Zircon Structure Research Articles

Derivation of the equation of state for a superionic conductor

The purpose of this article is an analytical consideration of the features of the physical characteristics of the quantities of a hightemperature ceramic solid oxide superionic conductor, using the example of an oxygen pump made of stabilized zirconia. Based on the consideration of an elementary axial section of a superionic tube with geometric data on the length, thickness, and diameter of the tube, an equation was obtained that relates all adjustable quantities of an oxygen pump in the entire range of oxygen dosing, in particular, to select the geometric dimensions of the device and the optimal ratios of controlled quantities. The derivation of such an equation for the pumping section of an oxygen pump is based on a number of assumptions as for an idealized oxygen pump. The currentvoltage characteristic of an oxygen pump in the region of deep pumping, associated with the appearance of electronic conductivity of the ceramics of the pumping section of the oxygen pump, leading to its destruction, electrochemical aging or degradation, has been studied. It is substantiated that the volt-ampere characteristic of the oxygen pump is the only informative curve, which is used to judge the correct mode of operation of the superionic pump and prevent the onset of electrochemical degradation. When developing a research method and setting problems for a ceramic oxide superionic conductor, a number of assumptions were taken into account, as for an idealized electrolyte. The considered solid oxide superionic conductor or solid electrolyte is a ceramic material in the form of tubes, test tubes, tablets, initially containing impurity cations of lower valence, such as calcium, yttrium, scandium, than zirconium. It is these impurity cations that create the presence of vacancies or holes in the solid cubic structure of zirconium dioxide. Through these vacancies, under the influence of external factors, high temperature and direct current electric field, only oxygen anions will be transported. The research method is based on the measurement of the electromotive force, which is recorded at the boundary section: air/electrode/superionic, unambiguously related mathematically to the oxygen concentration in the air flow. Mathematical formulas are given for calculating the desired oxygen concentration depending on various external conditions. Theoretical conclusions and substantiations on the possibility of using the phenomenological transport properties of a superionic conductor under production conditions are presented.

Relationship between bond characteristics and microwave dielectric properties of REVO4 (RE = Yb, Ho) ceramics

Two novel low- ε r REVO 4 (RE = Yb, Ho) microwave dielectric ceramics with the symmetry of the zircon structure, space group I 4 1 / amd , were prepared using the solid-state method. Dense REVO 4 (RE = Yb, Ho) ceramics sintered at 1200 °C and 1160 °C performed ε r ∼ 12.3 ± 0.1 and 13.3 ± 0.1, Q × f ∼ 28,200 ± 300 GHz and 24,100 ± 300 GHz, τ f ∼ −18.8 ± 0.5 ppm/°C and −17.4 ± 0.5 ppm/°C, along with thermal expansion coefficient ( α L ) of 9.0 ppm/°C and 8.1 ppm/°C, respectively. Bond valence results indicated that the slightly rattling RE 3+ cations at the A-site and compressed V 5+ at the B-site occurred in both ceramics. The positive deviations ( Δε r ) of porosity corrected ε r (Corr) from those calculated by the Clausius-Mosotti equation ε r (C-M) , 8.1% for YbVO 4 and 17.7% for HoVO 4 , were observed, implying that the rattling effect of RE 3+ in dodecahedral A-site were greater than those of compressed V 5+ in tetrahedral B-site. Rattling effect also led REVO 4 (RE = Yb, Ho) to develop higher ε r , and smaller τ ε and τ αm , then closer to zero τ f values than other zircon-structured REVO 4 (RE = Ce, Nd, Sm, Eu) ceramics with large negative τ f . The differences in sintering temperature and microwave dielectric performance of both ceramics were discussed using the packing fraction, full width at half maximum (FWHM) of Raman modes and Phillips-Van Vechten-Levine (P–V-L) theory.

Morphology, Structure, and Composition of Zircon from Metasandstones of the Alkesvozhskaya Sequence (Polar Urals)

A description of the features of morphology, internal structure, and analysis results of Th/U and Zr/Hf ratios in zircons from sandstones of the gold-bearing Alkesvozhskaya sequence, located at the basement of the Paleozoic section in the Subpolar Urals, is presented. It has been established that most of the studied zircons are primary igneous grains of the first weathering cycle. The detrital zircon source was probably in formations close in age, underlying or located nearby felsic and basic volcanics of igneous complexes of different stages of formation of Timanides-protouralides, associated granitoids, and intrusive mafic formations. Small part of well-rounded zircon Pre-Riphean grains can be redeposited from the Riphean metasedimentary formations, which, in turn, inherited it from the rocks of the ancient basement of the East European Platform.

