Materials Science Forum Vol. 850

Abstract: This paper study the migration characteristics and degradation kinetics of bisphenol A using TGA - gas chromatography - mass spectrometry and found that bisphenol A polycarbonate in the thermal oxidative aging conditions of 130 °C de-gradated to bisphenol A. At the range of 0 h to 120 h, the bisphenol A content of environmental hormones increased with time. When it reached 120 h, bisphenol A environmental hormone content decreased slightly with aging time. The content of bisphenol A reached 495mg/kg when the thermal oxidative aging time was 168 h, which was decreased compared to the content of 442mg/kg at 120 h. Polycarbonate thermal decomposition kinetics study showed that the thermal decomposition of polycarbonate can be divided into three phases. The first thermal decomposition occurred at the range of 415° C to 425 ° C, the polycarbonate end groups fracture of the second stage at 493.6°C , the main fracture of the main chain rearrangement and crosslinking, and the third stage at 598.7°C, the degradation of the chain continues to decompose and the decomposition of the crosslinked carbon precursor; thermal oxidation aging of polycarbonate decreased the heat stability and promote the thermal decomposition of polycarbonate. Comparing the oxidation induction period, thermal weight loss rate and activation energy of polycarbonate before and after thermal oxidative aging, it c found that the thermal stability of the hot oxygen aging of polycarbonate is reduced.

Abstract: The degradation of polycarbonate (PC) food contact materials was studied based on analysis with GC-MS, FTIR, UV-Vis and TG techniques. It was evident that the processing temperature of the materials significantly enhanced the release of bisphenol A, an endocrine disruptor. Investigation of the redshift of UV band also revealed that high temperatures accelerated the aging degradation of PC.

Abstract: Polyethylene terephthalate (PET) is usually used as food packaging materials. And the heavy metal introduced during the process of manufacture usually exists in the spaces between macromolecules as monomer form. When PET contacts with real food, some heavy metals will migrate into the food since the motion of these molecules overcomes the binding power. As a result, it does great harm to our health. In this article PET was disposed in different thermal ageing conditions in order to accelerate its aging process. Then the original and aged PET samples were tested by Different Scanning Calorimeter (DSC) to characterize its crystallinity. And migration experiments was conducted on them using 4% acetic acid (V/V) as food simulate, the heavy metal content in food simulates was detected by Inductively Coupled Plasma Mass Spectrometry (ICP-MS), so that we can get the migration characteristics of heavy metal. The results show that different aging conditions can do harm to the structure of PET in varying degrees by changing its crystallinity and molecules arrangement. But the difference of crystallinity has no obvious effect on Sb migration characteristic of PET samples. While, the migration quantity of Sb increases significantly with the increase of migrate temperature. It will provide an important reference to the evaluation of use security and service life of PET in real usage to study the relation between heavy metal migration features and aging degree.

Abstract: The monochromator for the new residual stress diffractometer at China Advanced Research Reactor (CARR) was simulated and optimized using SIMRES software. Objected the Fe (211) diffraction peak, the effect of horizontal and vertical curvature of Si (400) monochromator on Figure of Merit was studied to optimize the focusing parameters. With the optimal focusing condition, the influence of wafer thickness, number of wafers, packet height and gap of packets on performance of instrument was calculated consequently and the corresponding geometrical size was fixed. Finally, the design of the monochromator for the new residual stress diffractometer at CARR was completed.

Abstract: Neutron imaging (NI) has unique feature compared with X-ray imaging for the difference of the transmission characteristics through matters. The sensitivity to light elements, especially hydrogen, and the large penetration length through metals give it special advantages. NI has become a particularly useful universal technique for scientific and applied studies in various research disciplines. This article reviews the recent development of neutron imaging at China Advanced Research Reactor (CARR), including the instrumentations for indirect and real-time imaging and their application for non-destructive testing of nuclear fuel rod, two-phase flow, fuel cell, rock and concrete, etc.

Abstract: In order to serve a growing multidisciplinary community beyond the traditional scattering areas, an energy-selective neutron imaging instrument is proposed in the China Spallation Neutron Source (CSNS). The instrument is planned to provide analytical techniques such as state-of-the-art energy-selective neutron imaging, neutron radiography, tomography, polarized neutron imaging, neutron phase contrast imaging, and combined neutron diffraction. Coupled hydrogen moderator (CHM) will be chosen as its neutron source. A flight path of 40 m from moderator to sample will provide good energy resolution better than ~0.4%. Super mirror neutron guide will be used to transport neutron from moderator to aperture selector. Aperture selector with 5 apertures and a set of slits will be used to adjust the neutron beam for different modalities. The best spatial resolution will be 50 μm. Different types of detectors will be needed including high spatial resolution CCD camera, TOF detector, and scintillator detector. With a main emphasis on advanced materials and engineering studies, the instrument will enable 2D/3D mapping of the microstructure, chemical composition, and crystallographic structure (grain size, stress and strain, phase position, texture, and so on). It will also support a broad range of studies in archaeology, biology, biomedicine, geosciences, building technology, manufacturing processes, forensic, and homeland security applications.

Abstract: A plate (30mm thick) of aluminum alloy 7085-T76 was quenched into water at room temperature after solution treated at 470°C. The quenching residual stresses distributions were studied by both experimental measurement and FEM (Finite Element Method) simulation. The experimental measurement was accomplished by using the contour method, and the FEM simulation was carried out to verify the experimental results. The experimental quenching residual stress distributions showed the tensile stresses of 74.8MPa ~109MPa in the center part, and compressive stresses of 29MPa-63.6MPa on the surface. The prediction distributions showed the maximum tensile stress of 98.2MPa in the center and the maximum compressive stress of 50.5MPa on the surface. The experimental quenching residual stresses distributions agree favorably with the prediction results. The deviations of the maximum tensile stress were less than 25MPa in the center. The deviations may be attributed to the accuracy of the contour method and the idealization of the prediction model.

Abstract: In order to study the evolution of local crystal and electronic structure of Sr₂CuO₂F_2+x, the synchrotron radiation x-ray absorption (XAS) and x-ray absorption fine structure (XAFS) techniques were both performed on different amount of Sr₂CuO₂F_2+x materials. The relationship between high T_c superconductivity and valence state of cooper was mainly discussed. And the effect of by-reproduce SrF₂ in non-superconductive Sr₂CuO₂F_2+x on physical property of this material was considered. The experimental results showed that the valence state of Cu and the amount of SrF₂ was mainly related with high T_c superconductivity of Sr₂CuO₂F_2+x material, indicating a good method for improving T_c.

Abstract: Synchrotron X-ray radiography was used to in-situ study the growth of equiaxed dendrite during the solidification of Al-20 wt.% Cu alloy. Equiaxed dendrites with two different morphologies were formed in nearly isothermal conditions. The image processing was used to improve the image quality. The time evolution of the primary dendrite arm length and the corresponding growth rates were analyzed. The experimental results indicated that the solute interaction was the main factor to influence the equiaxed dendrites growth. Besides, the rotation and floating of the dendrites were also observed during the early growth phase.

Abstract: In this paper, synchrotron X-ray radiography was used to study the grain refining performance of direct current (DC) during the solidification of Sn-50 wt.% Pb alloy. Based on the radiographs, the variations of equiaxed grain number and dendrite growth rate with time were measured and analyzed. It is shown that DC mainly affects the microstructure formation through changing the nucleation behavior and the dendrite growth rate. When DC was applied during the whole process of solidification, the nucleation was enhanced and the dendrite growth was suppressed, which resulted in significant grain refinement.