Papers by Author: Wen Jun He

Abstract: The bioactivity of commercially pure titanium treated with H₂O₂ solution and/or heating process are evaluated by immersing the specimens in a simulated body fluid (SBF). Bone-like apatite with typical characteristics of low crystallinity and defective structure was deposited on the H₂O₂/SnCl₂-treated titanium surface. Heating treatment or immersion time can improve the deposition effect of apatite to a certain extent. The atom ratio of Ca/P in the formed apatite varies from 2.7 to 1.6, deviating from the equilibrium ratio 1.7 of HA. The mechanism for nucleation and growth of the apatite layer can be attributed to the amorphous titania sol, the morphology filled with numerous net and crack in Ti surface and the catalyze effect of Sn ion.

Abstract: Crystal structures and shape memory properties of Ti-rich Ti52Ni23Cu25 (at.%) ribbon annealed at 450°C for 10 min and 1 h were investigated by X-ray diffraction and dynamic mechanical analyzer. As-spun ribbon was full amorphous and its crystalline peak temperature is 455.4°C. The annealed ribbon is crystallized with strong preferential (110)-B2 orientation. It shows a well-defined shape memory effect and the transformation hysteresis for the annealed ribbon under an external load in the range of 3-9 N is about 38.5°C. With annealing time increasing from 10 min to 1 h, the maximum of transformation strain under the external stress decreases from 1.93% to 1.7%. The temperature dependence of the external stress increases from 0.3 N/°C to 0.43 N/°C. The residual plastic strain is up to about 0.4% at a load of 9 N.

Abstract: The lattice parameters, five independent elastic constants and the bulk modulus B on the applied pressure of hexagonal boron nitride (h-BN) are calculated by using a first-principles pseudopotential method. The calculation results are in good agreement with the experimental and theoretical values. It is found that the most stable structure of h-BN corresponds to the axial ratio c/a of about 2.652.

Abstract: Martensitic transformation (MT) and the internal friction (IF) behavior of the initially amorphous Ti-rich Ti-Ni-Cu melt-spun ribbon annealed at 400°C for 10 h were investigated by using DSC and dynamic mechanical analysis (DMA). The annealed ribbon shows B2 structure with strong preferential (110) orientation and exhibits B2↔B19 MT with the temperature hysteresis of 13°C. DMA tests show that the internal friction is frequencies dependence at 1-50 Hz. The tanδ values decrease with the increasing frequency, but it does not meet the 1/f dependence. Isothermal DMA tests show that the tanδ value at a temperature of 15°C in the MT zone increases quickly from 0.005 to 0.045 with the increasing isothermal intervals and keep stable subsequently. The isothermal time to complete the MT can be determined by the DMA tanδ curve directly.

Abstract: Nanostructured Lanthanum hexaboride (LaB6) powders were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectra (XPS). The average size of LaB6 nanoparticles is about 35nm, which are well crystallized with ball or ellipsoid with inconspicuous corners and covered by a 3-5nm thick amorphous layer containing oxygen and carbon. The absorption of LaB6 nanoparticles in visible and near infrared spectrum (NIR) was measured and compared with micron scale particles. The surface plasmon responance (SPR) of nanoparticles was very efficient at NIR blocking, which almost covered the whole NIR region. The influence of nanoparticles concentration on spectrum absorption was comparatively evident. Meanwhile, micron particles almost haven’t NIR blocking function.