Effects of spark plasma sintering on ferroelectricity of 0.8Bi3.15Nd0.85Ti3O12-0.2CoFe2O4 composite ceramic

The 0.8Bi_3.15Nd_0.85Ti₃O₁₂ (BNdT)-0.2CoFe₂O₄ (CFO) composite multiferroic ceramics have been fabricated by spark plasma sintering (SPS) at 850?°C. The relative density of as-sintered SPS ceramic reaches 97.4 (±0.3)%. The composites are composed of pure BNdT and CFO phases without any preferred c-orientation. The a-orientation preference is more obvious perpendicular to the pressure direction. The average grain-sizes of BNdT and CFO are 163 and 146?nm, respectively. The BNdT phase has more grains below 100?nm (～20%). The super energy-dispersive X-ray analyses suggest no serious reaction between BNdT and CFO. The Raman spectrum verifies the nano-structure of the SPS ceramic via the broadening bands and peak shifts. The Curie temperature of the SPS ceramic declines to 560?°C with stabilized dielectric loss. The grain boundary resistance plays a dominant role on impedance above 700?°C. The remanent polarization approaches to 15.2?μC/cm² (300?kV/cm) with lower coercive fields (?89/+95?kV/cm).     

Fabrication and in vitro characterization of antibacterial magneto-luminescent core-shell bioactive glass nanoparticles

When nanomaterials with antibacterial properties were sent to the infected area, it was predicted that infection and related complications could be prevented. The nanoparticles can be designed to possess magnetic and luminescence (magneto-luminescent) properties to be effectively targeted and localized at the infection foci without dispersing into the body. Simultaneously, the magneto-luminescent characteristic of particles allows visualization and confirmation of localized particles at the desired area. In this regard, there are no studies on the use of antibacterial magneto-luminescent bioactive glass for orthopedic applications and the treatment of orthopedic device-related infections. In this study, antibacterial magneto-luminescent 58S bioactive glasses were synthesized by the modified Stöber using coupled with a layer-by-layer assembly approach to possess core/shell particle morphology. SPION/Bioactive glass nanoparticles had an average size of 50 nm and displayed superparamagnetic behavior. While the saturation magnetization value (σ_s) of the undoped 58S sample was 25.32 emu/g, that of the co-doped sample (2% Eu, 2% Zn) was 21.74 emu/g; this showed that the doping slightly reduced the magnetization value. Europium (Eu) doping of SPION/Bioactive glass nanoparticles induced characteristic red emission originating from Eu emissions belonging to ⁵D₀–⁷F_J (J = 1–4) transitions and the strongest peak was at 612 nm (electric-dipole transition, ⁵D₀–⁷F₂). Color chromaticity coordinates confirmed emission in the red region. XPS spectrum revealed the existence of Eu and Zn dopant elements in 58S bioactive glass. After soaking characteristic peaks at 31.74° and 45.43° belonging to the hexagonal hydroxyapatite phase were detected in the XRD data, confirming the SEM images. 2% Eu doped SPION/Bioactive glass nanoparticles had the highest osteoblast viability up to 7 days in vitro, while doping the samples with 2% zinc did not yield bone cell viability as high as the Eu doped ones. Importantly, Eu doped SPION/Bioactive glass nanoparticles inhibited gram-positive Staphylococcus aureus (S. aureus) and gram-negative Escherichia coli (E. coli) growth up to 48 h in vitro. The results showed that Eu doping of SPION/Bioactive glass nanoparticles increased osteoblast viability and inhibited bacterial growth, while possessing superparamagnetic properties and exhibiting red luminescence.     

Anisotropies in structure and properties of hot-press sintered h-BN-MAS composite ceramics: Effects of raw h-BN particle size

Effects of raw h-BN particle size from 0.5 μm to 11 μm on the phase compositions, texture degree, bending strength, fracture toughness and thermal conductivity of hot-press sintered h-BN-MAS composite ceramics were investigated. Larger h-BN grain can facilitate the nanocrystallization of MAS phase due to the inhibiting crystallization effect of h-BN on α-cordierite. Texture degree of h-BN-MAS composite ceramics increased significantly with increasing raw h-BN particle size, and the 11.0μmBN-MAS composite ceramic shows typical textured structure. The h-BN-MAS composite ceramics show anisotropy in mechanical properties and thermal conductivity, and the anisotropy increased significantly with increasing raw h-BN particle size. The 0.5μmBN-MAS sample shows excellent mechanical properties, and the 10μmBN-MAS sample shows strong anisotropy in thermal conductivity.     

Structure/processing relationships and mechanical properties of freeze-cast B4C scaffolds with unidirectional channels

Journal of Materials Science - Freeze casting technique has become a promising way to assemble various components into multifunctional nacre-like materials. Surprisingly, although many ceramics...     

