Sunshin Jung

Microwave-accelerated energy-efficient esterification of free fatty acid with a heterogeneous catalyst.

This paper shows energy-efficiency of microwave-accelerated esterification of free fatty acid with a heterogeneous catalyst by net microwave power measurement. In the reaction condition of 5 wt% sulfated zirconia and 1:20 M ratio of oil to methanol at 60°C and atmospheric pressure, more than 90% conversion of the esterification was achieved in 20 min by microwave heating, while it took about 130 min by conventional heating. Electric energy consumption for the microwave heating in this accelerated esterification was only 67% of estimated minimum heat energy demand because of significantly reduced reaction time.

Electrically Robust Metal Nanowire Network Formation by In-Situ Interconnection with Single-Walled Carbon Nanotubes

Modulation of the junction resistance between metallic nanowires is a crucial factor for high performance of the network-structured conducting film. Here, we show that under current flow, silver nanowire (AgNW) network films can be stabilised by minimizing the Joule heating at the NW-NW junction assisted by in-situ interconnection with a small amount (less than 3 wt%) of single-walled carbon nanotubes (SWCNTs). This was achieved by direct deposition of AgNW suspension containing SWCNTs functionalised with quadruple hydrogen bonding moieties excluding dispersant molecules. The electrical stabilisation mechanism of AgNW networks involves the modulation of the electrical transportation pathway by the SWCNTs through the SWCNT-AgNW junctions, which results in a relatively lower junction resistance than the NW-NW junction in the network film. In addition, we propose that good contact and Fermi level matching between AgNWs and modified SWCNTs lead to the modulation of the current pathway. The SWCNT-induced stabilisation of the AgNW networks was also demonstrated by irradiating the film with microwaves. The development of the high-throughput fabrication technology provides a robust and scalable strategy for realizing high-performance flexible transparent conductor films.

One-Step Synthesis of PEG-Coated Gold Nanoparticles by Rapid Microwave Heating

Polyethylene Glycol- (PEG-) coated gold nanoparticles (PEG-AuNPs) are synthesized by a one-step route with rapid microwave heating. Homogeneous nucleation of the primary gold particles is enhanced by increasing the applied microwave power during the initial stage of the synthesis, increasing the temperature ramping rate () and resulting in decreased size and improved uniformity of the synthesized PEG-AuNPs. Using rapid microwave heating, we successfully produce uniform colloidal PEG-AuNPs with an average diameter of  nm within a few minutes. By appropriate tuning of the growth parameters, microwave synthesis can produce largely colloidal PEG-AuNPs with high uniformity.

Self-passivation of transparent single-walled carbon nanotube films on plastic substrates by microwave-induced rapid nanowelding

We developed a straightforward method for enhancing the environmental stability of transparent single-walled carbon nanotube (SWCNT) network films on plastic substrates using a rapid microwave heating to produce SWCNT film–substrate nanowelding without any chemicals. The selective heating of SWCNTs induced by microwave irradiation leads to embedding the SWCNTs in the substrate, even within 10 s, without distortion of the substrate. The SWCNTs-embedded surface of the substrate played the role of a self-passivation layer that protected the SWCNTs from water molecules. The sheet resistance values of the nanowelded films had not increased more than 10%.

Accelerated esterification of free fatty acid using pulsed microwaves

It was demonstrated that pulsed microwave irradiation is a more effective method to accelerate the esterification of free fatty acid with a heterogeneous catalyst than continuous microwave irradiation. A square-pulsed microwave with a 400 Hz repetition rate and a 10-20% duty cycle with the same energy as the continuous microwave were used in this study. The pulsed microwaves improved the esterification conversion from 39.9% to 66.1% after 15 min in comparison with the continuous microwave under the same reaction conditions. These results indicated that pulsed microwaves with repetitive strong power could enhance the efficiency of biodiesel production relative to the use of continuous microwave with mild power.

Investigation of the 100GHz reentrant linear magnetron using particle-in-cell simulation

The operating characteristics of the 100GHz linear magnetron employing the reentrant resonator are investigated by using a two-dimensional particle-in-cell simulation. The geometrical parameters calculated for the operation frequency of 100GHz are confirmed by the resonant modes and field distribution obtained by an electromagnetic simulation. With the synchronism condition, the effect of number of vane and beam voltage on the power density and the operation frequency are examined. When the beam voltage of 2kV and the external magnetic field of 0.79T are used, the reentrant linear magnetron is oscillated at about 100.2GHz, and the maximum power density with the injected current density of 60A∕cm2 is increased up to 220mW∕mm2 from 125mW∕mm2 due to the extension of interaction region as the number of vane is varied from 10 to 12.

Carbon nanotube-conducting polymer composite wires formed by fountain pen growth (FPG) route

We demonstrate the three dimensional (3D) growth of multiwalled carbon nanotube (MWNT)–PEDOT : PSS composite microwires by a fountain pen growth (FPG) route. The electrical conductivity of the grown composite wire is improved by enhancing the electrical network of entrapped MWNTs formed in the PEDOT : PSS matrix.

Rapid Cellulose-Mediated Microwave Sintering for High-Conductivity Ag Patterns on Paper

Cellulose-based paper is essential in everyday life, but it also has further potentials for use in low-cost, printable, disposable, and eco-friendly electronics. Here, a method is developed for the cellulose-mediated microwave sintering of Ag patterns on conventional paper, in which the paper plays a significant role both as a flexible insulating substrate for the conductive Ag pattern and as a lossy dielectric media for rapid microwave heating. The anisotropic dielectric properties of the cellulose fibers mean that a microwave electric field applied parallel to the paper substrate provides sufficient heating to produce Ag patterns with a conductivity 29-38% that of bulk Ag in a short period of time (∼1 s) at 250-300 °C. Significantly, there is little thermal degradation of the substrate during this process. The microwave-sintered Ag patterns exhibit good mechanical stability against 10 000 bending cycles and can be easily soldered with lead-free solder. Therefore, cellulose-mediated microwave sintering presents a promising means of achieving short processing times and high electrical performance in flexible paper electronics.

Particle-in-cell simulation of 100 GHz reentrant linear magnetron

100 GHz linear magnetron employing the ten-vane reentrant resonator is investigated by using a two-dimensional particle-in-cell simulation. The dynamics of electron beam, the time variation of electric energy in each vane, and the generated power density are examined when the injected current density is varied. The maximum power density is 180 mW/mm2 at 100 GHz when the current density of 80 A/cm2 is used.

Field-emission X-ray sources with an anisotropic focusing lens for isotropic X-ray focal spots

Hermetic-sealed field-emission X-ray sources with an anode voltage and current of 70 kV and 0.5 mA have been developed using an anisotropic focusing electron lens structure for an isotropic focal spot. The anisotropic focusing of an electron beam was achieved using an electrostatic electron lens with anisotropic aperture geometry integrated in a gate (or grid) electrode. The anisotropic geometry has an influence on the electron beam with different horizontal and vertical electric fields, thereby anisotropically focusing the beam on an anode target.