The effect of catalyst film thickness on the magnitude of the electrochemical promotion of catalytic reactions

The effect of catalyst film thickness on the magnitude of the effect of electrochemical promotion was investigated for the model catalytic reaction of C₂H₄ oxidation on porous Pt paste catalyst-electrodes deposited on YSZ. It was found that the catalytic rate enhancement ρ is up to 400 for thinner (0.2 μm) Pt films (40,000% rate enhancement) and gradually decreases to 50 for thicker (1 μm) films. The Faradaic efficiency Λ was found to increase moderately with increasing film thickness and to be described semiquantitatively by the ratio 2Fr _o/I ₀, where r _o is the unpromoted rate and I ₀ is the exchange current of the catalyst–electrolyte interface. The results are in good qualitative agreement with model predictions describing the diffusion and reaction of the backspillover O^2- species, which causes electrochemical promotion.     

Nylon 6 polymerization in the solid state

The postcondensation of nylon 6 in the solid state was studied. The reactions were carried out on fine powder in a fluidized bed reactor in a stream of dry nitrogen in the temperature range 110–205°C and during 1–24 h. The solid-state polymerization (SSP) did not follow melt kinetics, but was found to be limited by the diffusion of the autocatalyzing acid chain end group. Factors thought to influence SSP were studied, e.g., heat treatment, starting molecular weight, and remelting. Surprisningly, heat treatment had little effect, but the starting molecular weight had a strong effect on the reaction rate. The higher the starting molecular weight, the faster the reaction. This could be explained as a changing concentration distribution of the reactive groups in the solid state on SSP. The kinetics of the SSP had more than one region, and the rate of reaction for conversions of over 30% could be expressed as ? dc/dt = k(c/t), where k is a dimensionless constant independent of temperature with a value of 0.28. The integrated form has the form ? In(c/c_o) = k In(t/τ), where c_o is the acid end-group concentration at the start, t is the reaction time, and τ is the induction time. The value of τ is both dependent on the starting concentration c_o and the reaction temperature and has an activation energy of 105 kJ/mol.     

Electrodeposition from a fluidized bed electrolyte. II. Effects of bed porosity and particle size

Mass transfer from a fluidized bed electrolyte containing inert particles has been found to depend on bed porosity and particle size. The optimum porosity was found to vary from 0.52 – 0.57 with decreasing particle size but mass transport increased with particle size.A mass transfer entry length effect was observed on the cylindrical cathode but its position within the bulk of the bed was found not to be critical, thus indicating that the hydrodynamic entry length was small. The limiting current density was found to vary as (d _e/L _e)^0.15 whered _e is the annular equivalent diameter andL _e the electrode length.List of symbols Re_I modified Reynolds No. =U _o d _p /v(1–) - Re_II particle Reynolds No. =U _o d _p /v - Re_O sedimentation Reynolds No. =U _i d _p v (constant value) - Re_t terminal particle Reynolds No. =U _t d _p /v - Sc Schmidt No. =v/D - St_I modified Stanton No. =k _L /U _o - C _b bulk concentration, M cm^–3 - D diffusion coefficient, cm² s^–1 - d _t tube diameter, mm - d _e electrode equivalent diameter, mm - d _p particle diameter, mm - bed porosity - zF Faradaic equivalence - cd current density - i _L limiting current density, mA cm^–2 - i _LO limiting current density in the absence of particles - k _L mass transfer coefficient, cm s_–1 - L _e electrode length, mm - m, n constants or indices - v kinematic viscosity, cm² s^–1 - U _o superficial velocity, cm s^–1 - U _i sedimentation velocity, cm s^–1     

Cold rolling of polymers. 1 Influence of rolling on properties of amorphous polymer

Strips of ductile, amorphous thermoplastic polymers such as polycarbonates, acrylonitrile-butadiene-styrenes, polysulfones and polyphenylene oxides have been reduced in thickness by passing them through a metalworking rolling mill at room temperature. Properties of the rolled strips were studied as a function of the thickness reduction. In addition to rolling unidirectionally, cross rolling (biaxial rolling) was also studied using equal thickness reductions in each direction. The maximum thickness reduction (t_o — t_f)100/t_o which could be achieved was approximately 60 per cent regardless of the polymer studied here. Stress-strain curves, density changes, thermal stability, hardness and Izod impact strengths have been determined as a function of thickness reduction and sheet direction.     

