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排序方式: 共有3135条查询结果,搜索用时 10 毫秒
911.
Overall kinetic and potentiometric studies of the growth of porous anodic alumina films in saturated H2SO4+Al2(SO4)3 electrolyte showed non-saturation conditions inside the pores and supersaturation conditions at the pore surface/electrolyte
interface where the field and the solid surface catalyse the formation of colloidal Al2(SO4)3 micelles. Suitable high-strength field thermodynamically sustained electrochemical and chemical kinetic equations were formulated.
It was shown that the diameter and surface fraction of charge exchange at the pore bases, the real pore wall surface fraction
where oxide dissolution occurs, and its rate are strongly affected by the conditions. The mechanism of growth and structure
of the films are quite different from those in H2SO4. A mechanism of regular film growth is imposed and the critical current density, above which pitting appears, strongly increases.
The formulated theory may predict improved or new Al anodizing technologies.
Electronic Publication 相似文献
912.
913.
Elucidating the relationship between the spreading coefficient, surface-mediated partial coalescence and the whipping time of artificial cream 总被引:1,自引:0,他引:1
Natalie E. Hotrum Martien A. Cohen Stuart Ton van Vliet Serena F. Avino George A. van Aken 《Colloids and surfaces. A, Physicochemical and engineering aspects》2005,260(1-3):71-78
We studied the whipping of artificial creams composed of a blend of sunflower oil and hydrogenated palm fat stabilized by protein or a mixture or protein and low molecular weight (lmw) surfactant. It was found that an increased whipping speed, decreased protein concentration, and the addition of lmw surfactant leads to shorter whipping times. Further, shorter whipping times were observed for WPI-stabilized cream compared to cream stabilized by sodium caseinate. In all cases, the decrease in whipping time was due to a decrease in the length of the second stage of whipping, the stage characterized by the adhesion of fat droplets to the air bubble surface. The decrease in whipping time could be accounted for by considering the influence of the experimental variables on the fraction of bubble surface area at which fat droplet spreading is possible. The same changes in parameters that promote droplet spreading at the air/water interface cause a decrease in the whipping time of our model creams. Correlating the whipping time of cream with the spreading behavior of fat droplets at the air/water interface represents a new insight into the mechanisms involved in the whipping of cream. 相似文献
914.
Lakatos A Bertani R Kiss T Venzo A Casarin M Benetollo F Ganis P Favretto D;Solution Solid-State Study 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(5):1281-1290
The Al(III)-binding abilities of two aldaric acids, D-saccharic acid and mucic acid (the neutral form is denoted as H(2)L), were studied in solution by means of pH potentiometric, (1)H and (13)C NMR, and ESI-MS techniques. The most probable conformations and isomeric binding modes of the complexes formed in solution were determined by density functional theory (DFT) calculations. A solid D-saccharic acid complex K(2)[[Al(LH(-2))(H(2)O)](2)].H(2)O was isolated and crystallographically characterised. The two alcoholic hydroxy groups alpha to the terminal COO(-) groups were found to take part in the coordination, but in different ways. One of them coordinates in a bridging mode. Detailed ESI-MS and NMR studies proved that the complex retains its structure in solution. However, depending on the ligand and the pH, such complexes may exist in two isomeric forms. DFT calculations on the ion [[Al(LH(-2))(H(2)O)](2)](2-) revealed that several orbitals participate in stabilizing the dimeric arrangement. 相似文献
915.
Samsonova A. D. Krasnodubskaya S. V. Tyurin Yu. M. 《Russian Journal of Electrochemistry》2004,40(6):646-652
The kinetics of anodic dissolution of aluminum films electrodeposited on platinum via direct aluminum electrooxidation without preliminary discharge of electrolyte components is studied. The process probably involves adatoms and clusters Al* on the electrode surfaces, with limiting stage Al* – e (A1+)ads. 相似文献
916.
La2NiO4/Al2O3催化剂上CH4/CO2的重整 总被引:8,自引:1,他引:8
通过溶胶-凝胶方法制备了尖晶石结构的La2NiO4/Al2O3催化剂,采用BET,XRD和TG表征了催化剂的孔分布、比表面积、体相组成以及凝胶样品的热失重和热分解过程.将催化剂应用于CH4/CO2重整反应制合成气,考察了惰性气体和反应温度对转化率、选择性以及积碳的影响.结果表明,在高空速(GHSV=4.8×104ml/(g·h))下,CH4和CO2转化率分别为51%和60%,CO和H2的选择性约为98%和92%,惰性气体He的引入明显地提高了CH4和CO2的转化率. 相似文献
917.
