3-D Surface Morphological Characterization of CAD/CAM Milled Dental Zirconia: An In Vitro Study of the Effect of Post-Fabrication Processes

Objective: To investigate the effect on zirconia surface of the post-fabrication surface treatments on the morphological characteristics and mechanical properties of CAD/CAM milled dental zirconia specimens as well as to identify the critical parameters in the measurement of oral retention under in vitro circumstances. Method: The zirconia specimens (N = 20, n = 4) were subjected to CAD/CAM milling and divided into five groups. The specifications were: Group G1—sintered; Group G2—sintered followed by a polishing process; Group G3—sintered followed by polishing and sandblasting with alumina particles Al₂O₃ (110 µm); Group G4—sintered followed by sandblasting; Group G5—sintered followed by sandblasting with polishing as the end process. All the groups were subjected to Fretting wear tests, 3-D surface roughness measurements, and Vickers’s Micro hardness tests. Investigation of the phase transformation using XRD, and surface feature examination using SEM were also carried out. Additionally, one-way ANOVA, Tukey, and Pearson correlations were statistically analysed. Results: The fabrication processes had a significant effect on the performance of zirconia specimens in all the groups (p > 0.05). Specimens that underwent polishing as the last process exhibited lower surface roughness. The monoclinic phase of zirconia was observed in all the specimens before and after wear except for those in the G2 and G5 groups, where polishing was the end process. In G5, the post-wear surface properties revealed lower surface roughness and hardness. Further, the SEM and 3-D topography show grooves as seen by the dale void volume (Vvv) values; shallow valley depth (Svk); micro craters; and wear track. Conclusion: Specimens in G5 that were subjected to multistep post-fabrication process, namely sandblasting followed by polishing, yielded better results when compared to those in the other groups (G1, G2, G3, and G4). G5 with an interlayer of alumina is recommended for clinical applications due to its enhanced surface properties, mechanical properties, and low wear.     

Resin Cement–Zirconia Bond Strengthening by Exposure to Low-Temperature Atmospheric Pressure Multi-Gas Plasma

The purpose of this study was to investigate the effect of gas species used for low-temperature atmospheric pressure plasma surface treatment, using various gas species and different treatment times, on zirconia surface state and the bond strength between zirconia and dental resin cement. Three groups of zirconia specimens with different surface treatments were prepared as follows: untreated group, alumina sandblasting treatment group, and plasma treatment group. Nitrogen (N₂), carbon dioxide (CO₂), oxygen (O₂), argon (Ar), and air were employed for plasma irradiation. The bond strength between each zirconia specimen and resin cement was compared using a tension test. The effect of the gas species for plasma irradiation on the zirconia surface was investigated using a contact angle meter, an optical interferometer, an X-ray diffractometer, and X-ray photoelectric spectroscopy. Plasma irradiation increased the wettability and decreased the carbon contamination on the zirconia surface, whereas it did not affect the surface topography and crystalline phase. The bond strength varied depending on the gas species and irradiation time. Plasma treatment with N₂ gas significantly increased bond strength compared to the untreated group and showed a high bond strength equivalent to that of the sandblasting treatment group. The removal of carbon contamination from the zirconia surface and an increase in the percentage of Zr-O₂ on the zirconia surface by plasma irradiation might increase bond strength.     

Effects of Aluminum Oxide Addition on Electrical and Mechanical Properties of 3 mol% Yttria-Stabilized Tetragonal Zirconia Electrolyte for IT-SOFCs

Composite tetragonal zirconia (3Y-TZP) sinters with Al₂O₃ contents of 0, 1, 5, 10 and 15 mol% were obtained from a 3-YSZ powder prepared using the gelatin method, and the influence of alumina addition on the mechanical and electrical properties of the obtained sinters was investigated. Al₂O₃ was added via two different methods, namely during the preparation of the 3-YSZ powder and via impregnation using an alcohol solution of aluminum nitrate. The obtained green bodies were sintered for 2 h in air at 1773 K. The structure and morphology of the two series of sinters were investigated using XRD and SEM-EDS, their electrical properties were determined using impedance spectroscopy, and their hardness and critical stress intensity factor were measured using the Vickers indentation test. We established that both the amount of alumina and the method used to introduce it into the 3Y-TZP matrix significantly affect the physicochemical properties of the obtained polycrystalline material. The 3-YSZ/10 mol% Al₂O₃ sinter that had Al₂O₃ introduced during the preparation of the 3-YSZ powder was found to exhibit the most advantageous mechanical and electrical properties while still having sufficiently low porosity.     

