High performance aluminum–cerium alloys for high-temperature applications

Light-weight high-temperature alloys are important to the transportation industry where weight, cost, and operating temperature are major factors in the design of energy efficient vehicles. Aluminum alloys fill this gap economically but lack high-temperature mechanical performance. Alloying aluminum with cerium creates a highly castable alloy, compatible with traditional aluminum alloy additions, that exhibits dramatically improved high-temperature performance. These compositions display a room temperature ultimate tensile strength of 400 MPa and yield strength of 320 MPa, with 80% mechanical property retention at 240 °C. A mechanism is identified that addresses the mechanical property stability of the Al-alloys to at least 300 °C and their microstructural stability to above 500 °C which may enable applications without the need for heat treatment. Finally, neutron diffraction under load provides insight into the unusual mechanisms driving the mechanical strength

A generalized electrochemical aggregative growth mechanism

The early stages of nanocrystal nucleation and growth are still an active field of research and remain unrevealed. In this work, by the combination of aberration-corrected transmission electron microscopy (TEM) and electrochemical characterization of the electrodeposition of different metals, we provide a complete reformulation of the Volmer-Weber 3D island growth mechanism, which has always been accepted to explain the early stages of metal electrodeposition and thin-film growth on low-energy substrates. We have developed a Generalized Electrochemical Aggregative Growth Mechanism which mimics the atomistic processes during the early stages of thin-film growth, by incorporating nanoclusters as building blocks. We discuss the influence of new processes such as nanocluster self-limiting growth, surface diffusion, aggregation, and coalescence on the growth mechanism and morphology of the resulting nanostructures. Self-limiting growth mechanisms hinder nanocluster growth and favor coalescence driven growth. The size of the primary nanoclusters is independent of the applied potential and deposition time. The balance between nucleation, nanocluster surface diffusion, and coalescence depends on the material and the overpotential, and influences strongly the morphology of the deposits. A small extent of coalescence leads to ultraporous dendritic structures, large surface coverage, and small particle size. Contrarily, full recrystallization leads to larger hemispherical monocrystalline islands and smaller particle density. The mechanism we propose represents a scientific breakthrough from the fundamental point of view and indicates that achieving the right balance between nucleation, self-limiting growth, cluster surface diffusion, and coalescence is essential and opens new, exciting possibilities to build up enhanced supported nanostructures using nanoclusters as building blocks.info:eu-repo/semantics/publishe

A generalized electrochemical aggregative growth mechanism

The early stages of nanocrystal nucleation and growth are still an active field of research and remain unrevealed. In this work, by the combination of aberration-corrected transmission electron microscopy (TEM) and electrochemical characterization of the electrodeposition of different metals, we provide a complete reformulation of the Volmer-Weber 3D island growth mechanism, which has always been accepted to explain the early stages of metal electrodeposition and thin-film growth on low-energy substrates. We have developed a Generalized Electrochemical Aggregative Growth Mechanism which mimics the atomistic processes during the early stages of thin-film growth, by incorporating nanoclusters as building blocks. We discuss the influence of new processes such as nanocluster self-limiting growth, surface diffusion, aggregation, and coalescence on the growth mechanism and morphology of the resulting nanostructures. Self-limiting growth mechanisms hinder nanocluster growth and favor coalescence driven growth. The size of the primary nanoclusters is independent of the applied potential and deposition time. The balance between nucleation, nanocluster surface diffusion, and coalescence depends on the material and the overpotential, and influences strongly the morphology of the deposits. A small extent of coalescence leads to ultraporous dendritic structures, large surface coverage, and small particle size. Contrarily, full recrystallization leads to larger hemispherical monocrystalline islands and smaller particle density. The mechanism we propose represents a scientific breakthrough from the fundamental point of view and indicates that achieving the right balance between nucleation, self-limiting growth, cluster surface diffusion, and coalescence is essential and opens new, exciting possibilities to build up enhanced supported nanostructures using nanoclusters as building blocks.info:eu-repo/semantics/publishe

The Role of Nanocluster Aggregation, Coalescence, and Recrystallization in the Electrochemical Deposition of Platinum Nanostructures

info:eu-repo/semantics/publishe

Multipulse electrodeposition of Ag nanoparticles on HOPG monitored by in-situ by Small-Angle X-ray Scattering

A new experimental approach to study nanoparticle size distributions in electrochemical deposition processes by in-situ Small Angle X-ray Scattering (SAXS) is presented. A specifically designed flow cell was used to acquire SAXS frames after different nucleation and growth pulses in a potentiostatic multiple pulse approach. Measurements show that after a correct background subtraction, scattered intensity variations are only caused by electrodeposited silver nanoparticles and that size distribution evolution derived after modeling the SAXS data is in agreement with electrochemical particle growth.info:eu-repo/semantics/publishe

A method to detect retained gas during AC electrograining using in-situ small angle X-ray scattering

AC electrochemical processes have found applications in controlled surface roughening of aluminium (AC electrograining), fine-tip sharpening for field ion microscopy (AC machining) and thin film anodising (AC anodising). The formation of a surface layer and copious amounts of hydrogen gas are inherent in these AC processes. The presence of a resistance is observed in these processes but it is the source of the resistance that is important to the understanding of ionic transport through the surface film.The AC electrograining process is chosen here, as the annual worldwide production of aluminium plate for high quality lithographic printing and for energy storage super-capacitors is in excess of 800 km2. In this study, a method to detect gas in the surface layer (smut) in-situ with Small Angle X-ray Scattering (SAXS) is proposed. The total scattering from the in-situ SAXS is used with knowledge of the total volume of smut to explain how a gas fraction can be determined by comparing two samples. Results suggest that a gas fraction can be retained in smut during AC electrograining, the degree to which varies with smut properties. Keywords: SAXS, Gel, AC processes, Pitting, Electrograining, Gas retentio

Stability, Assembly, and Particle/Solvent Interactions of Pd Nanoparticles Electrodeposited from a Deep Eutectic Solvent

info:eu-repo/semantics/publishe

Ultra-low-density silver aerogels via freeze-substitution

Herein is reported a method for fabricating <10 mg/cm3 silver aerogels via the freeze casting of aqueous nanowire suspensions followed by freeze substitution and supercritical drying. This method overcomes the limitations of traditional freeze drying and yields highly uniform, crack-free monoliths that undergo no measurable shrinkage with excellent mold reproduction. Significantly, freeze substitution enables the use of high concentrations of cryoprotectants to control the freezing process and, hence, the pore architecture of the resulting aerogels. Due to its physical nature, this method is applicable to the fabrication of materials with a broad range of compositions