Alumina-zirconia Composites Research Articles

Understanding the Individual Role of Composition and Spark Plasma Sintering Temperature on the Microstructure and Hardness of Alumina–Zirconia Composites

Understanding the Individual Role of Composition and Spark Plasma Sintering Temperature on the Microstructure and Hardness of Alumina–Zirconia Composites

Effect of Hydroxyapatite on Sinterability, Mechanical Properties, and Bioactivity of Chemically Synthesized Alumina–Zirconia Composites

Effect of Hydroxyapatite on Sinterability, Mechanical Properties, and Bioactivity of Chemically Synthesized Alumina–Zirconia Composites

Novel protein stabilization in white wine: A study on thermally treated zirconia-alumina composites

A major concern for wineries is haze formation in white wines due to protein instability. Despite its prevalent use, the conventional bentonite method has shortcomings, including potential alteration of color and aroma, slow processing times, and notable wine wastage. Zirconium oxide (ZrO2) effectively removes proteins without affecting wine characteristics. However, producing cost-effective ZrO2 materials with efficient protein removal capabilities poses a significant challenge. This research aims to assess the viability of designing a porous material impregnated with zirconia to remove turbidity-causing proteins effectively. For this purpose, the support material alone (Al2O3) and the zirconia-impregnated support (ZrO2/Al2O3) were subjected to different calcination temperatures. It was observed that high-temperature treatments (750 °C) enhanced wine stability and protein adsorption capacity. The optimal adsorbent achieved a notable reduction in turbidity, decreasing the ΔNTU from 42 to 18, alongside a significant 44 % reduction in the total protein content, particularly affecting proteins in the molecular weight range of 10 to 70 kDa. This result is attributed to modifying the textural properties of ZrO2/Al2O3, characterized by the reduction of acidic sites, augmented pore diameters from 4.81 to 7.74 nm, and the emergence of zirconia clusters across the surface of the porous support. In summary, this study presents the first application of zirconia on the alumina support surface for protein stabilization in white wine. Combining ZrO2/Al2O3 and a high-temperature treatment emerges as a promising, cost-efficient, and environmentally sustainable strategy for protein removal in white wine.

Existence of monoclinic and tetragonal zirconia in MgO substituted alumina zirconia composites and studies of dielectric behavior

Magnesia stabilized zirconia-alumina composite were processed by auto-combustion method followed by solid-state sintering. Tetragonal zirconia with orthorhombic alumina phase has been ensured from XRD patterns and from Raman spectra. The optical band gap energy for 2%, 4% and 6% magnesium oxide substituted zirconia-alumina composites are 4.91, 5.03 and 3.48 eV, respectively. The dielectric behavior between the frequency range of 1 kHz–1 MHz shows frequency independent nature of dielectric constant with low loss tangent at various temperatures. The non-Debye type and grain-grain boundary effects were confirmed from Nyquist plot. Both PTCR and NTCR behavior were observed from AC conductivity study.

Features of calcium hexaaluminate formation in alumina-zirconia ceramics

Alumina-zirconia composites containing calcium hexaaluminate in the amount from 0 to 15 wt.% were investigated. The materials were obtained by water dispersion, granulation, axial pressing, and free sintering. Density and open porosity were determined by the hydrostatic weighing method. Phase analysis was performed using synchrotron radiation. Structural investigations were conducted using scanning and transmission electron microscopy. Vickers hardness was determined at a load of 10 kg. Fracture toughness was determined by the indentation method. With increasing CaAl12O19 content in the composites, the relative density decreased from 98.5% to 91.8%, and the open porosity increased from 0.2 to 1.4%. The lattice parameters of t-ZrO2 crystal lattice did not change up to 12 wt.% CaAl12O19, and the degree of tetragonality was 1.435. The degree of tetragonality decreased for the material with 15 wt.% CaAl12O19 and reached 1.420. The lattice parameters of CaAl12O19 decreased with increasing content. Platelet size increased with increasing calcium hexaaluminate content. For the materials containing up to 9 wt.% CaAl12O19, the average length of the platelets was 2 μm, the width was 0.4 μm, and the aspect ratio was 5. For the material with maximum calcium hexaaluminate content, the average length of the platelets was 4.2 μm, the width was 0.6 μm, and the aspect ratio was 7. With increasing CaAl12O19 content, the hardness decreased from 1700±25 to 1390±30 Hv, and the critical stress intensity factor increased by 34% to 6.7±0.3 MPa·m1/2.

