Preparation and Mechanical Properties of Zirconia Ceramics Doped with Different Y_(2)O_(3)Contents

The sintering behavior and mechanical properties of zirconia doped with 2.0mol%-3.0mol%Y_(2)O_(3)were studied by pressure-less sintering.The experimental results show that the densification temperature of zirconia ceramics increases gradually with the decrease of Y_(2)O_(3)doping content by which decreases the sintering driving force due to the lower oxygen vacancy concentration of the systems.Furthermore,the bending strength and fracture toughness of the prepared zirconia ceramics increase with the decrease of Y_(2)O_(3)doping content.It can be attributed to the fact that the phase stability of tetragonal zirconia decreases with the decrease of Y_(2)O_(3)doping content,which is easier to induce"phase transformation toughening"and dissipate impact energy.The relative density,bending strength and fracture toughness of 2.0 mol%Y_(2)O_(3)doped zirconia ceramics(2.0Y-ZrO_(2))sintered at 1525℃are 99.00%,1256.65±20.82 MPa and 9.85±0.13 MPa·m^(1/2),respectively.

Defects in the grain interiors of 3 mol%yttria-stabilized tetragonal zirconia polycrystal ceramics with 0.25 wt%alumina

The presence of high-density defects is rarely observed in bulk 3 mol%yttria-stabilized tetragonal zirconia polycrystal(3Y-TZP)ceramics obtained through conventional pressureless sintering.In the present work,fine-grained dense 147 nm 3Y-TZP ceramics were prepared by pressureless sintering of commercial 0.25 wt%alumina-doped zirconia powders at 1300℃.A novel discovery was reported in which large amounts of defects were present in the grain interiors of the sample.The phenomenon was further examined using three types of powder samples,and the reasons for defect formation were investigated by microstructural characterization using high-resolution transmission electron microscopy(HRTEM)analysis and Rietveld refinement.The results confirmed the essential dependence of the defect formation on the alumina addition.The authors attributed the defect formation to the significant difference in ionic radii of the solvent and solute during the dissolution of alumina into the zirconia lattice.The sintering kinetics were proposed to be enhanced by the presence of substantial defects,which consequently favored the low-temperature sintering of the alumina-doped zirconia ceramics.

Effect of Sintering Temperature on Aging Resistance and Mechanical Properties of 3Y-TZP Dental Ceramic

In order to investigate the effect of sintering temperature on aging properties and mechanical properties of 3Y-TZP dental ceramic in simulated oral environment, 3Y-TZP nanopowder compacts were pressurelessly sintered at 1 350℃, 1 400 ℃, 1 450 ℃,1 500 ℃, respectively, then were treated by soaking in artificial saliva （65 ℃, pH=7） for two months. The treated specimens sintered at 1 350 ℃ showed there was no phase transformation but whose strength and toughnesswere significantly improved （P〈0.05）, while those sintered at 1 400 ℃- 1 500 ℃ revealed a small amount of phase transformation and insignificant mechanical reinforcement （P〉0.05）. No microcracks were detected but increment in lattice volume was found in all specimens. Lowering sintering temperature favors aging resistance and mechanical reinforcement of 3Y-TZP in a simulated oral environment.

Microstructure and Fracture Toughness of Al_2O_3/3Y-TZP Composites

The composites were prepared by ball-milling ZrO_2(3%Y_2O_3) and γ-Al_2O_3 nanoparticles, pressing unidirectionally, cold-pressing isostatically and pressurelessly sintering in air. The phases of ZrO_2 in composites were examined by X-ray diffraction. The microstructure of Al_2O_3/3Y-TZP composites was observed by scanning electron microscope (SEM) and transmission electron microscopy (TEM) respectively. The X-ray analysis reveals that ZrO_2 of both surface and fracture surface is mainly t-ZrO_2. The SEM image shows that there are some intragranular particles in large granulars. The fracture toughness K_ 1c of Al_2O_3/70%ZrO_2(3%Y_2O_3(mole fraction)) composite tested by single-edge notched bending is 13.5 MPa·m 1/2. Being toughened by the ferroelastic domain switching and the intragranular microstructure explains high toughness of the composite.

Femtosecond laser ultrafast photothermal exsolution

Exsolution,as an effective approach to constructing particle-decorated interfaces,is still challenging to yield interfacial films rather than isolated particles.Inspired by in vivo near-infrared laser photothermal therapy,using 3 mol%Y_(2)O_(3)stabilized tetragonal zirconia polycrystals(3Y-TZP)as host oxide matrix and iron-oxide(Fe3O4/γ-Fe_(2)O_(3)/α-Fe_(2)O_(3))materials as photothermal modulator and exsolution resource,femtosecond laser ultrafast exsolution approach is presented enabling to conquer this challenge.The key is to trigger photothermal annealing behavior via femtosecond laser ablation to initialize phase transition from monoclinic zirconia(m-ZrO_(2))to tetragonal zirconia(t-ZrO_(2))and induce t-ZrO_(2)columnar crystal growth.Fe-ions rapidly segregate along grain boundaries and diffuse towards the outmost surface,and become‘frozen’,highlighting the potential to use photothermal materials and ultrafast heating/quenching behaviors of femtosecond laser ablation for interfacial exsolution.Triggering interfacial iron-oxide coloring exsolution is composition and concentration dependent.Photothermal materials themselves and corresponding photothermal transition capacity play a crucial role,initializing at 2 wt%,3 wt%,and 5 wt%for Fe3O4/γ-Fe_(2)O_(3)/α-Fe_(2)O_(3)doped 3Y-TZP samples.Due to different photothermal effects,exsolution states of ablated 5 wt%Fe_(3)O_(4)/γ-Fe_(2)O_(3)/α-Fe_(2)O_(3)-doped 3Y-TZP samples are totally different,with whole coverage,exhaustion(ablated away)and partial exsolution(rich in the grain boundaries in subsurface),respectively.Femtosecond laser ultrafast photothermal exsolution is uniquely featured by up to now the deepest microscale(10μm from 5 wt%-Fe_(3)O_(4)-3Y-TZP sample)Fe-elemental deficient layer for exsolution and the whole coverage of exsolved materials rather than the formation of isolated exsolved particles by other methods.It is believed that this novel exsolution method may pave a good way to modulate interfacial properties for extensive applications in the fields of biology,optics/photonics,energy,catalysis,environment,etc.

HEATING AND SINTERING CHARACTERISTICS OF Y-TZP AND Y-TZP/Al_2O_3 BY MICROWAVE

Dense Y-TZP ceramics and Y-TZP/Al_2O_3 composite ceramics are prepared successfully by microwave sintering using rectangle single mode (TE_(10n)) applicator. The heating characteristcs by microwave of the materials are related to the sample compositions. Higher Y-TZP content leads to a higher heating-up rate and a shorter time period needed for heating-up. The input power, short circuit plug position and the opening size of adjustable coupling iris are adjusted timely to maintain the resonance and the optimum coupling condition, and therefore a certain heating-up rate and final stable sintering temperature could be achieved. Relative densities above 98% TD are obtained for Y-TZP and 20 Vol% Al_2O_3-Y-TZP composite ceramics, with their grain sizes of about 0.4 and 1.0 μm, respectively. It is also found that the sample center can be over-sintered when the temperature is too high since a higher temperature at the sample center is usually reached than that at the surface.