Evaluation of hydrogen absorption behaviour during acid etching for surface modification of commercial pure Ti, Ti-6Al-4V and Ni-Ti superelastic alloys

The hydrogen absorption behaviour during acid etching for the surface modification of commercial pure Ti, Ti-6Al-4V and Ni-Ti superelastic alloys has been investigated on the basis of the surface morphology, electrochemical behaviour and hydrogen thermal desorption analysis. To simulate the conventional acid etching for the improvement of the biocompatibility of Ti alloys, the specimens are immersed in 1 M HCl, 1 M H₂SO₄ or 0.5 M HCl + 0.5 M H₂SO₄ aqueous solution at 60 °C. Upon immersion, commercial pure Ti absorbs substantial amounts of hydrogen irrespective of the type of solution. In H₂SO₄ or HCl + H₂SO₄ solutions, the hydrogen absorption occurs for a short time (10 min). For Ti-6Al-4V alloy, no hydrogen absorption is observed in HCl solution, whereas hydrogen absorption occurs in other solutions. For Ni-Ti superelastic alloy, the amount of absorbed hydrogen is large, resulting in the pronounced degradation of the mechanical properties of the alloy even for an immersion time of 10 min, irrespective of the type of solution. The hydrogen absorption behaviour is not necessarily consistent with the morphologies of the surface subjected to corrosion and the shift of the corrosion potential. The hydrogen thermal desorption behaviour of commercial pure Ti and Ni-Ti superelastic alloy are sensitively changed by acid etching conditions. The present results suggest that the evaluation of hydrogen absorption is needed for each condition of acid etching, and that the conventional acid etching often leads to hydrogen embrittlement.     

Transverse Acoustic Impedance Measurements for Surface States of Superfluid 3He A1 and A2 Phases

We measured the complex transverse acoustic impedance in both superfluid ³He A₁ and A₂ phases. This impedance is sensitive to surface states. In our preliminary results, the temperature dependence of the impedance in the A₁ phase is similar to that in A phase, and the imaginary part shows an anomaly in the A₂ phase. These anomalies occurred at the temperature defined as T _k , which is lower as the frequency gets higher. The similar frequency dependence of T _k in each phase suggests that the anomaly is attributed to the same origin. The frequency dependence of the T _k /T _c indicates that the shape of the surface density of each spin pair state did not greatly change in the present experimental temperature range.     

Size-controlled recrystallization of fullerene by gas–antisolvent process

Gas–antisolvent (GAS) process using CO₂ successfully prepared crystals of fullerene (C₆₀) from a toluene solution through a precipitation. Particle sizes of precipitated C₆₀ could be easily controlled by changing the initial pressurization rate of CO₂, the temperature at the initial pressurization, and the quantity of C₆₀. Fullerene particles obtained by GAS method had regular octahedral shapes, whereas the particles obtained by adding liquid ethanol as an antisolvent to C₆₀ solution did not have such shape. Particle sizes could be changed in a range of 1.0–8.5 μm by GAS method; they were wider than the range of particles obtained by ethanol addition (0.7–1.8 μm).     

Growth of ZnO crystal on sapphire and nitridated sapphire substrates at 1000 °C by halide vapor phase epitaxy

Using a halide vapor phase epitaxy (HVPE) technique in which the starting materials are ZnCl₂ generated by the reaction between high purity Zn metal (7 N grade) and Cl₂ gas, and H₂O, ZnO crystals have been grown at a high temperature of 1000 °C on sapphire substrates with and without surface nitridation treatment. It was found that the nitridation treatment resulted in a change of the (112?0) sapphire surface to a (0001) AlN structure, leading to two possible sets of orientations for (0001) ZnO crystals. In addition, the nitridation treatment leads to a smaller average ZnO grain size and a higher density of nuclei.     

Novel agarose and agar fibers: Fabrication and characterization

In this study, natural agarose and agar polysaccharides were successfully developed to novel fibrous form for the first time via wet-spinning. Dimethyl sulfoxide (DMSO)/H₂O = 9:1(v/v) mixture was used as an appropriate solvent which was amenable to the wet-spinning process that produced continuous agarose and agar fibers in ethanol coagulation bath. Results of SEM investigation, swelling ratio and tensile test suggested that the smooth and homogeneous agarose fibers had considerable water swelling capacity (400-500%) and tensile strength (30-50 MPa). The agar fiber showed better water swelling capacity than the agarose fiber; however the existence of agaropectin leads to its flexibility flaws. These results demonstrate that the agarose fiber fabricated in this study is a good candidate material for wound-dressing applications.     

