Search Results (14)

In order to cleanly and efficiently extract zirconium from zircon sand (the main component is ZrSiO₄), sodium hydroxide sub-molten salt was used to decompose ZrSiO₄ in this study. When ZrSiO₄ reacts with sodium hydroxide sub-molten salt, the formation of Na₂ZrSiO₅ (a water-insoluble product) considerably affects the separation efficiency of Zr and Si and increases production cost. Thus, it is necessary to control the formation of Na₂ZrSiO₅. The influence of NaOH content, reaction temperature, reaction time, and NaOH/ore mass ratio on the formation of Na₂ZrSiO₅ were systematically investigated. The optimum reaction parameters for the inhibition of Na₂ZrSiO₅ formation were as follows: 80% NaOH content, 245 °C reaction temperature, 4:1 NaOH/ore mass ratio, 10 h reaction time, and 400 r/min agitation speed. These results indicate that ZrSiO₄ is decomposed to Na₂ZrO₃ and Na₂SiO₃ by reacting with NaOH, realizing the separation of Zr and Si, and then the reactions between Na₂ZrO₃ and Na₂SiO₃ result in the formation of Na₂ZrSiO₅, during the decomposition of ZrSiO₄ using NaOH sub-molten salt. The sub-molten salt decomposition process can realize the clean extraction of zirconium, which is conducive to the sustainable development of zirconium resources. Full article

The Dovyren Intrusive Complex (Northern Baikal region, 728 ± 3 Ma) includes the dunite–troctolite–gabbronorite Yoko–Dovyren massif (YDM) associated with a sequence of underlying mafic-to-ultramafic sills, locally demonstrating interbedding relations with the most primitive rocks of the pluton. These sills and apophyses contain sulfide mineralization ranging from globular to net-textured and massive ores. Major types of the YDM cumulates and sulfide mineralization were examined for their PGE contents and Re-Os isotopic systematics. The ten analyzed samples included chilled and basal rocks, poorly mineralized troctolite, PGE-rich anorthosite, as well as three samples from a thick ore-bearing apophysis DV10 connected with the YDM. These samples yielded a Re-Os isochron with an age of 759 ± 36 Ma and an initial ¹⁸⁷Os/¹⁸⁸Os of 0.1309 ± 0.0026 (MSWD = 110), which is in consistent with the previously reported U–Pb zircon age. It is shown that being recalculated to γOs(t) at t = 728 Ma, these isotopic compositions demonstrate three clusters regarding the relationship between γOs(t) and ¹⁸⁷Re/¹⁸⁸Os: (i) the chilled gabbronorite (YDM) and subcontact olivine gabbronorite (DV10) yielded the most radiogenic values of γOs(t) 10.5 and 10.0 among basal ultramafics, (ii) plagiodunite, troctolite, and sulfide ores showed lower radiogenic compositions, with γOs(t) ranging from 7.3 to 8.7, (iii) olivine gabbronorite, plagioperidotite, and one sample of PGE-rich anorthosite yield very primitive γOs(t) in the range 4.5 to 5.6 (on average 5.2 ± 0.6). The lowest values of γOs(t) for the least fractionated rocks of the YDM suggest a primitive mantle source, formed from a partly contaminated Neoarchean protolith, which is considered to be anomalous in Upper Riphean due to very low εNd(t) of −16 for the most primitive Dovyren magma (Fo88-parent). The highest values of γOs(t) and relative enrichment in the ³⁴S isotope in the chilled gabbronorite (YDM) and subcontact olivine gabbronorite (DV10) evidence that their primitive to evolved magmatic precursors could be affected by a metamorphic fluid enriched in radiogenic ¹⁸⁷Os, originating in the exocontact halo due to the thermal decomposition of pyrite from the dehydrated country rocks. This is consistent with the second-stage contamination of the Dovyren magma by the hosting crustal rocks (probably of 10 wt% shists), generating more evolved Fo86-parent magma with higher εNd(t) of −14. Full article

