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Cordierite-acicular mullite composites containing 0, 25, 50, 75 and 100 wt% of mullite were fabricated from waste MoSi2 and commercial powders of Al2O3 and spinel (MgAl2O4). Careful oxidation of pulverised waste MoSi2 rendered a precursor mixture of MoO3 and amorphous SiO2, which served as pore forming agent and SiO2 source, respectively. Evaporation of MoO3 at ∼750 °C allowed production of highly porous cordierite-mullite ceramic composite after sintering in air at 1350 °C for 4 h. The combination of equiaxed cordierite grains and elongated (prism-like) mullite grains, resulted in unique microstructure with open porosity between 53.3 and 55.6 vol% which makes the obtained composite convenient for application as diesel particulate filter material. The presence of mullite affected four key thermo-mechanical properties which determine the thermal shock resistance of cordierite-mullite composite. The best thermal shock resistance was measured in composite containing 75 wt% of mullite. It was a result of improved thermal conductivity (1.081 W/mK) and bending strength (3.62 MPa) and relatively low values of coefficient of thermal expansion (3.8 × 10−6 K−1) and elastic modulus (2.27 GPa).

Debonding of zirconia cantilevered resin-bonded fixed dental prostheses (RBFDPs) remains the main treatment complication, therefore, the present in vitro study aimed to evaluate the effect of different surface pretreatments on the bonding of zirconia RBFDPs. Eighty milled zirconia maxillary central incisors, with complementary zirconia cantilevered RBFDPs, were randomly subjected to four different surface pretreatments (n = 20): as-machined (AM); airborne-particle abraded (APA); coated with nanostructured alumina coating (NAC); incisor air-abraded and RBFDP coated (NAC_APA). After bonding, half of each group (n = 10) was stored in deionized water (150 days/37 °C), thermocycled (37,500 cycles, 5–55 °C), and cyclically loaded (50 N/1.2 × 106). Load-bearing capacity (LBC) was determined using a quasi-static test. Additionally, finite element analysis (FEA) and fractography were performed. t-test and one-way ANOVA were used for statistical-analysis. Before aging, the NAC group provided superior LBC to other groups (p < 0.05). After aging, the AM specimens debonded spontaneously, while other groups exhibited comparable LBC (p ˃ 0.05). The FEA results correlated with the in vitro experiment and fractography, showing highly stressed areas in the bonding interface, cement layer, and in RBFDP’s retainer wing and connector. The NAC RBFDPs exhibited comparable long-term bonding performance to APA and should be regarded as a zirconia pretreatment alternative to APA.

Zirconia restorations, which are fabricated by additive 3D gel deposition and do not require glazing like conventional restorations, were introduced as "self-glazed" zirconia restorations into dentistry. This in vitro investigation characterized the surface layer, microstructure and the fracture and aging behavior of "self-glazed" zirconia (Y-TZP

Objective In vivo aging of biomedical grade 3Y-TZP ceramics in the oral environment was assessed and compared to artificially accelerated in vitro hydrothermal aging extrapolations at 37 °C. Methods 88 discs were pressed and sintered (1450–1500 °C) from two commercial 3Y-TZP compositions containing 0.25% Al2O3 to generate finer- and coarser-grained specimens. As-sintered (AS) and airborne-particle abraded (APA; 50 μm Al2O3) surfaces were investigated. In vivo aging was performed by incorporating specimens in lingual flanges of complete dentures of 12 edentulous volunteers who wore them continuously for up to 24 months. For comparison, in vitro hydrothermal aging at 134 °C was also performed and analysed by XRD and (FIB)-SEM. Data was statistically analysed with linear regression models. Results Finer and coarser-grained specimens exhibited statistically insignificant differences in aging in vivo. The monoclinic fraction (Xm) on AS surfaces abruptly increased to ∼8% after 6 months. The aging process then proceeded with slower linear kinetics (∼0.24%/month). After 24 months, Xm reached ∼12%. The calculated maximum transformed layer was 0.385 μm representing one layer of transformed grains. APA surfaces were highly aging resistant. The initial Xm of ∼4.0% linearly increased by 0.03%/month in vivo. In vitro aging exhibited an initial induction period, followed by linear aging kinetics. Coarser-grained AS surfaces aged significantly faster than fine-grained (2.41%/h compared to 2.16%/h). APA discs aged at a rate of 0.3%/h in vitro. Microcracking within a single grain and pull-out of grain clusters were observed on aged AS surfaces. Significance Biomedical grade 3Y-TZP was susceptible to in vivo aging. After 2 years in vivo, the aging kinetics were almost 3-times faster than the generally accepted in vitro-in vivo extrapolation.

