Bioactivating the surfaces of titanium by sol-gel process

In the present study, titanium (Ti) samples were surface-modified by titania (TiO₂), silica (SiO₂) and hydroxyapatite (HA) coatings using a sol-gel process. The bioactivity of the film-coated Ti samples was investigated by cell attachment and morphology study using human osteoblast-like SaOS-2 cells. Results of the cell attachment indicated that the densities of cell attachment on the surfaces of Ti samples were significantly increased by film coatings; the density of cell attachment on HA film-coated surface was higher than those on TiO₂ and SiO₂ film-coated surfaces. Cell morphology study showed that the cells attached, spread and grew well on the three kinds of film-coated surfaces. It can be concluded that the three kinds of film coatings can bioactivate the surfaces of Ti samples effectively. Overall, Ti sample with HA film-coated surface exhibited the best bioactivity.

Sol-gel derived hydroxyapatite/titania biocoatings on titanium substrate

A simple sol–gel method was successfully developed for a hydroxyapatite (HA)/TiO₂ double layer deposition on a pure titanium substrate. Phase formation, surface morphology, and interfacial microstructure were investigated by differential scanning calorimetry analysis (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The TiO₂ layer was coated by a spin coating method at a speed of 1500 rpm for 15 s, followed by a heat treatment at 560 °C for 20 min. The HA film was subsequently spin coated on the outer surface at the same speed and then heat-treated at difference temperatures. Results indicated that the HA phase began to crystallize after a heat treatment at 580 °C; and the crystallinity increased obviously at a temperature of 780 °C. The HA film showed a porous structure and a thickness of 5–7 μm after the heat treatment at 780 °C. SEM observations revealed no delamination and crack at the interfaces of HA/TiO₂ and TiO₂/Ti. The HA film with a porous structure is expected to be more susceptible to the natural remodeling processes when it is implanted in a living body.

Frictional behaviour and wear performance of a nitrocarburised coating sliding against AISI 1019 steel

This work employed a commercial nitrocaburising process to diffuse a coating onto M2 grade high speed tool steel. Properties of the nitrocaburised coating (CN) such as thickness, roughness and hardness were characterised using a variety of techniques including Glow-Discharge Optical Emission Spectrometry (GD-OES) and Scanning Electron Microscopy (SEM). A tribological test has been developed in which two nominally identical crossed cylinders slide over each other under selected test conditions. The test has been employed to investigate the wear performance of both CN coated and uncoated M2 specimens and frictional behaviour of the sliding interface between the tool and a AISI 1019 steel workpiece under unlubricated (dry) and lubricated conditions. Fourier Transform Infrared Spectroscopy (FTIR) was used to monitor the formation of chemical species from the oxidation of lubricant during tribological testing.

Fluidized bed CrN coating formation on prenitrocarburized plain carbon steel

CrN coatings were formed on plain carbon steel by prenitrocarburizing, followed by thermoreactive deposition and diffusion (TRD) in a fluidized bed furnace at 570 °C. During TRD, Cr was transferred from Cr powder in the fluidized bed to the nitrocarburized substrates by gas-phase reactions initiated by reaction of HCl gas with the Cr. The microstructural processes occurring in the white layer, caused by N diffusion toward the surface during this stage were studied. This study compares TRD atmospheres employing inert gas and HCl or inert gas, H2, and HCl. Surface characterization was performed by scanning electron microscopy (SEM), x-ray diffraction (XRD), and glow-discharge optical-emission spectroscopy (GDOES).

Cr(N,C) diffusion coating formation on pre-nitrocarburised H13 tool steel

The microstructural processes of Cr(N,C) coating formation by thermoreactive deposition and diffusion (TRD) on pre-nitrocarburised H13 tool steel were studied. Both nitrocarburising and TRD were performed in fluidized bed furnaces at 570 °C. During TRD, chromium was transferred from chromium powder in the fluidized bed, to the nitrocarburised substrates by gas-phase reactions initiated by reaction of HCl gas with the chromium. Addition of 30% H2 to the input inert gas was found to increase the rate of coating formation, although hydrogen reduction resulted in rapid loss of nitrogen to the surface. The reason for the increased rate of coating formation could not be established without further investigation, although several possible explanations have been proposed. It was found that porosity and the formation of an iron nitride ‘cover layer’ during nitrocarburising were the biggest influences on the microstructure of the Cr(N,C) coating. Microstructural characterization of the coatings was performed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and glow discharge optical emission spectroscopy (GDOES).

