Key Engineering Materials Vols. 353-358

Abstract: Synthesis of silicon carbide nanowires (SiC NWs) from an alumina doped silica-graphite rod is reported. The rod was gradually heated up to a growth temperature by passing current through it under constant flowing argon at atmospheric pressure. The as-grown layers, deposited on the rod surface were separated from the inner core and characterized using scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, selected area electron diffraction, X-ray diffraction and Raman spectroscopy. A non-uniform layer thickness of alumina coating on SiC NWs was clearly observed when the doping was increased from 1 to 2 and 3 wt.%.

Abstract: Iron oxide nanoparticles were prepared from an iron nitrate solution by a pyrosol technique. The precursor solution was atomized by a mist generator in order to form an aerosol which was brought into a tube furnace by a controlled flowing air stream. The pyrolysis of the aerosol was occurred to form the particles inside the furnace at 350 °C. Scanning electron microscopy images have shown that a mean diameter of the particles is in good agreement with the third root of the precursor concentration. X-ray diffraction patterns have revealed that the main peaks from the samples are corresponding to the α-Fe2O3 phase.

Abstract: The foot plays an important role in supporting the body and keeping body balance. An abnormal walking habit breaks the balance of the human body as well as the function of the foot. The foot orthotics which is designed to consider biomechanics effectively distributes the load of the human body on the sole of the foot. In this paper, gait analysis is performed for subjects wearing the orthotics. In this study, three male subjects were selected. The experimental apparatus consists of a plantar pressure analysis system and digital EMG system. The gait characteristics are simulated by ADAMS/LifeMOD. The COP (Center of Pressure), EMG and ground reaction force were investigated. As a result of gait analysis, the path of COP was improved and muscle activities were decreased with orthotics on the abnormal walking subjects.

Abstract: Calcium phosphate phases with laminar-plate structure were converted from calcite powders after soaking in phosphate buffer solutions of pH’s 6.0-8.0 at 37 °C for 9 days. The effect of pH values on the conversion of calcite crystals was investigated by X-ray diffraction, scanning electron microscopy and Fourier-transform infrared spectroscopy. If the pH value of a buffer solution is kept at 6.0, calcite powders are converted mainly to dicalcium phosphate dehydrate (DCPD) or octacalcium phosphate (OCP). If the pH value is kept at 6.4 or 7.0, calcite powders are converted mainly to OCP. Hydroxyapatite (HAP) with poorly crystalline can be obtained from calcite powders both by treatment of a basic buffer solution, and by treatment of an acid buffer solution without regulating its pH value during the reaction. The conversion mechanism of calcite crystals is a dissolution-precipitation reaction.

Abstract: Based on both molecular mechanics and computational structural mechanics, a three-dimensional (3D) equivalent beam element is developed to model a C-C covalent bond on carbon nanotubes (CNTs) whereas the van der Waals forces between atoms in the different walls of multi-walled CNTs are described using a rod element. The buckling characteristics of CNTs are conveniently analyzed by using the traditional finite element method (FEM) of a 3D beam and rod model, termed as molecular structural mechanics approach (MSMA). Moreover, to model the CNTs with large length or large diameter, the validity of Euler’s beam buckling theory and a shell model with proper properties defined from the results of MSMA is investigated. The predicted results by this simple continuum mechanics approach agree well with the reported experimental data.

Abstract: Chemical precipitation is a popular method for the preparation of hydroxyapatite(Ca10 (PO4)6 (OH)2, HA) because of its simple operation. In this work, nano-sized HA whiskers were synthesized at various synthetic temperatures and concentration by chemical precipitation with Ca (NO3) 2·4H2O and (NH4) 2HPO4 as raw materials. Heat treatment was carried out after they were synthesized. The HA powders were analyzed by using X-ray diffraction (XRD), transmission electron microscope (TEM) and strength test in order to find the favorable growing condition for HA whiskers. The results show that the HA prepared at different synthetic temperatures show no impurity diffraction peak, indicating that they have a high purity. Prior to heat treatment, the crystallinity and length/diameter ratio of the HA whiskers become larger with the increasing of synthetic temperature. So a higher synthetic temperature can promote the growth of the HA whiskers. There is no obvious difference in crystallinity after the heat treatment. Besides, a lower reaction concentration can also promote the growth of HA whiskers. The strength test results show that the compressive strength of the HA prepared gets a maximum value at 50°C.

Abstract: Hydroxyapatite coating was prepared by alternate soaking strategy in short period time and ambient condition. According to the pH near equality between chitosan acidic acid solution and H2PO4 - aqueous solution, we proposed to choose H2PO4 - as one of hydroxyapatite precursor instead of traditional candidate (HPO4 2-). The properties of chitosan hydrogel containing plenty of water provide enough spaces for hydroxyapatite precursor to diffuse into framework spontaneously. XRD, FTIR and SEM were used to characterize the component and microstructure of mineralized chitosan. The ageing process helps to transfer amorphous calcium phosphate in chitosan framework into hydroxyapatite. The hydroxyapatite coating is gradient structure according to the result of SEM.

Abstract: Due to exceptionally high strength and stiffness, carbon nanotubes have been attracted as promising materials for the applications to many nanoscale devices such as the ultrahigh frequency actuators and sensors. In this study, a dynamic continuum modeling method is used to evaluate the effective structural parameters of the armchair single-walled carbon nanotubes. The effective structural parameters obtained by the present dynamic continuum modeling method are shown to be in very good agreement with the results computed by using the Young’s muduli reported in the existing references.

Abstract: Diamond-Like carbon (DLC) films were prepared under different bias voltage by direct current magnetic filter cathode vacuum arc deposition (DC-MFCVAD). Bias voltages changed from 0 to -200 V. The study intends to investigate the effect on the properties of DLC films for biomedical applications. X-ray photoelectron spectrum (XPS) was used to investigate composition of the films. Nano-scratch tests were used to characterize effects of bias voltage to adhesion. Furthermore, the wettability of the DLC films was investigated by contact angle measurements using four common liquids. Finally, platelet adhesion experiments were done to evaluate the interaction of blood with DLC films. The results showed that the adhesion, wettability and hemo-compatibility of DLC films were affected by bias voltage.

Abstract: The fixation of the vertebral column using transpedicular screws is a well-establish technique. Multi-axial pedicle screw designs allow deviation of the screw away from the perpendicular to the longitudinal rod, which facilitates application of a screw-rod system such as Cervical Attachment System (CAS) into the curved spine. This study was performed a static (compression bending and torsion) and dynamic (compression bending fatigue) empirical analysis of CAS component such as pedicle screw, rod and set screw based on the guideline of ASTM F136- 98 using Ultra-high Molecular Weight Polyethylene (UHMWPE) blocks as test vertebral bodies.