2. Experimental

For modification by various nanoparticles, the rutile TiO2 powders with the average particle size of 240 nm and specific surface of 8 m2 /g were used. The anatase TiO2 powders with the average particle size of 260 nm and specific surface of 7 m<sup>2</sup> /g were used for modification with SiO2 nanoparticles (average particle size 12–14 nm). The TiO2 powder was mixed with oxide nanoparticles in a ratio 100:7, the distilled water was added, and it was evaporated at the temperature of 150C for 6 hours. Then, the mixture was heated in an oven for 2 hours at 400 or 800C. After heating, the mixture was grinded in agate mortar and was pressed into metal substrates with 28 mm diameter and 2 mm height. The prepared samples were mounted in space environment simulator "Spektr" [15]. Since the sample interaction with atmospheric oxygen after irradiation can lead to "bleaching"—a decrease in concentration of formed absorption centers of oxide reflective powders, the diffuse reflection spectra (rλ) were registered in vacuum (in situ) after irradiation with accelerated electrons (E = 30 keV, φ = <sup>1</sup>�1012 cm�<sup>2</sup> <sup>s</sup> �1 , F = (0.5, 1, and 2) � 1016 cm�<sup>2</sup> , Т = 300 K, Р = 10�<sup>6</sup> torr). The radiation stability was evaluated with using the difference spectra and the change in integral absorption coefficient of solar radiation (аs), which is computed from diffuse reflection spectra according to the following expression:

1. Introduction

486 Titanium Dioxide - Material for a Sustainable Environment

and 800C are presented.

size of 240 nm and specific surface of 8 m2

average particle size of 260 nm and specific surface of 7 m<sup>2</sup>

2. Experimental

The titanium dioxide powders are widely used in many branches of industry. They are utilized as effective photocatalyst [1–3], pigments of thermal control, and anti-reflective coatings of spacecraft [4, 5]. In recent years, the investigations of possibility of their usage as solar photoconverters are

Such fields of the use imply a work in conditions of an action of charged particle fluxes, UV, and visible radiations. The absorption centers, caused by cation and anion defect sublattices, are formed due to these radiations. That is why the method development of an increase in

Theoretical and experimental studies revealed [9–14] that the modification with nanopowders is sufficiently effective way to increase the radiation stability because they possess large specific surface and work as a "sink" for gathering electronic excitations formed during irradiation. However, the modification by nanopowders can lead to a deterioration of initial optical properties that can be induced by large absorption of native point defects in the UV and visible ranges and by absorption of chemosorbed gases in near-infrared (IR) range of spectrum. The modification is associated with high temperature heating of powders, an effect of

An influence of the modification by nanopowders on photo- and radiation stability of reflective powders is discussed in [9–14]. There are no data about an effect of modification conditions (temperature and heating time, type, and concentration of nanopowders) on the optical

In the present chapter, the data obtained by the authors regarding optical properties and radiation stability of titanium dioxide powders before and after modification with nanoparticles of various oxides are considered. The radiation stability of titanium dioxide powders of different sizes and different types of crystal structures is considered. The results of investigations of the rutile titanium dioxide powder modification by nanoparticles of oxide compounds at the temperature of 800C as well as the studies of an effect of the anatase titanium dioxide powder modification by SiO2 nanoparticles with large specific surface at the temperatures of 150, 400,

For modification by various nanoparticles, the rutile TiO2 powders with the average particle

SiO2 nanoparticles (average particle size 12–14 nm). The TiO2 powder was mixed with oxide nanoparticles in a ratio 100:7, the distilled water was added, and it was evaporated at the temperature of 150C for 6 hours. Then, the mixture was heated in an oven for 2 hours at 400 or 800C. After heating, the mixture was grinded in agate mortar and was pressed into metal substrates with 28 mm diameter and 2 mm height. The prepared samples were mounted in

/g were used. The anatase TiO2 powders with the

/g were used for modification with

conducted [6, 7]. But they have found the largest application as household paints [8].

radiation stability of titanium dioxide powders is a relevant problem.

which on optical properties and radiation stability is studied poorly.

properties of materials and their stability to an impact of ionizing radiations.

$$a\_s = 1 - R\_s = 1 - \frac{\int\_{\lambda\_1}^{\lambda\_2} \rho\_\lambda I\_\lambda d\lambda}{\int\_{\lambda\_1}^{\lambda\_2} I\_\lambda d\lambda} = 1 - \frac{\sum\_{i=1}^n \rho\_\lambda}{n},\tag{1}$$

where rλ—spectral reflectivity; Iλ—solar radiation intensity; λ<sup>1</sup> ÷ λ2—Sun spectrum range (the Sun radiates 98% of total energy in the range of 0.2 ÷ 2.5 μm); n—the number of equienergy ranges of the solar spectrum [16].

Changes in absorption coefficient а<sup>s</sup> were defined from subtraction its values before (аs0) and after (аs,irr) irradiation of powders by accelerated electrons:

$$
\Delta a\_s = a\_{s, \text{irr}} - a\_{s0} \tag{2}
$$
