Key Engineering Materials Vols. 317-318

Abstract: Reaction bonded MgSiN2 (RBMSN) was prepared by direct nitridation of a Si/Mg2Si/Mg/Si3N4 powder compact in a temperature range of 1350-1550°C. The oxygen content of MgSiN2 was in the range of 0.4 – 0.6 wt%. A thermal stability examination showed that MgSiN2 is stable up to 1400°C at 0.1 MPa N2 pressure. The activation energy of decomposition calculated from the temperature dependence of weight loss is H = 383 kJ⋅mol-1. The time dependence and nitrogen pressure dependence of MgSiN2 decomposition was also investigated at constant temperature. MgSiN2 is stable at 1560°C in 0.6 MPa nitrogen atmosphere. Using these experimental data together with the heat capacity published in a literature the Gibbs free energy of formation of MgSiN2 was calculated in a temperature range 300-2500 K. Dense MgSiN2 ceramics or MgSiN2/Si3N4 composites with fluorine-based additives were prepared by hot pressing. The composite materials had a 4-point bending strength of 427 MPa and Vickers hardness (HV1) of 20.8 GPa, respectively. The indentation fracture toughness was 5.3 MPa.m1/2, due to the presence of elongated β-Si3N4 grains. The dielectric constant of dense reaction bonded MgSiN2 at 100 kHz was 9.5-10, while that of MgSiN2/Si3N4 composite in a wide range 50 – 6000, depending on composition and heat treatment.

Abstract: A new type of ultrasonic spray nozzle was fabricated employing PZT and Pb-free piezoelectric device. The spray nozzle was designed to disperse chemicals in a water treatment mixing tank. The piezoelectrics were packaged in an aluminum case with silicone resin for the aqueous solution proof packaging. Chemicals were dispersed with high efficiency, and the ultrasonic fine particle spraying was able to reduce the chemicals consumption. The removal efficiencies of heterotrophic bacteria and Escherichia coli by chemicals injected using designed ultrasonic spray nozzle were higher than the conventional methods.

Abstract: Piezoelectric ceramic pressure sensors have been attracted great interest due to their simple and miniature structure compared with conventional sensors such as strain gauge sensor. A new type of static pressure sensor by using a change of permittivity upon applied mechanical pressure has been studied in this work. BaTiO3 ceramics with/without a small amount of Mn were used as sensing materials and the effect of poling treatment on their sensor performance was investigated. An anti-ferroelectric material, NaNbO3, was also examined. All materials could detect the change of pressure through the frequency shift of CR oscillator. Change of permittivity of non-doped BaTiO3 and Mn doped BaTiO3 without poling treatment were larger than that of PZT used as a reference, that is, BaTiO3 ceramics had higher-pressure sensitivity. BaTiO3 and relative materials, however, needed transit time to reach the steady state, while NaNbO3 was independent to the time. Conclusively, it seems that BaTiO3 and relative materials without poling treatment and the anti-ferroelectric material, NaNbO3, become possible candidates as a pressure sensor using permittivity change.

Abstract: Fe/MgO nanocomposites, which are applicable to high frequency electronic devices, were fabricated by ultrasonic spray pyrolysis and selective reduction processes. Transmission electron micrographs showed that nano ferromagnetic Fe particles were isolated by MgO insulating matrix. With the increase of the reduction temperature, the particle size and saturation magnetization of the nanocomposites increased, which resulted in the decrease of the coercive force and the increase of the permeability. Furthermore, the ferromagnetic resonance peak of the nanocomposites was not observed up to 9 GHz.

Abstract: LaxBa1-xTi1-xYxO3 (0≤x≤0.5) powders were synthesised in air at 1400°C by the conventional solid state method. According to the X-ray results, the tetragonal distortion in undoped (x=0) BaTiO3 (space group P4mm) decreases with x and samples with x ≥0.05 show cubic symmetry (space group Pm3m). For x≥0.05, the lattice parameter increases linearly with x, until orthorhombic LaYO3 appears as a secondary phase for x>0.45. Dielectric properties of dense (>95% of the theoretical X-ray density) ceramics were studied at both radio and microwave frequencies. The permittivity maximum is shifted towards lower temperatures with increasing x and a broad permittivity peak is observed for samples with 0.05

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