The generated process losses such as broken ware from shaping, if not recycled internally, are considered as waste. Furthermore, the collected process losses are provided to external recycling companies or waste disposal facilities. This study investigated the recycling potential of waste alumina powder, which was accumulated during industrial machining of the ceramic green body. The samples containing up to 20 dwb. % (dwb – weight amounts based on dry matter) of powdered waste alumina were prepared by slip casting method and conventionally sintered at various sintering conditions according to Box-Behnken design. Sintered samples were characterized for density, microstructure, hardness, and indentation fracture toughness and compared with samples made of pure commercial alumina. The study shows that the addition of waste alumina up to 20 dwb. % sintered at higher sintering temperature with dwell time 1–3 h did not negatively affect the hardness, nor the indentation fracture toughness of the sintered samples. The enabled recycling potential of waste alumina powder can have direct positive environmental impact, although economic benefits cannot be ignored.

The heat treatment of dental alloys prior to porcelain application/veneering has been proposed as a way to ensure sufficient oxide scale and to promote the porcelain’s adherence in porcelain-fused-...

Understanding aqueous dispersion, rheological properties and colloidal stabilisation mechanisms of hierarchically assembled ceramic powders is important for progress in the fields of catalysis, separation and/or adsorption. The present study was designed to evaluate the rheological and sedimentation behaviour of highly loaded aqueous suspensions (up to φA = 0.126) containing AlN-powder-hydrolysis-derived, micron-sized, mesoporous, gamma alumina (MA) particulates with a high surface area (∼180 m2/g) dispersed with sodium polyacrylate (NaPAA). The as-prepared suspensions were prone to sedimentation and segregation. However, when divalent cations (Mg2+, Ca2+) or cellulose nanofibers were added, the formation of interparticle association networks in the aqueous suspensions containing MA particles was triggered, facilitating their long-term resistance to sedimentation lasting more than 12 weeks.

3Y-TZP ceramics are commonly used in restorative dentistry for fixed partial dentures, implants, abutments and root posts. The stress-induced transformation-toughening mechanism leads to improved mechanical properties advocating 3Y-TZP to be ground or sandblasted for better clinical performance. Such invasive mechanical treatments facilitate the additional surface strengthening as a result of the residual compressive stresses, but the exact origin is not completely understood. This study evaluated the effect of continuous impacting between 3Y-TZP root posts during 500 -h-long shaking on the extent of (sub)surface microstructural changes affecting the fracture strength. With an increase of the shaking time the surface roughness decreased, where the grains were flattened and partially spalled. The observed 6-micrometre-thick altered subsurface region containing compressive residual stresses contributed to a systematic increase in the forces of fracture within the sample population; however, only for those containing the surface type of critical flaws that were in the form of mould imprints.

B has been proposed to extend persistent luminescence from minutes to > 10 h in Eu, Dy, and B co-doped Sr4Al14O25 (S4A7EDB) by facilitating the incorporation of Eu2+ and Dy3+ into adjacent Sr sub-lattice sites and enabling energy transfer between them. To evaluate additional influences of B on the kinetics of microstructural evolution and dopant distribution that support afterglow in S4A7EDB, the effect of heating rates to 1300 °C is compared for spark-plasma sintering and conventional sintering, with and without the addition of B2O3. Analysis of the microstructure and elemental distribution, by a combination of imaging, WDS, and CL in the SEM, XRD, dilatometry, and STEM-EELS, reveals that when the diffusivity of Eu and Dy is increased, Eu and Dy segregate to the intergranular phase. The partitioning of Eu and Dy concentrations to below their solubility limit in the grains appears to be essential to material structure enabling longer afterglow.

The percolation threshold for electrical conductivity of a binary system of electrically insulating and conducting spheres was studied theoretically to yield a roadmap for electrically conductive ceramic composites. Although the crystal grains in such matrix are of irregular shape, the spheres of different sizes are used in the model to keep calculations tractable, where insulating spheres (matrix) are considered to be much larger than conducting ones (filler). This difference influences spatial distribution of conducting spheres. Besides the rough analytical estimation of the percolation threshold, we also use the Metropolis algorithm. The latter must be adapted for the system of conducting spheres which are positioned at the surface of large insulating spheres. We give a suggestion for the modification of this algorithm. Analytical estimation and Metropolis method give qualitatively similar dependence of the percolation threshold on the radii of geometrical objects, but there are significant quantitative differences in the results.