A new method was developed for determination of micro amounts of nucleic acids based on near-infrared (near-IR) fluorescence recovery, employing a two-reagent system which is composed of an anionic tetracarboxy aluminum phthalocyanine (AlC4Pc) and a cationic tetra-N-hexadecylpyridiniumyl porphyrin (TC16PyP). The fluorescence of the AlC4Pc, with the maximum emission wavelength at 701 nm, could be quenched by TC16PyP at its proper concentration, but recovered by adding nucleic acids. Under optimal conditions, the recovered fluorescence is proportional to the concentration of nucleic acids. The calibration graphs are linear over the range of 1-200 ng mL−1 for fish sperm DNA (FS DNA) and 2-400 ng mL−1 for calf thymus DNA (CT DNA). The corresponding detection limits are 0.59 ng mL−1 for FS DNA and 0.82 ng mL−1 for CT DNA, respectively. Four synthetic and three real nucleic acid samples were determined with satisfactory results. 相似文献
918.
Cole ML Jones C Junk PC Kloth M Stasch A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(15):4482-4491
The reactivity of two sterically bulky amidines, ArNC(R)N(H)Ar (Ar=2,6-diisopropylphenyl; R=H (HFiso); tBu, (HPiso)) towards LiMH4, M=Al or Ga, [AlH3(NMe3)], and [GaH3(quin)] (quin=quinuclidine) has been examined. This has given rise to a variety of very thermally stable aluminum and gallium hydride complexes. The structural motif adopted by the prepared complexes has been found to be dependent upon both the amidinate ligand and the metal involved. The 1:1 reaction of HFiso with LiAlH4 yielded dimeric [{AlH3(mu-Fiso)Li(OEt2)}2]. Amidine HFiso reacts in a 1:1 ratio with [AlH3(NMe3)] to give the unusual hydride-bridging dimeric complex, [{AlH2(Fiso)}2], in which the Fiso- ligand is nonchelating. The equivalent reaction with the bulkier amidine, HPiso, yielded a related hydride-bridging complex, [{AlH2(Piso)}2], in which the Piso- ligand is chelating. In contrast, the treatment of [GaH3(quin)] with one equivalent of HFiso afforded the four-coordinate complex [GaH2(quin)(Fiso)], in which the Fiso- ligand acts as a localized monodentate amido-imine ligand. The 2:1 reactions of HFiso with [AlH3(NMe3)] or [GaH3(quin)] gave the monomeric complexes [MH(Fiso)2], which are thermally robust and which exhibit chelating amidinate ligands. In contrast, HPiso did not give 2:1 complexes in its reactions with either of the Group 13 trihydride precursors. For sake of comparison, the reactions of [AlH3(NMe3)] and [GaH3(quin)] with the bulky carbodiimide ArN=C=NAr and the thiourea Ar(H)NC(=S)N(H)Ar were examined. These last reactions afforded the five-coordinate thioureido complexes, [MH{N(Ar)C[N(H)(Ar)]S}2], M=Al or Ga. 相似文献
919.
Gaertner B Himmel HJ Macrae VA Downs AJ Greene TM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(14):3430-3443
Matrix isolation experiments give evidence for the formation of the loosely bonded metal-silane complex M.SiH(4) by the spontaneous reaction of Al or Ga atoms (M) with silane in a solid Ar matrix at 12 K; however, Ga(2) appears to insert spontaneously into an Si--H bond to form HGaGaSiH(3), probably with the structure HGa(micro-SiH(3))Ga. In M.SiH(4) the metal atom is eta(2)-coordinated by the silane, resulting in a species with C(2v) symmetry. The complex has a distinctive photochemistry: it can be converted on photolysis at lambda approximately 410 or approximately 254 nm to its tautomer, HMSiH(3), which also has a doublet ground electronic state and from which it can be regenerated with lambda approximately 580 nm radiation. Broadband UV-visible photolysis (lambda=200-800 nm) results in decomposition of HMSiH(3), the univalent species MSiH(3) being the only detectable product. The experimental data collected for several silane isotopomers (SiH(4), SiD(4), and SiD(3)H) and different reagent concentrations, together with the results of sophisticated quantum chemical calculations, are used to explore in detail the properties of the detected species and the reaction pathways compassing their formation. 相似文献
920.
Ju J Yang T Li G Liao F Wang Y You L Lin J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(16):3901-3906
A new anhydrous aluminoborate Al4B6O15 (PKU-5) has been synthesized in a boric acid flux in a closed system at 350 degrees C. PKU-5, which crystallizes in the space group R3 with the lattice constants a=11.43398(9) and c=6.48307(5) A, consists of Al octahedra and triangularly coordinated boron. The Al octahedron adopts the (10,3)-a network, in which each octahedron shares three edges with the neighboring octahedra forming ten-membered-ring channels. The octahedral backbone in PKU-5 can be considered as a primary octahedral framework topology and, setting out from the structures of the aluminoborates (PKU-1 and PKU-5), we propose construction rules for the octahedral frameworks. There are two types of connections for edge-sharing octahedra in porous frameworks, trans and cis type, by which various microporous octahedral frameworks of different topologies can be constructed. The borate groups share oxygens with the Al octahedral frameworks forming two kinds of three-membered-ring units consisting of two octahedra and one triangle (2Al+B) and one octahedron and two triangles (Al+2B), respectively. 相似文献