Chonghong Zhang

Chemical modifications in polyethylene terephthalate films induced by 35 MeV/u Ar ions

Abstract Semicrystalline polyethylene terephthalate (PET) foil stacks were irradiated under vacuum and at room temperature with 35 MeV/u Ar ions to fluences ranging from 1×10 10 to 5×10 12 ions/cm2. Ion induced modifications in crystalline and chemical structures were studied by means of differential scanning calorimetry (DSC), Fourier-transform infrared absorption spectroscopy (FTIR), and X-ray diffractometer (XRD). The DSC and XRD data show a significant loss of crystallinity at the absorbed doses higher than 4.0 MGy. FTIR measurements indicate that the loss of crystallinity of the irradiated PET is related to the scission processes of the main chains at the trans configuration of the ethylene glycol residue. Meanwhile, at the absorbed dose above about 4.0 MGy, bond breaking processes at the para position of benzene are also observed. The benzene ring structures are found to be more stable under irradiation.

Study of effects in polyethylene terephthalate films induced by high energy Ar ion irradiation

Abstract Semicrystalline polyethylene terephthalate (PET) foil stacks were irradiated with 1.373 GeV Ar ions to different fluences ranging from 1.0×1010 to 5.0×1012 ions/cm2. The induced effects were investigated by means of the Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible absorption spectroscopy (UV/VIS) and electron spin resonance spectroscopy (ESR). FTIR measurements show that bond breaking processes are mainly observed at the ethylene glycol residue of trans configuration and at the para position of benzene rings above a critical dose of about 4.0 MGy. Damage cross-section has been extracted for the band at 973 cm−1 from the dependence of the absorbance on fluence and it shows a linear dependence on the mean electronic energy loss. UV/VIS measurements show a strong increase in absorbance in the ultraviolet and visible regions. It is found that for the same absorbed dose, more increase in absorbance is induced at higher electronic energy loss. ESR measurements indicate the creation of free radicals. The radical concentration is found to increase rapidly with the increasing absorbed dose above 4.0 MGy.

Molecular conformation changes of PET films under high-energy Ar ion bombardment

Abstract Investigation of the surface modification in molecular structure of semicrystalline polyethylene terephthalate (PET) films induced by Ar ion bombardment is presented. The PET samples are analysed by using Fourier transform infrared spectroscopy (FTIR), X-ray diffractometer (XRD), and X-ray photoelectron spectroscopy (XPS). A significant loss of crystallinity is observed, which is related to the configuration transformation of ethylene glycol residue from the trans into the gauche. Chain scissions are observed at the para position of di-substituted benzene rings, –CO bonds and C–O bonds. The C–O bonds are destroyed more selectively than –CO bonds. The benzene ring structures show only small change under irradiation and do not participate in degradation process. Extra CC bonds and alkyne end groups are created above a critical dose of 4.0 MGy. The results are briefly discussed.

Formation of bubbles in helium implanted 316L stainless steel at temperatures between 25 and 550°C☆

Abstract This work studies the formation behavior of helium bubbles in 316L stainless steel implanted with 2.5 MeV He ions at temperatures ranging from 25 to 550°C. The dose and dose rate are 2.5 × 10 21 ions/m 2 and 3.2 × 10 16 ions/m 2 /s for each implantation. Bubble structures in each specimen are investigated with transmission electron microscopy. The temperature dependence of the measured number densities and mean diameters of bubble exhibits two distinctly different regimes with different apparent activation energies: the regime between 350 and 550°C with high apparent activation energies and the regime between 25 and 350°C with low apparent activation energies. The effect of the pre-implantation cold working is significant on bubble formation only in the regime between 350 and 550°C. Further analysis indicates that the regime between 350 and 550°C is controlled by He diffusion via the self-interstitial/He replacement mechanism and the regime between 25 and 350°C is controlled by He diffusion via the interstial mechanism. The results are compared with other experimental findings and show consitence with them.

