ABSTRACT
By designing a unimorph suitable for the material properties of (K, Na)NbO3-based lead-free piezoelectric ceramics (KNN), we have developed a piezoelectric sounder with a sound pressure level that is superior to that of similar devices based on Pb(Zr, Ti) [Formula: see text] (PZT) over a wide temperature range. The KNN ceramics used in this work have two disadvantages: their piezoelectric constant, d31 , at room temperature is less than 80% of that of PZT, and their piezoelectric properties deteriorate because of phase transitions to the orthorhombic phase at low temperatures. The former issue was alleviated via design of a thin-layer unimorph that uses the specific mechanical properties of KNN, i.e., a large Young's modulus and low specific gravity when compared with the corresponding properties of PZT; a unimorph was then fabricated with both a vibration velocity and a resonance frequency that are comparable to those of PZT unimorphs. The latter issue was then resolved by reducing the resonance frequency of the unimorph relative to the acoustic resonance frequency of the resonator, which produced a stronger vibration-acoustic coupling effect within the temperature range in which the piezoelectric properties of KNN are lower. The KNN sounder designed in this manner exhibited a sound pressure level that was 1.4 dB greater than that of a PZT sounder at room temperature, and the range of change in the sound pressure level from -20 °C to 90 °C was 2 dB less than that for the PZT sounder.
ABSTRACT
Size-controlled Pt nanoparticles were prepared on multi-wall carbon nanotubes (MWCNTs) decorated with polypyrrole matrix overlayers and exhibited superior oxygen reduction reaction (ORR) performance as electrocatalysts. The copolymerization of a new Pt4-pyrrole complex and pyrrole monomer in the presence of MWCNTs produced size-controlled Pt nanoparticles with diameters of 1.5 ± 0.5 nm. The present size-controlled Pt nanoparticles showed better durability than non-regulated Pt nanoparticles without polypyrrole and a commercial Pt/C catalyst during the ORR at the fuel cell cathode without substantial aggregation of the size-controlled Pt nanoparticles.
ABSTRACT
A novel multiwall carbon nanotube (MWCNT) and polypyrrole (PPy) composite was found to be useful for preparing durable Pt nanoparticle catalysts of highly regulated sizes. A new pyrene-functionalized Pt4 complex was attached to the MWCNT surface which was functionalized with PPy matrix to yield Pt4 complex/PPy/MWCNT composites without decomposition of the Pt4 complex units. The attached Pt4 complexes in the composite were transformed into Pt0 nanoparticles with sizes of 1.0-1.3 nm at a Pt loading range of 2 to 4 wt %. The Pt nanoparticles in the composites were found to be active and durable catalysts for the N-alkylation of aniline with benzyl alcohol. In particular, the Pt nanoparticles with PPy matrix exhibited high catalyst durability in up to four repetitions of the catalyst recycling experiment compared with nonsize-regulated Pt nanoparticles prepared without PPy matrix. These results demonstrate that the PPy matrix act to regulate the size of Pt nanoparticles, and the PPy matrix also offers stability for repeated usage for Pt nanoparticle catalysis.
