Alumina-Toughened-Zirconia with Low Wear Rate in Ball-on-Flat Tribological Tests at Temperatures to 500 °C

An alumina-toughened zirconia (ATZ) material, fabricated using a procedure consisting of the common sintering of two different zirconia powders, was tested using the ball-on-disc method in a temperature range between room temperature and 500 °C. Corundum balls were used as a counterpart. The ATZ composite behaviour during tests was compared with that of commonly used α-alumina and tetragonal zirconia sintered samples. At temperatures over 350 °C, a drastic decrease in the wear rate of the material was detected. SEM analyses proved that, in such conditions, nearly the whole surface of the sliding material was covered with a layer of deformed submicrometric grains, which limited contact with the part of material that was not deformed. The mentioned layer was relatively strongly connected with the material, increased its resistance, and decreased its coefficient of friction. As a reference, commonly used materials, namely commercial alumina and tetragonal zirconia, were tested. The wear parameters of the composite were significantly better than those registered for the materials prepared of commercial powders.

Phenomena Occurring upon the Sintering of a Mixture of Yttria–Zirconia Nanometric Powder and Sub-Micrometric Pure Zirconia Powder

Mixtures of powders essentially differing in their particle morphology and size were applied to prepare polycrystals in a Y2O3-ZrO2 system. An yttria–zirconia solid solution nanometric powder with a Y2O3 concentration of 3.5% was prepared by subjecting co-precipitated gels to hydrothermal treatment at 240 °C. The crystallization occurred in distilled water. The pure zirconia powders composed of elongated and sub-micrometer size particles were also manufactured through the hydrothermal treatment of pure zirconia gel, although in this case, the process took place in the NaOH solution. Mixtures of the two kinds of powder were prepared so as to produce a mean composition corresponding to an yttria concentration of 3 mol%. Compacts of this powder mixture were sintered, and changes in phase composition vs. temperature were studied using X-ray diffraction. The dilatometry measurements revealed the behavior of the powder compact during sintering. The polished surfaces revealed the microstructure of the resulting polycrystal. Additionally, the electron back scattering diffraction technique (EBSD) allowed us to identify symmetry between the observed grains. Hardness, fracture toughness, and mechanical strength measurements were also performed.

Effect of Sintering Temperature to the Mechanical Properties of Different Filler Loading of Zirconia Powder in Hydroxyapatite Composites

Hydroxyapatite (HA)-Zirconia (ZrO2) composite with varying zirconia composition ranging from 1 to 10 wt% was investigated for biomedical applications in order to produce high compressive strength. Precipitation method was used to prepare both hydroxyapatite and zirconia powders. To find the ideal composition, mixture-containing 1, 3, 5 and 10 wt% ZrO2 powder was added. Each mixture was sintered for 4 hours at 750oC, 1050oC and 1250oC. Hardness and compressive strength test were used for evaluation. It was found that with 1 wt% of ZrO2 sintered at 1250oC showed the greatest structural strength as its volume fraction porosity is the lowest. The hardness and compressive strength of this sample were found to be 2.75 GPa and 72.0 MPa respectively. This can be useful for biomedical applications especially in promoting osteo-integration.

Effect of Powder Characteristics on Slip Casting Fabrication of Dental Zirconia Implants

Dense zirconia compacts were fabricated by slip casting and sintering of nanoscale zirconia powders, and the effect of the powder characteristics (crystallite size, specific surface area, yttria content, and agglomeration) on the slurry and sintered properties was investigated. Three types of commercial 3 mol% yttria-stabilized tetragonal zirconia polycrystals powders were used as the starting powders after the powder characteristic analysis. A zirconia slurry for slip casting was prepared by mixing zirconia powder (solid loading of 60, 65, and 70 wt.%), distilled water, and a dispersant of Darvan C. The green compacts obtained from slip casting were cold isostatic pressed to enhance the close packing and densified by sintering at 1450 °C for 2 h. Highly dense zirconia compacts with a relative density of 99.5% and grain size of 350 nm were obtained based on the powder type and solid loading in the slurry. The microstructure and mechanical hardness of the sintered specimen after slip casting were dependent on the yttria content in the 3 mol% yttria-stabilized tetragonal zirconia polycrystal powder and the solid loading within the slurry.

Study of the Synthesis of Zirconia Powder from Zircon Sand obtained from Zircon Minerals Malaysia by Caustic Fusion Method

The zircon powder from Zircon Minerals Malaysia is a pure premium grade zircon sand milled 1.5 µm that contain ZrSiO4, ZrO2, HfO2, SiO2, Al2O3, TiO2, and Fe2O3. The monoclinic zirconia powders were synthesized from the zircon sand of Zircon Minerals Malaysia, by caustic fusion method at calcination temperatures between 500 °C to 800 °C. The as-synthesized zirconia was characterized through X-Ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric and differential thermal analysis (TG-DTA), and X-Ray fluorescence (XRF) techniques. The XRD results show two monoclinic phases of microcrystalline zirconia. Zirconia that was calcined at 600 °C obtained the highest value of ZrO2, which was 54.48%; followed by zirconia calcined at 700 °C, 800 °C, and 500 °C, which obtained the ZrO2 values of 53.58%, 52.41%, and 51.53%, respectively, based on the XRF analysis. As-synthesized zirconia showed monoclinic phases where the surface areas were 0.0635 m2/g, 0.135 m2/g, 0.0268 m2/g, and 0.0288 m2/g, for zirconia calcined at temperatures of 500 °C, 600 °C, 700 °C, and 800 °C, respectively. The surface structure of the powder that had been calcined at 600 C showed similarities with the commercial zirconia. The similarities of the synthesized zirconia and commercial zirconia showed that the zirconia powder could be synthesized using zircon sand by caustic fusion method, even though the content of zirconia was lower compared to that of the commercial zirconia powder.

Nanoporous zirconia microspheres prepared by salt-assisted spray drying

Nanoporous zirconia with high surface area and crystallinity has a wide range of industrial applications, such as in inorganic exchangers for ion exchange columns, catalyst substrates, and packing material for HPLC. Spherical particles of crystalline nanoporous zirconia are highly desired in various industries due to easy handling of the materials in a fluidized bed. Here, spray drying was adopted to produce spherical nanoporous zirconia powders in both laboratory scale and pilot plant scale. Effect of salts on spray-dried ZrO2 powders and their crystallization behavior was studied. It was found that addition of salts to the zirconia precursors has a huge effect on the crystallization of nanoporous zirconia powders. These results have a great impact on the development of microspheres of nanocrystalline ZrO2 and potentially open up a new opportunity to the low-cost production of porous ceramic microspheres with the salt templating method, in general.