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Designed component of 0.95Al 2 O 3 –0.015Yb 2 O 3 –0.01MgO–0.025SiO 2 (95Al 2 O 3 –Yb/Mg/Si) ceramics were prepared by the traditional mixed-oxide method in the sintering temperature range of 1450–1700 °C. The influence of sintering temperature on the crystal structure, densification, microstructure, mechanical, friction and wear properties of 95Al 2 O 3 -YbMgSi ceramics were systematically investigated. XRD and SEM analysis results revealed that the increase in sintering temperature was very beneficial to eliminate the pores, increase the density and grain size, which obeys the common grain growth law. Both the flexural strength and hardness of obtained samples were increased almost linearly when the sintering temperature increased from 1450 °C to 1700 °C. The ceramics sintered at 1650 °C showed the optimum properties: H v = 1812.3, σ = 151.3 MPa, μ = 0.41, ρ = 3.72 g/cm3 and K c = 8.06e−5 mm3/N·m, respectively. Furthermore, the results of friction and wear experiments suggested that the 95Al 2 O 3 –Yb/Mg/Si ceramic prepared at the optimizing sintering process exhibited more stable friction state and lower wear degree under non-lubricated conditions. The enhanced mechanical properties could be attributed to their structure densification, pore elimination and gain growth with the increase of sintering temperature. [ABSTRACT FROM AUTHOR]

To analyze the effect of PFN content on the microstructure and electrical properties of x Pb(Fe 0.5 Nb 0.5)O 3 –(0.57− x)Pb(Ni 1/3 Nb 2/3)O 3 –0.43Pb(Zr 0.3 Ti 0.7)O 3 , the doping of x PFN–PNN–PZT) were systematically studied with 0.015 ≤ x ≤ 0.075. XRD patterns and Raman spectra analysis reveal that PFN diffuses into PNN–PZT perovskite lattice and forms new quaternary solid solution. With the increase of PFN content x , the proportion of rhombohedral (R) phase decreases gradually, whereas the proportion of tetragonal (T) phase displays a contrary trend. In particular, R – T coexistence near MPB was observed at x = 0.045. Meanwhile, optimized electrical properties of d 33 = 961 pC/N, k p = 0.716, ε r = 6298, and tan δ = 3.1% are achieved for the 0.045PFN–PNN–PZT ceramics. Moreover, the ceramics at MPB showed larger remnant polarization P r = 24.55 μC/cm2, smaller coercive field E c = 0.36 kV/mm, and lower dielectric relaxor degree γ = 1.813. All these results reveal that the enhanced electrical properties could be attributed to synergistic phase boundary motion, dielectric relaxor behavior and ferroelectric hysteresis effect. [ABSTRACT FROM AUTHOR]

Quaternary piezoelectric ceramics Pb(Ni1/3Nb2/3)O3–Pb(Fe1/2Nb1/2)O3–Pb(Zr0.3Ti0.7)O3–xZnO (PNN–PFN–PZT–xZ, x=0.0–0.08 in molar ratio) were prepared by the conventional mixed-oxide method. The effects of ZnO content on the microstructure and piezoelectric properties were systematically investigated. Increasing ZnO additive promotes the phase structure transformation from rhombohedral to tetragonal, indicating the presence of the morphotropic phase boundary in the ZnO-modified PNN–PFN–PZT system. The results show that ZnO doping significantly improves the coercive field (E c ), Curie temperature (T c ), and temperature stability (Δf r /f r 30°C, Δd 31/d 31 30 °C) of the PNN–PFN–PZT–xZ ceramics, although the piezoelectric constant (d 33, d 31) decreases slightly with increasing ZnO content. Taking into consideration the piezoelectric property and temperature stability, the obtained ceramic sample with x=0.04 exhibited favorable properties, which are listed as follows: d 33=810pC/N, k p =0.647, ε r =6243, tan δ=2.74%, E c =4.7kV/cm, and T c =136°C. [ABSTRACT FROM AUTHOR]

Air bearing has been widely applied in ultra-precision machine tools, aerospace and other fields. The restrictor of the porous material is the key component in air bearings, but its performance is limited by the machining accuracy. A combination of optimization design and material modification of the porous alumina ceramic membrane is proposed to improve performance within an air bearing. Porous alumina ceramics were prepared by adding a pore-forming agent and performing solid-phase sintering at 1600 °C for 3 h, using 95-Al2O3 as raw material and polystyrene microspheres with different particle sizes as the pore-forming agent. With 20 wt.% of PS50, the optimum porous alumina ceramic membranes achieved a density of 3.2 g/cm3, a porosity of 11.8% and a bending strength of 150.4 MPa. Then, the sintered samples were processed into restrictors with a diameter of 40 mm and a thickness of 5 mm. After the restrictors were bonded to aluminum shells for the air bearing, both experimental and simulation work was carried out to verify the designed air bearing. Simulation results showed that the load capacity increased from 94 N to 523 N when the porosity increased from 5% to 25% at a fixed gas supply pressure of 0.5 MPa and a fixed gas film thickness of 25 μm. When the gas film thickness and porosity were fixed at 100 μm and 11.8%, respectively, the load capacity increased from 8.6 N to 40.8 N with the gas supply pressure having been increased from 0.1 MPa to 0.5 MPa. Both experimental and simulation results successfully demonstrated the stability and effectiveness of the proposed method. The porosity is an important factor for improving the performance of an air bearing, and it can be optimized to enhance the bearing's stability and load capacity. [ABSTRACT FROM AUTHOR]

