Intermetallic Structure Research Articles

Nitrogen-Doped Rhombohedral Ordered Intermetallic Nanocatalyst Boosts the Oxygen Reduction Reaction

Low platinum-group-metal (PGM) ordered intermetallic catalysts have been considered one of the most promising candidates for catalyzing the oxygen reduction reaction (ORR) in fuel cells, but achieving the desired performances in terms of activity, durability and cost is still a grand challenge for the fuel cell research field. We found that nitrogen (N)-doping through a thermal treatment in an NH3 gas to intermetallic-structured PtNi catalysts can boost their ORR performance.1 Herein, we report the synthesis of a rhombohedral L11-ordered PtCu catalyst for the ORR. We demonstrate that, by applying N-doping, the activity and stability of the N-doped, rhombohedral ordered PtCu (Int-PtCuN/KB) catalyst can be further enhanced.2 The mass activity and specific activity of the Int-PtCuN/KB catalyst is 1.15 A mgPt -1 and 1.81 mA cm-2 at 0.9 V, which are nearly 5-fold and 4-fold enhancement, respectively, relative to those of commercial Pt/C. In situ synchrotron X-ray absorption and pair-distribution-function measurements reveal that both the formation of the ordered intermetallic structure and N-doping synergistically improve the corrosion resistance of the PtCu catalyst by lowering the Cu diffusivity, and introduce a compressive strain effect regulating the adsorption of oxygenated species on the Pt surface, thus accounting for the improved ORR kinetics. This work provides valuable insights and possibilities to design binary even ternary Pt-based electrocatalysts with high performance and long-term durability for the ORR.

Ordered Mesoporous Carbon Confined Highly Dispersed PtCo Alloy for the Oxygen Reduction Reaction: The Effect of Structure and Composition on Performance

Pt-based catalysts are the most promising catalysts for proton exchange membrane fuel cells (PEMFCs) but still suffer from sluggish kinetics for the oxygen reduction reaction (ORR). Alloying Pt with transition-metal (M) elements is an efficient approach to modulate the electronic structure of Pt-based catalysts and improve the catalytic performance for the ORR. However, owing to the distinguishing surface state caused by different synthetic approaches, there still exist contradictory views about the relationship between the structure of Pt-based alloys and the catalytic performance for the ORR. In this work, PtCo alloys with a similar surface state but diverse structures and compositions are obtained by regulating the annealing temperatures and the precursor ratios. Accompanied by the structure and composition evolution, the electronic structure of Pt has also changed. PtCo@sOMC-900-1/3 with the intermetallic compound structure achieves the best kinetic activity as well as durability, indicating its potential for practical application. This work provides a more accurate understanding of the relationship between the alloy structure and the catalytic ORR performance and highlights a feasible strategy to mass-produce cathode catalysts for PEMFC applications.

Isolation of Metalloid Boron Atoms in Intermetallic Carbide Boosts the Catalytic Selectivity for Electrocatalytic N2 Fixation

AbstractThe electrochemical N2 reduction reaction (eNRR) is considered to be an attractive alternative to overcome the short‐comings of the Haber‐Bosch method, where the electrocatalysts play a vital role in the eNRR efficiency. Herein, isolated single‐B sites with electron deficiency in intermetallic carbide are rationally designed to trigger charge density redistribution, achieving excellent selectivity for eNRR. The B‐rich VC nanocrystals are in situ synthesized on carbon nanofibers (B‐VC/CNFs), and the ordered intermetallic structure of VC can isolate contiguous B atoms into single‐B sites with specific electronic structures. In light of density functional theory calculations, the as‐designed BCV configuration can regulate the adsorption behavior of N2 and decrease the energy barrier for the proton–electron coupling and transferring process (*NN → *NNH), endowing the distinguished activity and selectivity, as evidenced by excellent Faradaic efficiency of 46.1% and NH3 yield of 0.443 µmol h–1 cm–2. The operando Raman spectra reveals the formation of NH intermediates on the surfaces of B‐VC/CNFs, further confirming the calculated eNRR pathway. This intermetallic carbide host strategy for generating electron‐deficient single‐B sites offers powerful guidelines for designing advanced eNRR electrocatalysts to achieve effective ammonia production.

