悬浮液等离子喷涂制备氟代羟基磷灰石生物涂层

主要以氟代羟基磷灰石(FHA)悬浮液为原料,采用悬浮液等离子喷涂技术,在钛基体表面制备了FHA涂层。通过XRD,SEM,FT-IR以及XPS等测试手段,对不同喷涂功率制备的FHA涂层进行表征,并测试其性能。结果表明,粉体及制备的涂层主要晶相为HA,但是粉体进入等离子火焰形成涂层的过程中发生分解,生成α-磷酸钙(α-TCP),β-磷酸钙(β-TCP),以及磷酸四钙(TTCP)等分解产物。XPS结果证明F离子成功取代了OH基团进入HA晶格中,导致FHA涂层的抗溶解性明显提高。电化学实验结果表明,随着喷涂功率的增加,涂层的抗腐蚀性能提高。     

Experimental phase equilibria study and thermodynamic modelling of the PbO-“FeO”-SiO2-ZnO,PbO-“FeO”-SiO2-Al2O3 and PbO-“FeO”-SiO2-MgO systems in equilibrium with metallic Pb and Fe

Phase equilibria of the PbO-“FeO”-SiO₂-ZnO, PbO-“FeO”-SiO₂-Al₂O₃ and PbO-“FeO”-SiO₂-MgO slags with liquid Pb metal, solid or liquid Fe metal and solid oxides (cristobalite and tridymite SiO₂, willemite (Zn,Fe)₂SiO₄, wustite (Fe,Al)O_1+x, spinel (Fe,Al)₃O₄, olivine Fe₂SiO₄, corundum (Al,Fe)₂O₃, mullite Al₆Si₂O₁₃ and pyroxene (Mg,Fe)SiO₃) were investigated at 1125–1670 °C. These conditions correspond to the minimum solubility of PbO in slag in presence of Pb and Fe metals at reducing conditions and represent the limit of lead smelting and slag cleaning process. High-temperature equilibration on silica, corundum or iron foil substrates, followed by quenching and direct measurement of Pb, Fe, Si, Zn, Al and Mg concentrations in the liquid and solid phases with the electron probe X-ray microanalysis (EPMA) was used. Present data can be used to improve the thermodynamic models for all phases in this system.     

Design and computational analysis of a metal hydride hydrogen storage system with hexagonal honeycomb based heat transfer enhancements-part A

In this study, design and performance analysis is carried out for a 10 kWh metal hydride based hydrogen storage system. The system is equipped with distinctive aluminium hexagonal honeycomb based heat transfer enhancements (HTE) having higher surface area to volume ratio for effective heat transfer combined with low system weight addition. The system performance was studied under different operating conditions. The optimum absorption condition was achieved at 35 bar with water at room temperature as heat transfer fluid where up to 90% absorption was completed in 7200 s. The performance of the reactor was observed to significantly improve upon the addition of the HTE network at a minimal system weight penalty.     

Mechanical and thermal properties and microstructural evolution of Ta-doped Nb4AlC3

(Nb_1-xTa_x)₄AlC₃ (x = 0–0.5) ceramics were prepared by the hot press sintering method. The XRD results show that the second phase (Nb_1-xTa_x)C is formed when the Ta content increases to 25 mol%. The SEM micrographs show that (Nb_1-xTa_x)C has a core/rim structure, whose formation mechanism was also investigated. Substituting some Ta for Nb can significantly improve the mechanical properties of Nb₄AlC₃. (Nb_0.75Ta_0.25)₄AlC₃ exhibits an excellent fracture toughness of 8.3 ± 0.3 MPa m^1/2 at room temperature (RT). The highest Young's modulus (349 ± 16 GPa) and Vickers hardness (4.5 ± 0.3 GPa) at RT are exhibited by the (Nb_0.5Ta_0.5)₄AlC₃ sample, which correlate to increases of 18% and 80%, respectively, compared with those of Nb₄AlC₃. The flexural strengths of (Nb_0.5Ta_0.5)₄AlC₃ are 439 ± 18 MPa at RT and 344 ± 22 MPa at 1100 °C, which correlate to increases of 27% and 45%, respectively, compared with those of Nb₄AlC₃. The solid solution of Ta and the formation of (Nb_1-xTa_x)C are beneficial to the strengthening of Nb₄AlC₃. The coefficient of thermal expansion (CTE) increases slightly from 7.08 × 10⁻⁶ K⁻¹ for Nb₄AlC₃ to 7.24 × 10⁻⁶ K⁻¹ for (Nb_0.75Ta_0.25)₄AlC₃ at 25–1400 °C. The thermal conductivity of (Nb_0.75Ta_0.25)₄AlC₃ (28.4–29.8 W/m·K) is higher than that of Nb₄AlC₃ (18.1–21.2 W/m·K) over the whole test range (25–1000 °C). Owing to their excellent mechanical and thermal properties, Ta-doped Nb₄AlC₃ ceramics have good potential as structural materials.     