Effect of Simultaneous Sintering of Bioglass to a Zirconia Core on Properties and Bond Strength

This study aimed to assess bioglass sintering to a zirconia core on surface properties and bonding strength to resin cement. Zirconia specimens were divided into four groups: G I: sintered; G II: bioglass modified zirconia (a bioglass slurry was sintered with zirconia at 1550 °C); G III: sandblasted using 50 μm Al₂O₃ particles; and G IV: Z-prime plus application. Surface morphology and chemical analysis were studied using a scanning electron microscope and energy-dispersive spectroscopy. Surface roughness was evaluated using a profilometer. Surface hardness was measured using an indentation tester. For the microshear bond strength test, resin cement cylinders were bonded to a zirconia surface. Half of the specimens were tested after 24 h; the other half were thermocycled (5–55 °C) for 1000 cycles. A shearing load was applied at a crosshead speed of 0.5 mm/min on a universal testing machine. Data were analyzed with ANOVA using SPSS software at (p < 0.05). Results: tThe mean surface roughness of G II was significantly higher than G I and G III. The microhardness of G II was significantly lower than all groups. For bond strength, there was no significant difference between groups II, III, and IV after thermocycling. Conclusions: Bioactive glass can increase the bond strength of zirconia to resin cement, and is comparable to sandblasting and Z-prime bonding agents.     

Characterization of Al2O3 Matrix Composites Fabricated via the Slip Casting Method Using NiAl-Al2O3 Composite Powder

This work aimed to characterize Al₂O₃ matrix composites fabricated by the slip casting method using NiAl-Al₂O₃ composite powder as the initial powder. The composite powder, consisting of NiAl + 30 wt.% Al₂O₃, was obtained by mechanical alloying of Al₂O₃, Al, and Ni powders. The composite powder was added to the Al₂O₃ powder to prepare the final powder for the slip casting method. The stained composite samples presented high density. EDX and XRD analyses showed that the sintering process of the samples in an air atmosphere caused the formation of the NiAl₂O₄ spinel phase. Finally, the phase composition of the composites changed from the initial phases of Al₂O₃ and NiAl to Al₂O₃, Ni, and NiAl₂O₄. However, in the area of Ni, fine Al₂O₃ particles remaining from the initial composite powder were visible. It can be concluded that after slip casting, after starting with Al₂O₃ and the composite powder (NiAl-Al₂O₃) and upon sintering in air, ceramic matrix composites with Ni and NiAl₂O₄ phases, complex structures, high-quality sintered samples, and favorable mechanical properties were obtained.     

Phase Transformations and Subsurface Changes in Three Dental Zirconia Grades after Sandblasting with Various Al2O3 Particle Sizes

Although sandblasting is mainly used to improve bonding between dental zirconia and resin cement, the details on the in-depth damages are limited. The aim of this study was to evaluate phase transformations and subsurface changes after sandblasting in three different dental zirconia (3, 4, and 5 mol% yttria-stabilized zirconia; 3Y-TZP, 4Y-PSZ, and 5Y-PSZ). Zirconia specimens (14.0 × 14.0 × 1.0 mm³) were sandblasted using different alumina particle sizes (25, 50, 90, 110, and 125 µm) under 0.2 MPa for 10 s/cm². Phase transformations and residual stresses were investigated using X-ray diffraction and the Williamson-Hall method. Subsurface damages were evaluated with cross-sections by a focused ion beam. Stress field during sandblasting was simulated by the finite element method. The subsurface changes after sandblasting were the emergence of a rhombohedral phase, micro/macro cracks, and compressive/tensile stresses depending on the interactions between blasting particles and zirconia substrates. 3Y-TZP blasted with 110-µm particles induced the deepest transformed layer with the largest compressive stress. The cracks propagated parallel to the surface with larger particles, being located up to 4.5 µm under the surface in 4Y- or 5Y-PSZ subgroups. The recommended sandblasting particles were 110 µm for 3Y-TZP and 50 µm for 4Y-PSZ or 5Y-PSZ for compressive stress-induced phase transformations without significant subsurface damages.     

