Voltammetric study of halide ion adsorption on platinum in perchloric acid solutions

Periodic current/potential curves were taken potentiostatically at 30 mV/sec on smooth platinum in 1 N HClO₄ with different additions of HCl, HBr, and HI, in the potential range between hydrogen evolution and deposition of oxygen or of the respective halide ion. The effect of increasing halide ion concentration, starting at 10⁻⁶ M, on hydrogen adsorption and oxygen adsorption was studied systematically. Impedance measurements were made at 1000 c/s under the same conditions as the measurements of the current/potential curves. It is concluded from the dependence of the double layer capacitance upon the bulk concentration of halide ions in the double layer region that nearly a monolayer of adsorbed ions is present there for ₀c_Cl⁻ ≈ 10⁻² M, ₀c_Br ≈ 10⁻⁴ M, and ₀c_HI ≈ 10⁻⁵ M. The measurements at larger concentrations, especially for I⁻, show additional effects which are due to the deposition of halides and to the reverse reaction.     

The effect of the interface/interphase on fiber composite properties

The interfacial region between fibers and matrix in fiber composites governs the transfer of forces between the relatively weak and compliant matrix and the reinforcing fibers. An effective interphase can ensure that the mechanical properties of the composite reflect the high strength and modulus of the fibers. Although composites can be made with the expected strengths and moduli, it is not entirely clear why this is achieved: Tests with critical composites, i.e., those containing very short aligned fibers, do not show the expected stress-strain behavior. This paper examines the effect of an interphase having a shear modulus that is less than that of the matrix. It is found that to explain the Young's moduli of the short fiber composites, the interphase must have a very low modulus indeed; i.e., a few kPa at most. In addition, the strength results can be accounted for only if we assume that the short lengths of fiber used in the experiments had higher strengths than anticipated. Although agreement between experiments and theory is thus not very good, the small amount of experimental evidence available indicates a need for further systematic experiments on critical (i.e. short aligned fiber) composites before firm conclusions are drawn.     

The effect of interphase curing on interphase properties and formation

Fiber-optic evanescent wave FTIR spectroscopy was combined with phase imaging AFM to examine two thermosetting polymer matrix composite systems. The epoxy/NMA system data from the fiber-optic, evanescent wave FTIR analysis showed incomplete curing (～75% complete) in the region near the fiber, but essentially complete (～95% complete) curing in the bulk. Conversely, the unsaturated polyester system exhibited essentially complete curing (～95% complete) both near the fiber and in the bulk material. For the same samples, phase imaging AFM indicated that the epoxy/NMA system had an ～2.5 micron thick interphase, while the unsaturated polyester system showed no interphase between the fiber and the matrix. Therefore, the presence of the interphase in the epoxy/NMA system can be attributed to the incomplete curing next to the fiber. In addition, the systems chosen allowed the reactivity of adsorbed γ-APS coupling agent to be assessed simultaneously with polymer curing. For the epoxy/NMA system, the amine band decreased about 54% during curing. For the polyester system, the amine band decreased 43% during curing.     

Thermodynamic studies of phosphate adsorption on Pt(1 1 1) electrode surfaces in perchloric acid solutions

The thermodynamics of the so-called perfectly polarizable electrode was employed to analyze the total charge densities for a nearly defect-free Pt(1 1 1) electrode in a series of NaH₂PO₄ solutions with an excess of inert electrolyte (0.1 M HClO₄) at constant ionic strength and pH. Thermodynamic analysis using both electrode potential and charge density as independent electrical variables is described. The Gibbs excess, Gibbs energy of adsorption and charge numbers both at constant electrode potential and constant chemical potential for anion adsorption at the Pt(1 1 1) surface have been determined. The calculated electrosorption valencies and charge numbers at constant chemical potential are close to two electrons per adsorbed anion, suggesting that in the absence of co-adsorbed species, HPO₄²⁻ is the predominant adsorbed species. The maximum Gibbs excess of adsorbed hydrogenphosphate attains a value of ≈3.2 × 10¹⁴ ions cm⁻² which corresponds to a coverage of ≈0.22 ML.     

Comparative voltammetric study of methanol oxidation and adsorption on noble metal electrodes in perchloric acid solutions

Periodic current/potential curves were measured potentiostatically on smooth electrodes of platinum, iridium, rhodium, and gold at 30 mV/s in perchloric acid solutions with different additions of methanol (10⁻³ M to 1 M). Information on methanol adsorption was obtained from impedance measurements at 1000 c/s by volcammetry with superimposed a.c. voltage. The current/potential curves look similar on Pt and Pd on the one hand, and on Ir and Rh on the other hand. There is no noticeable methanol oxidation on gold. The peak current of the first wave during the anodic sweep decreases considerably in the order Pt> Pd> Rh> Ir. The capacitive component of the impedance shows methanol adsorption in the hydrogen and double layer region. The shape of the current/potential curves and the methanol adsorption are strongly influenced on platinum metals by oxygen layers which are formed or reduced electrochemically during the sweeps in different potential ranges.     

