John Graves

New evidence for the inverse dependence of mechanical and chemical effects on the frequency of ultrasound

Acoustic cavitation has been the subject of research and discussion for many years and it is the underlying driving force for sonochemistry. The collapse of acoustic cavitation bubbles in water near to a surface can bring about significant surface modification in terms of the mechanical damage caused by the asymmetric collapse of the bubbles which cause erosion and abrasion. A second effect of acoustic cavitation is the formation of short lived radicals caused by the breakdown of water inside the bubble. For the first time the dependence of these effects has been observed on the surface of a plastic material as a function of ultrasonic frequency.

The electrochemistry of Magnéli phase titanium oxide ceramic electrodes Part I. The deposition and properties of metal coatings

The electrodeposition of copper, gold, nickel, palladium and platinum onto Ebonex® ceramic cathodes has been studied. It is demonstrated that good quality deposits may be obtained and that the kinetics of the deposition and dissolution of metals are similar at Ebonex® to other common substrates (for example, Pt, C). In addition, the kinetics of some simple redox couples at coated and bare Ebonex® ceramic electrodes are compared; it is confirmed that such electron transfer reactions are very slow on the bare Ebonex® ceramic but when the surface is coated with a metal, the kinetics are similar to those on the bulk metal.

The reduction of oxygen on titanium oxide electrodes

Abstract The cathodic reduction of oxygen in 1 mol dm −3 sodium hydroxide solutions has been investigated at several types of titanium oxide cathodes. Layers of TiO 2 were prepared on titanium by spraying and thermal decomposition of solutions of titanium n -butoxide in 2-propanol and titanium tetrachloride in methanol+water and also by anodization; the reduction was also studied at Ebonex®, a conducting ceramic consisting mainly of Ti 5 O 9 . In all cases, the reduction of oxygen occurs largely by a 4e − reaction to water and the reaction occurs at potentials close to −1.0 V vs. SCE. Cyclic voltammetry in the absence of oxygen shows that, at these potentials, the surfaces undergo reduction and the electrochemistry of the Fe(CN) 6 4− /Fe(CN) 6 3− couple has been used to probe further the properties of the TiO 2 surfaces.

Controlled protein release from microcapsules with composite shells using high frequency ultrasound—potential for in vivo medical use

The possibility of protein release from polymeric microcapsules by means of low-power (up to a maximum of 3.2 W) high-frequency (850 kHz) ultrasound was studied. The release efficiency using these ultrasonic parameters that are close to those currently used in medical diagnostic and ultrasound treatment was compared to that achieved with a conventional 20 kHz 70 W ultrasonic probe. Microcapsules were made by polyelectrolyte multilayer assembly on 3–5 µm calcium carbonate particles with co-precipitated fluorescently labelled protein. Ultrasound induced protein release was monitored by supernatant fluorescence increase after sonication. The release efficiency is improved by the presence of gold nanoparticles in the microcapsule shell. The amount of gold nanoparticles in the shell was found to play an important role in release efficiency. The irradiation was carried out at several intensities and exposure times and evidence of microcapsule rupture after treatment was obtained by confocal and scanning electron microscopy.

The electrochemistry of Magnéli phase titanium oxide ceramic electrodes Part II: Ozone generation at Ebonex and Ebonex/lead dioxide anodes

Uncoated Ebonex is not a suitable anode material for the generation of ozone. By contrast, Ebonex electroplated with PbO2 can be highly stable in the forcing conditions essential to the formation of ozone and gives current yields comparable to lead dioxide on other substrates in both acid and neutral electrolytes.

The use of insoluble anodes in acid sulphate copper electrodeposition solutions

SUMMARY The use of insoluble anodes in horizontal acid copper electroplating machines is becoming the industry standard. Despite this fact there appears to be little published work on the optimisation of the anode material for this application. Although titanium coated with iridium dioxide is widely used for its long lifetime under oxygen evolution conditions, it appears that no consideration has been given to the effect of this oxide on other electroplating parameters, for example the oxidation of additives, pulse plating etc. This paper reviews the materials that have been employed as insoluble anodes in acid sulphate electrolytes including those used for electrodeposition, electrowinning operations, and other electrochemical processes. It considers the factors that affect the materials performance under oxygen evolving conditions and collates values from the literature for the oxygen evolution potential and Tafel slopes for this reaction that have been obtained for various metal oxides. From these data, a set of criteria is established which an insoluble anode material should meet if it is to be successfully employed in an acid copper horizontal electroplating machine.