Theoretical investigations on correlations between elastic behavior of Al-based alloys and their electronic structures

Abstract In this work, using the first-principles method, the alloying stability, electronic structure, and elastic properties of Al-based intermetallics were investigated. It was found that these alloys have a strong alloying ability and structural stability due to the negative formation energies and the cohesive energies. The valence bonds of these intermetallic compounds are attributed to the valence electrons of Cu 3δ states for AlCu3, Cu 3δ and Zr 4δ states for AlCu2Zr, and Al 3s, Zr 5s and 4δ states for AlZr3, respectively. Furthermore, the correlation between elastic properties of these intermetallic compounds and their electronic structures was revealed. The results show that structural parameters and elastic properties such as bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio and anisotropy agreed well with experimental results.

Design of bimetallic Au/Cu nanoparticles in ionic liquids: Synthesis and catalytic properties in 5‐(hydroxymethyl)furfural oxidation

AbstractIn alloyed nanoparticles, synergistic electronic and/or geometric effects may enhance the catalytic properties compared to their monometallic counterparts. Herein, we address the synthesis of bimetallic Au/Cu nanoparticles with different compositions by wet chemical reduction in ionic liquids. The nanoparticles were successively supported on carbon. The ionic liquid could be recycled after synthesis. Annealing of the carbon‐supported NPs at 400 °C led to NPs of the ordered intermetallic L10 AuCu phase. The nanoparticle‐derived catalysts were characterized by X‐ray diffraction analysis, transmission electron microscopy, X‐ray photoelectron spectroscopy and optical emission spectroscopy with inductively coupled plasma. Oxidation of biomass‐derived furans is a prominent process for biomass transformation into value‐added chemicals. Herein, the oxidation of 5‐hydroxymethyl‐2‐furfural (HMF) to 2,5‐furandicarboxylic acid (FDCA) was chosen as a model reaction to evaluate the effect of Cu addition and intermetallic structure on the catalytic performance. Particularly Au/Cu nanoparticles with an Au/Cu ratio of 3 : 1 showed very high conversion to FDCA.

Carboxylate-Decorated Aggregation of Octanuclear Co4Ln4 (Ln = Dy, Ho, Yb) Complexes from Ligand-Controlled Hydrolysis: Synthesis, Structures, and Magnetic Properties

One-pot reactions of an asymmetric carboxy-ether-phenol based Schiff base H2L (2-((2-hydroxy-3-methoxybenzylidene)amino)benzoic acid) with selected Ln(NO3)3·nH2O and [Co2(μ-OH2)(O2CCMe3)4(HO2CCMe3)4] (Co2-Piv) in basic MeOH medium resulted in a family of three octanuclear complexes, [CoII4LnIII4L4(μ1,3-Piv)4(μ1,1,3-Piv)2(η1-Piv)2(μ3-OH)4(MeOH)2]·mMeOH·nH2O (Ln = Dy; m = 3, n = 1 (1), Ho; m = 4, n = 0 (2), Yb; m = 3, n = 1 (3)). The coordination aggregates thus obtained were nicely sustained by four ligand anions and eight externally added carboxylate anions showing three different modes of intermetallic connectivity. The options for incorporating different 4f ions in an investigative synthesis, without altering the resulting intermetallic core structure, were successful for the three representative examples. Single-crystal X-ray diffraction studies revealed that the compounds are isostructural and built from two initially formed partial dicubane-type Co2Ln2L2 units. In each of the tetranuclear parts, the metal ion centers are held together by two L2-, two μ3-HO-, three Piv- bridges, one terminal Piv-, and one terminal MeOH. Four carboxylate ends of four L2- units are responsible for connecting two Co2Ln2 units into octanuclear structures. The unique distortion around the CoII centers is achieved from the facile coordination of bigger 4f ions to the adjacent hard OO sites. The distortion is further maintained by the presence of terminal COO- groups from L2-. The dc magnetic susceptibility data revealed ferromagnetic coupling between the CoII and LnIII centers within the series, whereas the ac magnetic susceptibility measurements identified only 1, having a highly anisotropic DyIII ion, as a single-molecule magnet in the absence of any external magnetic field, with an energy barrier Ueff of 12.5 K.

