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.     

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.     

Modified model of alkali-silica reaction

Experimental studies have been carried out for understanding why soft and fluid hydrated alkali silicate generated by the alkali-silica reaction (ASR) of aggregate with alkaline pore solution accumulates the expansive pressure for cracking the aggregate and the surrounding concrete. The elemental analysis of aggregate (andesite) embedded in a cement paste has revealed that the alkali silicate has no ability of generating expansive pressure unless the aggregate is tightly packed with a reaction rim. The reaction rim is slowly generated from the alkali silicate that covers the ASR-affected aggregate. Consumption of alkali hydroxide by the ASR induces the dissolution of Ca²⁺ ions into the pore solution. The alkali silicate then reacts with Ca⁺ ions to convert to an insoluble tight and rigid reaction rim. The reaction rim allows the penetration of alkaline solution but prevents the leakage of viscous alkali silicate, so that the alkali silicate generated afterward by the ASR is accumulated in the aggregate to give an expansive pressure enough for cracking the aggregate and the surrounding concrete. The ASR of very tiny aggregate such as fly ash and municipal waste incinerator bottom ash may not cause the deterioration of concrete, since the ASR is completed before the formation of reaction rims.     

ZnTe electrodeposition from organic solvents

The electrodeposition of zinc telluride was investigated from various organic solvent baths such as methanol, acetonitrile, propylene carbonate. The potential window increases with increasing boiling point of the solvents. In particular, ZnTe with high crystallinity could be obtained in propylene carbonate by the under-potential deposition (UPD) of Zn. The current efficiency for ZnTe deposition in propylene carbonate was enhanced considerably compared to that in acidic aqueous solutions. A single-phase ZnTe film close to the ideal stoichiometric composition of ZnTe could be obtained at 423 K and −0.8 V versus Ag/AgCl in propylene carbonate with a molar ratio of Zn(II)/Te(IV) = 10 and a low Te(IV) concentration; the film had a smooth and dense granular crystal morphology.     

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.

     

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.     

电化学沉积生物陶瓷新方法

在钛基板上电沉积了致密的、结合良好的磷酸钙生产陶瓷膜。在55℃下使用含钙离子0．01mol/dm^3。磷酸根离子0.006mol/dm^3,NaCl浓度为0.145mol/dm^3的溶液，考察了添加H2O2的影响，无论使用H2O2与否，所得的沉积物均为羟基磷灰石（hydroxyapatite,AHp)，但是在使用H2O2时，阴极电位约为-0.2V(vsSCE)即开始有阴有电流，而且没有氢气析出。与此形成对照的是在不使用H2O2时，需要极化到－1．4V(vsSCE)才有阴极电流，并且伴随着大量氢气析出。H2O2显著增强了膜的结合。     

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.