Creation of Ferroelectric, Single-Crystal Architecture in Sm0.5La0.5BGeO5 Glass

Using a novel, selective heating by Nd:YAG laser, a single-crystal architecture is created in a model glass system, Sm_0.5La_0.5BGeO₅, which devitrifies congruently into a ferroelectric phase of the same composition as the parent glass. The Sm³⁺ ions in glass absorb the light and heat the matrix locally resulting in devitrification. Initially, a polycrystalline spot is formed. However, with optimum laser power, scanning speed, and the depth of focus, one of the grains acts as the seed for further growth as a single crystal. By programming the relative displacement of the glass with respect to laser spot, desired single ferroelectric crystal architecture is created. The optical functionalities (guiding of light and second harmonic generation) of the architectures are shown, which demonstrate the viability of this method for constructing active elements in optical integrated circuits. The single-crystal nature of the architecture is confirmed from the electron backscattered diffraction results.     

Preparation of highly dispersed gold nanoparticles inside the porous support assisted by amphiphilic vinyl maleate copolymer

An amphiphilic copolymer composed of maleic acid and alkyl (C₁₈) vinyl monomer was encapsulated into the porous support. A series of colloidal gold nanoparticles of known size was substantially immobilized in the composite porous supports based on cross-linked polyacrylate ester and cross-linked polystyrene resin. Maleic acid moiety of the amphiphilic copolymer can act as a stabilizer for gold nanoparticles in analogy to citric acid, whereas alkyl chains play a role for the stable accommodation of the amphiphilic copolymer. Maleic acid stabilizes the gold nanoparticles by flexing the geometrical arrangement of the linear polymer. Presence of C₁₈ alkyl chain in the poly(C₁₈-vinyl maleate) is indispensable to act as spacing group that prevents mutual aggregation of gold nanoparticles. On the other hand, gold nanoparticles with average diameter of less than 8 nm were spontaneously formed by treatment of the composite resin beads with aqueous HAuCl₄ solution, subsequently dispersed inside the pores of resin beads as observed by TEM. We have also elucidated the catalytic activity of the material with the hydrogenation of cinnamaldehyde in supercritical carbon dioxide. Notably, apparent size effect of gold was observed in the selectivity of the reaction.     

Selective-catalyst formation for carbon nanotube growth by local indentation pressure

We studied the selective formation of Co catalyst particles as a function of indentation pressure. We subjected a Co (8 nm thickness)/Si substrate pre-annealed at 600 °C to indentation processing. The catalytic function was confirmed in the indentations by the selective growth of carbon nanotubes (CNTs) at 800 °C. The number density of CNTs against the indentation pressure was investigated against indentation loads for two types of indenter: a Berkovich indenter with a ridge angle of 115° and a Berkovich indenter with a ridge angle of 90°. The pressures above 7 GPa applied by the former indenter enhanced Co atomization acting as a catalyst function for CNT growth (35 CNTs in one indentation). In contrast to this, the number of CNTs was markedly reduced when the latter indenter was used with pressures less than 3 GPa. The pop-out phenomenon was observed in unloading curves at pressures above 7 GPa. These results indicate that metastable Si promotes the self-aggregation of catalyst particles (Co) leading to the selective growth of CNTs within indentations at pressures above 7 GPa.     

Synthesis and mechanical behaviour of chlorapatite and chlorapatite/β-TCP composites

Chlorine substituted hydroxyapatite (HAP) and biphasic mixtures (HAP + β-TCP) were prepared through an aqueous precipitation method. Characterization studies using XRD, thermograms, elemental analysis and FT-IR spectra have confirmed the incorporation of added chlorine into the apatite structure forming a solid solution. Substitution of chlorine in the calcium deficient apatites tends to form biphasic mixtures of HAP and β-TCP and the proportions in the formed mixtures were dependent on the deficiency of calcium in the precursors used. The thermal stability of the chlorine substituted apatites was evident up to 1200 °C from the present results. The cell parameters for chlorine substituted apatite powders tend to follow significant expansion with respect to those of stoichiometric HAP, being always smaller than those of the stoichiometric chlorapatite sample. The mechanical properties of the solid solution of chlorapatites have shown promising features when compared to the pure stoichiometric chlorapatite sample.     

Low-cycle fatigue prediction model for pb-free solder 96.5Sn-3.5Ag

Low-cycle fatigue (LCF) data of Sn-Ag eutectic solder (96.5Sn-3.5Ag) under various temperatures and frequencies has been described using three different prediction models, i.e., Coffin-Manson model, Smith-Watson-Topper (SWT) model, and Morrow energy model. The LCF behavior represented by the present prediction models showed temperature and frequency dependences, i.e., the fatigue ductility coefficient increased with increasing frequency and decreasing temperature. In order to better correlate the LCF data, a flow stress and/or frequency-dependent modifications were introduced to the Coffin-Manson and Morrow energy models. The frequency-modified Coffin-Manson model could not describe the influence of temperature on LCF behavior, while the flow stress-modified frequency-modified Morrow energy model, into which the metallurgical response (flow stress and frequency) was introduced to account for the effect of temperature and frequency on LCF behavior, gave reasonable predictions of LCF data under various temperatures and frequencies.     