Structural and magnetic properties of Sc1-xNbxFe2 intermetallics showing anomalous zero thermal expansion

Ternary intermetallics deriving from ScFe2 Laves phases can present a relatively unique case of ferro-ferromagnetic transition originating from an iron moment instability, which is potentially interesting for several applications. Yet, at the exception of (Sc,Ti)Fe2, their structural and magnetic phase diagrams remain scarcely explored. Here, we present a systematic investigation of the crystal structure and magnetic properties of Sc1-xNbxFe2 intermetallics. This series is found to mostly crystallize in the C14 hexagonal structure. But, in contrast to former studies, a C14/C15 hexagonal/cubic dimorphism is observed for the binary parent ScFe2, with the C15 structure that can be brought to the edge of stability depending on heat treatments. This led us to revisit the properties of ScFe2 via first-principles calculations. The total energy difference between C14 (stable) and C15 structures is found small, and C15 ScFe2 is predicted to be ferromagnetic with a saturation magnetization close to that of C14 ScFe2, which is fully compatible with experimental observations. Experimentally, Sc1-xNbxFe2 intermetallics with x ≤ 0.35 are ferromagnetic with Curie temperatures decreasing with increasing the Nb content; while such a long range ferromagnetic order with net magnetization is no longer observed for x > 0.6. A Néel transition is observed around 250 K in 0.6 ≤ x ≤ 0.9 alloys, this antiferromagnetic order is coexisting with a minor ferromagnetic phase, in line with former results from Mössbauer spectroscopy. For 0.2 ≤ x ≤ 0.3 samples, an ─unusual─ ferro.-ferromagnetic transition with a change in magnetization from ~1.2 μB/Fe to ~0.9 μB/Fe upon heating is found around 150 K in addition to the ferro-paramagnetic transition. This broad ferro.-ferromagnetic transition is isostructural as the C14 hexagonal crystal structure is preserved, but it leads to a virtually zero thermal expansion up to 250 K.

Influence of Chromium Concentration on the Abrasive Wear of Ni-Cr-B-Si Coatings Applied by Supersonic Flame Jet (HVOF)

This research work studies the characteristics of wear and wear resistance of composite powder coatings, deposited by supersonic flame jet (HVOF), which contain composite mixtures Ni-Cr-B-Si having different chromium concentrations—9.9%, 13.2%, 14%, 16%, and 20%, at one and the same size of the particles and the same content of the remaining elements. The coating of 20% Cr does not contain B and Si. Out of each powder composite, coatings have been prepared without any preliminary thermal treatment of the substrate and with preliminary thermal treatment of the substrate up to 650 °C. The coatings have been tested under identical conditions of dry friction over a surface of solid, firmly-attached, abrasive particles using tribological testing device “Pin-on-disk”. Results have been obtained and the dependences of the hardness, mass wear, intensity of the wearing process, and absolute and relative wear resistance on the Cr concentration under identical conditions of friction. It has been found out that for all the coatings the preliminary thermal treatment of the substrate leads to a decrease in the wear intensity. Upon increasing Cr concentration the wear intensity diminishes and it reaches minimal values at 16% Cr. In the case of coatings having 20% Cr concentration, the wear intensity is increased, which is due to the absence of the components B and Si in the composite mixture, whereupon no inter-metallic structures are formed having high hardness and wear resistance. The obtained results have no analogues in the current literature and they have not been published by the authors.

Synergy of Pt-Free Single Metal Sites for Promoting Pt and Pt3co Ordered Intermetallic Catalysts for Fuel Cells: Performance and Durability Improvements

The reduction of platinum use and improvement of its catalytic performance has become the most critical steps to accelerate the development of proton-exchange membrane fuel cells (PEMFCs). Here we report a novel and facile method to boost the performance of the Pt-cased catalyst by integrating with an atomic platinum-group metal (PGM)–free active sites. Using iron-doped zeolitic imidazolate framework-8 (ZIF-8) derived carbon as support, we achieved a uniform deposition of Pt and intermetallic Pt-Co nanoparticles (NPs) through one-step synthesis, with average particle size 2.4 nm for Pt, 3.4 nm for L10 PtCo, and 4.2 nm for L12 Pt3Co. Besides, easy phase transfer during synthesis between ordered intermetallic structures L10 PtCo and L12 Pt3Co was achieved, and a comprehensive comparison between their catalytic performance was established. Synergistic catalysis between Pt or Pt-Co NPs over a PGM–free catalytic substrate derived from iron-doped ZIF-8 led to excellent oxygen reduction reaction (ORR) performance under both rotating disk electrode (RDE) and membrane electrode assembly (MEA) testing. Resulting pure Pt catalysts achieved ORR mass activities of 0.451 A/mgPt and retained 80% initial values after 30,000 voltage cycles in a fuel cell, superior to the DOE 2020 targets without using Pt alloy. Both PtCo and Pt3Co catalysts achieved better performance and exhibited all-sided excellence among mass activity, stability, and power density. Among them, Pt3Co reached the power density at 0.67 V of 923 mW/cm2 and retained 86% initial mass activity after 30,000 voltage cycles in a fuel cell. Their performance dependences on support material particle size and ionomer content were discussed and optimized in MEAs.

