Mass transfer and electrocrystallization analyses of nanocrystalline nickel production by pulse plating

A comparison between the experimental process parameters employed for the pulse plating of nanocrystalline nickel and the solution-side mass transfer and electrokinetic characteristics has been carried out. It was found that the experimental process parameters (on-time, off time and cathodic pulse current density) for cathodic rectangular pulses are consistent and within the physical constraints (limiting pulse current density, transition time, capacitance effects and integrity of the waveform) predicted from theory with the adopted postulates. This theoretical analysis also provides a means of predicting the behaviour of the process subject to a change in the system, kinetic and process parameters. The product constraints (current distribution, nucleation rate and grain size), defined as the experimental conditions under which nanocrystalline grains are produced, were inferred from electrocrystallization theory. High negative overpotential, high adion population and low adion surface mobility are prerequisites for massive nucleation rates and reduced grain growth; conditions ideal for nanograin production. Pulse plating can satisfy the former two requirements but published calculations show that surface mobility is not rate-limiting under high negative overpotentials for nickel. Inhibitors are required to reduce surface mobility and this is consistent with experimental findings. Sensitivity analysis on the conditions which reduce the total overpotential (thereby providing more energy for the formation of new nucleation sites) are also carried out. The following lists the effect on the overpotential in decreasing order: cathodic duty cycle, charge transfer coefficient, Nernst diffusion thickness, diffusion coefficient, kinetic parameter () and exchange current density.Nomenclature A constant employed in Fig. 8, (nFi₀)/(RT _e C _a)(s^–1) - B constant in Equation 38 (V²) - C cation concentration (molcm^–3) - C _a capacitance of double layer (µFcm^–2) - C _s cation surface concentration (molcm^–3) - C _s ^* dimensionless cation surface concentration, C _s/C (–) - C cation bulk concentration (molcm^–3) - D diffusion coefficient of cation (cm²s^–1) - E total applied potential (V) - E ⁰ standard cell potential (V) - F Faraday constant (Cmol^–1) - function defined in Appendix C(–) - Fr frequency of waveform (Hz) - f _i,p function defined in Appendix C for pth period (–) - f _i, function defined in Appendix C for p period (–) - G _j function defined in Appendix B (–) - gi function defined in Appendix B (–) - i current density (Acm^¨) - i _ac unsteady fluctuating a.c. current density (Acm^–2) - i _c capacitance current density (Acm^–2) - i _dc steady time-averaged d.c. current density (Acm^–2) - i _F Faradaic current density (Acm^–2) - i _lim limiting d.c. current density (Acm^–2) - i ₀ exchange current density (Acm^–2) - i _PL limiting pulse current density, i ₁{Cs = 0 at t = (p – 1) T + t ₁(Acm^–2) - i ₁ cathodic pulse current density (Acm^–2) - i ₂ relaxed or low current pulse current density (Acm^–2) - iin anodic pulse current density (Acm^–2) - i ^* dimensionless current density, i/|i _lim| (–) - i ₀ ^* dimensionless exchange current density, i _dc/|i _lim| (–) - i _dc ^* dimensionless steady time-averaged d.c. current density, i _dc/|i _lim| (–) - i _PL ^* dimensionless limiting cathodic pulse current density, i _PL/|i _lim| (–) - i _PL,p ^* dimensionless limiting pulse current density at pth period, i ₁(C _s = 0)/|i _lim| (–) - i _PL, ^* dimensionless limiting pulse current density for p , i ₁(C _s = 0)/|i _lim| (–) - i ₁ ^* dimensionless cathodic pulse current density, i ₁/|i _lim| (–)     

Rheological properties of poly(vinyl chloride) / epoxidized natural rubber blends. Part II: The effect of processing variables

The effect of processing variables on the rheological properties of PVC/ENR blends was investigated. The role of crosslinking in determining the flow behavior of blends was also examined by means of dynamically cured blends. It was found that PVC/ENR blends yield melts that are power law fluids. The flow of the melts improves with an increase in temperature and shear rate. However, the introduction of crosslinks reverses this trend, although under more rigorous conditions, the influence of crosslinks is superseded, and subsequently, flow becomes shear rate and temperature dependent. PVC/ENR systems also manifested elastic phenomena. The dependence of the elastic phenomena such as die swell and melt fracture on L/D ratio of the die was demonstrated.     

Thermal Fatigue Behavior of Thick and Porous Thermal Barrier Coatings Systems

High-temperature thermal fatigue causes the failure of thermal barrier coating (TBC) systems. This paper addresses the development of thick TBCs, focusing on the microstructure and the porosity of the yttria partially stabilized zirconia (YPSZ) coating, regarding its resistance to thermal fatigue. Thick TBCs, with different porosity levels, were produced by means of a CoNiCrAlY bond coat and YPSZ top coat, both had been sprayed by air plasma spray. The thermal fatigue resistance of new TBC systems and the evolution of the coatings before and after thermal cycling was then evaluated. The limit of thermal fatigue resistance increases depending on the amount of porosity in the top coat. Raman analysis shows that the compressive in-plane stress increases in the TBC systems after thermal cycling, nevertheless the increasing rate has a trend which is contrary to the porosity level of top coat. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.     

