Xinghua Zhong

Single-crystalline nanowires of SiC synthesized by carbothermal reduction of electrospun PVP/TEOS composite fibres

Nanowires of SiC were synthesized by carbothermally reducing PVP/TEOS composite fibres obtained by electrospinning. High-resolution transmission electron microscopy (HRTEM) and selected-area electron diffraction (SAED) indicated that the SiC nanowires are single crystalline in nature. Both Fourier-transformed infrared spectroscopy and HRTEM indicated that a thin layer of SiO2 was formed on the outer surface of the nanowire as a result of post-heat treatment for the removal of residual carbon. Such SiO2 layer protects the inner SiC fibre from further oxidation. The formation mechanism of single-crystalline SiC nanowires was proposed based on our understanding and characterizations. The growth of the nanowire is believed to be along the (111) of its cubic cell.

Magnetic properties of Er2Fe17−xAlxNy compounds

Structural and magnetic properties of the Er2Fe17−xAlxNy compounds (0≤x≤3) have been investigated. All nitrides and parent compounds crystallize in the Th2Ni17 structure. Al substituted for Fe leads to an increase in lattice constants a and c. Introduction of nitrogen results in a further increase of lattice constants, but the magnitude of this increase is smaller for increasing x. As Al content increases, the Curie temperature of the parent compound increases, whereas the Curie temperature of the nitride decreases. The substitution of Al for Fe results in a decrease of Fe moment in both nitrides and parent compounds. Introduction of nitrogen leads to an increase in the uniaxial anisotropy of the Er sublattice and a spin reorientation. A tentative spin phase diagram has been constructed.

Magnetic properties of Sm2(Fe1−xGax)17 compounds (x = 0–0.5)

Abstract Sm 2 (Fe 1− x Ga x ) 17 ( x = 0–0.5) compounds were prepared by arc melting. X-ray diffraction patterns showed that all compounds were single phase with rhombohedral Th 2 Zn 17 -type structure. X-ray diffraction patterns of the aligned samples showed that the alloys with x = 0.15, 0.20 and 0.25 have uniaxial anisotropy at room temperature. The spin reorientation transition temperatures were measured by a superconducting quantum interference device (SQUID) and a magnetic balance. A tentative phase diagram was constructed. The substitution of Ga for Fe leads to an increase in the reorientation temperature and the lattice constants. The Curie temperature increases with the Ga concentration, and achieves a maximum at x = 0.2, then decreases. The saturation magnetization decreases monotonically with Ga concentration. The coupling constants A TT and A RT were derived using a mean molecular field model. A TT reaches a maximum at x = 0.3 and then decreases with x , but A RT is almost unchanged with varying x .

Effect of the Bond Coating Surface Morphology on Ceramic Splat Construction

In this work, yttria-stabilized zirconia splats deposited onto different bond coatings were characterized. The influence of both substrate topography and temperature on splat morphologies was investigated. The substrate surface was described using a method characterized by multi-level roughness. On non-heated substrate, the peak-valley structure in scale of micrometer contributed to the formation of crater-like holes on splats. The amount of such holes was reduced with the increase of substrate temperature. It was also observed that on micro-smooth surface, island-like fragments in the center of splat would warp and their edges could be detached from the underlying substrate, especially when the substrate was heated. The obtained results reveal that the influence of substrate pre-heating on the splat formation is realized via thinning the air film near substrate surface.

High Field Magnetization of Er2(Fe, Al)14B

A magnetization study in pulsed high magnetic fields up to 50 T has been performed on magnetically-aligned powder samples of ferrimagnetic Er 2 Fe 14- x Al x B ( x =0, 1, 2) compounds and field-induced transitions have been observed in high fields. Free-energy calculations with one Fe and four Er sublattices have been performed and the field-induced transitions can satisfactorily be explained. The Er- and Fe-sublattice moments, two kinds of anisotropy and molecular fields on Er ions have been determined.

Study on high performance Sm2Fe17Nx magnets

In this paper, the remanence properties of Co-Sn, Co-Ti and CO-Ti-Sn substituted Ba-ferrite (BaF) oriented particulate samples are compared with those of some oriented acicular particulate samples. A new parameter, the minor remanence distribution (MRD), is proposed to review the remanence properties of magnetic particles and the capabilities for resisting the recording demagnetization of magnetic recording media. It is shown that the MRD values of the oriented BaF particulate samples were smaller compared to oriented Co-gamma-Fe2O3 samples, even though the squareness ratios (SR) of some of the BaF samples were smaller than those of the Co-gamma-Fe2O3 samples. It is the small MRD, SFD(r), IRS and large DH(r) of a medium that can result in a large resistance to the effects of recording demagnetization and therefore in superior characteristics for high density magnetic recording. Since Co-Sn substituted BaF platelet-shaped particles exhibit these characteristics and have a very low temperature coefficient of coercivity, these particles can be expected to be a promising candidate for high density magnetic recording.

Structure and magnetic properties of GdMn1-xCoxSi compounds

Structural and magnetic properties of the GdMn1-xCoxSi compounds with x=0, 0.2, 0.4, 0.6, 0.8 and 1.0 have been investigated. All the compounds investigated are isotypical and crystallize in the tetragonal PbFCl-type structure. The GdMn1-xCoxSi compounds exhibit ferromagnetic coupling. Substitution of Co for Mn leads to a decrease of the unit-cell volume, of the saturation magnetization at 1.5 K and of the Curie temperature

Evolution of Residual Stresses in PS-PVD Thermal Barrier Coatings on Thermal Cycling

Plasma spray-physical vapor deposition (PS-PVD) is an advanced technique to fabricate quasi-columnar structured thermal barrier coatings (TBCs) with excellent thermal cyclic lifetime. In this study, PS-PVD TBCs were investigated via burner rig test. The residual stresses in both of the topcoat layer and the thermally grown oxide (TGO) scale were measured non-destructively using Raman spectroscopy and Cr3+ photoluminescence piezo-spectroscopy, respectively. Evolution of the microstructures and distribution of residual stresses in such kind structured TBCs before and after thermal cycling test were investigated. The accumulated tensile stress in the as-sprayed ceramic topcoat changed to compressive state after 100 cycles and then gradually increased. In addition, the mapping compressive stresses in the TGO measured through the ceramic topcoat surface decreased rapidly and then essentially maintained at a relatively stable state with further testing. Moreover, the pre-heating of the bondcoat could significantly affect the stress distribution in the TGO, in contrast, no obviously influence on the stresses in the YSZ topcoat.