Porous Alumina Matrix Research Articles

Magnetic Properties of Ni Nanowires in Porous Anodic Alumina Matrix

Magnetic Properties of Ni Nanowires in Porous Anodic Alumina Matrix

Microstructure and mechanical properties of Al2O3/Al2O3 composite densified through a slurry infiltration and sintering process

High fracture strength and fracture toughness are vital requirements for the Al2O3/Al2O3 composites. This advanced structural material is composed of two-dimensional alumina fiber fabrics with porous alumina matrices. However, the Al2O3/Al2O3 composites exhibit low delamination resistance under shear stress. In this study, an as-fabricated Al2O3/Al2O3 composite was densified through a slurry infiltration and sintering (SIS) process. The SIS-cycle-dependent mechanical properties of the Al2O3/Al2O3 composites were investigated. The results showed that the matrix was strengthened, and the fibers were unaffected after SIS process. With increasing SIS cycles, the flexural and interlaminar shear strengths increased, whereas the fracture toughness decreased. The best performance was reached after six SIS cycles, which had a flexural strength of 414.7 ± 41.6 MPa, an interlaminar shear strength of 25.6 ± 3.1 MPa, and a fracture toughness of 11.0 ± 0.3 MPa m1/2. The different changes in fracture strength and fracture toughness with the SIS cycles were attributed to matrix densification and enhanced interfacial bonding. The SIS process has the potential to improve the strength without sacrificing the damage tolerance.

Fabrication of SiCN(Fe)/Al2O3 wave-absorbing ceramics with enhanced electromagnetic performance

The SiCN(Fe)/Al2O3 composite ceramics containing C, α-Fe, and Al4C3 were designed by impregnating and pyrolysis polysilazane adding iron(III) acetylacetonate (FeAA) to porous alumina matrix. This composite material can absorb over 90% of electromagnetic wave in the range of 9–13 GHz with a thickness of 3.5 mm. The minimum reflectivity was −18 dB at 12 GHz with the addition of 3 wt% FeAA, demonstrating over 99% electromagnetic wave absorption at this frequency. Additionally, a circular metamaterial structure was designed and its wave absorption performance was simulated. The reflection coefficient of the sample in the range of 4.7–18 GHz is above 90%, and the electromagnetic absorption rate at 7.152 GHz is nearly 100%. This paper presents a novel porous alumina ceramic loaded with SiCN(Fe) composite material with excellent wave absorption performance. It also analyzes the loss and absorption mechanisms of electromagnetic wave at different frequencies, providing an experimental and theoretical basis for the practical application of porous ceramic matrix composite wave absorbing materials.

Effect of temperature on the mechanical behaviour of an oxide/oxide composite

Oxide/oxide composites are being considered in the aerospace industry for the design of next-generation exhaust components. This study aims to determine the mechanical behaviour of a composite consisting in Nextel™610 fibres fabric (8 HSW) embedded in a porous alumina matrix. The mechanical properties were studied in tension and four-point bending up to 1300 °C. Up to 800 °C, the material behaviour is elastic and exhibits a few damage with only a low effect of the temperature. Increasing the temperature leads to the progressive apparition of a viscous behaviour up to 1000 °C and a superplastic behaviour beyond 1200 °C.

To drill or not to drill? Creep of an oxide‐oxide composite with diamond‐drilled effusion holes at elevated temperature

Ceramic matrix composites (CMCs) are prime candidates for use in aircraft engines. Yet even with their high-temperature capabilities, many CMC components will need cooling. Film cooling technique requires rows of small holes through the component surface. Effects of multiple small holes on tensile stress-strain and tensile creep performance of an oxide-oxide CMC consisting of Nextel 720 alumina-mullite fibers in a porous alumina matrix were evaluated at 1200°C. Test specimens included 17 holes with a .5 mm diameter in the gage section. The holes were precision drilled using diamond coated drill bits. The presence of diamond-drilled holes noticeably lowered tensile properties and degraded creep performance of the CMC. Our earlier study considered the effects of small holes drilled using a CO2 laser on the tensile properties and tensile creep resistance of this composite. The presence of laser-drilled holes also considerably lowered the creep resistance of the Nextel 720/alumina CMC. In both cases the reductions in tensile strength and creep resistance are due to damage caused to composite microstructure by hole drilling. However, different drilling techniques result in different microstructure degradation mechanisms. Damage to the CMC microstructure caused by these two drilling techniques and implications for mechanical performance and durability are discussed.