Untersuchungen zur Charakterisierung des Mischsystems Sojaöl/epoxidiertes Sojaöl mittels FTIR/h-ATR-Spektroskopie

Characterization of Soybean Oil/Epoxidised Soybean Oil Mixtures by FTIR/h-ATR-Spectroscopy Controlling of technical production process requires a rapid method of analysis. This article describes a Fourier transform-infrared/horizontal attentuated total reflectance (FTIR/h-ATR) method to determine the iodine value and the degree of epoxidation in binary mixtures of soybean oil and epoxidised soybean oil. This analytical method will also be tested regarding the chemical reaction of epoxidation of soybean oil.     

New adhesion measurement technique for coated cutting tool materials

Adhesion properties of wear resistant coatings on cutting tool materials are essential to their performance in technical applications. It is therefore necessary to characterize the coating adhesion by an appropriate measurement technique which reveals both critical adhesion values as well as information on time dependent debonding. In particular, a quantitative and reproducible technique is required rather than largely qualitative methods such as indent or scratch tests. In addition, for multilayer coatings, the location of the weakest interface is required to facilitate improvement of interfacial integrity. Accordingly a sandwich double cantilever beam (DCB) test was developed and used to measure the adhesion properties of coatings on cermets. Additionally, the structure of the coatings in the as fabricated state and after mechanical testings were characterized by optical microscopy, SEM and TEM. With quantitative adhesion measurements and investigations of the interface microstructure, a comprehensive characterization of coating adhesion on cutting toolmaterials was achieved.     

Phase relationships in the systems RE2O3-Al2O3-SiO2 (RE = rare earth element, Y, and Sc)

A literature survey and recent results on phase relationships in the quasi-ternary systems RE₂O₃-Al₂O₃-SiO₂ are given. The investigated systems exhibit extended ternary solid solutions, RE_9.33+2x(Si_{1_x}Al_xO₄)₆O₂ (withx up to ~0.33) and/or RE₄Al_{2(1_X)}Si_2xO_9+x (withx up to ~0.3), which are based on the quasi-binary phases RE_9.33(SiO₄)₆O₂ and RE₄A1₂O₉, respectively. The former is encountered only in systems with laige RE³⁺ ions (e.g., La³⁺), whereas the latter is found in systems with small RE³⁺ ions (e.g., Yb³⁺); in systems with medium-sized KE³⁺ ions (e.g., Gd³⁺) both types exist Quasi-ternary compounds are known only in the La, Ce, and Sc systems. Severe discrepancies in reported ternary eutectic temperatures led to a need for their accurate redeteimination.     

Photoelectrochemical study of passive films on aluminum

Photocurrent spectroscopy and Photoelectrochemical Laser Imaging (PECLI) were performed on passive films on aluminum. Cathodic photocurrents were measured between 2.7 and 6.9 eV. Photoelectrochemical laser images of the oxide covered aluminum surface were recorded in the presence of non-corroding (no Cl⁻) and corroding (Cl⁻) electrolyte.     

Toward time-resolved soft X-ray microscopy using pulsed fs-high-harmonic radiation

Coherent soft X-ray sources open the way to new capabilities in high-resolution imaging, site- and element-specific spectroscopy and biomicroscopy. In this paper we demonstrate imaging with a table-top soft X-ray microscope. By combining a laser driven high-harmonic light source, optimized for having the maximum brightness at around 100 eV, a pair of multilayer mirrors to select a narrow spectral band and acting simultaneously as a condenser and a Fresnel zone plate as microscope objective, we were able to resolve 200 nm structures of a diatom sample. Further, the pulsed nature of our X-ray source offers the possibility of time-resolved spectromicroscopy with a temporal resolution in the order of a few femtoseconds.     

MICROSTRUCTURE AND EXTENDED SOLID SOLUBILITY OF Tb IN RAPIDLY SOLIDIFIED Ag-Tb ALLOY

The 0,05—0.08 mm thick splat foils of Ag-Tb alloy,containing Tb up to 10 at.-%,were made by the hammer-anvil technique.The cooling rate was in order of 10~6 K/s.The metastable extension of solid solubility of Tb in the alloy was measured to be up to 5 at.-% by lattice parameter method.The secondary phase in metastable eutectic structure was identi- fied as Ag_3Tb from diffraction pattern.The microstructure and micro-defect in as-quenched Ag-Tb splat foil were also observed.