Tetragonal Zirconia Polycrystal Ceramics Research Articles

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

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

Effects of surface modification techniques on zirconia substrates and their effect on bonding to dual cure resin cement - An in- vitro study.

This study aims to evaluate the effect of different surface treatments of monolithic zirconia on the bond strength of resin to zirconia and, to explore alternative methods to improve this bonding. In-Vitro study. Fifty rectangular sintered blocks of Yttria-stabilized Tetragonal Zirconia Polycrystal ceramics of dimensions were milled and sintered. These specimens were further divided into five groups (control, air abrasion, etching with primer application, air abrasion with primer application and novel glass infiltrated zirconia surface group), containing 10 samples each. The specimens were analyzed for surface roughness, tensile bond strength to resin cements, and adhesive and cohesive mode of failures. ANOVA and Post-Hoc Tukey test was perform to evaluate the significant differences in the mean values of the groups. Air-abraded samples showed the highest surface roughness (4.95 ± 0.65) (P < 0.05). The group with air abrasion followed by primer application showed the highest tensile bond strength (7.12 ± 0.69) (P < 0.05). The lowest surface roughness (0.638 ± 0.8093) and tensile bond strength (2.03 ± 0.58) was seen in samples that were subjected to etchant treatment followed by application of methacryloyloxydecyl di-hydrogen phosphate (MDP) primer. The changes in comparison to the control group were statistically insignificant (P > 0.05). Except Groups A (control) and C (etchant followed by primer), all other groups showed a cohesive failure. Air abrasion of the zirconia surface with 50 μm alumina particles increases the surface roughness without damaging the surface. Air abrasion followed by MDP primer application is the recommended method of surface treatment to achieve superior bonding. Glass infiltration also showed promising results in terms of tensile bond strength.

Effect of cementation delay on bonding of self-adhesive resin cement to yttria-stabilized tetragonal zirconia polycrystal ceramic treated with nonthermal argon plasma

Statement of problemNonthermal argon plasma (NTAP) has been reported to improve the bond strength of resin cements to yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramics. However, the effect of the inevitable delay before cementation and after treating Y-TZP ceramics with NTAP is unclear. PurposeThe purpose of this in vitro study was to investigate whether delays of 8, 12, and 24 hours between the Y-TZP ceramic treatment with NTAP and the cementation would affect the surface energy and the bond strength of a self-adhesive resin cement to Y-TZP ceramic. Material and methodsSixty plates and 50 blocks of 3Y-TZP ceramic were divided into 2 groups (n=30 and n=25): as-sintered (AS) and airborne-particle abraded with 50-μm Al2O3 (APA). These groups were further divided into 5 subgroups (n=6 and n=5) according to the delay between the NTAP treatment and the measurement of surface energy and microtensile bond strength (μTBS) evaluation: (0, 8, 12, and 24 hours). For both 3Y-TZP surface conditions (AS and APA), a control group without NTAP treatment was used (ASC and APAC). The surface energy (SE) was evaluated with a goniometer and the 3Y-TZP elemental composition with X-ray photoelectron spectroscopy (XPS). For the μTBS test, the 3Y-TZP ceramic blocks were cemented to composite resin blocks with a self-adhesive resin cement. After storage in distilled water at 37 °C for 24 hours, the 3Y-TZP-composite resin blocks were sectioned into beams and submitted to a μTBS test. Data were submitted to 2-way ANOVA and the Tukey HSD test (α=.05). ResultsFor the AS group, NTAP increased the SE irrespective of the delay before measurement: ASC<0 hour=8 hours=12 hours=24 hours (P<.05). For the APA group, except after 12 hours, NTAP also increased the surface energy (P<.05). XPS analysis showed an increase in the oxygen/carbon ratio after NTAP treatment for both groups. For the AS group, NTAP increased the μTBS after 0, 8, and 12 hours (P<.05), whereas for the APA group this occurred only after 8 hours (P<.05). For the AS and APA groups, the highest μTBS was reached after 8 hours (P<.05). ConclusionsTreatment of 3Y-TZP ceramic with NTAP improved the SE and increased the μTBS of self-adhesive resin cement to 3Y-TZP ceramic. These effects were time dependent, with better results at 8 hours after NTAP treatment.