Distribution-free double-sampling precedence monitoring scheme to detect unknown shifts in the location parameter

In most applications, parametric monitoring schemes are used to monitor the majority of industrial and nonindustrial processes in order to improve the quality of the outputs or services. However, parametric monitoring schemes are known to underperform when the normality assumption is not met or when there is not enough information about the symmetry or asymmetry nature of the process underlying distribution. Hence, in this paper, a new nonparametric Phase II Shewhart-type double-sampling (DS) monitoring scheme based on the precedence statistic is proposed in order to efficiently monitor quality processes when the underlying process distribution departs from normality. The performance is investigated using the average run length (ARL), standard deviation of the run length (SDRL), expected ARL (EARL) and expected average number of observations to signal (EANOS), and the average sample sizes (ASS) metrics. The latter metrics are computed using Monte Carlo simulation and exact formulae. In general, it is shown that the new DS precedence scheme outperforms the existing basic Shewhart precedence scheme with and without supplementary runs rules in many situations. A real-life illustrative example based on a filling process of milk bottles is provided to demonstrate the application and implementation of the new DS precedence monitoring scheme.     

High room-temperature pyroelectric property in lead-free BNT-BZT ferroelectric ceramics for thermal energy harvesting

Pyroelectrics are attracting increasing attention because they enable pyroelectric generators to extract energy from low-gradient-temperature heat for portable electronic devices. High pyroelectric coefficient around room temperature is essential for high-performance energy harvesters, which, unfortunately, is only commonly achieved in lead-based ferroelectrics. Herein we report a high room temperature pyroelectric response of 27.2 × 10^?4 C m^-2 K^-1 in 0.94(Bi_0.5Na_0.5)TiO₃-0.06Ba(Ti_0.75Zr_0.25)O₃ lead-free ceramics by modulating the Zr⁴⁺/Ti⁴⁺ ratio to tune the ferroelectric-relaxor antiferroelectric-like phase transition point to around ambient temperature, whose pyroelectric response is one order of magnitude higher than that of the sample without Zr and even comparable to those of lead-containing pyroelectrics. The theoretical analysis revealed that introduced Zr⁴⁺ could incorporate into the TiO₆ octahedral lattices and break the long-range translational symmetry of BaTiO₃ lattices, resulting in the reduction of B-site ion displacement activation energy and transition point of ferroelectric-relaxor antiferroelectric-like phase, giving rise to a pronounced room-temperature pyroelectric effect in BNT-BZT.     

Mechanical high-energy treatment of TiNi powder and phase changes after electrochemical hydrogenation

The paper presents the results obtained for the effect of ball milling of Ti–Ni powder, which is close in composition to the equiatomic one, on electrochemical hydrogenation. It is shown that the average size of the powder particles measured by BET and laser diffraction methods is found to reduce during milling, while the average size of the powder particles measured by SEM changes to attain its minimum within 30-s milling due to destruction and subsequent aggregation of particles. The powder in its initial state consists of a mixture of TiNi (austenite, martensite), Ti₂Ni, and TiNi₃ phases, and after ball milling, an X-ray amorphous phase is formed. The CDD size of the TiNi phase (austenite) reduces from 25 to 4 nm. It is found that the lattice parameters of the TiNi (austenite) and Ni₃Ti phases do not change during electrochemical hydrogenation, whereas the crystal lattice parameter of the Ti₂Ni phase increases, which indicates the predominant interaction of hydrogen with the Ti₂Ni phase. The lattice parameter of the Ti₂Ni based phase corresponds to Ti₂NiH_0.5 and Ti₂NiH_0.8 hydrides depending on the milling time and hydrogenation time. It is found that there is an “incubation period” of hydrogenation of the Ti₂Ni phase, which attains 90 min.     