Hydraulic calcium silicate-based cements (HCSCs) have become a superior bioceramic alternative to epoxy-based root canal sealers in endodontics. A new generation of purified HCSCs formulations has emerged to address the several drawbacks of original Portland-based mineral trioxide aggregate (MTA). This study was designed to assess the physio-chemical properties of a ProRoot MTA and compare it with newly formulated RS+, a synthetic HCSC, by advanced characterisation techniques that allow for in situ analyses. Visco-elastic behaviour was monitored with rheometry, while phase transformation kinetics were followed by X-ray diffraction (XRD), attenuated total reflectance Fourier transform infrared (ATR-FTIR), and Raman spectroscopies. Scanning electron microscopy with energy-dispersive spectroscopy, SEM-EDS, and laser-diffraction analyses was performed to evaluate the compositional and morphological characteristics of both cements. While the kinetics of surface hydration of both powders, when mixed with water, were comparable, an order of magnitude finer particle size distribution of RS+ coupled with the modified biocompatible formulation proved pivotal in its ability to exert predictable viscous flow during working time, and it was more than two times faster in viscoelastic-to-elastic transition, reflecting improved handling and setting behaviour. Finally, RS+ could be completely transformed into hydration products, i.e., calcium silicate hydrate and calcium hydroxide, within 48 h, while hydration products were not yet detected by XRD in ProRoot MTA and were obviously bound to particulate surface in a thin film. Because of the favourable rheological and faster setting kinetics, synthetic, finer-grained HCSCs, such as RS+, represent a viable option as an alternative to conventional MTA-based HCSCs for endodontic treatments.

Statement of problem Computer-aided design and computer-aided manufacturing (CAD-CAM) technologies have provided alternatives to lost-wax casting for the fabrication of titanium frameworks in metal-ceramic fixed dental prostheses (FDPs). The findings on varying metal surface characteristics resulting from application of different fabrication technologies indicate a need to reevaluate the traditional titanium surface conditioning protocols. Purpose The purpose of this in vitro study was to investigate the effects of surface airborne-particle abrasion (APA) and bonding agent application on the porcelain bond to titanium dental alloys fabricated by subtractive computer numerical controlled (CNC) milling and by additive selective laser melting (SLM) methods. Material and methods Eight groups of Ti-6Al-4V substrates (n=11) were fabricated—half of them by CNC milling and half by SLM. The groups represented a fully crossed experimental protocol of APA with 110-μm Al2O3 particles under a pressure of 0.2 MPa (intact—controls or abraded) and bonding agent application (with or without bonding agent) for the CNC milled and SLM titanium substrates. Ultra-low fusing dental porcelain was applied to the differently prepared titanium substrates, and the titanium-ceramic bond strength was determined by a 3-point bend test according to the International Organization for Standardization (ISO) standard 9693-1:2012. Average profile roughness (Ra) values were obtained for intact and APA titanium substrates fabricated by CNC milling and by SLM. Representative titanium-ceramic interfaces were analyzed by using a field emission scanning electron microscope (FE-SEM) and energy dispersive spectroscopy (EDS). Titanium-ceramic bond strength data were analyzed statistically by 3-way ANOVA and the Tukey HSD test. Ra data were analyzed by 2-way ANOVA, followed by regression analyses (α=.05). Results The method applied for the digital fabrication of titanium (either subtractive CNC milling or additive SLM) did not affect the titanium-ceramic bond (P=.247). APA (P Conclusions A protocol comprising APA and application of a bonding agent ensures the highest porcelain bond strength to both CNC milled and SLM titanium, with the obtained values being well above the minimal value for metal-ceramic systems as specified by ISO 9693-1:2012.

Zirconia-based (3Y-TZP) dental implants are being introduced as an alternative to established titanium counterparts. As 3Y-TZP’s bioinertness poses a challenge to osseointegration, modifications of the implants’ surface are necessary. Roughening is a common method to improve the cell response and should ideally combine micro- and nano-scale features. Here we show a simple synthesis procedure for the nano-roughening of sandblasted 3Y-TZP by precipitation of a nanostructured alumina coating. As-modified surfaces were characterised regarding their morphology and phase composition, roughness, wetting behaviour and zeta potential, and correlated to the behaviour of human osteoblasts and Staphylococcus aureus bacteria. Osteoblasts were successfully cultured on all surfaces regardless of their modification. Surfaces exhibiting a combination of micro- and nano-roughening performed best regarding initial attachment and proliferation of osteoblasts. Alumina-coated surfaces also limited the bacterial adhesion.

