Influence of the substitution of Y2O3 for CeO2 on the mechanical and microstructural properties of silicon nitride

Abstract

This work investigated the substitution of Y2O3 for CeO2 in liquid-phase sintered silicon nitride ceramics. Cost reduction as well as good physical, mechanical and microstructural properties are the main objectives of the present study. Two powder mixtures were prepared, varying the contents of alpha-Si3N4, Al2O3, AlN, Y2O3 and CeO2. The mixtures were homogenized in ethanol, dried in a rotating evaporator and kiln, respectively, and then uniaxially (100 MPa) and cold isostatically pressed (300 MPa). The samples were sintered at 1850ºC for 1 h in a graphite resistive furnace under nitrogen atmosphere. After sintering the density of the samples was higher than 97% of the theoretical value. The fracture toughness and hardness were higher than 5.28 MPa.m½ and 17.12 GPa, respectively. Phase analysis by X-ray diffraction and scanning electron microscopy revealed the presence of alpha-SiAlON and beta-Si3N4.

The Incorporation of the Ceramic Industry Firewood Ash into Clayey Ceramic

“…By the mid temperature of 1000°C, the phase change of microcline into leucite begins [8]. Finally, there is the exothermic peak at the temperature of 738.20°C, Finally, there is the exothermic peak temperature of 738.20°C, when the metakaolin is formed under these conditions, similar to the mica clay minerals group, according to chemical analysis [8]. Thermal transformations of clay analyzed by TG can be observed in Figure 2.b).…”

“…The mass loss of 03.45% observed at the temperature range of 345.08°C and 460.77°C due to the volatilization of organic matter [9], confirmed by the endothermic peak in the thermal differential curve in temperature 375.14°C. By the mid temperature of 1000°C, the phase change of microcline into leucite begins [8]. Finally, there is the exothermic peak at the temperature of 738.20°C, Finally, there is the exothermic peak temperature of 738.20°C, when the metakaolin is formed under these conditions, similar to the mica clay minerals group, according to chemical analysis [8].…”

“…Iron oxide (Fe 2 O 3 ) gives the red color to the parts as well as the titanium oxide (TiO 2 ) provides the variation in hue after firing. The presence of calcium and magnesium oxides is probably connected to the dolomite, gypsum and calcite; such flux have moderate effect on burning temperatures below 1100°C [8].…”

“…Between 50.04°C and 251.86°C, there was a process related to water loss, being of higher intensity at 105.77°C. In the approximate temperature range between 430°C and 750°C, the loss of the structural hydroxyl of the clay occurs [8]. In the curve corresponding to the differential thermal analysis of the clay, there is an endothermic peak at 110.44°C as a result of elimination of adsorbed water.…”

“…The sample continues to absorb energy, reaching an endothermic peak at 506.12°C, corresponding to the loss of structural water from kaolinite. The increasing release of energy from 580.26°C is probably due to the tendency of phase change of cristobalite (SiO 2 ) spinel, containing aluminum silicon (Mg 8 Al 16 O 32 ), detectable only from 1100°C becoming into mullite 3(Al 2 O 3 .SiO 2 ) [8].…”