Alloying and microstructure stability in the high-temperature Mo-Si-B system

Multi-phase alloys in the Mo-Si-B system are identified as high-temperature structural materials due to their high melting points (above 2000 °C) and excellent oxidation resistance attributed to the self-healing characteristics of borosilica layer up to 1400 °C. In the current study, the effect of alloying additions to achieve a reduced weight density has been examined in terms of changes in the microstructure and phase stability. The critical factor underlying the microstructural changes is related to the influence of the alloying additions on the stability of the high melting temperature ternary-based Mogt;5gt;SiBgt;2gt; (Tgt;2gt;) borosilicide phase.     

Analysis of a homologous series of non-reducing oligosaccharides from Arnica montana L. Roots

The oligosaccharide component compositions of a series of non-reducing oligosaccharides extracted from the roots of gt;Arnica montanagt; L. has been determined by gel permeation chromatography (g.p.c.). The range of oligosaccharides present was found to extend beyond the octasaccharide previously reported. with 16% to 19% of the oligosaccharides having a degree of polymerisation of between 11 and 19 and almost 3% having a degree of polymerisation greater than 20. The chromatographic behaviour of this series of oligosaccharides is compared with that observed for series of D-gluco-oligosaccharides.     

Novel application of nanocrystalline nickel electrodeposit: Making good diamond tools easily, efficiently and economically

Electrodeposition has been identified as a feasible and economical technique for nanomaterials application. This article details an improved approach to producing better diamond tools at lower cost and with higher productivity. Pulse-electroformed nanocrystalline nickel was used as the new matrix. The pulse parameters were determined after examination of the microstructure, grain size, hardness and tensile strength of the deposits obtained at different average current densities (gt;Jgt;gt;gt;mgt;gt;) with constant pulse-on time and pulse-off time. It is shown that, with gt;Jgt;gt;gt;mgt;gt; ranging from 1 Admgt;− 2gt; to 14 Admgt;− 2gt;, the grain size decreases sharply from 180 nm to about 10 nm while the hardness and tensile strength significantly increase at first and then reach their peaks respectively, although the strength fails to stay long. Current density gt;Jgt;gt;gt;mgt;gt; that produced the highest hardness and strength of deposit (with grain size of 20 nm) was chosen for new diamond tools that exhibited 20.2% longer service life than their usual Ni-Co counterparts. Therefore, nanocrystalline electrodeposits are expected to be an upgrading substitute for conventional polycrystalline matrix.     

V2O5/g⁃C3N4催化剂的制备及其模拟油中硫化物的脱除

以三聚氰胺、偏钒酸铵、硼酸为前驱体,通过煅烧法制备V₂O₅/g⁃C₃N₄催化剂。采用XRD、FT⁃IR、XPS、SEM和BET等技术对催化剂的结构与形貌进行表征。以V₂O₅/g⁃C₃N₄为催化剂,乙腈为萃取剂,H₂O₂为氧化剂对模拟油中二苯并噻吩（DBT）的脱除进行考察。探究了反应温度、催化剂质量、萃取剂体积、n(H₂O₂)/n(S)以及不同硫化物等因素对脱硫效果的影响。在模拟油体积为5.0 mL、萃取剂乙腈体积为3.0 mL、n(H₂O₂)/n(S)=8、催化剂质量为0.02 g、反应温度为30 ℃和反应时间为60 min的最佳条件下,DBT的脱除率达到91.9%,经过5次催化剂再生后脱硫率仍可以达到85.7%。     

H2O(g)对富氧燃烧超细颗粒物生成特性影响

为实现富氧燃烧技术的广泛推广,对煤粉燃烧在富氧气氛下的颗粒物排放特性进行了研究。在1800 K管式炉内进行煤焦燃烧试验,研究了富氧气氛下H₂O(g)体积分数(0、5%、10%、20%、30%)对煤焦燃烧超细颗粒物的影响;采用荷电低压撞击器(ELPI+)获得超细颗粒物质量和数量浓度粒径分布并进行分析。结果表明,H₂O(g)对超细颗粒物质量浓度和数量浓度粒径分布无影响,但会导致超细颗粒物的峰值波动。超细颗粒物总数量由最小粒径超细颗粒物决定,5种水蒸气浓度下EL?PI+第1级撞击器收集到的超细颗粒物数量占比均超过65%。超细颗粒物总质量由最大粒径超细颗粒物决定,5个水蒸气浓度下ELPI+第7级撞击器收集到的超细颗粒物质量占比均超过94%。低H₂O(g)浓度会抑制超细颗粒物生成,H₂O(g)体积分数为5%时的抑制作用最显著;高H₂O(g)浓度会促进超细颗粒物生成。这是因为一方面H₂O(g)与煤焦发生气化反应,使煤焦颗粒周围产生还原性气氛,促进矿物质还原为单质,进一步促进矿物质蒸发;另一方面气化反应是吸热反应,会降低煤焦颗粒燃烧温度,同时H₂O(g)加入也导致烟气热容增加进一步降低,煤焦燃烧温度抑制煤中矿物质的蒸发,导致超细颗粒物生成减少,是2种作用相互竞争的结果。此外,H₂O(g)的加入使超细颗粒物平均粒径增大,0~5%H₂O(g)时超细颗粒物平均粒径增大最迅速。     

