Effect of 64S bioglass addition on sintering kinetic,flexural strength and osteoblast cell response of yttria-partially stabilized zirconia ceramics

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.     

Sintering,microstructure and hardness of Y-TZP- 64S bioglass ceramics

3 mol% 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 19.9 vol% 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 19.9 vol%, 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 10.5 vol% 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.     

Enhanced mechanical properties of 3 Y2O3 stabilized tetragonal ZrO2 incorporating tourmaline particles

The current study reports on the improvement of mechanical properties of 3?mol% Y₂O₃ stabilized tetragonal ZrO₂ (3Y-TZP) by introduction of tourmaline through ball milling and subsequent densification by pressureless sintering at 800, 1200, 1300, 1400?°C. Findings demonstrate that no matter which sintering temperature the 3Y-TZP ceramic containing 2?wt% tourmaline reach a maximum value in flexural strength and fracture toughness as compared to other composite ceramics. As the tourmaline content is 2?wt% and the sintering temperature is 1300?°C, the flexural strength and fracture toughness of the composite ceramics are the highest, increases of 36.2% and 36.6% over plain 3Y-TZP ceramic respectively. The unique microstructure was systematically investigated through X-ray diffraction, scanning electron microscopy, energy dispersive spectrum, and flourier transform-infrared. The strengthening and toughening mechanism of tourmaline in 3Y-TZP ceramic were also discussed.     

Evaluation of the effect of low-temperature degradation on the translucency and mechanical properties of ultra-transparent 5Y-TZP ceramics

This study aimed to evaluate the effects of low-temperature degradation (LTD) on the translucency, flexural strength, and surface hardness of ultra-transparent 5Y-TZP ceramics. Three commercial zirconia materials were investigated, including 5Y-TZP and two 3Y-TZP samples. The LTD process was mimicked by hydrothermal aging at 134 °C for 20 h. The translucency parameters (TPs) corresponding to different thicknesses were analyzed. The surface volume fraction of the monoclinic phase was determined by X-ray diffraction (XRD). The three-point flexural strength was measured, and the surface hardness was measured by the indentation method. The translucency of all three ceramics showed a significant decrease with increasing thickness. A translucency gradient was present within a ceramic block of 5Y-TZP, whose translucency was higher than that of both 3Y-TZP products. Aging at 134 °C for 20 h did not reduce the TPs of the three ceramics. The XRD analysis showed a high monoclinic phase content in both 3Y-TZP surfaces after aging, while no monoclinic phase was detected in 5Y-TZP. Hydrothermal aging had no significant effect on the flexural strength; however, the flexural strength of 5Y-TZP was significantly lower than that of 3Y-TZP. No statistical difference in surface hardness was observed among the three products. In summary, 5Y-TZP presented higher LTD resistance than 3Y-TZP.     

Processing and properties of oxide matrix/oxide fibre composite

Abstract

An all-oxide composite was fabricated. Single crystal alumina fibres were coated with a carbon/zirconia slurry, dried, and uniaxially aligned by winding. Matrix material, alumina with 5 vol.-% unstabilised zirconia added, was tape cast on top of the fibres. Pre-pregs were cut, stacked, and laminated to cross-ply material. Final sintering was done by hot isostatic pressing. A heat treatment was added to remove the carbon and create a porous zirconia interphase. Flexure strengths around 200 MPa were obtained for composites at room temperature while a strength of 124 MPa was recorded at 1200°C. The mechanical properties and non-brittle behaviour was sustained after aging at 1400°C for 1000 h in air.     