Liquid Explosive Evaporative Removal of Submicron Particles from Hydrophilic Oxidized Silicon Surfaces

A pulsed CO₂ laser-based system, operating at a wavelength of 10.6 μm, was used as a cleaning tool to remove particles as small as 0.1 μm from hydrophilic, oxidized silicon surfaces. The laser beam served as a fast heating source to induce the explosive evaporation of a water film deposited on the particle-contaminated surface. The resulting explosive forces were high enough to expel particles from the surface efficiently. The contaminant particles used were 0.1 μm alumina, 0.1–0.2 μm silica, and 0.1 μm polystyrene latex.

For each of these, the cleaning efficiency was monitored as a function of the laser fluence, the thickness of the deposited water film and the number of cleaning cycles. Whatever the nature of the particles, the cleaning efficiency was characterized by an upper limit of the energy density, determined to be 1.5 J/cm², at which substrate damage occurred. At all lower laser fluences, the removal efficiency was particle-dependent.

The thickness of the deposited water film was varied by changing the time of exposure of the surface to water vapor, the vapor flow being fixed at 4700 ml/min. An exposure time of 1.5 s was found to be the most effective. Increasing the number of cleaning cycles permitted the evaluation of the effect of the zeta potentials of the particles with respect to that of the surface.     

A simple method for identifying bubbling/jetting regimes transition from large submerged orifices using electrical capacitance tomography (ECT)

The bubbling–jetting transition regimes from large orifice submerged in water were investigated for various orifice diameters. A simple and fast way for identifying the regime transition was successfully developed using electrical capacitance tomography (ECT). In all the experiments deionised water was liquid phase and air was gas phase. Orifice gas velocity (V_N) and orifice diameter (d_o) were varied from 0.8 to 186 m/s and 4–21 mm, respectively. It was found that the V_N,trans. strongly depends on the orifice diameter. In the small orifice diameter (d_o < 10 mm), V_N,trans. greatly decreases with the increase of orifice diameter. However, in the large orifice diameter (d_o > 10 mm), the effect of orifice diameter on the transition velocity is insignificant. Finally, the data obtained by ECT compares with other works and the dimensionless orifice Reynolds number (Re_o ～11,000) is preferred to identify the bubbling–jetting transition regimes.     

Photon transmission method for studying void‐closure kinetics during coalescence of hard latex particles

The contribution of viscous flow to void‐closure processes during film formation with hard latex particles was studied. Film optical clarity was used to follow the progress of this event. The latex films were prepared from poly (methyl methacrylate) (PMMA) particles and annealed in 10 min time intervals above the glass transition (T_g) temperature. Scanning electron microscopy (SEM) was used to detect the variation in the physical structure of the annealed films. To mimic the latex film‐formation process, Monte Carlo simulations were performed for photon transmission through the latex film and the number of transmitted and scattered photons are calculated as a function of the mean free path. A relation for transmitted light intensity, I_tr versus void closure (time)^1/2 (t^1/2) was derived by using the Vogel–Fulcher viscosity equation. The viscosity constant, B, was produced using this I_tr(t^1/2) relation at various temperatures and found to be 12.8 × 10³ K. It is shown that Monte Carlo results justified the I_tr(t^1/2) relation. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 981–988, 1999     