Phenomena Occurring upon the Sintering of a Mixture of Yttria–Zirconia Nanometric Powder and Sub-Micrometric Pure Zirconia Powder

Mixtures of powders essentially differing in their particle morphology and size were applied to prepare polycrystals in a Y₂O₃-ZrO₂ system. An yttria–zirconia solid solution nanometric powder with a Y₂O₃ concentration of 3.5% was prepared by subjecting co-precipitated gels to hydrothermal treatment at 240 °C. The crystallization occurred in distilled water. The pure zirconia powders composed of elongated and sub-micrometer size particles were also manufactured through the hydrothermal treatment of pure zirconia gel, although in this case, the process took place in the NaOH solution. Mixtures of the two kinds of powder were prepared so as to produce a mean composition corresponding to an yttria concentration of 3 mol%. Compacts of this powder mixture were sintered, and changes in phase composition vs. temperature were studied using X-ray diffraction. The dilatometry measurements revealed the behavior of the powder compact during sintering. The polished surfaces revealed the microstructure of the resulting polycrystal. Additionally, the electron back scattering diffraction technique (EBSD) allowed us to identify symmetry between the observed grains. Hardness, fracture toughness, and mechanical strength measurements were also performed.     

Relevant Aspects of Titanium and Zirconia Dental Implants for Their Fatigue and Osseointegration Behaviors

Osseointegration capacity and good mechanical behavior are key to the success of the dental implant. In many investigations, comparisons of properties are made using different dental implant designs and therefore the results can be influenced by the macrodesign of the dental implant. In this work, studies were carried out with the same dental implant model using different roughness and different materials—commercially pure titanium (grade 4) and zirconia. For this purpose, 80 smooth passivated titanium (Ti), 80 smooth zirconia (ZrO₂), and 80 rough passivated titanium (Ti-R) dental implants were used. The samples were characterized by their roughness, wettability, surface energy, residual stresses, and fatigue behavior. The implants were implanted in minipigs for 4 and 12 weeks. The animals were sacrificed, and histological studies were carried out to determine the osseointegration parameters for each of the implantation times. Ti and ZrO₂ dental implants have very similar wettability and surface energy properties. However, the roughness causes a decrease in the hydrophilic character and a decrease of the total surface energy and especially the dispersive component, while the polar component is higher. Due to the compressive residual stresses of alumina sandblasting, the rough dental implant has the best fatigue behavior, followed by Ti and due to the lack of toughness and rapid crack propagation the ZrO₂ implants have the worst fatigue behavior. The bone index contact (BIC) values for 4 weeks were around 25% for Ti, 32% for ZrO₂, and 45% for Ti-R. After 12 weeks the Ti dental implants increased to 42%, for Ti, 43% for ZrO₂, and an important increase to 76% was observed for Ti-R implants. In vivo results showed that the key factor that improves osseointegration is roughness. There was no significant difference between ZrO₂ and Ti implants without sandblasting.     

Comparative Study on Electrical Conductivity of CeO2-Doped AlN Ceramics Sintered by Hot-Pressing and Spark Plasma Sintering

Aluminum nitride (AlN) ceramics were prepared by both Hot-pressing (HP) and Spark-Plasma-Sintering (SPS) using cerium oxide as the sintering aid. The characterization of AlN raw powder denoted the presence of an amorphous layer that led to the formation of aluminum oxide. During the sintering process, CeO₂ introduced as a sintering aid was reduced into Ce₂O₃. The latter reacted with aluminum oxide to form a transient liquid phase that promotes sintering by both HP and SPS. A reactional path leading to the formation of secondary phases, such as CeAlO₃ and CeAl₁₁O₁₈, has been proposed according to the pseudo-binary Al₂O₃ – Ce₂O₃. Ceramics obtained from HP and SPS are presented as similar, except for the secondary-phase distribution. The influences of secondary phase composition and distribution on electrical conductivity were evaluated by leakage current measurements. The mechanism of DC conduction and the global conductivity of ceramics were discussed according to the sintering process and the number of secondary phases.     

