An argon plasma jet was sustained in open air and characterized for its chemical composition. The optically characterized plasma jet was used to treat industrial wastewater containing mixed textile dyes and heavy metals. Since plasma jet produces UV-radiations, the photocatalytic TiO2 was used to enhance plasma treatment efficiency especially for degradation of dyes. Mixed anatase and rutile phases of TiO2 (5.2–8.5 nm) were produced through surfactant assisted sol–gel approach. The emission spectrum confirmed the presence of excited argon, OH, excited nitrogen, excited oxygen, ozone and nitric oxide in the plasma jet. The spectral lines of excited Ar, NO, O3, OH−, N2, $${\mathrm{N}}_{2}^{+}$$
N
2
+
, O, $${\mathrm{O}}_{2}^{+}$$
O
2
+
and O+ species were observed at wavelength of 695–740 nm, 254.3 nm, 307.9 nm, 302–310 nm, 330–380 nm, 390–415 nm, 715.6 nm, 500–600 nm and 400–500 nm. These reactive species decompose the organic pollutants and separate the heavy metals from the water samples. The conductivity of plasma exposed water samples increased while pH and hardness decreased. The atomic absorption spectrophotometry analysis confirmed the presence of heavy metals in the samples, which were effectively removed through plasma treatment. Finally, the effect of plasma treatment on Staphylococcus aureus strains was more pronounced than Escherichia coli strains.
SUMMARYThis paper reviews the factors that influence the electrical stress required for initiation of electrical trees in crosslinked polyethylene (XLPE) insulation. Mathematical model relating the average tree inception stress with the defect tip radius of curvature has been provided for AC and impulse voltages. The resulting equation for AC treeing inception stress is verified by experimental measurements. Moreover, the effects of voltage magnitude, defect tip radius, and time of voltage application on partial discharge (PD) properties are studied, and the conditions for the initiation of bush-and branch-type trees are identified. For each type of tree, the variation of PD level with tree length is investigated experimentally. The results show that a minimum stress is required below which treeing cannot initiate in XLPE insulation. Moreover, during the early phase of tree propagation, tree length follows a self-limiting growth model and in this phase, tree length and the maximum PD levels are correlated.
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