Al2O3 ZrO2 Research Articles

Influence of Carbon Nanostructures on the Physical and Operational Properties in Al2O3–ZrO2 Structural Ceramic

Influence of Carbon Nanostructures on the Physical and Operational Properties in Al2O3–ZrO2 Structural Ceramic

Contribution to the Understanding of the Dielectric Breakdown Mechanism of ZTA Ceramics

Herein, the breakdown mechanism of alumina‐based ceramics (Al2O3–ZrO2) is studied. The specimens are characterized for their density, phase structure, micromorphology, breakdown process, and breakdown channel by micro computed tomography, high‐speed cameras, etc. The study reveals that the dielectric breakdown stability of the samples shows a decreasing trend and the dielectric loss shows an upward trend with the increase of ZrO2 content. The tetragonal phase zirconia is beneficial to enhance the dielectric breakdown strength of the sample, which is related to the martensitic transformation to prevent crack propagation. Before the ceramic breakdown, the insulating oil first breaks down, causing electric sparks. Once the ceramic breakdown occurs, the charges are rearranged, and a large amount of heat energy is generated instantly to melt the substance around the breakdown channel and erupt to the surface to form pits under the action of high internal stress.

Microstructure and phase transformation behavior of Al2O3–ZrO2 under microwave sintering

Zirconia is an inorganic, nonmetallic material with excellent properties. However, the brittleness of the zirconia, resulting from the thermal performance during the heating and cooling process, seriously limits the application of zirconia in the metallurgical, military, and aerospace industries. Al2O3 doped ZrO2 was developed to improve the potential material's toughness. This paper studied the evolution of the surface functional groups, phase composition, toughening mechanism, and particle morphology of Al2O3 doped ZrO2 during the heating process. Especially microwave heating was selected as the heating method during the experiments to save energy consumption. The results showed that the phase transition temperature was reduced by the microwave sintering technique, which also promoted the transformation between the m-ZrO2 and t-ZrO2, advancing the crystallinity and structural properties of the samples. The specific surface area shows a positive relationship with the microwave heating temperature, while the particle size of the powder decreased with the temperature increase. The optimized sintering effect appears at 1000 °C in the studied roasting temperature range (800 °C–1200 °C) for Al2O3–ZrO2 powders. With the optimized sintering temperature, the void of the granular zirconia material was controlled, and the best micromorphology was obtained. In practical production, the application of microwave sintering and alumina doping is beneficial to saving costs and protecting the environment.

Microstructure of Ultrafine-Grained Al2O3–ZrO2 Ceramics Produced by Two-Step Spark Plasma Sintering

Microstructure of Ultrafine-Grained Al2O3–ZrO2 Ceramics Produced by Two-Step Spark Plasma Sintering

Dimethyl ether (DME) synthesis from CO2 and H2 through ethanol-assisted methanol synthesis and methanol dehydration

Two steps of dimethyl ether (DME) synthesis from CO2 and H2 in a batch reactor were studied, including CO2 hydrogenation to methanol through ethanol-assisted method and methanol dehydration to DME. Additions of 10 wt% ZrO2, Al2O3 and ZrO2–Al2O3 into Cu/ZnO were investigated in low-temperature methanol synthesis using ethanol as catalytic solvent. Suitable zeolite (ZSM-5 and ferrierite) for methanol dehydration was also determined. Ethanol-assisted method offered high methanol yield and Cu/ZnO/ZrO2 catalyst provided the highest CO2 conversion (82.1%) and methanol yield (60.8%) at 150 °C and 50 bar since ZrO2 decreased CuO crystallite sizes and increased surface areas of the catalyst. For methanol dehydration to DME, zeolite's strong acidity related to DME formation. The Cu/ZnO/ZrO2 - Ferrierite provided the highest DME productivity at 0.44 mmolDME/gcat. In addition, DME synthesis from CO2 and H2 through ethanol-assisted methanol synthesis and methanol dehydration can be a potential method to simultaneously produce DME and ethylene. Under the operating conditions, ethylene was produced as a valued by-product of 5.65 mmolEthylene/gcat from dehydration of ethanol. In this study, rather high methanol yield was obtained from ethanol-assisted method. However, DME yield can be further improved by increasing synthesis temperature.

