Masahiro Nawa

• Doctor of Philosophy
• Centro de Investigación en Nanomateriales y Nanotecnología - CINN

The statistical fatigue strength evaluations in water of an intragranular type Ce-TZP/Al2O3 nanocomposite (Ce-TZP/A-N) were investigated in comparison to 3Y-TZP. The isothermal t-m transformation which causes low temperature aging degradation (LTAD) did not occur during fatigue tests for both materials. The strength degradations under static and cy...

The statistical fatigue strength evaluations of an intragranular type Ce-TZP/Al2O3 nanocomposite (Ce-TZP/A-N), such as its initial strength, static and cyclic fatigue lives, and its dispersion, were investigated in comparison to 3Y-TZP. The strength degradations during static and cyclic loading of Ce-TZP/A-N were fairly small, and the dispersions o...

An approximate permanent strain of 0.3% was generated in Ce-TZP/alumina nanocomposite during static fatigue tests carried out at room temperature under ≈800 MPa for up to 106 s. For the deformed specimens, changes in the crystalline phase, ferroelastic domain orientation, and residual stresses were investigated. No evidence to support crystalline o...

The surface of a ceria-stabilized tetragonal zirconia polycrystal (Ce-TZP/Al2O3) nanocomposite was sandblasted by alumina particles and veneered with feldspathic porcelain via a conventional condensation method. The part of each specimen containing the interface layer was sliced to ultrathin sections with an argon ion slicer, and these sliced secti...

The t–m transformation zone and related residual stress fields around two types of crack used for toughness measurements, i.e. SEVNB (arrested crack induced by a V-notch) and IF methods (indentation crack induced by a Vickers impression), are reported for a Ce-TZP/Al2O3 nanocomposite, in comparison with 3Y-TZP. The fact that Ce-TZP/Al2O3 exhibits s...

Objective: The aim of this study is to analyze static and cyclic fatigue behavior in air, according to a 4-point bending test, for a Ce-TZP/alumina nanocomposite in comparison with a conventional 3Y-TZP. Method: Developed Ce-TZP/alumina nanocomposite is composed of Ce-TZP/30 vol% alumina (Ce-TZP/30A), achieving 2-3 times the toughness and equ...

Objectives: The aim of this study is to provide microscopic information on the tetragonal-to-monoclinic (t-m) transformation and generated residual stress fields around a crack path induced from Vickers indentation and those of around a cross section of Vickers impression, according to in situ Raman and fluorescence spectroscopy, for newly develope...

Objectives: The low temperature degradation (LTAD) of Y-TZP and Ce-TZP/Al2O3 nanocomposite was evaluated through the measurement of fracture toughness before and after autoclaving. Materials and Methods: Y-TZP powders (Tosoh, TZ-3YB-E) and Ce-TZP/Al2O3 nanocomposite powders (NANOZR, Panasonic Electric Works, MACZ100) were pressed, fired at 1350˚C...

The purpose of the present study was to evaluate the mechanical durability of a zirconia/alumina nanocomposite stabilized with cerium oxide (Ce-TZP/Al(2)O(3) nanocomposite) in comparison to yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) and discuss its application on ceramic dental restorations. The disk-shaped specimens of both materia...

Mechanical properties and slow crack growth (SCG) behavior of a 10Ce-TZP/Al2O3 nanocomposite currently developed as a biomaterial are considered. Fracture toughness is determined for sharp, long (double torsion) and short (indentation) cracks and a good agreement is found between the two types of cracks. The main toughening mechanism in the nanocom...

Two types of tetragonal zirconia polycrystals (TZP), a ceria-stabilized TZP/Al2O3 nanocomposite (CZA) and a conventional yttria-stabilized TZP (Y-TZP), were sandblasted with 70-μm alumina and 125-μm SiC powders, then partially annealed at 500-1200℃ for five minutes. Monoclinic ZrO2 content was determined by X-ray diffractometry and Raman spectrosco...

The effect of sintering condition, sandblasting and heat treatment on biaxial flexure strengths of the zirconia/ alumina nanocomposite stabilized with cerium oxide (Ce-TZP/Al2O3 nanocomposite, referred to NANOZR) was evaluated in comparison to that of yttria stabilized tetragonal zirconia polycrystals (Y-TZP). The disc-shaped specimens of NANOZR an...

With elongation of average human life, problem such as bone embrittlement and osteoporosis call for quick solution and the expectation for artificial biomaterials heightens. Many ceramics widely used as artificial biomaterials are limited by their poor reliability characteristics. A CeO2 stabilized tetragonal zirconia polycrystalline (Ce-TZP) matri...

