Zirconia Composites Research Articles

Mechanical evaluation of DIW-printed carbon nanofibers - alumina-toughened zirconia composites

Direct ink writing (DIW) offers cost-effective fabrication of intricate ceramic structures. However, the mechanical properties (reliability) of DIW-obtained components have been inadequate for structural applications. This study aimed to improve mechanical properties of DIW alumina-toughened zirconia (ATZ) composite filaments with and without carbon nanofibers (CNFs). Optimized debinding and sintering conditions were determined for Conventional Sintering (CS) and Spark Plasma Sintering (SPS). The influence of nozzle diameter, CNF content and sintering method on the fracture strain, Young’s modulus, flexural strength and Weibull modulus was carefully assessed via correlation analyses. CNFs, although intended to enhance properties, were often agglomerated, which negatively affected mechanical properties. Smaller nozzle diameters enhanced Young’s modulus, with CS-sintered ATZ filaments showing transformation-induced plasticity (TRIP). Mechanical properties rivaled or surpassed those of conventional techniques (e.g., cold isostatic pressing, slip casting) with a good level of mechanical reliability achieved. Overall, DIW showed promise for ceramic materials, particularly ductile Ce-TZP-based composites.

Unveiling Key Interface Characteristics of Ni/Yttria-Stabilized Zirconia Solid Oxide Cell Electrodes in H2O Electroreduction Using Operando X-ray Photoelectron Spectroscopy.

Nickel/yttria-stabilized zirconia (YSZ) composites are the most commonly used fuel electrodes for solid oxide cells. While microstructural changes of Ni/YSZ during operational conditions have been thoroughly investigated, there is limited knowledge regarding Ni/YSZ surface chemistry under working conditions. In this study, we examine the interaction between Ni/YSZ electrodes and water vapor under open circuit and polarization conditions, utilizing near ambient pressure soft and hard X-ray photoelectron spectroscopies. Miniature cells with conventional porous Ni/YSZ composite cermet cathodes were modified to facilitate the direct spectroscopic observation of the functional electrode's areas close to the interface with the YSZ electrolyte. The results highlight dynamic changes in the oxidation state and composition of Ni/YSZ under H2 and H2O atmospheres. We also quantify the accumulation of impurities on the electrode surface. Through adjustments in the pretreatment of the cell, the correlation between the nickel surface oxidation state and the cell's electrochemical performance during H2O electroreduction is established. It is unequivocally shown that nickel surface oxidation in H2O electrolysis favors NiO over Ni(OH)x, providing critical insights into the mechanism of Ni-phase redistribution within the electrode during long-term operation. Depth-dependent photoemission measurements, combined with theoretical quantitative simulations, reveal that NiO and Ni phases are uniformly mixed on the surface during H2O electrolysis. This differs from the conventional expectation of a NiO-shell/Ni-core configuration in gas phase oxidation. These findings provide crucial insights into the surface chemistry of Ni/YSZ electrodes under conditions relevant to H2O electrolysis, elucidating their impact on the electrochemical performance of the cell.

Using compositions of zircon to reveal fertile magmas for the formation of porphyry deposits in the Loei and Truong Son fold belts, northern Laos

The Loei and Truong Son fold belts are well known as being the most geologically important and highly mineralized magmatic arc-related terranes in mainland southeast Asia. Numerous studies have examined the geology, geochemistry, and geochronology but only a few metallogenic and detailed deposit characterizations have been undertaken. This study of zircon geochemical analyses uses laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to provide U-Pb ages and magmatic fertility of felsic to intermediate volcanic and plutonic rocks from ten prospects in the Loei and Truong Son fold belts, in the northwest Laos region. The geochemical and geochronological analyses suggest at least three episodes of magmatism occurred: Silurian-Devonian (434–411 Ma), Early to Middle Permian (299–277 Ma), and Late Permian to Middle Triassic (253–243 Ma). The variable ranges of ɛHf values (−12 to + 12) suggest that mantle-derived and crustal contamination signatures are related to the history of subduction and arc magmatism in this region. Key trace elements and ratios associated with oxygen fugacity of magmas (e.g., Eu/Eu*, Dy/Yb, Ce/Nd, ΔFMQ) imply that the Phu Kham and the west of Vientiane along the Mekong River are likely to be fertile for porphyry copper deposits. In contrast, the Pha Gnai and other suites are less fertile. Using zircon as a fertility indication can be a valuable tool to distinguish between fertile and barren magmatic suites in this area.

