Effects of Temperature and Pressure on the Dielectric Properties of Plasma Sprayed Alumina Coatings

Dielectric spectroscopy at different pressure and temperature levels can provide crucial quantitative information on the properties of various insulating materials. Thermally sprayed ceramic coatings have the potential to be used in high temperature applications where conventional polymers are not suitable to retain their electrical insulation. In the present study, alumina
$(\mathrm{A}1_{2}\mathrm{O}_{3})$
coatings have been prepared on copper substrates by atmospheric plasma spraying. Different gas mixtures containing varying levels of hydrogen were utilized to assess the significance of energy input on coatings. The samples were tested by dielectric spectroscopy at temperatures ranging from −50 to
$150^{\circ}\mathrm{C}$
and different pressure levels in the frequency range of 10
⁻²
Hz to 10
⁻⁵
Hz. It was discovered that temperature increases both the dielectric constant and loss tangent at low frequencies. Moreover, the microstructure of the coatings has been linked to the dielectric behavior. The primary polarization mechanism at low frequencies is determined as space charge polarization, which is highly affected by different temperature and pressure levels. The results of our study offer valuable insights for the design of next-generation electrical insulation systems utilizing ceramic coatings.