In the area of dental treatment for crown and dental implants, ceramics restoration is becoming popular due to both aesthetic needs and release of metallic allergy. However, for the restoration of defected tooth, ceramics materials with higher reliability than that of conventional glass or alumina have been required, thus raising expectations for z...

The aim of this study was to investigate the effect of surface treatments on bonding strength of two kinds of zirconia to three kinds of resin cements. After thermal cycling, the shear bonding strength of both zirconia decreased in all the resin cements. The bonding strengths of two resin cements in which primer contains silane dramatically decreas...

The aim of this study was to evaluate the electrophoretic deposition (EPD) behavior of ceria-stabilized zirconia/alumina (Ce-TZP/Al2O3) granulated powder. Two types of slurry with powder-to-solvent ratios of 10 wt% and 20 wt% were used. Zeta potential of the slurries was measured using a spectrometer at different pH levels. Then, EPD was performed...

Zirconia ceramics were introduced in the seventhies for use as structural biomaterials after laboratory tests and simulator studies. However, nowadays concerns remain about their reliability in vivo, despite published clinical studies have already established the safety and the good tribological performance of these materials. It is still unclear w...

The effect of sandblasting and heat treatment on biaxial flexure strengths of the zirconia/alumina nanocomposite stabilized with cerium oxide (Ce-TZP/Al2O3 nanocomposite) was evaluated in comparison to that of yttria stabilized tetragonal zirconia polycrystals (Y-TZP). The disc-shaped specimens of the nanocomposite and Y-TZP were sandblasted with 7...

Zirconia ceramics have been widely used for new generation of bearing materials in biomedical applications. In this context, a zirconia-matrix, stabilized with cerium oxide and dispersed with fine alumina particles (Ce-TZP/Al2O3 nanocomposite) was recently developed and this material experienced significant improvements in both fracture toughness a...

This study was aimed to investigate the effect of grinding, sandblasting by alumina and SiC, and heat treatment on the phase transformation from tetragonal to monoclinic zirconia on the surface of yttria stabilized tetragonal zirconia (Y-TZP) and zirconia/alumina nanocomposite stabilized with cerium oxide (Ce-TZP/Al2O3 nanocomposite). The monoclini...

The aim of this study was to evaluate the electrophoretic deposition (EPD) behavior of ceria-stabilized zirconia/alumina (Ce-TZP/Al2O3) granulated powder. Two types of slurry with powder-to-solvent ratios of 10 wt% and 20 wt% were used. Zeta potential of the slurries was measured using a spectrometer at different pH levels. Then, EPD was performed...

Yttria stabilized tetragonal zirconia polycrystals (Y-TZP) have been applied to dental crown and bridges. Whereas, to further improve its mechanical strength, the zirconia/alumina nano-composite stabilized with cerium oxide (Ce-TZP/Al2O3 nano-composite) was developed. In the present study, biaxial flexure strength, fracture toughness and hardness w...

Ceramics have long been expected to be candidates for a wide variety of engineering applications due to their desirable properties of high refractory capability, good wear resistance, and chemical stability. However, they have not been advanced into many suggested applications due mainly to their poor toughness. It is therefore highly desirable to...

Recently zirconia/alumina composites have been examined by many researchers as the new generation of bearing materials in total joint replacements. In this study, the phase stability of a Ce-TZP/Al(2)O(3) nanocomposite and conventional Y-TZP after aging, and its influence on wear resistance, were investigated. Very slight phase transformation was o...

The objectives of this study were to investigate the biocompatibility, phase stability, and wear properties of a newly developed Ce-TZP/Al(2)O(3) nanocomposite, as compared to conventional ceramics, and to determine whether the new composite could be used as a bearing material in total joint prostheses. In tests of mechanical properties, this compo...

Induction of an apatite-forming ability on a nano-composite of a ceria-stabilized tetragonal zirconia polycrystals (Ce-TZP) and alumina (Al2O3) polycrystals via chemical treatment with aqueous solutions of H3PO4, H2SO4, HCl, or NaOH has been investigated. The Ce-TZP/Al2O3 composite is attractive as a load-bearing bone substitute because of its mech...

The porous hydroxyapatite (HAp) films were formed on the Ce-TZP/alumina substrate by the spray pyrolysis technique. The biocompatibility of the resulting HAp films were examined using osteoblastic cell. Twenty five types of the coatings were carried out by changing the combination of solutions for film adhesion (CMP solution) and solution for film...

The objectives of this study were to investigate the biocompatibility, phase stability , and wear properties of a newly developed Ce-TZP/Al 2 O 3 nanocomposite, as compared to conventional ceramics, and to determine whether the new composite could be used as a bearing material in total joint prostheses. In tests of mechanical properties, this compo...