Constraints on the subduction and closure of the Hegenshan Ocean: Magmatic and sedimentary records from central Inner Mongolia, China

Petrological, geochronological, and geochemical data from the volcano-sedimentary sequences, granitoids, and ophiolite relics of central Inner Mongolia, China, were used to reconstruct the subduction and final closure of the Hegenshan Ocean. Geochronological dating and compilation reveal four phases (ca. 360−355 Ma, 348−320 Ma, 320−310 Ma, and 310−275 Ma) of magmatism in the Uliastai continental margin. The ca. 356 Ma I-type Halatumiao granodiorite and Amanwusu ophiolite relics are subduction-related, and the Halatumiao granodiorite provides solid evidence of the northward subduction of the Hegenshan Ocean beneath the Uliastai continental margin at ca. 360−355 Ma. The ca. 348−320 Ma and 320−310 Ma volcanic rocks and granitoids constitute two linear magmatic belts roughly parallel to the Erenhot-Hegenshan ophiolite belt, which record two phases of continental arc magmatism in the Uliastai continental margin. Overall, the ca. 360−310 Ma arc magmatism shows landward migration and then oceanward migration in the Uliastai continental margin, which indicates advancing subduction and subsequent slab steepening of the Hegenshan Ocean. By contrast, the ca. 310−275 Ma magmatic rocks are dominated by I- and A-type felsic volcanic rocks, granites, and dikes, which are post-accretionary, extension-related, and pervasive in the Uliastai continental margin and Erenhot-Hegenshan ophiolite belt. A provenance shift was identified between the Benbatu and Amushan formations of the Amanwusu area of the Erenhot-Hegenshan ophiolite belt. The early detritus was derived from the early Paleozoic rocks in the Sonid Zuoqi arc belt, whereas the late detritus originated from the Early Carboniferous ophiolite relics in the Erenhot-Hegenshan ophiolite belt. The provenance shift and emplacement of pervasive extension-related magmatic rocks imply a Late Carboniferous closure of the Hegenshan Ocean. The Late Carboniferous oceanic closure event in the north of the southeast Central Asian Orogenic Belt is also evidenced by the transition of Hf isotopic composition of zircons dated between ca. 360−310 Ma and 310−275 Ma.

Characterization of a hydrothermally aged experimental alumina-toughened zirconia composite

ObjectivesTo assess the effects of different aging protocols on chemical, physical, and mechanical properties of an experimental ATZ composite compared to a zirconia. MethodsDisc-shaped specimens were obtained through uniaxial pressing of commercial powders (Tosoh), ATZ comprised of 80%ZrO2/20%Al2O3 (TZ-3YS20AB) and 3Y-TZP (3Y-SBE). The specimens of each material were divided into different groups according to the aging protocol: immediate, autoclave aging and hydrothermal reactor aging. The aging protocols were performed at 134 ºC for 20 h at 2.2 bar. Crystalline evaluations were performed using X-Ray Diffraction. The nanoindentation tests measured the elastic modulus (Em) and hardness (H). Biaxial flexural strength was performed, and Weibull statistics were used to determine the characteristic strength and Weibull modulus. The probability of survival was also determined. The Em and H data were analyzed by one-way ANOVA and Tukey test. ResultsDiffractograms revealed the presence of monoclinic phase in both materials after aging. The hydrothermal reactor decreased the Em for ATZ compared to its immediate condition; and the H for both ATZ and 3Y-TZP regarding their immediate and autoclave aging conditions, respectively. The aging protocols significantly increased the characteristic strength for ATZ, while decreased for 3Y-TZP. No difference regarding Weibull modulus was observed, except for 3Y-TZP aged in reactor. For missions of up to 500 MPa, both materials presented a high probability of survival (>99 %) irrespective of aging condition. SignificanceThe synthesized ATZ composite exhibited greater physical and microstructural stability compared to 3Y-TZP, supporting potential application of the experimental material for long-span reconstructive applications.