Microstructural changes in a low-activation Fe–Cr–Mn alloy irradiated with 92 MeV Ar ions at 450°C

In this work, a solution-annealed specimen of a low-activation Fe-Cr-Mn alloy was irradiated with 92 MeV Ar ions at 450 degreesC to a dose of 1.7 x 10(21) m(-2) which was expected to produce a peak displacement damage of 90 dpa. After irradiation, damage microstructure was investigated from the cross-sectional specimens using a transmission electron microscope. High number density cavities were observed in the peak dose region. Size of cavities was the largest at the peak displacement damage. Formation of alpha -phase was found at a grain boundary in the peak dose region. Well-dispersed carbide particles was found in the matrix. The carbide/matrix interfaces supplied favorable site for growth of large cavities, whereas only small cavities were found inside the particles

Chemical modifications of ion irradiated polystyrene probed by optical absorption measurements

Abstract Polystyrene (PS) films are irradiated at room temperature with 3 MeV silicon ions and 1.4 GeV argon ions to fluences ranging from 1×10 10 to 3×10 14 cm −2 . Fourier transform infrared (FTIR) specula reflection spectra and ultraviolet/visible (UV/Vis) transmission spectra are measured to investigate the radiation-induced chemical modifications. It is found that the intrinsic absorption bands show reduction in intensity with increasing fluence and electronic energy loss, indicating the degradation of the polymeric structure. For Si ion implanted specimens, significant chemical modifications occur above about 3×10 13 cm −2 , corresponding to an average energy deposition of about 45 MGy. For Ar ion irradiated specimens, the critical electronic energy loss is around 0.77 keV/nm at the fluence of 5.5×10 12 cm −2 , corresponding to an energy deposition of about 6.4 MGy. The increase in absorbance in the UV/Vis range and a shift of the absorption edge toward the visible is attributed to carbonization of the material. The results are discussed on the basis of ion fluence and energy loss.

Chemical modification of polycarbonate induced by 1.4 GeV Ar ions

Abstract Polycarbonate foil stacks were irradiated with 1.4 GeV Ar ions at room temperature. The induced modifications in chemical structure were studied by Fourier transform infrared (FTIR) and ultraviolet/visible absorption (UV/VIS) spectroscopies. FTIR measurements reveal that material degradation through bond breaking are the main effects. Significant reduction in absorbance of the typical infrared bands is observed at energy densities higher than 8×10 22 eV / cm 3 . Alkyne end groups are produced by the irradiations and the electronic energy loss threshold for production of the alkyne end group is found to be below 0.61 keV/nm. UV/VIS measurements indicate a shifting of the absorption edge from ultraviolet towards visible and a strong increase of absorbance in the ultraviolet and visible regions. The irradiation induced changes in absorbance at wavelengths of 380, 450 and 500 nm follow roughly linear relationship with fluence and scale rather good with the square of electronic energy loss. The results are briefly discussed.

Diffusion and agglomeration of helium in stainless steel in the temperature range from RT to 600°C

Abstract Diffusion of helium and formation of helium bubbles in stainless steel in conditions of atomic displacement in the temperature range from RT to 600°C are studied theoretically using standard rate equations. The dissociative mechanism via self-interstitial/He replacement is assumed to control helium diffusion and bubble formation. The numerical analysis shows that the temperature dependence of the effective diffusion coefficient of helium, the number density and the mean radius of bubbles has two distinctly different regimes with the transition occurring around 300°C. The effective diffusion coefficient of helium, the number density and the mean radius of bubbles show weak temperature dependence in the low temperature regime, while they change abruptly with temperature in the high temperature regime. The results are qualitatively in agreement with the results of our experimental study on helium diffusion and bubble formation in helium-implanted 316L stainless steel. However, the discrepancy in the absolute values of number density and mean radius of bubbles between theoretical and experimental studies indicates that helium diffusion and bubble formation may be controlled by some athermal mechanisms in the low temperature regime.

Thermal stability of small He-vacancy clusters in 316L stainless steel irradiated with 2.5 MeV He+ ions at 550°C

In this work, temperature-variation irradiations were performed with In this work, temperature-variation irradiations were performed with

Defects in SiO2 glass irradiated with high energy Ar ions

Abstract SiO2 glass specimens are irradiated at room temperature with 560 MeV and 1.15 GeV Ar ions. Defect production is investigated by positron lifetime spectra, EPR and UV absorption measurements. Free volumes of about 0.065 nm3 in size are found to be present in the virgin specimen from the corresponding Ortho-Positronium lifetimes. With increasing dose the intensity of the component corresponding to positronium decreases sharply. This is attributed to the preferred annihilation of positrons with the radiation-ionized-electrons wandering in free volumes of the material. Optical absorption bands are induced at about 5.8, 5 and 4.5 eV by the irradiations and the absorption coefficients increase gradually with increasing dose. The EPR spectra of the irradiated specimens show the occurrence of the E′ center, the number density of which reveals two distinct regimes according to its dependence on dose. In the low dose range the number density of E′ center follows a 0.23 power law dose dependence whereas at high dose it increases linearly with dose. Furthermore the EPR spectra show fine structure which changes with dose.