Production and Characterization of ZrO2–Al2O3–K2O Based Ceramic Whitening Agents

Production and Characterization of ZrO2–Al2O3–K2O Based Ceramic Whitening Agents

Flash sintering of Al2O3–ZrO2 ceramics under alternating current electric field

In this study, the influence of alternating current (AC) electric field on flash sintering and microstructural evolution of alumina–zirconia (Al2O3–ZrO2) composite was systematically investigated at furnace temperature of 800 °C. Compared with direct current (DC) electric field, AC electric field not only promoted densification and grain growth of Al2O3–ZrO2 composite, but also improved the uniformity of microstructure of ceramics. Grain size of AC flash-sintered samples was found to be inversely related to electric field, and positive correlation was observed with current density limit. Dense Al2O3–ZrO2 composite ceramic was fabricated via AC flash sintering under 60 mA mm−2 at low furnace temperature within 120 s, and as-sintered samples exhibited relatively good mechanical properties. The mechanism involving synergistic effect of Joule heating and defects generation under the influence of electric field was proposed to explain rapid densification during AC flash sintering. These results indicate the feasibility of preparation of dense composite ceramic with homogeneous microstructure via AC flash sintering.

Enhanced electrochemical performance of Li-rich manganese layered oxide Li1.2Mn0.54Ni0.13Co0.13O2 by surface modification with Al2O3–ZrO2 for lithium-ion battery

Enhanced electrochemical performance of Li-rich manganese layered oxide Li1.2Mn0.54Ni0.13Co0.13O2 by surface modification with Al2O3–ZrO2 for lithium-ion battery

Refractories for the processing of Fe–TiC alloy

In order to select the appropriate crucible material for Fe–TiC composite alloy processing, Al2O3, CaZrO3, and MgO-stabilized ZrO2 ceramic substrates were tested for interaction with a liquid Fe–TiC alloy at 1650 °C. The sessile drop method under protective gas was applied to conduct the experiment. The measured contact angle of Fe–TiC alloy followed the tendency of MgO-stabilized ZrO2˃CaZrO3˃Al2O3. After investigations, the Al2O3 substrate was strongly corroded by the liquid Fe–TiC alloy. The CaZrO3 substrate showed a smooth and non-corroded interface after the interaction. Reactions products TiOx and MgTiOx were detected between alloy and Mg–ZrO2 substrate. Obtained results were discussed under consideration of SEM/EDX analysis, which was conducted on the cross-section samples of metal/ceramic compound and on the top surface of the solidified Fe–TiC alloy; and of thermodynamic simulations of the Fe–TiC alloy interaction with the investigated substrates.

Effects of CeO2 on the phase, microstructure and mechanical properties of Al2O3-ZrO2(CeO2) nanocomposite ceramics (AZC-NCs) by solid solution precipitation

It is one of the most concerning issues to achieve fine nanostructures and a reasonable ZrO2 crystal structure in Al2O3–ZrO2 structural ceramics. Herein, Al2O3–ZrO2(CeO2) nanocomposite ceramics (AZC-NCs) with different CeO2 contents were prepared by sintering Al2O3–ZrO2(CeO2) supersaturated solid solution powders (AZC-SSSPs). The effects of CeO2 on the phase, microstructure, and mechanical properties of AZC-NCs were investigated systematically. During rapid solidification process, three phases of Al2O3, ZrO2 and CeO2 are dissolved together and form AZC-SSSPs with regular spheres. After sintering, the AZC-SSSPs transform into two-phase structure and compact into AZC-NCs. The AZC-NCs show an intragranular/intercrystalline nanoprecipitation structure, and large amounts of ZrO2 in AZC-NCs remain in a tetragonal structure at room temperature because of the addition of CeO2. Among the AZC-NCs, that with 6 mol% CeO2 shows the best mechanical properties with the highest values of strength and toughness: 865 ± 24 MPa and 8.4 ± 0.16 MPa·m1/2. Spark plasma sintering has no obvious influence on the microstructure and phase composition of AZC-NCs. This work provides guidance to optimize the microstructure and ZrO2 crystal structure of AZC-NCs.

