The effect of O 2 and O 3 bubbling on decolourization of methylene blue by pulsed corona discharges in water was studied. The pulsed corona discharges were produced by charging an 80 pF capacitor with a 40 kV DC source, through a 100 M resistor, and discharging it into a needle-plate type reactor at 60 Hz through a rotating spark gap switch. A 20 ml sample of 13.25 mg l −1 methylene blue in distilled water was decolourized in 120 min.Bubbling O 2 at 10 ml min −1 through the discharge region reduced the decolourization time to 25 min. Bubbling O 2 containing 1500 µmol O 3 l −1 at 10 ml min −1 reduced the decolourization time to 8 min. The O 3 was produced by fractionating input energy between a water treatment reactor and a O 3 generator, i.e. no additional energy was consumed for O 3 production. Under the same experimental conditions methylene blue solution in tap water was decolourized in >210 min by corona discharge in solution, in 30 min by corona discharge with O 2 bubbling, and in 11 min by corona discharge with bubbling of O 2 containing 1500 µmol O 3 l −1 .
The thermal properties of the aramid-polydimethylsiloxane block copolymers constituting various types of aramids and polydimethylsiloxane with different molecular weights have been studied by thermogravimetric analysis (TGA), derivative thermogravimetry (DTG) and differential thermal analysis (DTA) both in air and nitrogen atmospheres. In general, these block copolymers displayed excellent thermal properties even in those cases where products with low degree of polymerization were prepared. These block copolymers showed an optimized range of temperature of decomposition >400°C irrespective of having aramid block as terephthalamide or isophthalamide. But in aramid as parent polymer, the temperature of decomoposition strongly depends on the orientation of the constituting aromatic rings i.e., terephthalamide or isophthalamide and it specifies the use of aramids as heat resistant materials.
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