Optimisation of Composition and Firing Temperature for High-Voltage Porcelain Insulator Applications Using Tanzanian Triaxial Ceramic Raw Materials

Abstract

Tanzania possesses substantial domestic deposits of ceramic raw materials, including kaolin, quartz, and feldspar, yet high-voltage 
porcelain insulators are currently met entirely through importation because the suitability of these local minerals for high-voltage service has not been systematically characterised. This study investigated locally sourced Tanzanian ceramic materials, Pugu kaolin, KIDT quartz, and Kilimanjaro feldspar, for high-voltage porcelain insulator production. Six batch compositions (C1–C6) were prepared by systematically varying the constituent proportions. Specimens fabricated by slip casting were fired at 1100, 1200, and 1300 °C and evaluated for insulation resistance, bending strength, linear shrinkage, water absorption, and bulk density; X-ray diffraction was used to confirm mullite formation, a phase critical to both dielectric and mechanical performance. Batch C4, composed of 33 wt.% kaolin, 11 wt.% quartz, and 56 wt.% feldspar and sintered at 1200°C, gave the best overall performance, with an insulation resistance of 205,800 MΩ, a bending strength of 65.358 MPa, and a water absorption of only 0.01% (near-zero, indicating a near fully densified, essentially closed-pore microstructure). These values satisfy the minima specified by the International Electrical Testing Association (NETA) and the Japanese Industrial Standards (JIS). Under-firing at 1100 °C and over-firing at 1300 °C both reduced performance relative to the 1200 °C optimum. These results demonstrate that Tanzanian ceramic minerals, appropriately proportioned and fired, can support domestic high-voltage porcelain insulator manufacturing, providing a technical basis for reducing import infrastructure. dependency in Tanzania's electricity