Al2O3 ZrO2 Research Articles

Phase and microstructural evolution in lithium silicate glass‐ceramics with externally added nucleating agent

AbstractDevelopment of lithium disilicate‐based glass‐ceramics critically depends on use of nucleating agent in the glass matrix. The present study reports the effect of externally added nucleating agent Li3PO4 in Li2O–K2O–MgO–ZnO–ZrO2–Al2O3–SiO2 system which is compared with a reference composition (GC1) (SiO2:Li2O = 2.16:1) prepared with in situ formed Li3PO4. For externally added Li3PO4, two compositions were studied. In one case (GC2) before addition of Li3PO4, SiO2:Li2O ratio in glass was maintained as 2.87:1 and in another case (GC3) SiO2:Li2O ratio in glass was maintained same as reference GC1 that is, 2.16:1. The glasses were characterized by using MAS‐NMR spectroscopy. Sintering and crystallization behavior of the glass‐ceramics was characterized by using XRD, SEM, DTA. Due to in situ formation of Li3PO4, GC1 resulted in a dense sample with finer crystals of lithium disilicate. In GC2 and GC3, externally added lithium phosphate, which was in the form of ultrafine aggregated particles, formed flower‐like colonies of radially outward crystals. Higher SiO2:Li2O ratio in GC2 resulted in lithium disilicate crystals and high viscous glass causing large air entrapment and so less densification. GC3 with higher lithia in glass showed higher densification than GC2 but only lithium metasilicate crystals were formed.

Comprehensive study on graphene-based reinforcements in Al2O3–ZrO2 and Al2O3–Ti(C,N) systems and their effect on mechanical and tribological properties

The effect of graphene-based materials: multilayer graphene (MLG), graphene oxide (GO), and nickel-coated graphene (Gn-Ni-P) addition on the mechanical properties of commercial Al2O3–ZrO2 and Al2O3–Ti(C,N) materials is discussed in this paper. The influence of used reinforcements on relative density, microstructure, hardness, and fracture toughness was investigated. Moreover, the combination of strengthening effects deriving from the addition of graphene-based materials and the presence of zirconia or carbon nitride titanium particles was analysed. In order to determine the wear resistance of the obtained composites, tribology test was conducted.The added reinforcement had an evident effect on hardness of the obtained composites in both series, an almost 150 HV5 increase was observed for the TAZ+0.2 wt%GO composites. Fracture toughness remained unchanged or decreased, which was related to the complexity of the Al2O3 + ZrO2 + Ti (CN) + Graphene Family Nanomaterials system. Moreover, an almost 800% decrease of wear rate for the TACN based composite with a 0.2 wt% addition of GO was noted. Other composites also showed an increase in wear resistance depending on the type of matrix, the type of reinforcements and the load applied during the tribology test.

Selective laser melting of AISI 304 stainless steel composites reinforced by Al2O3 and eutectic mixture of Al2O3–ZrO2 powders

The effect of Al2O3 and eutectic mixture of Al2O3–ZrO2 reinforcements on the densification, microstructural, and mechanical behaviors of selective laser melted 304 stainless steel composites have been investigated in this study. An optimum volume content was identified for the eutectic mixture of Al2O3–ZrO2 reinforcement, while the samples reinforced by Al2O3 particles exhibited a detrimental trend with increasing Al2O3 content. The addition of ZrO2 particles led to the formation of regular and even scanning tracks, whereas swelling of the molten tracks was observed due to the melting-point depression in addition to the low viscous melt pools and greater fluidity. Moreover, process-induced cracks and voids were observed in the samples reinforced by Al2O3, while the use of the eutectic mixture of Al2O3–ZrO2 was observed to suppress the cracks, leading to a dense structure. The microhardness of the fabricated samples reinforced with the eutectic mixture of Al2O3–ZrO2 particles was observed to be considerably higher than that of those reinforced with Al2O3 composites due to the homogeneous dispersion of the eutectic structures. The results of this study confirm that the use of a eutectic mixture of Al2O3–ZrO2 particles suppresses process-induced cracks and significantly enhances the reinforcing effect on 304 stainless steel composites.

