Min Qi

Mechanical alloying of immiscible Pb-Al binary system by high energy ball milling

In the present work, mechanical alloying has been applied to the Pb-Al immiscible binary system by using the method of high energy ball milling. The microstructural features of the milled powder, such as grain size, lattice constant and morphology of phases have been studied by X-ray diffraction, analytical transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Besides, energy dispersive spectroscopy was used to analysis chemical composition of phases presented after milling. Differential Scanning Calorimetry measurement was also made on the milled Pb-Al powder. The results show that homogenous blending of Pb and Al can be easily achieved by high energy ball milling in spite of their mutual immiscibility and large difference in density. The obtained alloy exhibits nanocrystalline microstructure. Further more, the experiment result implies the formation of supersaturated solid solution in immiscible Pb-Al system by high energy ball milling.

Topology optimization of a novel stent platform with drug reservoirs

The new generation of drug-eluting stents (DES) is required to control drug release kinetics. A novel DES (the Conor stent) with drug reservoirs on struts has been engineered. Topology optimization of one Conor stent strut was based on the commercial finite element analysis code OptiStruct, with the aim of increasing the strut stiffness while retaining its drug holding capacity. Results show that the element density distribution of the strut model was optimized with manufacturing constraints of extrusion constraint and minimum member size control. The optimal result was directly transformed to a clear, manufacturable design concept using the OptiStruct utility OSSmooth. The final manufacturing design increased the strut stiffness and yielded better stress distribution, as compared to the original strut design under the same loading. Topology optimization may help designers devise novel stent platforms for future DES with drug reservoirs and adequate scaffolding.

Biodegradable radiopaque iodinated poly(ester urethane)s containing poly(ε-caprolactone) blocks: Synthesis, characterization, and biocompatibility

Biodegradable radiopaque iodinated poly(ester-urethane) (I-PU), consisting of poly(ε-caprolactone) (PCL) diol and iodinated bisphenol A (IBPA), has been successfully synthesized via a coupling reaction of PCL-diisocyanate and IBPA with varying compositions. The IBPA with four iodine atoms per molecule was applied as a chain extender to endow the I-PUs with intrinsic X-ray visibility. The chemical structure and molecular weights of I-PUs were characterized by Fourier transform infrared spectroscopy (FT-IR), proton-nuclear magnetic resonance, and gel permeation chromatography (GPC). The effects of IBPA on the physical properties of I-PUs were systematically studied by means of differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and wide-angle X-ray diffraction (WAXD). The DSC results showed that the crystallization of PCL segments in I-PUs was restrained with increasing amount of IBPA, which was also confirmed by WAXD. In the X-radiography analysis, all the synthesized I-PUs exhibited high radiopacity compared with an aluminum wedge of equivalent thickness. Enzymatic degradation tests showed that the incorporation of IBPA prolonged the degradation of I-PUs and distinct mass loss and degradation happened in the third month. Basic cytocompatibility conducted using rat adipose-derived cells proved that all the I-PUs and their biodegradation products were nontoxic. The radiopaque I-PUs is expected to possess a significant advantage over the traditional polymer counterparts in some related biomedical fields.

Morphology, crystallization and mechanical properties of poly(ɛ-caprolactone)/graphene oxide nanocomposites

A series of nanocomposites based on poly(ɛ-caprolactone) (PCL) and graphene oxide (GO) were prepared by in situ polymerization. Scanning electron microscopy observation revealed not only a well dispersion of GO but also a strong interfacial interaction between GO and the PCL matrix, as evidenced by the presence of some GO nanosheets embedded in the matrix. Effects of GO nanofillers on the crystal structure, crystallization behavior and spherulitic morphology of the PCL matrix were investigated in detail. The results showed that the crystallization temperature of PCL enhanced significantly due to the presence of GO in the nanocomposites, however, the addition of GO did not affect the crystal structure greatly. Thermal stability of PCL remarkably increased with the addition of GO nanosheets, compared with that of pure PCL. Incorporation of GO greatly improved the tensile strength and Young’s modulus of PCL without a significant loss of the elongation at break.

Mechanical alloying of ceramics in zirconia-ceria system

Abstract In this work, the zirconia and ceria crystalline powders mixture with a composition of ZrO2-30mol.%CeO2 has been subjected to high energy ball milling experiment to investigate whether mechanical alloying is possible in this ceramic system. The structure variation of the powders was followed mainly by X-ray diffraction technique. The result proves that mechanical alloying can occur in ceramic systems.

Fatigue crack growth in SiC particulates reinforced Al matrix graded composite

The SiC/Al graded composite was fabricated by powder metallurgy processing and its fatigue crack growth behavior was studied. The volume percentage of SiC particulates was distributed from 5 to 30% layer by layer on the cross section. Since the aluminium was dissolved together, there was no evident interface between the two layers with different volume fraction of SiC particulates. Fatigue crack growth was in direction of from 5 to 30% SiC layers under sinusoidal wave-form. The retardation of fatigue crack growth was found when crack propagated from low volume fraction of SiC to high volume fraction of SiC. The crack deflection and branching between two layers were observed, which decreased crack growth rates. In view of crack tip driving force, the plasticity mismatch between the layers shielded crack tip driving force, i.e. decreased the effective J-integral at the tip of the crack as the plastic zone of the crack tip spread from the weaker material into the stronger material.

