Indirect Measurement of Energy Density of Soft PZT Ceramic Utilizing Mechanical Stress

This paper reports on an indirect measurement of energy density of soft PZT ceramic utilizing mechanical stress. The method works analogous to the Olsen cycle and allows for a large amount of electro-mechanical energy conversion. A maximum energy density of 350 kJ/m³/cycle was found under 0–312 MPa and 1–20 kV/cm of applied mechanical stress and electric field, respectively. The obtained result is substantially higher than the results reported in previous studies of PZT materials utilizing a direct piezoelectric effect.     

Stress-dependent ferroelectric properties of Pb(Zr1/2Ti1/2)O3–Pb(Zn1/3Nb2/3)O3 ceramic systems

Effects of compressive stress on the ferroelectric properties of ceramics in PZT–PZN systems were investigated. (1 − x)Pb(Zr_1/2Ti_1/2)O₃(xPb(Zn_1/3Nb_2/3)O₃ or (1 − x)PZT–(x)PZN (x = 0.1–0.5) ceramics were prepared by a conventional mixed-oxide method. The ferroelectric properties under compressive stress of the PZT–PZN ceramics were observed at stress levels up to 170 MPa using a compressometer in conjunction with a modified Sawyer–Tower circuit. It was found that with increasing compressive stress the area of the ferroelectric hysteresis (P–E) loops, the saturation polarization (P_sat), the remanent polarization (P_r), and the coercive field (E_c) decreased. These results were interpreted through the non-180° ferroelectric domain switching processes.     

An Innovative Synthesis of Calcium Zeolite Type A Catalysts from Eggshells via the Sol–Gel Process

Calcium zeolite type A (CaNaAlSi₂O₇), called soda melilite, with a molar ratio of CaO:Al₂O₃:Na₂O:SiO₂ of 1:1:2:8 and calcined at 300 °C for 1 h was successfully synthesized by a sol–gel process using eggshell as the starting material. The CaNaAlSi₂O₇ catalysts had N₂ adsorption–desorption isotherms and good electrical properties. The specific surface area, pore volume, and average pore diameter were 55.15 m²/g, 0.51, and 37.19 nm, respectively. The dielectric constant, electrical conductivity, and loss tangent are 46.5785, 5.2360 × 10⁻³ (Ω m)⁻¹, and 2.75, respectively as measured at room temperature and at 1000 kHz (1 MHz). The transmission electron microscopy (TEM) images showed a moderately good dispersion of uniform particles with an average diameter of about 0.5 nm. X-ray diffraction patterns (XRD), Fourier transform infrared spectra, and simultaneous thermal analysis data (STA) were obtained to confirm the synthesis products.     

Preferential CO oxidation over Au/ZnO and Au/ZnO–Fe2O3 catalysts prepared by photodeposition

Preferential CO oxidation in a H₂-rich stream was studied over Au/ZnO and Au/ZnO–Fe₂O₃ catalysts prepared by photodeposition under UV–vis light. The high catalytic activities of both Au/ZnO and Au/ZnO–Fe₂O₃ catalysts are presented over a temperature range of 30–130 °C. TEM results revealed that the average particle size of Au over the Au/ZnO and Au/ZnO–Fe₂O₃ catalysts, is in the range of 3–5 nm. Moreover, DR/UV–vis spectra showed that the prepared catalysts contained Au^δ+ and Au⁰ (active sites for the PROX reaction) on the catalyst support. Based on the experiment observations, it can be concluded that the catalysts prepared by a photodeposition exhibited excellent catalytic activity, even when both CO₂ and H₂O were added to the simulated stream.     

Structural aspects of mesoporous AlPO4-5 (AFI) zeotype using microwave radiation and alumatrane precursor

A new route for preparation of mesoporous AlPO₄-5 (AFI) zeotype has been synthesized using alumatrane precursor, prepared from aluminum hydroxide and triisopropanolamine (TIS) by the oxide one pot synthesis (OOPS), via microwave technique using triethylamine (TEA) as a structure-directing agent. The influences of the reaction mixture composition, HF acid, water content and the crystallization temperature and time were investigated. The prepared materials were characterized using X-ray diffraction, SEM and BET. The results showed a mesoporous AlPO₄-5 zeotype having a uniform rod-like structure with surface area around 120–180 m²/g. The high crystallinity with narrow size distribution of crystals was obtained at a high amount of structure-directing agent (the mole ratio of TEA/Al₂O₃ = 3.5). The presence of fluorine ion retarded the nucleation and growth rate, leading to a bigger crystal size. The crystal of the AFI grew preferentially in the c-direction with the reaction time and the water content. The use of lower reaction temperature to obtain good crystalline material can be compensated by a longer reaction time.     