Fatigue resistance of monolithic and multilayer zirconia crowns using veneer layering or CAD-on technique.

This study aims to evaluate the fatigue resistance of monolithic zirconia (Yz) and multilayer ceramic structures using the CAD-on technique in different thicknesses. Fifty (N=50) standardized single crowns preparations were made in fiberglass-reinforced epoxy resin (NEMA grade G10), digitalized, and restorations were machined in CAD-CAM, composing 5 groups (n= 10): Control: 1.5 mm (milled zirconia framework + manual layered porcelain); Yz monolithic 1.5 mm; Yz monolithic 1.0 mm; CAD-on 1.5 mm; and CAD-on 1.0 mm (milled zirconia framework 0.5 mm thickness bonded by a low fuse ceramic to a milled lithium disilicate layer of 1.0 mm or 0.5 mm, respectively). The G10 bases were conditioned with 10% hydrofluoric acid; the crowns were air abraded with 110 μm alumina particles; and then luted onto each other with self-adhesive resin cement. A cyclic fatigue test was performed (initial load: 400N for 10,000 cycles, frequency of 20 Hz, step size of 200N) until failure, and the data was submitted to a survival statistical analysis. No failures were observed at Yz monolithic 1.5 mm. High and similar performance was observed for Cad-On groups and Yz monolithic 1.0 mm. The control group depicted the worst behavior. The Weibull modulus of CAD-on 1.5 mm was higher than the control while being similar to the other conditions. Both the monolithic systems and the CAD-on technique showed high and similar fatigue fracture behavior and survival rates, which were also higher than the control bilayer system. Both systems reduced the occurrence of delamination failures, making them suitable for clinical use.

PROVENANCE AND AGE CONSTRAINTS OF THE RIPHEAN SANDSTONES FROM THE IVANOVSKY GRABEN (THE KOLA PENINSULA) BASED ON THE U-Pb LA-ICP-MS DATING AND RAMAN SPECTROSCOPY OF DETRITAL ZIRCON

The results of U-Pb LA-ICP-MS dating of 150 detrital zircon grains from the Precambrian (Riphean?) sandstones of the Kildin group on the coast of the Ivanovka Bay (northeastern Kola Peninsula) are presented. A group of three youngest grains yielded constraint on the sandstone maximum depositional age of 1179±45 Ma. Detrital zircon age distribution is dominated by three maximums of 1.9, 2.4 and 2.7 Ga. The authors consider two complementary scenarios of interpretation of the data obtained. The first scenario involves the contribution of distant provenance out of granitoids in the Lapland-Kola orogen (~1.9 Ga) and adjacent areas of the Kola-Karelia region (~2.7 Ga), Imandra-Varzuga structure (~2.4 Ga), and Sveconorwegian belt (~1.2 Ga); the off-Baltic (Greenland?) sources of the detrital zircon also cannot be excluded. According to the second scenario, the Ivanovsky graben received zircons also from the proximal sources – sialic complexes formed upon melting of granite-gneiss substratum of the upper crust of the Murmansk craton during largescale episodic mafic magmatism 1.86, 2.50 and 2.68 Ga. The Raman spectroscopy showed that about 25 % of the analyzed detrital zircon grains experienced a 1.4-Ga-old thermal effect which did not lead to Pb losses but partially restored the crystalline structure of zircon. This result can be used as an additional constraint in the detailed provenance analysis of the northeastern East European Platform sedimentary basins and is indicative of 1.4-Ga-old large-scale magmatic events related to the breakup of the supercontinent Nuna.