Electron beam exposure- structural immunity and color tuning in Al2O3–ZrO2:Dy3+ binary matrix prepared by a hybrid approach

This work report site selective emission of Dy3+ in ZrO2–Al2O3 binary system. Exposing these phosphors to electron beam irradiation tuned the emission color from blue to white, however crystalline and structural properties revealed by PXRD and TEM indicates the samples are immune to electron beam exposure. These phosphors were prepared by a hybrid approach, i.e. by combining solution combustion method and solid-state method. Nano particles of ZrO2 and Al2O3 were prepared by solution combustion method and then they were used as starting materials for solid state method. XRD analysis revealed presence of cubic-ZrO2 and α-Al2O3 phases in the prepared binary system. PL excitation spectra contained four peaks with maximum absorption intensity centered at 350 nm due to 6H15/2→6P7/2 transmission of Dy3+ ions. The emission spectra of phosphors excited at 350 nm show three characteristics peaks of Dy3+ centered at 485 nm (4F9/2→6H15/2), 580 nm (4F9/2→6H13/2) and 675 nm (4F9/2→ 6H11/2). Structural and photoluminescence properties were studied again, after exposing those phosphors to high energy electron beam. PL emission spectra were used to probe the hitherto unidentified changes. The asymmetry ratio (Ir) was analyzed in detail to study the fine information on the effect of electron exposure left unnoticed in XRD and TEM. Also, the Commission Internationale d'Eclairage color-coordinates revealed color tuning of the phosphors from blue to white, upon electron beam irradiation. This work reports Photoluminescence emission spectra as a probe to study the ultra-fine effects of electron beam irradiation in the materials.

Catalytic hydrodeoxygenation of bio‐oil model compound for production of fuel grade oil

AbstractBio‐oil, a promising renewable fuel candidate obtained from the hydrothermal liquefaction/pyrolysis of agricultural waste, contains significant amount of oxygen in the form of oxygenated compounds such as aldehydes, ketones, aliphatic/aromatic acids, alcohols, and ethers. This prevents it from being used directly as a fuel. Technologies that can lower the oxygen content of bio‐oil are desired. The present work was driven towards the deoxygenation of bio‐oil. To understand the mechanism of deoxygenation, guaiacol was selected as a model compound. The deoxygenating ability of acid site (support) and hydrogenation ability of metal were leveraged in this work. Highly acidic mixed oxide support such as ZrO2–Al2O3 was used to synthesize a bimetal catalyst Ni–Mo/ZrO2–Al2O3, and the said catalyst was used for deoxygenation of bio‐oil/model compound in tetralin as hydrogen donor solvent. The effects of reaction time, temperature, and hydrogen pressure on the conversion were examined. Results showed that 100% guaiacol conversion was obtained with 45.3% phenol and 11.1% cyclohexane yield at 330°C and 30‐bar H2 pressure and reaction time of 10 hr.

Cyclodehydration of 1,4-butanediol over Zr-Al Catalysts: Effect of Reaction Medium.

The conversion of 1,4-butanediol (BDO) to tetrahydrofuran (THF) in aqueous phase is desirable because BDO production technology is shifting to bio-based aqueous fermentation routes. In this study, liquid-phase cyclodehydration of BDO to THF was studied in two reaction media (pure BDO and aqueous BDO feeds) at 200–240 °C using ZrO2-Al2O3 (ZA) mixed oxides, which were made with a co-precipitation method and were characterized with XRD, BET, SEM/EDX, pyridine and n-butylamine adsorptions. The maximum acidity and the largest surface area occurred at Zr/Al atomic ratios of 1/1 (ZA11) and 1/3 (ZA13), respectively. The reaction exhibited pseudo-first-order; aqueous BDO feed had much greater rate constant than pure BDO feed, ascribed to the acidic properties of adsorbed water molecules (coordinated to surface metal cations) for the former case. For pure BDO feed, linear relation was observed between rate constant and catalyst acidity, and ZA11 reached a THF yield of 90.1% at 240 °C. With aqueous BDO feed, rate constant increased linearly with increasing surface area and ZA13 reached a THF yield of 97.1% at 220 °C. The change of optimum catalyst composition with reaction medium suggests that active sites for catalyzing BDO cyclodehydration changed with the reaction environment.