Extraction of Zirconium from Its Oxide during Electrolysis of the KF–AlF3–Al2O3–ZrO2 Melts

Extraction of Zirconium from Its Oxide during Electrolysis of the KF–AlF3–Al2O3–ZrO2 Melts

Adsorption of CO2 by a novel zeolite doped amine modified ternary aerogels

Novel amine functionalized materials can capture greenhouse gas CO2. In this study, SiO2–Al2O3–ZrO2 ternary composite aerogel was prepared by sol-gel method, supercritical drying, ultrasonic non-in-situ synthesis and other processes using aluminum chloride hexahydrate as aluminum source, ethyl orthosilicate as silicon source and tetrabbutyl zirconate as zirconium source. The composite material was used as the carrier material. By impregnation method, the modified agent bis - (3-trimethoxy-silpropyl) amine and the composite were fully mixed and modified, and the novel zeolite doped amine functionalized ternary composite aerogel was obtained by doping acidification activation zeolite. The results show that the prepared novel zeolite amine-modified ternary aerogels have rich microporous structure and ordered mesoporous structure. After loading different contents of amine-based materials (CAA-X) in the ternary aerogels, the comparison between CAAZ-X and zeolite amine-modified ternary aerogels is conducted. Zeolite doped CAAZ-30 material shows the best adsorption performance, with a maximum adsorption capacity of 5.30 mmol/g. In the presence of water vapor, CAAZ-30 material also showed the best adsorption performance, with a maximum adsorption capacity of 5.33 mmol/g. This can help us design suitable adsorbent materials for CO2 capture in different practical applications.

A new strategy to obtain thin ZrO2–Al2O3 composite aerogel coating with prominent high–temperature resistance and rapid heat dissipation

High–temperature resistant aerogel coating usually prevents damage to walls and equipment in a harsh high–temperature environment, but these coating still has some disadvantages in practical application, such as short time of high–temperature resistance or low stability. In this work, ZrO2–Al2O3 composite aerogel coating with prominent high–temperature resistance and rapid heat dissipation was successfully fabricated by employing (Al(H2PO4)3, AHP) as high–temperature adhesive to form stable phosphates products. The thermal conductivity and thermal diffusivity of the obtained ZrO2–Al2O3 composite aerogel coating are 0.1602–0.1623 ​W/mK and 0.3488–0.4702 ​mm2/s, respectively. The resultant aerogel coating with a thickness of 1.4 ​cm showed good performance in heat resistance with tolerance of flame up to ∼1300oC for 15 ​min, and rapid heat dissipation that can be cooled to 32.7–38.4oC within 60–70 ​s. Phosphate products, such as AlPO4 and ZrP2O7, are mainly formed at high temperature with the introduction of AHP, which fundamentally improves the high–temperature resistance and flame retardant of aerogel coating. Different microstructure and pore structure are responsible for the heat dissipation performance of the aerogel coating, which shows high thermal diffusivity of 0.3488–0.4702 ​mm2/s. Overall, this work provides a new strategy for preparing aerogel coating with high–temperature resistance, flame retardant, thermal stability and rapid heat dissipation suitable for harsh conditions.

Mechanical properties and machinability of lithium silicate glass-ceramics with varying MgO content

This study focused on the role of lithium metasilicate crystalline phase and microstructural evolution on altering the mechanical properties and machinability of two glass-ceramic system, (Li2O–K2O–Na2O–CaO–MgO–ZrO2–Al2O3–P2O5–SiO2), previously developed by our research group. Our previous study showed that increasing MgO content introduced phase separation and thus controlling the crystallization and microstructure of the glass-ceramics. For this study we chose the glass ceramic system with 1.5 and 4.5 mol% MgO. The glass-ceramics were prepared by melt cast method followed by heat treatment at 650 °C to induce partial crystallization. The crystalline phase in the glass-ceramics was identified by x-ray diffraction and the quantification of crystalline and amorphous phase content was done using Rietveld refinement. The hardness and elastic moduli were measured by nanoindentation. Vickers hardness and fracture toughness were determined by micro indentation. Nano scratch test was performed and scratch morphology was characterized using AFM and FEG-SEM. In order to compare the machinability of the prepared glass-ceramic samples, milling experiments were carried out using CNC milling machine, and machining characteristics were compared by analysing machining force, surface roughness and microstructure of the machined surface. Presence of higher amount of lithium metasilicate (LS) crystals in higher magnesia containing glass-ceramic (G2) resulted in lower average force (Fyrms) as compared to lower MgO containing glass-ceramic. However, due to a wide range of variation in crystal size (150 nm - 2 μm) in higher MgO containing glass-ceramic, the force fluctuation was more than lower MgO containing glass-ceramics.

