicate that the nanotubes structure parameters, such as diameter, wall thickness and density, can be controlled by adjusting the anodization voltage. The peaks at 25.3° and 48.0° of X-ray diffraction pattern illuminate that the TiO₂ nanotube arrays annealed at 500 °C are mainly in anatase phase. The filed emission (FE) properties of the samples were investigated. A turn-on electric field 7.8 V/µm, a field enhancement factors approximately 870 and a highest FE current density 3.4 mA/cm² were obtained. The emission current (2.3 mA/cm² at 18.8 V/µm) was quite stable within 480 min. The results show that the FE properties of TiO₂/Ti have much relation to the structure parameters.     

Polycarbosilane derived Ti3SiC2

Titanium silicon carbide (Ti₃SiC₂) ceramic was synthesized by in-situ reaction of metal titanium and polycarbosilane. Reaction mechanisms which lead to the formation of Ti₃SiC₂ were suggested on the basis of XRD analysis. The content of Ti₃SiC₂ reached 93% in products obtained from heating the Ti/polycarbosilane green compact at 1400 °C in Ar. The morphology and compositions of the products were examined by SEM equipped with EDX. The typical laminate structure of Ti₃SiC₂ particles with 1-4 μm in thickness and 4-15 μm in length was observed. EDX results showed that the atomic ratio of Ti:Si:C of grains is close to 3:1:2, which agrees with Ti₃SiC₂ composition.     

Processing of porous Ti and Ti5Mn foams by spark plasma sintering

Titanium and its alloys are one of the best metallic biomaterials to be used for implant application. In this study, porous Ti and Ti5Mn alloy with different porosities were successfully synthesized by powder metallurgy process with the addition of NH₄HCO₃ as space holder and TiH₂ as foaming agent. The consolidation of powder was achieved by spark plasma sintering process (SPS) at 16 MPa and pressureless conditions. The morphology of porous structure was investigated by using scanning electron microscopy (SEM) and X-ray micro-tomography (μ-CT). Nano-indentation tester was used to evaluate Young’s modulus of the porous Ti and Ti5Mn alloy. Experimental results showed that pure Ti sample, which sintered under pressure of 16 MPa, full relative density was achieved even at a relative low sintering temperature 750 °C; however, in the case of pressureless condition at sintering temperature 1000 °C the porosity was 53% and Young’s modulus was 40 GPa. The Ti5Mn alloy indicated a good pore distribution, and the porosity decreased from 56% to 21% by increasing the sintering temperature from 950 °C to 1100 °C. Young’s modulus was increased from 35 GPa to 51.83 GPa with increasing of the sintering temperatures from 950 °C to 1100 °C.     

Ti/SiO2 composite fabricated by powder metallurgy for orthopedic implant

Titanium/silica (Ti/SiO₂) composites are fabricated using powder metallurgy (P/M). Nanoscale biocompatible SiO₂ particles are selected as reinforcement for the Ti/SiO₂ composite to enhance its biocompatibility and strength, especially when with high porosity. Effects of the SiO₂ particle addition and sintering temperature on mechanical properties of the Ti/SiO₂ composites are investigated. The results indicate that the mechanical property of Ti/SiO₂ composites sintered at 1100 °C are better than those at 900 and 1000 °C. The strength of the Ti/SiO₂ composites is significantly higher than that of pure titanium. The composite with the SiO₂ content of 2 wt% sintered at 1100 °C for 4 h shows an appropriate mechanical property with a relative density of 96.5%, a compressive strength of 1566 MPa and good plasticity (an ultimate strain of 15.96%). In vitro results reveal that the Ti/SiO₂ composite possesses excellent biocompatibility and cell adhesion. Osteoblast-like cells grow and spread well on the surfaces of the Ti/SiO₂ composites. The Ti/SiO₂ composite is a promising material for great potential used as an orthopedic implant material.     

Preparation, dielectric and ferroelectric properties of Pb5Ge3O11 and Pb5Ge2.85Si0.15O11 thin films fabricated by sol-gel process

Lead germanate-silicate (Pb₅Ge_2.85Si_0.15O₁₁) ferroelectric thin films were successfully fabricated on Pt/Ti/SiO₂/(100)Si substrates by the sol-gel process. The thin films were fabricated by multi-coating at preheating temperatures of 350 and 450 °C. After annealing the thin films at 600 °C, the films exhibited c-axis preferred orientation. The degree of c-axis preferred orientation of the thin films preheated at 350 °C was higher than that of films preheated at 450 °C. Grain growth was influenced by the annealing time. The thin films exhibited a well-saturated ferroelectric P-E hysteresis loop when preheated at 350 °C and annealed at 600 °C for 1.5 h. The values of the remanent polarization (Pr) and the coercive field (Ec) were approximately 2.1 μC/cm² and 100 kV/cm, respectively.     

