Filiz Cinar Sahin

Spark plasma sintered Al2O3–YSZ–TiO2 composites: Processing, characterization and in vivo evaluation

Al2O3 and Al2O3-YSZ composites containing 3 and 5 wt.% TiO2 were prepared by spark plasma sintering at temperatures of 1350-1400°C for 300s under a pressure of 40 MPa. The grain growth of alumina was suppressed by the addition of YSZ. Al2O3-YSZ composites showed higher hardness than monolithic Al2O3. There was not a considerable difference in hardness values for Al2O3-YSZ composites containing 10 and 20 vol.% YSZ and the addition of TiO2 decreased the hardness of the composites. The fracture toughness of Al2O3 increased from 2.8 MPa·m(1/2) to 4.3 MPa·m(1/2) with the addition of 10vol.% YSZ, further addition resulted in higher fracture toughness values. The fracture toughness values were increased with TiO2 addition and the highest value of fracture toughness, 5.3 MPa·m(1/2), was achieved with the addition of 20 vol.% YSZ and 5 wt.% TiO2. Preliminary in vivo tests demonstrated the biocompatibility and osseointegration of the composites after 6 week post-implantation in femur of Wistar rats.

Synthesis of Mn2O3 Nanopowders with Urea and Citric Acid by Solution Combustion Route

In this study, synthesis of Mn2O3 powders by solution combustion route was carried out. Urea (CH4N2O) and citric acid (C6H8O7.H2O) was used as a fuel material in solution combustion synthesis, while manganese nitrate (Mn(NO3)2.4H2O) was used as an oxidant. Surface area of Mn2O3 synthesised by urea was calculated as 19,37 m2/g and 25,07 m2/g after the calcination at 400 °C and 500 °C, respectively. Surface area of Mn2O3 synthesised by citric acid was calculated as 63,77 m2/g when fuel/oxidizer was 1/1, ignition temperature of 250 °C and calcination temperature at 500 °C. Spherical particles of Mn2O3 having average particle size of 50–60 nm was synthesised by using urea, while foam like porous structure of Mn2O3 was obtained when citric acid was used as a fuel in solution combustion synthesis. Pore diameters between 27 and 55 nm was determined for this powders.

Processing and mechanical characterisation of monolithic silicon carbide ceramic consolidated by spark plasma sintering (SPS)

Abstract Silicon carbide ceramics were fabricated using the spark plasma sintering technique without the use of additives. The sintering process was carried out at four different temperatures in the range of 2 073−2 223 K under two different pressures, 40 MPa and 80 MPa, under vacuum. The effects of different temperatures and pressures on the density, Vickers hardness, fracture toughness, and microstructure were examined. Fully dense monolithic silicon carbide ceramics with a relative density of approximately 99 % were obtained. Increasing the pressure from 40 to 80 MPa and the temperature from 2 073 to 2 223 K resulted in an increase in the relative densities of spark plasma sintered ceramics from 87 % to 97.5 % and 95.5 % to 99.7 %, respectively. The results revealed that the silicon carbide ceramic spark plasma sintered at 2 223 K while applying 80 MPa of pressure with a 5-minute soaking time under vacuum has the highest hardness and fracture toughness values of 31.9 GPa and 3.6 ± 0.3 MPa·m1/2, respectively.

Gamma and Neutron Shielding Behavior of Spark Plasma Sintered Boron Carbide-Tungsten Based Composites

In this study gamma and neutron attenuation properties of boron carbide-tungsten (B4C-W) based composites were investigated. B4C-W based composites were produced by spark plasma sintering (SPS) method. W additions were 5%, 10%, and 15% by volume. Samples with theoretical densities were obtained. Occurance of W2B5 phase with a reaction between B4C and W particles were observed with XRD and SEM investigations. The materials were subjected to gamma and neutron sources. Cs-137 and Co-60 gamma radioisotopes were used as gamma, and Pu-Be Neutron Howitzer was used as neutron source. Linear and mass attenuation coefficients of the composites were carried out for gamma sources by using gamma transmission technique. Furthermore, total macroscopic cross-sections of the samples were determined for Pu-Be neutrons. In conclusion, increasing W ratio in the B4C-W system causes higher gamma attenuation behavior for gamma sources, but the macroscopic cross-sections of the B4C-W composites decrease by increasing W concentration.

Consolidation of TiB2 Ceramics by Using Spark Plasma Sintering

Spark plasma sintering is a relatively new method for the consolidation of ceramics and metals with shorter sintering durations and lower sintering temperatures when it is compared to the conventional sintering methods. In this study, optimum sintering conditions of TiB2 were investigated by using Spark Plasma Sintering (SPS) system. Applied sintering temperatures were chosen at various temperatures varying from 1873 К to 2073 K. 50 MPa and 70 MPa sintering pressures were performed. Experiments were conducted under vacuum and argon atmospheres with 423 К per minute heating rate. Density measurement, HV micro hardness test, scanning electron microscopy (SEM) and X-Ray diffraction spectrometry (XRD) techniques were performed to the sintered TiB2 samples for characterization.

Spark Plasma Sintering of Si3N4/C Composites

Abstract Si3N4/C composites were prepared with carbon black and α-Si3N4 powder by a novel sintering method, i.e. spark plasma sintering. SiC particles formed through reactions between the carbon particles and the SiO2 on the Si3N4 surface. The samples were sintered at 1650 °C for 5 minutes in a nitrogen atmosphere. The microstructure, phase composition, mechanical properties, and dielectric properties of the composites were investigated. The relative densities of the C/Si3N4 composites decreased from 99 to 85% when the carbon black content increased from 0 to 20 wt.-%. Bending strength, hardness and dielectric properties were found to be influenced by the amount of carbon black introduced into the silicon nitride matrix.