Effects of Ti ion deposition on corrosion resistance of WE43 alloy

Ti films with different thicknesses were successfully deposited on the surface of WE43 alloy by filtered cathode vacuum arc technology, and the microscopic morphology, structural composition, and corrosion resistance of the films were studied by means of X-ray diffractometer, X-ray photoelectron spectroscopy and scanning electron microscope. The results show that when the deposition time of Ti ions is 800 s, the thickness of the Ti film is 2.35 μm, the surface of the film is dense, and there are few defects. Meanwhile, Ti800 alloy has the best corrosion resistance among the four modified alloys. It has a corrosion current density (I_corr) of 2.9 μA·cm⁻², which is about 50 times lower than that of unmodified alloy. This conclusion is also confirmed by the complete film layer of Ti800 alloy and the tight bonding with the substrate after immersion experiments. Good corrosion resistance is attributed to a dense and relatively chemically stable TiO₂/Ti structure in simulated body fluid corrosive media.     

Film formation of poly (methyl methacrylate) latex with pyrene functional poly (divinylbenzene) microspheres prepared by click chemistry

This work reports on the application of steady state fluorescence (SSF) technique for studying film formation from poly(methyl methacrylate) (PMMA) latex and poly(divinylbenzene) (PDVB) microsphere composites. Pyrene (P) functionalized PDVB cross‐linked spherical microspheres with diameters of 2.5 μm were synthesized by using precipitation polymerization technique followed by click coupling reaction. The diameter of the PMMA particles prepared by emulsion polymerization were in the range of 0.5–0.7 μm. PMMA/PDVB composite films were then prepared by physically blending of PMMA latex with PDVB microspheres at various composition (0, 1, 3, 5, 10, 20, 40, and 60 wt%). After drying, films were annealed at elevated temperatures above T_g of PMMA ranging from 100 to 270°C for 10 min time intervals. Evolution of transparency of the composite films was monitored by using photon transmission intensity, I_tr. Monomer (I_P) and excimer (I_E) fluorescence intensities from P were measured after each annealing step. The possibility of using the excimer‐to‐monomer intensity ratio (I_E/I_P) from PDVB microparticles as a measure of PMMA latex coalescence was demonstrated. Diffusion of the PMMA chains across the particle–particle interfaces dilutes the dyes, increasing their separation. The film formation stages of PMMA latexes were modeled by monitoring the I_E/I_P ratios and related activation energies were determined. There was no observable change in activation energies confirming that film formation behavior is not affected by varying the PDVB composition in the studied range. SEM images of PMMA/PDVB composites confirmed that the PMMA particles undergo complete coalescence forming a continuous phase in where PDVB microspheres are dispersed. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

The tearing test as a means for estimating the ultimate properties of rubber

SBR, unfilled and filled with glass beads, MT, and HAF carbon blacks, was tested for tearing energy, rupture values in simple tension, tear diameter, and strain distribution at four rates and seven temperatures. The energy density to failure at the tear zone W_t was obtained from the tearing energy τ and the natural tear diameter d using a modified Rivlin and Thomas relationship W_t ≈ τ/d. This was then compared with the nominal energy density at rupture in simple tension W. It is shown that always W_t > W (sometimes W_t/W = 10), that W_t is subject to a smaller statistical scatter than W, and that W_t is more amenable to the WLF type of superposition than W. It is concluded that W_t and not W is the strength-determining property. Where W data permitted superposition, it is followed the WLF equation. It is presumed that so would W_t. τ, although more superposable than W, showed a bigger shift factor than that dictated by WLF, the difference being the result of the temperature dependence of the diameter. The reinforcing effects of the various fillers are also discussed. It is shown that the carbon black fillers increase both W_t and d. Glass beads have only a small effect on d and none on W_t.     