The integrated reforming and isomerization of gasoline fractions for the production of eco-friendly motor gasolines

The paper reports data on the development and investigation of the advanced catalysts for reforming and isomerization of gasoline fractions, which were performed at the Center of New Chemical Technologies BIC SB RAS, particularly the commercial operation of the reforming catalyst PR-81. A new catalyst with an increased acidity, which provides a decrease in the content of aromatic hydrocarbons in reformate by 3–5 wt.%, was developed for the reforming of gasoline fractions. A new sulfated zirconia catalyst supported on the porous alumina matrix was devised for isomerization of the fraction of C5–C6 hydrocarbons. An efficient tungstated zirconia catalyst was suggested for isomerization of the fraction of C7 hydrocarbons. The indicated catalysts are employed in the proposed scheme of integrated reforming and isomerization processes, which ensures the production of motor gasolines Euro-5 and 6, as well as the promising gasolines with a decreased content of aromatic hydrocarbons.

Increasing the tensile strength of oxide ceramic matrix mini‐composites by two‐step sintering

AbstractAdapting conventional sintering (CS) techniques of monolithic ceramics for the production of oxide ceramic matrix composites (Ox‐CMCs) comes along with a few drawbacks, such as fiber degradation. Thus, the applicability of two‐step sintering (TSS) for the production of Ox‐CMCs based on Nextel™ 610 fibers and porous alumina matrix is investigated in this study for the first time. Uniaxial tensile tests were performed to evaluate the performance of mini‐composites produced by TSS and compared with those produced by CS. Parameters known for influencing the mechanical behavior of the mini‐composites, such as grain size, porosity, shrinkage, as well as matrix properties, were analyzed. Both sintering techniques resulted in similar grain size distributions, whereas TSS showed higher total porosity and lower amount of sintering‐induced cracks. As a result, TSS samples showed a higher tensile strength of 230±27 MPa when compared to 133±8 MPa for CS. In general, it was observed that most of the densification happens during the first phase of TSS, while the matrix is slowly strengthened during the second step. Therefore, the reported TSS process is a very promising and easy‐to‐apply heat treatment for producing Ox‐CMCs with controlled microstructure.

Fabrication and tribological behavior of self-lubricating composite impregnated with synthesized inorganic hollow fullerene-like MoS2

The impregnation of porous ceramic matrices with solid lubricants remains challenging. The inorganic hollow fullerene-like (IF) molybdenum disulfide (MoS2) solid lubricant immersed into the porous alumina matrix can improve the lubrication properties, and meanwhile maintain the exceptional mechanical properties of the matrix. In this study, porous alumina–IF–MoS2 matrix was fabricated as a self-lubricant composite; IF-MoS2 nanoparticles were synthesized by dispersion of ammonium tetra-thiomolybdate ((NH4)2MoS4) in an organic solvent, and vacuum impregnation and annealing were used to immerse IF-MoS2 nanoparticles into the porous alumina matrix. The obtained self-lubricant composite characterized by the field emission scanning electron microscope (FESEM) demonstrated hollow fullerene-like structure of IF-MoS2 nanoparticles on the porous alumina matrix, and the transmission electron microscopy (TEM) results revealed the morphology of laminated layers. The synthesized solid lubricant impregnated into the porous alumina matrix unveiled excellent lubrication behaviors.