Research progress in surface bonding pretreatment of dental zirconia ceramics

Yttria stabilized tetragonal zirconia polycrystal ceramics is widely used in the field of dentistry because of its excellent mechanical properties and biocompatibility. However, it has low hydroxyl content and does not contain silica. Therefore micro mechanical retention induced by hydrofluoric acid etching on its surface is not applicable. The bonding of zirconia is a difficult problem. Zirconia surface pretreatment is commonly used to improve bonding strength and durability. This review summarizes surface pretreatment of dental zirconia ceramic including air abrasion, laser etching, acid etching, silica coating, non-thermal plasmas treatment, et al. In addition, it presents advantages and disadvantages of each treatment, provides guidance for application and future research directions.

Chemical Bonding to Novel Translucent Zirconias: A Mechanical and Molecular Investigation.

To investigate direct bonding of a 10-MDP-based cement to two novel translucent yttria-stabilized tetragonal zirconia polycrystal ceramics (4Y-TZP, 5Y-TZP) and observe the influence of thermocycling on this bonding. Powders of presintered and isostatically pressed 5Y-TZP, 4Y-TZP and 3Y-TZP were mixed with a 10-MDP-based cement (Panavia F 2.0), then stored in deionized water for 48 h at 37°C or thermocycled 10,000 times. Raman spectroscopy and Fourier-transform infrared spectroscopy were used to assess the presence of a functional group (PO32-) that could indicate bonding before and after thermocycling. X-ray photoelectron spectroscopy was used to identify the presence of the suspected Zr-O-P bond in the same specimens. A shear-bond strength (SBS) test was conducted based on ISO 29022:2013. Marked peaks assigned to the asymmetric vibrations of the PO32- functional group were observed in both zirconias before and after thermocycling. The binding energy corresponding to Zr-O-P interactions (531.5 eV) was masked by the aluminosilicate in the filler of the cement. Shear bond strengths were approximately 20 MPa after water storage and approximately 6 MPa after thermocycling. No differences were found between the control group and the translucent zirconias. Direct bonding of the 10-MDP-based cement to both 4Y-TZP and 5Y-TZP was highly plausible. Both 4Y-TZP and 5Y-TZP may be promising alternatives to glass-ceramic restorations.

Effect of Air and Argon Sintering Atmospheres on Properties and Hydrothermal Aging Resistance of Y-TZP Ceramics

In this work, we investigated the role of sintering atmosphere and temperature on low-temperature degradation of 3 mol.% yttria tetragonal zirconia polycrystals ceramics. Green compacts were prepared by die-pressing followed by cold isostatic pressing at 200 MPa. The green bodies were sintered between the temperature range of 1250 and 1500 °C in air and argon gas atmosphere. Sintered samples were tested to determine bulk density, Young’s modulus, Vickers hardness and fracture toughness. The results revealed that the mechanical properties of air-sintered samples were better than that of argon-sintered samples sintered at 1400 °C and below while the argon sintering marginally improves the fracture toughness and hardness when sintered at 1450 °C and above. FESEM images showed that the tetragonal grain size was similar when sintered in argon atmosphere. However, regardless of sintering atmosphere, grain growth was inevitable as the sintering temperature was increased. Hydrothermal aging test in superheated steam was performed in an autoclave at temperature of 180 °C and 10 bar pressure up to 12 h. Effect of aging on tetragonal-to-monoclinic phase transformation was measured by using x-ray diffraction. The phase transformation was found to be strongly influenced by the sintering temperature and sintering atmosphere. The sample sintered at 1500 °C in argon atmosphere exhibited rapid phase transformation compared to air atmosphere, while the samples sintered at or below 1400 °C in argon showed no phase transformation after 12-h exposure in steam environment.

