Roberto de Oliveira Magnago

Compaction of ZrO2(Y2O3) Powders with Different Particle Sizes and Effects on the Sintering

In this work, compacting powders of different ZrO2(Y2O3) are investigated relating the particle size, compaction pressure, and use of binders. Powders of ZrO2 stabilized with 3mol % Y2O3 with an average particle size of 0.15 to 0.7μm presence of both bonding and 0.15μm without addition of binder, were uniaxially compacted with pressures of 30 to 115MPa. Green density between 40% and 50% were obtained. The results indicate that powders sized less densification above 1400°C, while the larger sizes only after reaching full densification above 1500°C. Crystallographic characterization indicates that the powders have a percentage of monoclinic phases in the range of 15% to 26%, but only after sintering tetragonal phase is identified.

Characterization of Al2O3-Al2TiO2 Ceramic Composites: Effects of Sintering Parameters on the Properties

This study aims to evaluate the effects of sintering parameters in crystalline phases, microstructure and mechanical properties of composites obtained through the Al2O3-TiO2 ceramic system. Cylindrical specimens, containing molar ratio of 3 Al2O3: 1 TiO2, were uniaxially pressed at 100 MPa. The applied sintering parameters were varied in five distinct temperature ranges (1300°C, 1400°C, 1500°C, 1575°C or 1600°C) for 2h and 1600°C for 10h. After sintering, samples were characterized by relative density, X-ray diffraction, scanning electron microscopy and mechanical properties (hardness and fracture toughness). After sintering the results point to a microstructure with grains near to 2.5mm, independent of the present phases and crystalline phases composed of: Al2O3 rhombohedral, TiO2 tetragonal e Al2TiO5 orthorhombic. The specimens sintered at 1600°C-10h feature densification 30% higher them the ones sintered at 1300°C-2h, reaching a density higher than 85% of theoretical density. The composite presents hardness higher than 1000HV and fracture toughness upper than 2.2MPam1/2. The better results for the mechanical properties were found in the composites sintered at 1600°C-10h, that showed a bigger relative density than all analyzed specimens, and only phases of Al2O3 and Al2TiO5 could be found, what means that all TiO2 was consumed in the sintering of the new composite.

Development and Characterization of Al2O3-ZrO2 Composites Using ZrO2(Y2O3)-Recycled as Raw Material

The objective of this work was the development of Al2O3-ZrO2 ceramic composites using recycled-source of ZrO2(Y2O3). Al2O3 powder was mixed with different proportions of ZrO2(Y2O3) arising from pre-sintered blocks used in dental prostheses manufacturing. The mixtures containing 3wt% to 15wt% ZrO2(Y2O3) were uniaxially pressed at 80MPa and sintered at 1600°C-2h. Raw materials and sintered samples were characterized by X-ray diffraction, scanning electron microscopy (SEM), relative density, hardness and fracture toughness. The results of X-ray diffraction showed α-Al2O3 and tetragonal-ZrO2 as crystalline phases after sintering. Furthermore, the relative density in all compositions was higher than 95%. The samples presented Vickers hardness and fracture toughness higher than 1300HV and 3.5MPa. m1/2, respectively.

Ceramics and Glass-Ceramics Dental Materials: Chemical Solubility, Cytotoxicity and Mechanical Properties

In this work three dental ceramics were characterized according to ISO 6872: yttria-stabilized zirconia (ZrO2-Y2O3), lithium disilicate (Li2Si2O5) and the spinel-zirconia composite (MgAl2O4-ZrO2). The zirconia ceramic and the zirconia-spinel composite were sintered at 1600°C-2h, while the lithium disilicate was thermally treated at 820°C-20min. These materials were characterized by relative density, X-ray diffraction, scanning electron microscopy, hardness, fracture toughness, chemical solubility and cytotoxicity. The XRD results showed for the stabilized zirconia only the tetragonal phase of ZrO2, and to the composite only the phase MgAl2O4, Li2Si2O5 was the only phase to lithium disilicate. Relative density results showed that the zirconia and the lithium disilicate showed high densification (> 99.5%) and the composite had a relative density of 75% (10% composite doped with ZrO2) and 90% (50% doped with ZrO2). Hardness and toughness showed 450HV and 3.2MPa.m1/2 to ZrO2-MgAl2O4 composites, 525HV and 1.8MPam1/2 to lithium disilicate and 1280HV and 8.0MPa.m1/2 to zirconia. The materials evaluated showed chemical solubility <30μg/cm2 and the results of cytotoxicity tests indicated cell viability of the samples near 100% for all the materials, showing good chemical stability and potential for dental applications.

