The oxidation properties of fourth generation single-crystal nickel-based superalloys

The fourth-generation nickel-based single-crystal superalloys, which contain large amounts of refractory metals for strengthening and platinum group metals for topologically close-packed phase prevention, show excellent high-temperature strength. However, these alloying elements seem to decrease high-temperature oxidation resistance. In this study, nickel-based superalloys with various amounts of tantalum, rhenium, and ruthenium were examined in isothermal and cyclic exposures at 1,100°C to investigate the effect on the oxide growth rate and resistance to scale spallation. Ruthenium and rhenium were found to degrade the oxidation resistance by the vaporization of their oxide. Tantalum-rich oxide in the spinel layer acts to stabilize ruthenium and rhenium oxide in the scale. The addition of hafnium and yttrium is effective in improving the oxidation resistance of ruthenium-containing nickel-based superalloys.     

Site-specific functionalization of proteins by organopalladium reactions

A new carbon-carbon bond has been regioselectively introduced into a target position (position 32 or 174) of the Ras protein by two types of organopalladium reactions (Mizoroki-Heck and Sonogashira reactions). Reaction conditions were screened by using a model peptide, and the stability of the Ras protein under the reaction conditions was examined by using the wild-type Ras protein. Finally, the iF-Ras proteins containing a 4-iodo-L-phenylalanine residue were subjected to organopalladium reactions with vinylated or propargylated biotin. Site-specific biotinylations of the Ras protein were confirmed by Western blot and LC-MS/MS.     

One-Step Synthesis of Luminescent Nanoparticles of Complex Oxide, Strontium Aluminate

An organic aqueous solution of metal acetylacetonate precursors was subjected to spray pyrolysis in order to fabricate SrAl₂O₄:Eu (SAO) nanoparticles. Non-agglomerated luminescent SAO nanoparticles, having a spherical shape with a size of 10–30 nm, were achieved in a single step, while only submicrometer-sized SAO particles were obtained from the conventional ultrasonic pyrolysis of the metal nitrates. Without any post-annealing process, the as-prepared SAO nanoparticles were observed to exhibit a strong photoluminescence, which is comparable with that of the submicrometer-sized SAO particles. A mechanism for the formation of the nanoparticles is also discussed.     

旋转流中预混合火焰的高速传播现象——Ⅰ.稳燃特性及燃烧效率的提高

旋转流中预混合火焰高速传播特性的研究为强化低热值燃气的稳定燃烧提供了新的开发思路.针对圆管内强制涡作用下的甲烷/空气预混合火焰,本工作采用数值模拟方法分析了混合气的进口速度和旋转角速度对预混合火焰稳定燃烧的影响.结果表明,在不同当量比条件下,使火焰稳定的混合气进口速度和旋转角速度之间存在线性关系,但随着旋转角速度的增大,火焰半径变小,燃烧效率减小.改变混合气进口速度的分布形式是提高燃烧效率的有效方法.研究结果为实际的稳燃燃烧器设计提供了理论指导.     

Flame flickering frequency on a rotating Bunsen burner

The empirical correlation (St^*2/Ri=0.00028Re^*2/3: St^* is the reduced Strouhal number, Ri the Richardson number, Re^* the reduced Reynolds number) proposed by Kostiuk and Cheng [1995. The coupling of conical wrinkled laminar flames with gravity. Combustion and Flame 103, 27-40] for predicting buoyancy-induced flame flickering frequency, has been experimentally investigated under the swirling flow conditions produced by a rotating Bunsen burner, focusing on how the flame flickering frequency changes with increasing swirl number S. Under low swirling conditions up to S≈0.1, the flame flickering frequency f_t did not change and monotonically increased with increasing the bulk flow velocity from the burner tube U. The trend of the data is similar to those obtained by Durox et al. [1995. Some effects of gravity on the behavior of premixed flames. Combustion and Flame 82, 66-74] and Kostiuk and Cheng (1995) and could be fitted well with the empirical correlation Kostiuk and Cheng (1995). However, under high swirling  conditions (S>1), f_t significantly decreased up to ≈80% of that with non-swirling condition, and became insensitive to U. As a result, the data under S>1 could not be correlated by the empirical equation. From results obtained by laser doppler velocimetry (LDV), this inconsistency is due to flow divergence shown by the change in the velocity distribution between the burner exit and the flame tip with burner rotation. A minimum value of the centerline velocity u_j,min between the burner exit and the flame tip fulfills an important role in controlling the flame flickering frequency. The use of this parameter allows the empirical correlation to be extended to the high swirling case by means of a modified empirical correlation St^*2/Ri=0.00028(Re^*exp(-0.64S^1.78))^2/3.     