Bonding surface pretreatment of zirconia ceramic dental restorations with a nanostructured alumina coating (NAC) provides a substantially stronger and durable bond than clinically established air-p...

This study was designed to better understand the microstructural and phase evolution of lead-free sodium potassium niobate based piezoceramics with a nominal composition (K0.5Na0.5)0.99Sr0.005NbO3 (KNNSr) during pressure-less spark plasma sintering followed by post-annealing in oxygen. The as-sintered samples were dark-coloured and electrically conductive as a result of partial reduction of Nb5+ to Nb4+ and formation of oxygen vacancies confirmed by X-ray photoelectron and Raman spectroscopy. The Rietveld refinement analysis showed that the as-sintered samples contained two perovskite phases with monoclinic Pm unit cell and slightly different unit-cell parameters. The microstructure with sub-micrometre-sized grains unambiguously confirmed that rapid heating and short dwell time hindered the grain growth. We found that post-annealing the samples at 950 °C in oxygen led to improvement in functional properties. The samples became white-coloured, the both perovskite unit cells decreased as a result of re-oxidation, while the microstructure remained essentially unchanged. The KNNSr sintered at nominal sintering temperature of 1300 °C for 3 min and post-annealed possessed a relative density of 88% and dielectric and piezoelectric properties similar to those of the conventionally sintered samples. Our findings contribute to the understanding of pressure-less spark plasma sintering of sodium potassium niobate-based materials and suggest that arrested grain growth and minimisation of alkali evaporation not necessarily lead to dense ceramic.

This study aims to evaluate the recycling potential of solid waste alumina powder (WAP) by utilization of the two-step sintering (TSS) process. For the study, WAP was collected as an industrial scrap after the machining process for the formation of green alumina compacts. The alumina samples were prepared according to the slip casting method by preparing suspensions containing commercial alumina with 0.8 μm average particle size and by adding up to 20 dwb. % (i.e., expressed on a dry weight basis) of WAP with 3.4 μm average particle size. The samples were sintered at optimized TSS conditions and compared with conventional one-step sintering (OSS) by conducting morphological analyses. The average grain size (AGS) was determined from the obtained field emission scanning electron microscopy (FESEM) images, while the sample porosity was calculated based on apparent densities. The obtained micrographs after TSS implementation revealed a partially textured microstructure. Furthermore, a comparison of the mechanical properties of alumina samples lacking or containing 20 dwb. % of WAP obtained after sintering is presented. The indentation fracture toughness (~3.2 MPa m1/2) and Vickers hardness data (~14.5 GPa) showed a positive effect of adding WAP to alumina samples. The slightly improved mechanical properties of ceramic samples containing waste alumina are a consequence of lower porosity, which is due to the remaining sintering additives in WAP. The collected results demonstrate the possibility of using TSS for sintering ceramic materials that contain WAP.

Freeze-casting is a powerful consolidation technique for the fabrication of highly porous and layered-hybrid materials, including ceramic-metal composites, and porous scaffolds for catalysis, bone substitutes and high-performance membranes. The aqueous suspensions to be freeze-casted usually contain dense particles facilitating macroporous, layered ceramics with dense (nonporous) struts. In the present study, hierarchical macro-mesoporous alumina (HMMA) monoliths were successfully prepared by freeze-casting of aqueous suspensions containing hierarchically-assembled, mesoporous γ‒Al2O3 (MA) powder and cellulose nanofibers (CNF). As-prepared monoliths were ultra-porous (93.1–99.2%), had low densities (0.01–0.25 ​g/cm3), and displayed relatively high surface areas (91–134 ​m2/g), but were still remarkably rigid with high compressive strengths (up to 52 ​kPa). Owing to the columnar porosity and mesoporous nature of the struts the freeze-casted HMMA monoliths exhibited high permeability and high thermal insulation, the latter ranging from 0.039 ​W/m∙K to 0.071 ​W/m∙K, depending on pore orientation.

