Papers by Author: Soo Wohn Lee

Abstract: In this work, porous alumina ceramics were obtained by controlled sintering of alumina-carbon black powder mixtures. In order to develop the porous alumina ceramics with high strength, as the amount of carbon black increased, the number of small pores increased because the pore characteristics and relative density the influence of SPS condition and carbon black content on was studied.

Abstract: The effect of calcination on the mechanical properties of hydroxyapatite and zirconia composite (HAp:ZrO2= 30:70, 50:50, 70:30 mass%) was investigated. The calcination of ball-milled mixture in air at 900°C for 0, 2 and 4 hours increased the crystallinity. Then, it was assigned that the particles form of hydroxyapatite was changed from needle-like to sphere-like by calcination. The calcined mixture was sintered by spark plasma sintering (SPS) at 1200°C with a pressure of 40MPa for 5 minutes. The calcination process caused the enhancement of flexural strength of the composite.

Abstract: Bone healing and growth are controlled by the rate of deposition of hidroxiapatite (HA). This process have been so far accredited to the work of osteoblasts, which are attracted by the electrical dipoles produced either by piezoelectricity, due to deformation of the bone, specially the collagen in it, or due to outside electrical stimuli. The present work shows that even without osteoblasts present, the piezoelectric dipoles produced by deformed collagen, can produce the precipitation of HA by electrochemical means, without catalyzer as in biomimetic deposition. These findings could clarify the contribution of osteoblasts in bone growth as compared to the electrochemical action by itself. Further studies ascertaining the osteoblastic activity due to the electric field are being advanced.

Abstract: The W coatings were prepared by applying the vacuum plasma spraying process (VPS). The phase composition, microstructure and laser irradiation property were characterized by XRD, SEM and laser. Results showed that no tungsten oxide appears in the coatings whose phase composition is similar to the original powder. A better melting state of the coating can be obtained by using the finer powder. The deposition efficiency of the coating is higher in the cases of a higher H2 flow. There is a pitch whose size is about 100μm when the substrate was irradiated by laser. However, there is clearly no change for the W coating surface which was also irradiated under the same condition. It indicates that the laser irradiation resistance is improved significantly for stainless steel after being deposited with W coating.

Abstract: Vacuum plasma sprayed (VPS) hydroxyapatite (HA) coatings with silver-loaded zirconium phosphate antimicrobial have been prepared on titanium substrate. Antibacterial effects of the coatings were studied by bacteria culturing using Porphyromonas gingivalis (Pg), Fusobacterium nucleatum (Fn) and Actinobacillus actinomycetemcomitans (Aa) as microorganisms. Simulated body fluid (SBF) test was carried out to evaluate the bioactivity of the coatings as well. The results obtained showed that the coatings exhibited a marked antibacterial effect against Pg, Fn and Aa when the content of antimicrobial was equal to or more than 5%. The antibacterial capability of the coatings decreased in the following order: Pg, Fn, Aa. Bone-like apatite layer was formed on the silver-containing HA coatings after immersed in SBF, suggesting that their bioactivities were not affected obviously by the addition of silver-zirconium phosphate antimicrobial. This study indicated that silver-containing VPS HA coating is a prospective candidate as dental material.

Abstract: Plasma sprayed coatings have been widely applied in modifying surface properties of metal components. It is also useful to prevent various types of wear, corrosion, erosion and thermal. But the residual stress is still an important problem which can effect the properties of sprayed coating. So it’s necessary to find out the reason of residual stress and the relationship between plasma sprayed condition and residual stress. Plasma spray coating layers with conventional ZrO2 powder was examined to calculate residual stress by X-ray diffraction method with various coating thickness.

Abstract: The brittleness of ceramics has been their weak spot when considering them for total hip replacements. There are several situations from which concentrated stresses can develop and induce failure of the components. It is not a problem of the material’s properties in particular but also its design. This means that even proof tested-third generation-ISO obeying ceramics may fail if the incidence of the design parameters on them is not carefully evaluated. In this paper, the finite element analysis technique is used to show how the change of ball diameter can affect the Vonmises stress on the ball head component when it is subjected to a high (trauma-like) load. The analysis is nonlinear and was carefully tested for convergence. 3D models of four different ball head diameters where constructed, two designs of the bore/cone interface with two sets of material properties (Alumina and Zirconia) were considered. The results from these analyses are given in the form of stress maps on the ball heads; such data may be useful for surgeons, patients, and designers because it shows a direct relationship between two important parameters on ball head design (diameter and bore) and material properties, on the stresses that can cause failure of the component when they are concentrated in small elements of volume.

Abstract: The commercial nano-sized TiO2 powder (P25) coated with PtO2 powder by a sonochemistry method was immobilized on the foamed waste-glass substrates by using plasma spray coating technology. The immobilized TiO2-Pt coatings were applied to treat both green tide and red tide under illumination of an UV light. Their photocatalytic characterizations were evaluated as functions of the number of residual algae, transmission as well as pH value with illumination time. It’s found that the plasma sprayed Pt-doped TiO2 nanostructured coatings on foamed waste-glass showed higher photocatalytic activity, which was effective to treat the green tide and red tide.

Abstract: TiO2 films were deposited by using mid-frequency twin magnetron reactive sputtering technique at ambient temperature on quartz and Si wafer. The films were annealed after deposition. The phase composition and surface morphology of the TiO2 films were characterized by X-ray diffraction, Raman spectroscopy, and scanning electron microscopy, while the optical properties and contact angle were measured using a UV-Vis spectrophotometer and a contact angle meter. It is indicated that anatase phase dominates below 900°C and a mixture of rutile and anatase exists in the film annealed at 1000°C. Furthermore, the hydrophilic property depends on phase composition and morphological change in TiO2 films.