Interaction between the coating characteristics of galvanneal steel and forming parameters during flat die drawing

Galvanneal steel is considered to be better for automotive applications than its counterpart, galvanized steel, mainly because of its superior coating and surface properties. Galvanneal steel is produced by hot dipping sheet steel in a bath of molten zinc with small, controlled, levels of aluminium, followed by annealing which creates a Fe-Zn intermetallic layer. This intermetallic layer of the coating improves spot weldability and improves subsequent paint appearance. However, if the microstructure of the coating is not properly controlled and forming parameters are not properly selected, wear of the coating could occur during stamping. Frictional sliding of the sheet between the tool surfaces results in considerable amount of coating loss. An Interstitial Free steel with a Galvanneal coating of nominally 60g/m2 was used for the laboratory experiments. Flat Face Friction (FFF) tests were performed with different forming conditions and lubricants to simulate the frictional sliding in stamping. Glow-Discharge Optical Emission Spectrometry (DG-OES) was used to measure the change in the coating thickness during sliding. Optical microscopy was considered for imaging the surfaces as well as an optical method to compare the changes in the coating thickness during the forming. The change to the Galvanneal coating thickness was found to be a function of forming parameters.

Photocatalytic production of methane and hydrogen through reduction of carbon dioxide with water using titania pellets

This paper presents an experimental study on employing a pellet form of catalyst in photo-reduction of carbon dioxide with water. Water was first absorbed into titania pellets. Highly purified carbon dioxide gas was then discharged into a reactor containing the wet pellets, which were then illuminated continuously for 65 hours using UVC lamps. Analysing the products accumulated in the reactor confirmed that methane and hydrogen were produced through photo-reduction of carbon dioxide with water. No other hydrocarbons were detected. Increasing the temperature in the reactor has showed little change on the amount of methane produced.

Enhanced degradation efficiency of toluene using titania/silica photocatalysis as a regeneration process

Three kinds of titania/silica pellets were prepared using the sol-gel method with surface areas of 50.4m² g-1, 421.1m².g^-1 and 89.1m².g^-1. An annular reactor was designed and built to determine the degradation efficiency of toluene and to investigate the relationship between the adsorption and desorption-photocatalytic processes. Surface area is an important factor influencing the adsorption-photocatalytic efficiency. Higher surface areas of pellets contribute to high rates of conversion of toluene. Un-reacted toluene and reaction intermediates accumulating on their surface deactivated the titania/silica catalyst. To overcome this problem, the adsorption and regeneration process were alternated in a dual reactor system. Connecting or disconnecting the toluene feed gas enabled one reactor to adsorb toluene, while the second reactor was regenerated by photocatalysis. Using UV irradiation and titania/silica pellets with high BET surface area (421.1 m².g^-1), the alternating adsorption/regeneration processes kept the degradation efficiency of toluene at 90% after 8 hours operation. By improving the adsorption-photocatalysis efficiency, and minimising the generation and accumulation of intermediate on the surface of pellets, the method extended catalyst life and maintained a high degradation efficiency of toluene.

Synthesis, polymerization and wool coating studies of 3-iso-butylpyrrole and 3-iso-pentylpyrrole

In a four-step method starting from pyrrole, the synthesis of 3-iso-butylpyrrole and 3-iso-pentylpyrrole, was achieved in 45 and 44% yields, respectively. Polymerization studies of these branched alkyl pyrroles are described and the results compared with those obtained for the unbranched structural isomers n-butyl and n-pentylpyrrole. A series of conductive textiles were produced by the chemical polymerization of the iso-alkylpyrroles using both solution and vapour polymerization techniques. Fabrics coated with poly-iso-alkylpyrrole formed using the solution polymerization method had a lower surface resistance than those formed using the vapour polymerization method. These conductivity results were in direct contrast to those previously obtained for 3-n-alkylpyrroles on fabrics. A remarkable crystal-like growth on the surface of the textile fabric was observed when solution polymerization of 3-iso-pentylpyrrole was employed—reinforcing the notion that subtle changes in monomer structure can drastically affect bulk polymer properties.

Polymerising pyrrole on polyester textiles and controlling the conductivity through coating thickness

The surface resistance of polypyrrole (PPy)-coated polyester fabrics was investigated and related to coating thickness, which was controlled by adjusting the reactant concentrations. The thickness of the coating initially increased rapidly followed by a steady increase when the concentration of pyrrole (Py) was larger than a concentration of approximately 0.4 mg/ml. The surface resistance decreased from 10⁶ to 10³ Ω with increase in pyrrole concentration within 0.2 mg/ml until the concentration reached a value of about 0.4 mg/ml, above which the rate of decrease diminished. The effect of initial treatment with monomer or oxidant prior to polymerisation reaction with regards to thickness and surface resistance was minimal. The immersion time of the textile into the monomer solution prior to polymerisation reaction did not have a significant effect on the abrasion resistance.

Improvement of adhesion of conductive polypyrrole coating on wool and polyester fabrics using atmospheric plasma treatment

In this paper wool and polyester fabrics were pretreated with atmospheric plasma glow discharge (APGD) to improve the ability of the substrate to bond with anthraquinone-2-sulfonic acid doped conducting polypyrrole coating. A range of APGD gas mixtures and treatment times were investigated. APGD treated fabrics were tested for surface contact angle, wettability and surface energy change. Effect of the plasma treatment on the binding strength was analyzed by studying abrasion resistance, surface resistivity and reflectance. Investigations showed that treated fabrics exhibited better hydrophilicity and increased surface energy. Surface treatment by an APGD gas mixture of 95% helium/5% nitrogen yielded the best results with respect to coating uniformity, abrasion resistance and conductivity.

