Amphiphilic and photocatalytic behaviors of TiO2 nanotube arrays on Ti prepared via electrochemical oxidation

Amphiphilic TiO₂ nanotube arrays (TiO₂ NTs) were fabricated through electrochemical oxidation of Ti in solution containing H₃PO₄ and NaF. Scanning electron microscopic analysis shows that the as-prepared TiO₂ NTs have an average pore diameter of 100 nm and a wall thickness of 15 nm. The electrochemical oxidation of Ti can be divided into four stages. In the first stage, when the potential is very low, oxygen formation and Ti dissolution are the major reactions. The second stage corresponds to a slightly higher potential, but less than 2.5 V. In this stage, the formation of TiO₂ film occurs. When the potential is increased to the even higher range from 2.5 V to 6 V, the TiO₂ film dissolves and nanoporous surface structure is generated. This is the third stage. Further increase of the potential enters stage four. The high potentials cause the self-organization of the nanostructure and allow the formation of well-aligned TiO₂ NTs. We also found that the change in surface condition of Ti by annealing heat treatment affects the film dissolution kinetics. As compared with TiO₂ thin film, the TiO2 NTs show higher photocatalytic activity on decomposing Rhodamine B. The surface of the TiO₂ NTs can be wetted by both water and oil. Such an amphiphilic property comes from the capillary effect of the nanochannel structure of the TiO₂ NTs. Because of the amphiphilic property and the photocatalytic activity, we conclude that the TiO₂ NTs have the capability of self-cleaning.     

A Composite Formation Route to Well‐Crystalline Manganese Oxide Nanocrystals: High Catalytic Activity of Manganate–Alumina Nanocomposites

Manganese oxide nanocrystals are combined with aluminum oxide nanocrystals to improve their crystallinity via calcination without a significant increase of crystal size. A nanocomposite, consisting of two metal oxides, can be synthesized by the reaction between permanganate anions and aluminum oxyhydroxide keggin cations. The as‐prepared manganese oxide–aluminum oxide nanocomposite is X‐ray amorphous whereas heat‐treatment gives rise to the crystallization of an α‐MnO₂ phase at 600 °C and Mn₃O₄/Mn₂O₃ and γ‐Al₂O₃ phases at 800 °C. Electron microscopy and N₂ adsorption‐desorption‐isotherm analysis clearly demonstrate that the as‐prepared nanocomposite is composed of a porous assembly of monodisperse primary particles with a size of ～20 nm and a surface area of >410 m² g^?1. Of particular interest is that the small particle size of the as‐prepared nanocomposite is well‐maintained up to 600 °C, a result of the prevention of the growth of manganate grains through nanoscale mixing with alumina grains. The calcined nanocomposite shows very‐high catalytic activity for the oxidation of cyclohexene with an extremely high conversion efficiency of >95% within 15 min. The present results show that the improvement of the crystallinity without significant crystal growth is very crucial for optimizing the catalytic activity of manganese oxide nanocrystals.     

Electrophoretic mobilities of dissolved polyelectrolyte charging agent and suspended non-colloidal titanium during electrophoretic deposition

Coarse (≤20 μm) titanium particles were deposited on low-carbon steel substrates by cathodic electrophoretic deposition (EPD) with ethanol as suspension medium and poly(diallyldimethylammonium chloride) (PDADMAC) as polymeric charging agent. Preliminary data on the electrophoretic mobilities and electrical conductivities on the suspensions of these soft particles as well as the solutions themselves as a function of PDADMAC level were used as the basis for the investigation of the EPD parameters in terms of the deposition yield as a function of five experimental parameters: (a) PDADMAC addition level, (b) solids loading, (c) deposition time, (d) applied voltage, and (e) electrode separation. These data were supported by particle sizing by laser diffraction and deposit surface morphology by scanning electron microscopy (SEM). The preceding data demonstrated that Ti particles of ∼1-12 μm size, electrosterically modified by the PDADMAC charging agent, acted effectively as colloidal particles during EPD. Owing to the non-colloidal nature of the particles and the stabilization of the Ti particles by electrosteric forces, the relevance of the zeta potential is questionable, so the more fundamental parameter of electrophoretic mobility was used. A key finding from the present work is the importance of assessing the electrophoretic mobilities of both the suspensions and solutions since the latter, which normally is overlooked, plays a critical role in the ability to interpret the results meaningfully. Further, algebraic uncoupling of these data plus determination of the deposit yield as a function of charging agent addition allow discrimination between the three main mechanistic stages of the electrokinetics of the process, which are: (1) surface saturation; (2) compression of the diffuse layer, growth of polymer-rich layer, and/or competition between the mobility of Ti and PDADMAC; and (3) little or no decrease in electrophoretic mobility of Ti, establishment of polymer-rich layer, and/or dominance of the mobility of the PDADMAC over that of Ti.     