Facile method for preparing lamellar structured alumina-zirconia ceramics with high toughness

This study describes a facile and effective method for fabricating alumina-zirconia composites with innovative lamellar structure as well as outstanding mechanical strength/toughness. To this end, the particle-stabilized foam method has been utilized to synthesize alumina ceramic foams built by single-layer pore wall firstly, providing the basic lamellar structure for the subsequently mixing with zirconia particles and hot-press sintering to achieve robust alumina-zirconia ceramics. The unique lamellar microstructure is composed of alumina sheets and zirconia grain layers alternated consistently, resulting in superior fracture toughness of 9.38 MPa m1/2, high flexural strength of 1.01 GPa and Vickers hardness of 17.04 GPa at the relative density of 99.63%. This approach opens up new possibilities for creating alumina-zirconia ceramics with exceptional mechanical performance.

A novel method for fabricating brick-mortar structured alumina-zirconia ceramics with high toughness

The present work reports a novel and simple approach to prepare alumina-zirconia composites with superior toughness. Alumina microspheres were innovatively used as the raw materials, followed by coating zirconia and hot-pressing sintering to fabricate alumina-zirconia ceramics. The resultant ceramics are given a unique brick-mortar microstructure, in which the zirconia “mortar” layers continuously distribute around the alumina “brick” matrix, leading to outstanding fracture toughness of 7.34 MPa·m1/2 and high strength of 635.84 MPa when prepared with zirconia contents of 10 wt%. The major explanation could be ascribed to that crack tips in sintered samples tend to propagate along the zirconia “mortar” layer, accompanied by deflection and branching, which effectively improve the fracture toughness of composites. The uniformity and integrity of the brick-mortar structure could be well tuned by varying the amount of zirconia. This method has reference significance for the preparation of high toughness alumina-based multiphase ceramics.

Definition of the parameters for the densification of ceramics by two-step solid state sintering

The two-step sintering (TSS) process is generally used to reduce the temperature conventionally required for the sintering of ceramics and to achieve a fine microstructure, but to date a general rule concerning the TSS parameters has not yet been identified. The TSS process was successfully applied to ZnO, Al2O3 and alumina-zirconia composites obtaining a comparable density to that achieved by the conventional process and with limited grain growth. A fine‐grained microstructure was maintained, avoiding the grain boundary migration, by the right selection of the operating conditions (essentially temperatures and holding time). A comparative study of the TSS on different advanced ceramic materials, such as SiC, ZnS and ZrO2, was also proposed, mainly based on the density, the microstructure and the grain size. Moreover, a general rule concerning the process temperatures with respect to the conventional sintering was defined to obtain the same densification preventing the grain growth.

Effect of airborne-particle abrasion with a novel spherical abrasive on the zirconia surface

