Influence of Moisture Absorption and Content of Graphite Filler on Electrical Property of Sensors and Transducers Enclosures and Phenomena of Electrostriction in Glass- Epoxy Composites

• Main Authors: B. Shivamurthy, Siddaramaiah, M. S. Prabhuswamy, B. S. Shailesh, T. K. Basak, N. A. Jnanesh
• Format: Article
• Language: English
• Published: IFSA Publishing, S.L. 2008-10-01
• Series: Sensors & Transducers
• Subjects: Glass epoxy composites; Graphite filler; Tan δ; AC conductivity; Dielectric constant; Electrostriction
• Online Access: http://www.sensorsportal.com/HTML/DIGEST/october_08/P_344.pdf
• ISSN: 2306-8515; 1726-5479

In this investigation E-glass epoxy composite filled with different amount of graphite particles were prepared by compression. Plain waived E-glass cloth with density 200g / meter square was used as reinforcement. Epoxy resin LY556 mixed with Hardener HT907 and accelerator DY063 in the ratio 100:80:2 were used as matrix. The graphite of 50 particle size was used as fillers. Four types of composites were prepared with different amount of graphite fillers viz 0 %, 3 %, 6 % and 9 % with unchanged reinforcement. After subjecting the samples to water absorption up to 96 hours in steps of 24 hrs, dielectric dissipation factor (tan δ), dielectric constant and a. c. conductivity have been measured by using a LCR meter at two different frequencies (100 Hz and 1 kHz). Results show that tan δ direct constant, a.c. conductivity increases with increase in % of graphite in the composites at both high and low frequency for dry samples. Samples with 24 hrs moisture absorption showed approximately same result. After 48 hrs, tan δ values showed variations. However, the fluctuations were less at 6 % of graphite in all samples after 48 and 72 hrs of moisture absorption. Dielectric constant increases with increase in graphite % in composites at higher frequency and there was not much variation at low frequency. In all samples after 24 and 48 hrs of moisture absorption, dielectric constant decreases with increase in graphite loading. It is observed that dielectric constant increases in all samples after 72 hrs of moisture absorption as compared to dry samples. A c. conductivity increases with increase in % of graphite content in dry sample. Up to 6% a. c. conductivity increases after 24 and 48 hrs of immersion, after 72 hrs the trend is reversed. Since Fermi level is initially shifted towards the conduction band and then after 72 hrs of moisture absorption shifted towards the valence band. a. c. conductivity increases with increase in moisture content. The phenomenon of electrostriction was observed in composites without graphite fillers.