Binder jetting printing of zirconia structures via grading powder and epoxy binder

ABSTRACT The binder jetting (BJ) process shows significant superiority in manufacturing ceramic parts with a complex structure. The performance of the green part is highly reliant on the features of raw materials. A kind of grading zirconia powder M0 was designed, its intrinsic characteristics including microstructure, size and size distribution, bulk density, porosity, hall velocity and spread performance were systematically evaluated. The design principles of M0 were illustrated in detail. Meanwhile, a kind of organic epoxy binder was prepared and its properties including density, viscosity and surface tension were estimated. The jet ability of binder was evaluated quantitatively. The compatibility and bonding strength between binder and powder were assessed through contact angle, infiltration time and microstructure of M0. As a result, M0 and epoxy binder can be successfully applied in the printer, the zirconia structure with good dimensional accuracy (shrinkage rate ≤ ±2%) and flexible strength (1.74 ± 0.28 MPa) were achieved.

Effect of Sintering Temperature on the Properties of Calcia-Stabilized Zirconia (Ca-SZ) Bioceramics

This paper highlights the study on effect of sintering temperature on the morphologies and compressive strength of zirconia ceramics doped with calcium oxide (CaO) as stabiliser to enhance the zirconia structure undergo sudden phase transformation. CaO reportedly has good stability in cubic phase at all temperature, which open up a new possibility for new material to evolve for zirconia ceramic dental application. CaO synthesis from calcium nitrate tetrahydrate (Ca(NO3)2.4H2O) is used as metal precursor to produce Calcia-Sabilized Zirconia (Ca-SZ). 8 wt. % of Ca(NO3)2.4H2O and 92 wt. % of zirconium oxide (ZrO2) mixed and stirred together with ethanol as solvent and sintered at temperatures 1200, 1300 and 1400°C. Surface morphologies are investigated by Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX) element analysis, X-ray Diffraction (XRD) for composition studies, as well as compressive strength to figure out the mechanical properties of Ca-SZ sample. Increment in sintering temperature enhance the surface morphologies, the phase of Ca-SZ become intensified and transformed from monoclinic to tetragonal ZrO2 also flexural strength increases as well. The compressive strength recorded the highest value of 4537 MPa for Ca-SZ at temperature of 1400°C. The optimal temperature of Ca-SZ suitable for dental application was 1400°C due to the good morphologies and mechanical properties suitable for teeth restoration. The development of Ca-SZ can establish a pathway as an alternative material for dental applications.

Microstructural changes and Pb mobility during the zircon to reidite transformation: Implications for planetary impact chronology

Abstract Impact events modify and leave behind a complex history of rock metamorphism on terrestrial planets. Evidence for an impact event may be recorded in physical changes to minerals, such as mineral deformation and formation of high P-T polymorphs, but also in the form of chemical fingerprints, such as enhanced elemental diffusion and isotopic mixing. Here we explore laboratory shock-induced physical and chemical changes to zircon and feldspar, the former of which is of interest because its trace elements abundances and isotope ratios are used extensively in geochemistry and geochronology. To this end, a granular mixture of Bishop Tuff sanidine and Kuehl Lake zircon, both with well characterized Pb isotope compositions, was prepared and then shocked via a flat plate accelerator. The peak pressure of the experiment, as calculated by the impedance matching method, was ~24 GPa although a broader range of P-T conditions is anticipated due to starting sample porosity. Unshocked and shocked materials were characterized via scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and Raman spectroscopy. These methods show that the starting zircon material had abundant metamict regions, and the conversion of the feldspar to glass in the post-shock material. Analyses of the shocked product also yielded multiple occurrences of the high-pressure ZrSiO4 polymorph reidite, with some domains up to 300 μm across. The possibility of U-Pb system disturbance was evaluated via laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and secondary ion mass spectrometry (SIMS). The isotopic data reveal that disturbance of the U-Pb geochronometer in the reidite was minimal (<2% for the main U-Pb geochronometers). To better constrain the P-T conditions during the shock experiment, we complement impedance matching pressure calculations with iSALE2D impact simulations. The simulated results yield a range of P-T conditions experienced during the experiment and show that much of the sample may have reached >30 GPa, which is consistent with formation of reidite. In the recovered shocked material, we identified lamellae of reidite, some of which interlock with zircon lamellae. Reidite {112} twins were identified, which we interpret to have formed to reduce stress between the crystal structure of the host zircon and reidite. These two findings support the interpretation that shear transformation enabled the transition of zircon to reidite. The size and presence of reidite found here indicate that this phase is probably common in impact-shocked crustal rocks that experienced ~25 to ~35 GPa, especially when the target material has porosity. Additionally, shock loading of the zircon and transformation to reidite at these pressures in porous materials is unlikely to significantly disturb the U-Pb system in zircon and that the reidite inherits the primary U and Pb elemental and isotopic ratios from the zircon.