The Influence of Manganese Oxide on the Sintering and Properties of the Eutectic Ceramics of the ZrO2–Al2O3–SiO2 System

The Influence of Manganese Oxide on the Sintering and Properties of the Eutectic Ceramics of the ZrO2–Al2O3–SiO2 System

Al2O3-Based Ceramic Composites with a High Brittle Fracture Resistance

We examine synthesis conditions of precursors to ZrO2–Al2O3–CeO2 powders modified with calcium cations. The precipitation procedure and the aging of reaction systems of precursors to the synthesized composites are shown to influence the morphology and particle size of the nanopowders and the evolution of the phase composition, microstructure, and mechanical characteristics of composites prepared from them. The composites offer a high brittle fracture resistance due to the combined effect of transformation and dispersion hardening owing to the presence of T-ZrO2-based solid solutions and calcium hexaaluminates (bending strength, up to 1000 MPa; fracture toughness KIc, up to 10.5 MPa m1/2).

Combustion synthesis assisted water atomization-solid solution precipitation: A new guidance for nano-ZTA ceramics

It is difficult to synthesize ceramics with ultra-fine nanostructures because of inevitable grain growth during the sintering process. In this work, a novel technique, i.e. combustion synthesis assisted water atomization (CSAWA) method, was invented to synthesize supersaturated Al2O3/ZrO2 solid solution powders. The huge cooling rate supplied by CSAWA greatly improved the solubility of Al3+ in ZrO2 lattice. Subsequently, the synthesized powders underwent a solid solution precipitation process. The ultra-fine ZrO2 nanoparticles and Al2O3 matrix are precipitated from metastable phase, and the ZrO2 nanoparticles are uniformly dispersed in Al2O3 matrix. Simultaneously, the powders were densified and formed compact ZTA ceramics. Together with detailed microstructure, phase composition, interface characteristic, mechanical properties, as well as the toughening mechanisms were collaboratively outlined. CSAWA-SSPP not only produces impressive comprehensive properties, but also much lower costs and simpler process than currently methods, which opens up a new route to industrially produce nano-ZTA ceramics with high performance.

Influence of a heterolayered Al2O3–ZrO2/Al2O3 ceramic protective overcoat on the high temperature performance of PdCr thin film strain gauges

The application of PdCr thin film strain gauges on gas turbine engines requires protective overcoats to prevent the oxidation of the PdCr sensitive element. In this work, a heterolayered Al2O3–ZrO2/Al2O3 ceramic film, which was fabricated by electron beam evaporation, is utilized as a protective overcoat over the PdCr sensitive thin film. The morphology and microstructure of the prepared films indicate that the composite Al2O3–ZrO2 film is smooth and compact, and the interface between the composite Al2O3–ZrO2 film and Al2O3 film is crack-free, which contributes to improving the protective performance of the heterolayered Al2O3–ZrO2/Al2O3 ceramic protective overcoat at high temperature. Moreover, the PdCr thin film strain gauge with heterolayered Al2O3–ZrO2/Al2O3 ceramic film as protective overcoat displays a minimum drift rate of less than 0.09%/h at 800 °C, and excellent cyclic repeatability such that the eight cyclic curves of the relative grid resistance are almost overlapped from room temperature to 800 °C, indicating the excellent protecting performance of the heterolayered Al2O3–ZrO2/Al2O3 ceramic overcoat. It also reveals the smallest temperature coefficient of resistance of 155.3 ppm/°C compared to the monolayer Al2O3 overcoat and composite Al2O3–ZrO2 overcoat.

Utility of ZrO2–Al2O3 in the synthesis of 2,3-dihydroquinazolin-4(1H)-ones

In this paper, we report the synthesis of a nano acid catalyst ZrO2–Al2O3 by using urea as a fuel and the evaluation of its catalytic efficiency in the synthesis of a series of novel substituted dihydroquinazolinones. The catalyst was found to be a highly effective solid acid catalyst, and it exhibited significant catalytic activity in converting substituted 2-aminobenzamides into corresponding 2, 3-dihydroquinazolin-4(1H)-ones under mild conditions. The optimized synthetic method is facile, rapid and efficient and may emerge as one of the best methodologies for accessing pharmaceutically useful dihydroquinazolines.

Simulating permeabilities based on 3D image data of a layered nano-porous membrane

The macroscopic properties of materials are strongly influenced by their microstructure. Essential micro-structural information can be obtained from high-resolution 3D images, usually obtained by computed tomography. Here, a layered nano-porous ZrO2 Al2O3 membrane for fluid filtration is investigated, whose two finer layers can not be resolved properly by computed tomography. 3D image data of these structures are therefore obtained by the combination of focused ion beam sectioning and scanning electron microscopy. Reconstruction of porous structures from this type of image data and subsequent numerical simulation of flow properties within the reconstructed structure bear several sources of error. Using stochastic geometry models for the solid component, we examine more closely the error due to the typical anisotropic voxel setting as well as the error due to the also typical uneven sample shape.

