Young Rang Uhm

Bio: Young Rang Uhm is an academic researcher from KAERI. The author has contributed to research in topics: Nanoparticle & Nanocrystalline material. The author has an hindex of 14, co-authored 84 publications receiving 643 citations.

Magnetic properties of nano-size Ni synthesized by the pulsed wire evaporation (PWE) method

Abstract: Nano-crystalline Ni has been synthesized by a pulsed wire evaporation (PWE) method, and its abnormal magnetic properties in a magnetic ordered state have been characterized using high and low magnetic fields. It was found that particles with the size ranges from 20 to 80 nm has a mean crystalline size of 40 nm which might influence the magnetic hysterisis behavior. Neutron powder diffraction (NPD) and saturation magnetization results indicate the antiferromagnetic NiO phase in prepared powder exist below the detection limit of 1 wt.%. The shifted hysterisis loop and irreversibility of magnetization in a high field were observed in the magnetic-ordered state of Ni. The initial magnetization curve for Ni is started to overlap the hysterisis loop at applied field of 750 Oe. This irreversibility in a high field can be explained by the non-collinear behavior and the existence of the metastable states of the magnetization at the surface layer (or core) of the particle in the applied magnetic field due to decrease of particle size.

Synthesis and characterization of nanoparticles of ZnO by levitational gas condensation

Abstract: Nanocrystalline ZnO powders have been synthesized by means of a novel and simple one-step method of levitational gas condensation. The Zn clusters evaporated from a surface of the levitated liquid Zn droplet and then condensed into nanoparticles of ZnO in a chamber filled with mixtures of Ar and O2 gases. As a result, ZnO was synthesized under an O2 flow rate of 0.1 ≤ V O 2 ( l / min ) ≤ 0.2 . The as-prepared ZnO powders, characterized by transmission electron microscopy and Brunauer–Emmet–Teller analysis, show high specific surface area of 38 m2/g and possess particle size of 30 nm having the web-like pattern with hexagonal structure. From the main peak intensities of X-ray diffraction, the amounts of ZnO and Zn in the sample are found to be 92% and 8%.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Hallmarks of mechanochemistry: From nanoparticles to technology

Abstract: The aim of this review article on recent developments of mechanochemistry (nowadays established as a part of chemistry) is to provide a comprehensive overview of advances achieved in the field of atomistic processes, phase transformations, simple and multicomponent nanosystems and peculiarities of mechanochemical reactions. Industrial aspects with successful penetration into fields like materials engineering, heterogeneous catalysis and extractive metallurgy are also reviewed. The hallmarks of mechanochemistry include influencing reactivity of solids by the presence of solid-state defects, interphases and relaxation phenomena, enabling processes to take place under non-equilibrium conditions, creating a well-crystallized core of nanoparticles with disordered near-surface shell regions and performing simple dry time-convenient one-step syntheses. Underlying these hallmarks are technological consequences like preparing new nanomaterials with the desired properties or producing these materials in a reproducible way with high yield and under simple and easy operating conditions. The last but not least hallmark is enabling work under environmentally friendly and essentially waste-free conditions (822 references).

New directions in screen printed electroanalytical sensors: an overview of recent developments.

Abstract: Screen printing is widely used to fabricate disposable and economical electrochemical sensors and has helped us to establish the route from ‘lab-to-market’ for a plethora of sensors We overview recent developments in the field where screen printed electrochemical sensors are utilised Starting with their fundamental understanding, through to highlighting new developments in bulk metal and mediator modified electrodes, as well as novel advantageous electrode designs, we demonstrate the wide and diverse range of applications that sensors based on this fabrication approach have achieved

Additive Manufacturing of Metallic and Ceramic Components by the Material Extrusion of Highly-Filled Polymers: A Review and Future Perspectives

Abstract: Additive manufacturing (AM) is the fabrication of real three-dimensional objects from metals, ceramics, or plastics by adding material, usually as layers. There are several variants of AM; among them material extrusion (ME) is one of the most versatile and widely used. In MEAM, molten or viscous materials are pushed through an orifice and are selectively deposited as strands to form stacked layers and subsequently a three-dimensional object. The commonly used materials for MEAM are thermoplastic polymers and particulate composites; however, recently innovative formulations of highly-filled polymers (HP) with metals or ceramics have also been made available. MEAM with HP is an indirect process, which uses sacrificial polymeric binders to shape metallic and ceramic components. After removing the binder, the powder particles are fused together in a conventional sintering step. In this review the different types of MEAM techniques and relevant industrial approaches for the fabrication of metallic and ceramic components are described. The composition of certain HP binder systems and powders are presented; the methods of compounding and filament making HP are explained; the stages of shaping, debinding, and sintering are discussed; and finally a comparison of the parts produced via MEAM-HP with those produced via other manufacturing techniques is presented.