One-pot synthesis of supported Ni@Al2O3 catalysts with uniform small-sized Ni for hydrogen generation via ammonia decomposition

Nickel based materials are the most potential catalysts for COx-free hydrogen production from ammonia decomposition. However, the facile synthesis of supported Ni-based catalysts with small size Ni particles, high porosity and good structural stability is still of great demand. In this work, uniform small-sized Ni particles supported into porous alumina matrix (Ni@Al2O3) are synthesized by a simple one-pot method and used for ammonia decomposition. The Ni content is controlled from 5 at.% to 25 at.%. Especailly, the 25Ni@Al2O3 catalyst shows the best catalytic performance. With a GHSV of 24,000 cm3gcat−1h−1, 93.9% NH3 conversion is achieved at 600 °C and nearly full conversion of NH3 is realized at 650 °C. The hydrogen formation rate of 25NiAl catalyst reaches 3.6 mmol gcat−1min−1 at 400 °C and 7.8 mmol gcat−1min−1 at 450 °C. The enhanced activity observed on 25Ni@Al2O3 catalyst can be attributed to the structural characteristic that large amounts of uniform-sized small (7.2 ± 0.9 nm) Ni particles are highly dispersed into porous alumina matrix. The aggregation of active metallic Ni particles during the high temperature reaction can be effectively prevented by the porous alumina matrix due to the strong interaction between them, thus ensuring a good catalytic performance.

Fabrication and tribological behavior of self-lubricating composite impregnated with synthesized inorganic hollow fullerene-like MoS2

The impregnation of porous ceramic matrices with solid lubricants remains challenging. The inorganic hollow fullerene-like (IF) molybdenum disulfide (MoS2) solid lubricant immersed into the porous alumina matrix can improve the lubrication properties, and meanwhile maintain the exceptional mechanical properties of the matrix. In this study, porous alumina–IF–MoS2 matrix was fabricated as a self-lubricant composite; IF-MoS2 nanoparticles were synthesized by dispersion of ammonium tetra-thiomolybdate ((NH4)2MoS4) in organic solvent, and vacuum impregnation and annealing were used to immerse IF-MoS2 nanoparticles into the porous alumina matrix. The obtained self-lubricant composite characterized by field emission scanning electron microscope (FESEM) demonstrated hollow fullerene-like structure, and transmission electron microscopy (TEM) results revealed the morphology of laminated layers. The synthesized solid lubricant impregnated into the porous alumina matrix unveiled excellent tribological behavior.

Formation and Corrosion Behavior of Nickel/Alumina Nanocomposites

Ni nanopillars (Ni NPs) composite materials formation technology was presented. The morphological and structural properties of the composite material were investigated using scanning electron microscopy, atomic force microscopy, X-ray diffraction. The corrosion resistance of the nanocomposite materials has been studied by potentiodynamic polarization curves analysis. The composite represents the array of vertically ordered Ni NPs with the identical size in alumina matrix. XRD investigation indicates that Ni NPs are polynanocrystalline material. It has been shown that Ni NPs and the composite material have sufficient corrosion resistance in a 0.9% aqueous NaCl solution. Porous alumina matrix is the neutral and protective component of the composite. These nanocomposite materials can be excellent candidates for practical use in different applications.

Magneto-Optical Effects in Au/Ni Based Composite Hyperbolic Metamaterials

The results of synthesis and experimental study of two types of nanocomposites based on Au/Ni nanorods in porous anodic alumina matrix are presented. The existence of two features in the optical spectra of such structures corresponding epsilon-near-zero and epsilon-near-pole points is shown. A significant modulation and enhancement of the alternating magneto-optical effects are observed in the spectral vicinity of these points.

