Frontiers of Materials Science (v.5, #1)

Shaped gold and silver nanoparticles by Yugang Sun; Changhua An (1-24).
Advance in the synthesis of shaped nanoparticles made of gold and silver is reviewed in this article. This review starts with a new angle by analyzing the relationship between the geometrical symmetry of a nanoparticle shape and its internal crystalline structures. According to the relationship, the nanoparticles with well-defined shapes are classified into three categories: nanoparticles with single crystallinity, nanoparticles with angular twins, and nanoparticles with parallel twins. Discussion and analysis on the classical methods for the synthesis of shaped nanoparticles in each category are also included and personal perspectives on the future research directions in the synthesis of shaped metal nanoparticles are briefly summarized. This review is expected to provide a guideline in designing the strategy for the synthesis of shaped nanoparticles and analyzing the corresponding growth mechanism.
Keywords: shaped nanoparticles; geometric symmetry; internal crystalline structure; multiple twins; gold; silver

Catalytic nanomotors are nano-to-micrometer-sized actuators that carry an on-board catalyst and convert local chemical fuel in solution into mechanical work. The location of this catalyst as well as the geometry of the structure dictate the swimming behaviors exhibited. The nanomotors can occur naturally in organic molecules, combine natural and artificial parts to form hybrid nanomotors or be purely artificial. Fabrication techniques consist of template directed electroplating, lithography, physical vapor deposition, and other advanced growth methods. Various physical and chemical propulsion mechanisms have been proposed to explain the motion behaviors including diffusiophoresis, bubble propulsion, interfacial tension gradients, and self-electrophoresis. The control and manipulation based upon external fields, catalytic alloys, and motion control through thermal modulation are discussed as well. Catalytic nanomotors represent an exciting technological challenge with the end goal being practical functional nanomachines that can perform a variety of tasks at the nanoscale.
Keywords: nanomotors; catalysis; glancing angle deposition (GLAD); bubble propulsion; self-electrophoresis

Optical and electrical nano eco-sensors using alternative deposition of charged layer by Syed Rahin Ahmed; Seong Cheol Hong; Jaebeom Lee (40-49).
This review focuses on layer by layer (LBL) assembly-based nano ecological sensor (hereafter, eco-sensor) for pesticide detection, which is one of the most versatile methods. The effects of pesticides on human health and on the environment (air, water, soil, plants, and animals) are of great concern due to their increasing use. We highlight two of the most popular detecting methods, i.e., fluorescence and electrochemical detection of pesticides on an LBL assembly. Fluorescence materials are of great interest among researchers for their sensitivity and reliable detection, and electrochemical processes allow us to investigate synergistic interactions among film components through charge transfer mechanisms in LBL film at the molecular level. Then, we noted some prospective directions for development of different types of sensing systems.
Keywords: pesticides; fluorescence; electrochemistry; layer by layer (LBL)

ZrO2-WC composites exhibit comparable mechanical properties as traditional WC-Co materials, which provides an opportunity to partially replace WC-Co for some applications. In this study, 2 mol.% Y2O3 stabilized ZrO2 composites with 40 vol.% WC were consolidated in the 1150°C-1850°C range under a pressure of 60 MPa by pulsed electric current sintering (PECS). The densification behavior, microstructure and phase constitution of the composites were investigated to clarify the role of the sintering temperature on the grain growth, mechanical properties and thermal stability of ZrO2 and WC components. Analysis results indicated that the composites sintered at 1350°C and 1450°C exhibited the highest tetragonal ZrO2 phase transformability, maximum toughness, and hardness and an optimal flexural strength. Chemical reaction of ZrO2 and C, originating from the graphite die, was detected in the composite PECS for 20 min at 1850°C in vacuum.
Keywords: ceramic composite; pulsed electric current sintering (PECS); grain size; mechanical property

The properties of bone tissue engineering scaffolds such as architecture, porosity, mechanical properties and surface properties have significant effects on cellular response and play an important role in bone regeneration. In this study, threedimensional nanocomposite scaffolds consisting of calcium phosphate (Ca-P) nanoparticles and poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) copolymer with controlled external and internal architectures were successfully produced via selective laser sintering (SLS), one of the versatile rapid prototyping techniques. The Ca-P/PHBV nanocomposite scaffolds had a porosity of (61.75±1.24)%, compressive strength of (2.16±0.21) MPa and Young’s modulus of (26.98±2.29) MPa. The surface modification of scaffolds by gelatin was achieved through physical entrapment. The amount of entrapped gelatin could be controlled by varying the solvent composition and reaction time. The surface modification improved the hydrophilicity of scaffolds but did not significantly affect the surface morphology and mechanical properties. Osteoblast-like cells (SaOS-2) were cultured on scaffolds with and without gelatin surface modification. The majority of SaOS-2 cells were viable and proliferated in both types of scaffolds for up to 14 d in culture, as indicated by MTT assay and live and dead assay. Surface modification significantly increased cell proliferation for surface modified scaffolds, which could be due to the improvement in hydrophilicity of the scaffolds.
Keywords: nanocomposite scaffold; selective laser sintering; surface modification; physical entrapment; cell behaviour

Laboratory study on the formation of Al2O3 inclusions at the on-set of deoxidation and during reoxidation by Marie-Aline Van Ende; Muxing Guo; Bart Blanpain; Patrick Wollants (69-76).
The formation of Al2O3 inclusions in liquid iron has been investigated in a resistance heated tube furnace to obtain deoxidation and reoxidation related data. The formation of inclusions during the early stages of deoxidation was simulated by bringing a piece of Al in contact for a short time with liquid Fe containing different dissolved oxygen levels. Reoxidation was studied by exposing Al containing Fe melts to a CO/CO2 atmosphere. Through modeling, an estimate of the local and time-dependent growth conditions for the inclusions can be made and linked to the inclusion characteristics.
Keywords: steel cleanliness; Al2O3 inclusions; deoxidation; reoxidation; morphology