摘要:

The principal characteristics of the cathode deposition of zinc oxide from slightly acidified aqueous zinc nitrate solution at 65 °C were studied via potentiodynamic electrolysis, potentiostatic electrolysis, and X-ray diffraction patterns. The results indicate the reliability of a low-temperature electrolytic path of synthesis, and avenues of further exploration.Keywords: zinc oxide, cathode deposition, XRD patterns, FBM theory.

ISSN:0008-4042    

DOI:10.1139/v97-173

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The apparent molar volumes and adiabatic compressibilities,of carboxylate surfactants, CnNa (n = 8, 10, 12), in aqueous solutions in the absence and presence of medium-chain-length alkoxyethanols, C4EOX(EO = ethylene oxide group,X = 0–4), and of alkoxyethanols,in aqueous solutions in the absence and presence of surfactant, were determined at 25 °C from density and sound velocity measurements as a function of both the surfactant and alcohol concentrations. The partial molar volumetric properties of CnNa and the transfer functions of C4EOXfrom water to aqueous surfactant solutions were calculated from the apparent molar properties. Values of the thermodynamic parameters of micellization for CnNa, i.e., the critical micelle concentration, the partial molar property of the monomer at infinite dilution,and in the micellar state,were obtained from simulations of the experimental data,using a mass-action model. As expected, these properties are strongly dependent on the surfactant chain length. The distribution coefficient of C4EOXbetween the micelle and aqueous phases,KD, and the change in the molar property of alcohols due to micellization,extracted from fitting the transfer function data of C4EOXusing a chemical equilibrium model, show that the solubilization of alkoxyethanols in carboxylate micelles is enhanced by increasing the surfactant chain length and the number of EO groups in the alcohol. The deeper penetration of C4EOXinto the micelles of longer chain surfactants is associated with increasingly stronger interactions between surfactant head groups and EO segments of the alcohol on (or near) the micelle surface. Aggregation numbers of CnNa–C4EOXmixed micelles show that addition of a small amount of C4EOXhas little effect on the structure of the micelles formed from C8Na and C10Na, but leads to significant change in C12Na micelles.Keywords: sodium carboxylate salts, alkoxyethanols, partial molar volume and compressibility, transfer functions, distribution coefficient, mean aggregation number.

ISSN:0008-4042    

DOI:10.1139/v97-174

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The thermodynamics of an electrochemical cell with an intercalation electrode is discussed in the light of two recent analyses (Gerischer et al. J. Electrochem. Soc.141, 2297 (1994) and Li et al. J. Electrochem. Soc.141, 2310 (1994)). The assumptions necessary to obtain a simple result are emphasized.Keywords: thermodynamics, intercalation electrode.

ISSN:0008-4042    

DOI:10.1139/v97-175

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Using the rotating ring-disk technique (RRDPt(hkl)E), the oxygen-reduction reaction (ORR) was studied in sulfuric acid solution over the temperature range 298–333 K At the same temperature, the exchange current density increased in the order,which gives the order of absolute kinetic activities of Pt(hkl) in 0.05 mol/L H2SO4: Pt(111) < Pt(100) < Pt(110). We found that at high current densities every crystal face has an ideally temperature-dependent Tafel slope, i.e., −2 × 2.3(RT/F). The activation energy for the ORR is independent of the surface geometry,. The insensitivity of the activation energy to surface structure implies that the reaction pathway for the ORR is the same on all three single-crystal faces. A "series" pathway for the ORR was proposed, with the first electron transfer being the rate-determining step. The structure sensitivity in the kinetics of the ORR on Pt(hkl) is attributed to the structure-sensitive adsorption of bisulfate and hydroxyl anions and a simple site-blocking effect of these adsorbed anions on the rate of the ORR.Keywords: platinum single crystals, oxygen reduction, peroxide reduction, temperature effects, activation energy.

ISSN:0008-4042    

DOI:10.1139/v97-176

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Hyperbranched glycodendrimers containing sialic acid residues were synthesized in order to further understand the multivalency effect and its role in carbohydrate–protein interactions. Gallic acid7as trivalent core and oligoethylene glycol derivatives as hydrophilic spacers were used to scaffold the dendritic backbones. α-Thiosialoside16was conjugated ontoN-chloroacetylated dendritic precursors13,14, and26by nucleophilic substitution to afford trivalent17,18, and nonavalent27sialodendrimers. Complete sugar deprotection furnished water-soluble α-thiosialodendrimers21,22, and29, which were used in protein-binding studies. Turbidimetric analysis confirmed the strong potential of sialodendrimers29having nine readily accessible sialic acid residues to bind, cross-link, and precipitate two different lectins. Preliminary results indicated that nonavalent α-sialodendrimer29had a greater affinity towards dimeric wheat germ agglutinin (WGA) and the lectin from the slugLimaxflavus(LFA) than the corresponding trivalent glycodendrimers21and22.Keywords: carbohydrate, dendrimer, sialic acid, gallic acid, lectin, wheat germ agglutinin,Limaxflavus.