Substituted tertiary arsine and phosphines as interfacial adsorption inhibitors for corrosion of zinc in perchloric acid

The effect of triphenylarsine, triphenylphosphine and tri-p-tolylphosphine on the corrosion of zinc in HClO₄ at 30° C was studied. A significant decrease in the corrosion rate of zinc is obtained by the addition of these compounds. The corrosion rate is a function of the temperature, pH of the medium and the concentration of the inhibitors. The percentage protection calculated from weight loss and polarization methods are in good agreement. The apparent free energies of adsorption of inhibitors for different possible modes of adsorption are evaluated. The experimental data obtained are in agreement with the corrosion inhibition of zinc by interfacial adsorption of inhibitors.     

The mechanism of the aqueous perchloric acid isomerization of oleic acid to γ-stearolactone

The migration of the double bond in the reaction of oleic acid with aqueous 67% deuteroperchloric acid occurs by the reversible intermolecular esterification of carboxylic acid by olefin; when a double bond reaches the Δ^4,5 position and intramolecular carboxylic acid-olefin, esterification occurs to yield γ-stearolactone. Presented in part at the AOCS Meeting, Houston, Texas, 1965.     

An EQCM study of polyethyleneglycol 8000 adsorption and its coadsorption with Cl ions on Pt in perchloric acid solutions

The adsorption of the additive polyethyleneglycol 8000 (PEG8) and its coadsorption with Cl⁻ ions was investigated by cyclic voltammetry and linear potential scans in conjunction with simultaneous measurements of the frequency change of an electrochemical quartz crystal microbalance (EQCM). Data obtained from the studies of EQCM for solutions of HClO₄ containing PEG8, shows the formation of a peak (IcI) in the potential range from 0.2 to 0.4 V during the cathodic potential scan, which is due to the adsorption of PEG8 onto Pt. Analysis of simultaneously recorded massograms and voltammograms revealed that the adsorption of PEG8 occurs via a non-Faradaic process, and that no adsorption of PEG8 is observed at the open circuit potential. As the concentration of PEG8 in the solution was increased over the range  M, the degree of coating by PEG8 on the Pt surface increased to 0.21. The presence of Cl⁻ ions in the solution inhibited PEG8 adsorption, and the degree of inhibition gradually increased with increasing Cl⁻ concentration.     

The effect of added solvents on soy oil lutein adsorption by silicic acid

It has been reported that addition of isopropanol to a soy oil miscella inhibits the binding of soy lutein to added silicic acid by competitive adsorption. It was suggested that the competition was based on the polarity of the miscella constituents. This investigation studied the effects of a homologous series of lower alcohols to competitively inhibit lutein binding to silicic acid from a soy oil hexane miscella. Lutein binding inhibition by molecules of carbon chains with the same lengths, but with different functional groups, was also examined. Minor differences were found between members of a homologous series of alcohols. A similar result was found with short-chain fatty acids. The ability of various functional groups to displace lutein from silicic acid was dependent on the molecules’ ability to form hydrogen bonds, rather than on polarity.     

The effect of a multicomponent silane primer on the interphase structure of aluminum/epoxy adhesive joints

The structure of films formed by a multicomponent silane primer applied to an aluminum adherend and the interactions of this primer with an amine-cured epoxy adhesive were studied using X-ray photoelectron spectroscopy, reflection-absorption infrared spectroscopy, and attenuated total reflectance infrared spectroscopy. The failure in joints prepared from primed adherends occurred extremely close to the adherend surface in a region that contained much interpenetrated primer and epoxy. IR spectra showed evidence of oxidation in the primer. Fracture occurred in a region of interpenetrated primer and adhesive with higher than normal crosslink density. The primer films have a stratified structure that is retained even after curing of the adhesive.     

732阳离子交换树脂吸附L-组氨酸的特性

测定25℃下732阳离子交换树脂吸附L-组氨酸的动力学曲线和吸附等温线,考察了pH值、硫酸铵浓度、L-赖氨酸和L-精氨酸对吸附的影响。结果表明,Freund lich方程可以较好地描述732阳离子交换树脂对L-组氨酸的吸附,由Freund lich方程求得其平衡吸附量为142.32 g/L;吸附率随pH值的增大而减小,适宜在小于5.4时吸附;NH4+的存在使L-组氨酸的吸附率明显下降,当NH4+浓度达到1.0 mol/L时吸附率仅为42.32%;L-赖氨酸或L-精氨酸的存在使吸附率略微减小。     

Effect of perchloric acid on the molecular weight and yield of poly-THF

Polytetramethylene glycol (molecular weight range 1000–8000) was prepared by the polymerization of tetrahydrofuran (THF) using a binary catalyst system of fuming sulfuric acid and perchloric acid. When 28% fuming sulfuric acid alone was used as the catalyst, the average molecular weight of polymer was low, the maximum value being 1000–1100. By the combination of fuming sulfuric acid with a small amount of perchloric acid, the average molecular weight of the polymer was increased to about 8000. Furthermore, the molecular weight was readily controlled in the range of 1000 to 8000 by varying the amount of the binary catalyst.     

