Fluxless joining of aluminium alloy to steel by laser irradiation method

A6061 aluminium alloy was joined with steel using Zn filler metal under laser irradiation process. The quality of joint was evaluated by the strength of a lap joint. The effects of laser power irradiation conditions such as travelling speed and defocused distance on the joint strength were investigated. The maximum joint strength was obtained at relatively medium laser travelling speed. The excess reaction between filler metal and aluminium formed thick brittle intermetallic compounds between steel and aluminium alloy. The compounds are considered to lead to the reduction in joint strength. It was found that low wetting at high travelling speed and excess reaction layer formation at low travelling speed were responsible for low joint strength. The study revealed that the relatively high joint strength between aluminium alloy and steel was obtained by laser joining method using Zn filler without the use of flux in air atmosphere.     

Development of a magnetron sputtering system with an extraordinary strong magnetic field near the target

We have developed a planar sputtering device that uses a melt-processed bulk superconductor to generate the magnetic field. The magnetic field that confines the plasma above the sputtering target is about 1.0 T, which is about 20 times larger than the field normally used for magnetron sputtering. Because of the large magnetic field, discharge at an Ar gas pressure as low as 10⁻³ Pa was possible. In this study, we used the ultra-strong-field sputtering technique for depositing Ga-doped ZnO which is attracting interest as a transparent electrode material. We also studied the effect of employing an auxiliary coil to tailor the magnetic field distribution and discuss how the discharge characteristic had changed.     

Preparation of titania-coated alumina film by electrolysis of TiCl4-containing solution

Direct current in the range from 50 to 390 mA/cm² was flowed between alumina/tin-doped indium oxide (indium tin oxide, ITO) composite (cathode) and carbon (anode) electrodes in an aqueous solution containing TiCl₄ and (NH₄)₂SO₄ at pH 0.5. The composite electrode dissolved in the solution and was precipitated again on the surface of the electrode. The thickness of precipitated layer increased at a higher applied charge. During the electrolysis, TiO₂ was also deposited on the surface of precipitated layer. The amorphous TiO₂ heated at 300 °C and sintered Al₂O₃–ITO composite showed a good adsorption property of electromagnetic energy in the wide wavelength of 200–800 nm.     

Chemoenzymatic synthesis of amylose-grafted polyacetylene by polymer reaction manner and its conversion into organogel with DMSO by cross-linking

This paper reports chemoenzymatic synthesis of amylose-grafted polyacetylene according to the following polymer reaction manner. At first, the amine-functionalized polyacetylene was prepared by the Rh-catalyzed copolymerization of a protected amine-substituted acetylene monomer (tert-butyl propargylcarbamate) with N-propargylethanamide, followed by deprotection process. Then, the maltooligosaccharide chains were introduced on the polyacetylene by the reaction with maltoheptaose lactone. Finally, the phosphorylase-catalyzed enzymatic polymerization from the oligosaccharides on the produced polyacetylene was performed using α-d-glucose 1-phosphate as a monomer to give the polyacetylene having amylose graft-chains. Furthermore, the cross-linking reaction of the remaining amino-groups on the amylose-grafted polyacetylene with hexamethylene diisocyanate was carried out in DMSO to give the insoluble material, which formed the organogel with DMSO. The mechanical property of the gel was evaluated by compressive stress–strain measurement.     

Water retention properties of porous geopolymers for use in cooling applications

A series of geopolymers were prepared with varying ratios of sodium silicate, metakaolinite, NaOH and H₂O and their porous properties, water retention and mechanical properties were determined, to develop materials for counteracting heat island effects. Samples were prepared with the molar ratios SiO₂:Al₂O₃:Na₂O:H₂O of 3.66:1:x:y, where x = 0.92–1.08 and y = 14.2–19.5. The porous and mechanical properties of the geopolymers showed a good correlation with the H₂O/Al₂O₃ ratio (y); an increase in y produced an increase in the pore volume (from 0.26 to 0.46 ml/g), the pore size (from 15 to 390 nm) and the water absorption (from 27.2 to 51.1%). The same increase in y decreased the bulk density (from 1.29 to 0.99 g/cm³), the bending strength (from 14.2 to <5 MPa) and the water retention. Thus, the H₂O/Al₂O₃ ratio is the most important factor for controlling the porous properties of these materials, since geopolymers with higher H₂O/Al₂O₃ ratios are more porous and have higher water absorption rates, making them suitable as materials for surface cooling by water evaporation. Geopolymers with lower H₂O/Al₂O₃ ratios are more suitable for water retention applications, and have the advantage of higher mechanical strength.     

Mechanism of high-pressure hydrogenolysis of Hokkaido coals (Japan). 2. Chemical structure of products

The chemical structure of each corresponding product in the mechanism discussed in our previous report¹ has been investigated and the mechanism further discussed in detail on the basis of the chemical structure of each product. Oil (S₂) proceeding through asphaltene (R) as an intermediate product is clearly different from asphaltene (R) with regard to molecular weight, but is comparatively similar with regard to aromatic ring structure. On the other hand the chemical structure of oil (S₁) forming directly from coal differs considerably from those of asphaltene (R) and oil (S₂). Therefore it was concluded that oil (S₁) and oil (S₂) whose production processes differ from each other have corresponding differences in their respective chemical structures. These results indicate that the coal-hydrogenolysis mechanism suggested on the basis of the reaction kinetic study is further supported by the differences in chemical structure of the corresponding products.     

Flat-response neutron detector using spatial distribution of thermal neutrons in a moderator

We propose a novel neutron detector that realized flat-response using information of a spatial distribution of thermal neutrons in a moderator. The proposed detector consists of a ³He position sensitive proportional counter (PSPC) and a cylindrical moderator surrounding the ³He PSPC. The cylindrical detector is irradiated by neutrons along the cylinder axis. The spatial response of the ³He PSPC is used to correct the detector response into flat-response. We adopt a weighting method to achieve flat-response, in which detected neutrons weighted depending on their detected positions are accumulated as the detector response. Through Monte Carlo simulation studies, we confirm that the flat-response neutron detector can be realized by correcting the response of the proposed detector using the weights determined by a multiple least square method (MLSM). Additionally, fundamental property of the ³He PSPC is experimentally investigated to check applicability to the proposed flat-response neutron detector. We conclude that we should take account of the end effect when determining the weights and correcting the detector response.     

Fibre laser welding of aluminium alloy

The objectives of this research are to investigate the effects of various welding conditions on penetration and defect formation, to clarify their welding phenomena and to develop the procedure of reduction of the defect. Fibre laser bead-on-plate welding was performed on several aluminium alloys, in particular A5083, at the power of 6 or 10 kW and several power densities from 0.4 kW/mm². It was found that the weld beads were narrower and deeper with an increase in the laser power density. For example, fully penetrated weld beads in 10 mm thick plates were produced at the laser power density of 640 kW/mm² and the welding speed of 10 m/min. However, convex–concave bead surfaces were formed. Moreover, in the case of the high power density, no porosity and many pores were present at high and low welding speeds, respectively. On the other hand, in the case of the ultra-high power density, few pores were generated in high speed welding. These reasons were interpreted by observing keyhole behaviour, bubble formation and the molten pool geometry during high power fibre laser welding with a high-speed video camera and microfocused X-ray transmission in situ observation method. Moreover, the porosity in the weld bead was reduced and prevented by the utilization of nitrogen gas instead of Ar gas, or the forward inclination angle of 40° (50° from the right angle) in Ar shielding gas.