ISSN:0008-4042    

DOI:10.1139/v97-177

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Electrodes of general composition IrxTi(1−x)O2with 0.2 ≤ x ≤ 1.0 were prepared on a Ti support by calcination of the chlorides at 450 °C. Ex situ and in situ characterization included the use of techniques such as scanning electron microscope (SEM), energy dispersive X-ray analysis (EDX), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). EDX showed a surface enrichment with Ti. The voltammetric charge was found to go through a maximum at 60% IrO2. O2evolution was studied in 1.0 mol dm−3HClO4by determining Tafel slopes and impedance parameters. Tafel slopes were found to vary between 40 and 60 mV depending on the overpotential range and the oxide composition. Solution and film resistance, film and double layer capacitance, and charge transfer resistance were determined as a function of potential and oxide composition. A reaction mechanism has been proposed. Separation of geometric and electronic effects has been attempted.Keywords: oxygen evolution, oxide electrode, electrocatalysis, electrochemical impedance spectroscopy, iridium dioxide.

ISSN:0008-4042    

DOI:10.1139/v97-178

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The lithium amide [3,5-Me2PhN(Ad)]Li•Et2O (L) reacts with ZrCl4(THF)2to give ZrClL3. Reactions of ZrClL3with MeLi and NaBH4produce the corresponding ZrMeL3(2) and Zr(BH4)L3(3), respectively. The molecular structures of2and3were determined by X-ray crystallography. Crystal data are as follows.2: C55H75N3Zr, FW 869.45, orthorhombic,Pcab;a = 19.2436(3) Å,b = 45.9342(4) Å,c = 21.2935(3) Å,V = 18822.2(4) Å3Z = 8; 3: C54H76BN3Zr, FW 869.25, orthorhombic;Pbc21,a = 11.5399(3) Å,b = 19.4091(4) Å,c = 20.4471(5) Å,V = 4579.72(19) Å3Z = 4.Keywords: zirconium, amide, alkyl, borohydride, structure.

ISSN:0008-4042    

DOI:10.1139/v97-179

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Electromotive force (EMF) measurements based on the redox reactionare reported for solutions of LiBr at concentrations 0.005 < cLiBr/(mol dm−3) < 0.1 in acetonitrile (AN), dimethyl sulfoxide (DMSO), andN.N-dimethylacetamide (DMA) in the temperature range 278.15 < T/K < 308.15. Gibbs energies of transfer and activity coefficients are estimated. The association constants of LiBr in AN, DMSO, and DMA from EMF measurements and the enthalpy of transfer AN → DMSO are compared to those from other methods of determination.Keywords: temperature-dependent EMF measurements, aprotic solvents, LiBr, TlBr(s) | TlxHg(l) electrode, activity coefficients, transfer quantities.

ISSN:0008-4042    

DOI:10.1139/v97-180

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The theory for the electrochemical impedance of surface reactions involving a single adsorbed species is presented. A new methodology is used, in which many harmonics are considered, and the differential equations are reduced to algebraic matrix equations. The amplitude of the ac potential perturbation is not assumed to be small, and nonlinear effects are taken into account. The amplitude dependence of the impedance and the second-harmonic response are investigated. The quasi-reversible electrosorption reaction and the hydrogen evolution reaction are considered in detail, assuming that the adsorbed species obeys the Langmuir isotherm.Keywords: electrochemistry, impedance, adsorption, hydrogen evolution reaction, second harmonic.

ISSN:0008-4042    

DOI:10.1139/v97-181

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Formal potentials from cyclic voltammetry and ionic conductivities from impedance measurements are used to probe anion–polymer interactions in electrochemically deposited films of polypyrrole. Hard anions (F−, Cl−, ClO4−) stabilize the oxidized form of the polymer more than soft anions (I−, SCN−). Anions of weak acids (F−and CN−) interact with the polymer particularly strongly and exhibit anomalously low mobilities. Hydrogen bonding with the N-H groups of oxidized polypyrrole is proposed.Keywords: conducting polymer, polypyrrole, impedance, ion transport, electrolyte effects, ion exchange.

ISSN:0008-4042    

DOI:10.1139/v97-182

出版商:NRC Research Press    

年代:1997

数据来源: NRC