Effect of β-spodumene additions on the phase composition, thermal, mechanical, and fracture behavior of zirconia toughened alumina composites

The fabrication of ceramic composites with low thermal expansion and excellent mechanical properties is essential for thermal barrier coating (TBC) applications. For this purpose, using the sol-gel process, novel ceramic composites were developed by combining varying weight percentages of β-spodumene (0–20 wt%) with zirconia toughened alumina (ZTA). The influence of β-spodumene addition on the densification, phase composition, microstructure, and mechanical, thermal, and fracture behavior of the studied composites was investigated experimentally and numerically. Increasing the β-spodumene content reduces the sintering temperature of the formed composites by 75 °C. Introducing 5 wt% β-spodumene to ZTA composite improves the densification process by serving as a mineralizer. X-ray diffraction (XRD) revealed that the t-m ZrO2 transformation was enhanced by increasing the β-spodumene content. The results demonstrated that composites with β-spodumene content of 5 wt% exhibited the best mechanical performance. The numerical prediction of fracture toughness agreed well with the experimental results for different composites.

In vitro Evaluation of the Cytotoxicity of Chairside CAD/CAM Block Materials for Fabricating Dental Restorations.

The increasing utilization of chairside computer-aided design/computer-aided manufacturing (CAD/CAM) block materials in dentistry necessitates a comprehensive evaluation of their cytotoxicity to ensure patient safety. This study aimed to assess the cytotoxic effects of commonly used chairside CAD/CAM block materials for fabricating dental restorations. Several chairside CAD/CAM block materials including zirconia, lithium disilicate, and resin-based composites were evaluated for cytotoxicity using an in vitro model. Human gingival fibroblasts were cultured and exposed to extracts from each material. Cytotoxicity was assessed using MTT assay after 24, 48, and 72 hours of exposure. Additionally, cell morphology and viability were examined using microscopy. The MTT assay revealed varying degrees of cytotoxicity among the tested materials. Zirconia demonstrated the least cytotoxicity with cell viability of 85% ± 5%, 82% ± 4%, and 79% ± 6% at 24, 48, and 72 hours, respectively. Lithium disilicate exhibited moderate cytotoxicity with cell viability of 70% ± 6%, 65% ± 7%, and 60% ± 5% at the corresponding time points. Resin-based composites displayed the highest cytotoxicity with cell viability of 55% ± 8%, 45% ± 6%, and 40% ± 4% at 24, 48, and 72 hours, respectively. Microscopic examination revealed altered cell morphology and reduced cell viability in the presence of resin-based composites. Chairside CAD/CAM block materials exhibit varying degrees of cytotoxicity, with zirconia demonstrating the least and resin-based composites showing the highest cytotoxic effects. These findings underscore the importance of considering cytotoxicity profiles when selecting CAD/CAM materials for dental restorations to ensure patient safety and biocompatibility.

Zircon compositional systematics from Devonian oxidized I-type granitoids: examination of porphyry Cu fertility indices in the New Brunswick Appalachians, Canada

Zircon is a common, widely distributed accessory mineral in most igneous rocks and its refractory nature records magmatic evolution in terms of oxygen and U-Th-Pb isotopes, and trace-element contents all of which reflect the intrinsic physio-chemical evolution of the magmatic systems in which it crystallized. Zircon compositions can be used as an indicator of relative fertility of hypabyssal intrusions in terms Cu ± Mo ± Au porphyry mineralization. To further characterize syn- to post-collisional adakitic Devonian oxidized I-type granitoids in the New Brunswick (specifically, those with Cu ± Mo ± Au porphyry-style mineralization), LA-ICP-MS analyses (guided by µXRF-EDS mapping and SEM-BSE imaging of polished thin sections) of zircons from 13 granitoids was conducted. The zircons studied were similar in terms of their textures (homogenous cores, patchy zoning, oscillatory zoning, and some unzoned zircon); however, they have a wide range of trace- and minor-element (Hf, HREE, Y, Th, U) compositions. Specifically, Zr/Hf ranges between 24–60, whereas Th/U ranges between 0.15 and 5.37. The presence of inherited zircon affects the concentrations of Th and U, as well as other key elements. Estimated crystallization temperatures of granitoids, ranging from 737 to 899°C, were calculated via Ti-in-zircon geothermometry assuming reduced TiO2 and SiO2 activities. The calculated log fO2 values for zircons from some of these granitoids indicate a highly oxidized magmatic signature. Zr/Hf, Eu/Eu⁎, and (Eu/Eu⁎)/Y in zircon, as well as zircon (Ce/Nd)/Y are some of the best indicators of porphyry fertility. The Ce/Ce* in zircon exhibit a large range (1.1–590), with higher Ce/Ce* reflecting more metallogenically favourable oxidizing conditions. If Eu/Eu⁎ in zircon is ≥0.4 (relatively oxidized conditions), it indicates a high potential for an ore-forming porphyry Cu mineralizing system. Lower Eu contents reflect relatively reducing conditions, as Eu anomalies vary with oxygen fugacity as well, and the relative abundance of Eu2+ is higher, but does not substitute into the zircon lattice. The evidence extracted from analyzing the zircon composition within New Brunswick’s I-type granitoids indicates the fertility of these hypabyssal intrusions.