High-toughness mullite ceramics fabricated by hot-press sintering of pyrophyllite and AlOOH at low temperatures

High-toughness mullite ceramics were fabricated through hot-press sintering (HPS) of pyrophyllite and AlOOH, which were wet-milled and well mixed using a planetary ball mill. The impacts of sintering temperatures and contents of AlOOH on mullite phase formation, densification, microstructure and mechanical properties in ceramic materials were investigated through XRD, SEM and mechanical properties determination. The results indicated that high-toughness mullite ceramics could be successfully prepared by HPS at temperatures higher than 1200°C for 120 min. Increasing the sintering temperature from 1000 to 1300°C significantly enhanced the flexural strength and fracture toughness of samples. The highest flexural strength of 297.97±25.32 MPa and fracture toughness of 4.64±0.11 MPa⋅m^1/2 were obtained for samples sintered at 1300°C. Further increase of temperature to 1400°C resulted in slight decrease of flexural strength and fracture toughness. Compared with the mullite ceramics prepared only using pyrophyllite as raw material, incorporation of AlOOH into raw material significantly increased the mechanical properties of final mullite ceramics. And stoichiometric AlOOH and pyrophyllite as starting material gave the best performance in fracture toughness. The high-toughness of mullite ceramics were ascribed to the high mullite phase content, fine mullite whiskers and in situ formed, intertwined three-dimensional network structure obtained through HPS at a low temperature of 1300°C.     

Evaluation of mechanical reliability of zirconia-toughened alumina composites for dental implants

Zirconia-toughened alumina composites containing 0–30 vol% of 3Y-TZP were fabricated by sintering at 1600 °C for 2 h in air. The effect of the 3Y-TZP content on the mechanical properties and microstructure of the alumina ceramics was investigated. The fracture toughness and biaxial flexural strength increased as the 3Y-TZP content increased. The Young's modulus decreased with 3Y-TZP content according to the rule of mixture, while the hardness showed the contrary tendency. The Weibull modulus of the Al₂O₃ with 20 vol% 3Y-TZP composite is higher than that of alumina. The residual hoop compressive stress developed in ZTA ceramic composites probably accounts for the enhancement of strength and fracture toughness, as well as for the higher tendency of crack deflection. No monoclinic phase and strength degradation were found after low temperature degradation (LTD) testing. The excellent LTD resistance can be explained by the increased constraining force on zirconia embedded in alumina matrix.     

Mechanical properties and resistance to low temperature degradation of surface nitrided 3Y-TZP

3Y-TZP has been one of the most applied ceramics in the biomedical field, specifically for hip, knee and dental implants, given its high strength, moderate fracture toughness and excellent biocompatibility. However, hydrothermal degradation has meant an important disadvantage, as surface t–m transformation, followed by microcracking, can lead to the premature failure of the implant. In this work, surface nitriding at 1600, 1500 and 1400 °C for 1, 2 and 4 h with N₂ gas and ZrN powder was applied and optimised to avoid hydrothermal degradation. Nitriding at 1600 and 1500 °C produces a harder low-toughness surface, not adequate for structural implants. It is shown that the most favourable condition is nitriding at 1400 °C for 1 h, since the mechanical properties of the original 3Y-TZP are not affected with the advantage of retarding hydrothermal degradation by a factor close to 10.     

Processing and mechanical properties of new hierarchical metal-graphene flakes reinforced ceramic matrix composites

Hierarchical tantalum-graphene flakes reinforced zirconia (3Y-TZP) ceramic matrix composites were fabricated by wet processing route and freeze drying followed by spark plasma sintering (SPS). The microstructures and mechanical properties were investigated. The results show that graphene and Ta particles are homogeneously dispersed in the ceramic matrix and the optimum sintering temperature for complete densification of composites and thermal reduction of the graphene oxide is 1500 °C. The addition of dual reinforcements of tantalum microflakes and graphene nanoflakes results in significant improvement in the mechanical properties of the ZrO₂ matrix. Approximately a 30% increase in flexural strength vs the zirconia-Ta composite and a 175% increase in fracture toughness vs the monolithic zirconia have been achieved by introducing 0.5 vol% GO and 20 vol% Ta particles.     

