Investigation on Sn grain number and crystal orientation in the Sn–Ag–Cu/Cu solder joints of different sizes

Polarized light microscopy and electron backscatter diffraction have been used to quantify the number of β-Sn grains and to examine the Sn crystallographic orientation in Sn–Ag–Cu/Cu solder joints, respectively. The effect of solder joint size on the Sn grain features was investigated due to the miniaturization of solder joints. The Sn–Ag–Cu solder joints of different sizes were found to contain only several β-Sn crystal grains and most solder joints were comprised of no more than three Sn grains. The solder joints showed a preferred crystal orientation. The c crystal axis of β-Sn grains tended to be at a small angle with solder pads. Specific orientation relationships were observed to be prevalent between neighboring β-Sn grains. The grain number, crystal orientation and misorientation were independent of solder joint size.     

Bone cell–material interactions on metal-ion doped polarized hydroxyapatite

The objective of this work is to study the influence of Mg²⁺ and Sr²⁺ dopants on in vitro bone cell–material interactions of electrically polarized hydroxyapatite [HAp, Ca₁₀(PO₄)₆(OH)₂] ceramics with an aim to achieve additional advantage of matching bone chemistry along with the original benefits of electrical polarization treatment relevant to biomedical applications. To achieve our research objective, commercial phase pure HAp has been doped with MgO, and SrO in single, and binary compositions. All samples have been sintered at 1200 °C for 2 h and subsequently polarized using an external d.c. field (2.0 kV/cm) at 400 °C for 1 h. Combined addition of 1 wt.% MgO/1 wt.% SrO in HAp has been most beneficial in enhancing the polarizability in which stored charge was 4.19 μC/cm² compared to pure HAp of 2.23 μC/cm². Bone cell–material interaction has been studied by culturing with human fetal osteoblast cells (hFOB) for a maximum of 7 days. Scanning electron microscope (SEM) images of cell morphology reveal that favorable surface properties and dopant chemistry lead to good cellular adherence and spreading on negatively charged surfaces of both Sr²⁺ and Mg²⁺ doped HAp samples over undoped HAp. MTT assay results at 7 days show the highest viable cell densities on the negatively charged surfaces of binary doped HAp samples, while positive charged doped HAp surfaces exhibit limited cellular growth in comparison to neutral surfaces.     

Effects of pore sizes on the electrical properties for porous 0.36BS–0.64PT ceramics

Porous BiScO₃–0.64PbTiO₃ (0.36BS–0.64PT) ceramics were fabricated by using burnable plastic sphere technique. Self-synthesized polystyrene microsphere (PS, φ0.36 μm) and poly methyl methacrylate (PMMA, φ2, 10 and 18 μm) micro-balls were selected as PFA. The porosity, microstructure and electrical properties were investigated for porous 0.36BS–0.64PT ceramics fabricated with different particle sizes of pore forming agents (PFA). With increasing particle sizes of PFA, the pore size and porosity increased. Meanwhile relative permittivity (ε _r), piezoelectric coefficient (d ₃₃, ?d ₃₁) and electromechanical coupling coefficients (k _p, k _t) decreased. The mechanical quality factor (Q _m), elastic coefficient (s ¹¹), hydrostatic voltage coefficient (g _h) and hydrostatic figure of merit increased accordingly. Finally, the effects of particle sizes of PFA on the microstructure and electrical properties were discussed.     

Two novel propylenedioxythiophene-based copolymers with donor–acceptor structures for organic solar cell materials

Two novel conjugated copolymers consisting of alternating electron-rich propylenedioxythiophene and electron-deficient 2,3-diphenyltheno[3,4-b]pyrazine or 6,7-diphenyl[1,2,5]thiadiazole units have been synthesized through palladium catalyzed Sonogashira triple-bond coupling reaction. The structures and properties of the two copolymers, P ₁ , P ₂ , were characterized by FT-IR, NMR, UV–Vis absorbance (Abs), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), and cyclic voltammetry (CV). UV–Vis absorption spectra of the polymers show two absorption bands both in CHCl₃ solution and films. The absorption peak maxima of P ₁ , P ₂ are 600 nm, 766 nm in solution and 627 nm, 823 nm in films, respectively. Thermal gravimetric analysis demonstrates that the two polymers are stable below 300 °C. Cyclic voltammetry studies reveal that the band gaps of P ₁ , P ₂ are 1.62 eV and 1.50 eV, suggesting their potential for applications as organic solar cell materials.     