Statement of problem The debonding of zirconia cantilevered resin-bonded fixed dental prostheses remains a technical complication because zirconia’s chemical inertness impedes adequate surface preparation for bonding. Limited clinical evidence on the performance of various pretreatment methods for the bonding surface of zirconia resin-bonded fixed dental prostheses is available. Purpose The present prospective, randomized, controlled clinical trial aimed at evaluating the performance of zirconia resin-bonded fixed dental prostheses prepared with nanostructured alumina coating. Material and methods The study adopted a prospective, randomized, controlled, double-blind (patients, operator) design to compare the performance of nanostructured alumina coating with that of conventional airborne-particle abrasion. Twenty-seven healthy patients needing a replacement of a missing maxillary or mandibular central or lateral incisor were screened and rated to be eligible, and 31 zirconia cantilevered resin-bonded fixed dental prostheses were randomly allocated into 1 of 2 groups. The first group (n=15), where the restoration bonding surface was airborne-particle abraded with 50-μm alumina, served as a control group. In the second group (n=16), the restorations were pretreated with nanostructured alumina coating. Treatment and data collection were standardized. The primary outcome evaluated was the survival of the RBFDPs as defined by the restoration not debonding. The Kaplan-Meier analysis of cumulative survival was performed, and nonparametric tests were used to determine patient-specific differences between both study groups (age, sex, restored arch, tooth replaced, bonding surface area) (α=.05). Retainer wing surfaces of debonded resin-bonded fixed dental prostheses were inspected under a scanning electron microscope. Results Within a mean ±standard deviation observation period of 22.4 ±7.7 months (minimum, 8.3; maximum, 37.9 months), 3 debondings occurred, and the survival rate was 90.3%. The survival rate was 93.8% for the nanostructured alumina coating and 86.7% for the control group, with no statistically significant differences (log-rank, P=.54). No patient-specific differences were found between study groups (P>.05). As per the scanning electron micrographs, the majority of the nanostructured alumina-coated surfaces had large areas of nanostructured alumina residue, whereas the airborne-particle abraded surfaces exhibited predominantly adhesive failure with less cement residue. Conclusions Over a mean observation period of 2 years, both zirconia pretreatments showed promising and comparable clinical results; therefore, nanostructured alumina coating could be regarded as a viable alternative pretreatment method to airborne-particle abrasion.

Statement of problem Monolithic zirconia restorations have been evaluated with in vitro studies, but limited clinical evidence of their longevity and reliability is available. Purpose The purpose of this clinical study was to evaluate the clinical performance of posterior multiunit glazed monolithic zirconia fixed dental prostheses. Material and methods A total of 20 participants received 33 monolithic posterior zirconia fixed dental prostheses (Zolid white; Amann Girrbach AG) with minimally invasive preparations. Bilaterally supported fixed dental prostheses with a connector area of at least 9 mm2 were luted with resin-modified glass ionomer cement. The clinical evaluations were performed after 1 week, 6 months, and then annually after completion of the treatment. The biologic outcomes were evaluated by assessing the pocket depth, attachment level, plaque control, bleeding on probing, caries, and tooth vitality. Esthetics and the functional performance of the prostheses (color match, cavosurface marginal discoloration, anatomic form, marginal adaptation) were evaluated as per the rating scales of Cvar and Ryge. An analysis of survival was made by using the Kaplan-Meier method. Results After 39.8 ±16.7 months of observation, the overall survival rate of the monolithic zirconia multiunit posterior prostheses was 93.9%. No caries were found on the abutment teeth, signs of gingivitis were noted in 1 participant after 24 months, and increased probing depths of the abutment teeth were detected in 5 prostheses (15.1%). No loss of retention was detected. Two prostheses had to be replaced: 1 because of a biologic complication and 1 because of a technical complication. The remaining 31 prostheses received Alfa scores for marginal adaptation, cavosurface marginal discoloration, and caries. Twenty-seven (87.1%) prostheses were rated as Alfa and 4 (12.9%) as Bravo for anatomic form. The color match was noted as Alfa in 15 (48.3%) prostheses, and 16 (51.6%) were rated as Bravo. Conclusions Monolithic zirconia restorations demonstrated a reliable treatment option after medium-term clinical use for the replacement of missing posterior teeth.

We report on a new approach to increase the fracture resistance of endodontically treated teeth. We propose a preparation of horizontal internal plateau (IP) in dentine and the use of retentive zir...

International audience; Phosphorus incorporation into carbon can greatly modify its chemical, electronic, and thermal stability properties. To date this has been limited to low levels of phosphorus. Now a simple, large‐scale synthesis of carbon–nitrogen–phosphorus (CNP) materials is reported with tunable elemental composition, leading to excellent thermal stability to oxidation and fire‐retardant properties. The synthesis consists of using monomers that are liquid at high temperatures as the reaction precursors. The molten‐state stage leads to good monomer miscibility and enhanced reactivity at high temperatures and formation of CNP materials with up to 32 wt % phosphorus incorporation. The CNP composition and fire‐retardant properties can be tuned by modifying the starting monomers ratio and the final calcination temperature. The CNP materials demonstrate great resistance to oxidation and excellent fire‐retardant properties, with up to 90 % of the materials preserved upon heating to 800 °C in air.