Roles of In-Situ Forming Hard Particles in a Zr-Based Bulk-Metallic Glass during Monotonic and Cyclic Loading

Zr₆₇Ni₂₀Cu₅Al₈ (in at. pct) is a bulk-metallic glass (BMG) with in-situ forming hard particles. Some crystalline particles can be observed in the polished beam samples under optical microscopy (OM). The hardness measurements show that these crystalline particles are harder than the matrix of Zr₆₇Ni₂₀Cu₅Al₈. The energy-dispersive spectroscopy (EDS) analyses demonstrate that there is little difference in the compositions between the crystalline particles and the matrix. The Zr₆₇Ni₂₀Cu₅Al₈ BMG under compressive loading exhibits yield strength of 1580 MPa with an up to 7.7 pct fracture strain. The fatigue behavior of Zr₆₇Ni₂₀Cu₅Al₈ is investigated under four-point-bending loading. The fatigue results show that the fatigue limit of Zr₆₇Ni₂₀Cu₅Al₈ is approximately 361 MPa, based on the stress range. It is generally found that the fatigue cracks initiate from the hard particles. The influence of the hard inclusions on the fracture and fatigue behavior of Zr-based BMGs is discussed.     

Ni-Nb-Sn Bulk Metallic Glass Matrix Composites Fabricated by Microwave-Induced Sintering Process

Using a gas-atomized Ni_59.35Nb_34.45Sn_6.2 metallic glassy alloy powder blended with Sn powder of various contents, Ni-Nb-Sn bulk metallic glassy matrix composites were fabricated by a microwave (MW)–induced sintering process in a single-mode 2.45 GHz MW applicator in a separated magnetic field. The Ni_59.35Nb_34.45Sn_6.2 glassy alloy powder and its mixed powders containing Sn particles could be heated well in the magnetic field. The addition of Sn particles promoted densification of the sintered Ni_59.35Nb_34.45Sn_6.2 metallic glassy powder. Bulk samples without crystallization of the glassy matrix and with good bonding state among the particles were achieved at a sintering temperature of 833 K.     

Evaluation method of dam behavior during construction and reservoir filling and application to real dams

In this paper we analyzed a real fill-type dam, named the Minami-Aiki Dam, to verify a numerical consolidation method with an elastoplastic model for unsaturated soils. The validities were conducted by comparing the analyzed and measured values during construction and impounding. The settlements calculated showed good agreement to those observed. Though the changing patterns of the measured and calculated pore water pressures were similar, the amounts of pore water pressures induced by the self-weights of embankment and the dissipation speeds were different. The earth pressures measured at the bottom of the core zone showed good agreement with those calculated. This method is valid for estimating behavior of fill-type dams during construction and impounding.     

An Efficient Algorithm to Construct an Orthonormal Basis for the Extended Krylov Subspace

Subspace projection methods based on the Krylov subspace using powers of a matrix $A$ have often been standard for solving large matrix computations in many areas of application. Recently, projection methods based on the extended Krylov subspace using powers of $A$ and $A^{−1}$ have attracted attention, particularly for functions of a matrix times a vector and matrix equations. In this article, we propose an efficient algorithm for constructing an orthonormal basis for the extended Krylov subspace. Numerical experiments indicate that this algorithm has less computational cost and approximately the same accuracy as the traditional algorithm.     

Design Study of Top Lid with Clamp Structure in JT-60SA Cryostat

JT-60SA is a fully superconducting coil tokamak upgraded from the JT-60U. This paper focused on the integrity of the top lid of cryostat in JT-60SA. The design requirement for the cryostat in normal operations is to achieve vacuum insulation of 10 3 Pa, and the top flange of the top lid is lightly welded onto its body flange. The weld is tensile-loaded by bending deformation of the top lid due to vacuum pressure of external 0.1 MPa. This weld integrity is evaluated with tensile-load reduction, which results in clamp reinforcement. The structural integrity of the top lid is validated.