Hydroxyapatite/titania sol-gel coatings on titanium-zirconium alloy for biomedical applications

A simple sol–gel method was developed for hydroxyapatite/titania (HA/TiO2) coatings on non-toxic titanium–zirconium (TiZr) alloy for biomedical applications. The HA/TiO2-coated TiZr alloy displayed excellent bioactivity when soaked in a simulated body fluid (SBF) for an appropriate period. Differential scanning calorimetry, thermogravimetric analysis, X-ray diffraction and scanning electron microscopy-energy dispersive spectrometry were used to characterize the phase transformations and the surface structures and to assess the in vitro tests. The HA/TiO2 layers were spin-coated on the surface of TiZr alloy at a speed of 3000 rpm for 15 s, followed by a heat treatment at 600 °C for 20 min in an argon atmosphere sequentially. The TiO2 layer exhibited a cracked surface and an anatase structure and the HA layer displayed a uniform dense structure. Both the TiO2 and HA layers were 25 μm thick, and the total thickness of the HA/TiO2 coatings was 50 μm. The TiZr alloy after the above HA/TiO2 coatings displayed excellent bone-like apatite-forming ability when soaked in SBF and can be anticipated to be a promising load-bearing implant material.

Photochromic wool fabrics from a hybrid silica coating

In this work, a photochromic wool fabric has been prepared by applying a photochromic-dye hybrid silica sol-gel onto the surface of fabric. The photochromic fabric was found to have a very quick optical response. Two types of silica were used as the matrix material, and the type of silica had a small effect only on the photochromic performance, the fabric washing fastness, and water contact angle, but affected the fabric handle property considerably. The silica from a precursor containing a long alkyl chain showed very little influence on the fabric handle and better photochromic performance than that containing a phenyl group.

Using titania photocatalysts to degrade toluene in a combined adsorption and photocatalysis process

Three types of titania supported materials including titanium dioxide and silicon dioxide composite, titania-coated activated carbon and titania-coated glass beads were prepared and used as photocatalysts to remove toluene from an air stream. Their surface areas were analysed. TEM image reveals titania-silica composites were nanostructured aggregates. XRD was used to determine their crystalline phase which was 100% anatase for the titania component. A fixed bed reactor was designed and built in the laboratory, the toluene with initial concentration of 300 ppm (1149 mg/m³) was fed into the reactor, the destruction efficiencies of toluene were determined by the gas analyser. It was also found that TiO₂-SiO₂ aggregates with high surface area (421.1 m²/g) achieved high destruction efficiencies. The combined effects of adsorption and photocatalysis were further studied by comparing the performance of pure activated carbon (surface area of 932.4 m²/g) and TiO₂ coated activated carbon with BET surface area of 848.4 m²/g. It was found that the TiO₂ coated activated carbon demonstrated comparable results to pure activated carbon, and most importantly, the TiO₂-coated activated carbon can be effectively regenerated by UV irradiation, and was reused as adsorbent. The experimental result of titania-coated glass beads demonstrated a steady degradation efficiency of 15% after a period of 17 hours. It helped to understand that photocatalysis degradation ability of the TiO₂ was constant regardless of the adsorption capacity of the catalysts. This photocatalytic property can be used to degrade the adsorbed toluene and regenerate the catalyst. This study revealed that if the experiments were designed to use adsorption to remove toluene and followed by regeneration of adsorbent using photocatalysis, it could achieve a very high removal efficiency of toluene and reduce the regeneration cost of saturated adsorbent.

Sol-gel derived HA/TiO2 double coatings on Ti scaffolds for orthopaedic applications

Hydroxyapatite/titania (HA/TiO₂) double layers were coated onto Ti scaffolds throughout for orthopaedic applications by sol-gel method. Differential scanning calorimetry (DSC), thermogravimetric analysis (TG) and X-ray diffractometry (XRD) were used for the characterisation of the phase transformations of the dried gels and coated surface structures. Scanning electron microscope (SEM) equipped with energy dispersive spectrometry (EDS) was used for the observation and evaluation of the morphology and phases of the surface layers and for the assessment of the in vitro tests. The in vitro assessments were performed by soaking the HA/TiO₂ double coated samples into the simulated body fluid (SBF) for various periods. The TiO₂ layer was coated by a dipping-coating method at a speed of 12 cm/min, followed by a heat treatment at 600 °C for 20 min. The HA layer was subsequently dipping-coated on the outer surface at the same speed and then heat-treated at difference temperatures. The results indicat that the HA phase begins to crystallize after a heat treatment at 560 °C. The crystallinity increases obviously at 760 °C. SEM observations find no delamination or crack at the interfaces of HA/TiO₂ and TiO₂/Ti. The HA/TiO₂ coated Ti scaffolds displays excellent bone-like apatite forming ability when it is soaked into SBF. Ti scaffolds after HA/TiO₂ double coatings can be anticipated as promising implant materials for orthopaedic applications