A simple route to fabricate TiC–TiB2/Ni composite via thermal explosion reaction assisted with external pressure in air

The dense TiC–TiB₂/Ni composite was successfully fabricated through the pressure-assisted thermal explosion reaction from Ti, B₄C and Ni powder blends in air. The ignition temperature (625 °C) in air was 415 °C lower than that in vacuum. The decreased ignition temperature resulted from a chemical oven mechanism in which the oxidation and nitrification of Ti and the oxidation of B₄C released the heat and promoted the occurrence of the thermal explosion reaction. The composites prepared in air and vacuum had similar phase constituents and microstructure. Moreover, the composite prepared in air possessed comparable hardness, flexural strength and fracture toughness to the composite prepared in vacuum.     

Microstructure evolution and oxidation behaviour of Tif/TiAl3 composites

In this paper, Ti_f/TiAl₃ composites were fabricated by infiltration–in situ reaction method and its oxidation behaviours were investigated by cyclic oxidation testing at 700 °C, 800 °C and 900 °C. The microstructure evolution and oxidation of Ti_f/TiAl₃ composites were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray diffraction (EDX). The reaction between Ti₃Al particles and Al was more violent than that of Ti fibres and Al. Ti₃Al/Al reaction consumed a large amount of Al and inhibited the reaction of Ti fibres indirectly. Reactant of Ti fibres was TiAl₃ at 700 °C, and four reaction layers surrounding Ti fibre (Ti₃Al, TiAl, TiAl₂ and TiAl₃ from inner to outside) were observed above 800 °C. The thickness of the total reaction layers increased little with temperature and time, while the thickness of inner reaction layers increased remarkably. A model corresponding to the microstructure evolution process was drawn schematically. Oxidation resistance of Ti_f/TiAl₃ composites decreased with increasing of temperature, and changed from cubic law at 700 °C to parabolic law at 900 °C. The oxidation weight gain of Ti_f/TiAl₃ composite was dominated by the exposed Ti fibres. Due to outward diffusion of Ti and Al element, the oxide of Ti fibre at 900 °C changed to mushroom-shape. Fortunately, when TiAl₃ was oxidized, a thin and continuous Al₂O₃ layer was formed, protecting matrix from further oxidation.     

Synthesis, characterization and dielectric properties of europium-doped barium titanate nanopowders

Europium-doped cubic barium titanate (BT) nanocrystals with % [Eu/Ti] mol ratio varying from 0.05 to 0.25 were prepared through hydrothermal route. The nano nature of these powders was confirmed by XRD and TEM studies. Pellets were prepared after calcining the powders at 1000 °C for 2 h. These pellets were annealed at 200, 500, 700 and 1000 °C for 2 h at each temperature and used for dielectric measurements. Raman spectra of two typical pellets with %[Eu/Ti] Eu/Ti mol ratios of 0.15 and 0.25 showed all the peaks characteristic of tetragonal BaTiO₃. Pure BT showed a low dielectric constant (DC) with a value of 398. Doping with small amounts of Eu resulted in many fold increase of DC values. A maximum value of 10576 at 1 KHz frequency was observed for the sample with % [Eu/Ti] mol ratio of 0.15. Lowering of Curie temperature T_c (95 to 110 °C) was observed for pure as well as Eu-doped barium titanate.     