Material extrusion additive manufacturing of zirconia parts using powder injection molding feedstock compositions

The aim of this study is the evaluation of powder injection molding (PIM) binder compositions for the material extrusion (MEX) additive manufacturing of zirconia parts. Four commercial PIM binder compositions were selected and mixed with 45 vol% of yttria-stabilized zirconia powder. Due to the brittle characteristic of the obtained ceramic feedstocks, a screw based pellet printing head was used for printing dense zirconia structures. To compare 3D printing performance, additionally a commercially available zirconia filament was used in this study. Application of PIM binder compositions was limited either due to phase separation during processing, poor printing performance or delamination during solvent debinding. Only one of the PIM based feedstock compositions could be successfully printed, debound and sintered. A ring-on-ring setup was used to investigate the equibiaxial flexural strength after sintering for both pellet and filament printed disks. For benchmarking, cold isostatic pressed (CIP) ceramic discs were fabricated by commercial, ready-to-press, zirconia powder. The ring-on-ring results showed a low Weibull modulus (3 <m<5) for all samples, regardless of the manufacturing process. Fractography on selected samples demonstrated, that the origins of failures are close to the area of the loading ring which indicates an uneven stress distribution along the contact area between the setup and the sample. The pointwise stress concentration is the reason for the immature failure of the samples and the low Weibull modulus. The characteristic strength and 90% confidence intervals were used to compare the strength of ceramic samples produced via additive manufacturing and CIP. Almost similar mechanical properties were obtained for the CIP pressed (σ0 = 657 MPa) and filament printed (σ0 = 531 MPa) samples. However, a lower strength was obtained by the pellet printed samples based on commercial PIM Binder (σ0 = 203 MPa). Fractography analysis indicated poor fusion of printed layers for the samples produced with PIM binder composition as the main reason for poor mechanical performance.

Formation of zircon‐type (Zr,Ti)1−x(Dy)x(SiO4)1−x(PO4)x solid solution and their optical and magnetic characteristics

AbstractThe present study is aimed to tailor the structure of zircon (ZrSiO4) for potential application in hard tissue replacements. In this context, zircon (Zr,Ti)1−x(Dy)x(SiO4)1−x(PO4)x type solid solution has been formed through a simple sol–gel technique. Zircon formation is induced by the Ti4+ substitution, whereas the progressive addition of Dy3+/PO43− led to their accommodation at the resultant lattice sites. The maximum occupancy limit of Dy3+/PO43− is determined as 20 wt.% beyond, in which the ZrSiO4 structure is destabilized to enable the exclusion of Ti4+ and Zr4+ and subsequently yields ZrTiO4 trace alongside the crystallization of DyPO4. Dy3+ accommodation facilitated the improved absorption and emission (blue [483 nm] and yellow [576 nm]) phenomena and further the paramagnetic features are also induced in the resultant ZrSiO4.

Effect of Speed Sintering on Low Temperature Degradation and Biaxial Flexural Strength of 5Y-TZP Zirconia.

Translucent zirconia is becoming the material of choice for the esthetic restorative material. We aimed to evaluate the surface structure, phase determination, translucency, and flexural strength of 5Y-TZP Zirconia (Katana STML Block and Disc) between the regular sintering and the speed sintering with and without low-temperature degradation (LTD). A total of 60 zirconia discs (30 per group; regular sintering and speed sintering) were used in this study. A CAM machine was used to mill cylinders out of the zirconia blanks and then cut into smaller discs. For the speed sintering, the zirconia blocks were milled into smaller discs. The zirconia discs were subjected to regular and speed sintering with and without LTD. Scanning electron microscopy was used to characterize the zirconia specimens and the zirconia grain size. Furthermore, the zirconia specimens were analyzed for elemental analysis using energy dispersive spectroscopy and phase identification using X-ray diffraction. The zirconia specimens were subjected to translucency measurements and biaxial flexural strength testing. The results of the zirconia specimens were compared among the groups. Statistical analysis was completed using SPSS version 20.0 to detect the statistically significant differences (p value = 0.05). A one-way ANOVA with multiple comparisons was performed using Scheffe analysis among the groups. The speed sintering presented smaller grain sizes. The zirconia specimens with and without LTD in regular and speed sintering presented a similar surface structure. Regular sintering showed more translucency compared to speed sintering. Multiple comparisons of the translucency parameter were a significant difference (p value < 0.05) between the various groups except for the comparison between speed sintering and speed sintering LTD. The regular sintering showed bigger gain sizes and slightly more translucency compared to speed sintering. The speed sintering showed higher biaxial flexural strengths compared to regular sintering. This shows that speed sintering can be considered a suitable method of sintering zirconia.