Influence of Preaging Temperature on the Indentation Strength of 3Y-TZP Aged in Ambient Atmosphere

Yttria-stabilized zirconia (3Y-TZP) containing 0.25% Al₂O₃, which is resistant to low temperature degradation (LTD), was aged for 10 h at 130–220 °C in air. The aged specimens were subsequently indented at loads ranging from 9.8 to 490 N using a Vickers indenter. The influence of preaging temperature on the biaxial strength of the specimens was investigated to elucidate the relationship between the extent of LTD and the strength of zirconia restorations that underwent LTD. The indented strength of the specimens increased as the preaging temperature was increased higher than 160 °C, which was accompanied by extensive t-ZrO₂ (t) to m-ZrO₂ (m) and c-ZrO₂ (c) to r-ZrO₂ (r) phase transformations. The influence of preaging temperature on the indented strength was rationalized by the residual stresses raised by the t→m transformation and the reversal of tensile residual stress on the aged specimen surface due to the indentation. The results suggested that the longevity of restorations would not be deteriorated if the aged restorations retain compressive residual stress on the surface, which corresponds to the extent of t→m phase transformation less than 52% in ambient environment.     

The Influence of Reactive PS-PVD Process Parameters on the Microstructure and Thermal Properties of Yb2Zr2O7 Thermal Barrier Coating

Ytterbium zirconate (Yb₂Zr₂O₇) is one of the most promising materials for yttria-stabilized zirconia (YSZ) replacement as a thermal barrier coating (TBCs) application. In the presented report, the experimental synthesis of Yb₂Zr₂O₇ coating using novel Reactive Plasma Spray Physical Vapor Deposition (Reactive PS-PVD) is described. The obtained coating, irrespective of the power current (1800, 2000 and 2200 A), was characterized by a hybrid structure and a thickness of about 80–110 μm. The results of XRD phase analysis showed the formation of ytterbium zirconate in the coating but the presence of ytterbium and zirconium oxides was also detected. The oxides were not observed in calcinated powder. The decrease in thermal conductivity with power current increase was observed. It was the result of higher thickness and better columnar structure of the coating obtained using higher power current of the plasma torch.     

Characterization of Human Gingival Fibroblasts on Zirconia Surfaces Containing Niobium Oxide

It was indicated that tetragonal zirconia polycrystal (TZP) containing yttria (Y₂O₃) and niobium oxide (Nb₂O₅) ((Y,Nb)-TZP) could be an adequate dental material to be used at esthetically important sites. The (Y,Nb)-TZP was also proved to possess its osteogenic potential comparable with those conventional dental implant material, titanium (Ti). The objective of the current study was to characterize cellular response of human gingival fibroblasts (HGFs) to smooth and rough surfaces of the (Y,Nb)-TZP disc, which were obtained by polishing and sandblasting, respectively. Various microscopic, biochemical, and molecular techniques were used to investigate the disc surfaces and cellular responses for the experimental (Y,Nb)-TZP and the comparing Ti groups. Sandblasted rough (Y,Nb)-TZP (Zir-R) discs had the highest surface roughness. HGFs cultured on polished (Y,Nb)-TZP (Zir) showed a rounded cell morphology and light spreading at 6 h after seeding and its proliferation rate significantly increased during seven days of culture compared to other surfaces. The mRNA expressions of type I collagen, integrin α2 and β1 were significantly stimulated for the Zir group at 24 h after seeding. The current findings, combined with the previous results, indicate that (Y,Nb)-TZP provides appropriate surface condition for osseointegration at the fixture level and for peri-implant mucosal sealing at the abutment level producing a suitable candidate for dental implantation with an expected favorable clinical outcome.     

