Electroless deposition of nickel-boron coatings using low frequency ultrasonic agitation: Effect of ultrasonic frequency on the coatings.

The effect of ultrasound on the properties of Nickel-Boron (NiB) coatings was investigated. NiB coatings were fabricated by electroless deposition using either ultrasonic or mechanical agitation. The deposition of Ni occurred in an aqueous bath containing a reducible metal salt (nickel chloride), reducing agent (sodium borohydride), complexing agent (ethylenediamine) and stabilizer (lead tungstate). Due to the instability of the borohydride in acidic, neutral and slightly alkaline media, pH was controlled at pH 12±1 in order to avoid destabilizing the bath. Deposition was performed in three different configurations: one with a classical mechanical agitation at 300rpm and the other two employing ultrasound at a frequency of either 20 or 35kHz. The microstructures of the electroless coatings were characterized by a combination of optical Microscopy and Scanning Electron Microscope (SEM). The chemistry of the coatings was determined by ICP-AES (Inductively Coupled Plasma - Atomic Emission Spectrometry) after dissolution in aqua regia. The mechanical properties of the coatings were established by a combination of roughness measurements, Vickers microhardness and pin-on-disk tribology tests. Lastly, the corrosion properties were analysed by potentiodynamic polarization. The results showed that low frequency ultrasonic agitation could be used to produce coatings from an alkaline NiB bath and that the thickness of coatings obtained could be increased by over 50% compared to those produced using mechanical agitation. Although ultrasonic agitation produced a smoother coating and some alteration of the deposit morphology was observed, the mechanical and corrosion properties were very similar to those found when using mechanical agitation.

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 effect of ultrasound on the gold plating of silica nanoparticles for use in composite solders.

In order to produce electronic devices that can survive harsh environments it is essential that the solder joints are very reliable and this has led to the development of composite solders. One approach to the manufacture of such solders is to disperse silica nanoparticles into it to improve their mechanical and fatigue characteristics. However, this is difficult to achieve using bare silica particles because they are not "wettable" in the solder matrix and so cannot be dispersed efficiently. In an attempt to alleviate this issue it has been found that if the silica nanoparticles are first plated with gold then this problem of wetting can, to some extent, be overcome. However, the particles must be completely encapsulated with gold which, using the method previously described by workers at Kings College London, was found to be difficult to accomplish. In this short communication the effect of ultrasound on the gold coverage is described. Different frequencies of ultrasound were used (20, 850 and 1176 kHz) and it was found that higher frequencies of ultrasound improved the coverage and dispersion of the gold nanoparticles over silica during the seeding step compared to simple mechanical agitation. This subsequently led to a more complete encapsulation of gold in the plating stage.

Further developments in self-fertilising geotextiles for use in pervious pavements.

Geotextiles incorporating inorganic nutrients (particularly phosphorous) to enhance the growth of oil degrading microoganisms when geotextiles are used in pervious pavement applications have been shown to be effective in the past. However the cost and manufacturing difficulties have been a barrier to their use. A polypropylene random mat geotextile incorporating an alternative polymer additive as a source of phosphorus has been investigated as a potential self-fertilising geotextile. Experiments are reported which investigate nutrient leach rates, biofilm formation and biodegradation activity.

Increased levels of soluble P-selectin correlate with iron overload in sickle cell disease.

Homozygous sickle cell disease (SCD) is characterised by increased soluble P-selectin (sP-selectin), suggesting increased platelet activation, and high non-transferrin-bound iron (NTBI), reflecting iron overload, possibly due to blood transfusion. Hypothesising a relationship between these processes, we measured both markers in 40 SCD patients and 40 age/gender/race-matched controls, finding increased levels of each marker in the patients (both P<0.001), but more pertinently a significant NTBI/sP-selectin correlation (r=0.52, P<0.001). Both indices were increased in the blood of 15 recently-transfused patients compared with 25 three-month transfusion-free patients (P<0.001), but only sP-selectin was higher in present sickle crisis (P<0.001). We suggest that increased NTBI associated with blood transfusion iron overload in SCD may promote platelet activation.