Y‐TZP (YZ) and Al2O3‐doped Y‐TZP (AYZ) bioceramics with addition of different contents of a refractory bioglass were fabricated. The influence of the glass addition and sintering temperature on the ...densification behavior, microstructure, and mechanical properties of YZ and AYZ was studied. The developed ceramics contained small amounts of ZrSiO4 and Ca2P2O7 phases within the ZrO2 matrix. The incorporation of glass to YZ promoted the ZrO2 phase partitioning and enhanced the ZrO2 grain growth at all the sintering temperatures, whereas the glass addition in AYZ prevented the Y2O3 redistribution between ZrO2 grains and limited the ZrO2 grain growth at 1300–1400°C. The hardness of the samples with glass was not significantly altered by using either YZ or AYZ. A slight increase in the fracture toughness with increasing glass content was found for YZ, while the fractured toughness of AYZ decreased by the glass addition. The more pronounced ZrO2 phase partitioning of YZ with glass decreased the flexural strength, whereas AYZ maintained almost unaltered its flexural strength at a high level by the glass incorporation.
Well‐dispersed concentrated aqueous suspensions of Al2O3‐doped Y‐TZP (AY‐TZP), AY‐TZP with 5.4 vol% of CaO–P2O5–SiO2 (CaPSi) glass (AY‐TZP5) and 10.5 vol% CaPSi glass (AY‐TZP10), with ammonium ...polyacrylate (NH4PA) dispersant were prepared to produce slip cast compacts. The rheological properties of 35 and 40 vol% slips were studied. The densification, microstructure as well as hardness and fracture toughness were investigated as a function of CaPSi glass content at 1300°C‐1500°C. The optimum NH4PA concentration of 35 vol% AY‐TZP5 and AY‐TZP10 slips at pH ~9 was found to be about 43% and 67% greater than that of AY‐TZP slips; this behavior was related to the greater amounts of Ca2+ ions leached out from the CaPSi glass surface. The viscosity of stabilized 40 vol% slips with NH4PA attained a minimum value at 5.4 vol% CaPSi glass addition, and resulted in a more dense packing of cast samples. AY‐TZP5 can be sintered at a lower temperature (1300°C) compared to that of AY‐TZP. AY‐TZP5 exhibited a fine microstructure of tetragonal ZrO2 (grain sizes below 0.3 µm), and ZrSiO4–Ca2P2O7 particles homogeneously distributed within the zirconia matrix. It presented similar fracture toughness and a slightly lower hardness compared to those of AY‐TZP.
3mol% yttria-partially stabilized zirconia (Y-TZP) powder and a sol-gel derived CaO- P2O5- SiO2 (64S) bioglass, were used to produce Y-TZP- 64S slip cast compacts. The compacts with 10.5 and 19.9vol% ...64S were sintered at different temperatures up to 1500°C using 5 and 10°C/min heating/cooling rates. The densification behaviour, crystalline phase formation and zirconia grain growth were investigated as a function of sintering temperature and 64S glass content. Ca3(PO4)2 along with SiO2 as a major phase were obtained from thermal decomposition of the 64S glass at 950–1500°C. Both 64S additions, 10.5 and 19.9vol%, promoted the sintering process at a lower temperature with respect to Y-TZP (1500°C); the SiO2 phase markedly increased the Y-TZP solid state sintering rate at the intermediate stage. The rapidly cooling at 10°C/min inhibited the t-m transformation of Y-TZP and markedly reduced that of Y-TZP- 64S at 1300–1500°C. Sintered Y-TZP with 10.5vol% 64S, nearly fully densified at 1300–1400°C, was constituted by polygonal ZrSiO4 particles and elongated Ca2P2O7 particles uniformly distributed in the tetragonal zirconia fine grain matrix. This ceramic exhibited similar hardness to that of Y-TZP sintered at 1500°C; the in situ formation of calcium phosphate will have the potential to improve the Y-TZP biological properties without significantly affecting its hardness.