Evaluation of Hardness and the Fracture Toughness of Composite Biphasic Alumina-YAG

Currently the composite two-phase Al2O3-YAG laser has been widely exploited by having good properties such as high abrasion resistance and deformation in harsh environments. Thus, one can predict that this material has very attractive applications such as fins of jet engines and gas turbines. In this study, five mixtures were processed Y2O3-Al2O3-Nb2O5, in proportions of 0, 1, 5, 15 and 35 wt% Y2O3 and 4% by weight of Nb2O5. These samples were sintered at 1550 to 1650 °C in air where it was detected by X-Ray Diffraction (XRD) with Rietveld refinement training YAG and also two intermediate stages, and AlNbO4 YNbO4. Finally they were characterized by hardness by Vickers microindentation and fracture toughness. The highest hardness and fracture toughness were 15 GPa and 5.5 MPa.m1/2, respectively.

Infiltrated Spinel-Based Ceramic (MgAl2O4) for Dental Application

This work developed a ceramic material for dental application, spinel-base (MgAl2O4), a ceramic material with recognized translucency. Spinel powders were uniaxially pressed at 100 MPa and pre-sintered in order to obtain porous ceramic blocks. The pre-sintered blocks were characterized and indicated 80% of relative density. X-ray diffraction (XRD) only showed MgAl2O4 phase. Samples with 15 x 15 x 1 mm were submitted to infiltration using glass rich in lanthanum (La). The products were characterized by scanning electron microscopy (SEM) and mechanical properties, as hardness and fracture toughness. Results were compared to the commercial product VITA-InCeram Spinell. Relative densities exceeding 92%, hardness around 900 HV and high toughness 2.5 MPa.m1/2 were obtained for both examined systems.

Preparation and Characterization of Composites Obtained of Polymeric Waste Coming from Boards Electronic Equipment

The objective of this work is to recycle the printed circuit boards of electronic equipment discarded and mix them with polypropylene (PP) to produce a new composite. Six types of mix of discarded printed circuit boards were analyzed: new boards with and without copper, used boards without components and with and without copper, used boards without components and without copper, used boards with copper track, used boards with copper track and burned and used boards with components. Boards were disintegrated and employed as reinforcement with polypropylene matrix (5% m/m). Specimens were produced for flexural and impact tests. Results showed that specimen’s properties depend on the mix composition. In all of the cases, pure PP properties were enhanced when it was replaced by 5% of waste materials discard.

Use of Composite SiO2 (62-68)-MgO + CaO (29-39) in Ceramic Protection Mass Injection Machines in the Iron Notch and Liquid Slag Hole in Blast Furnaces

The article describes the use of protection ceramic composed of SiO2 (62-68)-MgO+CaO (29-39) in the frontal region of machines that inject refractory mass to stop pig iron running and liquid slag in blast furnaces. The new protection model (prototype) showed an annual saving of approximately R

MgAl2O4-ZrO2(Y2O3) Ceramic Composite: Sintering and Characterization

32,000 compared to the compound previously used CaO-Al2O3-SiO2. It also presented lower toxicity, once it has in its morphology less amount of fiber. These fibers when inhaled cause damage to internal lungs tissues becoming harmful to health. Production rates remained, since in all the new ceramic protection samples that were tested the frontal part was preserved allowing the refractory mass to be injected in proper quantity and pressure for reconstitution of the hole length, which removes iron and slag from blast furnace. Therefore, this enables a larger internal volume in order to produce more. The protection models used were from the company Morganite-Brasil. The material morphology and crystallographic characterization were realized by Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD), respectively.

Properties of ZrO2(Y2O3) Used as Metal-Free Dental Restorations

Spinel is a ceramic material of excellent translucence when sintered in high densification, however, its low sinterability and toughness difficulty limit its use as an interesting material for dental applications. The use of stabilized zirconia ZrO2(Y2O3) as Spinel agent is studied in this work. Zirconia contents between 10% and 50% were mixed to Spinel and samples were uniaxially and isostatically pressed. The specimens were sintered at 1575oC with isothermal holding time of 120 minutes. Samples were characterized by X Ray Diffraction (XRD), SEM, relative density, microhardness and fracture toughness. The samples which showed better mechanical performance were the ones with 50% zirconia and sintered at 1575oC, with 90% relative density, hardness of 400HV and KIC of 2.4MPa.m1/2.