9.
The solid state reactions between TiO
2 and Na
2S
2O
8 or K
2S
2O
8 have been investigated using TG, DTG, DTA, IR, and X-ray diffraction studies in the range of 20 to 1000°C.It has been shown that TiO
2 reacts stoichiometrically (1 : 1) with Na
2S
2O
8 in the range of 160 and 220°C forming the complex sodium monoperoxodisulfato—titanium(IV) as characterized by IR and X-ray analysis. The new complex then decomposes into the reactants above 190°C.An exothermic reaction has been observed between TiO
2 and molten K
2S
2O
7 at mole ratio 1:2 respectively and higher, in the range of 280 and 350°C. The IR and X-ray analyses have shown the formation of a complex namely, potassium tetrasulfato titanium(IV) for which the formula and structure have been proposed. This complex decomposes at higher temperatures into K
2SO
4 and a mixed sulfate of potassium and titanium. The mixed sulfate melts at 620°C and decomposes into K
2SO
4, TiO
2, and the gaseous SO
3.On the other hand, Na
2S
2O
8 decomposes in a special mode producing a polymeric product of Na
10S
9O
32. Decomposition of this species occurs after melting at 560°C into Na
2SO
4 and sulfur oxides. The decomposition reaction has been proved to be catalysed by TiO
2 itself.
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