In order to evaluate the durability of paint layers exposed to simultaneous action of climatic and electrical stresses, the influence of 50 Hz electrical field and of aging by thermal cycling on the resistance to the action of molds of some painting materials was evaluated by specific microbiological determinations. Comparative measurements were carried out on initial paint samples and samples aged by applying of 1000 successive thermal cycles (between -38oC and 85oC, with the duration of a cycle of 90 min), exposed to Czapek-Dox culture media (with and without sucrose), inoculated with a salt solution containing approximately 106 mold spores (of 10 different species), and incubated at 30�2oC and RH 90�5%. It was found that for the samples exposed to a controlled field of 5V/cm and 50Hz the resistance to the action of molds is almost two times less than in the absence of the disruptive electric field. Also, it was noticed that the field of 5V/cm and 50Hz stimulates the growth of Aspergillus niger, but completely inhibit those of Trichoderma viride and Aspergillus flavus.

UV radiation has a long-term effect on the durability of anti-corrosive coatings applied by painting, generating conditions for accelerated localized corrosion of the protected metallic structure with adverse effects on operational safety. This paper presents a comparative study of the behavior of some painting materials ageing by exposure to UV radiation relevant by the investigation of dielectric behavior using dielectric spectroscopy in conjunction with the thermal stability investigated by coupled techniques of thermal analysis. From a practical point of view, the UV radiation behavior of two materials based on epoxy resins and polyurethane resin used as paints for protective decorative coatings was studied. The results of experimental investigations have shown that in the aging process of the studied painting materials there is a direct correlation between the evolution of the maximum temperature characteristic of the first thermooxidation process and the evolution of the dielectric performances (dielectric loss - tgd).

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For the purpose of using three different types of painting materials for the inner protection of the transformer vats, their behavior was studied under actual conditions of operation in the transformer (thermal stress in electro-insulating fluid based on the natural ester in contact with copper for electro-technical use and electro-insulating paper). By comparing determination of the content in furans products (HPLC technique) and gases formed (by gas-chromatography) in the electro-insulating fluid (natural ester with high oleic content) thermally aged at 130 �C to 1000 hours in closed glass vessels, it have been found that the presence the investigated painting materials lead to a change in the mechanism and kinetics of the thermo-oxidation processes. These changes are supported by oxygen dissolved in oil, what leads to decrease both to gases formation CO2, CO, H2, CH4, C2H4 and C2H6) and furans products (5-HMF, 2-FOL, 2 -FAL and 2-ACF). The painting materials investigated during the heat treatment applied did not suffer any remarkable structural changes affecting their functionality in the electro-insulating fluid based on vegetable esters.

ATR / FTIR and DSC techniques have been used to evaluate the thermal stability of some ageing paint materials by heat treatment while immersion in natural ester-based electro-insulating oil. Experimental determinations have highlighted the fact that the investigated paint materials (epoxy resins) have a high oxygen affinity and thus, in closed systems (such as power transformers), they oxidize before coming into contact with the transformer oil. This behavior indicates that the paint layer (suitably chosen) applied on the inside of the transformer vat functions as an antioxidant and results in increasing the thermal stability of the oil.