Hydrothermal Synthesis of Nanocrystalline ZrO2-8Y2O3-xLn2O3 Powders (Ln = La,Gd, Nd,Sm): Crystalline Structure,Thermal and Dielectric Properties

Zirconium dioxide (ZrO₂) is one of the ceramic materials with high potential in many areas of modern technologies. ZrO₂ doped with 8 wt.% (~4.5 mol%) Y₂O₃ is a commercial powder used for obtaining stabilized zirconia materials (8 wt.% YSZ) with high temperature resistance and good ionic conductivity. During recent years it was reported the co-doping with multiple rare earth elements has a significant influence on the thermal, mechanical and ionic conductivity of zirconia, due complex grain size segregation and enhanced oxygen vacancies mobility. Different methods have been proposed to synthesize these materials. Here, we present the hydrothermal synthesis of 8 wt.% (~4.5 mol%) YSZ co-doped with 4, 6 and 8 wt.% La₂O₃, Nd₂O₃, Sm₂O₃ and Gd₂O₃ respectively. The crystalline phases formed during their thermal treatment in a large temperature range were analyzed by X-ray diffraction. The evolution of phase composition vs. thermal treatment temperatures shows as a major trend the formation at temperatures >1000 °C of a cubic solid solutions enriched in the rare earth oxide used for co-doping as major phase. The first results on the thermal conductivities and impedance measurements on sintered pellets obtained from powders co-doped with 8 wt.% Y and 6% Ln (Ln = La, Nd, Sm and Gd) and the corresponding activation energies are presented and discussed. The lowest thermal conductivity was obtained for La co-doped 8 wt.% YSZ while the lowest activation energy for ionic conduction for Gd co-doped 8 wt.% YSZ materials.     

Evaluation of Mechanical and Electrical Performance of Aging Resistance ZTA Composites Reinforced with Graphene Oxide Consolidated by SPS

This paper presents a study of Al₂O₃–ZrO₂ (ZTA) nanocomposites with different contents of reduced graphene oxide (rGO). The influence of the rGO content on the physico-mechanical properties of the oxide composite was revealed. Graphene oxide was obtained using a modified Hummers method. Well-dispersed ZTA-GO nanopowders were produced using the colloidal processing method. Using spark plasma sintering technology (SPS), theoretically dense composites were obtained, which also reduced GO during SPS. The microstructure, phase composition, and physico-mechanical properties of the sintered composites were studied. The sintered ZTA composite with an in situ reduced graphene content of 0.28 wt.% after the characterization showed improved mechanical properties: bending strength was 876 ± 43 MPa, fracture toughness—6.8 ± 0.3 MPa·m^1/2 and hardness—17.6 ± 0.3 GPa. Microstructure studies showed a uniform zirconia distribution in the ZTA ceramics. The study of the electrical conductivity of reduced graphene oxide-containing composites showed electrical conductivity above the percolation threshold with a small content of graphene oxide (0.28 wt.%). This electrical conductivity makes it possible to produce sintered ceramics by electrical discharge machining (EDM), which significantly reduces the cost of manufacturing complex-shaped products. Besides improved mechanical properties and EDM machinability, 0.28 wt.% rGO composites demonstrated high resistance to hydrothermal degradation.     

Effect of Air-Abraded Versus Laser-Fused Fluorapatite Glass-Ceramics on Shear Bond Strength of Repair Materials to Zirconia