Zirconates of rare earth elements have emerged as promising candidates for thermal barrier coatings (TBC). This study investigates the hot corrosion resistance of single-layered ceramic coatings composed of Gd₂Zr₂O₇, Sm₂Zr₂O₇, and Nd₂Zr₂O₇. The coatings were prepared using air plasma spraying and applied to an Inconel [IN] 625 substrate. Experimental assessments were conducted to examine the hot corrosion behaviour by subjecting the coatings to pure magnesium sulfate (MgSO₄) salt at 1000 °C for 24 h and a 50/50 mole percent Na₂SO₄ and MgSO₄ mixture at 900 °C for cyclic durations of 5, 10, 15, and 20 h. This combination of salts creates a highly corrosive environment. This short test was carried out due to the necessity of the initial stages of the destruction process characterization. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersion spectroscopy (EDS) techniques were utilized to identify and analyse the reaction products. At 1000 °C, no chemical reaction products were observed between MgSO₄ and Gd₂Zr₂O₇, Sm₂Zr₂O₇, and Nd₂Zr₂O₇. However, in the presence of the MgSO₄ + Na₂SO₄ mixture, the zirconate coatings reacted, resulting in the formation of reaction products such as Gd(SO₄)₃, Gd₂O₂SO₄, Gd₂O₃, Sm₂O₂SO₄, Sm₂(SO₄)₃, Sm₂O₃, MgO, Nd₂(SO₄)₃, Na₂O, and m-ZrO₂. These compounds are formed due to the interaction of rare earth oxides with a low-temperature-melting eutectic Na₂SO₄+ (3MgSO₄ × Na₂SO₄) melted at 666 °C. Despite the aggressive nature of the corrosive environment, the decomposition of rare earth zirconates was relatively limited, indicating satisfactory resistance to hot corrosion. Among the zirconate systems studied, Gd₂Zr₂O₇ exhibited the lowest resistance to the MgSO₄ + Na₂SO₄-based corrosive environment, while Sm₂Zr₂O₇ and Nd₂Zr₂O₇ demonstrated better corrosion resistance. Full article

The emergence of the Tibetan Plateau is one of the most significant geological events in East Asia. The Central Qilian Shan connects North and South Qilian Shan in the northeastern part of the Tibetan Plateau. However, the exhumation history of the Central Qilian Block from the Mesozoic to Cenozoic remains unclear. Determining the cooling ages of detrital zircon and apatite in modern river sediments is an ideal method for tracing the evolutionary processes of orogenic belts. In this study, we present the first single-grain detrital apatite (153) and zircon fission-track (108) data for the Huangshui River sediments from the Central Qilian Shan. The decomposition of the dataset revealed major Mesozoic and Cenozoic age peaks at ca. 145–93, and 11 Ma. The Central Qilian Shan entered the intracontinental orogeny stage dating back to the Cretaceous (ca. 145–93 Ma) and Late Cenozoic (ca. 11 Ma) caused by the subduction of the Neo-Tethys and Indian–Asian collision. Therefore, we propose that the geomorphic framework of the northeastern margin of the Tibetan Plateau was initially established during the Mesozoic and further consolidated in the Late Miocene. Full article

Lightweight aluminum composite is a class of foam material that finds many applications. These properties make it suitable for many industries, such as the transportation, aerospace and sports industries. In the present work, closed-cell foams of an Al-Si12CuFe alloy and its composite are developed by a stir casting process. The optimization of the foaming temperature for the alloy and composite foams was conducted in terms of the ligament and node size of the alloy and also the volatility of the zircon with the melt, to provide strength to the cell walls. CaCO₃ as a blowing agent was homogeneously distributed in the molten metal without adding any thickener to develop the metal foam. The decomposition rate of CaCO₃ is temperature-dependent, which is attributed to the formation of gas bubbles in the molten alloy. Cell structure, such as cell size and cell wall thickness, is controlled by manufacturing process parameters, and both the physical and mechanical properties are dependent on the foam cell structure, with cell size being the major variable. The results show that the increase in cell wall thickness with higher temperature leads to a decrease in cell size. By adding the zircon to the melt, the cell size of the composite foam first increases, and then the thickening of the wall occurs as the temperature is increased. The uniform distribution of the blowing agent in molten metal helps in the formation of a uniform cell structure. In this work, a comparative structural study of alloy foam and composite foam is presented regarding cell size, cell shape and foam stability at different temperatures. Full article

