Thermally Stimulated Discharge Currents in Tubular Magnetoelectrets of Polymethyl Methacrylate

Abstract

Thermally stimulated discharge currents (TSDC) have been obtained from Perspex tubular magnetoelectrets(M.E.) using different linear heating rates (1.0°, 1.5°, 2.0°, 2.5° and 3.0°C/min), for samples prepared at various polarizing fields (Hf) and forming temperatures (Tf), in M.E. containers made of ferro–as well as diamagnetic materials. TSDC spectra consist of three peaks with temperature maxima of 54^°±3°C, 134^°±3°C and 148^°±3°C which are termed as β, α and ρ peaks respectively. The values of activation energy and pre-exponential factor of relaxation time have been calculated for α peak which is quite isolated from β and ρ peaks and are found to be 0.68 eV and 6.55×10-15 seconds respectively. The variation of relaxation time and peak current with Tf indicates that far too many dipoles must be aligned to produce the observed effect. TSDC using different heating rates shows that low heating rates are preferable. Ferromagnetic material (cast iron) seems to be more suitable than diamagnetic (brass) for the preparation of tubular M.Es.

Open- and short-circuit thermally stimulated currents in ethyl cellulose (EC): polymethyl methacrylate (PMMA) blend

“…Several reports on TSDC behaviour of EC and PMMA thermoelectrets and different relaxation processes contributing to the observed peaks in the corresponding thermograms are. available (Shrivastava et al 1978;Vanderschueren and Linkens 1978;Jiska et al 1981;Khare andSrivastava 1993, 1994;Khare et al , 1994c. However, the role of various polarization processes and their relative contribution to the electret state of the polymers is not yet fully understood.…”

Thermally stimulated currents of poly(methyl methacrylate): Comments on the molecular origin of a Debye‐type signal between the α‐ and β‐relaxation modes

“…A representative example of a polar thermoplastic material, poly(methyl methacrylate) (PMMA) may be considered one of the best characterized polymers and was among the first macromolecular substances studied by TSC 9–11. PMMA presents a primary (α) transition ascribed to the large‐scale conformational rearrangements of the polymer backbone (cooperative motion involving 8–20 bonds), which corresponds to the glass‐to‐rubber transition [at the glass‐transition temperature ( T g ), with the TSC band maximum at T α ≈ 105 °C for atactic PMMA].…”

Sensor de corrente baseado na tecnologia de magneto-piezoeletretos termoformados

“…No entanto, atualmente, não existem propostas ou estudos na literatura que abordem sensores ou transdutores que combinem os efeitos magnetoestritivos (materiais multiferroicos) e piezoelétricos (materiais poliméricos) em um único dispositivo de monitoramento, modelado fisicamente para detectar o campo magnético gerado por equipamentos elétricos ou fios condutores com características adaptativas. Por características adaptativas, entende-se um equipamento que possa ser facilmente instalado e removido, sem os inconvenientes mencionados anteriormente [9][10][11][12].…”

“…O magneto-eletreto, com a adição de Fe, aumentou a concentração do campo magnético, bem como retenção de cargas elétricas. O magneto-eletreto, com adição de Cu e Zn, obteve uma concentração de campo elétrico pequena, o que impossi-bilitou a retenção de cargas elétricas [12] Qureshi et al (2005) desenvolveram magneto-eletretos utilizando o material fotocondutor Poli-imida (PI), mais conhecido como filmes de Kapton. O novo tipo de magnetoeletreto foi nomeado de foto-magneto-eletreto, pois para o processo de aquecimento, a energia térmica foi substituída por energia óptica.…”