Zirconia repair could be a feasible alternative option to total replacement in fractured zirconia-based restorations. Maximising the bond strength by enriching zirconia with fluorapatite glass-ceramics (FGC) powder has been addressed and compared to other surface treatments. Besides resin composite, other repair materials have been proposed and compared. Zirconia blocks received different surface treatments (A—sandblasting with tribochemical silica-coated alumina (CoJet). B—sandblasting with FGC powder (FGC), C—fluorapatite glass-ceramic coat+ neodymium-doped yttrium aluminum garnet laser irradiation (FGC + Nd: YAG), and D—no surface treatment). The surface roughness, topography, and crystallinity were investigated by a profilometer, scanning electron microscopy (SEM), and X-ray diffraction (XRD) analyses, respectively. For each surface treatment, three repair materials (feldspathic porcelain, lithium disilicate, and resin composite) were bonded to zirconia with 10, Methacryloyloxydecyl dihydrogen phosphate (MDP)–Monobond Plus/ Multilink Automix. Bonded specimens were thermocycled for 10,000 cycles and tested for shear bond strength (SBS) at a speed of 1 mm/min, followed by the analysis of the mode of failure. FGC + Nd: YAG laser group reported the highest surface roughness and monoclinic content compared to CoJet, FGC, and control groups. The highest mean SBS was found in FGC-blasted zirconia, followed by FGC + Nd: YAG laser and CoJet treated groups. However, the lowest SBS was found in control groups regardless of the repair material. Sandblasting zirconia with FGC powder increased SBS of resin to zirconia with lower monoclinic phase transformation compared to FGC + Nd: YAG or CoJet groups.     

Alumina and Zirconia-Reinforced Polyamide PA-12 Composites for Biomedical Additive Manufacturing

This work aimed to prepare a composite with a polyamide (PA) matrix and surface-modified ZrO₂ or Al₂O₃ to be used as ceramic fillers (CFs). Those composites contained 30 wt.% ceramic powder to 70 wt.% polymer. Possible applications for this type of composite include bioengineering applications especially in the fields of dental prosthetics and orthopaedics. The ceramic fillers were subjected to chemical surface modification with Piranha Solution and suspension in 10 M sodium hydroxide and Si₃N₄ to achieve the highest possible surface development and to introduce additional functional groups. This was to improve the bonding between the CFs and the polymer matrix. Both CFs were examined for particle size distribution (PSD), functional groups (FTIR), chemical composition (XPS), phase composition (XRD), and morphology and chemical composition (SEM/EDS). Filaments were created from the powders prepared in this way and were then used for 3D FDM printing. Samples were subjected to mechanical tests (tensility, hardness) and soaking tests in a high-pressure autoclave in artificial saliva for 14, 21, and 29 days.     

Effect of Ni-Cr Alloy Surface Abrasive Blasting on Its Wettability by Liquid Ceramics

An adequate surface is essential in ensuring a solid bond between the metal and dental ceramics for metal framework wettability. This work is aimed at investigating the effect of variable abrasive blasting parameters on Ni-Cr alloy surface’s ability to be wetted with liquid ceramics at elevated temperatures. One-hundred and sixty-eight samples were divided into 12 groups (n = 14), which were sandblasted using variable parameters: type of abrasive (Al₂O₃ and SiC), the grain size of the abrasive (50, 110, and 250 µm), and processing pressure (400 and 600 kPa). After treatment, the samples were cleaned in an ultrasonic cleaner and dried under compressed air. Dental ceramics were applied to the prepared surfaces via drops, and the wettability was tested in a vacuum oven at temperatures in the range of 850–1000 °C. The results were statistically analyzed using ANOVA (α = 0.05). For all surfaces, the contact angles were less than 90° at temperatures below 875 °C. For Al₂O₃, the best wettability was observed for the smallest particles and, for SiC, the largest particles. The ability to wet the surface of a Ni-Cr alloy is related to its sandblasting properties, such as roughness or the percentage of embedded abrasive particles. It should not be the only factor determining the selection of abrasive blasting parameters when creating a prosthetic restoration.     

Pulse Plasma Sintering of NiAl-Al2O3 Composite Powder Produced by Mechanical Alloying with Contribution of Nanometric Al2O3 Powder