A facile and replicable stepwise chemical method was explored to synthesise magnetically separable Ru-based nanocatalyst. Structural investigation revealed that nanocatalyst is a hierarchical multiphase nanocomposite, consisting of highly magnetic Fe3C (and Fe) nanoparticles, distributed within a high-surface-area graphitic carbonaceous matrix, uniformly decorated with superiorly active catalytic ruthenium nanoparticles and clusters. The nanocatalyst showed an improved catalytic activity and selectivity for the hydro-deoxygenation of bio-resource-related compound eugenol when compared to the commercial Ru/C. In combination with ultrafast magnetic separation, it holds a good emerging potential in the valorisation of renewable resources and recycling of noble metals.

Purpose The aim has been to determine the effect of thermo-mechanical cycling on shear-bond-strength (SBS) of dental porcelain to Co–Cr and Ti-based alloys fabricated by casting, computer-numerical-controlled milling, and selective-laser-melting (SLM). Methods Seven groups ( n =22/group) of metal cylinders were fabricated by casting (Co–Cr and commercially pure-cpTi), milling (Co–Cr, cpTi, Ti-6Al-4V) or by SLM (Co–Cr and Ti-6Al-4V) and abraded with airborne-particles. The average surface roughness ( R a ) was determined for each group. Dental porcelain was applied and each metal–ceramic combination was divided into two subgroups — stored in deionized water (24-h, 37°C), or subjected to both thermal (6000-cycles, between 5 and 60°C) and mechanical cycling (10 5 -cycles, 60N-load). SBS test-values and failure modes were recorded. Metal–ceramic interfaces were analyzed with a focused-ion-beam/scanning-electron-microscope (FIB/SEM) and energy-dispersive-spectroscopy (EDS). The elastic properties of the respective metal and ceramic materials were evaluated by instrumented-indentation-testing. The oxide thickness on intact Ti-based substrates was measured with Auger-electron-spectroscopy (AES). Data were analyzed using ANOVA, Tukey's HSD and t -tests ( α =0.05). Results The SBS-means differed according to the metal–ceramic combination ( p p R a were dependent on the metal substrate ( p Conclusions Ti-based alloys are more susceptible than Co–Cr to reduction of porcelain bond strength following thermo-mechanical cycling. The porcelain bond strength to Ti-based alloys is affected by the applied metal processing technology.

We have investigated the magnetism of CoCrFeNiZr x (x = 0.4–0.5) eutectic high-entropy alloys (HEAs) in relation to their microstructure by XRD, SEM, magnetization, specific heat and electrical resistivity measurements. Two structural phases develop in the CoCrFeNiZr x HEAs, a Zr-free fcc solid solution and a Zr-containing C15 Laves-phase intermetallic compound, where in both phases magnetic transition elements Co, Cr, Fe and Ni substitute each other in a random-like manner. Relative fractions of the two phases change substantially with the Zr concentration. Microstructurally, the two phases form alternatively grown fine lamellar structure typical of eutectic alloys. In addition, bulky dendrites of the fcc solid solution form in large number for the x = 0.40 concentration and in small number for x = 0.45. Two magnetic structures coexist in the CoCrFeNiZr x HEAs. The first is a disordered ferromagnetic (FM) phase that develops in the interior of large dendrites of the fcc solid solution and in some larger lamellas of this phase. The second phase is superparamagnetic-like and originates from the remaining spins of the fcc solid solution fraction, located at the surfaces and in the interfaces, and from all spins of the C15 Laves-phase fraction. The relative magnitude of the disordered FM-state magnetization with respect to the superparamagnetic magnetization in the samples with different Zr concentration is predominantly determined by the volume fraction of the fcc bulky dendrites. There is no one-to-one relation between the two magnetic structures on one side and the two structural components of the CoCrFeNiZr x eutectic mixtures on the other side. The magnetism of multi-phase HEAs containing magnetic elements cannot be described as a compositional average of magnetic properties of the constituent phases.

