Full Length Research Paper

Investigation of direct pressureless sinterability of Si3N4 produced from brown sepiolite and its characterisation

Cengiz Bagci1* and Halil Arik2

1Department of Machine and Metal Technologies, Vocational High School of Akdagmadeni, Bozok University, 66300, Yozgat, Turkey.

2Department of Metallurgy, Faculty of Technical Education, Gazi University, 06500, Ankara, Turkey.

*Corresponding author. E-mail: cengizbagci@gmail.com.

Accepted 14 January, 2010

   Abstract

In this paper, production of Si3N4 powders by using sepiolite obtained from Turkish deposits was carried out via Carbo-Thermal Reduction and Nitridation (CTRN). Two different sepiolites and carbon black were used for silica and carbon source to prepare specimens with a C/SiO2 molar ratio of 4. The CTRN processes were conducted in atmosphere-controlled tube furnace under nitrogen flow of 5 cm3/min at 1420°C for 10 h. After powder characterization with XRD, SEM and EDX, synthesized powders were compacted into pellets by uniaxial at 25 MPa and then isostaticaly at 300 MPa separately. Following, the pellets were pressureless sintered under 1 bar nitrogen atmosphere at 1650, 1725, 1775 and 1800°C for 1 h. Resultant microstructures, hardness and fracture toughness were investigated by XRD, SEM-EDX and Vickers diamond indenter. Consequently, Si3N4 powders synthesized from the sepiolite specimens were pressureless sintered without any sintering additives. Optimum mechanical properties were obtained from the pellet sintered at 1775°C. Hardness and fracture toughness of this specimen were determinated 14 Gpa and 5 MPa m1/2 respectively.

Key words: CTRN, sepiolite, Si3N4.