Investigation of shocked materials provides unique information about behavior of substances in extreme thermodynamic conditions. Near surface nuclear tests have induced multiple transformations of affected soils. Examination of nuclear glasses and relics of entrapped minerals provides a unique database on their behavior under an intense temperature flash. In this work, several types of nuclear fallout particles from historic tests at the Semipalatinsk test site are investigated using complementary analytical methods. Distribution of radionuclides in all types of samples is highly heterogeneous; domains with high content of radionuclides are often intermixed with non-active materials. There is no general correlation between chemical composition of the glassy matrix and content of radionuclides. In aerodynamic fallout, the main fraction of radionuclides is trapped in the outer glassy shell. Relics of quartz grains are always devoid of radionuclides, while glass regions of high activity have different composition. In contrast to underground tests, iron-rich minerals are not necessarily radioactive. In most cases, the glassy matrix in anhydrous and is strongly polymerized, and the Q³ silicate groups dominate. Temperature-induced transformations of entrapped minerals are discussed. Investigation of zircon grains shows absence of a direct correlation between degree of decomposition into constituting oxides, morphology of resulting baddeleyite, and maximum experienced temperature. For the first time, temperature history of a nuclear ground glass is estimated from Zr diffusion profiles from decomposing zircon grain. Full article

Timber has been commonly used in the field of civil engineering, and the health condition of timber is of great significance for the whole structure in practical scenarios. However, due to mechanical load and environmental impact, timber-based constructions are vulnerable to termite attack, microbial corrosion and fractures within their service lives. Thus, the damage monitoring of timber structures is very challenging under real situations. This paper presents an intelligent timber damage monitoring approach using Lead Zirconate Titanate (PZT)-enabled active sensing and intrinsic multiscale entropy analysis. The proposed approach adopts PZT-enabled active sensing to collect the signals depicting dynamic characteristics of the timber structure. The proposed intrinsic multiscale entropy analysis utilizes variational mode decomposition (VMD) to deal with the collected response signals. Decomposition of the response signals into a set of band-limited intrinsic mode functions (BLIMFs) denoting nonlinear and nonstationary characteristics. Then multiscale sample entropy (MSE) is employed to extract quantitative features, which are adopted as health condition indicators of timber structures. Finally, the convolutional neural network (CNN) fulfills the intelligent timber damage monitoring by using the quantitative features as the effective input. The research findings reveal the efficacy and superiority of the proposed method. Full article

