Fatih Çalışkan

Carbothermal reduction and nitridation of quartz mineral for the production of alpha silicon nitride powders

In this study, α-Si3N4 powder was produced by carbothermal reduction and nitridation (CRN) of quartz from Can-Canakkale. Carbon with a specific surface area of 110 m2g−1 and quartz powders were mixed then the powder mix was placed in an alumina tube furnace and reacted in between 1300-1500°C for 4 hours under nitrogen flow. The quartz powder was carbothermally reduced and nitrided to form silicon nitride powders. XRD results showed that the reaction product was mainly α-Si3N4 and contained some β-Si3N4 and residual quartz. In order to reduce amount of unreacted quartz, the raw materials mixture was grinded either with carbon black or with no carbon. After CRN reactions of separate grinded quartz powders with carbon, residual quartz was disappeared, reaction temperature was decreased and α-Si3N4 rate was increased. Hence, a better mixing of carbon and fine silica enhanced the α phase formation. SEM images and XRD pattern showed that sub micron particles (0.6–0.87m), high α-phase content Si3N4 powders can be produced at 1450°C for 4 h in flowing nitrogen gas during the CRN process.

Fabrication of Porous β-SiAlON Preforms from Kaolin for Liquid Metal Infiltration

In this study, the production of β-Si6-zAlzOzN8-z (z =3) powders by the carbothermal reduction and nitridation of kaolin (Al2O3.2SiO2.2H2O) of Turkish origin (Can-Canakkale) was carried out with different processing parameters. It was found that the morphology of the produced SiAlON powder was mixture of irregular and whisker like grains. Therefore this morphology is suitable for liquid metal infiltration since the powders are already high porous. The kaolin powder containing stoichiometric rate carbon black and 30 % charcoal were pressed and reacted under nitrogen flow (2 lt/min) between 1400-1475°C for 4 h. After a carbothermal reduction and nitridation (CRN) process, porous β- SiAlON ceramic was produced from natural kaolin. Residual carbon and charcoal in the produced ß-SiAlON ceramic were fired at 1000°C giving extra porosity. The porous ß-SiAlON ceramics were sintered under N2 atmosphere at 1550°C for 2 h to make preform for infiltration process. SEM image analyses were carried out to determine preform and pore morphology and XRD analysis were performed for phase transformation.

Gözenekli Biyoaktif Hidroksiapatit Seramiklerinin Üretimi

The main subject of this study was to produce a net shaped micro porous hydroxyapatite ceramics. For this aim, initially fabrication of hydroxyapatite powder was achieved by a thermal extraction method which is inexpensive processing route. Phase determination of the yield of the process was carried out by X-ray diffraction method. Replica technique was used to produce a reticulated structure from hydroxyapatite powder. The foams were produced with various rates of additive as binder and additive-free compositions. After the HAp daubed on surfaces of substrate polymer was fired and sintered in the process at > 1100°C. The obtained ceramic foam was characterized using optical microscopy. The preform exhibited different pore sized structures depending binder rate and sintering temperature. As a result, hydroxyapatite preforms was produced with high porosity and their properties were improved by adding the binder which supports biocompability of HAp.

α-Si3N4-β SiAlON Seramiklerinin Kesici Takım Potansiyelinin İncelenmesi

One of the ceramic products is ceramic cutting edges and these are used as cutting tools for fabrication of metal products (ferrous and non ferrous metals) at very high speeds. These cutting tools can mainly be classified silicon nitride, alumina, mixed-ceramics, titanium carbonitride, cubic boron nitride and hard ceramic particle reinforced metals. Ceramic cutting tools offer a high productivity because of their superior hardness, fracture toughness and resistance of elevated temperature which allows higher cutting speeds. In addition to these, resistance to chemical attacks is important in selection of cutting tool materials. In this research, high dense Si3N4 ceramic parts were fabricated, and cutting performance of the produced α/β Si3N4 ceramics were investigated. The microstructure analyses were carried out by SEM and optical microscopy.