Qingchang Meng

Fabrication and in vitro characterization of magnetic hydroxycarbonate apatite coatings with hierarchically porous structures

Hydroxycarbonate apatite/Fe(3)O(4) composite coatings (MHACs) with hierarchically porous structures were fabricated by electrophoretic deposition of CaCO(3)/Fe(3)O(4) particles on Ti6Al4V substrates followed by treatment with phosphate buffer solution (PBS) at 37 degrees C. The effects of Fe(3)O(4) on the conversion rate of calcium carbonate to hydroxycarbonate apatite and the porous structures and in vitro bioactivity of MHACs were investigated. After soaking CaCO(3)/Fe(3)O(4) coatings in PBS, hydroxycarbonate apatite nucleates heterogeneously on the surfaces of CaCO(3)/Fe(3)O(4) particles and forms a plate-like structure. Fe(3)O(4) increases the velocity of nucleus formation of hydroxycarbonate apatite. After soaking for 1day, the percentage of unreacted calcium carbonate for MHACs is approximately 9.1%, lower than the approximately 41.0% for hydroxycarbonate apatite coatings (HCACs). As the CaCO(3)/Fe(3)O(4) coatings are converted to MHACs, macropores with a pore size of approximately 4mum on the coatings and mesopores with a pore size of approximately 3.9nm within the hydroxycarbonate apatite plates are formed. The mesopores remain in the MHACs after treatment with PBS for 9 days, while they disappear in the HCACs. Simulated body fluid immersion tests reveal that Fe(3)O(4) improves the in vitro bioactivity of biocoatings. The amount of bone-like apatite precipitated on the surfaces of MHACs is greater than that on the surfaces of HCACs.

Dislocation Behavior in ZrC Particles during Elevated Temperature Compressive Deformation of a 30 vol.% ZrCp/W Composite

A 30 vol.% ZrCp/W composite has been deformed in compression in the temperature range of 1200–1600°C. Dislocation nucleation mechanism in ZrC particles is discussed by analyzing the harmonious deformation between tungsten-matrix and ZrC particles. Thermal activation apparently increases the mobility of screw segments, resulting in the formation of many kinetics jogs and thermodynamics jogs above 1300°C. The formation mechanisms of the dislocation configurations are studied.

Evolution of Phase, Microstructure and ZrC Lattice Parameter in Solid-solution-treated W-ZrC Composite

Zirconium carbide (ZrC) reinforced tungsten (W) composite was hot-pressed at 2200 °C for 1 h in vacuum, which was subsequently heat treated in the temperature range of 2200 to 2500 °C for 1.5 or 2 h. The relative ratios of ZrC phase were 21.0, 23.3 and 25.9 mol.% for the mixture of starting powders, composites sintered for 1 h and solid-solution treated at 2500 °C for 1.5 h, respectively. The solid solubility of W in ZrC increased with the increment in heat-treating temperature and time to a maximum value of 18.9 mol.% at 2500 °C for 1.5 h. The lattice parameter of cubic ZrC phase diminished from 0.4682 nm in the starting powder to 0.4642 nm in the solid-solution composite treated at 2500 °C for 1.5 h. This work demonstrated that the relationship between the solid solubility of W in ZrC and the lattice parameter of ZrC is linear, with a slope of −1.93 × 10−4 nm/at.%. Overall, more W atoms diffused into ZrC lattice after heat treatment, meanwhile, the previous precipitated nano-sized W dissolved in the supersaturated (Zr,W)C solid-solution, as detected by SEM and TEM.

Mechanical Properties and Plasma Erosion Resistance of ZrO2p(3Y)/BN-SiO2 Ceramic Composites under Different Sintering Temperature

ZrO2p(3Y)/BN-SiO2 ceramic composites were hot pressed under different sintering temperature. The ceramic composites were composed by BN, m-ZrO2, t-ZrO2 and SiO2. The relative density, bending strength, elastic modulus and fracture toughness increase with the sintering temperature increasing, the maximum value of which at the sintering temperature of 1800°C are 97.5%, 229.9MPa, 60.8GPa and 3.55MPam1/2, respectively. The erosion resistance ability of ZrO2p(3Y)/BN-SiO2 ceramic composites rise gradually with the sintering temperature increasing, and the erosion rate of the ceramic composite sintered at 1800°C is 8.03×10−3mm/h.

Synthesis and formation mechanism of hollow carbon spheres encapsulating magnetite nanocrystals

Hollow carbon spheres encapsulating magnetite nanocrystals were obtained in high-pressure argon at 600 °C followed by hydrolysis of Fe(NH 3 ) 2 Cl 2 in the hollow interiors at room temperature and heat treatment in argon at 450 °C for 2 h. The structure, morphology, and properties of the products were characterized by x-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, and vibrating sample magnetometry. The hollow carbon spheres have diameters of 1–10 μm and wall thicknesses of hundreds of nanometers; the wt% of magnetite nanocrystals in them is ∼13.2%. Equiaxed magnetite nanocrystals range in size from 15 to 90 nm, while acicular magnetite nanocrystals have diameters of ∼20 nm and lengths of 120–450 nm. The saturation magnetization value of the hollow carbon spheres encapsulating magnetite nanocrystals is 4.29 emu/g.

Interface structure and mechanical properties of Al2O3-20 vol% ZrO2-20 vol% SiCW ceramic composite

The microstructure, mechanical properties, fracture behaviour and toughening mechanisms of Al2O3-20 vol% ZrO2 (2 mol% Y2O3)-20 vol% SiCW ceramic matrix composite were investigated by X-ray diffraction, scanning and transmission electron microscopies, energy dispersive analysis of X-rays, high-resolution electron microscopy techniques and three-point bending tests. The results show that the Al2O3 matrix is simultaneously strengthened and toughened by both ZrO2 particles and SiC whiskers. The interfacial amorphous layers between SiC whiskers and ZrO2, and Al2O3 grains were observed by both TEM dark-field and high-resolution electron microscopy techniques.