PSI - Issue 50

S.A. Filin et al. / Procedia Structural Integrity 50 (2023) 91–99 S. A. Filin at al. / Structural Integrity Procedia 00 (2022) 000 – 000

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stabilizer in an amount of 0.1-12 weight %. In the presence of tert-butanol, the concentration of hydrobromic acid in freon-114B2 decreased from 0.93 g-ion/l to 0.23 g-ion/l (4 times) when it was boiled for 10 hours. This is probably because the resulting azeotrope has a lower boiling point than freon-114B2 itself. Therefore, degradation at a lower temperature and possible spatial difficulties preventing the interaction of freon-114B2 with hydroxyl groups are reduced. Because of the conducted research, it was concluded, that the physicochemical cleaning of metal optics is reco mmended to be carried out in azeotropes № 10, № 11 and № 17 with tert -butanol as an inhibitor. It is preferable to use the above components in the form of an azeotrope, in which freon-114B2 must be present (the azeotrope "freon-114B2 - tert-butanol" is pre sented in table 1 (№ 18)). The choice of solvents is also due to their high dissolving power in relation to the main types of technological contaminants, present on the mirrors (Fig. 1). Freon 114B2 is relatively inexpensive, low scarcity, more resistant to decomposition, low toxicity and fireproof. Other freons are too volatile or extremely scarce and expensive (Rysaev et al. (2007)), or contain chlorine atoms, as a result of which they are prone to destruction. Experiments (Drobot et al. (1996); Akasaka et al. (2015)) showed that the main principles of physical and chemical cleaning of metal optics are: 1) high degree of purity (not lower than 10 -8 G/cm 3 ) of the washing mixture; 2) removal of the contaminated washing mixture from the processing zone and the continuous flow of clean; 3) controlled cooling of the washing mixture, depending on the material of the processed mirror; 4) lack of contact of the treated surface with the products of thermal dissociation of the azeotrope; 5) continuous monitoring of the cleaning process, including input and output control of the cleanliness of mirrors; 6) closed environmentally friendly cycle of the whole process. These principles were implemented on an optics cleaning facility (Fig. 2).

Fig. 2. Installation for optics cleaning: container for solvent 1; distillation column 2; heaters 3; heat exchanger 4; ion-exchange filter 5 for absorbing products of partial thermal decomposition of solvents; working chamber for mirror cleaning 6; siphon 7; polymer membrane 8. The washing mixture "freon-114B2 - acetone - tert-butanol" is heated in the bottom (lower) part of the distillation column of the packed tray type to the boiling point (48- 49°C) according to the feedback principle. This allows for controlled heating of the washing mixture to a predetermined temperature, above which the energy supply stops, thereby reducing thermal dissociation. Pairs of azeotropes "freon-114B2 - acetone" and "freon-114B2 - tert-butanol" enter the distillation column, where they are purified. Then the vapors enter the heat exchanger, condense and cool down to a temperature of 25- 30 °C, and pass through an ion -exchange filter to absorb the products of partial thermal decomposition. The purified and cooled solvent enters the optics-cleaning bath. Contaminated solvent through the