Formation of radiation-generated color centers using single crystals of magnesium oxide is discussed. Crystal structure of magnesium oxide is described. Chemical processes used to produce magnesium oxide with desired color center kinetics are presented. Proton irradiation of magnesium oxide crystals was conducted to determine lattice defects

Berggren, C. C.

Levin, H.

Peffley, W. M.

English

NASA Technical Reports Server

August 1972	 B72-10424 
NASA TECH BRIEF 
Ames Research Center
	 4r 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
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be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Improved Magnesia for Thermal Control Coatings 
Magnesia is often used as the basis pigment for 
white thermal control coatings on spacecraft. How-
ever, the service life of magnesia-based coatings is 
limited because even low-level space radiation (e.g., 
1-keV protons) discolors the white pigments. The 
radiation-induced discoloration of magnesia was 
known to be the result of the interaction of radiation 
with impurities; for example, for a cubic lattice of the 
MgO type, iron constitutes a characteristic impurity 
defect in which iron(II)—iron(III) pairs are involved 
in color formation. 
A study of color-center formation in single crystals 
(high purity) and in commercially available powders 
of magnesia upon irradiation with 1-keV protons was 
performed in order to gain understanding of impurity 
and intrinsic lattice defects which are conducive to 
the formation of radiation-generated color centers. 
It was found that discoloring of magnesia by iron(III) 
can be suppressed nearly completely by heating high-
purity magnesia (less than 10 ppm atomic Fe content) 
at 1200° to 1500°C in nitrogen, hydrogen, or in a 
vacuum; less pure material does not respond as well. 
Magnesia which has been properly processed for 
use in thermal control coatings should have transition 
metal contents in concentrations less than 5 to 10 ppm 
(atomic); furthermore, the valence of the transition 
metal ions should be largely the reduced state, as can 
be readily accomplished by chemical reduction pro-
cedures. Magnesium oxide single crystal was pre-
pared at an iron(II) concentration of 5 x 1017 atoms per 
ml and an iron(III) concentration of about 0.4 x 10' 
atoms per ml (total iron 5 ppma). Upon irradiation 
with 1-keV protons (total 2.3 x 1017 protons/cm2), the
estimated solar absorbance (as 0.03) increased less 
than about 5%. 
The results of the study also revealed that discolor-
ation of pigments by radiation can be reduced mark-
edly by introduction of controlled densities of selected 
defects. Typical deliberately introduced defects in-
volve impurities, native lattice defects, or a combina-
tion of both. For example, increasing the iron content 
from 2.0 ppma to 541 ppma effectively suppresses 
radiative discoloration. The iron (11)—iron (III) pairs 
act as recombination centers for both radiation-gen-
erated electrons and holes and, in sufficient concentra-
tions, dominate the color center (coloration) kinetics. 
However, the iron redox pair (substitutional) imparts 
an undesirable yellowish coloration to the magnesia. 
A more desirable ion pair is the ceric-cerous redox 
system which has a coloration in the near-UV spec-
trum, but even more desirable is the lattice-defect 
pair, F—F+ which shifts coloration deep into the near 
UV. The pair can be produced in magnesium oxide 
in controlled density by additive coloration in mag-
nesium vapor. 
Notes: 
1. The following documentation may be obtained 
from: 
National Technical Information Service 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.95) 
Reference: 
NASA CR-73337 (N69-31983), Study of 
Color Center Formation in White Powder 
Compounds.
(continued overleaf) 
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2. Requests for further information may be directed 
to:
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California 94035 
Reference: TSP 72-10424 
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to:
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Mail Code 200-1A 
Ames Research Center 
Moffett Field, California 94035 
Source: Herman Levin, Cedric C. Berggren, 
and Willard M. Peffley of 
Hughes Aircraft Company
under contract to
Ames Research Center 
(ARC-10677) 
B72-10424	 Category 04 
•III


Improved magnesia for thermal control coatings

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