Ceramic layers based on calcium silicate non-substituted and substituted by Zn with different thickness, were developed by immersing porous Y-TZP disks into SiO2–CaO–ZnO–P2O5 glass suspensions with ...ZnO contents in the range of 0–20 mol%. The effect of the disk surface porosity and the slip solid loading on the formation of the dip coated layer was investigated. Special emphasis was given to the ZnO content of the dip coating slurries and its influence on the thickness and composition of the sintered layer. The greater chemical stability of the 20 mol% ZnO-substituted glass powder during aqueous colloidal processing resulted in slips with low viscosity values; whereas the high dissolution rate of the glass having 10 mol% ZnO significantly increased the slip viscosity. The liquid entrainment mechanism at the initial stage was accelerated either by using 10 mol% ZnO-substituted glass slips or by increasing the slip solid loading. The casting rate for longer immersion times markedly increased by increasing the surface porosity of Y-TZP disks. Sintered layers with thickness ~30–70% lower were produced using the glass dip coating slip with 20 mol% ZnO in comparison to 10 mol% ZnO. The main crystalline phase of the coated sintered layers was Ca3Si3O9, Ca2ZnSi2O7 and ZnSiO4 for the glasses with 0, 10 and 20 mol% ZnO, respectively.
Yttria-partially stabilised zirconia (Y-TZP) of 3 mol-% with 5.4, 10.5 and 19.9 vol.-% 64S bioglass compacts was sintered at 1300-1500°C. The influence of 64S content and sintering temperature on the ...mechanical properties and aging behaviour of Y-TZP ceramics were studied. Among Y-TZP ceramics with 64S additions, maximum hardness and flexural strength values were found for Y-TZP with 10.5 vol.-% 64S at 1400°C. Y-TZP with 19.9 vol.-% 64S at 1500°C presented the highest fracture toughness; crack deflection and pinning by ZrSiO
4
particles combined with zirconia microcracking contributed to the fracture toughness. Y-TZP at 1500°C was extremely susceptible to hydrothermal degradation and its flexural strength markedly decreased after aging. On the contrary, Y-TZP with 10.5 vol.-% 64S at 1400°C remained almost unaltered; it maintained its flexural strength at a high level during aging, becoming the most promising ceramic in terms of mechanical properties and aging behaviour.
Two commercial 3mol% yttria–partially stabilized zirconia powders, with 0.3wt% Al2O3 (Y–PSZA) and without Al2O3 (Y–PSZ), and a Zr (IV) precursor were used to produce alumina (Al2O3)–zirconia (ZrO2) ...slip cast composites. The influence of both the zirconia content and the reduction of zirconia particle size on the sintering behavior, microstructure development and mechanical properties were investigated. The increase in the zirconia content from 10.5 to 22vol% increased the hardness; whereas, above 22vol% ZrO2 the hardness decreased. A significant increase in the fracture toughness with increasing the ZrO2 content over 22vol% was obtained by the stress-induced phase transformation. The flaw size limited the strength below 22vol%; whereas, above 22vol% ZrO2 the strength was controlled by the stress-activated phase transformation. For 10.5vol% ZrO2, the smaller ZrO2 grains produced by using the Zr (IV) precursor were more effective in preventing the Al2O3 grain growth resulting in higher hardness. However, the tetragonal–monoclinic (t–m) transformation of some unstabilized ZrO2 grains during cooling reduced Young's modulus and fracture toughness.
In order to produce stable aqueous fluorapatite (FA) suspensions, its surface reactivity in an aqueous solution having two initial pH values with a concentration of ammonium polyacrylate (NH
4
PA) ...was investigated as a function of time. The rheological behaviour of concentrated aqueous FA slips stabilized with NH
4
PA was studied; besides, the effect of poly(vinyl)alcohol (PVA) addition on the relative viscosity of the suspensions was investigated. The influence of the slip rheology on the microstructure of the resultant green slip cast compacts and their sintering behaviour were determined. Upon the FA introduction in the aqueous solutions, an initial release of F anions located at the surface was found, which was not dependent on the pH and the presence of dispersant. The increase in the initial pH of the solution above 7 and/or the addition of NH
4
PA markedly reduced the Ca
++
/H
+
exchange reaction rate. As a result, well-stabilized concentrated aqueous suspensions could be obtained at pH close to 9. The minimum viscosity of 40 vol.% slips at pH 8.9 occurred at 0.6 wt% of NH
4
PA added. The addition of 0.5 wt% PVA to a well-stabilized FA slip caused aggregation of particles by a depletion flocculation mechanism, thereby increasing the slip viscosity. The greater permeability of cakes produced from slips with high viscosity values (0.5 wt% PVA) increased the casting rate. The highest sintered densities were obtained for the compacts prepared from the slips without PVA, due to the denser particle packing achieved in the green bodies.