Functional Multicomponent Metal Oxide Films Based on Sr, Sn, Fe, and Mo in the Anodic Alumina Matrices

Low‐profile anodic alumina matrices of 1 μm thick with pore sizes of 105 and 160 nm are formed by two‐step anodizing of Al layers and are used as templates for the deposition of multicomponent metal oxide films on their surfaces. The metal oxide systems of Sr2FeMoO6−δ, FexMoyOz, and SnxMoyOz composites with carbon nanotubes are synthesized by electrophoretic deposition, sol–gel method, and drop method using aqueous salt solutions and are annealed at 373–473 K for 1–2 h and at 773–1123 K for 2–10 h. The morphology, microstructure, and composition of the porous alumina matrices with multicomponent metal oxides films are examined by scanning electron microscopy, energy‐dispersive X‐ray microanalysis, and X‐ray phase analysis. The use of anodic alumina matrices allows reducing the grain dimensions and gives uniformity to the microstructure and properties of the metal oxide films. The carbon nanotubes increase the working surface of the functional layer and its electrical conductivity. The variation in the synthesis conditions of deposited films and anodic alumina matrices configuration allows forming of different complex composition compounds with reproducible structure and properties.

Improved Components for High Temperature Alkaline Water Electrolysis

Hydrogen production from water electrolysis is attractive due to its high efficiency, fast ramp rates, and high-pressure capability. However, current hydrogen production from electrolysis comprises only a small fraction of the global hydrogen market due to the high cost associated with expensive stack materials and electricity consumption. Currently commercial alkaline electrolyzers or proton exchange membrane electrolyzers operate at low temperatures. Intermediate or high temperature can effectively boost electrode kinetics and lower cell over-potential, thus improving the efficiency of water electrolysis. In this regards, Giner has developed a high-temperature alkaline water electrolysis (HTAWE), which employs lithium, sodium, or potassium hydroxides impregnated into a porous alumina or zirconia matrix [1]. The operating temperature can vary from 350 to 550 °C, depending on the category and ratio of binary or ternary electrolytes. In this work, both aluminate and zirconia-based matrix metal oxides were used as the matrix support materials. Thin aluminate and zirconia based matrices were fabricated using the tape casting method. Precious or non-precious electrodes (e.g. Ir, Ni, Co-based) were optimized using a solvent-based slurry formulation process. Green sheet electrodes with a variety of thicknesses were developed using a doctor blade approach. Design of experimental techniques were applied to optimize the ceramic membrane properties and to select hydrogen evolution reaction (HER)/oxygen evolution reaction (OER) catalysts. The impact of various catalyst and electrode designs on the HTAWE will be evaluated. Polarization curves and long-term durability will be demonstrated at variety of temperatures. Hot-corrosion mitigation strategies will also be discussed to extend the lifetime of HTAWE cells in this work. References Hui Xu and Kailash Patil, “High Temperature Alkaline Water Electrolysis,” presented at the 2018 DOE Annual Merit Review and Peer Evaluation Meeting, Washington, DC, June 2018. Acknowledgement: The project is financially supported by the Department of Energy’s Fuel Cell Technology Office under the Grant DE-EE0007644

Size effects in a ferroelectric NH4IO3

The temperature dependences of the linear permittivity ε' and the harmonic coefficient γ of composite materials obtained by introducing the ferroelectric NH4IO3 into the porous Al2O3 alumina matrix with a pore diameter of 60 nm are studied. It is found that the phase transition is smeared out and the Curie temperature shifts to the low-temperature region ΔT ∼ 25 K. The results obtained are consistent with the Ising model and are discussed within the framework of the phenomenological Landau theory.

Encapsulation of Al and Ti-Al alloy 1-D nanorods into oxide matrix by powerful pulsed discharge method

Encapsulated metal nanostructures were prepared using the powerful pulsed discharge method. Metal nanorods were obtained in porous titania and alumina matrix by direct electrodeposition from 1-ethyl-3-methylimidazolium chloride-based ionic liquids. The deposition process was characterized by cyclic voltammetry. Morphology of the encapsulated structures was studied by scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) for morphological and elemental analysis. It was found that the most efficient method for electrodeposition of pure aluminum into titania nanotubes is the potential cycling method, while for deposition of the Al-Ti alloy in alumina pores a pulsed method with three different steps is preferable. Closing the titania nanotubes was found to be possible both with empty and metal-filled pores, whereas in alumina matrix this procedure can be performed only when pores are filled with a conductive material. The obtained results throw light on the mechanism of porous film encapsulation under high-voltage pulses and allow preparing encapsulated nanostructures in the oxide films.