Effects of uniaxial stress on dielectric properties of 0.9PMN–0.1PT ceramics

This study deals with the influence of uniaxial stress on the dielectric properties of electrostrictive PMN–PT ceramic. The dielectric properties of lead magnesium niobate-lead titanate prepared by a mixed-oxide method with composition ratio 9:1 were measured under uniaxial compressive stress up to 22 MPa. The experimental results revealed that the superimposed compression load significantly reduced both the dielectric constant and the dielectric loss tangent in every measuring frequency. The observations were interpreted in terms of clamping of domain walls and de-poling under the compressive loading. The change of the dielectric properties with stress was attributed to competing influences of the intrinsic contribution of non-polar matrix and the extrinsic contribution of re-polarization and growth of micro-polar regions. In addition, the results reported here also suggested a significant influence of the experimental conditions on the uniaxial stress dependence of dielectric properties of the PMN–PT ceramic.     

Effect of synthesis time on morphology of CeO_2 nanoparticles and Au/CeO_2 and their activity in oxidative steam reforming of methanol

Ceria(CeO_2)supports,synthesized by hydrothermal treatment with different synthesis time(CeO_2-X h,where X is the synthesis time in h)in the presence of the surfactant cetyltrimethyl ammonium bromide,were used as supports for gold(Au)catalysts.The synthesis time significantly affects the morphological structure and crystallite size of CeO_2,where CeO_2-2 h has the smallest crystallite size with coexisting nanorods and nanoparticles.Transmission electron microscopy analysis confirms the morphology of CeO_2 with distinctive(110),(100)and(111)planes,in agreement with interplanar spacings of 0.19,0,27 and 0.31,respectively.However,the morphology of CeO_2-8 h and CeO_2-48 h is mainly a truncated octahedral with crystal planes(111)and(100)accompanied by an interplanar spacing of 0.31 and0.27 nm,respectively.The CeO_2-X h supports and those with a 3 wt%Au loading(Au/CeO_2-X h)were investigated in the oxidative steam reforming of methanol at temperatures between 200 and 400 ℃.The Au/CeO_2-2 h gave the highest methanol conversion level and hydrogen yield at a low temperature of 250 ℃.This superior catalytic performance results from the good interaction between the metal and support and the well-distributed Au species on the CeO_2 support.     

Hierarchical architecture of Bi12TiO20 via ethylene glycol-mediated synthesis route

Hierarchical architecture of cubic sillenite bismuth titanate (Bi₁₂TiO₂₀) is successfully synthesized using simple ethylene glycol-mediated self-assembly; followed by calcination under air at 600 °C for 30 min. The products are characterized using field emission scanning electron microscopy (FE-SEM), fourier transform infrared spectroscopy (FT-IR), thermogravimetric-differential thermal analysis (TG-DTA), and X-ray diffraction (XRD). The reaction time has an effect on the product morphology, which changed from a leaf- and circular plate-like structure to a completely formed hierarchical structure within 2 h. The hierarchical structure of Bi₁₂TiO₂₀, having a size around 3 μm, is composed of 2D twist nanoplates, and each twist nanoplate has a thickness around 10–30 nm.     

The electrochemical reduction of PdCl4 and PdCl6 in polyaniline: Influence of Pd deposit morphology on methanol oxidation in alkaline solution

The controlled uptake and electrochemical reduction of metal precursors PdCl₄²⁻ and PdCl₆²⁻ in polyaniline (PANI) is demonstrated. The formation of PANI/Pd composites is achieved with a reduction in proton doping and an increase in the oxidation of the polymer with Pd deposits physically blocking the nitrogen groups. High surface area filaments (PdCl₄²⁻) or a rough encapsulation (PdCl₆²⁻) of Pd metal on PANI are obtained. The structural differences highlight the influence of the metal precursor oxidation state on the morphology of the Pd deposits in PANI. Thermal gravimetric analysis provides an estimate of the Pd content for each composite of ∼40%. X-ray Photoelectron Spectroscopy and X-ray-excited Auger Electron Spectroscopy analyses confirm the deposition of Pd metal. The catalytic oxidation of methanol was demonstrated for both PANI/Pd composites in alkaline solutions that prohibit proton doping of the polymer. The data indicates that Pd metal acts as a solid-state dopant that may delocalize the charge on the polymer backbone to maintain conductivity. Methanol oxidation at PANI/Pd composites produced using PdCl₄²⁻ was enhanced relative to the composite produced using PdCl₆²⁻ and a planar Pd electrode. Comparison of PANI/Pd composite produced using PdCl₄²⁻ with other Pd catalysts from the literature indicates surface poisoning is reduced when Pd is coupled with the polymer. The composite is robust and stable in alkaline solution with the charge density decreasing by 5% on the positive scan and 13% on the negative scan after 200 voltammetric cycles. The data also indicates that the reductive desorption of surface contaminants is possible, minimizing the catalytic loss due to surface poisoning.