Enhanced transduction coefficient in piezoelectric PZT ceramics by mixing powders calcined at different temperatures

Large transduction coefficient ($d_{33}\times g_{33}$) is difficult to obtain in piezoelectric ceramics because these two parameters show opposite trends with compositional modifications. Herein, the Pb(Zr_0.53Ti_0.47)O₃ ceramic powders were calcinated under different temperatures (A:830 °C, B:860 °C, and C:890 °C), and then mixed together according to different weight ratios (1A:1B:1C, 1A:2B:1C, 1A:2B:3C and 3A:2B:1C) for ceramics preparation. Both d₃₃ and g₃₃ are improved successfully, and the transduction coefficient with the weight ratio of 1A:2B:3C reaches up to 17,500 × 10⁻¹⁵ m²/N, which is 60 % higher than that with the powders calcinated under 830 °C, and at least twice those of commercial PZT-4, PZT-5A and PZT-8 ceramics. The improved transduction coefficient is owing to the enhanced piezoelectric constant and spontaneous polarization resulted from the increased grain size, relative density and the fraction of tetragonal phase. These results indicate that this is a simple but effective way to tailor the transduction coefficient in piezoelectric ceramics.     

Fabrication of high-quality flexible transparent conductive thin films with a Nb2O5/AgNWs/Nb2O5 sandwich structure

Different sandwich structures of flexible transparent conductive thin film (TCFs) composed of Nb₂O₅ layers and Ag nanowires (AgNWs) have been prepared onto flexible polyethylene terephthalate (PET) substrate at room temperature to develop an indium-free TCF. The AgNWs are synthesized by a modified polyol method and inserted into the Nb₂O₅ layers that are prepared by radio frequency magnetron sputtering. The optical and electrical properties can be modified by changing the number of spin-coating cycle of AgNW suspension. At optimized condition, we achieve a flexible Nb₂O₅/AgNWs/Nb₂O₅ sandwich thin film with a low sheet resistance of 9.61 Ω/square and a high optical transmittance of 84.3%. Meanwhile, the resistance remains nearly constant after 30 tape tests, suggesting a strong adhesion to the PET substrate. The sandwich thin films show high long-term stability to oxidation, humid heat, and chemicals compared with that of AgNW networks, which can be attributed to the effective covering of Nb₂O₅ layer on the AgNWs. In addition, the Nb₂O₅/AgNWs/Nb₂O₅ sandwich thin films show good stability after repeated bending. This Nb₂O₅/AgNWs/Nb₂O₅ sandwich thin film can therefore serve as a high-performance transparent conductive electrode for numerous flexible electronic devices.     

High-entropy titanate pyrochlore as newly low-thermal conductivity ceramics

Low-thermal conductivity ceramics play an indispensable role in maximizing the efficiency and durability of hot end components. Pyrochlore, particularly zirconate pyrochlore, is currently a highly promising and widely studied candidate for its extremely low thermal conductivity. However, there are still few pyrochlores that offer both stiffness, insulation, and good thermal expansion properties. In this work, the solidification method was innovatively introduced into the preparation of titanate pyrochlore, and combined it with the compositional design of high-entropy. Through careful composition design and solidification control, the high-density and uniform elements distributed high-entropy titanate pyrochlore ceramics were successfully prepared. These samples possess high hardness (15.88 GPa) and Young’s modulus (295.5 GPa), low thermal conductivity (0.947 W·m^?1·K^?1), excellent thermal expansion coefficient (11.6 ×10^?6/K) and an exquisite balance between stiffness and insulation (E/κ, 312.1 GPa·W^?1·m·K), in which the E/κ exhibits the highest value among the current reported works.     

Hydroxyapatite reinforced with Ti–Fe particle: correlation between composition,microstructure and mechanical properties

Abstract

Composites of hydroxyapatite (HA) with 5 wt-% Ti–Fe reinforcing particles were pressureless sintered in vacuum at a temperature range between 950 and 1100°C. It was found that although the decomposition of HA and interaction between HA and Ti occurred, the desirable Ti phase still remained in the composites sintered at all temperatures. The outer Ti shell thickness of the distinctive core–shell Ti–Fe particles was observed to become larger as the sintering temperature increased. It was also found that minor pores appearing near the interface were beneficial to obtain appropriate interfacial bonding between HA matrix and Ti–Fe particles. The composite sintered at 1050°C exhibited superior flexural strength, fracture toughness, and fatigue resistance owing to the remained Ti phase and dense microstructure as well as good interfacial bonding.     

