Iron-based microstructured or nanostructured materials, including Fe, γ-Fe2O3, and Fe3O4, are highly desirable for magnetic applications because of their high magnetization and a wide range of magnetic anisotropy. An important application of these materials is use as an electromagnetic wave absorber to absorb radar waves in the centimeter wave (2−18 GHz). Dendrite-like microstructures were achieved with the phase transformation from dendritic α-Fe2O3 to Fe3O4, Fe by partial and full reduction, and γ-Fe2O3 by a reduction−oxidation process, while still preserving the dendritic morphology. The investigation of the magnetic properties and microwave absorbability reveals that the three hierarchical microstructures are typical ferromagnets and exhibit excellent microwave absorbability. In addition, this also confirms that the microwave absorption properties are ascribed to the dielectric loss for Fe and the combination of dielectric loss and magnetic loss for Fe3O4 and γ-Fe2O3.

Hierarchical Dendrite-Like Magnetic Materials of Fe3O4, γ-Fe2O3, and Fe with High Performance of Microwave Absorption

Li deposition is observed and measured on a solid electrolyte in the vicinity of a metallic current collector. Four types of ion-conducting, inorganic solid electrolytes are tested: Amorphous 70/30 mol% Li2S-P2S5, polycrystalline β-Li3PS4, and polycrystalline and single-crystalline Li6La3ZrTaO12 garnet. The nature of lithium plating depends on the proximity of the current collector to defects such as surface cracks and on the current density. Lithium plating penetrates/infiltrates at defects, but only above a critical current density. Eventually, infiltration results in a short circuit between the current collector and the Li-source (anode). These results do not depend on the electrolytes shear modulus and are thus not consistent with the Monroe–Newman model for “dendrites.” The observations suggest that Li-plating in pre-existing flaws produces crack-tip stresses which drive crack propagation, and an electrochemomechanical model of plating-induced Li infiltration is proposed. Lithium short-circuits through solid electrolytes occurs through a fundamentally different process than through liquid electrolytes. The onset of Li infiltration depends on solid-state electrolyte surface morphology, in particular the defect size and density.

Mechanism of Lithium Metal Penetration through Inorganic Solid Electrolytes

http://fulltext.calis.edu.cn/rsc/Green%20Chemistry/b804703k.pdf

Green synthesis of silver and palladium nanoparticles at room temperature using coffee and tea extract

Metal nanocrystals with highly branched morphologies are an exciting new class of nanomaterials owing to their unique structures, physicochemical properties, and great potential as catalysts, sensing materials, and building blocks for nanoscale devices. Various strategies have recently been developed for the solution-phase synthesis of metal nanocrystals with branched morphologies, such as multipods and nanodendrites. In this Minireview, the procedures and mechanisms underlying the formation of branched metal nanocrystals are presented in parallel with recent advances in synthetic approaches based on kinetically controlled overgrowth, aggregation-based growth, heterogeneous seeded growth, selective etching, and template-directed methods, as well as their properties for catalytic or electrocatalytic applications.

Metal nanocrystals with highly branched morphologies.

This Review is focused on the recent progresses in the synthetic approaches to the precise control of structure, size, shape, composition and multi-functionality of metal and metal alloy nanoparticles. Many of these strategies have been developed based on colloidal methods, and to limited extent, the galvanic and other methods. The shape, size and composition often govern the chemical and catalytic properties that are important for electrochemical energy applications. The structure–property relationship and the design in controllable structures and morphologies for specific reactions such as oxygen reduction reaction (ORR) are emphasized.

Synthesis of colloidal metal and metal alloy nanoparticles for electrochemical energy applications

In this study, a well-defined dendritic silver nanostructure can be large-scale synthesized in AgNO3 (aqueous) at room temperature. The nonequilibrium and anisotropic growth at different silver ion concentrations result in controllable morphologies and morphological evolution. At high silver ion concentrations, a strong anisotropic growth contributes to a fine single crystalline silver dendrite. As the reaction proceeds, the dendritic structure transforms into a thermodynamically stable hexagonal structure. At a relatively low silver ion concentration, a particle-aggregated fractal pattern can be obtained due to relatively small anisotropy. As the reaction time increases, the transition from polycrystalline aggregates to a single crystal during silver dendritic growth can be observed. An oriented attachment mechanism can be used to explain the structural and morphological evolution of silver nanostructures. Silver nanostructures with various morphologies are expected to have significant potential applicat...

Dendritic Silver Nanostructure Growth and Evolution in Replacement Reaction

Thermodynamic and kinetic competition in silver dendrite growth

A size-dependent crystal growth mechanism is studied by molecular dynamics simulations. The amorphous silver firstly deposits under the coordinated actions between the lattice mismatch and interactions between silver atoms and the surrounding water. Then, silver nuclei spontaneously form once the amorphous layer exceeds a critical thickness. Water molecule absorption on the outmost surface of silver clusters contributes to the continuous deposition of silver amorphous phase.

Size-dependent structure transformation from amorphous phase to crystal

The molecular dynamics simulations were applied to study the crystallization of Ag from an amorphous matrix. The results show that the spontaneously crystallized nuclei interact with the amorphous phase, undergoing a rotation and realignment process, promote the crystallization of amorphous phase, and finally form a single crystalline nanostructure. Our results not only provide a system for the theoretical study on the amorphous formation and its function in the crystal growth but also break a path for producing single crystals.

Peng Kong

Papers

Dendritic Silver Nanostructure Growth and Evolution in Replacement Reaction

Thermodynamic and kinetic competition in silver dendrite growth

Size-dependent structure transformation from amorphous phase to crystal

Single crystal growth via a grain rotation mechanism within amorphous matrix