NiAl-Al₂O₃ composites, fabricated from the prepared composite powders by mechanical alloying and then consolidated by pulse plasma sintering, were presented. The use of nanometric alumina powder for reinforcement of a synthetized intermetallic matrix was the innovative concept of this work. Moreover, this is the first reported attempt to use the Pulse Plasma Sintering (PPS) method to consolidate composite powder with the contribution of nanometric alumina powder. The composite powders consisting of the intermetallic phase NiAl and Al₂O₃ were prepared by mechanical alloying from powder mixtures containing Ni-50at.%Al with the contribution of 10 wt.% or 20 wt.% nanometric aluminum oxide. A nanocrystalline NiAl matrix was formed, with uniformly distributed Al₂O₃ inclusions as reinforcement. The PPS method successfully consolidated NiAl-Al₂O₃ composite powders with limited grain growth in the NiAl matrix. The appropriate sintering temperature for composite powder was selected based on analysis of the grain growth and hardness of Al₂O₃ subjected to PPS consolidation at various temperatures. As a result of these tests, sintering of the NiAl-Al₂O₃ powders was carried out at temperatures of 1200 °C, 1300 °C, and 1400 °C. The microstructure and properties of the initial powders, composite powders, and consolidated bulk composite materials were characterized by SEM, EDS, XRD, density, and hardness measurements. The hardness of the ultrafine-grained NiAl-Al₂O₃ composites obtained via PPS depends on the Al₂O₃ content in the composite, as well as the sintering temperature applied. The highest values of the hardness of the composites were obtained after sintering at the lowest temperature (1200 °C), reaching 7.2 ± 0.29 GPa and 8.4 ± 0.07 GPa for 10 wt.% Al₂O₃ and 20 wt.% Al₂O₃, respectively, and exceeding the hardness values reported in the literature. From a technological point of view, the possibility to use sintering temperatures as low as 1200 °C is crucial for the production of fully dense, ultrafine-grained composites with high hardness.     

Effects of Different Air Particle Abrasion Protocols on the Biaxial Flexural Strength and Fractography of High/Ultra-Translucent Zirconia

In this study, the biaxial flexural strength (BFS) and fractography of high/ultra-translucent monolithic zirconia ceramics subjected to different mechanical surface pretreatments were evaluated. A total of 108 disc-shaped samples (12 mm diameter, 1.2 mm thickness) of three zirconia materials (5Y-ZP KATANA Zirconia UTML (ML), 3Y-TZP DD Bio ZX2 (DB), and 5Y-ZP DD cube X2 (DC)) were used. The BFS was investigated after subjecting the samples to surface treatment using air abrasion particles of two types (aluminum oxide or glass microbeads). The data were analyzed using two-way analysis of variance, followed by Scheffe’s post hoc test for multiple comparisons. The mean ± standard deviation BFS for DB was highest after treatment with 50 µm Al₂O₃ (1626.05 ± 31.9 MPa), with lower values being observed following treatment with 50 µm glass microbeads (1399.53 ± 24.2 MPa) and in the control sample (1198.51 ± 21.1 MPa). The mean ± standard deviation (SD) BFSs for DC and ML were the highest in the control groups. Surface air abrasion with 50 µm Al₂O₃ particles and 2 bar pressure is recommended for 3Y-TZP translucent zirconia, while no abrasion of 5Y-ZP translucent zirconia ceramic.     

Al2O3/ZrO2 Materials as an Environmentally Friendly Solution for Linear Infrastructure Applications

The present work deals with the evaluation of the effect of ZrO₂ on the structure and selected properties of shapes obtained using the centrifugal slip casting method. The samples were made of alumina and zirconia. The applied technology made it possible to produce tubes with a high density reaching 99–100% after sintering. Very good bonding was obtained at the Al₂O₃/ZrO₂ interphase boundaries with no discernible delamination or cracks, which was confirmed by STEM observations. In the case of Al₂O₃/ZrO₂ composites containing 5 vol.% and 10 vol.% ZrO₂, the presence of equiaxial ZrO₂ grains with an average size of 0.25 µm was observed, which are distributed along the grain boundaries of Al₂O₃. At the same time, the composites exhibited a very high hardness of 22–23 GPa. Moreover, the environmental influences accompanying the sintering process were quantified. The impacts were determined using the life cycle analysis method, in the phase related to the extraction and processing of raw materials and the process of producing Al₂O₃/ZrO₂ composites. The results obtained show that the production of 1 kg of sintered composite results in greenhouse gas emissions of 2.24–2.9 kg CO₂ eq. which is comparable to the amount of emissions accompanying the production of 1 kg of Polyvinyl Chloride (PVC), Polypropylene (PP), or hot-rolled steel products.