Formation of TiAlSi intermetallics during heating Ti-A356 Al mixed powder compact at semisolid temperature

• The local breakage of oxide films determine the formation of τ1 and τ2 crystals and their morphologies. • Both τ1 and τ2 crystals have an intrinsic plate morphology, but τ2 crystals were thinner due to their more anisotropic growth. • τ1 lamellar domains generate during growth of τ2 crystals accompanied by decrease in density of SFs. • τ1 crystals coarsen at the expense of τ2 crystals, leading all reaction products to finally convert into large τ1 plates. Due to the similarity in composition and crystal structure of some TiAlSi ternary intermetallics, it is quite difficult to accurately confirm their physic characteristics, and thus, to tailor microstructure to improve mechanical properties of metal materials related to the TiAlSi intermetallics. Therefore, the formation process of TiAlSi intermetallics was investigated during heating Ti-A356 mixed powder compact at a A356 alloy semisolid temperature of 595 °C. The results indicated that two kinds of intermetallics of τ1 (tetragonal, I41/amd) and τ2 (orthorhombic, Cmcm) generated, and both the concentration and supply direction of Ti atoms, which are related to local breakage of oxide films on neighboring Ti and A356 alloy powders, determined the phase and morphology of the intermetallics. τ1 and τ2 crystals all had an intrinsic plate morphology, but τ2 crystals were thinner due to more anisotropic growth resulted from their high density of stacking faults (SFs). τ1 lamellar domains generated during growth of τ2 crystals, which were accompanied by decrease in density of SFs. The combined effect of size difference and internal energy difference between τ1 and τ2 crystals made large τ1 crystals coarsen at the expense of τ2 crystals in Ostwald ripening, leading them to finally evolve into an agglomerate of large τ1 plates.

A facile solution phase synthesis of directly ordering monodisperse FePt nanoparticles

The ordered Pt-based intermetallic nanoparticles (NPs) with small size show superior magnetic or catalytic properties, but the synthesis of these NPs still remains a great challenge due to the requirement of high temperature annealing for the formation of the ordered phase, which usually leads to sintering of the NPs. Here, we report a simple approach to directly synthesize monodisperse ordered L10-FePt NPs with average size 10.7 nm without further annealing or doping the third metal atoms, in which hexadecyltrimethylammonium chloride (CTAC) was found to be the key inducing agent for the thermodynamic growth of the Fe and Pt atoms into the ordered intermetallic structure in the synthetic process. In particular, 10.7 nm L10-FePt NPs synthesized by the proper amount of CTAC show a coercivity of 3.15 kOe and saturation magnetization of 45 emu/g at room temperature. The current CTAC-assisted synthetic strategy makes it possible to deeply understand the formation of the ordered Pt-based intermetallic NP in solution phase synthesis.

Exploring crystal structures, stability and mechanical properties of Fe, Mn-containing intermetallics in Al-Si Alloy by experiments and first-principles calculations

Separation of Fe-containing intermetallics is an effective method to decrease Fe content in Al-Si alloys. Regular morphology and higher precipitation temperature are necessary for physical separation of Fe-containing phases. So far, there have been few studies about the three-dimensional (3D) morphology evolution, crystal structure variation and physical mechanism for the precipitation temperature improvement of Fe-containing phases. Combined with experiments and first-principles calculations, the effects of Mn on 3D morphology, crystal structure and precipitation temperature of Fe-containing phases are systematically investigated. The DSC and first-principles calculations show that the precipitation temperature of Fe-containing phase improves prominently after the addition of Mn and the high precipitation temperature of α-AlFeMnSi attributes to its stronger chemical bonding strength of Mn-Si validated by binding energy and Mulliken population analysis, which also leads to high Young’s modulus and hardness of α-AlFeMnSi. It demonstrates that the crystal structure of Fe-containing intermetallics is transformed from monoclinic β-AlFeSi to cubic α-AlFeMnSi and the morphology changes from plate-like to dodecahedron shapes.