Statement of problemA novel zirconia-alumina composite (ZAC) particle has yet to be studied for airborne-particle abrasion in a bonding protocol for the zirconia surface. PurposeThe purpose of this in vitro study was to evaluate the shear bond force of resin cement to yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) when using spherical ZAC particles to conduct airborne-particle abrasion and modify the topography of Y-TZP. Material and methodsSpherical 30- to 70-μm ZAC particles were fabricated by using a hybrid gel technique. A total of 160 Ø6.6×4.0-mm zirconia disks were fabricated from 4 commercially available zirconia blanks, e.max ZirCAD zirconia (EM), NexxZr T zirconia (NE), Lava Plus High Translucency zirconia (LP), and Imagine High Translucency Zirconia (IM), by using computer-aided manufacturing technology. As-sintered specimens without further surface treatment were used as controls (ZR0). Surface treatment groups included sharp-edged alumina airborne-particle abrasion (ABC), 50 μm, 0.2 MPa; airborne-particle abrasion with ZAC particle at 0.2 MPa (2ZA); and airborne-particle abrasion with spherical ZAC particle at 0.4 MPa (4ZA). All surface treatment groups were airborne-particle abraded at the specified pressures for 10 seconds at a standardized distance of 10 mm. The surface roughness (Ra) and area roughness (Sa) of specimens from each group were measured. Following the application of an adhesive (Scotchbond Universal), Ø6.6×4.0-mm resin cement (RelyX Ultimate) buttons were fabricated for shear bond testing by using a universal testing machine at a 5-mm/min crosshead speed (n=10). The data were analyzed by using a 2-way ANOVA, Tukey HSD test, and regression analysis (α=0.05). Scanning electron microscopy (SEM) was performed to observe changes of the zirconia surface and the failure modes of each group before and after shear bond testing. ResultsThe mean ±standard deviation shear bond force values ranged from 272.6 ±41.4 N to 686.7 ±152.8 N. Statistically significant higher force values than those of the controls (P<.05) were obtained by using airborne-particle abrasion. No significant differences were found among any of the airborne-particle abrasion treatment groups (P>.05). The mean of Ra values ranged from 0.27 μm to 0.74 μm, and the mean of Sa values, from 0.48 μm to 1.48 μm. SEM observation revealed that the zirconia surface was made jagged by abrasion with sharp-edged alumina particles. The spherical ZAC particles create microcraters on the zirconia surface. Fractographic observation disclosed that failures were adhesive-cohesive failure modes with residual resin cement attached on the zirconia surface. ConclusionsThe surface treatment of zirconia with sharp-edged alumina or the spherical ZAC abrasives improved the bonding force between the zirconia and resin cement. No statistically significant differences in shear bond force values were found between airborne-particle abrasion surface treatment groups.

Modeling of elastic properties and conductivity of partially sintered ceramics with duplex microstructure and different grain size ratio

The elastic constants and conductivity of partially sintered single-phase and two-phase ceramics (exemplified by alumina ceramics and alumina-zirconia composites, respectively) with different grain size ratio (from 1:1 to 1:4) are investigated by numerical modeling. The relative elastic moduli of partially sintered two-phase ceramics are shown to be relatively similar to those of single-phase ceramics, whereas the relative conductivity is significantly lower, because of the higher phase contrast. The more the grain size ratio deviates from unity, the higher is the initial packing fraction, and the lower are the relative elastic moduli and conductivity of the partially sintered ceramics. The porosity dependence of the Poisson ratio shows a decreasing trend which is only very weakly affected by the grain size ratio. Correlations between relative Young’s modulus and relative conductivity lie between upper and lower cross-property bounds. For single-phase materials the correlation lies below, for two-phase materials above, the Pabst-Gregorová cross-property relation.

Influence of material composition on nanosecond pulsed laser micromachining of zirconia-alumina composites

Due to their excellent mechanical properties and biocompatibility, zirconia-alumina composites are promising materials for bio-implant applications, including dental and hip-joint implants. A higher content of zirconia phase is beneficial for the fracture toughness of the composite material and therefore is more suitable for dental implant applications, while alumina is more resistant to wear than zirconia, and alumina dominated composite is therefore more often used in hip-joint implants. Studies about laser micromachining of both single phase zirconia-alumina and their composites are available in literature. However, the understanding on how the relative content of the two phases will affect the micromachining performance is lacking. In this paper, the influence of material composition on nanosecond-pulsed laser micromachining performance of zirconia-alumina composites is investigated by varying alumina content. Single pulse spot machining and groove machining experiments were performed on four graded ceramics with different alumina contents. The influence of laser parameters, including laser pulse energy, pulse width, pulse repetition rate, and scanning speed on material removal behavior and surface characteristic were investigated experimentally. It was found that materials with lower content of alumina phase were easier to be machined, which characterized by higher material removal rates, than high alumina contained materials. In addition, lower alumina content ceramics were more susceptible to thermal cracking than higher alumina content ceramics under excessive laser energy input. Besides, the inhomogeneity of the microstructure of the zirconia-alumina composites was found to have substantial influence on the morphology of the spots machined with short laser pulses. This research shows the significant influence of material composition on laser processing performance and should be helpful in selecting of optimal laser parameters for achieving desirable machining quality in laser processing of zirconia-alumina composites.

