Electrochemical and structural influence on BaZr0.8Y0.2O3-δ from manganese,cobalt, and iron oxide additives

Proton conductive BaZr_0.8Y_0.2O_3−δ (BZY20) is a promising electrolyte candidate with perspective application in electrochemical devices, including fuel cells, electrolyzer cells. Mn, Fe, and Co are commonly incorporated into BZY20, to improve the sinterability (CoO), or due to possible inter-diffusion by calcining with cathode materials (eg, La_1−xSr_xMnO_3−δ, La_1−xSr_xCo_1−yFe_yO_3−δ) for cell preparation. This work was performed to investigate the influence of Mn, Fe, and Co on the structural and electrochemical properties of BZY20. As reported in literature, the sinterability of BZY20 was improved by adding CoO. XANES analysis shows that Mn, Fe, and Co are possibly incorporated into the perovskite crystal structure of BZY20, and are partially reduced when the samples were exposed to hydrogen at 600°C for 24 hours. However, through electrochemical analysis, we found that all these three elements decrease both the proton conductivity and transport numbers of proton conduction of BZY20. Therefore, the BZY20 electrolyte should be carefully handled to avoid the incorporation of these transition metal elements, to fabricate the cells with high performance.     

Gas—liauid mass transfer in three-phase stirred tank reagors: Newtonian and non-newtonian fluids

Gas—liquid mass transfer has been investigated in gas—liquid-solid three-phase stirred tank reactors with Newtonian and non-Newtonian liquids. Volumetric mass transfer coefficients and gas hold-ups were measured in a 0.2 m i.d. stirred tank reactor and the effects of low-density polymeric particles (ρ_s, =1030 and 1200 kg/m³; up to 15 vol%) on gas—liquid mass transfer were examined. The volumetric mass transfer coefficients in water were found to decrease due to the presence of solid particles at constant impeller speed and superficial gas velocity. On the other hand, solids loading led to higher mass transfer rates in non-Newtonian carboxymethyl cellulose aqueous solutions. Our previously proposed model for mass transfer in gas—liquid two-phase systems was extended to gas—liquid—solid three-phase systems. Reasonable agreement was found between the predictions of the proposed model and the experimental data.     

Effects of Insert Metal Type on Interfacial Microstructure During Dissimilar Joining of TiAl Alloy to SCM440 by Friction Welding

Although the welding zone of direct bonding between a TiAl alloy and SCM440 can be obtained by friction welding, martensitic transformation and the formation of intermetallic compounds (IMCs) and cracks result in a lower tensile strength of the joints relative to those of other welding techniques. Insert metals were used as a buffer layer to relieve stress while increasing the bond strength. In this study, the microstructure and mechanical properties on welded joints of a TiAl alloy and SCM440 with various insert metals, were investigated. The TiAl/Cu/SCM440 and TiAl/Ni/SCM440 joints were fabricated using a servo-motor-type friction welding machine. As a result, it was confirmed that the formation of a welding flash was dependent on the insert metal type, and the strength of the base metal. At the TiAl/Cu/SCM440 interface, the formation of IMCs CuTiAl and Cu₂TiAl was observed at TiAl/Cu, while no IMC formation was observed at Cu/SCM440. On the other hand, at the TiAl/Ni/SCM440 interface, several IMCs with more than 100 μm thickness were found, and roughly two compositions, viz., Ti₂NiAl₃ and TiNi₂Al, were observed at the TiAl/Ni interface. At the Ni/SCM440 interface, 10 μm-thick FeNi and others were found.     

气体温度对冷喷涂7075铝合金涂层性能的影响

目的研究气体温度对冷喷涂7075铝合金涂层性能的影响,以期为制备高性能涂层提供重要参考。方法利用冷喷涂技术,在较高的工作气体压力(5 MPa)下,通过改变工作气体温度(450、500、550、600℃),采用氮气在纯铝基体上制备了大厚度7075铝合金涂层。采用光学显微镜(OM)、扫描电子显微镜(SEM)对涂层组织结构及孔隙率进行了分析测定,用维氏显微硬度法测定涂层硬度,通过拉伸实验测定涂层结合强度,研究了冷喷涂工作气体温度对7075铝合金涂层组织及沉积特性的影响。结果工作气体温度在450～550℃范围时,对涂层组织及力学性能影响有限。当工作气体温度为450℃时,涂层孔隙率为0.14%,显微硬度为117.8HV0.1,结合强度超过55.3 MPa。但过高的工作气体温度并不利于冷喷涂7075铝合金涂层的制备,当喷涂气体温度达到600℃时,涂层孔隙率升高到4.2%。结论仅采用廉价的氮气即可制备高致密度和高结合强度的冷喷涂7075涂层,当主气温度在450～550℃区间时,涂层微观组织和性能随气体温度变化不大,而过高的工作气体温度(600℃)并不利于冷喷涂7075涂层相关性能的提升。     

Influence of trimethylsilylation and detrimethylsilylation on the molecular weight of chitin: Evaluation of viscometry and gel permeation chromatography for molecular weight determination

In view of the high potential of trimethylsilylated chitin as a reaction precursor, the influence of trimethylsilylation and detrimethylsilylation on the molecular weight characteristics has been studied. Chitin was trimethylsilylated, and the product was detrimethylsilylated to regenerate chitin. The molecular weights of the original and regenerated chitins were determined by viscometry and GPC. The viscosity measurements, with either an Ubbelohde or a rotational viscometer, gave highly reproducible values, which were quite similar to each other. The molecular weight of the regenerated chitin was found to be a little over a half that of the original chitin despite after the silylation-desilylation reactions. GPC also supported a similarly low extent of main chain scission. These results indicate that the silylation-desilylation reactions are reproducible without a significant damage to the chitin main chain, and both viscometry and GPC have proved reliable in elucidating the molecular weight characteristics. Trimethylsilylation of chitin can thus be conveniently used as a key intermediate for further controlled modification reactions to prepare well-defined derivatives.     