Novel Method of Developing Nanosilica Coated Alumina Micro Abrasives Using Silicon Nanoparticles Generated from Spark Erosion as the Source

Silica coated alumina abrasives, used for abrading the surface of Yttria stabilized tetragonal zirconia polycrystal ceramics, were produced in order to achieve successful bonding with resin luting cement. The source of the silica coating was from Silicon Nanoparticles (SiNPs) that were produced from spark erosion in high pressure flushing of deionized water. SEM images verified average size distribution of the SiNPs to be between 30-50nm. In contrast to the tribochemical methods that are used widely to produce such abrasives, a completely novel dry physical process was opted for this experiment. By optimization of the conditions, 2g of purified SiNPs was mixed with 20g of alumina μ-particles (approximated diameter of 100μm), in presence of 25ml ethanol, mixed thoroughly to form slurry. Heated up to 120°C for 20 minutes to evaporate the ethanol, the resultant powder mix was compacted and uploaded in furnace at temperature of 1100°C for 2hrs. This formed an oxide layer on the SiNPs which consequently formed bonding with the alumina particles. SEM/EDS results validate substantial amount of coating of silica on alumina. The paper hereby demonstrates a novel method of producing silica coated alumina abrasives, which is a dry and cleaner substitution method compared to tribochemical approach.

Densification Behaviour and Mechanical Properties of Aluminium Oxide and Cerium Oxide-Doped Yttria Tetragonal Zirconia Polycrystal Ceramics Using Two-Step Sintering

The densification behaviour, mechanical properties, and microstructure of high-purity Al2O3 and CeO2-doped Y-TZP with different weight percentage varied from 0.3 to 1 wt% were investigated. The samples were pressed uniaxially at 200 MPa into rectangular bars and discs and pressureless-sintered at temperature ranging between 1250°C and 1450°C for 2 h while the microstructure was characterized with a scanning electron microscope (SEM). Two-step sintering process works well for temperature higher than 1400°C and it created most tetragonal phase arrangement for stable structure to delay ageing through phase transformation. The mechanical properties in terms of bulk density, Young’s modulus, Vickers hardness, and fracture toughness were also measured. The results indicate that the addition of dopants accelerated the densification parameters and reinforced and toughened the obtained bodies. The maximum values for the mechanical properties of the Al2O3 and CeO2-doped Y-TZP ceramics were 6.01, 220 GPa, 13.8 GPa, and 7 MPa for density, Young’s modulus, Vickers hardness, and fracture toughness, respectively, which are higher than those of the doped samples.

Influence of surface topography and surface physicochemistry on wettability of zirconia (tetragonal zirconia polycrystal)

Surface modification technologies are available for tetragonal zirconia polycrystal (TZP) to enhance its bioactivity and osseointegration capability. The surface wettability of an implant material is one of the important factors in the process of osseointegration, possibly regulating protein adsorption, and subsequent cell behavior. The aim of this study was to clarify the effect of topographical or physicochemical modification of TZP ceramics on wettability to determine the potential of such treatment in application to implants. Several types of surface topography were produced by alumina blasting and acid etching with hydrofluoric acid; surface physicochemistry was modified with oxygen (O(2)) plasma, ultraviolet (UV) light, or hydrogen peroxide treatment. The obtained specimens were also subjected to storage under various conditions to evaluate their potential to maintain superhydrophilicity. The results showed that surface modification of surface topography or physicochemistry, especially of blast/acid etching as well as O(2) plasma and UV treatment, greatly increased the surface wettability, resulting in superhydrophilicity. X-ray photoelectron spectroscopy revealed that a remarkable decrease in carbon content and the introduction of hydroxyl groups were responsible for the observed superhydrophilicity. Furthermore, superhydrophilicity was maintained, even after immersion in an aqueous solution, an important consideration in the clinical application of this technology.

Estimation theory for random force exerted on grains during superplastic deformation of ceramics

This paper focuses on grain motion during superplastic deformation in TZP (Tetragonal Zirconia Polycrystal) ceramics. After estimation theory for random force was developed, the kinetic data of grains were stochastically analyzed, and random force acting on grains was estimated: At an earlier stage of superplastic deformation, distribution of random force differs between the loading direction and its normal direction. As superplastic deformation advances, however, it becomes identical in two directions. Such the change in the random force is discussed in terms of constraint by surrounding grains.

Grain motion statistics of polycrystalline zirconia during superplastic deformation

This study focuses on grain motion in tetragonal zirconia polycrystal ceramics during superplastic deformation. Since grains were found to move in a zigzag motion in previous experiments, the present study attempts to analyze the grain motion based on random walk theory. The analysis shows that the zigzag motion results from changes in constraint by surrounding grains. The constraint is spatially distributed at first, and its distribution gradually becomes uniform as superplastic deformation advances.

