Carboxylic acids were investigated as a means to fabricate a superhydrophobic and corrosion resistant aluminum surface. Alkaline etching produced a hierarchically rough, superhydrophilic and hydroxylated Al surface which could then be modified by immersion in ethanol solution of carboxylic acids of different alkyl chain lengths, from hexanoic to octadecanoic. Acids with chain length longer than seven carbon atoms acted as corrosion inhibitors, but only those with long chains (e.g., octadecanoic acid) acted as a corrosion barrier and made the surface superhydrophobic with water contact angles over 150 degrees. The morphology, topography and chemical composition of unmodified Al and etched Al modified by carboxylic acids were studied using surface analytical tools (scanning electron microscopy with chemical analysis, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry). Modelling based on density functional theory was performed to help explain experimental observations and to provide a rationale of why only carboxylic acids with long enough chains were effective in reducing the rate of corrosion. The reason was attributed to their ability to form more stable and protective organic films. Aluminum surface prepared under appropriate conditions was superhydrophobic, corrosion resistant and durable and showed self-cleaning and delayed ice-melting properties.
We studied the effect of porosity and pore morphology on the functional properties of Pb(Zr 0.53 Ti 0.47 )O 3 (PZT) ceramics for application in high frequency ultrasound transducers. By sintering a powder mixture of PZT and polymethylmetacrylate spherical particles (1.5 and 10 mm) at 10808C, we prepared ceramics with ,30% porosity with interconnected micrometer sized pores and with predominantly ,8 mm spherical pores. The acoustic impedance was ,15 MRa for both samples, which was lower than for the dense PZT. The attenuation coefficient a (at 2.25 MHz) was higher for ceramics with ,8 mm pores (0.96 dB mm 21 MHz 21 ), in comparison to the ceramic with smaller pores (0.56 dB mm 21 MHz 21 ). The high a value enables the miniaturisation of the transducer, which is crucial for medical imaging probes. The dielectric and piezoelectric coefficients, polarisation, and strain response decreased with increased porosity and decreased pore/grain size. We suggest a possible role of pore/grain size on the switching behaviour.
Electrophoretic deposition (EPD) is an attractive method for the fabrication of a few tens of micrometer-thick piezoelectric layers on complex-shape substrates that are used for manufacturing high-frequency transducers. Niobium-doped lead-zirconate titanate (PZT Nb) particles were stabilized in ethanol using poly(acrylic acid) (PAA). With Fourier-transform infrared spectroscopy (FT-IR), we found that the deprotonated carboxylic group from the PAA is coordinated with the metal in the perovskite PZT Nb structure, resulting in a stable ethanol-based suspension. The hydroxyl group from the polyvinyl butyral added into the suspension to prevent the formation of cracks in the as-deposited layer did not interact with the PAA-covered PZT Nb particles. PVB acts as a free polymer in ethanol-based suspensions. The electrophoretic deposition of micro- and nanometer-sized PZT Nb particles from ethanol-based suspensions onto electroded alumina substrates was attempted in order to obtain uniform, crack-free deposits. The interactions between the PZT Nb particles, the PAA, and the PVB in ethanol will be discussed and related to the properties of the suspensions, the deposition yield and the morphology of the as-deposited PZT Nb thick film.
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