The effect of a surfactant on mixer—settler operation

A single stage mixer—settler was used to investigate the effect of surfactant on the mass transfer rate in the system water—HNO₃—30 vol.% TBP/dodecane. The interfacial tension of this system first falls then rises with increasing sodium lauryl sulphate (SLS) concentration. The addition of SLS makes the stage efficiency, which is closely related to k_ha, the product of the individual mass transfer coefficient of HNO₃ in the aqueous phase, and average interfacial area per unit volume of mixing chamber, to increase significantly due to an increase in the value of a. A maximum k_ha value of 0.53 litres^?1, a minimum value of interfacial tension, and phase inversion which converted the aqueous phase from continuous to dispersed were observed at around the critical micellar concentration (100 parts 10^?6) of SLS in the system of an aqueous to organic phase ratio of 0.2.     

The effect of competitive adsorption on the rate of diffusion

Evidence is presented that the apparent diffusion coefficient of one penetrant can be increased by competition from another penetrant for the same adsorption sites in polyester. The competition is governed by the relative diffusivities of the penetrants and their affinities for the adsorption sites.     

Characterization of soybean protein concentrate—stearic acid/palmitic acid blend edible films

The effect of incorporating commercial stearic acid/palmitic acid blend (SA/PA, 63/37 wt %) into hydrophilic soybean protein concentrate (SPC) film‐forming solutions at neutral and alkaline pH on some selected properties of edible cast films was investigated. SA/PA‐added SPC film exhibited a significant increase in translucency, being more relevant for films obtained at pH 7. This was associated with the more heterogeneous morphology of such films as observed by scanning electron microscopy. Calorimetric measurements and X‐ray diffraction studies confirmed the presence of crystalline fatty acids in films at pH 7 and new crystalline structures at pH 10 due to interactions or reactions between SPC and SA/PA blend. Fourier Transform infrared spectroscopy results confirmed the incorporation of fatty acids into SPC and revealed the occurrence of interactions between both components, depending on the film‐forming emulsion pH. Moisture absorption isotherms at high relative humidity (RH) were determined and experimental data were adequately fitted by Peleg's empirical equation. Control SPC films produced at pH 7 were distinctly more moisture resistant than those at pH 10 owing to the more charged protein molecules at alkaline pH. The increased moisture resistance of SA/PA‐added‐SPC film at pH 10 was related to the more homogeneous dispersion of fatty acid particles within the protein matrix. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Organofunctionalized montmorillonite/epoxy nanocomposites: The effect of interlayer cation distribution on mechanical properties

The present study indicates that a distribution of alkylammonium chain lengths in the interlayer of montmorillonite (MM) results in a greater degree of dispersion into an epoxy matrix (or possibly different polymer matrices) and improved ultimate tensile strengths. This hypothesis is supported by x‐ray diffraction (XRD) data from the modified MM clays, which clearly shows that an increase in d‐spacing does not result in an improvement in tensile strengths. Additional support is obtained from DSC analyses of the first and second heats of the treated clays which indicate that the C6 alkyl amine in a deposited (C18 + C6) alkyl ammonium mixture results in intercalation pathways for the epoxy resin. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers     

The electrochemical reduction of ruthenium(IV) in perchloric acid solutions on platinum electrodes

Two reversible waves are observed for the reduction of Ru(IV) on platinum electrodes. Each wave is the sum of two one-electron steps according to:

Potentials (vs nhe) and species are given for 1.0 M HClO₄ solutions; more hydrolysed products are formed in less acid solutions. The tetrameric Ru(III) ion slowly decomposes to a more stable Ru(III) species, probably a dimeric ion.     

Particle agglomeration and the value of the exponent n in the richardson—zaki equation

The expansion data of Mogan for fine solids fluidized with gas under pressure have been re-examined. By assuming that particle aggregation had occurred, a modified Richardson-Zaki relationship was derived involving an “effective” porosity. An improved correlation of the data was obtained and the index n was reduced to the range 3.0 – 3.5 from the value 6.0 used by Mogan . It is suggested that the large values of n often reported in the literature for fine particles may be due to increased effective particle volume caused by agglomeration or irregular particle shape.