Experimental liquidus study of the binary PbO-ZnO and ternary PbO-ZnO-SiO2 systems

Phase equilibria of the binary PbO-ZnO and ternary PbO-ZnO-SiO₂ systems have been experimentally investigated at 1033–1898?K (760–1625?°C) for oxide liquid in equilibrium with air and solid oxide phases: tridymite or cristobalite (SiO₂), willemite (Zn₂SiO₄), zincite (ZnO), larsenite (PbZnSiO₄) and lead-zinc melilite (Pb₂ZnSi₂O₇) covering the ranges of concentrations not studied before. High-temperature equilibration on primary phase or inert metal (platinum) substrates, followed by quenching and direct measurement of the Pb, Zn and Si concentrations in the phases with the electron probe X-ray microanalysis (EPMA) has been used. Liquidus phase equilibrium data is essential for the development of the thermodynamic model.     

Phase equilibria in CaNaPO4-CaKPO4 system and their influence on formation of bioceramics based on mixed Ca-K-Na phosphates

An investigation of the two-component phase diagram of the CaNaPO₄- CaKPO₄system performed using various analysis techniques is reported. The continuous solid solution series of α-CaMPO₄ existing above 700 °C undergoes eutectoid decomposition during cooling to β-CaMPO₄-based solid solutions enriched with Na and K, and to an intermediate nonstoichiometric compound with an ideal composition of CaK_0.6Na_0.4PO₄. All three compounds exhibit significant volumetric effects associated with first-order phase transitions, with positive volume changes under cooling for the intermediate compound. Increased K content in ceramics based on CaK_yNa_1-yPO₄ compositions enhances the strength properties of those ceramics, including their fracture toughness, which is associated with increased density. Increased K content also has a smaller effect of inducing phase transformations accompanied by strong volume changes.     

Phase composition,microstructure and thermophysical properties of the Srx(Zr0.9Y0.05Yb0.05)O1.95+x ceramics

Sr_x(Zr_0.9Y_0.05Yb_0.05)O_1.95+x (x=1.0, 0.9, 0.8, 0.7) ceramics were prepared by solid state reaction sintering. The sintered Sr_1.0(Zr_0.9Y_0.05Yb_0.05)O_2.95 is a single-phase solid solution while the sintered Sr_x(Zr_0.9Y_0.05Yb_0.05)O_1.95+x (x=0.9?0.7) are composites, and a significant grain growth inhibition is observed in the sintered Sr_x(Zr_0.9Y_0.05Yb_0.05)O_1.95+x (x=1.0, 0.9). Rare-earth elements distribution in the bulk materials indicates that Yb and Y preferentially substitute Zr-sites in SrZrO₃, and the highest solubility of RE₂O₃ in pure SrZrO₃ is ～0.8 mol%. The sintered Sr_x(Zr_0.9Y_0.05Yb_0.05)O_1.95+x have high thermal expansion coefficients up to ～11.0×10^?6 K^-1 (1200°C). Sr_0.8(Zr_0.9Y_0.05Yb_0.05)O_2.75 has the lowest thermal conductivity of 1.38 W·m^-1·K^-1 at 800°C. Sr_x(Zr_0.9Y_0.05Yb_0.05)O_1.95+x (x=1.0, 0.9, 0.8) show no phase transition from 600 to 1400°C, whereas Sr_x(Zr_0.9Y_0.05Yb_0.05)O_1.95+x (x=0.9, 0.8) have excellent high-temperature phase stability over the whole investigated temperature range. Therefore, Sr_x(Zr_0.9Y_0.05Yb_0.05)O_1.95+x (x=1.0, 0.9, 0.8) are considered as promising TBCs materials that might be operated at higher temperatures compared to YSZ.