Heterocoagulation and SPS sintering of sulfonitric-treated CNT and 8YZ nanopowders

ABSTRACTReinforcement of ceramic composites using carbon nanotubes (CNT) has been extensively studied for materials such as Al2O3, Si3N4 and tetragonal ZrO2. Knowledge concerning CNT composites based on a matrix of cubic zirconia (8YZ) is in short supply, however. This paper presents a study on the addition of 1 wt% CNT to an 8YZ matrix. CNT was functionalized by sulfonitric treatment at three different temperatures: 50, 90 and 130°C. To obtain strong bond between the CNT and the 8YZ particles, the composites were produced by electrostatic heterocoagulation followed by consolidation by spark plasma sintering (SPS). Dense 8YZ-CNT composites were successfully processed by the proposed route. A study of the influence of the surface treatment temperature of CNT on the final properties of ceramics is also presented. CNTs are dispersed uniformly and individually within the 8YZ matrix in 8YZ-CNT90 and 8YZ-CNT130 composites. 8YZ-CNT50 displayed a less uniform CNT distribution and the largest grain size, suggesting that the lowest temperature acid pretreatment is less effective for the subsequent heterocoagulation mixture. The reinforcement of ceramic materials by the addition of 1 wt% CNT was confirmed by an evaluation of fracture toughness.

Effect of doping SiC particles on cracks and pores of Al2O3–ZrO2 eutectic ceramics fabricated by directed laser deposition

Melt growth Al2O3–ZrO2 eutectic ceramic has excellent high-temperature strength, creep resistance, oxidation resistance and ultra-high-temperature microstructural stability, which is expected to become one of the ideal high-temperature structural materials. Directed laser deposition (DLD) is a new technology for fabrication of melt growth eutectic ceramics, which can rapidly fabricate net-shaped ceramics. Aiming at decreasing crack and pore defects in samples prepared by DLD, different proportions of SiC particles (SiCp) are doped into Al2O3–ZrO2. Results show that SiCp distributes uniformly in Al2O3–ZrO2 eutectic ceramic matrix. Interfacial reaction occurs between SiCp and matrix. Two kinds of white phases rich in C, Si, Zr elements are formed around SiCp, and they are closely bonded with SiCp and matrix. The number and the maximum length of cracks in sample decrease obviously with the addition of SiCp. When the content of SiCp increases from 0 to 25 wt%, the number of cracks decreases 93% and the maximum cracks length decreases 92%. Some energy dissipation mechanisms such as crack pinning, transgranular fracture, crack deflection and bifurcation have remarkable effect on crack suppression. In addition, SiCp plays a significant role in eliminating pores, which reduces the porosity from 11.71 to 0.20%. Doping SiCp can increase the temperature and enhance the convection and disturbance of melt pool. Also, it can provide discharge channels for bubbles in melt pool.

Assessment of the role of ζ- and δ-phases in ZrO2–Al2O3 composite based hot dip zinc galvanized coating by layer wise tuning

Effective performance of hot dip galvanized coatings depends on the composition of intermetallic layers and layer wise morphology and topography. In the present work, a corrosion resistant ZrO2–Al2O3 composite hot dip zinc coating was developed. The role of mixed ζ- and δ-phases in the Fe–Zn intermetallic layer of the ZrO2–Al2O3 composite coating was evaluated. Each of the intermetallic layers in the coating was subjected to anodic dissolution at optimized time intervals. Mixed ζ- and δ-phases in the coating had inter-penetrable nature since the phases were dissoluted together and had a combined cross sectional morphology. A uniform and homogeneous surface morphology was developed in the mixed ζ- and δ-phases due to the incorporation of the ZrO2–Al2O3 composite. A low corrosion rate of 1.764 mmpy was achieved with respect to the mixed ζ- and δ-phases of the coating. The role of mixed ζ- and δ-phases on overall performance of the ZrO2–Al2O3 composite zinc coating was also assessed. This study provides an insight into the criteria of basic tuning for targeted high temperature coatings, e.g. corrosion, mechanical, plasticity etc.