The fracture resistance of glazed four-unit posterior dental bridges after mechanical fatigue testing and artificial ageing was evaluated. Thirty identical monolithic bridges were fabricated from “translucent” zirconia and divided into three groups of ten. The first group was monotonically loaded to fracture; the second group was dynamically loaded in water (0–300 N, 106 cycles) prior to fracture, while the third group was first subjected to accelerated ageing (in a diluted acetic acid solution at 134 °C for 12 h), then to mechanical fatigue and finally monotonically loaded to fracture. Two tested bridges did not survive 106 cycles of dynamic loading, one in Group 2 and one in Group 3. Mean monotonic fracture loads (N) were: Group 1: 547.3 ± 66.3, Group 2 (n = 9): 465.2 ± 118.0, and Group 3 (n = 9): 408.8 ± 58.9. According to the fractographic analysis the glaze embrittlement during artificial ageing and the stress corrosion during fatigue loading are proposed to be responsible for the reduced fracture resistance.

The yttrium-segregation-dependent phase partitioning and residual stress development that influence both the aging and the fracture behaviour in 3Y-TZP bioceramics were studied by sintering alumina-free 3Y-TZP, varying the sintering temperature and the time, to yield ceramics with identical grain size distributions, but with different phase compositions. The structure and stability of the resulting tetragonal phases, in the form of transformable, yttria-lean t-ZrO2 (YLZ) and non-transformable, yttria-rich t″-ZrO2 and/or t′-ZrO2 (YRZ), were studied by X-ray diffraction (XRD) and focused ion beam scanning electron microscopy (FIB-SEM). The accelerated aging kinetics was fitted to the Mehl-Avrami-Johnson equation. The specimen sintered at the lowest sintering temperature but with the longest dwell time contained the smallest and the largest concentrations of yttria in the YLZ and YRZ phases, respectively, as well as the largest amount of YRZ. As a consequence, it exhibited the fastest linear aging kinetics accompanied by more extensive micro-cracking of the transformed layer, as well as largest amount of intergranular fracture and the greatest resistance to fracture. These properties were ascribed to the increased transformability of the YLZ phase and the greatest propensity of the YRZ phase to relax the accumulated residual stresses during transformation (tetragonal to monoclinic, t–m) manifested as a ∼2.4% unit-cell volume increase. The observed relaxation provides additional understanding of the t–m transformation mechanism, which governs both the aging and fracture behaviour of 3Y-TZP. Statement of Significance A novel approach to understanding the effect of yttrium segregation on t–m transformation of 3Y-TZP zirconia bioceramics is presented. Carefully designed sintering strategy facilitated fabrication of ceramics with identical grain size distributions but with different yttrium concentrations. The influence of phase partitioning on stability and structure of transformable yttria-lean tetragonal phase (YLZ) and non-transformable yttria-rich phases (YRZ; t″– and t′–prime) and on the formation of residual stresses in YRZ were investigated. It is shown that YRZ phases are under compressive stresses in YLZ matrix, since a systematic relaxation after ageing was observed and explained for the first time. It puts additional perspective on the understanding of the t–m transformation mechanism ultimately governing both the ageing and fracture behaviour of 3Y-TZP.

Ruthenium catalyzed and magnetically heated hydrogenation of furfural in a slurry-type reactor is demonstrated in this work. We have developed a catalyst composed of magnetic nanoparticles which contains alumina carrying Ru nanoparticles on its surface. When exposed to an AC magnetic field, the conversion of furfural to furfuryl alcohol over the catalyst in the same time interval reached 95%, but only 63% when conventional heating was applied.

This study presents a fabrication route for an electrically conductive ZrO2−TiN ceramic nanocomposite with a nanoscale TiN phase occupying ≤30 vol% to improve the mechanical reinforcement of the zirconia matrix, and at the same time provide electrical conductivity to facilitate electro-discharge machining (EDM). The TiN nanoparticles were incorporated into a 3 mol% yttria-stabilized tetragonal zirconia (Y-TZP) powder, either by admixing a TiN nanopowder (MCP) or by using in-situ synthesis (ISS) via the forced hydrolysis of a titanyl sulphate aqueous solution and the direct nitriding of as-synthesized titania nanoparticles, followed by consolidation and rapid sintering in a spark plasma sintering (SPS) system. The initial phase composition and crystal structure of the as-synthesized powders and the sintered samples were characterized by transmission electron microscopy (TEM) and X-ray difraction (XRD). The influence of the different fabrication routes on the microstructural evolution, electrical and mechanical properties, and affinity for EDM were assessed using TEM, focused ion beam scanning electron microscopy (FIB-SEM, Vickers indentation, electrical conductivity measurements, and profilometry. The MCP synthesis route resulted in finer microstructures that are less prone to microstructural inhomogeneities; however, using the ISS route, it was possible to fabricate electrically conductive Y-TZP nanocomposites containing only 15 vol% of the TiN nanoparticulate phase. Both synthesis routes resulted in an increase of the fracture toughness with an increase of the TiN phase due to the nanoparticulate TiN reinforcement of the Y-TZP ceramic matrix via crack-bridging toughening mechanisms. As both synthesis routes yielded Y-TZP nanocomposites capable of successful EDM machining at a TiN content of ≥30 vol% for the MCP and ≥ 15 vol% TiN for the ISS, a possible mechanism was developed based on the microstructure evolution and grain growth.

