Zirconia stabilization assisted by high energy ball- milling

J. Hernández,J. Zárate-Medina,G. Rosas 한양대학교 세라믹연구소 2009 Journal of Ceramic Processing Research Vol.10 No.2

Different zirconia (ZrO2) − x (x = CaO, ZnO mol%) solid solutions have been produced by high energy ball-milling (HEBM). The ZrO2 + oxide powder mixtures were milled for 15 and 25 hours, and thermal experiments were subsequently carried out. Experimental findings demonstrate a relationship of the powders’ morphology and crystal structure with zirconia stabilization. After the different milling times, X-ray diffraction (XRD) studies did not show any sign of zirconia stabilization; however, after thermal experiments total cubic ZrO2-CaO stabilization was obtained. According to the lattice parameter measurements, solid solutions were formed with the oxides and zirconia powders during the HEBM. These results did not show zirconia stabilization in the ZnO2 addition case. Both scanning electron microscope (SEM) and XRD structural observations indicate greater crystalline structural deformation of the ZrO2-ZnO high energy ball-milled powders in comparison to that of the ZrO2-CaO powders. Furthermore, the behaviors in the lattice parameter values of the ZrO2-CaO system showed a tendency toward increasing the monoclinic symmetry of the cell, which could be beneficial in obtaining total zirconia stabilization (TZS). In the dilatometer and XRD experiments monoclinic (m)→cubic (c) (CaO) or m→tetragonal (t) (ZnO) temperature changes for each oxide addition to zirconia were observed. Different zirconia (ZrO2) − x (x = CaO, ZnO mol%) solid solutions have been produced by high energy ball-milling (HEBM). The ZrO2 + oxide powder mixtures were milled for 15 and 25 hours, and thermal experiments were subsequently carried out. Experimental findings demonstrate a relationship of the powders’ morphology and crystal structure with zirconia stabilization. After the different milling times, X-ray diffraction (XRD) studies did not show any sign of zirconia stabilization; however, after thermal experiments total cubic ZrO2-CaO stabilization was obtained. According to the lattice parameter measurements, solid solutions were formed with the oxides and zirconia powders during the HEBM. These results did not show zirconia stabilization in the ZnO2 addition case. Both scanning electron microscope (SEM) and XRD structural observations indicate greater crystalline structural deformation of the ZrO2-ZnO high energy ball-milled powders in comparison to that of the ZrO2-CaO powders. Furthermore, the behaviors in the lattice parameter values of the ZrO2-CaO system showed a tendency toward increasing the monoclinic symmetry of the cell, which could be beneficial in obtaining total zirconia stabilization (TZS). In the dilatometer and XRD experiments monoclinic (m)→cubic (c) (CaO) or m→tetragonal (t) (ZnO) temperature changes for each oxide addition to zirconia were observed.

Synthesis and characterization of YAG : Eu spray dryed powders

J. Zárate-Medina,R. López-Juárez,E. A. Aguilar-Reyes,J. Muñoz-Saldaña 한양대학교 세라믹연구소 2008 Journal of Ceramic Processing Research Vol.9 No.1

YAG compounds doped with Eu have been successfully synthesized by spray drying a solution of precursor nitrates. Aluminum and yttrium nitrates, europium oxide, ethylene glycol and citric acid were used as reagents. The resultant solution was fed to a spray dryer to obtain precursor powders, which were in turn heat treated at 800, 850 and 900oC and characterized by X-ray diffraction. Morphology of the synthesized powders was observed by scanning and transmission electron microscopy. Results showed that the crystallization temperature of the powders is below 850oC without the presence of intermediate phases. The powders consist of spherical agglomerates constituted of primary particles of 40 nm diameter approximately. YAG compounds doped with Eu have been successfully synthesized by spray drying a solution of precursor nitrates. Aluminum and yttrium nitrates, europium oxide, ethylene glycol and citric acid were used as reagents. The resultant solution was fed to a spray dryer to obtain precursor powders, which were in turn heat treated at 800, 850 and 900oC and characterized by X-ray diffraction. Morphology of the synthesized powders was observed by scanning and transmission electron microscopy. Results showed that the crystallization temperature of the powders is below 850oC without the presence of intermediate phases. The powders consist of spherical agglomerates constituted of primary particles of 40 nm diameter approximately.

Evaluation of Hardness and Fracture Toughness in a Porcelain Stoneware with Pseudoboehmite Additions

O. Aguilar-García,S. Bribiesca-Vazquez,J. Zárate-Medina 한양대학교 세라믹연구소 2009 Journal of Ceramic Processing Research Vol.10 No.1

The effect of pseudoboehmite additions to conventional stoneware porcelain is investigated. Green compacts were formed by slip casting of stabilized aqueous suspensions and then sintering at 1,150℃, 1,200℃ and 1,250℃. The phase evolution was followed by XRD, the densification degree was calculated from densities and the microstructures were studied by SEM. Hardness, H and fracture toughness, KIC were measured by Vicker’s indentation. When vitrification occurs the presence of the pseudoboehmite leads to a extra mullitization, which has two consequences: a volume expansion resulting in a high porosity and a decrease of the amount of liquid which causes problems with the densification, by these facts the pseudoboehmite particles decrease the fracture toughness of the bodies. The effect of pseudoboehmite additions to conventional stoneware porcelain is investigated. Green compacts were formed by slip casting of stabilized aqueous suspensions and then sintering at 1,150℃, 1,200℃ and 1,250℃. The phase evolution was followed by XRD, the densification degree was calculated from densities and the microstructures were studied by SEM. Hardness, H and fracture toughness, KIC were measured by Vicker’s indentation. When vitrification occurs the presence of the pseudoboehmite leads to a extra mullitization, which has two consequences: a volume expansion resulting in a high porosity and a decrease of the amount of liquid which causes problems with the densification, by these facts the pseudoboehmite particles decrease the fracture toughness of the bodies.

Mixture design to optimize the amount of deflocculants in aqueous porcelain precursor suspensions

O. Aguilar-García,S. Bribiesca-Vazquez,J. Zárate-Medina 한양대학교 세라믹연구소 2009 Journal of Ceramic Processing Research Vol.10 No.2

The performance of dispersants poly(acrylic acid), a poly(methacrylic acid), sodium silicate, as well as binary and ternary deflocculant mixtures was compared for highly concentrated aqueous porcelain suspensions. These were formulated in ten stoneware recipes which were processed in the laboratory under fixed conditions, similar to those used in the ceramics industry, and viscosity measurements were made. The use of this methodology enabled the calculation of valid regression models (equations) relating viscosity with the contents of different deflocculant mixtures. The performance of dispersants poly(acrylic acid), a poly(methacrylic acid), sodium silicate, as well as binary and ternary deflocculant mixtures was compared for highly concentrated aqueous porcelain suspensions. These were formulated in ten stoneware recipes which were processed in the laboratory under fixed conditions, similar to those used in the ceramics industry, and viscosity measurements were made. The use of this methodology enabled the calculation of valid regression models (equations) relating viscosity with the contents of different deflocculant mixtures.