ABSTRACT
The realization of a c-axis oriented aluminum nitride thick film on aluminum substrates is a promising step in the development of transducers for applications with a working temperature up to about 600 °C. The present paper deals with the realization of AlN thick films by means of reactive magnetron sputtering with a pulsed DC power supply, operating in continuous mode for 50 h. Two values (0.4 and 0.8) of nitrogen concentration were used; operative pressure and power were set at 0.3 Pa and 150 W, respectively. The thickness of the obtained aluminum nitride films on the aluminum substrate, assessed with a profilometer, varied from 20 to 30 µm. The preferential orientation of AlN crystals was verified by X-ray diffraction. Finally, as the main focus of the investigation, the films underwent electrical characterization by means of an LCR-meter used on a parallel plate capacitor set-up and a test system based on a cantilever beam configuration. AlN conductivity and ε33 permittivity were derived in the 100 Hz-300 kHz frequency range. Magnetron sputtering operation with nitrogen concentration equal to 0.4 resulted in the preferred operative condition, leading to a d31 piezoelectric coefficient, in magnitude, of 0.52 × 10-12 C/N.
ABSTRACT
The addition of magnetic particles to inorganic matrices can produce new composites exhibiting intriguing properties for practical applications. It has been previously reported that the addition of magnetite to concrete improves its mechanical properties and durability in terms of water and chloride ions absorption. Here we describe the preparation of novel magnetic geopolymers based on two different matrices (G1 without inert aggregates and G2 with inert quartz aggregates) containing commercial SrFe12O19 particles with two weight concentrations, 6% and 11%. The composites' characterization, including chemical, structural, morphological, and mechanical determinations together with magnetic and electrical measurements, was carried out. The magnetic study revealed that, on average, the SrFe12O19 magnetic particles can be relatively well dispersed in the inorganic matrix. A substantial increase in the composite samples' remanent magnetization was obtained by embedding in the geopolymer SrFe12O19 anisotropic particles at a high concentration under the action of an external magnetic field during the solidification process. The new composites exhibit good mechanical properties (as compressive strength), higher than those reported for high weight concretes bearing a similar content of magnetite. The impedance measurements indicate that the electrical resistance is mainly controlled by the matrix's chemical composition and can be used to evaluate the geopolymerization degree.