Creep of a Nextel™720/alumina ceramic composite containing an array of small holes at 1200°C in air and in steam

AbstractTensile stress‐strain and tensile creep behaviors of an oxide‐oxide composite containing an array of small circular holes were evaluated at 1200°C. The composite consists of Nextel™720 alumina‐mullite fibers in a porous alumina matrix. Test specimens contained an array of 17 holes with 0.5‐mm diameter drilled using a CO2 laser. The presence of holes caused reduction in tensile strength and modulus. Tensile creep tests were conducted at 1200°C in air and in steam at creep stresses ranging from 38 to 140 MPa. Primary, secondary, and tertiary creep regimes were noted in air and in steam. The presence of the laser‐drilled holes accelerates the steady‐state creep rates. Creep run‐out, defined as 100 hours at creep stress, was attained for stress levels <60 MPa in air and for stresses <40 MPa in steam. The presence of the laser‐drilled holes significantly degrades creep resistance of the composite. The retained tensile properties of all specimens that attained run‐out were determined. Composite microstructure was examined; the damage and failure mechanisms were considered. The degradation of tensile properties and creep resistance are attributed to damage caused to composite microstructure by laser drilling.

Electrical properties of copper iodide nanoparticles embedded into porous alumina matrix

CuI/porAl2O3 nanocomposite was prepared by synthesis of copper iodide (CuI) nanoparticles within porous alumina (porAl2O3) matrix. Electrical conductivity and Seebeck coefficient of bulk copper iodide and those of CuI/porAl2O3 samples were measured at different temperatures. Optical characteristics of the samples were obtained by spectral ellipsometry. Type and the temperature dependence of electrical conductivity of the materials under study are discussed.

Damage to an A-N720 ceramic matrix composite under simulated gas turbine static component conditions using laser heating

A ceramic matrix composite material constructed from a porous alumina matrix and Nextel™ 720 fibers was subjected to a novel type of experiment designed to reproduce the operating conditions of a gas turbine static component. Material specimens were exposed to cyclic laser heating on one side and active air cooling on the other side while being constrained in their bending deflection. For most specimens, accumulation of damage under the constant-amplitude heat load resulted in a temperature increase above the material limit of 1200℃ at the heated surface. Stress relaxation was observed due to inflicted sudden damage, like surface fiber buckling or ply delamination, and due to gradual permanent deformation of the material. The amount of damage was quantified by the variation of a stiffness parameter based on the measured reaction force and through-thickness temperature difference. While the level of damage was significant at the hot face, with the depth of cracking and delamination reaching up to half of the specimen thickness, the specimen back face remained intact. Stabilization of the damage was observed due to stress relaxation and decoupling of the damaged plies from the non-affected ones.

Encapsulation of Aluminium and Titanium-Aluminium Nanorods into Oxide Matrix By Powerful Pulsed Discharge Method

Encapsulated metal nanostructures were prepared using the powerful pulsed discharge method. Metal nanorods were obtained in porous titania and alumina matrix by direct electrodeposition from 1-ethyl-3-methylimidazolium chloride-based ionic liquids. The deposition process was characterized by cyclic voltammetry. Morphology of the encapsulated structures was studied by SEM. It was found that the most efficient method for electrodeposition of pure aluminium into titania nanotubes is the potential cycling method, while for deposition of the Al-Ti alloy in alumina pores a pulsed method with three different steps is preferable . Closing the titania nanotubes was found to be possible both with empty and metal-filled channels, whereas with alumina matrix this procedure can be performed only when pores are filled with conductive material. The obtained results throw light on the mechanism of porous film encapsulation under high-voltage pulses and allow preparing encapsulated nanostructures in the oxide films.