Effect of heat treatment on phase transition of nanotubular titanium oxide arrays

The purpose of this study was to investigate the effects of heat treatment on the cystallinity of titanium nanotubes. The titanium nanotubes had diameters ranging from 90-95 nm, lengths between 400-500 nm, and thicknesses of 11 nm. After heat treatment at high temperatures, the diameter and length of the nanotubes decreased, whereas the thickness increased. The titanium nanotubes exhibited amorphous + anatase phases at 300 degrees C, anatase + rutile phases at 500 degrees C and a rutile phase at 800 degrees C.     

Preparation method of low-oxygen Ti-6Al-4V alloy by solid state re-deoxidation using calcium

The oxygen concentration in commercial Ti-6Al-4?V alloys was reduced to less than 400?ppm in this study by the method of solid state re-deoxidation, using calcium as a reductant. The concentration of oxygen in the deoxidised Ti-6Al-4?V alloy was 630?ppm at the optimum deoxidation temperature of 1000°C. When the degree of vacuum was increased and re-deoxidation was carried out, the oxygen concentration decreased to 355?ppm. Therefore, it is possible to prepare a Ti-6Al-4?V alloy with an oxygen concentration of less than 400?ppm by using the solid state re-deoxidation method at a high degree of vacuum of 1.5?×?10-6 Torr.     

General Log‐Likelihood Ratio Expression and Its Implementation Algorithm for Gray‐Coded QAM Signals

A simple and general bit log‐likelihood ratio (LLR) expression is provided for Gray‐coded rectangular quadrature amplitude modulation (R‐QAM) signals. The characteristics of Gray code mapping such as symmetries and repeated formats of the bit assignment in a symbol among bit groups are applied effectively for the simplification of the LLR expression. In order to reduce the complexity of the max‐log‐MAP algorithm for LLR calculation, we replace the mathematical max or min function of the conventional LLR expression with simple arithmetic functions. In addition, we propose an implementation algorithm of this expression. Because the proposed expression is very simple and constructive with some parameters reflecting the characteristic of the Gray code mapping result, it can easily be implemented, providing an efficient symbol de‐mapping structure for various wireless applications.     

Enhancement of Drucker-Prager yield model by adding corner points for pressure-dependent materials

Journal of Mechanical Science and Technology - To flexibly describe the pressure-dependent behaviors of materials, Drucker-Prager yield model is enhanced by introducing corner points. We call it...     

Dimensional changes and phase transformation of TiO2 nanotubes heat-treated under oxygen-containing atmosphere

The purpose of this study was to investigate the dimensional changes and phase transition of nanotubular titanium oxide arrays after heat treatment under an oxygen-containing atmosphere. The thermodynamic background for the oxidation of titanium to titanium oxide was theoretically investigated as a function of the oxygen partial pressure. The anodized titanium nanotubes had lengths between 400 and 500 nm, thicknesses of 11 nm and an amorphous structure. The specimens heat-treated at higher oxygen partial pressures preferentially had rutile phase rather than anatase phase. The thickness of the TiO2 nanotubes was increased at a lower oxygen partial pressure.     

Histomorphometric evaluation of an implant with a nanotubular surface treatment in a beagle femur

This study examined the effects of a nanotubular surface treatment on an implant by anodic oxidation. Forty two screw-shaped implants were classified into 3 groups; machined surface (control group), nanotube formation on the machined surface (group N) and nanotube formation on the RBM surface (group RN). A total of 36 implants were inserted into a beagle femur. Two implants from each group were observed by scanning electron microscopy. Histomorphometric analyses were performed after 4 and 12 weeks. After 4 weeks, the average bone to implant contact (BIC) ratio of groups N and RN was significantly higher than that of the control group (P < .05). After 12 weeks, a nanotubular surface treatment showed a significantly higher BIC ratio only in the marrow space adjacent to the implant apex (P < .05). This in vivo study revealed the enhanced osseointegration of nanotubes.     

