Carlos Vianna - Academia.edu (original) (raw)
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Papers by Carlos Vianna
Radiation Effects and Defects in Solids, 1991
ABSTRACT Ionic thermocurrents (ITC) were measured in pink (morganite) and colourless (goshenite) ... more ABSTRACT Ionic thermocurrents (ITC) were measured in pink (morganite) and colourless (goshenite) samples of natural beryl from 77K up to 250K at a constant rate b = 0.1 Ks?1. The spectra present three distinct bands, at 170K, 200K and 220K. The band at 200K predominates in the untreated crystals. After thermal treatments between 700K and 1300K, the ITC bands at 170K and 220K become prominent, masking the 200K band. The reduction of Fe3+ into Fe2+ in two distinct positions in the beryl lattice justify this observation. Infrared (IR) spectra show that treatments above 1000K remove water from the channels of the beryls. Ultraviolet (UV) irradiation of these thermally treated samples enhance the two bands at 170K and 220K.
Radiation Effects and Defects in Solids, 1995
The purpose of this study is an investigation upstream of polymer insulator ageing and rupture. W... more The purpose of this study is an investigation upstream of polymer insulator ageing and rupture. We studied the electrical and physicochemical properties of a low-density polyethylene (LDPE) used in high-power insulated cables. Space charge measurements using pulsed electroacoustic method and thermally stimulated depolarization current (TSDC) were carried out on LDPE samples, with and without antioxidant, at different temperatures. TSDC peaks were observed only in the presence of an anti-oxidant. Furthermore, a TSDC anomalous peak was revealed for the sample containing an antioxidant and polarized at 508C. All the TSDC peaks are interpreted as trapped charges and can be explained by measuring the space charge distribution within the sample bulk.
Radiation Effects and Defects in Solids, 1991
ABSTRACT Ionic thermocurrents (ITC) were measured in pink (morganite) and colourless (goshenite) ... more ABSTRACT Ionic thermocurrents (ITC) were measured in pink (morganite) and colourless (goshenite) samples of natural beryl from 77K up to 250K at a constant rate b = 0.1 Ks?1. The spectra present three distinct bands, at 170K, 200K and 220K. The band at 200K predominates in the untreated crystals. After thermal treatments between 700K and 1300K, the ITC bands at 170K and 220K become prominent, masking the 200K band. The reduction of Fe3+ into Fe2+ in two distinct positions in the beryl lattice justify this observation. Infrared (IR) spectra show that treatments above 1000K remove water from the channels of the beryls. Ultraviolet (UV) irradiation of these thermally treated samples enhance the two bands at 170K and 220K.
Radiation Effects and Defects in Solids, 1995
The purpose of this study is an investigation upstream of polymer insulator ageing and rupture. W... more The purpose of this study is an investigation upstream of polymer insulator ageing and rupture. We studied the electrical and physicochemical properties of a low-density polyethylene (LDPE) used in high-power insulated cables. Space charge measurements using pulsed electroacoustic method and thermally stimulated depolarization current (TSDC) were carried out on LDPE samples, with and without antioxidant, at different temperatures. TSDC peaks were observed only in the presence of an anti-oxidant. Furthermore, a TSDC anomalous peak was revealed for the sample containing an antioxidant and polarized at 508C. All the TSDC peaks are interpreted as trapped charges and can be explained by measuring the space charge distribution within the sample bulk.