Effect of sol infiltrations on electrical properties of PZT

Abstract

Thin PZT films with a thickness of approximately 1 μm can readily be fabricated using a layered sol-gel deposition technique. The maximum thickness obtainable is limited by the time taken and the tendency of the films to crack and spall when many layers are deposited. Thicker layers may be obtained by depositing a powder-sol slurry whereby a PZT powder is mixed with a sol of approximately the same composition. Using this layered slurry deposition technique it is possible to obtain films with a thickness in excess of 20 μm. The resulting films, however, are often porous, leading to poor properties and making subsequent patterning difficult. A technique for increasing the density of such films through the use of controlled heat treatments and sol infiltration is presented. It is shown that with increased levels of sol infiltration the density and dielectric constant of the films are maximised. Measurements of piezoelectric properties indicate that sol infiltrations have no significant effect on d₃₃. A sample with approximately 10% closed porosity was obtained following four infiltration steps per layer. This resulted in a maximum dielectric constant of approximately 700 and a d₃₃ of 70 pC N ^-1 (poling conditions: 8 V μm ^-1 for 5 min at 200°C). Examination of cross-sections of the films produced shows that for intermediate levels of sol infiltration (typically between 1 and 3) a density gradient is obtained with higher densities observed nearer the base of the film. It is postulated that the observed density gradient is a result of continued infiltration from the upper layers when further layers of slurry are deposited. The effects of changing process variables such as the number of infiltration steps and firing temperature on film structure and properties are discussed.     

Stress relaxation of elongated strip of poly(vinylidene fluoride) in ethyl acetate vapor

Poly(vinylidene fluoride) films in ethyl acetate vapor were studied at 30°C for vapor pressures of p = 0, 12, 30, 40, 66, 85 torr and elongations ε = 4.5%, 7%, 9.5%, 19%, 29%, and 44%. A cyclic experiment was also performed at ε = 7% and p = 40 torr for three sorption/desorption cycles. Assuming, as a first approximation, that the stress relaxation of the “dry” and “wet” polymers is proportional to the elastic strain, ε_el, empirical calculations were performed and compared to experimental results. In general, the presence of a vapor or gas in a polymer matrix enhances the stress relaxation by softening or plasticizing the polymer and transforming a portion of the elastic strain, ε_el, into the plastic strain, ε_pl. As the transformation continues, the sorption and stress of the wetted elongated sample change simultaneously with time until an optical “overshoot” and a mechanical or stress “undershoot” is observed. This result seems to be the consequence of the differential change of the stress of the “dry” and “wetted” samples with sorption time, τ = t ? t_o(t = time; t_o = initial sorption time), which depends on the differential time dependencies of the transformations of the elastic and plastic strains.     

New approach for the estimation of kinetic parameters in emulsion polymerization systems. II. Homopolymerization under conditions where n̄ > 0.5

A new approach for the estimation of kinetic parameters in emulsion polymerization systems in which the average number of radicals per particle exceeds 0.5 is presented. The approach uses the time evolution of the conversion in chemically initiated systems and is based on a model that includes fundamental parameters such as the propagation rate constant, k_p, the termination rate constant in the polymer particles, k_t, the rate coefficient for initiator decomposition, k_I, and the entry, k_a, and exit, k_d, rate coefficients. It was found that k_p, k_t, k_I, k_a, and, under some circumstances, k_d can be accurately estimated provided that termination in the aqueous phase is significant. When the extent of the aqueous phase termination is negligible, only k_p, k_t, and k_I can be estimated. The effect of both the experimental noise level and the run-to-run irreproducibility on the accuracy of the estimates was studied. In addition, it was found that significant inaccuracies resulted from the poor determination of the exact time when polymerization begins. A method to circumvent this problem was proposed.     

