Sealing effects of anodic oxide films formed on Mg-Al alloys

Mg alloys were anodized in alkaline NaOH solutions with various additives as a non-chromate method. Specimen AZ91 was anodized at a potential that produced a strong surface dissolution reaction and generated a large amount of Mg(OH)₂. The effect of sealing after anodizing was investigated, focusing on the effects of sealing time, temperature and solution conditions. The current density decreased with increasing A1(OH)₃ concentration in 1 M NaOH solution during anodizing; sparking occurred at potentials above 80 V. The best corrosion resistance with anodizing in 1 M NaOH solution occurred at a potential of 4 V, which caused the strongest active dissolution reaction. The sealing effect improved with increasing time and temperature, and corrosion resistance was proportional to the relative ratio of Mg(OH)₂. If the oxygen thickness observed by EDX equaled the film thickness, the film formed at 4 V in 1 M NaOH was 10–15 Μm thickness. The optimum corrosion resistance in sealing at various solutions after anodizing was 1M-NaOH solution.     

A novel decomposition technique of friable asbestos by CHClF2-decomposed acidic gas

Asbestos was widely used in numerous materials and building products due to their desirable properties. It is, however, well known that asbestos inhalation causes health damage and its inexpensive decomposition technique is necessary to be developed for pollution prevention. We report here an innovative decomposition technique of friable asbestos by acidic gas (HF and HCl) generated from the decomposition of CHClF(2) by the reaction with superheated steam at 800 degrees C. Chrysotile-asbestos fibers were completely decomposed to sellaite and magnesium silicofluoride hexahydrate by the reaction with CHClF(2)-decomposed acidic gas at 150 degrees C for 30 min. At high temperatures beyond 400 degrees C, sellaite and hematite were detected in the decomposed product. In addition, crocidolite containing wastes and amosite containing wastes were decomposed at 500 degrees C and 600 degrees C for 30 min, respectively, by CHClF(2)-decomposed acidic gas. The observation of the reaction products by phase-contrast microscopy (PCM) and scanning electron microscopy (SEM) confirmed that the resulting products did not contain any asbestos.     

Mechanical properties of a new type of apatite-containing glass-ceramic for prosthetic application

A new type of apatite-containing glass-ceramic in the system MgO-CaO-SiO₂-P₂O₅ can form a tight chemical bond with bones and has a high mechanical strength. The cause for its high mechanical strength was examined by comparing mechanical properties of the glass-ceramics which have an identical chemical composition and different microstructures. It was found that the mechanical strength of the apatite-containing glass-ceramics is considerably increased by the precipitation of-wollastonite crystals due to an increase in fracture surface energy resulting in an increase in fracture toughness.     

Mechanical characterization of Sn–Ag-based lead-free solders

Recently, preventing environmental pollutions, lead-free (Pb-free) solders are about to replace tin–lead (Sn–Pb) eutectic solders. However, the mechanical properties of Pb-free solders have not been clarified. Hence, the following study was conducted; first, a rate-dependent plasticity was characterized to represent the inelastic deformation behavior for Sn–Ag-based lead-free solders. The material parameters in a constitutive model were determined in a direct method combining both rate-dependent and rate-independent plastic strains. The constitutive model unifies both rate-dependent creep behavior and rate-independent plastic behavior occurring concurrently at the same time in the solders. Secondly, the strength of solders with a variety of plating materials was studied. Intermetallic compounds (IMC) between solder and electrical pads are formed during reflow process and gradually grow in service. By using the Cu-plates on which Cu or Ni or Ni/Au plating was deposited, the specimens of solder joints were fabricated with Sn–Ag-based lead-free solders. After aging the specimens in an isothermal chamber, tensile tests were performed. From scanning electron microscope (SEM) microscope observation and EDX microprobe analysis, the growth and components of the IMC layer were also examined. Based on the experimental tests, the relations between solder joint strength and the aging period were discussed. Furthermore, the validation of fracture strength of solder joints resulting from the tensile tests was verified with package-mounted board level reliability tests.     

Electron microscopy of actin rods and bundles in Dictyostelium discoideum by high-pressure freezing

A new type of actin rods comprising actin tubules appears in dormant spores of Dictyostelium discoideum. Occasionally, the rods in the nucleus were observed in an amorphous state using a combination of high-pressure freezing and freeze-substitutions. Also in the case of actin bundles formed in the nudeus of vegetative cells exposed to dimethyl sulphoxide, actin filaments seemed to be embedded in matrices. The karyoplasm of spores fixed by the above method appeared to be denser than that obtained by other methods. As soluble materials may be efficiently retained in the nucleus, actin tubules or actin filaments embedded in those materials may result in hazy images of actin rods and bundles.     