Detrital-zircon U-Pb geochronology is extensively used to imply provenance histories as one of the most common methods to constrain the tectonic evolution of ancient sedimentary systems. The rapid accumulation of detrital-zircon thermochronology data in the eastern Tien Shan region brought great convenience for understanding the basin–mountain evolution in the region. In this work, 41 samples for zircon U-Pb dating from the Jurassic–Cretaceous strata of the Turpan-Hami basin and its adjacent region were compiled. Based on the systematic investigation, comparison, and summarization of Late Mesozoic sources in the eastern Tien Shan region and the quantitative characterization of source variations, we further explored and dissected the Late Mesozoic tectonic evolution of the eastern Tien Shan orogenic belt. Data from detrital-zircon age spectra, KS tests, MDS plots, Monte Carlo simulations, etc., suggested that eastern Tien Shan was also highly active during the Mesozoic, and especially, Bogda was the most remarkable. Moreover, there was a sig-nificant differential segmental exhumation before the Late Jurassic. In general, from the Early Ju-rassic to the Cretaceous, the proportion of Bogda provenance gradually increased, especially the large-scale uplift and denudation that occurred after the development of the Qigu Formation. The provenance of central Tien Shan and Jueluotag gradually stabilized before the Cretaceous. From the Late Jurassic to the Cretaceous, the decreasing tendency of the central-Tien-Shan-provenance percentages decreased, while that of Jueluotag provenance increased. Furthermore, central Tien Shan provenance had a slightly growing trend from the Early Jurassic (38%) to the Middle Jurassic (41.3%) and then gradually decreased to 20.3%. The Central Tien Shan still accounted for a sizeable proportion of the provenance, the genesis of which suggests that it may be that provenance as-cribable to central Tien Shan still crossed the poorly uplifted Jueluotag to the Turpan-Hami basin. Similar to central Tien Shan, the provenance ascribable to Jueluotag gradually decreased from an initial 51.8% to 14.9% in the Late Jurassic, but the proportion of the provenance increased again to 26% during the Cretaceous. These features opened the prelude to the Cenozoic tectonic activities in this region. In addition, the decomposition results revealed that the inverse Monte Carlo mixed model for dissecting the provenance of sandstone samples was subject to large biases in complex geological settings, such as detrital-zircon populations, the age spectra of source areas, contempo-raneous magmatism, and recovered older strata. Full article

Medical ultrasound and other devices that require transducer arrays are difficult to manufacture, particularly for high frequency devices (>30 MHz). To enable focusing and beam steering, it is necessary to reduce the center-to-center element spacing to half of the acoustic wavelength. Conventional methodologies prevent co-sintering ceramic–polymer composites due to the low decomposition temperatures of the polymer. Moreover, for ultrasound transducer arrays exceeding 30 MHz, methods such as dice-and-fill cannot provide the dimensional tolerances required. Other techniques in which the ceramic is formed in the green state often fail to retain the required dimensions without distortion on firing the ceramic. This paper explores the use of the cold sintering process to produce dense lead zirconate titanate (PZT) ceramics for application in high frequency transducer arrays. PZT–polymer 2-2 composites were fabricated by cold sintering tape cast PZT with Pb nitrate as a sintering aid and ZnO as the sacrificial layer. PZT beams of 35 μm width with ~5.4 μm kerfs were produced by this technique. The ZnO sacrificial layer was also found to serve as a liquid phase sintering aid that led to grain growth in adjacent PZT. This composite produced resonance frequencies of >17 MHz. Full article

Chemically and thermally stable ceramics are required for many applications. Many characteristics (electrochemical stability, high thermomechanical properties, etc.) directly or indirectly imply the use of refractory materials. Many devices require the association of different materials with variable melting/decomposition temperatures, which requires their co-firing at a common temperature, far from being the most efficient for materials prepared by conventional routes (materials having the stability lowest temperature determines the maximal firing temperature). We review here the different strategies that can be implemented to lower the sintering temperature by means of chemical preparation routes of oxides, (oxy)carbides, and (oxy)nitrides: wet chemical and sol–gel process, metal-organic precursors, control of heterogeneity and composition, transient liquid phase at the grain boundaries, microwave sintering, etc. Examples are chosen from fibers and ceramic matrix composites (CMCs), (opto-)ferroelectric, electrolytes and electrode materials for energy storage and production devices (beta alumina, ferrites, zirconia, ceria, zirconates, phosphates, and Na superionic conductor (NASICON)) which have specific requirements due to multivalent composition and non-stoichiometry. Full article