Abstract: 0.55Pb(Ni1/3Nb2/3)O3–0.45Pb(Zr0.3Ti0.7)O3(PNN–PZT) ceramics with different concentration of xFe2O3 doping (where x =0.0, 0.8, 1.2, 1.6mol%) were synthesized by the conventional solid state sintering technique. X-ray diffraction analysis reveals that all specimens are a pure perovskite phase without pyrochlore phase. The density and grain size of Fe-doped ceramics tend to increase slightly with increasing concentration of Fe2O3. Comparing with the undoped ceramics, the piezoelectric, ferroelectric and dielectric properties of the Fe-doped PNN–PZT specimens are significantly improved. Properties of the piezoelectric constant as high as d 33 ~956 pC/N, the electromechanical coupling factor k p ~0.74, and the dielectric constant ε r ~6095 are achieved for the specimen with 1.2mol% Fe2O3 doping sintered at 1200°C for 2h. [Copyright &y& Elsevier]

BaTiO nanoparticles were prepared for the first time employing a solvothermal process from the synthetic precursors of KTiO nano-whiskers. The obtained samples were characterized by X-ray diffraction, transmission electron microscopy, selected area electron diffraction, and high-resolution transmission electron microscopy, etc. The results indicate that well-crystallized single-phase BaTiO nanoparticles are synthesized using KTiO as precursors under solvothermal conditions at as low as 0.9 M. The solvothermal method facilitates the crystallinity and formation of the BaTiO nanoparticles. However, the K ions cannot be completely replaced by Ba by the hydrothermal method even at 10 M due to its unique and extremely stable 'tunnel' structure. The solvothermal method provides new avenues for the ion-exchange synthesis of a variety of other perovskite-type materials such as MTiO (M = Pb, Sr, Ca, etc.). [ABSTRACT FROM AUTHOR]

• The metakaolin-based geopolymers added with RHA were prepared. • The incorporation of RHA enhanced the strength and refined the pore structure. • The improved mechanism of RHA in geopolymer was revealed successfully. • The recycling of RHA in an efficient way was realized. The influences of rice husk ash (RHA) on the reaction kinetics, mechanical property, and microstructure of metakaolin-based geopolymer (MG) were investigated. Geopolymer pastes containing different contents of RHA were prepared by sodium silicate activation. Analysis results show that both metakaolin and rice husk ash are involved in the geopolymerization, contributing to the development of mechanical properties and formation of compact microstructure. The longer reaction duration of setting time in the group incorporated RHA was ascribed to the procedure of SiO 2 dissolution. The geopolymers added with RHA have a compact pore structure, which show a relatively high compressive strength. The replacement of metakaolin by RHA did not cut the total quantity of gel phase formation, but changed the form of partial gels existence and an optimal mixed point was reached at the 20% replacement level. The abundant in gel along with the pore channel and secondary filling effects make a significant contribution to the development for refinement of pore and improvement of strength. This study can be used as an indicator for the application of RHA in geopolymer, which is of great value in urging RHA towards realization in recycling. [ABSTRACT FROM AUTHOR]

Recycled utilization of agricultural waste would make great contributions to the environmental protection and create significant economic benefits. This study focused on the use of rice husk ash (which was abbreviated as RHA), and the metakaolin-based geopolymer (MG) added with RHA were manufactured by alkali activation. The waterproof property and microstructure of samples were investigated and characterized systematically. The SiO 2 particles dissolved from the loose layers of RHA could be a potential filler and high active agent, which both played a vital role on the development of enhancement in waterproof property. However, the excessive incorporation of RHA in the synthesis process of geopolymer would also make a side effect on the development of geopolymer comprehensive property. A predictable balance with the optimal property was achieved at the 20% content replacement of MK by RHA. This research would provide a reference for the reuse of agricultural by-product, which is of great value in the realization of diversification in supplementary cementitious materials and recycling in agricultural wastes. • The recycling and utilization of rice husk and its ash in an efficient way were realized. • The metakaolin-based geopolymers incorporated with rice husk ash were formulated by alkali-activator. • The waterproof property of geopolymer was improved significantly with the use of RHA and the mechanism gained explanation. • This study provides a reference for the reuse of agricultural waste: rice husk. [ABSTRACT FROM AUTHOR]

