Papers by Keyword: Crystallization Behavior

Abstract: We investigated the electrical and structural effects of silicon (Si), yttrium (Y) and lanthanum (La) doping in 10-45 nm thick hafnium dioxide (HfO₂) films on silicon carbide (SiC) and Si substrates. We show that the introduction of Si dopants leads to a significant enhancement of the electric breakdown field and a reduction of the leakage current density by elevating the crystallization temperature. This effect becomes stronger with higher Si content. In contrast, Y and La doping does not raise T_C but increases the tetragonal and orthorhombic phase portion within the crystalline films and therefore enhances the dielectric constant k. Furthermore, we show that larger grains in crystalline films are associated with a higher leakage current density.

Abstract: Poly(lactic acid) (PLA) is a potential biodegradable polymer to replace petroleum-based plastic, however, its main drawback is brittleness because of slow crystallization rate. To overcome this limitation, compounding with some additives is the most chosen choice due to easy and effective preparation. In this study, an epoxidized soybean oil (ESO) and a microcrystalline cellulose (MCC) were applied as a plasticizer and a nucleating agent, respectively. The PLA was compounded with ESO and MCC by using a twin-screw extruder. The product sheets were prepared by using a chill-roll cast film extruder. Change of thermal property after adding ESO and MCC was investigated by a differential scanning calorimeter. Mechanical property of the prepared sheet was carried out by using a universal testing machine in a tensile mode. Microstructure of the sheets was also studied by wide angle X-ray diffraction (WAXD) and small angle X-ray scattering (SAXS) techniques. The results showed that ESO assisted plasticization while the MCC induced crystallization of PLA. Also, ESO and MCC eased flowability and alignment of PLA microstructure in machine direction.

Abstract: Hot-drawing of polyacrylonitrile (PAN) fibers is an important step in the production of carbon fibers. In this article, we investigated the effect of strain on the crystallization behavior and mechanical properties of PAN fibers treated in supercritical carbon dioxide (Sc-CO₂) fluid. We mainly used the methods of X-ray diffraction (XRD), monofilament strength analysis and differential scanning calorimeter (DSC) to study the crystallization behavior, mechanical properties and thermal behavior of PAN fibers during hot-drawing process. The experimental results showed that the crystallinity and mechanical properties of PAN fibers both increased a lot under the action of strain during hot-drawing in Sc-CO₂ fluid. This provides an important method for preparation of higher performance PAN precursor for PAN-based carbon fibers.

Abstract: Poly (trimethylene terephthalate) (PTT)/Poly (ethylene-butylacrylate-glyciyl methacrylate) (PTW) blends have been prepared in composition by weight 95/5, 90/10, 80/20 and 70/30 using the twin screw extruder approach. Their morphologies, crystallization behavior and mechanical properties were investigated. Scanning electron microscopy observation shows the uniform dispersion of PTW in PTT matrix with weight-average particle size from 0.98 to 3.64μm when the PTW content increases from 5wt% to 30wt% in the blends. The presence of the PTW increased the crystallinity of PTT matrix in PTT/PTW blends. A nucleation activity of the PTW appears in PTT/PTW blends.

Abstract: This study focus on synthesis of α-phase cordierite using different non-stoichiometric cordierite composition through solid state reaction by adjusting the ratio of magnesia, MgO and alumina, Al₂O₃ in the cordierite composition formulation respectively. The qualitative and quantitative of phase analysis was carried out by X-ray diffractive (XRD) technique and Rietveld structural refinement method. Differential thermal analysis (DTA) was employed to investigate the crystallization behavior of various cordierite formulations as the function of temperature. The scanning electron microscopy (SEM) was also performed. Cordierite with formulation of 2.5MgO.1.8Al₂O₃.5SiO₂ constitutes up to 96.4 wt% when the samples was sintered for 2 hours at the optimal temperature of 1375 °C. The SEM micrograph revealed that the approaching single α-Cordierite sample obtained densified body with well alignment of crystal structure.

Abstract: In this work, Cu₅₀Zr₄₃Al₇ metallic glass powders were produced by gas atomization method. The structure and crystallization characteristics of the as-prepared powders with different particle size distributions were studied in detail. The amorphous state of the alloy powders was confirmed by X-ray diffraction (XRD), in which amorphous phase formed. The scanning election microscopy (SEM) result showed that the selected metallic glass powder performed excellent owned good spherical morphology, which was also observed on an optical microscope (OM). At the same time, the particle size distributions ranging from 20 μm to 200 μm of as-prepared metallic glass powders were determined by laser diffraction. Moreover, the crystallization behavior of the Cu₅₀Zr₄₃Al₇ metallic glass powders was investigated by differential scanning calorimetry (DSC).

Abstract: Polypropylene (PP)/ethylene-vinyl acetate (EVA) blends were prepared using a twin-screw extruder by melt blending method. The influences of the EVA contents in PP/EVA blends on crystallization behavior and mechanical properties were investigated by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). XRD results show that the EVA not change the crystal structure in the blends but only decrease the intensity of the diffraction peak. DSC results showed that the melting point and crystallization point decreased when EVA added to the blend. The tensile properties of PP/EVA blend become much better.

Abstract: Polypropylene (PP)/Maleic anhydride grafted poly (ethylene-octene) (POEg) were prepared by melt blending method. The crystallization behavior and crystal morphology were studied by differential scanning calorimetry (DSC), X-ray diffraction (XRD), and polarzing optical microscope (POM). Differential scanning colorimetry (DSC) experiments showed that the melting point and crystallization point decreased when POEg added to the blend. XRD results show that the POEg not change the crystal structure in the blends but only decrease the intensity of the diffraction peak. The spherulitic structure could also observed when added POEg to the matix of PP, but the shape of the spherulites distorted.

Abstract: A sorbitolum compound and an aryl amide compound were applied to prepare α-nucleated PP (α-PP) and β-nucleated PP (β-PP), respectively. Effects of UV irradiation on the molecular structure and tensile properties of pure PP, α-PP and β-PP were investigated. The relationship of tensile strength with carbonyl index was discussed. The change of relative content of β-modification in β-PP during photodegradation was examined by WAXD. The carbonyl index calculated from FTIR spectra arranged as α-PP > PP > β-PP, however, the tensile strength retention at the UV irradiation time of 792h arranged as PP > β-PP > α-PP. The relative content of β-crystal nearly unchanged during the photodegradation.

Abstract: The composites of PP/Talc modified by stearic acid were prepared and its effect on the properties of PP/Talc composites was investigated in this paper. The tensile strength and impact strength of PP/Talc composites increased about 15% and 30% compared with pure PP respectively. Based on surface analysis by scanning electron microscope (SEM), the Talc particles buried well in PP matrix when the Talc was coated with the stearic acid. At the same time, it was found that Talc significantly increased the crystallization temperature and crystallization rate of PP by differential scanning calorimetry (DSC).