Thin films of low density polyethylene (LDPE) and crosslinked polyethylene (XLPE) were aged under an AC electric field while kept in sodium chloride aqueous solution. After aging the samples showed water trees (localized damaged with the appearance of hydrophilic ramified structures whose size ranges from a few microns to I mm). Some of the samples suffered dielectric breakdown showing small channels (1-2 mm. diameter) crossing the film and sometimes also signs of carbonization. In order to identify the oxidation mechanisms contributing to aging, FTIR was used to analyze both unaged and aged specimens. Comparing between unaged and aged LDPE an increase in the FTIR spectrum for bands at 1720 cm(-1), 1640 cm(-1) and 1590 cm(-1) was visible for the aged samples. The first region corresponds to carbonyl groups (C=O bonds) resulting from oxidation (most probably ketones). While the second one is related to carbon double bonds formed due to chain scission. Finally the third one is due to carboxylates. For the XLPE the analysis is more difficult. Besides aging it needs to be taken into account the by-products of crosslinking that will tend also to diffuse out with time. The main effect of aging is an increase in the concentration of 1640 cm(-1) band (C=C bonds). For the water treed regions dry and wet samples were compared. In the wet ones the absorbance is larger for the 3380 cm(-1) exhibiting, as expected, water absorption in the water treed regions (hydrophilic characteristics were increased).

Thin films of low density polyethylene (LDPE) and crosslinked polyethylene (XLPE) were aged under an AC electric field while kept in sodium chloride aqueous solution. After aging the samples showed water trees (localized damaged with the appearance of hydrophilic ramified structures whose size ranges from a few microns to I mm). Some of the samples suffered dielectric breakdown showing small channels (1-2 mm. diameter) crossing the film and sometimes also signs of carbonization. In order to identify the oxidation mechanisms contributing to aging, FTIR was used to analyze both unaged and aged specimens. Comparing between unaged and aged LDPE an increase in the FTIR spectrum for bands at 1720 cm(-1), 1640 cm(-1) and 1590 cm(-1) was visible for the aged samples. The first region corresponds to carbonyl groups (C=O bonds) resulting from oxidation (most probably ketones). While the second one is related to carbon double bonds formed due to chain scission. Finally the third one is due to carboxylates. For the XLPE the analysis is more difficult. Besides aging it needs to be taken into account the by-products of crosslinking that will tend also to diffuse out with time. The main effect of aging is an increase in the concentration of 1640 cm(-1) band (C=C bonds). For the water treed regions dry and wet samples were compared. In the wet ones the absorbance is larger for the 3380 cm(-1) exhibiting, as expected, water absorption in the water treed regions (hydrophilic characteristics were increased).

Aqueous suspensions of cordierite-based glass ceramics were prepared by using four types of dispersants and binders and different solids loading. The experiments were designed according to the Taguchi method, which shows great advantages in optimising more than two factors that need to be considered in an experimental design. Different parameters such as the type and concentration of the dispersants and the binders, and the solids loading were optimised to obtain homogeneous and crack-free green tapes. Dolapix CE 64 (1.0 wt.%) and Duramax B-1080 or Duramax B-1070 (10 wt.%) with 65 wt.% solids loading represent an optimal selection of the parameters to obtain low viscosity suspension, and crack-free green tapes with the highest green and sintered density. Microstructural differences between crack-free and cracked samples were observed by scanning electron microscopy (SEM). The crack-free green tapes show homogenous microstructures from top to bottom with organic additives uniformly surrounding the powders, whereas cracked samples exhibit heterogeneous microstructures and non-uniform distribution of the organics. © 2002 Elsevier Science B.V. All rights reserved.