Evolution of Highly Biocompatible and Thermally Stable YVO4:Er3+/Yb3+ Upconversion Mesoporous Hollow Nanospheriods as Drug Carriers for Therapeutic Applications.

In recent times, upconversion nanomaterials with mesoporous hollow structures have gained significant interest as a prospective nano-platform for cancer imaging and therapeutic applications. In this study, we report a highly biocompatible YVO4:1Er3+/10Yb3+ upconversion mesoporous hollow nanospheriods (YVO4:Er3+/Yb3+ UC-MHNSPs) by a facile and rapid self-sacrificing template method. The Rietveld analysis confirmed their pure phase of tetragonal zircon structure. Nitrogen adsorption–desorption isotherms revealed the mesoporous nature of these UC-MHNSPs and the surface area is found to be ~87.46 m2/g. Under near-infrared excitation (980 nm), YVO4:Er3+/Yb3+ UC-MHNSPs showed interesting color tunability from red to green emission. Initially (at 0.4 W), energy back transfer from Er3+ to Yb3+ ions leads to the strong red emission. Whereas at high pump powers (1 W), a fine green emission is observed due to the dominant three-photon excitation process and traditional energy transfer route from Er3+ to Yb3+ ions. The bright red light from the membrane of HeLa cells confirmed the effective cellular uptake of YVO4:Er3+/Yb3+ UC-MHNSPs. The resonant decrease in cell viability on increasing the concentration of curcumin conjugated YVO4:Er3+/Yb3+ UC-MHNSPs established their excellent antitumor activity. Therefore, the acquired results indicate that these YVO4:Er3+/Yb3+ UC-MHNSPs are promising drug carriers for bioimaging and various therapeutic applications.

Raman-XPS Spectroscopy, REE Chemistry, and Morphological Studies of Detrital Zircon and Monazite – Implications for Metamict State and Provenance

Abstract A combination of advanced characterisation techniques was applied to study the structure, chemistry, and surface morphological features of detrital zircon and monazite grains from the coasts of Varkala and Kovalam situated in the south-west part of India, showing implications to their metamict state, Rare Earth Element (REE) chemistry, and provenance. Raman, X-ray photoelectron spectroscopy (XPS), and Ultraviolet-Visible-near- IR (UV-Vis-NIR) spectroscopic techniques were used to detect the disorder in crystal structure due to self irradiation damage. The rare earth, radioactive, and trace elements present in these minerals were identified using high resolution inductively coupled mass spectrometer (HR-ICP-MS). These studies are also complimented by scanning electron microscope (SEM) analysis for understanding the morphological features. The present study depicts a low degree of metamictization in natural detrital zircon and monazite grains with information regarding their REE chemsitry and the surface morphological changes that occurred due to mechanical impacts caused during transportation and deposition. These vivid datasets of information facilitate the mining industry and scientific community for determining their grades.

Bonding and Debonding of Zirconia Using Laser Approaches.

To describe the current findings regarding the use of lasers to enhance the bonding properties of zirconia and to enable its debonding. The PudMed database was searched for literature up to July 2021. The keywords used for zirconia surface treatment were: laser irradiation; zirconia; and bond strength. For ceramic laser debonding, the keywords were: laser irradiation; ceramic; and debonding. A total of 36 studies were included for zirconia surface treatment, and 12 for ceramic laser debonding. Nd:YAG, CO2, Er:YAG, Er,Cr:YSGG, and ultrashort lasers were used for surface treatment, whereas only Er:YAG and Er,Cr:YSGG lasers were applied to debond zirconia structures. The use of laser irradiation to improve the bonding properties of zirconia depends on the type of laser and the parameters used. Among the laser types included in this review, ultrashort lasers have shown the most promising results; however, more studies are needed to prove their superiority over the other lasers for enhancing zirconia bond strength. In terms of debonding, irradiation with different lasers was effective regardless of the ceramic type; however, well-established protocols (ie, laser irradiation time and motion, laser settings) are still needed for different thicknesses and material ceramic types.