Ultrashort pulsed laser ablation of zirconia-alumina composites for implant applications

• Influence of alumina content on fs-laser machining of zirconia-alumina composites was studied. • Significant influence of material composition on material removal behavior was demonstrated. • Single phase materials have larger laser ablation thresholds and smaller material removal rate than their composites. • A lower scan speed is preferred for single phase materials while a higher scan speed is beneficial for the composites. Laser texturing of zirconia-alumina ceramics is a promising surface modification method for many applications, such as enhancing osseointegration of alumina toughened zirconia (ATZ) dental implants or improving friction behavior of zirconia toughened alumina (ZTA) hip replacement bearing components. The common problems in laser texturing of ATZ/ZTA ceramics are thermal cracking, low material removal rate (MRR), and laser-induced phase transformation (LIPT). Furthermore, the compositional variation of those ceramics will complicate these problems. In order to improve the manufacturing processability, ultrashort pulsed laser ablation behavior of ATZ/ZTA composites was investigated in this research. Single phase zirconia and alumina were found to have smaller MRRs than their composites, and this behavior was negatively correlated to the materials single-pulse laser ablation threshold. However, under multi-pulse laser irradiation, the ablation thresholds of all materials saturated to the same level, indicating that single phase materials were more sensitive to the incubation effect than their composites. This led to the MRRs of the single phase materials being reduced at larger scan speeds, while the MRRs of their composites remained independent of scan speed. It was also shown that single phase materials were less susceptible to thermal cracking than their composites under excessive heat accumulation. These results suggest that a lower scan speed is preferred for single phase materials in order to achieve a larger MRR, while a higher scan speed is beneficial for the composites for suppressing thermal cracking without compromising ablation efficiency. In addition, no LIPT was detected for zirconia dominated materials after laser ablation.

New Perspectives on Zirconia Composites as Biomaterials

Zirconia–alumina composites couple the high toughness of zirconia with the peculiar properties of alumina, i.e., hardness, wear, and chemical resistance, so they are considered promising materials for orthopedic and dental implants. The design of high performance zirconia composites needs to consider different aspects, such as the type and amount of stabilizer and the sintering process, that affect the mechanics of toughening and, hence, the mechanical properties. In this study, several stabilizers (Y2O3, CuO, Ta2O5, and CeO2) were tested together with different sintering processes to analyze the in situ toughening mechanism induced by the tetragonal–monoclinic (t–m) transformation of zirconia. One of the most important outcomes is the comprehension of the opposite effect played by the grain size and the tetragonality of the zirconia lattice on mechanical properties, such as fracture toughness and bending strength. These results allow for the design of materials with customized properties and open new perspectives for the development of high-performance zirconia composites for orthopedic implants with high hydrothermal resistance. Moreover, a near-net shape forming process based on the additive manufacturing technology of digital light processing (DLP) was also studied to produce ceramic dental implants with a new type of resin–ceramic powder mixture. This represents a new frontier in the development of zirconia composites thanks to the possibility to obtain a customized component with limited consumption of material and reduced machining costs.

Classification and Properties of Dental Zirconia as Implant Fixtures and Superstructures.

Various types of zirconia are widely used for the fabrication of dental implant superstructures and fixtures. Zirconia–alumina composites, such as ATZ and NanoZR, are adequate for implant fixtures because they have excellent mechanical strength in spite of insufficient esthetic properties. On the other hand, yttria-stabilized zirconia has been used for implant superstructures because of sufficient esthetic properties. They are classified to 12 types with yttria content, monochromatic/polychromatic, uniform/hybrid composition, and monolayer/multilayer. Zirconia with a higher yttria content has higher translucency and lower mechanical strength. Fracture strength of superstructures strongly depends on the strength on the occlusal contact region. It suggests that adequate zirconia should be selected as the superstructure crown, depending on whether strength or esthetics is prioritized. Low temperature degradation of zirconia decreases with yttria content, but even 3Y zirconia has a sufficient durability in oral condition. Although zirconia is the hardest dental materials, zirconia restorative rarely subjects the antagonist teeth to occlusal wear when it is mirror polished. Furthermore, zirconia has less bacterial adhesion and better soft tissue adhesion when it is mirror polished. This indicates that zirconia has advantageous for implant superstructures. As implant fixtures, zirconia is required for surface modification to obtain osseointegration to bone. Various surface treatments, such as roughening, surface activation, and coating, has been developed and improved. It is concluded that an adequately selected zirconia is a suitable material as implant superstructures and fixtures because of mechanically, esthetically, and biologically excellent properties.

