Precursor-Derived Si-B-C-N Ceramics: Oxidation Kinetics

The oxidation behavior of three precursor-derived ceramics—Si_4.46BC_7.32N_4.40 (AMF2p), Si_2.72BC_4.51N_2.69 (AMF3p), and Si_3.08BC_4.39N_2.28 (T2/1p)—was investigated at 1300° and 1500°C. Scale growth at 1500°C in air can be approximated by a parabolic rate law with rate constants of 0.0599 and 0.0593 μm²/h for AMF3p and T2/1p, respectively. The third material does not oxidize according to a parabolic rate law, but has a similar scale thickness after 100 h. The results show that at least within the experimental times these ceramics develop extremely thin scales, thinner than pure SiC or Si₃N₄.     

前驱体结构对多环芳烃选择性开环Pt/Beta催化剂的影响

以海绵铂为原料合成出［Pt（NH₃）₆］Cl₄络合物,采用热重分析（TG）、扫描电镜-能谱（SEM-EDS）、紫外-可见分光光度计（UV-Vis）、质谱（MS）、X射线光电子能谱（XPS）等手段确定了［Pt（NH₃）₆］Cl₄的结构组成;以H₂PtCl₆、Pt（NH₃）₄Cl₂和［Pt（NH₃）₆］Cl₄为前驱体,采用等体积浸渍法制得Pt/Beta催化剂,采用X射线衍射（XRD）、X射线荧光光谱（XRF）、氨程序升温脱附（NH₃-TPD）、氢氧滴定（H₂-O₂）、透射电镜（TEM）、氢气程序升温脱附（H₂-TPD）等表征了Pt/Beta催化剂的物化性质,并考察了Pt/Beta催化剂的多环芳烃选择性开环性能。结果表明,［Pt（NH₃）₆］Cl₄络合物具有更高的“抗自还原”能力,可从前驱体结构上降低铂氨前驱体受热分解时的自还原现象。前驱体结构对铂纳米颗粒的几何尺寸及分布有较大影响,一方面络合物的价态显著影响前驱体与分子筛间的静电作用,进而影响铂纳米颗粒的落位与尺寸;另一方面络合物的空间结构影响前驱体在分子筛微孔中的分布,影响铂纳米颗粒的Ostwald熟化速率。前驱体结构可调变Pt/Beta催化剂的双功能匹配关系,显著影响Pt/Beta催化剂转化甲基萘的活性、稳定性,采用［Pt（NH₃）₆］Cl₄前驱体制备的Pt/Beta催化剂具有更优的活性及长周期稳定性。     

C/C–SiC composites derived from single-source poly(silylene–acetylene) precursors

Carbon-fiber-reinforced carbon–silicon carbide (C/C–SiC) composites were prepared by impregnating carbon fibers with ethynylphenyl-terminated poly(silylene–acetylene) (EPTSA) as a single-source precursor with subsequent hot pressing and pyrolysis. The structural evolution, crystallization behavior, and graphitization of bulk C–SiC ceramics, as well as their mechanical properties and ablation behavior, were investigated. The EPTSA precursor starts to transform into inorganic SiC ceramic materials at 800°C, which is characterized by an amorphous structure with weight loss, shrinkage, and densification between 800 and 1000°C. The formation of SiC crystals inhibited the growth of the graphitic structure between 1000 and 1200°C. As the temperature was raised, both graphite and SiC crystals continued to grow, and the crystalline forms became more complete. The carbon-fiber cloth (T300CF)-reinforced C–SiC composite (T300CF/C–SiC) prepared using polymer infiltration and pyrolysis (PIP) exhibited excellent mechanical properties. After five PIP cycles, the flexural strength, flexural modulus, and interlaminar shear strength of the T300CF/C–SiC composite reached 169 MPa, 32.5 GPa, and 9.38 MPa, respectively. In addition, the chopped-carbon-fiber-reinforced C–SiC composite fabricated using the PIP process demonstrated good oxyacetylene-torch ablation properties.     

Oxidation resistant ceramic foam from a silicone preceramic polymer/polyurethane blend

Silicon oxycarbide (SiOC) ceramic foams, produced by the pyrolysis of a foamed blend of a methylsilicone preceramic polymer and polyurethane (PU) in a 1/1 wt.% ratio, exhibit excellent physical and mechanical properties. The proposed process allows to easily modify the density and morphology of the foams, making them suitable for several engineering applications. However, it has been shown that, due to residual carbon present in the oxycarbide phase after pyrolysis, the foams are subjected to an oxidation process that reduces their strength after high temperature exposure to air (12 h 1200°C). A modified process, employing the same silicone resin preceramic polymer but a much lower PU content (silicone resin/PU=5.25/1 wt.% ratio), has been developed and is reported in this paper. Microstructural investigations showed that carbon rich regions deriving from the decomposition of the polyurethane template are still present in the SiOC foam, but have a much smaller dimension than those found in foams with a higher PU content. Thermal gravimetric studies performed in air or oxygen showed that the low-PU containing ceramic foams display an excellent oxidation resistance, because the carbon-rich areas are embedded inside the struts or cell walls and are thus protected by the dense silicon oxycarbide matrix surrounding them. SiOC foams obtained with the novel process are capable to maintain their mechanical strength after oxidation treatments at 800 and 1200°C (12 h), while SiOC foams obtained with a higher amount of PU show about a 30% strength decrease after oxidation at 1200°C (12 h).     

Psychological perspectives on acting.