One-step synthesis of t-ZrO2 from Zircon using magnesium-calcium minerals as stabilizers

Stabling crystal structure at room temperature is a classic problem in the study of Zirconium dioxide (ZrO2). However, there are few investigations on making tetragonal zirconia (t-ZrO2) in one step at a low cost. In this research, t-ZrO2 is synthesized using a one-step high-temperature solid-state sintering technique with magnesite, dolomite, and limestone as stabilizers and zircon as the raw material. The most suitable stabilizers and reaction conditions are determined, and the mechanism of zirconia structure stabilization is explored. The findings suggest that magnesite has the lowest effect as a crystal structure stabilizer, whereas dolomite and limestone are pretty close, but dolomite introduces more impurities. The ideal reaction conditions were 60% mol limestone at 1500 °C. The stabilization mechanism is zirconia gap correction, according to XRD and EPR data. The characterization of the SEM demonstrates that the heat treatment temperature and stabilizer had little effect on the morphology of t-ZrO2. When limestone was introduced throughout the process, EDS data revealed that some amorphous silicon-calcium compounds occurred in the product. The focus of follow-up work will be on how to lessen the impact in this area. This research offers vital reference value for reducing the cost of the synthetic t-ZrO2 process.

Effect of Sintering on Phase Transformation Behavior and Morphology of Calcinated 5 Wt% Mg-PSZ

The zirconia structure can undergo a transformation during cooling after the sintering. The zirconia phase is stabilized by adding a doped magnesia stabilizer to the zirconia matrix. This study observed the effect of calcination temperature on the synthesis of Mg-PSZ on its phase transformation. The synthesis process was carried out with various calcinated temperatures of 600, 800 and 1000°C, with a concentration of MgO 5 wt%. Based on XRD analysis, Mg-PSZ crystal size was in the nanometer scale. The Mg-PSZ phases with 5% MgO at calcinated temperatures of 600, 800 and 1000°C were cubic, tetragonal and monoclinic respectively with each space group being Fm3m, P42/nmc and P21/c. In addition to the phase transition, the calcination temperature also affected the crystallinity of Mg-PSZ; the higher is calcination temperature, the lower is crystallinity. Based on TEM analysis at a calcination temperature of 800°C, the Mg-PSZ microstructure showed predominantly spherical nanoparticles.

On the possibility of technosphere safety by superionic

The purpose of this article is an attempt to substantiate the possibility of using a new technology for cleaning the industrial atmosphere in a separate workshop of the Taldykorgan battery plant "Kainar AKB", which produces, in particular, powerful batteries for K–700 tractors for agriculture. The innovative technology of air purification proposed by us in the technosphere of the manufacture of batteries for the agricultural production complex is based on the use of transport ion-conducting properties of solid electrolytes made of stabilized zirconium dioxide. The traditional methods of industrial atmosphere purification in enterprises and factories known to us, in our opinion, are morally outdated in terms of bulky external dimensions, noise generation, and need for systematic maintenance. The installation developed by us from a superionic conductor is devoid of these disadvantages, it is low-inertia, does not create a noise effect, compact and small-sized. Our ion conducting solid electrolyte is a ceramic material in the form of pipes, test tubes, tablets, initially containing impurity cations of lower valence, such as calcium, yttrium, scandium, in comparison with zirconium. Actually, these impurity cations create the presence of vacancies or holes in the solid cubic structure of zirconium dioxide. Only oxygen anions will be transported through these vacancies under the effect of external factors, high temperature, and DC electric field. The research method is based on the measurement of the electromotive force, which is recorded at the boundary section: air/superionic/air, which is uniquely mathematically related to oxygen concentration in air stream.

Effects of Different Polishing Systems on Surface Roughness and Crystal Structure of Zirconia.