Zircon Petrochronology of Au-Rich Porphyry and Epithermal Deposits in the Golden Quadrilateral (Apuseni Mountains, Romania)

Abstract The Golden Quadrilateral of the Apuseni Mountains (Romania) represents the richest Au(-Cu-Te) porphyry and epithermal district of Europe and the Western Tethyan metallogenic belt. The Au(-Cu-Te) mineralization is associated with Neogene calc-alkaline magmatism along graben structures growing during the late stages of the Alpine-Carpathian orogeny. We use zircon petrochronology to study the time-space distribution, sources, composition, and timescales of the Au(-Cu-Te)-mineralizing magmatism and explore its link to regional tectonics. Our own and published U-Pb zircon ages document ore-forming magmatic activity between ~13.61 and 7.24 Ma. In combination with available paleomagnetic data, the new zircon ages corroborate the hypothesis that the magmatism in the Golden Quadrilateral evolved in a tectonic environment dominated by major (up to 70°) crustal block rotation. Hafnium isotope composition of Neogene zircon (εHf between –2 and 10) supports the predominant origin of the magmas from a heterogeneous lithospheric mantle, which may have been fertilized during an earlier Cretaceous subduction event and possibly by concurrent Miocene subduction. Xenocrystic zircon shows involvement of crustal sources resembling European continental basement. Fertility indicators, including Eu/Eu* and oxygen fugacity based on zircon composition, show no systematic correlation with the mineralizing events and/or age. High-precision (isotope dilution-thermal ionization mass spectrometry) U-Pb zircon geochronology demonstrates that the magmatic systems exposed at district scale evolved over less than ~100 k.y. and that durations of hydrothermal mineralization pulses were even shorter.

Geochronology, mineralization and prospecting implication of the Paleoproterozoic Shaliuquan Nb-Ta pegmatite deposit in the northern Tibetan Plateau

A large number of Archean and Paleoproterozoic pegmatite rare-metal deposits exist worldwide, but few Precambrian pegmatite deposits have been reported in China, especially in the Tibetan Plateau. The Precambrian pegmatite deposits are still poorly studied. The Shaliuquan pegmatite, located in Quanji Massif, is a rare pegmatite-type Nb-Ta deposit in the northern Tibetan Plateau. Columbite-tantalite group minerals (CGMs) from three pegmatite samples give the U-Pb ages of 1844.2 ± 8.1 Ma, 1831.2 ± 12.2 Ma and 1848.0 ± 18.7 Ma, respectively. The U-Pb ages of CGMs show that the Shaliuquan pegmatite is a rare Paleoproterozoic pegmatite rare-metal deposit in the Tibetan Plateau. This is supported by the Precambrian 40Ar/39Ar plateau age of muscovites from two pegmatite samples (1094–1518 Ma), representing the metamorphic events after formation. As for the formation of Shaliuquan pegmatites, we argue that the hydrothermal processes in the late stage of the pegmatite evolution play a vital role for the enrichment and mineralization of Ta, which is evidenced by texture and compositions of CGMs and zircons. The formation of the Shaliuquan pegmatites is a response to the assembly of the Columbia supercontinent. The discovery of the Precambrian Shaliuquan pegmatite deposit implies that the Quanji Massif in the northern margin of the Qaidam Basin, which has an ancient mature metasediments basement and thick continental crust, has great potential for prospecting the Paleoproterozoic pegmatite rare-metal deposits.

