Browsing by Author "Tzanova N."

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    Castables in Si3N4-Al2O3 system
    (2013-05-21) Tzanova N.; Djambazov S.; Mitsev P.
    This work investigates the behavior of hydratable alumina in the presence of several forms of aluminum oxide and silicon nitride used for the production of refractory castable, which can find application in high temperature sensors for gas temperature measurement. Four compositions based on aluminum oxide and silicon nitride in quantity of 25, 30 and 40% have been studied. Silicon nitride is used to improve the thermal stability. Hydratable alumina, reactive aluminium oxide, electrofused aluminum oxide and silicon nitride were mixed and fired at 850°C. X-ray diffraction (XRD) and scanning electron microscopy (SEM) and confocal microscopy were used to characterize structure of the obtained castable and also compressive strength measurements were performed after firing. It was found that after a given number of working cycles, the sensor with corundum castable was defected, due to its low thermal resistance leading to a significant increase in step response of the sensor. The composition of 30 % silicon nitride is characterized by a compressive strength of 41.70 MPa and relatively homogeneous structure. This sensor showed no cracks and the step response was significantly lower compared with the composition based on alumina.