Objective Intraoral polishing systems have become an alternative method for reglazing, which is important to prevent or minimize rapid wear of the opposing teeth. To assess the influence of different polishing systems and duration on surface roughness and crystal structure of zirconia was compared, contributing to the preparation and effect improvement of clinical zirconia restorations. Methods Forty-eight zirconia specimens with equal size were fabricated by cutting and sintering zirconia discs. Then X-ray diffractometer (XRD) was adopted for examination of the specimens. Six specimens were selected as the grinding-polishing group (GL) after polishing, grinding, and glazing. Then six specimens were randomly selected from the remaining specimens as the grinding-unpolished group (GR) after surface conditioning by dental diamond burs. Subsequently, based on different polishing systems and duration, the rest of specimens were divided into following groups (n = 6): Youdent-20s group (Y20), Youdent-40s group (Y40), Youdent-60s group (Y60), Toboom-20s group (T20), Toboom-40s group (T40), and Toboom-60s group (T60). Additionally, a contour graph was applied for assessing the surface roughness of zirconia, scanning electron microscope (SEM) for observing surface topography, and X-ray diffraction analysis (XRD) for determining crystal structure of zirconia. Results The GR group had the highest roughness, and the roughness of the specimens polished for 20 s with different polishing systems was significantly higher than those polished for 40 s and 60 s with the same polishing systems. There were no significant difference between the Y20 and T20 groups, while the roughness of the specimens in both Y40 and Y60 groups was significantly higher than that of the T40 and T60 groups. And with the increasing polishing duration, the surface morphology of the specimen was gradually smooth and the morphology was gradually regular. Besides, the surface scratches of the T group were shallower than that of the Y group at the same polishing duration. The peak value of XRD profile of the specimen after grinding and polishing process was consistent with the baseline pattern of that the original specimen. Conclusion Glazing can reduce the surface roughness of the specimens. Besides, the polishing effect of Toboom (TOB) system (polishing duration = 60 s) is the best. And different polishing durations of TOB system have no significant effect on the crystal surface structure of the specimen.

Porous Zirconia Blocks for Bone Repair: An Integrative Review on Biological and Mechanical Outcomes

The aim of this study was to conduct an integrative review of the biological and mechanical outcomes of porous zirconia structures for extensive bone repair. An electronic search was performed on the PubMed database using a combination of the following scientific terms: porous, scaffold, foam, zirconia, bone regeneration, bone repair, bone healing. Articles published in the English language up to December 2021 and related to porosity, pore interconnectivity, biocompatibility and strength of the material, and the manufacturing methods of zirconia porous structures were included. Randomized controlled trials and prospective cohort studies were also evaluated. The research identified 145 studies, of which 23 were considered relevant. A high percentage of pores and the size and interconnectivity of pores are key factors for cell migration, attachment, proliferation, and differentiation. In addition, pore interconnectivity allows for the exchange of nutrients between cells and formation of blood vessels. However, a decrease in strength of the porous structures was noted with an increase in the number and size of pores. Therefore, yttria-stabilized zirconia tetragonal polycrystal (Y-TZP) has mechanical properties that make it suitable for the manufacture of highly porous structures or implants for extensive bone repair. Additionally, the porous structures can be coated with bioactive ceramics to enhance the cell response and bone ingrowth without compromising pore networking. Porous structures and mesh implants composed of zirconia have become a strategy for extensive bone repair since the material and the pore network provide the desired biological response and bone volume maintenance.

Microstructure and electrical properties of new high-entropy rare-earth zirconates

In the present work, a series of new high-entropy rare-earth zirconates were prepared by a solid state reaction method. The crystal structure, microstructure and electrical properties of high-entropy rare-earth zirconates were characterized by means of X-ray diffraction, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy and electrochemical impedance spectroscopy. All the high-entropy rare-earth zirconates have a single-phase pyrochlore structure with a relative density of more than 95.7%. The grain sizes of high-entropy rare-earth zirconates are 1.3–2.4 µm, which are finer than low-entropy rare-earth zirconates prepared by the same process. (Nd0.2Sm0.2Eu0.2Gd0.2Dy0.2)2Zr2O7 has the excellent electrical conductivity of 7.1 × 10–3 S·cm–1 at 1073 K.