铝电解用TiB_2阴极涂层固化、炭化的升温制度

采用DTG ,DDTA等热分析手段 ,研究了高温固化、炭化过程中 ,铝电解用TiB2 阴极涂层糊料的质量和能量的变化速率 ,制定了涂层的变速固化、炭化升温制度 ;在此基础上 ,研究了升温制度对TiB2 阴极涂层性能的影响。结果表明 :变速升温制度优于匀速升温制度 ,采用变速固化、炭化升温制度所制备的涂层形变小、无裂纹 ,其抗拉强度达 3.13MPa,电阻率为 2 3.2 μΩ·m ;而采用升温速度为 10 .3℃ /h的匀速固化、炭化升温制度制备的涂层形变大、裂纹多 ,抗拉强度小 (2 .6 9MPa) ,电阻率大 (2 8.6 μΩ·m)。     

Fluorinated Polyphosphazenes: A Survey

A general survey of fluorinated phosphazene polymers starting from their synthesis in 1965 to recent times is presented. Various types of fluorinated phosphazenes are described depending on the way fluorine atoms are connected to the polyphosphazene skeleton. The characterization, properties and practical utilization of these compounds in different domains are critically discussed.     

Surface properties of ZSM-5 modified by phosphorus

Phosphorus modification of ZSM-5 leads to extra framework Pgt;5+gt; and probably incorporation of +3 valence state of P in the framework. The resulting system has increased Brønsted acidity. Theoretical calculations also favour the postulate that phosphorus in +3 valence state can be incorporated into the lattice.     

Role of La2O3 in Pd-Supported Catalysts for Methanol Decomposition

Systems of Pd supported on various Lagt;2gt;Ogt;3gt;-modified g src="/content/g7q17741x5388455/xxlarge947.gif" alt="gamma" align="MIDDLE" BORDER="0">-Algt;2gt;Ogt;3gt; and CeOgt;2gt;–Algt;2gt;Ogt;3gt; catalysts were tested for catalytic methanol decomposition and characterized by means of XRD, BET, TPR, Hgt;2gt;-chemisorption and CO–FTIR. The addition of lanthanum significantly improved the selectivity of CO and Hgt;2gt; for all the catalysts but showed a different influence on the catalytic activity in two systems. Methanol conversion decreased on Lagt;2gt;Ogt;3gt;-modified Pd/g src="/content/g7q17741x5388455/xxlarge947.gif" alt="gamma" align="MIDDLE" BORDER="0">-Algt;2gt;Ogt;3gt; catalysts, in line with the reduction of Pd dispersion, while the addition of Lagt;2gt;Ogt;3gt; improved the dispersion of Pd and reinforced Pd–CeOgt;2gt; interaction for Lagt;2gt;Ogt;3gt;-modified Pd/CeOgt;2gt;–Algt;2gt;Ogt;3gt; catalysts, which resulted in a high production rate of CO and Hgt;2gt;. Thus, a synergistic effect between CeOgt;2gt; and Lagt;2gt;Ogt;3gt; was observed on g src="/content/g7q17741x5388455/xxlarge947.gif" alt="gamma" align="MIDDLE" BORDER="0">-Algt;2gt;Ogt;3gt;-supported Pd catalyst for methanol decomposition.     

Structure–Function Relations in Supported Ni–W Sulfide Hydrogenation Catalysts

Ni–W catalysts were prepared by impregnation of commercial g src="/content/g0805166532221m8/xxlarge947.gif" alt="gamma" align="MIDDLE" BORDER="0">-alumina and silica supports. The sulfidation, performed directly after drying at 100°C, yielded fully sulfided Ni–W species on both supports (SEM-EDAX, XPS, XRD). At optimal metals loading (g src="/content/g0805166532221m8/xxlarge8764.gif" alt="sim" align="MIDDLE" BORDER="0">50 wt% NiO + WOgt;3gt;, Ni/W = 2), the sulfided catalysts had similar texture (Ngt;2gt; adsorption) and displayed similar activity in dibenzothiophene hydrodesulfurization (DBT HDS), while the activity of the Ni–W/SiOgt;2gt; catalyst in toluene hydrogenation (HYD) was six times higher than that of Ni–W/Algt;2gt;Ogt;3gt;. This is due to the more than two times higher WSgt;2gt; slabs stacking number in Ni–W/SiOgt;2gt; compared with Ni–W/Algt;2gt;Ogt;3gt; (XRD, HR-TEM), yielding stronger adsorption of toluene (TPD).