R.F. magnetron sputtering of multilayered c-BN films on cemented carbide tool

A c-BN thin film was deposited using a B4C target in a r.f. magnetron sputtering system. The c-BN layer was coated with a TiAIN adhesion layer (approximately 2 microm), boron carbide (approximately 1 microm) and BCN (10 approximately 15 nm) nano-gradient layer system. The c-BN layers with thicknesses of more than 0.5 microm were successfully deposited onto cemented carbide substrates. The high resolution XPS spectra analysis of B1s and N1s revealed that the c-BN film was mainly composed of sp3 BN bonds.     

Development of sputtered nanoscale titanium oxide coating on osseointegrated implant devices and their biological evaluation

Nanoscale titanium oxide (TiO₂) coating was deposited on titanium (Ti) disks and Ti dental implants using r.f. magnetron sputtering technique. The coating was characterized using grazing angle X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), contact angle measurement, profilometry and nano-scratch test. The coating also was evaluated with in vitro cell culture and in vivo dog femur model. Three groups of samples were prepared, including as-sputtered Ti (AS-Ti), sputtered Ti with a post-deposition heat treatment at 600 °C (SH-Ti) and machined Ti (MA-Ti) as controls. The AS-Ti and SH-Ti were dense surfaces consisting of nanoscale grains of 40 nm and 80 nm, respectively. Post-deposition heat treatment increased the coating adhesion. The SH-Ti and AS-Ti significantly decreased the water contact angles compared to the MA-Ti. The nanoscale AS-Ti and SH-Ti significantly improved cell adhesion within the first hour of incubation compared with the MA-Ti. No significant differences were observed in osteoblast proliferation and differentiation in vitro as well as reverse torque and histology in vivo among the three groups. In the present study, it was not observed that the nanoscale dense TiO₂ coating improved the osseointegration compared to the microscale dense Ti.     

Effect of metal chloride solutions on coloration and biaxial flexural strength of yttria-stabilized zirconia

The effect of three kinds of transition metal dopants on the color and biaxial flexural strength of zirconia ceramics for dental applications was evaluated. Presintered zirconia discs were colored through immersion in aqueous chromium, molybdenum and vanadium chloride solutions and then sintered at 1450 °C. The color of the doped specimens was measured using a digital spectrophotometer. For biaxial flexural strength measurements, specimens infiltrated with 0.3 wt% of each aqueous chloride solution were used. Uncolored discs were used as a control. Zirconia specimens infiltrated with chromium, molybdenum and vanadium chloride solutions were dark brown, light yellow and dark yellow, respectively. CIE L*, a*, and b* values of all the chromium-doped specimens and the specimens infiltrated with 0.1 wt% molybdenum chloride solution were in the range of values for natural teeth. The biaxial flexural strengths of the three kinds of metal chloride groups were similar to the uncolored group. These results suggest that chromium and molybdenum dopants can be used as colorants to fabricate tooth colored zirconia ceramic restorations.     

Enhancement of the analytical solution for double torsion test using extended finite element techniques

The double torsion (DT) testing technique is not yet standardized for fracture mechanics characterization of brittle materials because previous analytical solutions are insufficient to represent accurate load-displacement (P-h) relationship and stress intensity factor (SIF) in experiments. Therefore, we attempt at enhancing the analytical solutions based on three-dimensional extended finite element (XFE) analysis to obtain reproducible results from DT tests. As a result, the P-h relationship in DT test can be efficiently described by combining the bending deformation of a DT specimen with torsional deformation. Weighting factors are proposed as functions of thickness, moment arm and crack length. DT experiments are conducted with sodalime glass specimens to further validate the proposed weighting factors. Finally, correction terms are provided for SIF and fracturs toughness evaluation in DT specimen with straight and curved crack fronts. Fracturs toughness values of sodalime glass specimens with various thickness are consistent, and in good agreement with literature values.