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

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

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

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

Magmatic evolution and metallogenic diversity of the late Cretaceous granites in the Yidun terrane: Constraints from zircon and apatite geochemistry

Porphyry-hydrothermal type Cu-Mo(−W) deposits in the southern Yidun terrane (SYT) and hydrothermal-skarn type Sn-Pb-Zn-Ag deposits in the northern Yidun terrane (NYT) are closely related to late Cretaceous granitic intrusions in time and space. However, the genetic mechanisms and controlling factors responsible for the metallogenic diversity remain unclear. We investigated zircon and apatite compositions of the Sn-Pb-Zn-Ag-associated granites in northern Yidun terrane and the Mo-W-Cu and Mo-Cu-associated granites in southern Yidun terrane. The Cretaceous granites are distributed along a N–S-trending belt having ages ranging from 106 to 73 Ma, with a transition from predominant plagioclase crystallization to amphibole-dominated crystallization. Our data show that the granites from the NYT have lower zircon Eu/Eu* (0.06 ± 0.04), Ce4+/Ce3+, and ΔFMQ (FMQ is fayalite-magnetite-quartz) values compared to the granites in the SYT, indicating that the granites from the NYT are relatively reduced (ΔFMQ = -1.03 ± 1.02) in contrast to the oxidized granites in the SYT (ΔFMQ = 1.10 ± 1.05). Furthermore, apatite can record the volatile compositions of magma before fluid exsolution. Apatites in granites from the NYT with low XF/XCl ratios (≤120) are interpreted to have crystallized from volatile-undersaturated magma. These apatites are characterized by low Cl contents ranging from 0.04 to 0.12 wt% (0.07 ± 0.02 wt%; n = 21) and low SO3 contents of 0.01–0.06 wt%. In contrast, apatites in granite from the SYT with low XF/XCl ratios (≤80) have high Cl contents of 0.05 to 0.34 wt% (0.16 ± 0.07 wt%; n = 52) and SO3 contents of 0.01–0.46 wt%. The chemical compositions of zircon and apatite indicate that the Mo-W-Cu and Mo-Cu-associated granites in the SYT have higher fO2 and melt S contents before fluid exsolution than the Sn-Pb-Zn-Ag-associated granites in the NYT. Therefore, the contrasting magmatic oxidation states and S contents are critical in controlling the metallogenic diversity of the Cretaceous granites in the Yidun terrane. The Xingguolongba and Cuopu granites, first reported in this article, have U-Pb ages consistent with the Rongyicuo and Cuomolong granites. Furthermore, they exhibit similar geochemical properties, such as oxygen fugacity and volatiles, suggesting the possibility of forming Sn-Pb-Zn-Ag deposits.

Regional trends and petrologic factors inhibit global interpretations of zircon trace element compositions

The trace element composition of zircon reveals information about the melt that they are derived from, as such, detrital zircon trace element compositions can be used to interrogate melt compositions, and thus the evolution of the continental crust in time and space. Here, we present a global database of detrital zircon compositions and use it to test whether average global trends for five common petrogenetic proxies truly represent secular changes in continental evolution. We demonstrate that the secular trend is broadly comparable across continental regions for Ti-in-zircon temperatures, but for other trace element ratios interrogated, secular trends are highly variable between continental regions. Because trace element ratios result from multiple petrologic variables, we argue that these petrogenetic proxies can be overinterpreted if projected to global geologic processes. In particular, we caution against the interpretation of crustal thickness from trace elements in zircon, and we argue that our results negate current hypotheses concerning secular changes in crustal thickness.

The effects of phase interfaces in SmFeN/YSZ composite thermal barrier materials on electromagnetic wave-absorbing properties