Mechanical,dielectric and thermal properties of porous boron nitride/silicon oxynitride ceramic composites prepared by pressureless sintering

Porous boron nitride/silicon oxynitride (BN/Si₂N₂O) composites were fabricated by pressureless sintering at 1650 °C with Li₂O as sintering aid. The influence of Li₂O and hexagonal boron nitride (h-BN) contents on phase, microstructure, mechanical, dielectric and thermal properties of the resulting porous BN/Si₂N₂O composites was investigated. Increasing Li₂O content facilitated densification and decomposition of Si₂N₂O into Si₃N₄. The apparent porosity of the composites increases with the h-BN content increases and Si₂N₂O grain growth was restrained by the dispersed h-BN particles. The dielectric properties and thermal conductivities (TC) were affected mainly by porosity. Porous BN/Si₂N₂O ceramic composites with 4 mol% Li₂O and 25 mol% BN exhibit both low dielectric constant (3.83) and dielectric loss tangent (0.008) with good mechanical and thermal performance, suggesting possible use as high-temperature structural/functional materials.     

Microstructural Stability and Mechanical Properties of Directionally Solidified Alumina/YAG Eutectic Monofilaments

Fiber strength retention and creep currently limit the use of polycrystalline oxide fibers in ceramic matrix composites making it necessary to develop single crystal fibers. Two-phase alumina/YAG single crystal structures in the form of monofilaments show that the room temperature tensile strength increases according to the inverse square root of the microstructure size. Therefore, microstructure stability will play a significant role in determining the ‘use temperature’ of these fibers along with its creep resistance. In this work, the effects of temperature on microstructural stability and the creep behavior of directionally solidified alumina/YAG eutectic monofilaments were studied. Microstructural stability experiments were conducted in air from 1200 to 1500°C and creep tests at temperatures of 1400 to 1700°C. Inherent microstructure stability was found to be very good, however, extraneous impurity-induced heterogeneous coarsening was significant above 1400°C. The creep strength of monofilaments with aligned microstructures were superior to ones with low aspect ratio morphologies. Mechanisms for microstructural coarsening and creep behavior are discussed.     

Ambient and elevated temperature mechanical properties of hot-pressed fused silica matrix composite

The ambient and elevated temperature mechanical properties of two kinds of hot-pressed fused silica matrix composites, SiO₂+5 vol.% Si₃N₄ and SiO₂+5 vol.% Si₃N₄+ 10 vol.% C_f, were investigated. Si₃N₄ additions greatly enhanced the ambient strength and fracture toughness, while, further incorporation of chopped carbon fibers only but sharply increased the fracture toughness value from 1.22 to 2.4 MPa m^1/2. The strength of the two composites synchronously exhibited anomalous gains at certain elevated temperature range especially from 1000 to 1200 °C, and reached their maximum values at 1000 °C, 168.9 and 130.6 MPa, which were 77.0 and 77.4% higher than their ambient strength, respectively. The two composites exhibited catastrophic fracture even at 1000 °C, but manifested prominent plastic deformation at 1200 °C and usually no fracture occurred during the strength test. Vickers’ indentation crack propagation behavior, combined with fractographs studies, suggested that toughening from carbon fiber was attributed primarily to the fiber bridging, pull-out and crack deflection.     

Thermodynamic calculation of Ms in ZrO2–CeO2–Y2O3 system

The difference of Gibbs free energy between tetragonal and monoclinic phases in ZrO₂–CeO₂–Y₂O₃ as a function of composition and temperature is thermodynamically calculated from the three related binary systems. In 8 mol% CeO₂–0.5 mol% Y₂O₃–ZrO₂, the equilibrium temperature between tetragonal and monoclinic phases, T₀, is obtained as 832.5 K and the M_s temperature of this alloy with a mean grain size of 0.90 μm is calculated as 249.9 K using the approach derived by Hsu et al. [J. Mater. Sci., 18(1983)3206; 20(1985)23; Acta Metall., 37(1989)3091; Acta Metall. Mater., 39(1991)1045; Mater. Trans. JIM, 37(1996)1284], which is in good agreement with the experimental one of 253 K.     

Ultra-high temperature ceramics based on ZrB2 obtained by pressureless sintering with addition of Cr3C2, Mo2C,and WC

ZrB₂-MeC and ZrB₂-19 vol% SiC-Me_xC_y where Me=Cr, Mo, W were obtained by pressureless sintering. The capability to promote densification of ZrB₂ and ZrB₂-SiC matrices is the highest for WC and lowest for Cr₃C₂. The interaction between the components results in the formation of new phases, such as MeB (MoB, CrB, WB), a solid solution based on ZrC, and a solid solution based on ZrB₂. The addition of Cr₃C₂ decreases the mechanical properties. On the other hand, the addition of Mo₂C or WC to ZrB₂-19 vol% SiC composite ceramics leads increased mechanical properties. Long-term oxidation of ceramics at 1500 °C for 50 h showed that, in binary ZrB₂-Me_xC_y, a protective oxide scale does not form on the surface thus leading to the destruction of the composite. On the contrary, triple composites showed high oxidation resistance, due to the formation of dense oxide scale on the surface, with ZrB₂-SiC-Mo₂C displaying the best performance.