High‐temperature oxidation behaviour of model Co?Re?Cr alloys at low oxygen partial pressure

The oxidation behaviour of four model Co? Re? Cr alloys and a commercial Co‐based alloy was investigated at 1000 °C and a low‐oxygen partial pressure of p(O₂) = 10^?16 bar, in order to prove the feasibility of a pre‐oxidation treatment. Under suitable conditions of the pre‐oxidation treatment, the oxidation of the highly reactive alloying element Cr is possible. All the studied alloys form a continuous and dense Cr₂O₃ scale on the metal surface. The transport of chromium to the surface occurs mainly from the Cr‐rich σ‐phase, which becomes completely dissolved in the surrounding matrix after long exposure times. As a result of the Cr₂O₃ scale, growth depletion of Cr occurs in the near surface region, leading to internal oxidation.     

3-丙酰氨基-N,N-二丙酸甲酯基苯胺的合成研究

用无水三氯化铝作催化剂在较低温度下将3-氨基丙酰苯胺和丙烯酸甲酯转化为3-丙酰氨基-N,N-二丙酸甲酯基苯胺,其产品收率达到89%,纯度高于92%。     

碳纤维热氧化行为及其机理

对聚丙烯腈(PAN)基碳纤维进行热氧化处理,借助扫描电子显微镜、X射线光电子能谱,拉曼光谱等手段表征了PAN基碳纤维的热氧化行为,研究了其热氧化机理。结果表明:热氧化使PAN基碳纤维表面氧元素含量大幅升高,碳含量下降,氧以C—OH或C—O—C基团的形式吸附到表面、在550℃左右以C=O基团大量分解的形式腐蚀纤维,破坏纤维形貌;同时热氧化腐蚀纤维中的非石墨碳,使得有序的石墨结构向非石墨无序结构转变,破坏碳纤维的晶体结构。     

High pressure organic colloid method for the preparation of high performance carbon nanotube-supported Pt and PtRu catalysts for fuel cell applications

Highly dispersed,high performance Pt and PtRu catalysts,supported on multiwalled carbon nanotubes(CNTs),were prepared by a high pressure organic colloid method.The particle sizes of the active components were as small as 1.2 nm for Pt and 1.1 nm for PtRu,and the active Pt surface areas were 295 and 395 m2/g,respectively.The catalysts showed very high activities toward the anodic oxidation of methanol,evaluated by cyclic voltammetry,being up to 4 times higher than that of commercial Johnson Matthey Hispec 20...     

Estimation of temporal changes in oxidation rates of sulphides in copper mine tailings at Laver, Northern Sweden

Tailings containing pyrrhotite were deposited in an impoundment at a copper mine at Laver, Northern Sweden, which operated between 1936 and 1946. Since then the oxidation of sulphides has acidified recipient water courses and contaminated them with metals. Measurements from surface water sampled in 1993, 2001 and 2004-05 from a brook into which the tailing impoundment drains indicate that the amounts of sulphide-associated elements such as Cu, S and Zn released into the brook have decreased over time, while pH has increased. The mass transport of S in the brook during 1993 and 2001 corresponded well with the amount of S estimated to be released from the tailings by oxidation. Secondary precipitates such as covellite and gypsum, which can trap sulphur, were shown in earlier studies to be present in only low amounts. The annual release of elements from the tailings was estimated from the volume of tailings assumed to oxidise each year, which depends on movement of the oxidation front with time. The results indicate that the oxidation rate in the tailings has decreased over time, which may be due to the increased distance over which oxygen needs to diffuse to reach unoxidised sulphide grains, or their cores, in the tailings.     

峰值电流控制模式微等离子体氧化电源研究

针对微等离子体氧化技术的特点,利用IGBT和峰值电流控制模式设计了一种高频大功率微等离子体氧化电源,它可以克服目前普遍使用的晶闸管整流式电源的缺陷,并能满足微等离子体氧化技术对电源的要求。