Yttria-stabilized zirconia (YSZ) oxide ceramic powder is a thermal-barrier material used to fabricate thermal barrier coatings (TBC). In this study, to improve the electromagnetic wave (EMW) absorbing properties of TBCs, microwave-absorbing samarium iron nitrogen (SmFeN) particles were used to prepare SmFeN/yttria-stabilized zirconia (YSZ) composites. To study the effect of the SmFeN/YSZ interfaces on the EMW-absorbing properties of the SmFeN/YSZ composite, SmFeN/YSZ interfaces were built in different ways in composite materials having the same mass ratio of 1:1, for example, SmFeN and YSZ particles homogeneously mixed together, SmFeN/YSZ interfaces perpendicular and parallel to the EMW incident direction, and different interfaces between YSZ and SmFeN. Thus, the microwave absorbing performance of the samples, including the electromagnetic parameters, attenuation coefficient, eddy-loss current (C0), impedance matching, and minimum reflection loss (RLmin) values were examined and analyzed. The results demonstrate that interfaces perpendicular to the direction of the EMWs can increase the contact area and enhance the interfacial absorption effect. Further, when the wave-absorbing agent was placed in the middle of the composite, its wave-absorbing effect was the best among all the samples, yielding RLmin = −27.824 dB and effective absorption bandwidth (EAB) = 8.5453 GHz (effective absorption frequency range 7.9256–16.4709 GHz for a 7.2-mm-thick layer). Crucially, the frequency and bandwidth at which the best absorption occurred could be tuned by adjusting the thickness of the coating. This is because the interfaces in the samples resulted in polarization enhancement and anomalous dispersion, leading to large dielectric losses. Overall, the use of a coaxial measurement technique is highly efficient for EMW absorbing body design and process simulations.

Optical-spectroscopic and isotope-geochemical characteristics of zircons from diamond-bearing placers in Yakutia as indicators of diamond ore bodies

Research subject. Zircon grains from diamond placers of the Molodo and Ebelyakh rivers of the Yakut Arctic. Aim. To study the indicator characteristics of zircon to determine sources of diamonds and ways of their transfer to placers; to analyze optical-spectroscopic and isotope-geochemical parameters of zircon grains, their microelemental, U-Pb, and Lu-Hf isotope composition. Materials and methods. A LA-ICP-MS analysis of the U-Pb isotopic and trace element composition of zircon was carried out using a NexION 300S mass spectrometer with an NWR 213 attachment. An analysis of the Lu-Hf isotope system was carried out using a Neptune Plus mass spectrometer with an NWR 213 attachment, located in a room of cleanliness class 7 ISO at the Geoanalitik Center for Collective Use (IGG Ural Branch of the Russian Academy of Sciences, Ekaterinburg). Raman spectra were obtained using a LabRAM HR800 Evolution confocal spectrometer. CL spectra were obtained using a Jeol JSM6390LV scanning electron microscope equipped with a Horiba H-CLUE iHR500 attachment. Results. The local optical spectroscopic characteristics (Raman spectra and catholuminescence) of zircon grains were established, which made it possible to substantiate the conclusion about their high crystallinity and homogeneity (monochrony), as well as to select international zircon standards with similar characteristics for use in LA-ICP-MS analysis to ensure similar conditions for evaporation of the substance and fractionation parameters of the U and Pb elements. LA-ICPMS data on the microimpurity, U-Pb and Lu-Hf isotopic composition of zircon grains from diamond placers, as well as the dose values of their self-irradiation, are presented. Conclusions. The obtained U-Pb dating contributes to reconstructing a more precise history, character, and sequence of manifestation of kimberlite magmatism, tectonic processes, and migration routes of kimberlite material and diamonds across the Siberian craton, within the Yakut kimberlite province.

Al2O3/Y3Al5O12 (YAG)/ZrO2 composites by single-step powder synthesis and spark plasma sintering

Alumina-yttrium aluminum garnet (YAG)-zirconia composites are often produced by the melt solidification method. In the present study, we investigated the fabrication of α-Al2O3/Y3Al5O12 (YAG)/ZrO2 composite by Spark Plasma Sintering (SPS) of powders synthesized by Pechini’s sol-gel method. The ternary composites with homogenous microstructure and high density were produced by SPS at 1300 °C for 15 min. The addition of ZrO2 promoted the sintering of composites, resulting in a higher density and, in turn, higher hardness. A change in the indentation fracture behavior as the result of ZrO2 addition was observed.

Paedodontic preformed crowns in primary teeth and relative degree of dental wear.

