Dual Particle Size Research Articles

Formation of ultrafine uniform gold nanoparticles by sputtering and redeposition

Uniformly distributed Au nanoparticles with controllable size were fabricated by focused ion beam bombardment of thin gold films. In situ scanning electron microscopy and ex situ transmission electron microscopy were used to characterize the nanoparticles. Results show that a dual particle size distribution was generated at low ion fluence, while highly uniform Au particles with diameters around 2 nm formed at high fluence. The balance between sputtering and redeposition is responsible for the formation and size control of the nanoparticles. Optical absorption measurement revealed strong size dependant resonances that are attributed to the surface plasmon resonance of the Au particles.

Tribological behavior of dual and triple particle size SiC reinforced Al‐MMCs: a comparative study

PurposeThe aim is to study the tribological behavior of dual particle size (DPS) and triple particle size (TPS) SiC reinforced aluminum alloy‐based metal matrix composites – MMCs (Al/SiCp MMC).Design/methodology/approachAl‐MMCs with DPS and TPS of SiC were prepared using 20 wt% SiC and developed using stir‐casting process. The TPS composite consist of three different sizes of SiC and DPS composite consist of two different sizes of SiC. The tribological test was carried out using a pin‐on‐disc type tribo‐test machine under dry sliding condition.FindingsThe TPS composite exhibited better wear resistance properties compared to DPS composite. It is anticipated that when a composite is integrated with small, intermediate and large SiC particle sizes (which is known as TPS) within the same composite could be an effective method of optimizing the wear resistance properties of the developed material.Practical implicationsThis study provides a way to enhance the tribological behavior of automotive tribo‐components such as brake rotor, piston, cylinder, etc.Originality/valueThis investigation compares the tribological behavior of DPS and TPS SiC reinforced aluminum MMCs.

Toughening of polycarbonate: Effect of particle size and rubber phase contents of the core‐shell impact modifier

AbstractThe toughening behavior of polycarbonate modified with core‐shell type particles was investigated. The alloys were found to exhibit maximum impact strength upon addition of a modifier with a poly(butyl acrylate) rubbery core of 0.25 μm diameter. The incorporation of particles with diameter greater than 0.25 μm resulted in decreased impact strength. The influence of rubber phase contents on toughness was also studied. It was observed that the alloys exhibited maximum impact strength upon addition of 4 wt % rubber phase. Further increase in the rubber phase content resulted in reduced impact strength. Fractography of the samples showed that, below 4 wt % rubber phase content, the fracture occurs mainly by internal crazing and, from 4 wt % onward, only by shear deformation. When the effect of dual particle size distribution was analyzed, it was found that there was only a moderate increase in toughness compared with alloys containing monosized particles. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 748–755, 2005

Dual particle size (DPS) composites: effect on wear and mechanical properties of particulate metal matrix composites

Al–Si–Mg alloy composites reinforced with up to 15 vol.% of SiC particles were prepared by the melt-stirring process. The wear behavior, under low loads, of the unreinforced Al–Si–Mg alloy and the metal matrix composites (MMCs) was investigated using a ball-on-disc test at room temperature under dry conditions. It was found that the maximum effective increase in wear resistance (ratio of percentage reduction in weight loss and volume percent of SiC added to achieve the reduction) occurred for the composite with about 7 vol.% SiC. Metallographic investigations have revealed that the wear zone of the unreinforced alloy consisted of a hardened layer, in which fragmented Si phase was observed to be redistributed and aligned parallel to the wear direction. The delamination of material from the hardened layer was responsible for higher wear loss observed in the unreinforced alloy. The thickness of the hardened layer formed on the MMC specimens (10–30 μm as against 30–60 μm in the unreinforced specimens) was reduced by the fragmentation of the incorporated SiC particles. The fragmentation of Si phase was also found to be of much lesser magnitude in the MMC specimens. This led to lesser wear in the case of the MMC specimens. It is proposed that an effective method of optimizing the wear resistance and mechanical properties of low volume fraction composites is to incorporate small and large SiC particle sizes (DPS) within the same composite. The improvement in wear resistance of the DPS composites could be attributed to the ability of the larger SiC particles to carry a greater portion of the applied load, as well as to the function of the larger SiC particles in protecting the smaller SiC particles from being gouged out during the wear process. Furthermore, the incorporation of larger particles increased the charpy impact energy of the DPS composites with respect to the composite with fully small sized particles.