Insect sex pheromones

The half-lives (t _1/2) for evaporative loss ofn-alkyl andn-alkenyl acetates from rubber septa were determined at temperatures varying from 15 to 35 °C. The changes int _1/2 with temperature gave high correlations with the equation, Int _1/2 = H/RT+y _o where H is the heat of vaporization,R is the gas constant,T is the absolute temperature, andy _o is a constant. Half-lives changed dramatically with temperature and the degree of change with temperature increased with increasing molecular weight. For mixtures, component ratios changed with temperature, but the degree was modest. At 20 °C there was a 7.5-fold ratio oft _1/2 between members of the homologousn-alkyl orn-alkenyl acetates differing by two carbon atoms. The large change int _1/2 with temperature and with number of carbon atoms is a consequence of the thermodynamic relationships and the temperature range of pheromone usage. Therefore, a similar degree of change inf _1/2 with temperature and number of carbon atoms will apply to other formulations of the same type (those in which the rate of evaporation is first order). The values oft _1/2 at 20 °C mainly agreed very well with those reported previously at room temperature. However, our previously reported values for pentadecyl and hexadecyl acetate were revised. Half-lives were shown to depend on the vapor pressure of a compound in the formulation substrate, but not on the vapor pressure of the pure compound.Mention of a commercial or proprietary product does not constitute an endorsement by the USDA.     

Application of chronopotentiometry and derivative chronopotentiometry with an alternating current to the study of a slow charge transfer in a surface confined redox system

General analytical expressions for the potential-time (E-t) and derivative-potential ((dt/dE)-E) curves of a electroactive monolayer exhibiting a quasi-reversible behaviour, corresponding to the application of an alternating current time function of the form I(t) = I₀ cos(ωt), are presented. The use of this programmed current gives rise to singular and characteristic electrochemical responses. The alternating current also allows to obtain cathodic or both anodic and cathodic responses depending on whether the depletion of the adsorbed species was complete or not, and without using more than one applied current. Moreover, in this last case, it is possible to distinguish a reversible or an irreversible process by means of a simple visualisation of the E-t or (dt/dE)-E curves. Easy methods for estimating thermodynamic and kinetic parameters of the electroactive film are proposed and experimentally tested and compared with those previously obtained by using Cyclic Voltammetry.     

Axial mixing of liquid in a turbulent-bed contactor

The axial dispersion of liquid in a 12-in. turbulent-bed contactor has been investigated for three packing sizes: ½-in., 1-in. and 1½-in. The gas and liquid flow rates were varied from 500 to 2700 lb./(hr.)(sq. ft.) and from 1500 to 11,000 lb./(hr.)(sq. ft.) respectively. The transient response technique using KCl solution as the tracer was employed for this purpose. The experimentally determined residence-time distribution curves were interpreted by means of a one-dimensional dispersion model. The axial dispersion coefficient, D_L, was found to increase with increasing gas flow rate, liquid flow rate, or packing size. In terms of Peclet number (N_Pe = ū d_p/D_L), the present data showed that N_Pe was dependent on Reynolds number (N, = d_p ū ρ/μ), Gallileo number (N_Ga = d_p³ ρ³ g/μ²), and reduced gas mass velocity (Δ = (G-G_mf)/G_mf), but the ratio of the Peclet number for a turbulent contactor to the Peclet number for a fixed-bed contactor, N_Pe/N_Peo, depended only on Δ, and the diameter ratio d_p/d_t. A correlation of N_Pe/N_Peθo with Δ and d_p/d_t is presented.     

Mixing Time in Intermediate‐Sized Orbitally Shaken Reactors with Small Orbital Diameters

Orbitally shaken reactors (OSR) are widely used in bioprocess development; however, a scaling law between large reactors, usually shaken in incubators at an orbital diameter of d_o = 1.5–5 cm, and microwell plates, shaken in benchtop thermomixers at d_o = 3 mm, is still missing. Here, the mixing time was measured in two reactors with the same volume but either cylindrical or square geometry for d_o = 3 mm. For such a small d_o, the acceleration mode to reach the final speed in the cylinder was found to greatly affect the free surface oscillations and thus the mixing time. The stepwise mode resulted in mixing times approximately six times smaller than in the direct mode. The natural frequency of the reactor, which is independent of d_o, was found to be an effective scaling parameter for systems with small d_o.     