Two commercial 3mol% yttria-partially stabilized zirconia powders, 0.3wt% Al2O3-doped (Al-doped Y-PSZ) and without Al2O3 (Y-PSZ), were used to produce alumina (Al2O3)-zirconia (ZrO2) slip cast ...composites. The influence of the substitution of Al2O3 either by different Al-doped Y-PSZ contents or 50vol% Y-PSZ on the sintering kinetic at the intermediate stage was investigated. In addition, the microstructure of Al2O3 and the different composites at temperatures in the range of 1100–1600°C was studied and related to the sample hardness. An increase in the sintering rate was observed when Al-doped Y-PSZ increased from 22 to 50vol% or when 50vol% Y-PSZ was substituted by 50vol% Al-doped Y-PSZ. 50vol% ZrO2 was the most effective concentration to reduce the rate of Al2O3 grain growth in the final sintering stage; the Al2O3 grain growth began at lower temperatures and became greater with decreasing the Al-doped Y-PSZ content. On the contrary, the ZrO2 grain growth slightly increased with increasing the Al-doped Y-PSZ concentration. However, for 50vol% Al-doped Y-PSZ a smaller ZrO2 grain size distribution compared with 50vol% Y-PSZ could be achieved. As the average Al2O3 grain size of the sintered samples became greater than about 1µm a markedly decrease in the hardness was found; this occurred at temperatures higher than 1400°C and 1500°C for Al2O3 and the composite with 10.5vol% Al-doped Y-PSZ, respectively.
A quantity of 3 mol% yttria‐partially stabilized zirconia (Y‐TZP) with 10.5 and 19.9 vol% 64S bioglass compacts was sintered at different temperatures up to 1500°C. The influence of 64S glass ...addition on the sintering kinetic, flexural strength, and osteoblast cell response of Y‐TZP ceramics was investigated. The addition of 64S glass increased the initial sintering rate through the decrease in the activation energy and the increase on the order of diffusion with respect to those previously reported for Y‐TZP. Y‐TZP at 1500°C exhibited the highest flexural strength. Within Y‐TZP ceramics with 64S additions, a maximum flexural strength occurred for 10.5 vol% 64S at 1400°C, its flexural strength was able to approach that of Y‐TZP at 1500°C. The polished sintered surfaces became rougher as the 64S content increased. Cell viability experiments on the less nanoroughness Y‐TZP and Y‐TZP with 10.5 vol% 64S surfaces revealed their good biocompatibility; on the contrary, the high level of nanoroughness of Y‐TZP with 19.9 vol% 64S significantly reduced cell survival. However, the matrix mineralization was not adversely affected by the surface roughness; larger amounts of calcium phosphate phases on Y‐TZP‐19.9 vol% 64S surfaces appeared to promote the osteogenic potential of UMR‐106 cells.
Y‐TZP containing Ca2P2O7 are promising bioceramics with potential applications in dental implants and dentistry. These ceramics were developed by the introduction of a refractory sol‐gel derived ...CaO‐P2O5‐SiO2 bioglass into Y‐TZP; Ca2P2O7, and ZrSiO4 phases were formed in situ after sintering. The aging process of Y‐TZP with different glass additions was studied. The effect of glass addition on the flexural strength and osteoblastic cell response of non‐aged and aged Y‐TZP was investigated. Y‐TZP exhibited the most pronounced tetragonal (t) to monoclinic (m) transformation of zirconia (ZrO2) during aging; the addition of glass contents between 5 and 20 vol% improved the aging resistant of Y‐TZP. Y‐TZP flexural strength markedly decreased with increasing aging time; in contrast, the ceramics with glass did not alter their flexural strength upon aging. An increase in the Ca2P2O7 content with increasing glass up to 10 vol%, promoted both the cell viability and the osteogenic differentiation of UMR‐106 cells on non‐aged and aged samples. The high micro‐roughness of Y‐TZP with 20 vol% glass after aging, limited the proliferation and the osteogenic potential of the cultures. Y‐TZP with 10 vol% glass had the best combination of properties in terms of flexural strength and osteoblast cell response.
