Effect of heat treatment on the reflective spectrum of zinc oxide powders
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V.V. Neshchimenkoa) Amur State University, Blagoveshchensk, Amur Region 675027, Russia
Chundong Li, Shiyu He, and Dezhuang Yang Harbin Institute of Technology, Harbin 150001, China (Received 7 March 2008; accepted 13 June 2008)
To determine the optimum baking temperatures for nanopowder introduction, the variation of reflective spectrum of baked zinc oxide powders, which are used as pigments for thermal control coatings of spacecraft, has been investigated over the wavelength range of 0.225–2.5 mm after being baked at temperatures between 400 C and 850 C. It has been established that baking temperatures over 750 C result in a reduction of spectral reflectance in the visible light spectrum region. This is due to the formation of absorption bands of intrinsic point defects and thus increasing the spectral reflectance in the nearinfrared region. The optimum temperature is 650 C at which the bleaching effect was observed long after heat treatment. Moreover, an increase in the reflection coefficient occurs in the regions of 380–450 nm and 1100–2500 nm in this case. I. INTRODUCTION
Metallic oxides with high reflectance in the ultraviolet, visible, and near-infrared regions are used as pigments in thermal control coatings for spacecraft. Zinc oxide is found in coatings such as AK-573, BC-16, TPCO-1, TPCO-2, S-13, S-13G, and Z-93. It is still a serious issue to increase the optical stability of pigments used in thermal control coatings under conditions of outer space radiation. A promising way of increasing photo-radiation resistance is to modify the pigment with “white” oxide nanopowders. There have been some data reported on nanopowder modification to enhance the optical stability of the pigments under visible light and radiation. It has been established that the introduction of Al2O3 (7 wt%) and ZrO2 (1 wt%) nanopowders into TiO2 pigment via a 2 h baking process at 800 C could produce coatings with high reflectivity and good resistance to the radiation damage of energetic electrons and solar radiation.1,2 In Mikhailov and Verevkin3 it was shown that the modification of ZrO2 pigment with Al2O3 nanopowders (1 wt% and 3 wt%) at 800 C increases the coating resistance to simultaneous irradiations of EMR, protons, and electrons. The purpose of the present work is to research the influence of baking temperatures on optical properties a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0033 J. Mater. Res., Vol. 24, No. 1, Jan 2009
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of the coating and optimize the baking procedures for the introduction of nanopowders into ZnO pigments. II. EXPERIMENTAL
According to the “X Ty 10262-73” standard, commercial zinc oxide powders were selected as the pigments. The content of the impurities in the powder were measured and found to be less than (in wt%): 0.0001 (Cd), 0.005 (Pb), 0.0008 (Na), 0.00005 (As), 0.0001 (Cu), 0.0001 (Mn), 0.0008 (Ca), 0.004 (K), 0.0002 (Fe), 0.0004 (phosphates), 0.0004 (chlorides), 0.004 (sulfates), a
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