Performance of spray deposited Gd-doped barium cerate thin films for proton conducting SOFCs

Doped barium cerate is a promising solid electrolyte for intermediate temperature fuel cells as a protonic conductor. In the present paper, the nanocrystalline Gd-doped barium cerate (BaCe_0.7Gd_0.1Y_0.2O_2.9) thin films have been successfully deposited on alumina substrate by spray pyrolysis technique. The films deposited from 0.1 M concentration and annealed at five different temperatures were characterized with different physio-chemical techniques. The BCGY is crystallized in orthorhombic perovskite structure with slight shift to the lower 2θ value compared with barium cerate (BC) and yttrium doped barium cerate (BCY). The grain growth and hence densification is also investigated by using SEM and AFM. The grain growth is almost complete at 1000 °C and the surface of the film appears to be smooth with typical roughness of 152 nm. Raman spectrum of BCGY film shows intense band at 463.8 cm⁻¹ compared to pure BC and BCY indicating the presence of more oxygen vacancies due to Gd doping. The proton conductivity of BCGY thin film in moist atmosphere is 1×10⁻³ Scm⁻¹.     

Investigation of the performance of a direct borohydride fuel cell with low Pt/C catalyst loading under different operating conditions

Fuel cells are promising alternative energy converters in terms of preventing pollution, efficiency, and noise. Direct borohydride fuel cells (DBFCs) which are defined as a sub-class of polymer electrolyte membrane fuel cells (PEMFCs) and direct liquid fuel cells (DLFC) have increased attention recently since they offer a solution for hydrogen storage problem. However, the commercialization of DBFC is hindered by the need of high platinum loadings. Therefore, reducing the platinum content is crucial to develop cost-effective DBFC without compromising performance. This research focuses on the effects of operational parameters on the DBFC performance with low level Pt/C catalyst loading (anode: 0.32 mg/cm², cathode: 0.36 mg/cm²). The gas diffusion electrode was prepared by spray-coating technique. The peak power density of 19.95 mW/cm² was obtained at 80 ^°C when 1 mL/min was used as a flow rate of fuel.     

Modeling the mechanics and dynamics of arbitrary edge drills

This paper presents a new approach for modelling the cutting forces and chatter stability limits in drills with arbitrary lip geometry. The oblique cutting geometry at each point on the drill lip is modelled using parametric curve equations. The cutting force and process damping coefficients at different parts of the drill lip are identified empirically; the cutting force coefficients are identified from non-symmetric drilling tests, and the process damping coefficients are identified from chatter-free orthogonal turning tests. The presented approach provides a practical method for modelling the cutting forces and vibration stability without needing the detailed geometry of drill lips. The accuracy of presented model in predicting lateral and torsional-axial chatter stability limits is verified by conducting drilling tests using drills with various edge geometries.     

Performance analysis of vapor injection heat pump system for electric vehicle in cold startup condition

In this study, a vapor-injection (VI) cycle designed for indoor heating of electric vehicle (EV) was investigated for low temperature heating purposes. The heating capacity variation was observed both in mathematical and experimental ways to verify the influence of vapor injection at different injecting positions and under different intermediate pressure. From this study, the optimal injection position of the scroll compressor and intermediate pressure ratio were evaluated that maximizes heating capacity and coefficient of performance (COP) of the cycle. To validate the numerical results, the experiment was also conducted in the prototype of a vapor-injection (VI) heating system for electric vehicle. The experiment was carried out under the steady-state condition and the same parameters as those of numerical analysis were employed. The comparison between the results of numerical analysis and that of experiments showed a good agreement. For the increase of heating capacity, the optimal injecting port position was observed in specific value which was close to 300°. As the opening of the main expansion valve was decreased, the performance of the VI system generally got better but the system had much restricted intermediate pressure ratio in which the performance was drastically decreased. As a result, the optimal intermediate pressure ratio occurred in specific value below 0.25 in startup condition.     

A method for the compound fault diagnosis of gearboxes based on morphological component analysis

An improved morphological component analysis (MCA) method is proposed for the compound fault diagnosis of gearboxes. When gear fault and bearing fault occur simultaneously, the compound fault signal of the gearbox contains meshing components (related to the gear fault) and periodic impulse components (related to the bearing fault). The corresponding fault characteristics can be separated by MCA according to the morphological differences of the components. In the proposed method, the optimal dictionary, which can represent the characteristics of bearing faults, is first selected based on the principle of minimum information entropy. Then, the compound fault signal is decomposed into the meshing component and the periodic impulse component using MCA. Finally, the separated components are subjected to the Hilbert envelope spectrum analysis. The faults of the gear and the bearing can be diagnosed according to the envelope spectra of the separated fault signal components. Simulation and experimental studies validate the effectiveness of the proposed method for the compound fault diagnosis of gearboxes.