Production of silicon nitride (Si3N4) type technological ceramic material from sepiolite and its characterization

Production of silicon nitride (Si3N4) ceramic powder from raw materials containing silica (SiO2) via carbotermal reduction and nitridation (CTRN) is one of the methods which has been used frequently in recent years. In this study, production of Si3N4 ceramic powder from brown sepiolite obtained from Türktaciri area located in south of Ankara-Polatlı was carried out by means of CTRN and then by getting block piece from produced powder, microstructure and mechanical properties were investigated. Carbon black was employed as the source of carbon and mixtures of sepiolite-carbon black with a C/SiO2 molar ratio of 4 were prepared. Two different sepiolites, as original and enriched, were used for preparing the specimens. The CTRN processes were conducted in atmosphere-controlled tube furnace under flowing nitrogen (0,2 cm/min) at 1420 oC for 10 h. Si3N4 transformation and approximately ?, ß ratios were determined by performing XRD analysis of transformed specimens after CTRN. Morphology and chemical composition except for Si3N4 of products were determined by performing SEM-EDX. Furtermore, particle size measuring was performed before producing blocks. In these characterization procedures, it was determined that ?, ß ratios, morphology, chemical composition and particle size of samples synthesised from original and enriched mixtures were approximately same. Having been characterized the powders vii produced from two different spiolite mixtures, by taking 2 g samples from these powders were compacted into pellets by uniaxial at 25 MPa and then isostatic pressing at 300 MPa. Pellets were pressureless sintered under 1 bar nitrogen atmosphere at (1650, 1725, 1775, 1800) oC for 1 hour. After sintering, firstly by measuring the density of the samples, sinterability was determineted. Phases formed depending on sintering process and microstructure were determined by XRD, SEM-EDX analysis too. For mechanical test analyses, hardness and fracture toughness were measured using a Vickers diamond indenter on the polished surface with a 0,3 kg load. Consequently, it was found that powders produced from both mixtures after CTRN had approximately same properties. Mean Vickers value of Pellets sintered at 1800 oC was measured as 14 GPa and fracture toughness was determineted as 5 MPa m1/2. Science Code : 710.3.022 Key Words : CTRN, Sepiolite, Si3N4 Page Number : 129 Adviser : Assoc. Prof. Dr. Halil ARIK