4.2. Radiation stability of modified powders

nanoparticles was, nm: Al2O3—30, ZrO2—30, ZnO—50, MgO—60, SiO2—55, and TiO2—60.

MgO—26, SiO2—60, and TiO2—26. All nanopowders possess a crystalline structure except the

Modification effects on r<sup>λ</sup> spectra are shown in Figure 4. In the range of 440 nm, the reflectivity of heated and modified powders increases by 2–3% (Figure 5). An exception is a powder modified with n-ZnO, the r value of which reduces by 2–4%. In the range of 580 nm, the reflectivity increases for powders doped by n-MgO and n-TiO2 only. For other modified powders, the reflectivity does not change noticeably, for the powder doped with ZnO

The r value of powders modified with n-TiO2 and n-SiO2 increases noticeably in the near-IR range at 850 nm. For other modified and heated powders, the r changes insignificantly. The increase in r is detected in the spectra of powders modified with n-MgO, n-ZrO2, n-ZnO, and n-SiO2 at 1200 nm. The largest increase is 4%. The increase in r in the range of 1800 nm is observed at both heating and modification by all nanopowders. The largest value, equaled to

The change in r<sup>λ</sup> spectra of powders at heating and high-temperature modification can be because of the distinction between the reflection coefficient of nanoparticles and the reflection coefficient of micropowder. This distinction is determined by large value of nanoparticle scattering coefficient in comparison to micro-sized particles and will appear, mainly, in the visible range

Figure 4. The diffuse reflection spectra of heated at 150 and 800C unmodified TiO2 powder and modified with

nanoparticles of various oxide compounds in quantity of 7 mass% at 800C.

/g: Al2O3—49, ZrO2—25, ZnO—20,

The specific surface area of the powders was equal to m2

SiO2 powder, which was amorphous.

492 Titanium Dioxide - Material for a Sustainable Environment

nanoparticles—it decreases as well.

of spectra.

4.7%, belongs to powder modified with n-ZnO.

Radiation stability was estimated from the difference diffuse reflection spectra (Δrλ), in which two parts can be distinguished, determined by the absorption bands. In the visible range the bands at 420–580 nm are registered, in the near-IR range at 850–1200 nm (Figure 6). The position of maximums changes depending on type of nanopowder. Two bands appear in some spectra and one band in others. Based on types and number of absorption bands in these ranges of TiO2 absorption spectra, it can be assumed that these integral contours include a large number of elementary bands. The Δr values in these regions are different: for some powders, they are approximately the same; for others, the intensity of the band in the near-IR region is substantially larger.

Judging by the Δr<sup>λ</sup> values, it can be concluded that the largest changes occur during irradiation in the visible range in the powder heated at 150С and in the powders modified with n-MgO and n-ZnO. The changes in r<sup>λ</sup> spectra reach 27% after exposure.

4.3. The effect of temperature at heating and modification by SiO2 nanoparticles on the

is formed in the difference spectrum determined by the relation:

length with a maximum value Δr = 8.7% is recorded.

without certain regularities, the Δr values are 2–3%.

A comparison of the r<sup>λ</sup> spectra of heated TiO2 powders shows (Figure 7) that with an increase in the heating temperature from 150 to 400�C, the reflection coefficient varies in different regions of the spectrum according to various regularities [26]. In the region from the absorption edge up to 600 nm, it increases so that an absorption band with a maximum at 400–405 nm

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

where rλ<sup>150</sup> and rλ<sup>400</sup> are the reflection coefficients of the powder heated at a temperature of

In the 600–900 nm region, the reflection coefficient slightly decreases with a minimum value of 1.7% at 700 nm. In the longer wavelength region, it increases in accordance with power law of

An increase in the heating temperature up to 800�C leads to the appearance of an absorption band at 380–390 nm in the difference spectrum (Δr<sup>λ</sup> = rλ<sup>150</sup> � rλ800). At 450–680 nm, the changes are close to zero, and in the region of 680–2100 nm, a power function of the wave-

Modification of the TiO2 powder with SiO2 nanoparticles and heating at 400�C, both lead to a decrease in the reflection coefficient over the entire spectrum (Figure 8). At the same time, an absorption band is recorded in the region from the absorption edge up to 600 nm with a maximum at 500 nm, and in the longer wavelength region, the reflection coefficient changes

An increase in the heating temperature up to 800�C at modifying TiO2 powder leads to a decrease in the reflection coefficient in the region from the absorption edge up to 600 nm and

Figure 7. The diffuse reflection spectra of unmodified titanium dioxide powders heated at various temperatures.

Δr<sup>λ</sup> ¼ rλ<sup>150</sup> � rλ<sup>400</sup> (9)

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

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radiation stability of TiO2 powders

150 and 400�C, respectively.

the wavelength [30, 31].

Figure 6. The Δr values of heated and modified TiO2 powders by nanoparticles of different oxide compounds for various wavelengths.

The radiation stability of TiO2 powders modified by all types of nanoparticles is higher compared to unmodified powder but heated at 150С. A reduction in Δr values of modified powders is registered in entire range of Δr<sup>λ</sup> spectra (Figure 6). The effectiveness of modification (Δr150/Δrmod) reaches almost two times in the visible range. In the near-IR range, it is even larger and reaches more than six times. The best result in the visible range corresponds to n-ZrO2 modification, in the near-IR range—n-SiO2.

Radiation stability in the visible region of the spectrum of TiO2 powder heated at 800С is the same or even higher in comparison to the modified powders. Only the modification with n-ZrO2 gives, although not significant, an increase in radiation stability compared to the heated powder. Modification with n-SiO2 nanopowder results in a slight decrease and the modification with n-MgO, n-ZnO, n-Al2O3, and n-TiO2 to a noticeable decrease in radiation stability in comparison to the heated powder.

In the near-IR region, the modification with some nanopowders has a significant effect on the radiation stability. The largest effect was obtained using n-SiO2 and n-ZrO2. Then, mixtures with n-Al2O3 and n-TiO2 follow. The least effect from the modification was obtained using n-MgO and n-ZnO.

With respect to the aggregate values of Δr in the visible and near-IR regions of the spectrum, the series of the largest effect at modifying with nanoparticles is as follows: 1—SiO2, 2—ZrO2, 3—Al2O3, 4—TiO2, 5—MgO, and 6—ZnO. The largest effect in increasing the radiation stability of micropowders of titanium dioxide is obtained by modifying with n-SiO2 and n-ZrO2 and the smallest by the modification with n-MgO and n-ZnO.