Psychologists know surprisingly little about the cognitive and affective underpinnings of acting, and this stands in sharp in contrast to what has been learned about the psychological skills involved in music and the visual arts. In this article, the author discusses findings on the childhood precursors of acting talent and outlines a program of research she is initiating to test the hypothesis that acting training fosters strength in reading others' mental states, feeling others' feelings, and regulating one's own emotions in an adaptive manner. This research has implications for understanding the malleability of these outcomes and expertise in these abilities. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of activation temperature on the surface copper particles and catalytic properties of Cu–Ni–Mg–Al oxides from hydrotalcite-like precursors

The Cu–Ni–Mg–Al oxides catalysts for furfural hydrogenation were prepared from the hydrotalcite-like precursors, and the effect of activation temperature on the Cu⁰ particles and catalytic properties of the catalyst was thoroughly investigated. The catalyst activated by H₂ at 300 °C was found to exhibit the best catalytic activity, due to the presence of the smallest Cu⁰ particles with a high dispersion. Moreover, the bigger Cu⁰ particles were active for furfuralcohol hydrogenolysis to 2-methylfuran in the liquid-phase (ethanolic solution), and the hydrogenation of the furan ring of furfuralcohol and 2-methylfuran on Cu⁰ particles was easily achieved in the vapour-phase.     

Fractionation of glycoside aroma precursors in neutral grapes. Hydrolysis and conversion by Saccharomyces cerevisiae

Glycoconjugated aroma precursors from neutral grape varieties were fractionated on 5 g C18 RP cartridge. Each of the seven fractions collected was divided in three parts: first part was hydrolysed with Pectinol in order to determine total aromatic heterosides, while the second part was treated with an active strain of the yeast Saccharomyces cerevisiae UCLM 325 and the third part with acetonic powder of the same yeast strain. The studied strain proved effective in the hydrolysis of the heterosides of nerol and geraniol, cis-8-hydroxy-linalool, 8-hydroxy-dihydro-linalool, some benzenoids and some norisoprenoids derivatives such as vomifoliol and 3-oxo-α-ionol. Only whole cells are able to convert geraniol to citronellol.     

高浓度煤粉燃烧低NOx排放特性的试验研究

为了探讨高浓度煤粉燃烧对NOx排放特性影响的内在机理，在一维火焰炉试验台上，对3种典型煤在不同煤粉浓度燃烧下的NOx前驱物HCN与NH3在主燃区进行了测试，对气相催化还原剂CO及沿炉膛轴向的NOx释放特性进行了分析。试验结果表明：与常规浓度相比，高浓度煤粉燃烧条件下的NOx排放量最大可降低2.2倍。对于不同煤种，最大限度抑制NOx排放的最佳煤粉浓度控制在过量空气系数0.7左右，煤粉燃烧过程中的NOx主要在着火区距炉膛入口0.2~0.4m处产生。在高煤粉浓度下，燃料氮向HCN与NH3的转化率均远远低于常规浓度，同时燃烧过程中产生的大量CO对NOx还原分解的加速是高浓度煤粉燃烧低NOx排放的关键所在。     

Shape‐Controlled Synthesis of High‐Quality Cu7S4 Nanocrystals for Efficient Light‐Induced Water Evaporation

Copper sulfides (Cu_2–xS), are a novel kind of photothermal material exhibiting significant photothermal conversion efficiency, making them very attractive in various energy conversion related devices. Preparing high quality uniform Cu_2‐xS nanocrystals (NCs) is a top priority for further energy‐and sustainability relevant nanodevices. Here, a shape‐controlled high quality Cu₇S₄ NCs synthesis strategy is reported using sulfur in 1‐octadecene as precursor by varying the heating temperature, as well as its forming mechanism. The performance of the Cu₇S₄ NCs is further explored for light‐driven water evaporation without the need of heating the bulk liquid to the boiling point, and the results suggest that as‐synthesized highly monodisperse NCs perform higher evaporation rate than polydisperse NCs under the identical morphology. Furthermore, disk‐like NCs exhibit higher water evaporation rate than spherical NCs. The water evaporation rate can be further enhanced by assembling the organic phase Cu₇S₄ NCs into a dense film on the aqueous solution surface. The maximum photothermal conversion efficiency is as high as 77.1%.     

Transformation of amorphous silica colloids to nanosized MEL zeolite

Si-MEL molecular sieve is prepared from aged colloidal precursor solutions under hydrothermal treatment (HT) at 90 °C. In situ dynamic light scattering (DLS) investigations of the precursor solutions and the crystalline Si-MEL sols are performed with the original concentrations. Sub-colloidal particles with a mean radius of about 1 nm and colloidal aggregates with a radius of 10 nm are detected in the precursor colloidal solutions after 5 h aging at room temperature. Consumption of the sub-colloidal particles with time and an increase of the colloidal fraction of 10 nm particles after 48 h aging is observed. After heating of the aged precursor solution at 90 °C for 30 h, three particle populations of 1, 10, and 100 nm radius are formed. Complete transformation from amorphous to crystalline colloidal particles is observed after 68 h extended HT of the aged precursor solution. The mean hydrodynamic radius of the crystalline Si-MEL particles is about 100 nm based on the DLS measurements. The size of the MEL crystals was also confirmed with SEM. Additional time-dependent ²⁹Si NMR measurements of the aged precursor colloidal solutions prior to further crystal growth show that the amount of Q⁰ species (δ=−71.2) decreases, while signals of high intensity in the range between δ=−88.6 and −98.9 indicating the formation of Q³₆ and Q³₈ silicon species appear. IR data reveal that with aging of the precursor colloidal solutions at room temperature, an increased ordering of the silica species similar to those found in the final MEL product is observed.