Fabrication of porous alumina–zirconia ceramics by gel-casting and infiltration methods

Porous alumina–zirconia ceramics were obtained by infiltrating porous alumina ceramics, which were prepared by tert-butyl alcohol (TBA)-based gel-casting method. Back scattering images of the fracture surface and energy dispersive spectroscopy were performed to obtain composition profiles on the fracture surface and across sections of the sintered composites. The porosity, pore size distribution and compressive strength were also investigated. The results show that the content of zirconia can be adjusted effectively by infiltration times and it decreases with increasing distance from the surface of the samples. The porosity and compressive strength can also be controlled by the infiltration times. With increases of the infiltration times from 1 to 3 cycles, the open porosity decreases slightly from 62.43% to 56.62%, while the compressive strength of the porous alumina–zirconia ceramics increases from 13.57 ± 1.21 to 26.87 ± 2.01 MPa, indicating that the porous ceramics with high porosity and high strength can be prepared by TBA-based gel-casting method combined with the infiltration process.     

Evolution of the microstructure and phase composition of materials based on the fluorohydroxyapatite–zirconia–alumina system during sintering

We have studied the influence of the sintering temperature, Al₂O₃ additions, and liquid-forming sintering aids on the phase composition and microstructure of fluorohydroxyapatite-based composite ceramic materials containing 20 and 60% zirconia. The addition of alumina has been shown to prevent secondary recrystallization processes during sintering and contribute to stabilization of tetragonal zirconia. The addition of the sintering aid has made it possible to lower the sintering temperature to 1200°C.     

The effect of investment materials on the surface of cast fluorcanasite glasses and glass–ceramics

Modified fluorcanasite glass–ceramics were produced by controlled two stage heat-treatment of as-cast glasses. Castability was determined using a spiral castability test and the lost-wax method. Specimens were cast into moulds formed from gypsum and phosphate bonded investments to observe their effect on the casting process, surface roughness, surface composition and biocompatibility. Both gypsum and phosphate bonded investments could be successfully used for the lost-wax casting of fluorcanasite glasses. Although the stoichiometric glass composition had the highest castability, all modified compositions showed good relative castability. X-ray diffraction showed similar bulk crystallisation for each glass, irrespective of the investment material. However, differences in surface crystallisation were detected when different investment materials were used. Gypsum bonded investment discs showed slightly improved in vitro biocompatibility than equivalent phosphate bonded investment discs under the conditions used.     

Improved interaction of osteoblast-like cells with apatite–nanodiamond coatings depends on fibronectin

New apatite (AP)/nanodiamond (ND) coating has been developed to improve physical and biological properties of stainless steel (SS) versus single AP coating. Homogeneously electrodeposited AP–ND layer demonstrates increased mechanical strength, interlayer cohesion and ductility. In the absence of serum, osteoblast-like MG63 cells attach well but poorly spread on both AP and AP–ND substrata. Pre-adsorption with serum or fibronectin (FN) improves the cellular interaction—an effect that is better pronounced on the AP–ND coating. In single protein adsorption study fluorescein isothiocyanate-labeled FN (FITC-FN) shows enhanced deposition on the AP–ND layer consistent with the significantly improved cell adhesion, spreading and focal adhesions formation (in comparison to SS and AP), particularly at low FN adsorption concentrations (1 μg/ml). Higher FN concentrations (20 μg/ml) abolish this difference suggesting that the promoted cellular interaction of serum (where FN is low) is caused by the greater affinity for FN. Moreover, it is found that MG63 cells tend to rearrange both adsorbed and secreted FN on the AP–ND layer suggesting facilitated FN matrix formation.     

Effect of beam interaction time on laser alloying with pulsed Nd–YAG laser

Abstract

Surface alloying of aluminium with nickel was carried out using a pulsed Nd–YAG laser. The effect of beam interaction time on laser alloying of aluminium with pulsed Nd–YAG laser has been studied. It was found that the beam interaction time of a pulsed laser has a significant effect on microstructure and properties of alloyed layers. The results indicated that with changes in the beam diameter, higher thickness of alloyed layer and higher microhardness are both obtained at a lower effective interaction time. When travel speed changes, the same conditions are obtained at a higher effective interaction time.     

Interchain interaction effects on polaron–bipolaron transition on conducting polymers

We investigate the effects of interchain interaction on the polaron–bipolaron transition on conjugated polymer. We use a Su-Schrieffer-Heeger model modified to include interchain interaction, an external electric field and electron–electron interaction via extended Hubbard terms. We study the dynamics within the time-dependent unrestricted Hartree-Fock approximation. We find that adding a hole in interacting conducting polymer chains bearing a single positively charged polaron leads to the direct transition of polaron to bipolaron state. The transition which is produced is single-polaron to bipolaron transition whose excitation spectrum explains the experimental data. The competing mechanism of two polarons merging to form a bipolaron is also observed under special circumstances. We also find that depending on how fast the hole is inserted, a structure that contains a bipolaron coupled to a breather is created. The bipolaron-breather pair can be decoupled under the action of an external electric field.     