Ultrasound assisted dispersal of a copper nanopowder for electroless copper activation

This paper describes the ultrasound assisted dispersal of a low wt./vol.% copper nanopowder mixture and determines the optimum conditions for de-agglomeration. A commercially available powder was added to propan-2-ol and dispersed using a magnetic stirrer, a high frequency 850 kHz ultrasonic cell, a standard 40 kHz bath and a 20 kHz ultrasonic probe. The particle size of the powder was characterized using dynamic light scattering (DLS). Z-Average diameters (mean cluster size based on the intensity of scattered light) and intensity, volume and number size distributions were monitored as a function of time and energy input. Low frequency ultrasound was found to be more effective than high frequency ultrasound at de-agglomerating the powder and dispersion with a 20 kHz ultrasonic probe was found to be very effective at breaking apart large agglomerates containing weakly bound clusters of nanoparticles. In general, the breakage of nanoclusters was found to be a factor of ultrasonic intensity, the higher the intensity the greater the de-agglomeration and typically micron sized clusters were reduced to sub 100 nm particles in less than 30 min using optimum conditions. However, there came a point at which the forces generated by ultrasonic cavitation were either insufficient to overcome the cohesive bonds between smaller aggregates or at very high intensities decoupling between the tip and solution occurred. Absorption spectroscopy indicated a copper core structure with a thin oxide shell and the catalytic performance of this dispersion was demonstrated by drop coating onto substrates and subsequent electroless copper metallization. This relatively inexpensive catalytic suspension has the potential to replace precious metal based colloids used in electronics manufacturing.

An electrochemical pretreatment and catalysation process for acrylonitrile-butadiene-styrene utilising silver(II) chemistry

SUMMARY The formation of silver(II) ions in nitric acid was studied using a rotating disc electrode at temperatures of 25°C and 50°C and a preparative H-type divided cell was used to generate dark brown silver(II) solutions at 50 mA cm−2, 50°C. When acrylonitrile-butadiene-styrene (ABS) samples were etched in this highly oxidising medium, residual silver(I) species trapped within the polymer cavities were reduced to metallic silver with a reducing agent and, upon exposure to an electroless copper solution, deposition was observed. An FM-01LC Laboratory Electrolyser was used to scale-up the process and peel strengths between the ABS substrate and metallic coating were measured. Adhesion equivalent to a chromic acid pretreatment was achieved. Hence a novel process based upon the aqueous electrochemistry of silver(II) has been developed for etching, catalysing and subsequently metallising ABS.

Additive process for patterned metallized conductive tracks on cotton with applications in smart textiles

Abstract The selective patterning of silver nanoparticles by a patent pending process to act as a catalyst for metallization with electroless copper was explored on cotton, with a view towards application in the wearable technology sector. Whole area coverage or tracks serving as point-to-point connections were achieved by depositing the catalyst via spraying, or in more controlled manner using a microdispenser, respectively. Optimization of the catalyst deposition is described, including substrate characterization via contact angle, FTIR and surface charge measurement. The effects of the copper plating bath temperature and dwell time in the plating bath are examined. With plating times as short as 10 min, samples of good conductivity (sheet resistance, R = <10 Ω/sq) and consistency were produced. A higher or lower plating temperature (compared to supplier recommended conditions) increased or reduced the amount of copper deposited, respectively. The technology was used to produce well-defined conductive tracks on cotton with widths between 1.5 and 4.0 mm.

Functionalised copper nanoparticles as catalysts for electroless plating

Electroless copper plating of insulating substrates, such as printed circuit boards, typically requires the pre-deposition of a catalyst layer onto the surface to initiate the chemical reactions. Pd/Sn based catalysts are widely used, but carry a high cost and in many cases require specialist pre-treatment of the substrate to achieve good adhesion. In this work, functionalised copper nanoparticles have been investigated as alternative catalysts for electroless deposition. Commercially available copper nanoparticles were functionalised with different organic molecules and their functionalisation was confirmed with X-ray photoelectron spectroscopy. The ability of these particles to act as a catalyst was demonstrated, however their effectiveness was found to depend on the nature of the organic molecules that were used in the functionalisation. Furthermore, significant variability was found between batches of samples in both the particle dispersion and attachment to the substrate surface, which affected the reproducibility of the coverage and adhesion of the subsequent electroless plating, for which further work is required to understand these effects.