Angkhana Jaroenworaluck

Nucleation and early growth of anodized TiO2 film

Anodized films of titanium were prepared under different controlled conditions in a water-based electrolyte containing fluorine ions, using either a constant potential or a potential gradually rising to 20 V. The films were then examined using transmission electron microscopy at different stages of growth, in particular, the very early stages of growth (30 s, 200 s, and 10 min) and when the ordered nano-tubular structure was finally established (2–4 h). The use of ramped voltage during the early stages of anodization allowed a well-interconnected porous network to develop and maintained active oxidation throughout anodization. The film, as formed, consisted mainly of amorphous oxide/hydroxides of titanium with small regions of nano-sized crystals. These were found more often in the denser regions of the amorphous network, particularly the arms of the coral-like structure that formed. As the anodized film grew in thickness, the pores tended to become aligned, leading to a surface layer of nanotubes on the electrode material. Electron optical characterization revealed that the nanotubes consist of a stack of rings where the passage of the current had been optimized.

A synthesis route to nanoparticle dicalcium silicate for biomaterials research

Dicalcium silicate (Ca₂ SiO₄) has been reported as an interesting candidate for biomaterials use due to its attractive bioactive properties. Here, we report on how dicalcium silicate was prepared by a sol-gel route using calcium nitrate tetrahydrate and tetraorthosilicate as the precursors chemicals for CaO and SiO₂ , respectively. The synthesized powders were characterized using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) method, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). High purity dicalcium silicate at a CaO/SiO₂ molar ratio of 2:1 could be formed by the sol-gel method without a washing process and was then calcined at 800°C. The effects of the molar ratio of CaO/SiO₂ , the washing process, and the calcination temperature have been shown to affect the purity, the formation, and the particle size of the nanoparticles, which have been investigated and discussed.

Hydroxyapatite nanoparticles formed under a wet mechanochemical method

Hydroxyapatite (HA) nanoparticles were synthesized using a wet mechanochemical method without a calcination process. Dicalcium phosphate dihydrate (CaHPO4 ·2H2 O) and calcium carbonate (CaCO3 ) were mixed and milled in a planary mill using ethanol or water as liquid media in the two different synthesized routes. Effects of rotation speed and milling time on the final products formed have been studied. Experimental results showed that HA phase having a characteristic of low crystallinity could be formed under the synthesis route using water. The original phases of both starting chemicals were remained without HA formation in the synthesis route using ethanol. Particle size and morphology of HA nanoparticles were obviously depended on optimum conditions of rotation speed and milling time. Differences on phase formation in both synthesized routes have been considered and discussed based on occurring chemical reaction possibilities.

3D interconnected porous HA scaffolds with SiO2 additions: Effect of SiO2 content and macropore size on the viability of human osteoblast cells†

3D interconnected porous scaffolds of HA and HA with various additions of SiO2 were fabricated using a polymeric template technique, to make bioceramic scaffolds consisting of macrostructures of the interconnected macropores. Three different sizes of the polyurethane template were used in the fabrication process to form different size interconnected macropores, to study the effect of pore size on human osteoblast cell viability. The template used allowed fabrication of scaffolds with pore sizes of 45, 60, and 75 ppi, respectively. Scanning microscopy was used extensively to observe the microstructure of the sintered samples and the characteristics of cells growing on the HA surfaces of the interconnected macropores. It has been clearly demonstrated that the SiO2 addition has influenced both the phase transformation of HA to TCP (β-TCP and α-TCP) and also affected the human osteoblast cell viability grown on these scaffolds.

Nanosized Titania, a Smart Material or is it just Clever?

Titanium oxide (TiO2) nanopowders can be reproducibly formed by hydroxylation of titanium organic complexes. The crystallisation to anatase and rutile can be controlled by systematic calcination and a complex range of properties optimized for specific applications. Characterisation of the powders has been undertaken using advanced physical techniques. The morphology of the TiO2 powders is determined by solution concentration and precipitation phenomena, particularly temperature and stirring regime. However the fine powders have limitations in terms of processing flexibility particularly when nanostructured and organised features are desired, due to their fine particle structure and inability to be sintered without undergoing complete phase change. Anodising titanium metal can overcome these difficulties and under appropriate conditions semi-ordered nanotubes of TiO2 have been prepared. These can be heat treated to develop the phase of choice, anatase or rutile. A mechanism for the formation of the nanotubes has been proposed which is based on the linkage of pores developed in the anodized oxidation product. The pores are driven to into alignment by the applied potential and link up to form the tubular structures. A degree of control of the tube size and wall thickness is shown possible by control of applied voltage. The nanotubes have been investigated using SEM, TEM, XRD and Raman spectroscopy to elucidate the structure and postulate the formation mechanism.