Effect of grain boundary migration in Cu–Cr–Zr–Ti manufactured using different casting processes

Grain boundary migration in different casting processes directly affects the grain size of the ingot, which affects the mechanical properties of the alloy. In this study, Cu–Cr–Zr–Ti rods are manufactured using upward continuous casting and casting-extrusion processes followed by drawing. It is found that the strength of the upward continuous casting rods is 621?MPa, greater than that of the casting-extrusion rods 571?MPa, which is a result of different microstructure evolution during solution treatment. Calculations of the driving force and resistance of grain boundary migration were performed to explain the observations.     

Evaluation of the microstructure of ß-SiAlON solid solution materials containing different amounts of amorphous grain boundary phase

In order to test the possibility of quantitative microstructural anlaysis in Si₃N₄ ceramics, solid solution materials containing different amounts of an amorphous phase were examined by transmission electron microscopy. The results show the amount and distribution of the amorphous phase and the influence of this phase on the grain morphology. This shows that within certain limits, set by the transmission electron microscopy, such a characterization is possible.     

The grain refinement efficiency of Ni–C on Mg–Al alloys

In this article, two kinds of Ni–C alloys which contain flake-like graphite and spherical graphite were prepared and the alloys were added into Mg–Al alloys in order to bring the C element into them. It is found that C can be easily and stably added into Mg–Al alloys. It is considered that the graphite in Ni–C alloys will react with Al in melt to form Al₄C₃ phase, but the formed Al₄C₃ will aggregate to the particle-like Al–Ni phase, and these duplex particles are powerful nuclei for α-Mg during solidification. It is also found that the morphology of graphite can remarkably influence the refinement, and the refining efficiency of the spherical graphite is much higher than that of the flake-like one.     

Controlled crystallization of glass–ceramics with two nucleating agents

The optimum nucleating agent had been investigated in Li₂O–Al₂O₃–SiO₂ glass–ceramics system with 2% ZrO₂ and different amounts of TiO₂ as nucleating agents. The activation energy (E) of crystallization and the Avrami parameter (n) for the LAS glasses obtained from the DTA and results show that the most effective addition of TiO₂ was about 2.36 wt.%. With the optimum nucleating agents (2% ZrO₂ + 2.36% TiO₂) addition, LAS glass–ceramics with fine grain, high transparency and good mechanical properties were obtained, due to the β-quartz solid solution formed after the crystallization process.     

Electrode materials based on a Ti–Al–C MAX phase

Long-length electrode materials based on Ti–Al–C MAX phases have been produced by self-propagating high-temperature synthesis (SHS) in combination with extrusion and their structure and performance parameters have been studied. The results demonstrate that, varying the composition of the starting mixture and parameters of the SHS extrusion process, one can obtain materials based on the MAX phases Ti₃AlC₂ and Ti₂AlC and containing intermetallic and carbide inclusions or free of carbide components. Using the SHS extrusion process, we have produced MAX phase-based rods up to 10 mm in diameter and 350 mm in length, ranging in porosity from 2 to 16%.     

Nano iron oxide–hydroxyapatite composite ceramics with enhanced radiopacity

Hydroxyapatite has been widely used for a variety of bone filling and augmentation applications. But the poorly resolved X-ray image of certain hydroxyapatite (HA) based implants such as porous blocks and self setting HA cements is a radiological problem to surgeons for monitoring of the implant and early diagnosis complications. In the present work the practical difficulty related to the reduced X-ray opacity was overcome by exploiting the contrast enhancement property of iron oxide nano particles. Sintered nano iron oxide–HA composite ceramics were prepared from powders produced through a co-precipitation route. The phase purity and bioactivity of the composites were analyzed as a function of percentage iron oxide in the composite. The X-ray attenuation of dense and porous composites was compared with pure HA using a C-arm X-ray imaging system and micro computed tomography. In all the prepared composites, HA retains its phase identity and high X-ray opacity as obtained for a composition containing 40 wt% iron oxide. The increased cell viability and cell adhesion nature depicted by the prepared composite offers considerable interest for the material in bone tissue engineering applications.     

Fixed-point fluid–structure interaction solvers with dynamic relaxation

A fixed-point fluid–structure interaction (FSI) solver with dynamic relaxation is revisited. New developments and insights gained in recent years motivated us to present an FSI solver with simplicity and robustness in a wide range of applications. Particular emphasis is placed on the calculation of the relaxation parameter by both Aitken’s method and the method of steepest descent. These methods have shown to be crucial ingredients for efficient FSI simulations.