Highly Selective Syngas/H2 Production via Partial Oxidation of CH4 Using (Ni, Co and Ni–Co)/ZrO2–Al2O3 Catalysts: Influence of Calcination Temperature

In this study, Ni, Co and Ni–Co catalysts supported on binary oxide ZrO2–Al2O3 were synthesized by sol-gel method and characterized by means of various analytical techniques such as XRD, BET, TPR, TPD, TGA, SEM, and TEM. This catalytic system was then tested for syngas respective H2 production via partial oxidation of methane at 700 °C and 800 °C. The influence of calcination temperatures was studied and their impact on catalytic activity and stability was evaluated. It was observed that increasing the calcination temperature from 550 °C to 800 °C and addition of ZrO2 to Al2O3 enhances Ni metal-support interaction. This increases the catalytic activity and sintering resistance. Furthermore, ZrO2 provides higher oxygen storage capacity and stronger Lewis basicity which contributed to coke suppression, eventually leading to a more stable catalyst. It was also observed that, contrary to bimetallic catalysts, monometallic catalysts exhibit higher activity with higher calcination temperature. At the same time, Co and Ni–Co-based catalysts exhibit higher activity than Ni-based catalysts which was not expected. The Co-based catalyst calcined at 800 °C demonstrated excellent stability over 24 h on stream. In general, all catalysts demonstrated high CH4 conversion and exceptionally high selectivity to H2 (~98%) at 700 °C.

Mechanochemical Activation of Precursor Powders for the Preparation of Dense Al2O3–ZrO2〈Y2O3〉 Nanoceramics

A process has been demonstrated for the preparation of precursor powders and nanocrystalline (60–90 nm) alumina-based ceramics in the Al2O3–ZrO2〈Y2O3〉 system. We have studied the influence of mechanochemical activation (MA) on the structure and particle size of precursor powders and found the most effective MA time. MA has been shown to lower the α-Al2O3 formation temperature and accelerate the powder sintering process. We have optimized powder consolidation conditions for the fabrication of dense nanoceramics and studied their physicochemical and mechanical properties.

Synthesis of Highly Dispersed Al2O3–ZrO2–MgO Materials Using Electrogenerated Reagents

We have studied the morphology and phase composition of precursors for the preparation of highly dispersed alumina-based Al2O3–ZrO2–MgO materials. The precursors were synthesized in a coaxial diaphragmless electrolyzer with a soluble anode. Zr(IV) and Mg(II) ions were added during the synthesis process. It has been shown that varying electrolysis conditions allows the particle size and phase composition of the precipitate to be controlled. Synthesis in the Al2O3–ZrO2–MgO system is accompanied by Al2MgO4 spinel formation. Increasing the spinel concentration helps the metastable phase θ-Al2O3 to persist.

TRIBOLOGICAL PROPERTIES OF Al2O3/ZrO2 SINTERED CERAMICS

The paper presents mechanical and tribological properties of Al2O3/ZrO2 composite sinters with different proportions of Al2O3 and ZrO2 phases. These materials are commonly used in dry friction contact due to relatively low manufacturing costs of even complex shapes of products and the possibility of working at elevated temperatures. The tests were carried out by the ball-on-disc method at temperatures of 20, 150, 300, and 500°C. A ball made of Al2O3 was used as a counterpart. The results were compared with the following sintered mono-phase materials: Al2O3(alumina) and tetragonal yttria-stabilized ZrO2 polycrystallines (Y-TZP). The tests showed the significantly better properties of composite materials.

Preparation and heat-insulating properties of Al2O3-ZrO2(Y2O3) hollow fibers derived from cogon using an orthogonal experimental design.

Bionic design is efficient to develop high-performance lightweight refractories with sophisticated structures such as hollow ceramic fibers. Here, we report a four-stage procedure for the preparation of Al2O3–ZrO2(Y2O3) hollow fibers using the template of cogon—a natural grass. Subsequently, to optimize the thermal performance of the fibers, four sets of preparation parameters, namely, x(Al2O3), solute mass ratio of the mixture, dry temperature, and sintering temperature were investigated. Through an orthogonal design, the optimal condition of each parameter was obtained as follows: x(Al2O3) was 0.70, solute mass ratio of the mixture was 15 wt%, dry temperature was 80 °C, and sintering temperature was 1100 °C. Overall, Al2O3–ZrO2(Y2O3) hollow fibers show relatively low thermal conductivity (0.1038 W m−1 K−1 at 1000 °C), high porosity (95.0%), and low density (0.05–0.10 g cm−3). The multiphase compositions and morphology of Al2O3–ZrO2(Y2O3) hollow fibers, which may contribute to their thermal properties, were also discussed.