Thin, non-retentive, monolithic restorations fabricated from novel translucent zirconia ceramics are widely used in contemporary dentistry. Because of the chemical inertness of zirconia, debonding of such restorations remains the main clinical complication. Limited evidence on the bonding performance of novel translucent zirconia exists, therefore, the present study aimed to evaluate, in vitro, the shear-bond strength (SBS) of translucent zirconia modified with a nanostructured alumina coating (NAC). The SBS of resin cement to translucent zirconia, materials containing 3, 4 or 5 mol.% of yttria modified with NAC, was measured and related to airborne-particle abraded (APA) zirconia surfaces. Half of each of the specimen groups (n = 20) were subjected to 37,500 thermocycles in water. In addition, to evaluate the effect of NAC on thin translucent zirconia discs (n = 10), the translucency parameter (TP) was measured and compared with APA. The results were statistically analyzed using a t-test and one-way ANOVA. NAC provided higher resin-zirconia SBS compared to APA, not affecting the zirconia optical properties. APA, on the other hand, lowered TP for all types of zirconia. NAC did not impair the mechanical or optical properties of translucent zirconia materials and should be regarded as a zirconia pretreatment alternative to APA.

Hierarchical macroporous–mesoporous alumina (HMMA) and hierarchical mesoporous alumina (HMA) monolithic green bodies were fabricated by cold isostatic pressing (CIP) of mesoporous alumina (MA) powder, which was prepared by a quick, facile and very pure synthesis route that involved exploitation of the naturally self-driven aluminum nitride powder hydrolysis. The hierarchically self-assembled, nanocrystalline, yet micron-sized MA powder exhibited a controlled porosity, a fine crystallite size, a relatively large surface area and large pore volumes. The textural characteristics of the MA powder were analyzed, while the effect of the consolidation pressure on the pore size evolution, mechanical and permeability properties of the consolidated HMMA and HMA monoliths were investigated. At the lowest CIP pressures, the HMMA monoliths possessed favorable permeability characteristics with Darcian permeability constants up to 2 × 10−15 m2, also exhibiting a low thermal conductivity (≥0.185 W/mK), sufficient flexural strength (≥6 MPa) with an accessible porosity of ≤65%, a pore volume of ≤0.69 cm3/g and a macropore opening diameter of ≤370 nm at a constant mesopore opening diameter of about 4.5 nm. Increasing the CIP pressure resulted in the shrinkage of the macropores and a consequent suppression of the permeability characteristics; however, the flexural strength of the HMA monolith CIPed at 800 MPa increased to 51 MPa, which is the highest reported strength for a dry-pressed, binderless ceramic green body with an accessible porosity of 42% and a theoretical density of 44.3%.

Translucent, high-performance, mullite ceramics with anisotropic grains were prepared by the spark plasma sintering (SPS) of a powder mixture consisting of commercial mullite powder, which already contained small amounts of alumina (θ and α) and silica (cristobalite) (≤3 wt% in total), to which 2 and 1 wt% of yttria and amorphous silica was admixed, respectively. The combination of low-viscosity Y2O3–Al2O3–SiO2 transient liquid formation and SPS sintering provided enhanced densification, also provoking anisotropic grain growth (which became exaggerated after 20 min of SPS dwell time), at a relatively low sintering temperature of 1370°C. In this way, it was possible to meet the conflicting demands for obtaining a dense mullite ceramic with anisotropic grains, ensuring good mechanical properties, while preserving a noticeable light transmittance. In terms of mechanical and optical properties, the best results were obtained when SPS dwell times of 5 and 10 min were employed. The as-sintered samples possessed densities in the range 3.16–3.18 g/cm3, anisotropic grains with an aspect ratio (AR) of 7 and a grain thickness of approximately 0.45 μm, a flexural strength between 350 and 420 MPa, a Vickers indentation toughness and a hardness of approximately 2.45 MPa·m1/2 and 15 GPa, respectively, and an optical transmittance of between 30% and almost 50% in the IR range.