It has been revealed that a zirconia gel forms an apatite on its surface in a simulated body fluid (SBF). This indicates that Zr-OH group is able to induce apatite nucleation. However, it is not yet clear what kind of Zr-OH group is effective for inducing apatite nucleation in the body environment. In the present study, apatite-forming ability of z...

To compensate the definite disadvantages of lower strength and lower hardness in Ce-TZP, an intragranular type of 12Ce-TZP/0–30 vol% Al2O3 nanocomposite was investigated. Furthermore, the effect of TiO2 addition on strengthening and toughening was also examined for the optimum component of 30 vol% Al2O3, which showed a maximum strength of 866 MPa....

To develop a new attractive Ce-TZP ceramic, which possesses a high strength while still preserving significant high toughness, we investigated an intragranular type of nanocomposite in lower CeO2 content for 0–1 mol% TiO2 doped Ce-TZP/Al2O3 system. These composites partly possessed an intragranular microstructure, in which several of 10–100 nm size...

To develop a new attractive ceramic material in which both high strength and high toughness might be achieved, we have established the new concept of an interpenetrated intragranular nanostructure based on the general design of the nanocomposites. The composite system designed according to the above concept possesses a novel microstructural feature...

Yttria stabilized tetragonal zirconia polycrystal (Y-TZP)/0-100 vol % molybdenum (Mo) composites were fabricated by hot-pressing a mixture of Y-TZP powder containing 3 mol % yttria (Y2O3) and a fine Mo powder in vacuum. This composite system possessed a novel microstructural feature composed of an interpenetrated intragranular nanostructure, in whi...

To compensate the definite disadvantages of ceria stabilized tetragonal zirconia polycrystal (Ce-TZP) as compared to Y-TZP ceramics, such as lower strength and lower hardness, we applied the idea of the nanocomposite to Ce-TZP/Al2O3 composite system. Zirconia matrix in these composites consisted of primarily the tetragonal phase and a small amount...

Static and dynamic fracture toughnesses in precracked Y-TZP/Mo composites fabricated by hot-pressing through a nanocomposite approach are investigated. Fracture toughnesses in these composites are virtually unaffected by loading velocity. The composite containing 70 vol%Mo, whose microstructure exhibits a continuous Mo phase, shows the highest frac...

Two types of Al2O3/Mo composites were fabricated by hot-pressing a mixture of - or -Al2O3 powder and a fine molybdenum powder. For Al2O3/5 vol% Mo composite using -Al2O3 as a starting powder, the elongated molybdenum layers were observed to surround a part of the Al2O3 grains, which resulted in an apparent high value of fracture toughness (7.1 Mpa...

Yttria stabilized tetragonal zirconia polycrystal (Y-TZP)/0-100 vol% molybdenum (Mo) composites were fabricated by hot-pressing a mixture of Y-TZP powder containing 3 mol% yttria and a fine Mo powder in vacuum. This composite system possessed a novel microstructural feature composed of a mutual intragranular nanostructure, in which either nanometer...

A ceramic/metal nanocomposite in tetragonal zirconia-molybdenum system possesses a novel microstructural feature composed of a mutual intragranular nanostructure, in which either nanometer sized Mo particles or equivalent sized zirconia particles are located within the zirconia grains or Mo grains, respectively. It achieves a simultaneous improveme...

Four whiskers; β-SiC, β-Si3N4, α-Si3N4 and 9Al2O3⋅2B2O3, were tested as a reinforcement material of the cordierite glass ceramics. The composites containing of 10 or 30vol% whisker and the monolithic glass ceramics were sintered by hot-pressing at 1000°C in Ar under 30MPa for 60min. Their sinterability and mechanical properties were investigated. F...

The Al2O3/5-20vol%Mo composites were fabricated by hot-pressing a mixture of a-Al2O3 and fine Mo powders under a vacuum. In these composites, nanometer size Mo particles were dispersed within theAl2O3 grains and relatively large Mo particles, above 1μm, were located at the grain boundaries. Thus, it was confirmed that ceramic/metal nanocomposites c...

The Mechanical properties and microstructure of AlO/W composites have been investigated. These composites were fabricated by hot-pressing a mixture of y- or a∼ phase alumina (Al203) and fine tungsten (W) powders, hi these composites, fine W particles were located both within the AI2O3 matrix grains and at the grain boundaries. The fracture strength...

The Mechanical properties and microstructure of Al2O3/ W composites have been investigated. These composites were fabricated by hot-pressing a mixture of γ⁻ or α⁻ phase alumina (Al2O3) and fine tungsten (W) powders. In these composites, fine W particles were located both within the Al2O3 matrix grains and at the grain boundaries. The fracture stren...