Microstructural regulation and properties enhancement of MgO-CaO ceramics by doping Y_(2)O_(3)

MgO-CaO ceramics with enhanced microhardness and hydration resistance were successfully prepared by doping Y_(2)O_(3) in this work.The effects of introducing Y_(2)O_(3) on the microstructure and properties of MgO-CaO ceramics were investigated.The microstructural regulation effects of Y_(2)O_(3) additive on MgO,CaO,and MgO-CaO ceramics were analyzed comparatively.The results show that Y_(2)O_(3) dissolves into the CaO lattice to form solid solution in CaO ceramics,and no obvious intergranular phase forms.While the Y_(2)O_(3) additive leads to the micro structural reconstruction in MgO and MgO-CaO ceramics.By adding Y_(2)O_(3),SiO_(2) impurity from magnesium source reacts with CaO to form the silicate phases containing Y^(3+)ions in MgO-CaO ceramics.The increase in the MgO/CaO interface and the microstructural reconstruction synergistically improves the microhardness and hydration resistance of MgO-CaO ceramics markedly.

Effects of Sm_(2)O_(3) addition on sintering behavior of pre-synthesized magnesia-rich magnesium aluminate spinel

The effects of Sm_(2) O_(3) as an additive on the densification of a pre-synthesized magnesia-rich spinel were investigated.The sintering behavior of the material was characterized by analyzing its dilatometric characteristics,linear shrinkage,bulk density,apparent porosity,phase structure,and micro structure.Moreover,the cold modulus of rupture(CMOR) and microhardness of the spinel were measured.The results show that samarium oxide reacts with the spinel to form SmAlO_(3)(a rare-earth aluminate) to improve the sintering performance and mechanical properties of the spinel. The formation of magnesite phases decreases the rupture strength of the spinel.However,this MgO phase is inlaid in spinel grains boundary,has a pinning effect which can improve the sinterability of the spinel.

Enhancing mechanical properties and air permeability of corundum porous materials by in situ formation of LaAl11O18 in bonding phase

Corundum porous materials of particle-packing type with different contents of in situ formed LaAl11O18were prepared using tabular corundum,reactive alumina and La2O3 powder as raw materials.The effects of the introduction of LaAl11O18 on the microstructure.phase composition and properties of the porous materials were investigated.The specimens were characterized by scanning electron microscopy.X-ray diffraction and mercury porosimetry.Results show that platelet-like LaAl11O18 is formed in situ by the reactions of La2O3 and Al2O3.With a certain amount of La2O3 added.the cold crushing strength,cold modulus of rupture and hot modulus of rupture(1400 x 0.5 h) of the specimens are increased,and the air permeability is improved simultaneously.However.upon further increasing the amount of La2O3 added,the mechanical properties and air permeability of the porous materials then decrease gradually owing to the increased numbers of pores and cracks in the bonding phase.The enhanced mechanical properties of the specimens with La2O3 added are attributed to the strengthening effects of plate-like LaAl11O18 in the bonding phase and to the activated sintering of both Al2O3 powder and corundum coarse aggregate for the diffusion of La3+in Al2O3 lattice.In addition,the improved air permeability of the specimens should be related to the decreased content of pores in the bonding phase and the reduced number of interfacial cracks.