Solid-state characterization of polyethylene reactor powders and their structural changes upon annealing

Polyethylene reactor powders prepared under different conditions were characterized using transmission electron microscopy, ¹H nuclear magnetic resonance and X-ray diffraction techniques. The molecular weight of the polyethylene reactor powders was around 1 × 10⁵. A unique domain morphology, quite different from the usual melt- or solution-crystallized lamellar structure, was observed, independent of polymerization temperature (T_poly). Annealing of reactor powders caused the aggregation of these crystalline domains, due to the significant molecular motion of the amorphous chains, before melting. The critical temperature was 20 °C higher than each T_poly, and corresponded to the temperature at the active catalyst site producing the chain growth. The morphologies of powders prepared at the lower T_poly contained smaller crystals that exhibited a constrained monoclinic form. In contrast, only usual orthorhombic crystals of larger size were found within the powder prepared at the higher T_poly. These results suggest that the competitive processes of chain propagation and crystal growth upon polymerization may lead to unique variations of the crystalline and amorphous phases, but with similar intermediate components in the phase that connects them.     

Convenient preparative method for lactones from 3-hydroxy propanoic acids using iodine under solvent-free conditions

Intramolecular cyclization of 3-hydroxy acids was investigated using iodine as a catalyst under solvent-free conditions. The reaction proceeded to completion in the heterogeneous system. Lactones were obtained by intramolecular cyclization of 3-hydroxy acids. Propella lactone (11-oxatricyclo[4.4.3.0(1,6)]tridecan-12-one) was conveniently synthesized from 3-hydroxy acid ((6-hydroxyspiro[4.5]dec-6-yl)acetic acid) in 88% yield with carbon skeleton rearrangement. Spiro lactones and bicyclic lactones were also obtained from the corresponding 3-hydroxy acids in yields of over 75%. The most suitable reaction conditions were a temperature of 80 degrees C, a molar ratio of 3-hydroxy acid:iodine = 1:0.1, and a time period of 6 h. In addition, terpenic lactones were efficiently synthesized from the corresponding 3-hydroxy acids, derived from (+)-camphor, (-)-fencone, and (-)-pulegone, with skeleton rearrangement. The yield of the solvent-free reaction was as high as that of the corresponding reaction in solution.     

Preparation and applications of novel fluoroalkyl end-capped acrylic acid oligomers/silica nanocomposites-encapsulated fullerenes

Fluoroalkyl end-capped acrylic acid oligomers/fullerenes nanocomposites reacted smoothly with tetraethoxysilane (TEOS) and silica nanoparticles under alkaline conditions to give fluoroalkyl end-capped oligomers/silica composites-encapsulated fullerenes. Interestingly, these isolated fluorinated composites were found to afford nanometer size-controlled colloidal particles with a good dispersibility in a variety of organic solvents including water. More interestingly, these fluorinated silica nanocomposites-encapsulated fullerenes were applied to a new type of surface modification agent, and these nanocomposites were able to disperse well above the poly(methyl methacrylate) films to exhibit not only surface active property imparted by fluorine but also a unique characteristic related to fullerenes in the nanocomposites on the surface, effectively.     

Optical properties of colloidal crystalline arrays composed of hollow polystyrene spheres

We have evaluated the optical properties of close‐packed and non close‐packed colloidal crystalline arrays made of hollow polystyrene spheres. Close‐packed colloidal crystalline arrays were fabricated by simple evaporation of dispersions, whereas nonclose‐packed colloidal crystalline arrays were fabricated by exploiting electrostatic interactions between the spheres in aqueous dispersion. Optical properties of the arrays were estimated from angle‐resolved reflection spectra. The Bragg diffraction peak of the colloidal crystalline array made of hollow spheres was of shorter wavelength than in the case of solid spheres, not only for the close‐packed array but also for the nonclose‐packed array. These shifts were caused by a decrease in the effective refractive index n_eff with decreasing particle refractive index. We have found that this relationship could be explained by the simple equation n_eff = n_particle?+ n_solvent (1 ? ?), where ? is the volume fraction of the particles, for both close‐packed and non close‐packed arrays. The current work suggests new possibilities for the creation of advanced colloidal crystals. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2364–2368, 2007     

聚氨酯弹性体电致伸缩性能研究

以聚(己二酸-丁二醇-新戊二醇)酯二元醇、甲苯二异氰酸酯、1,4-丁二醇和三羟甲基丙烷为原料,经聚合得到了一系列聚氨酯弹性体。利用LCR阻抗分析仪研究了所得聚氨酯弹性体的介电性能。在1kHz频率下聚氨酯弹性体的相对介电常数为7左右,相对介电常数随测试频率的增加而降低。采用数字散斑相关测量方法研究了聚氨酯弹性体在电场诱导下的应变─电致伸缩响应之间的关系。结果表明,聚氨酯弹性体在外加高压电场的作用下,随着高压电源的开合,其应变也随之呈现出相应的收缩与回复,其电致伸缩系数随聚氨酯弹性体密度的增加及相对介电常数的减小而降低。