The rotating cylinder electrode

The transfer of mass onto a rotating cylindrical nickel electrode was investigated at relatively low rates. The simple electrochemical reaction of ferricyanide ion in an alkali medium was applied for this purpose. In the investigations particular attention was paid to the phenomenon of the penetration of eddies into the laminar sublayer. A modification and broadening of the basic Taylor expression, namely Taylor's linear theory, was proposed for the systems with a greater interelectrode distance. The experimental results can be better interpreted with a thus modified expression.Symbols A surface area - b constant - c _b,c _s bulk and surface concentrations - d _c diameter of rotating inner cylinder - D diffusion coefficient - zF Faradaic equivalence - h height - k _f friction factor - i ₁ limiting current density - I ₁ limiting current - dimensionless number - k _L mass transfer coefficient - N rotation per minute - r _i,r _o radii of inner and outer cylinders - = r _i peripheral velocity - x distance along the electrode - y distance normal to the electrode - _N, _Pr thickness of Nernst diffusion and Prandtl hydrodynamic boundary layers - _o thickness of laminar or viscous sublayer - coefficient of viscosity - density - kinematic viscosity - angular velocity - (Re) Reynolds number,d _c/ - (Sc) Schmidt number,/D - (Sh) Sherwood number,k _L d _c/D - (St) Stanton number,k _L/     

Dynamic mechanical property and interlaminar shear strength of the carbon fabric reinforced polyetherimide composite based on the polyetherimide resin films

In this study, the laminates reinforced with the concentrated nitric acid or acetone treated carbon fabrics were prepared based on polyetherimide films with different thickness including 30 μm and 50 μm, respectively. 4 Harness Satin (4HS) and 5 Harness Satin (5HS) carbon fabrics were used as the reinforcements of the composite laminates. Three impact factors, including the polyetherimide film thickness, fabric treatment method and fabric type, were considered in this study. Interlaminar shear strength (ILSS) measurement shown that the thicker polyetherimide film (50 μm), 4HS carbon fabric and the nitric acid treatment of the fabric could be used to increase the ILSS value because of the improvement of the interfacial property for the laminate. The 50 μm thickness polyetherimide films used in the laminates improved the storage modulus, and decreased the glass transition temperatures (T _gs) by DMA or DSC. It was because that the better interfacial property and the stronger mobility of the polymer chain under the greater residual internal stress in the laminate was obtained with the increase of the polyetherimide film thickness. The nitric acid treatment of the fabric increased the T _gs measured by DMA and DSC, and decreased the tan δ peak values of the laminates because of the stronger interfacial adhesion between the fiber and the resin and the decreased mobility of the polymer chain. In addition, the effects of above three impact factors on the ILSS, storage modulus, loss modulus, tan δ and the T _g of the laminate were discussed in detail by ILSS, DMA and DSC measurement, respectively. POLYM. COMPOS., 38:663–672, 2017. © 2015 Society of Plastics Engineers     

Drainage of thin films beneath parabolic and spherical caps

The variation in film thickness h with time t for the approach of an infinite sphere to a plane horizontal surface (β = 1) or of two infinite spheres (β = 2) is given by: For finite spherical caps with edge radius r_f the variation is much more complicated and also involves the parameter S = βr²_f/2ah_o. Fortunately, the gradient is the same in both cases, providing t is large enough (the critical value of t increases with decreasing S). A similar result is obtained if the spherical cap is approximated by a parabolic cap with apex curvature 1/a equal to that of the sphere. In both cases the variation in dynamic pressure close to the centre of the draining film is identical and independent of the radial position where the dynamic pressure falls to zero when the film thickness is small. MacKay and Mason (1961) measured the film thickness beneath a sphere of finite size approaching a horizontal plane and experimentally verified Equation (b). This does not however, as they assumed, prove the correctness of Equation (a), which only applies to infinite spheres. The more complicated equations describing the approach of finite spheres and parabolic caps are presented in this paper.