Steering the Catalytic Properties of Intermetallic Compounds and Alloys in Reforming Reactions by Controlled in Situ Decomposition and Self-Activation.

Based on the increasing importance of intermetallic compounds and alloys in heterogeneous catalysis, we explore the possibilities of using selected intermetallic compounds and alloy structures and phases as catalyst precursors to prepare highly active and CO2-selective methanol steam reforming (MSR) as well as dry reforming of methane (DRM) catalyst entities by controlled in situ decomposition and self-activation. The exemplary discussed examples (Cu51Zr14, CuZn, Pd2Zr, GaPd2, Cu2In, ZnPd, and InPd) show both the advantages and pitfalls of this approach and how the concept can be generalized to encompass a wider set of intermetallic compounds and alloy structures. Despite the common feature of all systems being the more or less pronounced decomposition of the intermetallic compound surface and bulk structure and the in situ formation of much more complex catalyst entities, differences arise due to the oxidation propensity and general thermodynamic stability of the chosen intermetallic compound/alloy and their constituents. The metastability and intrinsic reactivity of the evolving oxide polymorph introduced upon decomposition and the surface and bulk reactivity of carbon, governed by the nature of the metal/intermetallic compound-oxide interfacial sites, are of equal importance. Structural and chemical rearrangements, dictating the catalytic performance of the resulting entity, are present in the form of a complete destruction of the intermetallic compound bulk structure (Cu51Zr14) and the formation of an metal/oxide (Cu51Zr14, InPd) or intermetallic compound/oxide (ZnPd, Cu2In, CuZn) interface or the intertranformation of intermetallic compounds with varying composition (Pd2Zr) before the formation of Pd/ZrO2. In this Perspective, the prerequisites to obtain a leading theme for pronounced CO2 selectivity and high activity will be reviewed. Special focus will be put on raising awareness of the intrinsic properties of the discussed catalyst systems that need to be controlled to obtain catalytically prospective materials. The use of model systems to bridge the material’s gap in catalysis will also be highlighted for selected examples.

Corrosion and High Temperature Oxidation Behavior of Structural Steels Coated with Aluminum Alloys

Structural steels are among the most widely used materials in today's industry. Various surface coating processes are used to protect structural steels from corrosion in atmospheric or aggressive environments. The most commonly used method is the galvanizing process based on forming zinc coating on the steel surface by using the hot dip method. Zinc coatings are insufficient to protect against corrosion, especially in chlorinated environments. Aluminum and its alloys stand out as an alternative material group to zinc in chlorinated environments. In this study, aluminum and aluminum alloy coatings, which are thought to be an alternative to zinc coating, were coated on the structural steel surface using the hot dip method. To examine how different aluminum alloys affect the corrosion and high-temperature oxidation properties of steels, nearly pure AA1050, high Cu content AA2024, and high Mg content AA5083 alloys were coated on structural steels. The coating process was carried out by dipping the structural steels into molten aluminum baths kept at a constant temperature of 700°C for 1, 3, and 5 minutes. The optimum adhesion and surface properties were obtained from dipping time for 3 minutes. The properties of coatings and intermetallic structures formed at the coating-steel interface were examined using an optical microscope, X-ray Diffractometer (XRD), Scanning Electron Microscope (SEM), and Energy Scattering Spectroscopy (EDS) systems. To examine the high-temperature oxidation properties of the coatings, the coated samples were oxidized for 24 hours at 750°C under open-air conditions, and the changes in weight were investigated. Immersion corrosion tests were performed in 3.5% NaCl solution, and corrosion losses and degradation patterns were investigated. As a result of the studies, it has been determined that the Al coatings produced by the hot dip process significantly increase the oxidation and corrosion resistance of the structural steels.

Atomic‐Scale Engineering: Anion Constructor for Atomic‐Scale Engineering of Antiperovskite Crystals for Electrochemical Reactions (Adv. Funct. Mater. 16/2021)

In article number 2009241, Docheon Ahn, Pil Kim, Sung Jong Yoo, and co-workers synthesize monolithic antiperovskite crystals through atomic-scale engineering. The nitride PdNi alloy achieves excellent catalytic activity and durability under acidic media, resulting from the synergistic effect of nitride and intermetallic structures. This strategy will pave the way for overcoming the catalytic performance of potential materials.