Influence of Tetragonality on Tetragonal-to-Monoclinic Phase Transformation during Hydrothermal Aging in Plasma-Sprayed Yttria-Stabilized Zirconia Coatings

The influence of tetragonality, which is defined as the lattice parameter ratio c / a , on the tetragonal-to-monoclinic phase transformation during hydrothermal aging was investigated in yttria-stabilized zirconia coatings. The yttria content was adjusted in the range of 4–8 mass% (denoted as x YZ, where x = 4–8 and YZ represents the yttria-stabilized zirconia). The tetragonality of the zirconia in the as-sprayed coatings was less than that in the powders. To change the tetragonality for each yttria content, the coatings were annealed at 1273 K before aging. Without annealing, the phase transformation was prevented only in 8YZ. When annealing was applied, an increase of the tetragonality (i.e., recovery of the tetragonality) was observed, and transformation during hydrothermal aging was also suppressed in 6YZ. It was concluded that the increase in tetragonality that occurred without a change in the yttria content was suggested to be caused by the lattice relaxation of the tetragonal phase, and this relaxation is believed to cause a reduction of the critical yttria concentration, thus preventing the phase transformation.     

Thermoresponsive core–shell nanoparticles with cross-linked π-conjugate core based on amphiphilic block copolymers by RAFT polymerization and palladium-catalyzed coupling reactions

Well-defined amphiphilic block copolymers composed of S-vinyl sulfides and N-isopropyl acrylamide (NIPAM) were synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization. Thermoresponsive core–shell nanoparticles with cross-linked π-conjugate cores were obtained by in situ cross-linking reactions between 4-bromophenyl moieties in the block copolymers and diboronic acids or a diamine compound in the presence of a palladium catalyst following micelle formation in ethanol/H₂O or ethanol. We initially investigated RAFT polymerization of two S-vinyl sulfide derivatives, namely phenyl vinyl sulfide (PVS) and 4-bromophenyl vinyl sulfide (BPVS), using a dithiocarbamate-type chain transfer agent (CTA). Then, RAFT polymerization of NIPAM using poly(S-vinyl sulfide) macro-CTAs was conducted to synthesize the amphiphilic block copolymers. Suzuki and Buchwald-Hartwig coupling reactions were found to be effective in the preparation of core–shell nanoparticles with thermoresponsive shells and cross-linked optoelectronic cores. The resulting nanoparticles showed characteristic thermoresponsive properties, as confirmed by turbidity and dynamic light scattering measurements. Stable and uniform core cross-linked nanoparticles were successfully prepared by the in situ palladium-catalyzed coupling reactions, and the optoelectronic and thermoresponsive properties of the nanoparticles could be tuned depending on the nature of the difunctional coupling agents, reaction conditions, and comonomer composition of the block copolymers.     

pH‐sensitive shrinking of a dextran sulfate/chitosan complex gel and its promotion effect on the release of polymeric substances

A pH‐sensitive gel was prepared by polyelectrolyte complex formation between dextran sulfate and chitosan. When the complex gel contained more amino groups than sulfate groups, it shrank pronouncedly at around pH 7 in NaCl solutions of various concentrations, probably because of the deionization of protonated amino groups remaining free from electrostatic interaction with the sulfate groups. Using the complex gel loaded with dextran by absorption, releasing behaviors were studied under various conditions. It was shown that shrinking of the complex gel had a promotion effect on the release of dextran. In 170 mM NaCl solution, the complex gel released dextran more rapidly at pH 8 than at pH 2, because the degree of shrinking was greater at pH 8. Thus, the promotion effect of the complex gel on the release of dextran was pH dependent, though the release rates at the two pHs became closer as the average molecular weight of dextran loaded was lowered. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 667–674, 2001     

Conformational Analysis of Misfolded Protein Aggregation by FRET and Live-Cell Imaging Techniques

Cellular homeostasis is maintained by several types of protein machinery, including molecular chaperones and proteolysis systems. Dysregulation of the proteome disrupts homeostasis in cells, tissues, and the organism as a whole, and has been hypothesized to cause neurodegenerative disorders, including amyotrophic lateral sclerosis (ALS) and Huntington’s disease (HD). A hallmark of neurodegenerative disorders is formation of ubiquitin-positive inclusion bodies in neurons, suggesting that the aggregation process of misfolded proteins changes during disease progression. Hence, high-throughput determination of soluble oligomers during the aggregation process, as well as the conformation of sequestered proteins in inclusion bodies, is essential for elucidation of physiological regulation mechanism and drug discovery in this field. To elucidate the interaction, accumulation, and conformation of aggregation-prone proteins, in situ spectroscopic imaging techniques, such as Förster/fluorescence resonance energy transfer (FRET), fluorescence correlation spectroscopy (FCS), and bimolecular fluorescence complementation (BiFC) have been employed. Here, we summarize recent reports in which these techniques were applied to the analysis of aggregation-prone proteins (in particular their dimerization, interactions, and conformational changes), and describe several fluorescent indicators used for real-time observation of physiological states related to proteostasis.