Dezhuang Yang

Effect of heat treatment on the reflective spectrum of zinc oxide powders

To determine the optimum baking temperatures for nanopowder introduction, thevariation of reflective spectrum of baked zinc oxide powders, which are used as pigmentsfor thermal control coatings of spacecraft, has been investigated over the wavelengthrange of 0.225–2.5 mm after being baked at temperatures between 400 C and 850 C. Ithas been established that baking temperatures over 750 C result in a reduction of spectralreflectance in the visible light spectrum region. This is due to the formation of absorptionbands of intrinsic point defects and thus increasing the spectral reflectance in the near-infrared region. The optimum temperature is 650 C at which the bleaching effect wasobserved long after heat treatment. Moreover, an increase in the reflection coefficientoccurs in the regions of 380–450 nm and 1100–2500 nm in this case.I. INTRODUCTIONMetallic oxides with high reflectance in the ultra-violet, visible, and near-infrared regions are used as pig-ments in thermal control coatings for spacecraft. Zincoxide is found in coatings such as AK-573, BC-16,TPCO-1, TPCO-2, S-13, S-13G, and Z-93. It is still aserious issue to increase the optical stability of pigmentsused in thermal control coatings under conditions ofouter space radiation. A promising way of increasingphoto-radiation resistance is to modify the pigment with“white” oxide nanopowders.There have been some data reported on nanopowdermodification to enhance the optical stability of the pig-ments under visible light and radiation. It has beenestablished that the introduction of Al

An analysis on changes in structure, tensile properties of polytetrafluoroethylene film induced by protons

Abstract Effect of 100xa0keV proton radiation on the structure and tensile properties of PTFE film was investigated. The change in structure before and after proton radiation was mainly evaluated by means of differential scanning calorimetry. The experimental results show that under radiation of 100xa0keV protons for the fluence less than 7×1015xa0p/cm2, the DSC characteristics including the phase enthalpy of transformations at room temperature ΔHrt1 and ΔHrt2, the melting enthalpy ΔHm1 and ΔHm2, the crystallization exothermal enthalpy ΔHc, and Tg II were decreased, while the melting temperature was increased a little with the fluence increase. The change in crystallization enthalpy ΔHc indicated the increase of molecular weight of the PTFE film, but for 150xa0keV when the fluence exceeded the fluence of 1016/cm2, the molecular weight decreased gradually. With increasing proton fluence, the thermal gravity loss was decreased, while the initial decomposition temperature increased, demonstrating that crosslinking of molecular chains occurred. With the increase of the proton fluence, for proton with energy less than 150xa0keV, the tensile fracture strength increased at first, but when the fluence exceeded 1016/cm2, the tensile fracture strength showed a decreasing trend. While for the proton of 170xa0keV, the tensile fracture strength σf increased abruptly at the fluence of 2×1013/cm2, with the fluence increasing further, the tensile fracture strength σf decreased gradually. The change of tensile properties could be related with the competition of branching crosslinking and the scission degradation.

Effect of electron exposure on optical properties of aluminized polyimide film

The effect of the irradiation of electrons with 10–70 keV on optical properties, including spectral reflectance ρ and solar absorptance a s , of aluminized polyimide films was investigated. The spectral reflectance was measured in situ before and after electron exposure. Experimental results showed that the reflective properties of aluminized polyimide film were apparently degraded in the 500–1200 nm wavelength range of the solar spectrum. Under the exposure of electrons, no charging effects were found on the aluminized polyimide film serving as an ion-conductive polymer. After the exposure, an “annealing” or “bleaching” effect occurred. At a given irradiation fluence, the change in solar absorptance (Δ a s ) of the aluminized polyimide film was increased with electron energy. There is a threshold value of electron flux φ cr which affects the change in Δ a s of the aluminized polyimide film, approximately φ cr = 6 × 10 12 electrons/cm 2 s. When φ cr , the change in Δ a s is independent from the flux; when φ > φ cr , Δ a s increases with the flux monotonically. The change in Δ a s with electron fluence Φ can be expressed in the form of a power function: Δ a s = αΦ β . The factors α and β are related to electron energy and show a maximum and a minimum value at 50 keV, respectively.

EFFECT OF VUV RADIATION ON PROPERTIES AND CHEMICAL STRUCTURE OF POLYETHYLENE TEREPHTHALATE FILM

The effect of VUV radiation on polyethylene terephthalate (PET) film was investigated. A gas-jet type of VUV source with the wavelengths of 5-200 nm was used. The experimental results show that under the VUV irradiation, both the tensile fracture strength and elongation decrease slightly. The spectral absorbance of the PET film increases noticeably with increasing VUV dose. The absorption band mainly forms in the near-ultraviolet region. The XPS, FTIR, and ESR analyses indicate that in the skin layer of PET film irradiated with VUV, the C-O bonds could be broken and decarbonylation occurs, leading to the formation of free radicals of benzene rings as well as a trend of carbonification. The scission of the macromolecule chains, the increase in radical concentration, and the carbonification would cause the degradation in optical properties for the PET film under VUV exposure.

Changes in properties and structure of polyethylene terephthalate film under vacuum ultraviolet

The effect of vacuum ultraviolet (VUV) radiation on polyethylene terephthalate (PET) film was investigated on a gas-jet VUV source with a wavelength of 5‐200 nm. The experimental results show that under VUV irradiation both tensile fracture strength and elongation decrease slightly. The spectral absorbance of the PET film increases noticeably with increasing dose. An absorption band mainly forms in the ultraviolet-to-visible region. X-ray photoelectron spectroscopy, Fourier transform infrared, and electron spin resonance analyses indicate that in the skin layer of PET film under VUV radiation, the C‐O bonds are broken and decarbonylation occurs, leading to the formation of free radicals as well as a trend to carbonification. The scission of the macromolecule chains, the increase in radical concentration, and the carbonification are considered to be major contributors to the change of optical properties for PET film under VUV exposure.