Synthesis and bioactivity of porous Ti alloy prepared by foaming with TiH2

A novel porous Ti–6Al–4V with an open cell structure was fabricated by powder metallurgy process with the addition of TiH₂ as the pore forming and active agent. Control of porosity of porous Ti alloy made it possible to obtain the porous Ti with the Young's modulus value of 5.8–9.5 GPa, which was similar to that of human cancellous bone. This kind of porous Ti alloy with good biomechanical properties is potential to alleviate the problem of mechanical mismatch between the bone and the Ti implant. The porous Ti alloy prepared by the addition of TiH₂ as foaming agent had a uniform distribution of pores with pore size of 90–190 μm and porosity of 43–59%. In order to improve the biological properties, the duplex titania/apatite coatings were applied onto the surface of porous Ti alloy. The titania coating was deposited by chemical treatment and the apatite coating was subsequently applied by immersing the samples in a simulated body fluid. Results showed that a homogeneous nanocrystallite titania coating with a thickness of 0.8 μm was formed on the surface of the Ti alloy after chemical treatment. The carbonate-containing apatite coating with a thickness of 1 μm was deposited on the surface of titania coating after immersion in simulated body fluid for 7 days. The nucleation of the carbonate-containing apatite can be induced from the electrostatic interaction between the OH-containing groups on the surface of titania coating and the calcium and phosphate ions in the metastable simulated body fluid on those specific superficial sites. The growth kinetics of the coatings was also discussed. Cell culture test showed the well stretched and proliferated cells on the surface of the sample, indicating the good biocompatibility of porous Ti alloy.     

Fabrication of dye-sensitized solar cells using TiO2-nanotube arrays on Ti-grid substrates

Self-aligned TiO₂ nanotube arrays (20 μm in length) were fabricated by anodic oxidation of Ti-grid with a thickness of 100 μm in an ethylene glycol electrolyte with an addition of H₂O (1.5 vol.%) and NH₄F (0.2 wt.%). Voltage applied between Ti and Pt cathodes is 60 V at ~ 22 °C. Dye-sensitized solar cell utilizing photoanode structure of TiO₂-nanotube/Ti-grid was fabricated with no transparent conducting oxide (TCO) layer, in which Ti-grid replaces TCO. Overall photoconversion efficiency is very low (< 0.5%) due to the large pore size (100 nm in diameter) of the nanotubes, which may cause insufficient dye molecules to be attached, thus limiting light harvesting.     

In-situ production of Fe-TiC composite

A TiC/Fe composite was produced by a novel process which combines in situ with powder metallurgy techniques. The microstructure of the Fe-TiC composite was studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD); with the help of differential thermal analysis (DTA), the reaction path of the Fe-Ti-C system was discussed. The results show that the production of an iron matrix composite reinforced by TiC particulates using the novel process is feasible. TiC particles exhibit homogeneous distribution in the α-Fe matrix. The reaction path is as follows: first, allotropic change Fe_α → Fe_γ at 765.6 °C; second, formation of the compound Fe₂Ti at 1078.4 °C because of the eutectic reaction between Ti and Fe; third, reaction between carbon and melted Fe₂Ti causing formation of TiC at 1138.2 °C; finally, Fe₃C formation due to the eutectic reaction between remanent C and Fe at 1146.4 °C.     

Effect of partially oxidized Ti powders on the microstructure and PTCR characteristics of (Ba,Sr)TiO3

Rutile TiO₂ (a=4.594 å and c=2.958 å) phase was formed on the outer region of Ti powders after oxidation at 600 °C for 1–300 h. Porous (Ba,Sr)TiO₃ ceramics were fabricated by adding partially oxidized Ti powders (4–8 vol %) into (Ba,Sr)TiO₃ powders, and showed excellent positive temperature coefficient of resistivity (PTCR) characteristics after paste-baking treatment at 580 °C in air. The PTCR characteristics of the porous ceramics were mainly attributed to the adsorption of oxygen at the grain boundaries. The microstructure and electrical properties of the porous (Ba,Sr)TiO₃ ceramics containing the partially oxidized Ti powders oxidized at 600 °C for different oxidation times (1–300 h) were investigated.     

Preparation and properties of Ti/SnO2-Sb2O5 electrodes by electrodeposition

Sb and Sn coatings were deposited on Ti substrate by the method of cathode deposition, and the Ti/SnO₂-Sb₂O₅ electrodes were obtained by annealing at different temperatures for 3 h. Ti/SnO₂-Sb₂O₅ coating was characterized using technique such as X-ray diffraction (XRD), and scanning electron microscopy (SEM). Ti/SnO₂-Sb₂O₅ electrode calcined at 550 °C exhibits the best catalytic capacity. Ti/SnO₂-Sb₂O₅ electrode obtained by electrodeposition had longer service life and faster degradation capacity compared with that obtained by dip-coating. Accelerated service life tests were carried out in 0.5 mol L^− 1 H₂SO₄ solution with the current density of 100 mA cm^− 2. Service life of Ti/SnO₂-Sb₂O₅ electrode prepared in present study was 15 h, and it was only 0.14 h for Ti/SnO₂-Sb₂O₅ electrode obtained by dip-coating.