Microstructural refinement and mechanical response of Al2O3–ZrO2 eutectics fabricated by a novel pulse discharge plasma assisted melting method

In the present work, microstructural refinement and mechanical response of Al2O3–ZrO2 eutectics fabricated by a pulse discharge plasma assisted melting (PDPAM) method were investigated. The solidified microstructure evolves from polygonal eutectic colonies into irregular cellular colonies with increasing the superheating temperature of the melt from 1820 °C to 1900 °C. The average eutectic spacing inside the colonies decreases from 1.80 ± 0.10 μm to 0.25 ± 0.06 μm, and the coarse inter-colonial structure is refined, which is attributed to the increase in undercooling temperature. High-temperature microstructural stability of Al2O3–ZrO2 eutectics is improved significantly as contrasted with the as-sintered ceramics. Besides, the load dependence of Vickers hardness for Al2O3–ZrO2 eutectics is investigated.

PRODUCTION AND CHARACTERIZATION OF ZrO2–Al2O3–K2O BASED CERAMIC WHITENING AGENTS

Zircon-containing whitening agents are indispensable components increasing the cost of ceramic tiles. In the ceramic industry, the developing of unique and low-cost whitening agents with comparable final product quality is an essential motivation. In this study, a unique ZrO2–Al2O3–K2O-based whitening agent was developed by mixing zircon silicate, Al2O3, K-feldspar, and marble with various weight concentrations to reduce costs and give a valid alternative to the commercially available R6-coded ZrO2–Al2O3–Na2O whitening agent. To test the innovative ZrO2–Al2O3–K2O-based whitening agent’s efficiency, a systematic characterization procedure was utilized to reveal factors affecting the tile opacity, including size, shape, and distribution of opacifier particles and the incident light wavelength. First, X-ray diffraction and X-ray fluorescence analyses examined the initial grain sizes and structural properties of the whitening agent constituents. Second, a wet milling process in industrial mills was utilized to produce a homogenized ZrO2–Al2O3–K2O-based composite whitening agent. Structural, mineralogical, and morphological properties of the final product were determined after the drying process. The efficiency of the wet milling process was proved according to scanning microscopy analysis revealing homogenous particle size distribution of constituents with mainly composed of ZrO2, Al2O3, and SiO2 phases. Energy dispersive X-ray analysis reveals that Si–Al–O–Zr and Ca were major elements whereas Na was obtained as minor element. The full article will be published in the translated version of the journal Glass and Ceramics, 2022, V. 79, No. 5–6.

Synthesis and performance of aluminous cements containing zirconium and strontium as alternatives to the calcium aluminate cements designed for the production of high performance refractories

Composite cements belonging to the CaO–Al2O3–ZrO2 (C-A-Z) and CaO–SrO–Al2O3–ZrO2 (C–Sr-A-Z) systems were evaluated as alternatives to calcium aluminate cements (CACs) for use in the refractory castables technology. The mineralogical phases in the as-synthesized C-A-Z and C–Sr-A-Z clinkers confirmed by XRD and SEM-EDS were CaAl2O4, Ca7ZrAl6O18 and CaZrO3 or (Ca,Sr)Al2O4, (Ca,Sr)Al4O7 and (Ca,Sr)ZrO3, respectively. The present work aimed at developing novel Zr-containing cements with excellent mechanical performance, i.e. modulus of rupture and cold crushing strength. Both hydration behavior of the C-A-Z, C–Sr-A-Z, CAC and their hydration products, were studied with isothermal calorimetry, XRD, SEM-EDS and NMR. Impedance camera instrument was firstly successfully applied for time-resolved electrochemical impedance spectroscopy measurements under nonstationary conditions and record the time-dependent evolution of the Nyquist plots for hydrating cement pastes. A sharp increase in the real part of impedance Z’ versus hydration time were corresponded to the second exothermic peak detected on the calorimetry curves.