Nature inspired dough processing of alumina-zirconia composites: Rheology, plasticity and weibull analysis towards net shaping

Advanced ceramic composites of alumina/zirconia are widely used in structural, functional and biomedical applications owing to superior physico-mechanical properties and biocompatibility. Unlike clays/bread dough, green shaping of ceramics was limited to slip casting due to insufficient plasticity. Herein, we introduce a ceramic dough forming inspired by the natural chemistry and mechanism of wheat flour dough. Ceramic blends were kneaded into a soft visco-plastic dough with vinyl polymer assuming the role of gluten matrix. A weakly linked dough matrix with a higher loss modulus enhanced the rate of powder deagglomeration and homogeneous distribution of the different phases during kneading. High plasticity index of the dough offers replication of intricate features with good dimensional retention. Dental prosthesis like root form implant, dental crown and bridge were successfully machined on a dried blank. Shape forming by this route is a viable alternative for dental prosthesis as evidenced by microstructure, strength and Weibull modulus values.

Microstructure and properties of zirconia-alumina composites fabricated via powder injection molding

This study aimed to fabricate zirconia-alumina composites via powder injection molding and investigated the effects of alumina addition on microstructure as well as physical properties of the composites. Zirconia-alumina composites were prepared using polyethylene glycol (PEG) and polyvinyl butyral (PVB) as binders. The powder loading was fixed at 38 vol%, and PEG: PVB binder weight ratio was fixed at 80:20. Alumina content within ceramic component was varied at 0, 10, 20, 30, 40 and 50 vol% to observe the effect of alumina on the composite structures and properties. The injection molding was done at 190℃ followed by water debinding of PEG at 40℃. Thermal debinding of PVB at 450℃ was performed prior to sintering at 1450℃. From the density measurement via Archimedes’ method, the relative density of sintered samples was found to be highest at 10 vol% alumina and gradually lower at higher alumina content. The condition with highest density yielded the highest flexural modulus and flexural strength. XRD indicated that tetragonal zirconia phase coexisted with alumina when alumina was added. Above 20 vol% alumina, monoclinic zirconia was also detected. The increased porosity in samples with high alumina content, as confirmed in SEM morphological observation, correlated with lower flexural strength and lower flexural modulus. The results illustrated the feasibility of powder injection molding in the production of zirconia-alumina composites and the optimum condition in this study was 10 vol% alumina.

A Novel Approach by Spark Plasma Sintering to the Improvement of Mechanical Properties of Titanium Carbonitride-Reinforced Alumina Ceramics.

Ti(C,N)-reinforced alumina-zirconia composites with different ratios of C to N in titanium carbonitride solid solutions, such as Ti(C0.3,N0.7) (C:N = 30:70) and Ti(C0.5,N0.5) (C:N = 50:50), were tested to improve their mechanical properties. Spark plasma sintering (SPS) with temperatures ranging from 1600 °C to 1675 °C and pressureless sintering (PS) with a higher temperature of 1720 °C were used to compare results. The following mechanical and physical properties were determined: Vickers hardness, Young’s modulus, apparent density, wear resistance, and fracture toughness. A composite with the addition of Ti(C0.5,N0.5)n nanopowder exhibited the highest Vickers hardness of over 19.0 GPa, and its fracture toughness was at 5.0 Mpa·m1/2. A composite with the Ti(C0.3,N0.7) phase was found to have lower values of Vickers hardness (by about 10%), friction coefficient, and specific wear rate of disc (Wsd) compared to the composite with the addition of Ti(C0.5,N0.5). The Vickers hardness values slightly decreased (from 5% to 10%) with increasing sintering temperature. The mechanical properties of the samples sintered using PS were lower than those of the samples that were spark plasma sintered. This research on alumina–zirconia composites with different ratios of C to N in titanium carbonitride solid solution Ti(C,N), sintered using an unconventional SPS method, reveals the effect of C/N ratios on improving mechanical properties of tested composites. X-ray analysis of the phase composition and an observation of the microstructure was carried out.

