1. Introduction

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

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 =

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

> Ð λ2 λ1

> > Ð λ2 λ1 Iλdλ

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

Changes in absorption coefficient а<sup>s</sup> were defined from subtraction its values before (аs0) and

3. Optical properties and radiation stability of micro and nanopowders

The study objects were the TiO2 submicron sized powders of industry production with an average particle size of 240 nm (m�240), as well as nanopowders with an average particle size of 60 (n�60), 80 (n�80), and 160 (n�160) nm. The specific surface of m�240, n�160, n�80, and

The m�240 powder possessed rutile lattice, and the nanopowders were the mixture of anatase and rutile. The ratio of these phases changed with the change in particle size. With a decrease in particle size from 160 down to 80 and 60 nm, the concentration of rutile changed from 50 down to 33.9 and 98.7 mass%, the anatase concentration was 49.8, 66.1, and 1.3 mass%.

The largest value of the reflection coefficient (r0) was registered in rλ<sup>0</sup> spectra of micropowder m�240. The nanopowders n�160, n�80, and n�60 follow in order of its decrease (Figure 1). The absolute values of the reflection coefficient on the various regions of the spectrum reduce with decreasing powder particle sizes. Its largest values are registered in the range from 500 to 1200 nm. The reflection coefficient reduces in more short-wavelength (λ < 500 nm) and more long-wavelength (λ >1200 nm) ranges. The more is the decrease, the less is the size particles of powders. In the short-wavelength region, the decrease in the reflection coefficient is sharp with pronounced outlines of the absorption bands, and in the long-wavelength region, the decay is

/g, respectively [17].

rλIλdλ

¼ 1 �

Investigation of Optical Properties and Radiation Stability of TiO2 Powders before and after…

Pn i¼1 rλ

Δа<sup>s</sup> ¼ аs,irr � аs0 (2)

, Т = 300 K, Р = 10�<sup>6</sup> torr). The radiation stability

http://dx.doi.org/10.5772/intechopen.74073

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<sup>n</sup> , (1)

<sup>1</sup>�1012 cm�<sup>2</sup> <sup>s</sup>

�1

ranges of the solar spectrum [16].

following expression:

, F = (0.5, 1, and 2) � 1016 cm�<sup>2</sup>

after (аs,irr) irradiation of powders by accelerated electrons:

of titanium dioxide before modification

<sup>n</sup>�60 powders was 8.0, 13, 16, and 28 m<sup>2</sup>

as ¼ 1 � Rs ¼ 1 �

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 radiation stability of titanium dioxide powders is a relevant problem.

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 which on optical properties and radiation stability is studied poorly.

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

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, and 800C are presented.