Facile preparation of poly(ε-caprolactone)/Fe3O4@graphene oxide superparamagnetic nanocomposites

The main goal in this work was to prepare and characterize a kind of novel superparamagnetic poly(ε-caprolactone)/Fe3O4@graphene oxide (PCL/Fe3O4@GO) nanocomposites via facile in situ polymerization. Fabrication procedure included two steps: (1) GO nanosheets were decorated with Fe3O4 nanoparticles by an inverse co-precipitation method, which resulted in the production of the magnetite/GO hybrid nanoparticles (Fe3O4@GO); (2) incorporation of Fe3O4@GO into PCL matrix through in situ polymerization afforded the magnetic nanocomposites (PCL/Fe3O4@GO). The microstructure, morphology, crystallization properties, thermal stability and magnetization properties of nanocomposites were investigated with various techniques in detail. Results of wide-angle X-ray diffraction showed that the incorporation of the Fe3O4@GO nanoparticles did not affect the crystal structure of PCL. Images of field emission scanning electron microscope and transmission electron microscopy showed Fe3O4@GO nanoparticles evenly spread over PCL/Fe3O4@GO nanocomposites. Differential scanning calorimeter and polar optical microscopy showed that the crystallization temperature increased and the spherulites size decreased by the presence of Fe3O4@GO nanoparticles in the nanocomposites due to the heterogeneous nucleation effect. Thermogravimetric analysis indicated that the addition of Fe3O4@GO nanoparticles reduced the thermal stability of PCL in the nanocomposites. The superparamagnetic behavior of the PCL/Fe3O4@GO nanocomposites was testified by the superconducting quantum interference device magnetometer analysis. The obtained superparamagnetic nanocomposites present potential applications in tissue engineering and targeted drug delivery.

Mechanical alloying process of the zirconia–8 mol % yttria ceramic powder

The phase transformation process of zirconia–8 molu2009% yttria powder mixtures during a high energy ball milling process has been studied by means of x‐ray diffraction analysis. It has been found that the m‐ZrO2 (monoclinic zirconia) transforms first to m‐ZrO2 solid solution and then to t‐ZrO2 (tetragonal zirconia) solid solution. Finally, a single cubic zirconia solid solution phase forms after prolonged milling. The structural transformation is discussed and explained in terms of the phase relations in zirconia‐yttria ceramics and the nonequilibrium nature of the mechanical alloying.

Properties of cobalt nanofiber-based magnetorheological fluids

Co nanofibers were synthesized by a surfactant-assisted solvothermal method. They were characterized by XRD, EDS, SEM, TEM and SQUID. The results indicated that the obtained products were hexagonal close-packed cobalt nanofibers with high purity. They presented large length to diameter ratio, and a high saturation magnetization of 142 emu g−1. Two magnetorheological (MR) fluids were prepared by the Co nanofibers and carbonyl iron particles with 12% particles volume fraction, respectively. Their magnetorheological properties and sedimentation stability were tested and compared. The results indicated that the Co nanofiber-based MR fluid presented higher yield stress than the carbonyl iron particles-based one at low field levels (0–150 kA m−1). The strong chains or column structure caused by the specific morphology and high magnetization of the Co nanofibers is responsible for their significant MR properties. In 15 days setting, the Co nanofibers-based MR fluid presented little sedimentation, while the sedimentation ratio of the carbonyl iron particles-based MR fluid was 50%. The Co nanofibers are ideal candidates to prepare MR fluids with good sedimentation stability as well as good magnetorheological properties.

Effect of copper addition on mechanical properties, corrosion resistance and antibacterial property of 316L stainless steel

The effects of addition of different Cu content (0, 2.5 and 3.5wt%) on mechanical properties, corrosion resistance and antibacterial performance of 316L austenitic stainless steel (SS) after solution and aging treatment were investigated by mechanical test, transmission electron microscope (TEM), X-ray diffraction (XRD), electrochemical corrosion, X-ray photoelectron spectroscopy (XPS) and antibacterial test. The results showed that the Cu addition and heat treatment had no obvious influence on the microstructure with complete austenite features. The yield strength (YS) after solution treatment was almost similar, whereas the aging treatment obviously increased the YS due to formation of tiny Cu-rich precipitates. The pitting and protective potential of the solution treated Cu-bearing 316L SS in 0.9wt% NaCl solution increased with increasing Cu content, while gradually declined after aging, owing to the high density Cu-rich precipitation. The antibacterial test proved that higher Cu content and aging were two compulsory processes to exert good antibacterial performance. The XPS results further indicated that aging enhanced the Cu enrichment in passive film, which could effectively stimulate the Cu ions release from the surface of passive film.