چكيده به لاتين
Zirconia (ZrO2), as an engineering ceramic, because of special combination of optical, electrical, mechanical, thermal and chemical properties has attracted much attention. Studies have shown that composite making of zirconia with silicon carbide could improve it's mechanical properties (strength, toughness and hardness) especially at high temperatures. Due to the simplicity and low cost, Zircon (ZrSiO4) carbothermal reduction, is an effective method for the synthesis of zirconia-silicon carbide composite powders with uniform distribution and large-scale production. In this project, zirconia-silicon carbide (whisker) composite powders were synthesized by carbothermal reduction method, and inexpensive and industrial zircon with activated carbon have used as raw materials. Raw materials were mixed in ball mill and then were pressed in pellet form with 2.5Cm diameter and 0.5Cm thickness; The samples were placed in alumina crucibles and the crucibles were immerged in carbon and heated in furnace. Factors affecting the process includes the synthesis temperature (1450-1650 °C every 50 degrees), synthesis time (3, 4 and 6 hours) and carbon molar ratio (carbon to zircon molar ratios equal to 3, 4, 5, 6 and 10) were examined. Synthesized products were investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis. XRD results showed that because of the carbon bed, some silicon oxynitride (Si2N2O) phase was formed in the samples which it's value is nearly constant in the samples. Optimum conditions for the synthesis of composite powders with a maximum amount of silicon carbide was achieved in carbon to zircon molar ratio 5 (or 6) and temperature 1650 °C for 6 hours. Yttria nanopowder in amounts of 3, 5, 8 and 10 wt% was added to the raw material mixture and it was found that the addition of yttria could stabilized zirconia in the form of tetragonal or cubic during the reduction process. SEM results showed that the synthesized powders have uniform distribution of zirconia and silicon carbide and formed silicon carbide is in the fiber (whiskers) form.