Coloring and distortion variants of the bcc packing and for the aristotypes BaAl4 and CeMg2Si2

Abstract The huge number of intermetallic structure types with many representatives calls for structural systemization. The combination of crystal chemistry with group theory is an efficient tool for such systemization and can be displayed in a concise and compact way via group-subgroup schemes. The present overview deals with such group-subgroup schemes (Bärnighausen trees) for coloring and distortion variants of the bcc packing as well as superstructures that derive from the aristotypes BaAl4 and CeMg2Si2.

Effect of copper concentration on the structure of intermetallics and graphite additives of Al–Cu/C powder composites

The structure of hypo-eutectic and eutectic Al–Cu/C powder composites, as well as the powders with composition in the region of equilibrium Al4Cu9 phase, were studied using X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and nuclear magnetic resonance (NMR) after high-energy ball milling of Al and Cu elemental powders with 5 wt.% of graphite additives and heat treatment at the temperature of 500 °C. Mechanical energy dose transferred into the powder composites during milling for 8 h was estimated to be 32 kJ/g and leads to the formation of the metastable disordered bcc-Al4Cu9 phase (A2 structural type) in a wide composition range. Effect of copper concentration on the peculiarities of its structure, chemical composition and the possibility of A2 → D83 first range ordering after heat treatment has been examined. Graphite additives structure evolution after milling and heat treatment of copper-rich Al–Cu/C powder composites was also specified.

Fully ordered L10-PtCoAu electrocatalyst derived from PtAu@CoO precursor with enhanced performance for oxygen reduction reaction

Alloying Pt with other transition metal is a promising method to accelerate the kinetics of oxygen reduction reaction (ORR). Herein, fully ordered Au-doped PtCo nanoparticles (L10-PtCoAu NPs) with a size of sub-4 nm are successfully synthesized by annealing the PtAu alloy which coated by CoO shell (PtAu@CoO) under H2 atmosphere. The artificially introduced vacancies during annealing process can accelerate the atomic diffusion, which is beneficial to the conversion from disordered alloy structure to intermetallic structure. And the addition of Au and Co atoms synergistically tunes the crystal and electronic structure of Pt. As a result, the electrochemical tests show that the mass activity of fully ordered L10-PtCoAu0.1/C catalyst is 1.08 A mgPt−1, which is 6 times higher than that of commercial Pt/C catalyst. Due to the protective effect of Au atoms and the stable ordered structure, the prepared L10-PtCoAu0.1/C catalyst show enhanced durability compared with commercial Pt/C after 20,000 potential cycles. This work provides a facile and scalable method to prepare small-sized Pt-based intermetallic alloy catalyst with improved activity and durability for ORR.

The role of three-dimensional bulk clusters in determining surface morphologies of intermetallic compounds: Quasicrystals to clathrates.

Nanostructured alloy surfaces present unique physical properties and chemical reactivities that are quite different from those of the close-packed low-index surfaces. This can be beneficial for the design of new catalysts and electronic and data-storage devices. However, the growth of such surface nanostructures is not straightforward at the atomic scale. The cluster-based bulk structure of intermetallic compounds presents an original alternative to build surfaces with specific morphologies, in comparison to more traditional methods based on mechanical, chemical, or plasma treatments. It relies on their specific electronic structures-built from a network of bonds with a combination of ionic, covalent-like, and metallic characters, and also depends on the experimental conditions. In this paper, a few surface structures of cluster-based intermetallics are reviewed, with a special emphasis on quasicrystals and clathrates. We show how the intrinsic electronic properties of such compounds, as well as the surface preparation conditions, impact their surface morphologies, which can further influence the growth of atomic and molecular thin films at their surface.

Pore constitution and tortuosity factor of reactively synthesized porous TiAl intermetallic compound

The pore constitution and tortuosity factor of porous TiAl intermetallic were studied on the basis of the variation behavior of pore structure parameters and the discrete particle model. The pore formation mechanism of porous TiAl is mainly ascribed to three aspects: the clearance space in green compact, the diffusive pores in the reaction process and the phase transition pores, resulting in the open porosities of 5.6%, 42.9% and 1.3%, respectively. According to the Hagen−Poiseuille equation, the tortuosity factor of porous TiAl is determined in the range of 1.3−2.2. Based on the discrete particle model and the variation rule of the tortuosity factor, the tortuosity factor depends mainly on the parameters of fabrication constant, particle shape factor, clearance distance and powder particle size. The quantitative relationships among them have been established, which can be used as the basis for adjusting the pore structure of porous intermetallics.