Relation between Degree of Conversion and Post-Cured Properties of Light Cured Composite Systems Used as Filling Materials

The composite, based on a polymer matrix such as Bisphenol A glycol dimethacrylate (Bis-GMA), urethane dimethacrylate (UDMA), and triethyleneglycoldimethacrylate (TEGDMA) and a reinforced-ceramic filler has been used in dental restorative materials. The light curing composite consists of Bis-GMA, TEGDMA, UDMA, Bis-GMA/TEGDMA, Bis-GMA/UDMA, or UDMA/TEGDMA polymer systems and a fumed silica filler with 35 weight ratio loading was synthesized using camphorquinone (CQ) and 2-(dimet6hyloamino)ethyl methacrylate (DMAEMA) as an initiator system. FTIR spectroscopy was used to determine the degree of conversion (DC) of the composites. Polymerization shrinkage and physical properties such as hardness strength and flexural strength were correlated with the composites containing different polymer systems.

Surface Characteristics of Zirconia-Coated TiO2 and its Phase Transformation

Recently, zirconia has been considered as a suitable material for surface coating nanosized TiO2 for use as an electrode in a solar cell application. In this study, the TiO2 (P-25) coated ZrO2 was synthesized from P-25 TiO2 and coated with zirconium n-propoxide in the range of 2.5-50 wt.%. The surface of the TiO2 coated with ZrO2 were examined by X-ray diffraction (XRD) analysis, high resolution transmission electron microscope (HRTEM), which showed zirconia could coat onto the P-25 TiO2 surface. Any excess of zirconia has been deposited as separated particles. Peaks for tetragonal zirconia were observed from the XRD patterns in zirconia-coated P-25 containing more than 20 wt. % of zirconia after calcinations at 500 °C, 800 °C and 1300 °C. In addition, peaks of anatase could be observed from XRD patterns of the samples after calcination at 1300°C. The results show that coating zirconia onto the TiO2 grain surfaces may act to retard the phase transformation from anatase to rutile.

Surface Characteristics of HA and β-TCP Immersed in SBF

Bioactivity of biomaterials is recognized to be of importance and the behavior of nanosized HA and β-TCP particles is described and compared. The study focuses on the influence of the phase transformation and grain size on the reprecipitation of calcium phosphate and the effect of immersion time in SBF on the surface characteristics of the samples. The HA and β-TCP samples were fabricated by mixing the powders in a ball mill, drying, uniaxial pressing and sintering at 1150oC for 240 minute using fixed heating and cooling rates. The densified samples were then immersed in a simulated body fluid (SBF) for controlled periods of time in order to investigate their bioactivities. Changes in the surface structure were examined to investigate and characterize phase formation and the chemical functionality of the samples.

Preparation of Calcium Phosphate Cement Utilizing Dicalcium Phosphate Dihydrate and Calcium Carbonate

Calcium phosphate cement has been widely used as a bone substitute because of its chemical similarity to natural bone. In this study, calcium phosphate cement was prepared using dicalcium phosphate dihydrate (CaHPO4.2H2O) and calcium carbonate (CaCO3) as starting raw materials. The cement pastes were mixed and the chemistry adjusted with two different aqueous solutions of sodium hydroxide (NaOH) and disodium hydrogen phosphate (Na2HPO4). Concentrations of the solution were varied in the range 0.5 to 5.0 mol/L with the ratio of solid/liquid = 2 g/ml. The cement paste was then poured into a silicone mold having a diameter of 10 mm and a height 15 mm. Setting times for the cement were measured using a Vicat apparatus. XRD, FT-IR, and SEM techniques were used to characterize properties and microstructure of the cement. From the experimental results, it is clear that different concentrations of Na2HPO4 and NaOH have affected the setting times of the cement. The relationship between concentration of NaOH and Na2HPO4 and setting time, including final properties of the cement, is discussed.

Synthesis, preparation and catalytic activities of V-doped TiO2 gel coating on porous α-Al2O3 beads

TiO2 and V-doped TiO2 gel were synthesized and coated onto porous α-Al2O3 beads to study the thermal catalytic activities of oxidation reactions. Titanium isopropoxide (Ti(OPr)4) and 1,2-butadiol(Bu(OH)2) were used as starting chemicals for preparation of TiO2 gel without Vdoping. After aging at ambient temperature for one week, a TiO2 gel was obtained. The concentration of Ti(OPr)4 was varied, 0.2, 0.3, 0.7 and 2.4 M was used. For V-doping of the TiO2 gel, 0.05, 0.20 and 0.75 mole% of V was prepared by ultrasonically dissolving vanadium acetylacetone (V(acac)2) in 1,2-butadiol. The solutions were then added to Ti(OPr)4. Finally, the mixed solutions were kept under ambient temperature for one week to form the V-doped TiO2 gel. TiO2 and V-doped TiO2 were calcined at 300, 400, 500, 600, 700, and 800 °C. XRD analysis, SEM and TEM in conjunction with EDS analysis were used to identify the phases present, grain size and morphology. The TiO2 grains have a particle size in the nano-scale range. Doping TiO2 with V could retard growth of the TiO2 particles and affect phase transformation at higher calcination temperatures. Both the TiO2 and V-doped TiO2 gels were prepared and coated onto α-Al2O3 beads to test oxidation reactions in a purpose-designed reactor. The results of the catalytic reactions indicated that V-doped TiO2 had a higher oxidation activity than the undoped TiO2 gel. The content of vanadium was related to the reaction efficiency.