Yong K. Kim

Fabrication and Rate Performance of a Microfiber Cathode in a Mg-H2O2 Flowing Electrolyte Semi-Fuel Cell

Three-dimensional electrodes based on an array of carbon microfibers were prepared by a process called direct-charging electrostatic flocking. The cathodes comprised carbon fibers 11 μm in diameter and 500 μm long that protruded from a titanium foil support like blades of grass. The fiber density was 125,000 fibers per cm 2 of geometric area. The fibers were coated with an alloy of Pd and Ir to catalyze hydrogen peroxide reduction. The electrochemical performance of catalyst-coated carbon microfiber arrays (CMAs) was investigated in a flowing electrolyte Mg-H 2 O 2 semi-fuel cell. In these studies, CMA-based cathodes showed higher voltages at high current densities, better power densities, and equivalent H 2 O 2 utilization compared to planar cathodes with the same loading of catalyst.

Surface flocking as a possible anti-biofoulant

Abstract Fouling organisms create difficulties for aquaculturists by weighing down materials and constricting net openings. Research on anti-fouling began with toxic chemicals and has more recently moved to non-toxic methods focusing on settlement cues of invertebrates. Surface texture is one physical cue to which both invertebrate larvae and algal spores respond. Flocking is a process that makes smooth surfaces fibrous by adding electrostatically charged fibers to an adhesive coated surface. To test the effects of flocking on recruitment, polyvinyl chloride (PVC) plastic panels that were untreated, primed with adhesive, and flocked were deployed subtidally in the Westport River estuary, Westport, MA, USA for 1 month exposure periods in 1998. Species composition was determined and compared among treatments. To test for effects only on barnacle recruitment, wood panels were deployed subtidally in Clarks Cove, New Bedford, MA and PVC panels were deployed in the subtidal of Eel Pond, Woods Hole, MA; Cape Cod Canal at Massachusetts Maritime Academy, Bourne, MA; and in Point Judith Pond, RI. Flocking surfaces resulted in lower recruitment of green and brown algae, but had no effect on red algae. For invertebrates, flocking was effective at inhibiting the recruitment of encrusting animals, had no effect on stoloniferous animals, and increased the abundance of tube-building polychaetes and solitary ascidians.

Comparing the fracture toughness of 3-D braided preform composites with z-fiber-reinforced laminar composites

Organic polymer engineering composite materials based on layered fabrics have many advantageous properties and processing features. However, performance properties of the layered OPECs, especially impact strength, delamination resistance, and fracture toughness are poor. Three-dimensional preforms fabricated with 3-D weaving, knitting and braiding techniques, are employed to improve the shortcomings of 2-D layered fabric reinforcements. z-directional microfiber-reinforced laminar composites were recently developed to improve impact strength and fracture toughness without reducing in-plane performance properties at minimal added cost and at higher productivity in the Flock Materials Laboratory at the University of Massachusetts Dartmouth. The effectiveness of laminar composite z-directional microfiber reinforcement (by a flocking process) in improving fracture toughness was compared with that of a 3-D braided 8-layer glass fiber preform/epoxy composite plate. The results show that the Mode I fracture toughness (GI) of the 3-D braided preform reinforced composites are about 10 times of the 2-D layered glass fabric laminar composites (control) as expected. This is comparable to the results of z-directional microfiber-reinforced composites; up to 9 times increase in GI over that of 2-D glass fabric/epoxy laminar composite (control). The presence of through-thickness microfiber (flock fiber) reinforcements in the matrix resin between reinforcement layers is found not to reduce the in-plane mechanical properties; the fracture toughness however, increases significantly.

Manufacture of Thick Cross-Section Composites Using a Pre-Catalyzed Fabric Technique

The development of a technique is reported for the manufacture of thick unsaturated polyester matrix resin composites using pre-catalyzed glass fabric. Composites over 2 cm thick using glass fabric that was pre-catalyzed (sized) with benzoyl peroxide were compared to composites made using conventional premixed catalyst and resin compounds. The pre-catalyzed fabric is shown to result in reduced internal temperatures during curing. This allows for the construction of thick fiber reinforced composite materials that do not suffer thermal degradation during the curing process. Mechanical testing of prepared thick composites demonstrated that the pre-catalyzed glass fabric composites were significantly stronger than conventionally prepared composites. The center regions of pre-catalyzed composites were about 80% stronger under tension, 25% stronger in compression and 35% stronger under shear than those of conventionally prepared composites of the same thickness. The pre-catalyzed composites were also more uniformly consolidated. Previous work aimed at the manufacture of thick composites has utilized controlled curing by use of expert systems, local resistance heating within the composite or the addition of chemical inhibitors. A method for staged curing has also shown considerable promise. None of these methods, however, has enabled high volume production of high quality thick composites. This paper presents the results of a new method for manufacture of thick composites based on a pre-catalyzed fabric technique.

Damage Analysis of Projectile Impacted Laminar Composites

The bending toughness, strength retention, resistance to damage and bending stiffness of glass fiber mat, laminar composites under high strain rate impact loading conditions was studied. One of the main disadvantages of laminar composite materials is their poor interlaminar shear strength. Recent work has demonstrated a method of Z-direction reinforcement of these composites using electrostatic flocking techniques improve delamination resistance and fracture toughness without degrading the composite’s tensile strength or other in-plane properties when loaded quasi-statically. The Z-direction reinforcement is accomplished by electrostatically flocking short fibers perpendicular to and between the composite ply layers. In this study, composite samples were prepared using the flocking method in two fabrication modes by the; so-called Z-Axis “wet” and ZAxis “dry” procedures. In this work, Z-direction reinforced composite panels (including a non reinforced control) that were previously projectile impact damaged, were tested using established mechanical testing procedures. Damage areas were quantified and compared using image processing techniques. Three point bending tests were also conducted on these projectile impact damaged panels to determine and compare their bending toughness, strength retention and modulus. The results show that Z-Axis reinforcement by the flocking technique improves the overall mechanical strength and stiffness properties of glass fiber mat laminar composites. For example, Z-Axis reinforced projectile damaged and not damaged glass fiber mat composite laminates are found to have flexural strengths 9% to 15% higher and a flexural modulus (stiffness) 22% to 26% higher than comparable (not Z-Axis flock reinforced) glass fiber mat samples.

Impact force loss behavior of flocked surfaces

The impact force loss behavior of flocked energy absorbing materials (FEAM) was experimentally studied in the context of double-side flocked FEAM element layered structures. A ball drop test determined the force loss per cent (FL%) properties of various assembled panels. This study showed that: (a) FEAM layers are most effective when used in multiple layer configurations. (b) When fabricating multi-layer two-side flocked FEAM layer configurations, a film or fabric divider sheet should be placed between adjacent flocked layers to prevent the flocked fibers from intermeshing with each other during compressional deformation. (c) FEAM elements perforated with 6.4u2009mm (¼”) diameter holes, 12.7u2009mm (½”) off staggered centers, exhibit a higher FL% per areal density compared to non-perforated FEAM panels. (d) Promising improvements in FL% properties are found by sandwiching either foam or spacer fabric between two FEAM layers. These three-layer structures are found to have higher FL% values than individual foam or spacer fabric components. A possible synergistic effect might be operating. (e) Low strain rate (5 and 50u2009mm/min) compressional load deflection rate data on combination FEAM/ vinyl nitrile foam/FEAM layers have shown that the initial ‘hump’ in the foam’s stress–strain curve is eliminated. FEAM layers and their foam and spacer fabric combinations should lead to creating effective impact energy absorbing pads for sport, military and civil servant applications.