Highly efficient coupling of photons from nanoemitters into single-mode optical fibers

Highly efficient coupling of photons from nanoemitters into single-mode optical fibers is demonstrated using tapered fibers. A percentage (7.4 ± 1.2%) of the total emitted photons from single CdSe/ZnS nanocrystals were coupled into a 300 nm diameter tapered fiber. The dependence of the coupling efficiency on the taper diameter was investigated and the coupling efficiency was found to increase exponentially with decreasing diameter. This method is very promising for nanoparticle sensing and single-photon sources.     

Electrochemical studies of titanium in fluoride-chloride molten salts

The interaction between titanium and Ti⁴⁺ ions (K₂TiF₆), the electroreduction reaction of Ti⁴⁺ ions and the anodic reaction of Ti in KCl–NaCl–KF melts with K₂TiF₆ at 973 K were studied by means of electrochemical and physical measurements. It was found that the fluoride ions played a very important role in these reactionsIn KCl–NaCl-3 wt % K₂TiF₆ molten salts with less than 3 wt % KF, the interaction reaction was considered to proceed as Ti⁴⁺+Ti=2Ti²⁺. If the bath contained more than 10 wt% KF, the reaction 3Ti⁴⁺+Ti=4Ti³⁺ occurred.The electrochemical reduction of Ti⁴⁺ (K₂TiF₆) ions in the molten salts with less fluoride ions was observed to proceed according to three reaction steps, i.e. Ti⁴⁺+e=Ti³⁺, Ti³⁺+e=Ti²⁺, Ti²⁺+2e=Ti. In the case of the fluoride ion concentration being higher, two reduction steps, i.e. Ti⁴⁺+e=Ti³⁺, Ti³⁺+3e=Ti were suggested.     

Electrochemical studies of the reaction between titanium metal and titanium ions in the KCl-NaCl molten salt system at 973 K

The reaction between titanium metal and titanium ions in the KCl?NaCl molten salt system was investigated by means of electrochemical and physical methods at 973 K in an inert gas atmosphere (argon). It was found that the reaction between titanium metal and Ti³⁺ in the molten salts with TiCl₃ followed a simple reaction (I). However, in the case of the concentration of K₂ TiF₆ being higher than 2.7 mol % the reaction was (II); in the case of it being less than 0.8 mol %, reactions (III) and (III′) were followed. $$\begin{gathered} 2Ti^{3 + } + Ti = 3Ti^{2 + } (I) \hfill \\ 3Ti^{4 + } + Ti = 4Ti^{3 + } (II) \hfill \\ Ti^{4 + } + Ti = 2Ti^{2 + } (III) \hfill \\ 3Ti^{2 + } = Ti + 2Ti^{3 + } (III')(on cooling) \hfill \\ \end{gathered} $$ It was also found that these reactions were controlled by charge transfer and diffusion simultaneously.     

A numerical study of wave propagation and run-up in water channels

It is important to understand how water waves propagate through water channels in order to reduce inundation damages induced by surges and/or tsunami run-up. For this purpose, a two-dimensional numerical model is developed based on Nonlinear Shallow Water Equations. In order to appropriately describe the strongly nonlinear hydrodynamics, a high-order TVD scheme is implemented. Model capabilities are confirmed through comparison with existing analytical studies including the dam-break problems, run-up and back-wash on a sloping bathymetry. The model is then applied to the study on the inundation of bore propagating in a channel of parabolic cross-section from a side breach.

     

The role of lipids in heme synthesis

The effect of lipids on protoheme ferrolyase, which combines ferrous iron with protoporphyrin, was investigated. The enzyme extracted with 1% Na cholate from acetone-dried powder of chicken erythrocyte stroma showed high enzymic activity, while that extracted with 0.4 M KCl showed little activity. The former contained lipids, the main components of which were lecithin and phosphatidylethanolamine, whereas the latter contained little lipid. Crude lipids of several sources restored the enzyme activity of 0.4 M KCl extracts. The activating effects of purified lipids, especially phospholipids which showed the strongest activation, were further examined. Phospholipids were divided into three groups: the choline-containing group, lecithin and sphingomyelin, was inhibitory or slightly accelerative on heme synthesis; the acidic phospholipids, namely phosphatidylethanolamine, cardiolipin, phosphatidic acid and phosphatidylinositol, were strong activators and the intensity of activation was in the order of the acidity of the phospholipids; and the lysophospholipids, namely lysolecithin, lysophosphatidylethanolamine and sphingosylphosphorylcholine, activated the heme synthesis most effectively. In the presence of cholate, choline-containing lipids were highly effective, while acidic phospholipids were inhibitory and lysophospholipids were neutral. Palmitic acid showed slight stimulative effect. Tripalmitin was neutral or inhibitory. Anionic, cationic and neutral synthetic detergents were slightly stimulative in low concentration and inhibitory in high concentration. An activation mechanism of phospholipids was proposed in which the hydrophilic anionic part of lipid in the lipoprotein enzyme molecule attracts ferrous iron. After being stripped of solvation water, the ferrous iron is transferred to the hydrophobic part of the enzyme molecule to be inserted into porphyrin.