PZT-silsesquioxane-based 0-3 hybrid materials are prepared by mixing lead zirconate titanate (Pb(Zr,Ti)O₃; PZT) powder with a [R-SiO_3/2]_n (R = H, CH₃, CH=CH₂, C₆H₅) silsequioxane preceramic polymer. A PZT load up to 55 vol.% can be reached in the final composite. The piezoelectric and mechanical properties are investigated as a function of the filler content and are compared with theoretical models and reference samples made of the pure preceramic polymer or PZT filler. The piezoelectric response of the composites, as expressed by the relative permittivity and the piezoelectric coefficients d₃₃ and g₃₃, increases with an increasing PZT content. The bending strength of the composites ranges between 15 MPa and 31 MPa without a clear correlation to the filler content. The thermal conductivity increases significantly from 0.14 W∙m⁻¹∙K⁻¹ for the pure polymer-derived ceramic (PDC) matrix to 0.30 W∙m⁻¹∙K⁻¹ for a sample containing 55 vol.% PZT filler. From X-ray diffraction experiments (XRD), specific interactions between the filler and matrix are observed; the crystallization of the PDC matrix in the presence of the PZT filler is inhibited; conversely, the PDC matrix results in a pronounced decomposition of the filler compared to the pure PZT material. Full article

Mullite-Zirconia refractories are well known for their good resistance to corrosion and thermal shock. In this study, several mullite-zirconia composites were developed from andalusite, alumina and zircon sintered at 1600 °C for 10 hours. The samples were subjected to thermal shock carried out after heating at 1200 °C, in order to study the mechanical and thermomechanical behaviour as a function of the amount of zirconia dispersed in the mullite matrix. It appears that that the amorphous phase (SiO₂), determined by X-ray diffraction, produced by the decomposition of andalusite, increases considerably with the amount of final zirconia in the composite and has a very important influence on the porosity. This amorphous phase seems also to have an important influence on the mechanical properties of the material. The characterisation of the thermomechanical behaviour (elastic properties and damage monitoring) was carried out thanks to ultrasonic techniques (US echography and Acoustic Emission). The “surprising” evolution (increase) of the Young’s modulus E of the material after being submitted to repeated thermal shocks is highlighted and explained. The acoustic emission technique carried out at high temperature and also coupled to 4-points bending tests (at room temperature) demonstrates its effectiveness for providing a better understanding of the chronology of the involved mechanisms involved at microstructural scale. Full article

In this work, the inkjet printing of proton conducting Y-substituted barium zirconate (BZY) thin films was studied. Two different kinds of precursor inks, namely a rather molecular BZY precursor solution and a BZY nanoparticle dispersion, have been synthesized and initially investigated with regard to their decomposition and phase formation behavior by thermal analysis, X-ray diffraction, and scanning electron microscopy. Their wetting behavior and rheological properties have been determined in order to evaluate their fundamental suitability for the inkjet process. Crystalline films have been already obtained at 700 °C, which is significantly lower compared to conventional solid-state synthesis. Increasing the temperature up to 1000 °C results in higher crystal quality. Permittivity measurements gave values of around 36 that are in good agreement with the literature while also proving the integrity of the materials. A modification of the as-synthesized BZY stock solution and nanoparticle dispersion by dilution with propionic acid improved the jetability of both inks and yielded homogeneous BZY coatings from both inks. In order to study the electrochemical properties of BZY films derived from the two printed inks, BZY coatings on sapphire substrates were prepared and characterized by electrochemical impedance spectroscopy. Full article

Lead zirconate titanate (PZT) was plasma sprayed onto various substrates of different character. Additionally, a free-standing body made by plasma spraying was investigated. X-ray diffraction analyses of a decomposition of the as-sprayed coating products detected components of the PT-PZ system as well as binary oxides—PbO and ZrO₂. Due to the comparatively complex phase character, the Curie temperature monitored by DTA, had a smeared appearance without pronounced maxima. The corresponding electrical properties are comparable with those typically observed for CaTiO₃, but are worse than the normal values of bulk PZT due to defective stoichiometry. Full article