Prosthetic rehabilitation of deciduous teeth in paediatric age using pre-formed crowns has been considered one of the best methods of dental restoration since their introduction. Their main advantages are related to durability, longevity and a low rate of recurrent cavities. Since stainless steel crowns do not coincide with aesthetic needs of parents and patients, preformed paedodontic crowns made of zirconia and nano-hybrid composite was introduced. The aim of the study is to evaluate the degree of wear on the enamel and on themselves of the different paedodontic crowns. Nine bovine teeth and nine paedodontic crowns for deciduous molars were selected for the study, three of which in zirconia, three in nano-hybrid composite and three in stainless steel. Wear test was carried out on the Rtech™ Instruments tribometer applying a force of 50 N. After that, both the bovine teeth and the paedodontic crowns were observed using a stereo microscope (Zeiss Stemi C-500) and a scanning electron microscope (SEM, Cambridge Stereoscan 440). The areas of wear were calculated with a software [ImageJ, version 1x, Wayne Rasband, Maryland, USA]. Pre-formed paediatric crowns in zirconia, nano-hybrid composite and stainless steel are a valid aid for the restoration of deciduous teeth and do not compromise the physiological wear characteristic of the phases of the dental exchange. The stainless steel crown is preferable for the restorations in the posterior sectors as its behaviour is the most similar to that of a natural tooth. Zirconia and nano-hybrid composite crowns showed an inversely proportional behaviour between their wear volume and that of the opposing tooth.

First identification of the Early Cretaceous Suolong Cu-rich porphyry in the Geji area, central Tibet: A new clue for regional porphyry Cu exploration

The Tibetan Plateau hosts the majority of porphyry Cu deposits in China. There are two large metallogenic belts, the Gangdese and Bangong-Nujiang belts, in the Lhasa Terrane, Central Tibet. The Lhasa Terrane experienced multistage magmatic activity from the Mesozoic to Cenozoic, and the subaerial volcanic areas of the western part of the terrane are regarded as favorable targets of porphyry Cu deposits. In this paper, we describe the geology of our newly identified Early Cretaceous Suolong Cu-rich porphyry in the western Lhasa Terrane and present new U–Pb ages, trace element and Hf isotopic compositions of zircon and whole-rock elemental and Sr–Nd isotopic compositions. The Suolong porphyry contains zircon grains with ages ranging from 136 to 135 Ma, εHf(t) values ranging from −1.5 ∼ +2.7 and logfO2 values ranging from −16.27 ∼ −9.92. Geochemically, the porphyry rocks are peraluminous in nature, with whole-rock εNd(t) values of −5.7 ∼ −5.4. We infer that the Suolong porphyry originated from a mixture of ∼53 % enriched lithospheric mantle and ∼47 % ancient lower crustal melt, triggered by the roll-back of the northward-subducting Neo-Tethyan Ocean. The conditions of high oxygen fugacity and water content and tectonic transition promoted the formation of the Suolong Cu-rich porphyry, but the condition of a thinned crust may have constrained the mineralization scale of the Cu deposits. This new identification of Early Cretaceous mineralization event provides important clues for identifying new potential exploration targets for porphyry Cu deposits in the western segment of the Lhasa Terrane.

First-Principles and Experimental Investigation of ABO4 Zircons as Calcium Intercalation Cathodes.

Identifying next-generation batteries with multivalent ions, such as Ca2+ is an active area of research to meet the increasing demand for large-scale, renewable energy storage solutions. Despite the promise of higher energy densities with multivalent batteries, one of their main challenges is addressing the sluggish kinetics in cathodes that arise from stronger electrostatic interactions between the multivalent ion and host lattice. In this paper, zircons are theoretically and experimentally evaluated as Ca cathodes. A migration barrier as low as 113 meV is computationally found in YVO4, which is the lowest Ca2+ barrier reported to date. Low barriers are confirmed across 18 zircon compositions, which are related to the low coordination change and reduced interstitial site preference of Ca2+ along the diffusion pathway. Among the four materials (BiVO4, YVO4, EuCrO4, and YCrO4) that were synthesized, characterized, and electrochemically cycled, the highest initial capacity of 81 mA h/g and the most reversible capacity of 65 mA h/g were achieved in YVO4 and BiVO4, respectively. Despite the facile migration of multivalent ions in zircons, density functional theory predictions of the unstable, discharged structures at higher Ca2+ concentrations (Cax>0.25ABO4), the low dimensionality of the migration pathway, and the defect analysis of the B site atom can rationalize the limited intercalation observed upon electrochemical cycling.