Microstructure and Young’s modulus evolution during re-sintering of partially sintered alumina-zirconia composites (ATZ ceramics)

Partially and fully sintered alumina-zirconia composites (ATZ ceramics), with porosities decreasing from 53.5 to 1 %, have been prepared by uniaxial pressing and firing at 1000–1500 °C and characterized by the Archimedes method and mercury intrusion porosimetry. Young’s modulus has been measured via the impulse excitation technique at room temperature, resulting in an almost exponential porosity dependence (which is unusual for partially sintered ceramics in which the microstructure is dominated by concave pore surfaces), and at elevated temperatures up to 1500 °C during heating and cooling, resulting in a temperature master curve with a low-temperature inflection point around 200 °C (accompanied by a damping maximum). Both results confirm previous findings for zirconia and are typical for zirconia-containing ceramics. When the original firing temperature is exceeded, sintering and densification continues, albeit with a temperature lag when the sintering activity (specific surface area) is reduced as a consequence of previous firing.

Designing alumina-zirconia composites by DLP-based stereolithography: Microstructural tailoring and mechanical performances

Digital Light Processing (DLP) is attracting high interest thanks to the possibility to prepare dense or complex ceramic parts starting from a photosensitive ceramic slurry. ZrO2 and Al2O3 are the most studied ceramic materials for DLP, while few studies deal with their composites in spite their wide range of applications. In this work, three alumina-zirconia composites (at 15, 50 and 85 vol% of ZrO2) were prepared by mixing ready-to-use ZrO2 and Al2O3 slurries. The mechanical and physical properties of the composites prepared via DLP technique were investigated and compared to those of neat alumina and zirconia materials used as a reference. For each composite, the sintering temperature was optimized on the ground of final density and microstructural development, with the aim to achieve a target density (i.e. ρ > 98.5%TD), while keeping a fine microstructure. The composites were characterized by quite homogeneous microstructures, with a good distribution of the two phases, in line with the materials prepared by conventional techniques. Flexural strength, elastic modulus and Vickers hardness of fabricated alumina-zirconia composites ranged between 415 and 843 MPa, 188–318 GPa and 15–21 GPa, respectively. These results show that the well-known microstructure-properties relationship, which dominates the conventionally fabricated materials, also plays an important role in stereolithography processed samples. In fact, once optimized the fired densities and the microstructures, the 3D-printed alumina-zirconia composites reached mechanical properties higher than almost all previous investigations for the same composites fabricated by stereolithography, and in most cases even higher than those of conventional composites of analogous compositions.

Zirconia-Alumina Composites Obtained by Centrifugal Slip Casting as Attractive Sustainable Material for Application in Construction.

This paper focuses on the possibility of adapting the centrifugal slip casting method to obtain zirconia–alumina composite materials in the form of finished tube-shaped products. These types of products, due to their unique properties, can be utilised, for example, in the transport of aggressive substances, even in extreme temperatures or corrosive conditions. The study reports on the two series of zirconia–alumina composites differing in the content of ZrO2—2.5 and 25 vol%. The fabricated and sintered materials were characterised using scanning electron microscopy (SEM), X-ray diffraction (XRD) and stereological analysis. Moreover, a life cycle assessment (LCA) was provided in accordance with the requirements of the ISO 14044 and EN 15805 standards. The obtained data clearly show that the centrifugal slip casting method allows obtaining samples with high density and extremely uniform distribution of the ZrO2 phase in the alumina matrix. The stereological analysis results proved also that the addition of ZrO2 is effective in reducing the growth of Al2O3 grains during the sintering process. The phase analysis carried out by means of XRD showed that during the sintering process, in the case of composites with a lower ZrO2 content (2.5 vol%), the monoclinic to tetragonal transformation of ZrO2 was total, while for samples containing 25 vol% ZrO2, the monoclinic phase remained in a small amount in the final product.