Structural dependence of corrosion resistance of amorphous carbon films against nitric acid

To investigate the structural dependence of the corrosion resistance of amorphous carbon (a-C:H) films, three different types of a-C:H films etched by nitric acid were evaluated using a surface plasmon resonance (SPR) device with a multilayer structure consisting of an a-C:H layer on Ag. Two non-hydrogenated amorphous carbon (a-C) films and one hydrogenated a-C:H film were synthesized to estimate the effects of the sp²/sp³ ratio and hydrogenation, respectively. A flow cell for the introduction of nitric acid solution was placed on the amorphous carbon layer of the multilayer structure. A 0.3 mM nitric acid solution was used in the etching tests. The Kretschmann configuration was used for SPR measurement, and the SPR angle was determined as the angle with minimum reflectivity. The SPR angle decreased with increasing duration of nitric acid injection into the flow cell, indicating that the film was corroded by the nitric acid. The thickness of the films was calculated from the SPR angle. The rates of decrease in the thickness were 2.2, 0.8, and 1.6 nm/h for the a-C films with lower and higher sp² contents and the 17 at.% hydrogenated a-C:H film, respectively. Although the hydrogen content had little effect on the rate of change in the film thickness, the film thickness clearly decreased with decreasing sp²/sp³ ratio. These results indicate that the sp²/sp³ ratio is an important factor determining the chemical resistance to nitric acid solution.     

Development of a strain for efficient degradation of polychlorinated biphenyls by patchwork assembly of degradation pathways

Rhodococcus jostii RHA1 accumulates chlorobenzoates (CBA) during the degradation of polychlorinated biphenyls (PCBs). CBA degradation is considered one of the rate-limiting steps in the complete degradation of PCBs. To reduce the accumulation of CBAs, the upper pathway enzyme genes for PCB degradation of RHA1 were introduced into a CBA-degrading bacterium, Burkholderia sp. NK8. The resulting recombinant strain exhibited no biphenyl 2,3-dioxygenase (BphA) activity encoded by bphAaAbAcAd genes, which encode the large and small subunits of the terminal oxygenase component and the ferredoxin and reductase subunits responsible for electron transfer from NADH to the large subunit. The remaining enzyme genes involved in the transformation of biphenyl to benzoate, bphB2C1D1, which encode dehydrogenase, ring-cleavage dioxygenase and hydrolase, conferred activities to NK8. To obtain the BphA activity of RHA1 in NK8, sets of BphA genes were constructed by combining the bphAaAbAcAd genes of RHA1 and bphA3A4 of Pseudomonas pseudoalcaligenes KF707, encoding the ferredoxin and reductase subunits. Hybrid derivatives of BphA containing the KF707 bphA3 conferred BphA activity to NK8, and a derivative containing the RHA1 bphAaAb and KF707 bphA3A4 genes exhibited the highest BphA activity. A plasmid containing the RHA1 bphAaAb and KF707 bphA3A4 genes plus the RHA1 bphB2C1D1 genes was constructed and introduced into NK8. The resulting recombinant strain efficiently degraded 2-, 3- and 4-chlorobiphenyls with an apparent reduction in CBA accumulation in comparison to the recombinant mutant strain, which had an insertion in the cbeA gene to inactivate CBA dioxygenase.     

Application of microalgae hydrolysate as a fermentation medium for microbial production of 2-pyrone 4,6-dicarboxylic acid

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Multiple crack healing of a Ti2AlC ceramic

A highly attractive self-healing material would be one which combines excellent mechanical properties with a multiple healing capability. Self-healing ceramics have been studied for over 40 years to obtain some performance recovery and to prevent material failure during service, but so far only materials with the capability of single healing event per damage site have been realized. Here we report on a self-healing Ti₂AlC ceramic capable of repeatedly repairing damage events. The Ti₂AlC ceramic achieves at least seven healing cycles after repeated cracking at a given location. The main healing mechanism at high temperature is the filling of the cracks by the formation well adhering α-Al₂O₃ and the presence of some rutile TiO₂. For healed samples, the flexural strength returned or even slightly exceeded the virginal strength. The fracture toughness recovery has been quantified for multiple healing cycles.     

Anisotropic thermal conductivity of silicon nitride ceramics containing carbon nanostructures

Silicon nitride (Si₃N₄) composites containing carbon nanotubes (CNTs) or graphene nanoplateles (GNPs) are of great relevance in the electronic and aerospace industries where the search for new materials with enhanced and anisotropic thermal conductivity to work in harsh environments is a strategic guideline. Here we study thermal conduction in Si₃N₄ composites with different amounts of carbon nanostructures. The effects of the nanostructure orientation respect the heat flux, the testing temperature and the α/β Si₃N₄ phase ratio are analyzed. The addition of CNTs and GNPs leads to an anisotropic thermal response, decreasing the through-thickness thermal conductivity of the Si₃N₄ composites and raising the in-plane thermal conductivity, especially for GNPs that enhance it up to twice that of the monolithic Si₃N₄. This effect is related to the preferred orientation of the nanostructures that gives a less resistive network in the in-plane direction and the intrinsic anisotropy of their thermal conductivity.