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

This paper presents a study of Al2O3–ZrO2 (ZTA) nanocomposites with different contents of reduced graphene oxide (rGO). The influence of the rGO content on the physico-mechanical properties of the oxide composite was revealed. Graphene oxide was obtained using a modified Hummers method. Well-dispersed ZTA-GO nanopowders were produced using the colloidal processing method. Using spark plasma sintering technology (SPS), theoretically dense composites were obtained, which also reduced GO during SPS. The microstructure, phase composition, and physico-mechanical properties of the sintered composites were studied. The sintered ZTA composite with an in situ reduced graphene content of 0.28 wt.% after the characterization showed improved mechanical properties: bending strength was 876 ± 43 MPa, fracture toughness—6.8 ± 0.3 MPa·m1/2 and hardness—17.6 ± 0.3 GPa. Microstructure studies showed a uniform zirconia distribution in the ZTA ceramics. The study of the electrical conductivity of reduced graphene oxide-containing composites showed electrical conductivity above the percolation threshold with a small content of graphene oxide (0.28 wt.%). This electrical conductivity makes it possible to produce sintered ceramics by electrical discharge machining (EDM), which significantly reduces the cost of manufacturing complex-shaped products. Besides improved mechanical properties and EDM machinability, 0.28 wt.% rGO composites demonstrated high resistance to hydrothermal degradation.

Fabrication of porous gehlenite coating on Al2O3-ZrO2-SiC composite ceramics and its in vitro biological activities.

Porous gehlenite coatings on Al2O3-ZrO2-SiC composite ceramics were prepared by electro-spraying technique combined with reactive sintering method. The influences of gehlenite coating on the mechanical property of the ceramics and biological activity of the coating were investigated. The results indicated that the gehlenite coating has limited influences on flexural strength and fracture toughness of the ceramics, and the coating has elastic modulus of 82GPa, hardness of 2.2 GPa, and adhesive strength of 1512mN, suggesting its potential application in load-bearing ceramic implants. Simulated body fluid soaking test, CCK-8 and alkaline phosphatase activity assay demonstrated that the porous gehlenite coating has strong mineralization ability, which promotes proliferation and differentiation of MC3T3-E1 cells. These excellent biological performances can be attributed to the synergistic effect of the porous surface of the coating and its release of Ca2+ and Si4+.

Structure and Electrical Properties of Zirconium-Aluminum-Oxide Films Engineered by Atomic Layer Deposition

Thin films containing either multilayer ZrO2:Al2O3 structures or ZrO2 deposited on ZrxAlyOz buffer layers were characterized. The films were grown by atomic layer deposition (ALD) at 300 °C from ZrCl4, Al(CH3)3, and H2O. The multilayer ZrO2:Al2O3 structures were grown repeating different combinations of ZrO2 and Al2O3 ALD cycles while the ZrxAlyOz layers were obtained in a novel process using ALD cycles based on successive adsorption of ZrCl4 and Al(CH3)3, followed by surface reaction with H2O. The films were grown on TiN electrodes, and supplied with Ti top electrodes, whereby ZrxAlyOz films were exploited as thin buffer layers between TiN and ZrO2. The as-deposited ZrO2 films and ZrO2:Al2O3 structures with sufficiently low concentrations of Al2O3 were crystallized in the form of cubic or tetragonal ZrO2 polymorph possessing relative permittivities reaching 35. Notably, multilayered ZrO2:Al2O3 films could exhibit resistive switching behavior with ratios between low- and high-resistive-state current values, extending up to five orders of magnitude. Implications of multilevel switching were recorded. In the double-layered ZrxAlyOz-ZrO2 stacks, the ON/OFF current ratios remained below 40, but the endurance could become extended over 3000 cycles. Remarkably, instabilities, when detected in endurance behavior expressed by reduction in an ON/OFF current ratio could be compensated and the current values restored by real time readjustment of the programming voltage amplitude.