Random walk analysis of grain motion during superplastic deformation of TZP

This study focuses on grain motion in TZP (Tetragonal Zirconia Polycrystal) ceramics during superplastic deformation. The specimen was 16 times elongated repeatedly at 1400°C in air. The increment of true plastic strain was set to be 2%, and the specimen was deformed up to 30.3% true plastic strain finally. After each deformation, displacement vectors of specified 748 grains were measured from their position vectors determined by FE-SEM micrographs. As a result, the grains move to the tensile loading direction in zigzag way. And also, the zigzag motion changes with plastic strain: The grains move randomly (random walk motion) by the first 15% true plastic strain, and then grain motion becomes spatially uniform gradually. It is related to changes of constraint of surrounding matrix.

Kinematical Analysis of 748 Grains in TZP Ceramics during Superplastic Deformation

This paper describes motion of 748 grains during superplastic deformation of TZP (Tetragonal Zirconia Polycrystal) ceramics. In the same way as the latest paper of the present authors, the same TZP specimen was 4 times further deformed at 1673K (=1400°C) in air under tensile loading. The increment of true plastic strain was set to be about 2%, and the final true plastic strain reached 25.3%. After each deformation, a position vector of the same grain was read out from a FE-SEM photograph, and thereby its displacement vector was determined. By changing the increment of true plastic strain in calculation, various displacement vector maps were obtained in consideration of the previous data also. At an increment of about 25% of true plastic strain; most of the grains seem to move along stationary streamlines similar to laminar flow. When we look at the grain motion at increments of about 5%, several tens of grains move to the same direction instantaneously, and therefore a kind of domain is formed at the first loading. In a subsequent deformation, however, the domains gradually disappear and each grain seems to move randomly, indicating that grain motion becomes spatially uniform. At increments of about 2%, convergence and divergence in grain motion gradually diminish with increasing the true plastic strain and this tendency corresponds to the observation at increments of about 5%, although each grain moves in a zigzag way gradually turning to the loading direction. From these results, the grain motion has a similarity to diffusion phenomenon because the observed time period makes a profound effect on the motion. As for time evolution of grain structure, by the first 15% of true plastic strain, local deformation resistance (viz. constraint by neighbor grains) is gradually homogenized, and consequently spatially uniform grain motion is attained leading to superplasticity in TZP ceramics.

Low Temperature Degradation of Yttria Stabilized Zirconia

This paper explores the effects of dopant content on the aging behavior of tetragonal zirconia polycrystal (TZP). TZP powders with varying Y2O3 content (1.75-3mol%) were synthesized by co-precipitation. After the green body of as-prepared TZP powders being isostatically pressed at 200 MPa and sintered at 14000C for 3 h in air, a range of TZP ceramics were fabricated. As-synthesized TZP ceramics annealed at relatively low temperatures with the presence of water or water vapor. XRD analysis was conducted for phase identification and determined a tetragonal to monoclinic transformation. Microscope imaging displayed the changes of aged TZP surface structure. It is believed that the degradation of TZP might be caused by the reaction between Y2O3 and H2O. The mechanism of low temperature degradation of TZP was discussed.

Microstructure and Mechanical Properties of Zr(Y,Ce)O&lt;sub&gt;2&lt;/sub&gt; TZP Ceramics

Tetragonal zirconia polycrystal ceramics prepared by sintering compacts of 3 mol.% Y2O3- and 12 mol.% CeO2-doped ZrO2 powders, in air at 1400o and 1500o C have been characterized in terms of microstructure and mechanical properties. With increasing 12 mol.% CeO2-doped ZrO2 content, the average grain size of sintered materials increased in the range 0.27-1.93 μm. The bend strength and indentation fracture toughness were 374-962 MPa and 6-10 MPa.m1/2 respectively, dependent on batch composition.

Recombinant domain movement mechanism in superplastic deformation of TZP ceramics

High-temperature tensile tests were repeatedly carried out for a tetragonal zirconia polycrystals (TZP) specimen, and the position vectors of 500 grains were measured by FE-SEM image analysis. The displacement vector map showed that several grains moved to the same direction and a kind of domain was formed; these domains (several micrometer in size) moved in the sea of randomly moving grains; however, these domains were soon constrained by the surrounding sea and disappeared; subsequently, new domains were formed in other places by re-combination of grains in order to continue superplastic deformation. Based on these phenomena, the authors proposed a new deformation mechanism called “Recombinant Domain Movement” in this paper.

