Insulating enamels with improved dielectric properties

The effect of the content of alkali oxides on the physicomechanical and dielectric properties of glasses of the SiO₂ - B₂O₃ - R₂O - BaO system is studied. The optimum ratio of (Na + K) : Li providing for manifestation of the polyalkali effect at different concentrations of B₂O₃ is established. The considered compositions can be used as an insulating coating on ozonizer parts. Translated from Steklo i Keramika, No. 4, pp. 27 – 29, April, 1999.     

Influence of Zn2+ ion addition on properties of aluminous electrical porcelain

Abstract

ZnO was added as a dopant, in concentrations of 2, 3, and 4 wt-%, to alumina based porcelain batches, in order to study its effect on the fired materials characteristics. An additional composition containing 4 wt-%ZnO and 1 wt-%LiF was also investigated. The results showed that the addition of 4 wt-%ZnO decreased the maturing temperature and improved the electrical properties. It also promoted the development of a mullite phase from the glassy phase. On the other hand, the combination of ZnO and LiF had a negative effect on the electrical properties and on the mullite content. The Li⁺ ions caused the dissolution of mullite crystals and the crystallisation of new phases.     

On the physico-mechanical,electrical and dielectric properties of mullite-glass composites

Mullite-glass composites were obtained by solid-state reactive sintering of kaolinite clay and kaolin waste mixtures with waste additions up to 100 wt%. The structural and microstructural analysis of starting powders and sintered samples were evaluated by X-ray diffractometry (XRD) and field-emission scanning electron microscopy (FESEM). The mechanical properties were evaluated by measuring the flexural strength of sintered bodies. Electrical properties of the composites were assessed by impedance spectroscopy (at 30 °C and from 400 to 700 °C) in air. A viscous flux mechanism resulting from the glassy phase filled up the open porosity and increased the mechanical strength. Electrical conductivity, dielectric constant and dielectric loss were strongly dependent on the microstructural features, namely glassy phase and porosity. The activation energies (0.89–0.99 eV) for electrical conduction were lower than typical literature values of mullite-based materials. The results indicated that the herein synthesized mullite-glass composites with up to 53.6 wt% mullite are promising low-cost materials for electronics-related applications.     

Simultaneously improved toughness and dielectric properties of epoxy/graphite nanosheet composites

Very thin graphite nanosheets are obtained using an ultrasonic irradiation method, and epoxy/graphite nanosheet composites with different filler content are fabricated using the diglycidylether of bisphenol A epoxy matrix. An investigation of structural characteristics and mechanical and dielectric properties of the nanocomposites is carried out. SEM micrographs shows that the thickness of a single layer graphite nanosheet is about 20 nm whereas FTIR studies indicates that the surfaces of the graphite nanosheets are enriched with hydroxyl and carbonyl groups. The dielectric constants of the composites are increased with increases in graphite nanosheet content lower than 3.5 wt%, and are still higher than 100 in the high frequency range with 3.5 wt% graphite filler content. The tensile strength and storage modulus of the composites increase with increasing nanosheet concentration. These epoxy/graphite nanosheet composites, which show both high dielectric constant and toughness, could have potential application in embedded capacitor technology. POLYM. ENG. SCI., 50:1734–1742, 2010. © 2010 Society of Plastics Engineers