Highlights • The surface-modified fly ash containing active agents (β-C 2 S and C 3 S) was formed. • The freezing resistance of the geopolymer was enhanced by the level of fly ash replacement. • The modified fly ash substitution leads to better freezing resistance and higher strength than the original fly ash. Abstract The surface of Grade III fly ash particles was modified by addition of gypsum and mineralizing agent (anhydrous calcium chloride) at 960 °C for 2 h. The mineral phase formation, structure and chemical compositions of the modified fly ash were analyzed by XRD, FESEM and EDS. Moreover, the influences of surface-modified fly ash on the compressive strength and freezing resistance of slag based geopolymer were also investigated in this work. The results showed that the β-2CaO·SiO 2 (β-C 2 S) and 3CaO·SiO 2 (C 3 S) phases were formed on the surface of fly ash particles after surface-modification. When adding modified fly ash into slag based geopolymer, due to the filling effect and functions of active agents (β-C 2 S and C 3 S), the strength and freezing resistance were improved markedly compared with that of the geopolymer added with original fly ash. [ABSTRACT FROM AUTHOR]

Abstract: Li/Ta/Sb co-doped lead-free (K0.4425Na0.52Li0.0375)(Nb0.93−x Ta x Sb0.07)O3 (abbreviated KNLNST x ) piezoelectric ceramics, with Ta-doping ratio of x ranging from 0.0275 to 0.0675, were synthesized using the conventional solid-state reaction method at the sintering temperature of 1130°C. The effects of Ta content on the microstructure, dielectric properties, and phase transition behavior of the prepared ceramics were systematically investigated. The X-ray diffraction results show that all KNLNST x ceramics formed a secondary phase, which is assigned to the tetragonal tungsten-bronze type (TTB) structure phase, and showed a phase transition from an orthorhombic symmetry to a tetragonal symmetry across a composition region of 0.0375

Abstract: Two-step sintering was applied to manufacture a typical Li- and Ta/Sb-modified alkaline niobate-based lead-free piezoelectric ceramics. The sintering condition dependences of dielectric constants and piezoelectric properties were investigated. Under the optimal condition, dense specimens have an average grain size of approximately 5μm, and show good dielectric and piezoelectric properties. Significantly, the (K0.4425Na0.52Li0.0375) (Nb0.8925Sb0.07Ta0.0375)O3 ceramics sintered under the condition “1130/10/1020/15” show the peak values of the piezoelectric coefficient (d 33), electromechanical coupling coefficient (k p), and dielectric constant (ɛ), which are 281pC/N, 50% and 1500, respectively, owing to the densest microstructure of typical bimodal grain size distributions. Furthermore, the KNLNST ceramics maintain relatively low dielectric loss over wide temperature ranges. The result indicates that the KNLNST ceramics sintered by two-step sintering exhibit good temperature stability. [Copyright &y& Elsevier]

The 0.55Pb(Ni1/3Nb2/3)O3–0.45Pb(Zr0.3Ti0.7)O3 (0.55PNN-0.45PZT) ceramics were prepared by conventional solid state reactions. The effects of calcining temperature on the particle size and piezoelectric properties of 0.55PNN-0.45PZT piezoelectric ceramics were investigated. The particle size and crystallinity of 0.55PNN-0.45PZT ceramic powders are influenced by calcining temperature, and therefore the microstructure and final piezoelectric properties of 0.55PNN-0.45PZT are different. The highest piezoelectric properties (d 33 = 720pC/N, k p = 0.55. ϵ r = 6255) were observed at the sample fabricated from the powder calcined at 1100°C, which was attributed to the improved crystallinity and the homogeneous distribution of the particles. [ABSTRACT FROM PUBLISHER]

Heavy lanthanide element-based NaREF 4 nanocrystals have recently been proposed as a promising replacement of classical hexagonal NaYF 4 for their efficient luminescence and excellent X-ray attenuation property. However, synthetic control over their particle size remains challenging due to the fast growth and slow nucleation. Herein, a simple and robust approach for the controlled synthesis of small NaYbF 4 and NaLuF 4 nanocrystals is presented as well as a mechanistic investigation of the nanocrystal growth process. The injection order of NaOH and NH 4 F plays critical role in controlling the nanocrystal growth by accelerating phase transformation from cubic phase to hexagonal phase. We also verify experimentally that control of the hexagonal-phase nucleation rather than growth process is crucial for controlling the final particle size of NaYbF 4 and NaLuF 4. After coating an inert shell, we found enhanced downshifting emission of NaYbF 4 :Er nanocrystals compared with less Yb3+ doping. The results shown here provide a reliable method for preparing small-sized hexagonal NaYbF 4 nanocrystals with enhanced downshifting emission, which favors their further applications in bioscience. The injection order of NaOH and NH 4 F plays critical role in controlling the nanocrystal size by accelerating phase transformation from cubic phase to hexagonal phase. [Display omitted] • The controlled synthesis of small hexagonal NaYbF 4 and NaLuF 4 nanocrystals via tuning the addition order of NaOH and NaH 4 F. • NaYbF 4 :Er@NaLuF 4 nanocrystals exhibit enhanced 1530-nm emission compared with the nanocrystals with low Yb3+ content. • Small NaYbF 4 nanocrystals with enhanced downshifting emission favor further applications in biological science and medicine. [ABSTRACT FROM AUTHOR]