Microstructure and Fracture Toughness of Yttria-Daped Tetragonal Zirconia Polycrystal/Mullite Composites Prepared by an in Situ Method

Yttria-daped tetragonal zirconia polycrystal (Y-TZP)/ mullite composites were prepared by three methods: in situ whisker growth (IS), physical mixing (PM) of zirconia powder and mullite whiskers, and reaction sintering (RS). Microstructures and fracture toughness values were compared. All the composites with 15 vol% of mullite could be densified to more than 95% relative density by firing at 1500° to 1500°C for 10 h. The fracture toughness of the composites as measured by the indentation method showed a clear enhancement compared with that of pure Y-TZP; the ranking was Y-TZP ≦ RS composite < PM composite < IS composite. Enhancement of the fracture toughness in composites was found to relte strongly to the aspect ratio of mullite particles.     

Effect of zirconia content on mechanical and thermal properties of mullite–zirconia composite

Abstract

Mullite–zirconia composites were prepared by adding various zirconia contents in the mullite ranging from 0 to 30 wt-% and sintering at 1400–1600°C for 2 h. The phase composition examined by X-ray diffraction showed that mullite was the major phase combined with developed t-ZrO₂ and m-ZrO₂ phase as a function of zirconia content, especially at 1600°C, wherein m-ZrO₂ predominated. Density increased when the zirconia content and sintering temperature were increased ranging from 2·2 to 3·53 g cm^?3. The morphology of mullite grain showed elongated grains, whereas dispersed zirconia showed equiaxed and intergranular grains. Flexural strength was continuously improved by adding zirconia during the sintering temperature ranging from 1400 to 1500°C, whereas flexural strength was initially improved up to 5 wt-% of zirconia addition and deteriorated with more than 5 wt-% of zirconia content during sintering between 1550 and 1600°C. The maximum strength, 190 MPa, was obtained when sintering mullite with 30 wt-% of zirconia content at 1500°C. The degradation of strength at high sintering temperature may be a result from more occurrence of m-ZrO₂ phase. Thermal expansion of sintered specimens indicated linear change and hysteresis loop change. The hysteresis loop obtained with increased zirconia content resulted in the t–m phase transformation. Martensitic start temperature M_s was determined to be 530°C for 15 wt-% zirconia sintered at 1500°C, implying that the t–m phase transformation occurred.     

Physicomechanical properties of ultrahigh temperature heteromodulus ceramics based on group 4 transition metal carbides

Abstract

Abstract

Highly densified TiC, ZrC and HfC based ultrahigh temperature heteromodulus ceramics (HMC), containing 10-50?vol.-% of low modulus phase in the form of particulate graphite, were prepared by hot pressing at 2700°C and 12?MPa in argon atmosphere. The microstructure, elastic characteristics, flexural and compressive static strength, fracture toughness, impact resistance, hardness and thermal expansion were investigated and compared with those available in earlier works for clear understanding the composition-property correlations and anisotropy of this type of HMC composites. Different thermal shock resistant parameters for the HMC were calculated on the basis of obtained experimental data. A new principle of optimum materials design for the compositions in the refractory carbide-graphite systems is exemplified by the TiC-C HMC materials.     

Effect of microwave sintering on the properties of copper oxide doped Y-TZP ceramics

The effect of various amounts of copper oxide (CuO) up to 1?wt% on the densification behaviour and mechanical properties of 3?mol% yttria-tetragonal zirconia polycrystal (Y-TZP) were studied by using microwave (MW) sintering method. The MW sintering was performed at temperatures between 1100?°C and 1400?°C, with a heating rate of 30?°C/min. and holding time of 5?min. The beneficial effect of MW in enhancing densification was also compared for the undoped and 0.2?wt% CuO-doped Y-TZP when subjected to conventional sintering (CS) method. The results showed that significant enhancement in the relative density and Vickers hardness were observed for the undoped Y-TZP when MW-sintered between 1100?°C and 1250?°C. It was revealed that the 0.2?wt% CuO-doped Y-TZP and MW sintered at 1250–1300?°C could attain ≥?99.8% of theoretical density, Vickers hardness of about 14.4?GPa, fracture toughness of 7.8 MPam^1/2 and exhibited fine equiaxed tetragonal grain size of below 0.25?µm. In contrast, the addition of 1?wt% CuO was detrimental and the samples exhibited about 50% monoclinic phase upon sintering coupled with poor bulk density and mechanical properties. The study also revealed that the addition of 0.2?wt% CuO and subjected to conventional sintering produced similar densification as that obtained for microwave sintering, thus indicating that the dopant played a more significant role than the sintering method.     

