Israel O. Owate

ac breakdown characteristics of ceramic materials

ac breakdown properties of alumina, aluminum nitride, and glass ceramic (SiO2‐Al2O3‐MgO‐TiO2) materials have been investigated. The breakdown strength of glass ceramics (∼65 kV/mm) was found to be higher than that of alumina (∼31 kV/mm) and aluminum nitride (∼16 kV/mm). The specimens were characterized for their density, porosity, and microstructural parameters, such as grain size and distribution, as they are believed to influence the breakdown properties significantly. In all the cases, the prebreakdown and breakdown conduction were found to be associated with visible‐light emission at the electrode‐specimen interface. The samples that underwent breakdown were found to exhibit irregular puncture channel, terminated with craters at both ends. Several types of crystallization structures were observed at the rim of the craters and in some cases at the edges of the breakdown channels. It is suggested that the breakdown process of the ceramic materials is a combination of electronic, electromechanical, and t...

The electrical properties of some cordierite glass ceramics in the system MgO-Al2O3-SiO2-TiO2

The a.c. dielectric breakdown and electrical resistivity of glass ceramics in the system MgO-Al2O3-SiO2-TiO2 have been studied using three sets of samples having different crystallinity contents. Standard a.c. (50 Hz) breakdown tests were performed at room temperature (18 °C) using planar disc specimens and hemispherically-ended brass contact electrodes. The breakdown process caused the formation of a breakdown channel which terminated at the specimen surface in a crater. The breakdown strength was independent of the rate of voltage rise, but decreased exponentially (60 to 10 kV mm−1) with increasing specimen thickness. A high crystallinity content, good surface finish and a homogeneous microstructure yielded high breakdown strengths whilst poor microstructural development caused a reduction in breakdown strength. The breakdown mechanism is believed to be a combination of electronic, thermal and electromechanical processes.

Scattering State of Klein-Gordon Particles by q -Parameter Hyperbolic Poschl-Teller Potential

The one-dimensional Klein-Gordon equation for equal vector and scalar -parameter hyperbolic Poschl-Teller potential is solved in terms of the hypergeometric functions. We calculate in detail the solutions of the scattering and bound states. By virtue of the conditions of equation of continuity of the wave functions, we obtained explicit expressions for the reflection and transmission coefficients and energy equation for the bound state solutions.

Electrochemical Study of Corrosion Inhibition of Mild Steel in Acidic Solution Using Gnetum africana Leaves Extracts

Weight loss and electrochemical (open circuit potential (OCP), linear sweep voltammetry (LSV) and Potentiodynamic polarization (PDP)) techniques were used to assess the effectiveness of Gnetum africana leaves extracts as corrosion inhibitor for mild steel in 1.0 M hydrochloric acid (HCl) solution at 30-45°C. It was found that Gnetum africana leaves extracts retarded the dissolution of mild steel in 1.0 M HCl solution. The inhibition efficiency increased with increase in extract concentration and did reasonably well at increased temperature, which is suggestive of physical and chemical adsorption mechanism. Open circuit potential shows reduction of resistance polarization R p with the addition of the Gnetum africana extract. Potentiodynamic polarization result suggests that Gnetum africana extracts functioned as mixed-type inhibitor. The adsorption of Gnetum africana extracts onto the mild steel surface followed Langmuir and Temkin adsorption isotherm models. The mechanism of physisorption of the extracts onto the mild steel surface is proposed from the trend of inhibition efficiency with temperature which is corroborated by the values of activation parameters obtained from the experimental data.

The Dielectric Properties of Nitrides

Most nitrides have a relative permittivity (e r) of ~10 at low frequencies and low temperature, but resistivities which vary from 10 to 1012 Ωcm at ambient conditions. The stability of many nitride ceramics at elevated temperature makes them attractive as dielectrics in harsh environments. The main trends in the published dielectric data are outlined, and discussed in detail for Si3N4-based ceramics. New data are presented for the electrical resistivity, relative permittivity, loss factor and breakdown strength of AlN and Si3N4 ceramics, and Si3N4-A1N ceramic composites. The effect of microstructural features on dielectric properties are discussed.