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.     

High birefringence photonic bandgap fiber with elliptical air holes

In this paper, we proposed a high birefringence photonic bandgap fiber (PBGF) with elliptical air holes in cladding and circular air hole in core. The forbidden gaps of the honeycomb structure are calculated when the circular air holes are deformed to the elliptical shape. And the birefringence of the PBGFs is investigated by using a full-vector finite element method (FEM) and the numerical results are presented.     

Electrical conductivity and gas sensitivity of Zn-Sb-O thick films

The thick film of Zn-Sb-O was prepared by coating the paste of nanoparticles mixture (Sb₂O₃:ZnO=1:3) on the alumina substrate, followed by sintering at 500-900 °C for 2 h in air. The electrical resistance and gas-sensing properties to benzene, alcohol and acetone of Zn-Sb-O films were found to be dependent on the change of phase structure caused by sintering temperature.     

Oil agglomeration of a lignite treated with microwave energy: Effect of particle size and bridging oil

Oil agglomeration of Sivas–Divriği (S–D) Uluçayır lignite fines was carried out using kerosene and kerosene–extract oil (which was obtained from lignite treated with microwave energy) mixture as a bridging oil. The effects of parameters such as the amount and type of bridging oil, microwave time and particle size on the agglomeration performance were investigated. The amount of kerosene was varied from 5 to 30 wt.% of the initial lignite loading. The values of the grade and recovery increased with an increase in the amount of kerosene added. Extract oil fraction of the lignite extract at various ratios in kerosene increased the agglomeration recovery from 95.88% to 98.55%. The effect of microwave time was investigated and it was found that the grade was also increased with increasing microwave time (4, 8 and 10 min). The grade of char (microwave time: 8 min) was increased in comparison with the original lignite while decreasing its recovery. Dense medium separations of the lignite were conducted and the results of their grade recovery performances were compared with those of agglomeration of the particles. During the inspection of particle size effect on the dense medium separation, the recovery was increased remarkably (from 12.07% to 89.50%) with increasing particle size, while decreasing the grade (from 0.732 to 0.697). In the oil agglomeration of lignite the recovery values were increased with increasing particle size.     

Formation mechanism of 21R AlN-polytypoids in aluminothermic reduction and nitridation process

Synthesis of 21R AlN polytypoids was investigated using Al and ultrafine SiO₂ powder in a flowing nitrogen atmosphere by means of thermal gravity (TG), differential scanning calorimeter (DSC), X-ray diffractometer (XRD) and scanning electronic microscope (SEM) linked with energy dispersive spectrometer (EDS). The results showed that the formation mechanism of AlN polytypoids was different from that in reaction sintering process using Si₃N₄, AlN, Al₂O₃ and other sintering additive as raw materials. It was suggested that firstly Al reduce SiO₂ into Si and is also nitrided into AlN, then AlN, Al₂O₃ and SiO₂ dissolve into silicon liquid until the AlN polytypoids precipitate in saturated liquid in a flowing nitrogen atmosphere at lower than 1700 °C.     

Synthesis of Mg-α-sialon from the mixture of silicon, aluminum and magnesia powders in a flowing nitrogen atmosphere

Synthesis of Mg-α-Sialon has been investigated by the mixture of silicon, aluminum and magnesia powders in a flowing nitrogen atmosphere in the range of 1300–1600 °C, when Mg-α-Sialon is designed with a chemical formulation of Mg _x Si_12−3x Al_3x O _x N_16−x in present work. The results showed that Mg-α-sialon initially occurred at 1400 °C and basically increased with elevated temperatures. For the samples of x = 0.6, 0.8 and 1.0 the products mainly consisted of Mg-α-Sialon with small amounts of Si, AlN and 21R AlN-polytypoid phases at 1600° C. However, in final products of x = 1.2, 1.4 and 1.6 only a little of Mg-α-Sialon formed and a great amount of Si remained in these samples at all the fired temperatures. Fortunately, the content of Mg-α-Sialon in these samples were obviously increased by adding a small amount of α-Si₃N₄ as seeds before nitridation.     

Moving beyond the fourth dimension with an IFC-based single project database

4D CAD has been an active research area for many years. The first generation 4D tools simulated construction schedules and demonstrated the potential benefits in several case studies. Researchers tried to improve the functionality of the first generation 4D tools by adding annotations and highlighting the building elements that have problems. The future generation 4D tools are expected to include more than these. It has been envisioned that 4D models would be part of project databases in order to take decisions related with different project dimensions.This paper presents the development and implementation of a new 4D planning tool which is a part of a product model-based project database. This tool brings the 4D simulation and cost estimation together and aims to contribute to what-if analysis in construction projects. The last part of the paper presents a case study in which the proposed prototype is evaluated.     

Properties of gap-aggregate gradation asphalt mixture and permanent deformation

Aggregate of natural crush stone in hot mix asphalt is applied to gap gradation mixed with the AC-20 binder, in accordance with Marshall mix design. Laboratory tests were conducted, and the single-factor variance analysis (ANOVA) is employed to estimate the significance of the gradation mixture properties. Based on permanent deformation tests and analytical results, sieve of 2.36 mm may be omitted for nominal maximum aggregate size (NMAS) of 12.5 mm, and sieve of 4.75 mm may be omitted for NMAS of 19 mm, in the case of the shortage of aggregate.     

钒钛渣对刚玉莫来石耐火材料的侵蚀研究

通过不同温度下钒钛渣对刚玉莫来石耐火材料的侵蚀实验，分析了炉渣、温度对材料的影响，认为致密结构、低气孔率是提高炉衬寿命的关键，板条状莫来石的存在利于减缓渣的侵蚀过程。     

Residual Stress Simulation of Injection Molding

In this study, distribution and history of residual stresses in plaque-like geometries are simulated based on linear thermoviscoelastic model, which helps to understand the mechanics and evolution of the residual stresses in the injection molding process. The numerical calculation of direction, combined with the specified boundary conditions. Results show that the stress variation across the thickness exhibits a high surface tensile value changing to a compressive peak value close to the surface, with the core region experiencing a parabolic tensile peak. Residual stress distribution throughout the thickness is almost same along the flowpath and the final residual stresses value near the gate is lower than the value near the end of flowpath.