Effect of experimental primers on hydrolytic stability of resin zirconia bonding

This study assessed the effect of experimental silane primers and two adhesive resin cements on resin zirconia adhesion strength. The surfaces of cut Y-TZP zirconia blocks (Lava? Frame), 16 mm × 16 mm × 4.5 mm, were pretreated twice. First, they were grit-blasted with Korox? alumina powder (110 μm) followed by silica-coating with Rocatec? Soft. Next, the blocks were randomly assigned into eighteen sub-groups (n = 6, N = 108) according to three primers (control ESPE Sil?, 1.0 vol.-% 3-acryloxypropyltrimethoxysilane, and 1.0 vol.-% 3-acryloxypropyltrimethoxysilane + 0.5 vol.-% bis-12-(triethoxysilyl)ethane), two in dentistry used resin cement products (Multilink? Speed, and Multilink? N), and three storage conditions (24 h dry, 1 month immersed in distilled water, and 6 months immersed in distilled water at room temperature) used. Onto each pretreated zirconia block, four cylindrical resin composite cement stubs were prepared and light-cured. The surface roughness, contact angle, and adhesion (shear bond) strength (SBS) were measured, and statistically analyzed (ANOVA, the Tukey’s test, p < 0.05). No statistical differences were observed in surface roughness values of different primer-treated zirconia groups. After six months of water aging, the shear bond strength of the groups that employed 1.0 vol.-% 3-acryloxypropyltrimethoxysilane (9.0 MPa ± 0.8 MPa), and the blend of 1 vol.-% 3-acryloxypropyltrimethoxysilane + 0.5 vol.-% bis-12-(triethoxysilyl)ethane (8.9 MPa ± 2.0 MPa) with Multilink? Speed resin composite cement were statistically insignificantly higher compared to using ESPE Sil? (8.7 MPa ± 1.8 MPa). The experimental primers may have potential to be used for long-term resin zirconia adhesion.     

Influence of sintering pressure on the microstructure and tribological properties of low temperature fast sintered hot-pressed Y-TZP

Contrarily to conventional sintering (CS) method where longer cycles and high temperature (1400–1500?°C) are applied to sinter yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) ceramics, this work presents a faster and low temperature (1175?°C) way through hot pressing (HP) to produce full densified zirconia with good mechanical and tribological properties. This work is concerned with the influence of sintering pressure on the microstructure and tribological properties of hot-pressed Y-TZP. For this purpose, four sintering pressures 5, 20, 60 and 100?MPa were tested. The wear tests were carried out by reciprocating ball-on-plate as a simplified test for tooth-to-restorative material contact under 37?°C using artificial saliva to mimic oral conditions. The results demonstrated that density, hardness and tribological properties are strongly influenced by the sintering pressure, namely an improvement with pressure increase was achieved. The highest density, hardness values and wear resistance were achieved for Y-TZP samples produced at P?=?100?MPa. Furthermore, it was revealed that a smaller grain size for Z100 samples (full densification condition) was achieved comparatively to conventional-sintered Y-TZP. This work proves that it is possible to produce dense Y-TZP materials under low sintering temperature and faster cycles with reduced grain size without compromise mechanical and tribological properties.     

Comparison of a laboratorial scale synthesized and a commercial yttria-tetragonal zirconia polycrystals ceramics submitted to microwave sintering

Conventional sintering techniques of yttria-tetragonal zirconia polycrystals (Y-TZP) ceramics have presented limitations regarding the sintering time and temperature, increasing the cost of the final dental and biomedical products. Herein, microwave sintering comes to be an interesting alternative by providing fast heating, high densification, and grain-size control. The aim of this study was to compare the effect of microwave sintering of Y-TZP dental ceramics prepared from a pre-sintered commercial block and produced from powders synthesized in a laboratorial scale by the precipitation route. The synthetized and commercial discs were submitted to microwave sintering at 1450°C and 1350°C for 15, 30, and 60 minutes. Densification, fracture toughness, grain size, and crystalline phase quantification of the sintered groups were evaluated. Both synthetized and commercial groups sintered at 1450°C for 15 and 30 minutes showed the higher densification results (98% TD). XRD quantitative phase analysis indicates that samples present 89% tetragonal and 11% cubic phases, except for the group prepared from coprecipitated powders sintered at 1450°C for 30 minutes, that presented 79% and 21% of tetragonal and cubic phases. The microwave sintering at 1450°C allows hardness and fracture toughness values comparable to conventional sintering.     

