The Influence of Microstructure, Temperature and Sintering Level on Electric Properties of Electrical Insulators Obtained from Raw Materials of Rio Grande do Norte - Brazil

The technical porcelain is usually obtained by mixing different raw materials, which are generally clay, kaolin, quartz, and a fluxing agent, in appropriate amounts. These porcelains are used in the production of electric and electronic devices for several applications, ranging from high and low power capacitors to low, medium, high and extra high voltage insulators. In this work, we studied technological properties of dielectric porcelain, obtained from raw materials found in large quantities and excellent quality in the Rio Grande do Norte state in Brazil. Test samples were produced by powder technology for two different compositions: composition A (20% clay, 28% kaolin, 32% feldspar and 20% quartz) and composition B (15% clay, 31% kaolin, 33% feldspar and 21% quartz), and sintered at temperatures, T1=1150°C, T2=1200°C, T3=1250°C, T4=1300°C and T5=1350°C with isotherms P1=0.5 hours, P2=1 hour, P3=1.5 hours and P4=2 hours. Then after sintered, the sample microstructure was characterized by scanning electron microscopy (SEM) and analysis of dielectric strength with direct and alternating voltage. The best results for electrical properties were obtained in temperature of 1250oC for composition A, and confirms the electrotechnical porcelain production feasibility.

Evaluation Of The Ml Lute Hypothesis In Respect Of Electrotec Hnical Porcelains

The paper presents the evaluation of the mullite hypothesis explaining the strength of porcelains. There was researched the influence of the mullite phase on the short- and long-term mechanical strength of electrotechnical porcelain of different types (C 110, C 112, C 120 and C 130). The total mullite phase content, the size and distribution of precipitates and dispersed single crystals in the glassy matrix were considered. Mechanoacoustic and microscopic techniques as well as ultrasonic testing were used during the investigation. The role of the mullite phase in the increase of strength and resistance to aging processes of electrical porcelain of various types was described. Mullite hypothesis is valid in reference to siliceous (C 110), cristobalite (C 112) and aluminous C 120 type materials of a typical raw components content and phase composition. In the case of modern strengthened C 120 and C 130 type aluminous materials advantageous are only dispersed fine mullite needles. The precipitates of mullite phase, especially of bigger size, are undesirable.