Evaluation of wear mechanisms of Y-TZP and tungsten carbide punches

Tool wear is one of the major concerns in the tooling industry. A comparative evaluation of different tool materials and tool wear will help preventing frequent replacement of tools thus reducing the costs incurred due to such replacements. In this paper, tool wear mechanism of tetragonal zirconia polycrystal (TZP) punch is compared with that of commercially available WC (tungsten carbide) punch during stamping. The tool life for the TZP punch was found to be over 2.5 times higher than that of commercial tungsten carbide. The worn-out tools were analysed using scanning electron microscope and optical microscope for studying the tool wear mechanisms. Tool wear and chemical action possibly cause the failure of the tungsten carbide punch, whereas wear of TZP punch is predominantly caused by mechanical shearing of asperity and plastic deformation. Due to their inherent high melting point and the absence of the second-phase binder, ceramics materials do not soften at higher temperature unlike the carbide tools. Hence, they can be used at high cutting speeds without initiating deformation/diffusion wear. This assists in improving the tool life significantly. In addition, TZP ceramics is inert, corrosion resistant and non-wetting when contacting metals. Exposed carbide grains act as a site for increased wear and metal pickup during precision, high-speed metal stamping and forming. Moreover, cobalt-depleted carbide tools can create burring of the strip being stamped, leading to poor part quality. The performance of TZP punch tool will be evaluated thoroughly based on experimental data in this paper.

Wear and friction of transformation-toughened CMC and MMC

The sliding wear properties of transformation-toughened CMC and MMC coupled with high-speed steel have been studied at speeds in the range 0.9–9.4m/s for MMC and 0.2–11.1m/s for CMC and at a pressure of 5MPa. It was shown that at low sliding speeds (0.2–4m/s), both friction coefficient and wear rate of the yttria-doped tetragonal zirconia polycrystal ceramics (Y-TZP) increased with sliding speed and then decreased after reaching the maximum. The wear rate of TiC–NiTi increases with the increase in the sliding speed in the range of 0.9–9.4m/s, whereas the friction coefficient followed an inverse trend. At low speeds, the tribological behavior of both ceramics and hard was controlled by the action of the transformation-toughening mechanism. In case of ceramics, a continuous transfer layer formed to serve as a protective transfer layer on the specimen surface during high-speed wear. In case of TiC–NiTi, softened or even melted binder is extruded from an interparticle area onto pin/disk interface and thus determines wear behavior of such a system at sliding speed higher than 4m/s.

Synthesis of nanocrystalline zirconia powders for TZP ceramics by a nitrate–citrate combustion route

A nitrate–citrate combustion route to synthesise nanocrystalline yttria-doped zirconia powders for tetragonal zirconia polycrystal (TZP) ceramics is presented. This route is based on the gelling of nitrate solutions by the addition of citric acid and ammonium hydroxide, followed by an intense combustion process due to an exothermic redox reaction between nitrate and citrate ions. X-ray diffraction characterisation of powders showed the stabilisation of the tetragonal phase at room temperature because of their small crystallite size (about 10 nm). Dense ceramic samples prepared by uniaxial pressing and sintering in air were also studied.

In vitro evaluation of the mutagenic and carcinogenic power of high purity zirconia ceramic

Tetragonal zirconia polycrystal (TZP) is a new interesting ceramic for the manufacture of medical devices. Its wide use in orthopedic and odontoiatric implants was limited till now by the high chemical and radiochemical impurities of the raw materials. Purification processes now available allow to obtain high purity ceramic grade powders suitable for TZP ceramics manufacture, even if their possible mutagenic and transforming effects are still unclear. The aim of this work is to study in vitro the mutagenic and oncogenic effects of a new zirconia ceramic stabilized by yttria (Y-TZP). This ceramic was sintered from high purity powders obtained by a process developed under a project carried out within the Brite EuRam programme. For comparison, ceramics made from unpurified zirconia powder were also tested. Fibroblasts irradiated by a linear accelerator were used as positive control. The results obtained show that Y-TZP ceramic does not elicit either mutagenic or transforming effect on C3H/10T 1/2 (10T 1/2) cells and demonstrate that ceramic from high purity powders can be considered suitable for biomedical applications from the point of view of the effects of its radioactive impurity content.