Fabrication of highly bioactive zirconia ceramics via grain-boundary activation for dental implants

Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramics with outstanding mechanical properties and aesthetic origins are expected to be used in dental implant applications. However, tetragonal zirconia ceramics are not bioactive, which affect the osseointegration and reliability as dental implant materials. Herein, in this study, Y-TZP ceramics were modified by grain-boundary activation via coating a bioactive glass (BG) sol with different content on the crystal surfaces of zirconia powder and followed by being gelled, dried, granulated, low-temperature treated, molded and sintered at 1450°C for 3 h in air. The effects of BG content on the morphology, phase compositions, mechanical properties, in vitro mineralization ability and cell biological properties of the bioactivity modified Y-TZP ceramics were evaluated. The BG additive did not affect the tetragonal–monoclinic phase transformation of ZrO₂. However, the addition of BG decreased the flexural strength of the modified Y-TZP ceramics compared to that of Y-TZP. The in vitro mineralization results showed that a homogeneous apatite layer was produced on the surface of the Y-TZP ceramics when they were immersed in the simulated body fluid for 21 days. The cell response results indicated that the bioactive surface modification of Y-TZP ceramics could promote cell adhesion, propagation and osteogenic differentiation performance. Thus, our research results suggest that the highly bioactive Y-TZP ceramics could be a potential candidate for dental implant material.     

Differences in microstructure and mechanical properties between Y-TZP and AL2O3-doped Y-TZP/bioglass ceramics

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.     

Preparation and study of the mechanical and optical properties of infrared transparent Y2O3–MgO composite ceramics

In this study, fine Y₂O₃–MgO composite nanopowders were synthesized via the sol–gel method. Dense Y₂O₃–MgO composite ceramics were fabricated by pre-sintering the green body in air at different temperatures for 1 h and then subjecting the sintered bodies to hot isostatic pressing at 1300°C for 1 h. The effects of pre-sintering temperature on the microstructural, mechanical, and optical properties of the resulting ceramics were studied. The average grain size of the ceramics was increased, whereas their hardness and fracture toughness were decreased with increasing pre-sintering temperature. A maximum fracture toughness of 1.42 MPa·m^1/2 and Vickers hardness of 10.4 GPa were obtained. The average flexural strength of the ceramics was 411 MPa at room temperature and reached 361 MPa at 600°C. A transmittance of 84% in the 3–5 µm region was obtained when the composite ceramics were sintered at 1400°C. Moreover, a transmittance of 76% in the 3–5 µm region was obtained at 500°C.     

SiC_w/莫来石和SiC_w/Y-TZP/莫来石复合材料的力学性能与显微结构

以莫来石为基体,SiC晶须(SiC_w)和Y-TZP(Y_2O_3稳定的四方ZrO_2多晶)为两种补强剂,采用热压烧结工艺,制备SIC_w/莫来石和SIC_w/Y-TZP/英来石复合材料。研究了复合材料的力学性能与显微结构,并对强化增韧机制进行了分析。结果表明,SiC晶须补强莫来石,可以改善其强度和断裂韧性。若SiC晶须和Y-TZP共同补强英来石,则可以进一步提高其强度和断裂韧性。晶须引起裂纹偏转,晶须拔出以及由ZrO_2相变引起的微裂纹增韧是该复合材料的主要增韧机制。SiC晶须和Y-TZP两种补强剂的共同作用,对莫来石强度和断裂韧性的提高具有叠加或协同效应。