arXiv subjects

Ju-Myong Han

Publications and source records attributed to Ju-Myong Han.

3 recordsLinked to original sources

arXiv2020

Molecular dynamics study of the effect of moisture and porosity on thermal conductivity of tobermorite 14 Å

The effect of moisture and porosity on thermal conductivity of tobermorite 14 Å~as the major component of cement paste is studied by using molecular dynamics simulation with ClayFF potential. The calculated results show that the thermal conductivity increases monotonically as the moisture content by mass within the interior pores increases and the slope of the linear fitting function decreases as the porosity increases. Meanwhile, the normalized thermal conductivity is found to increase exponentially as increasing the moisture content by volume. Phonon density of states of porous and moist tobermorite 14 Å~is used to explain the contribution of individual atoms and molecules to the thermal properties. The results can be potentially used to design higher thermal insulating materials with cement and concrete for energy saving buildings.

cond-mat.mtrl-sci↗

arXiv2017

Ab initio thermodynamic study of SnO$_2$(110) surface in an O$_2$ and NO environment: a fundamental understanding of gas sensing mechanism for NO and NO$_2$

For the purpose of elucidating the gas sensing mechanism of SnO$_2$ for NO and NO$_2$ gases, we calculate the phase diagram of SnO$_2$(110) surface in contact with an O$_2$ and NO gas environment by means of {\it ab initio} thermodynamic method. Firstly we build a range of surface slab models of oxygen pre-adsorbed SnO$_2$(110) surfaces using (1$\times$1) and (2$\times$1) surface unit cells and calculate their Gibbs free energies considering only oxygen chemical potential. The fully reduced surface containing the bridging and in-plane oxygen vacancies in the oxygen-poor condition, while the fully oxidized surface containing the bridging oxygen and oxygen dimer in the oxygen-rich condition, and the stoichiometric surface in between, were proved to be most stable. Using the selected plausible NO-adsorbed surfaces, we then determine the surface phase diagram of SnO$_2$(110) surfaces in ($Δμ_\text{O}$, $Δμ_\text{NO}$) space. In the NO-rich condition, the most stable surfaces were those formed by NO adsorption on the most stable surfaces in contact with only oxygen gas. Through the analysis of electronic charge transferring and density of states during NO$_x$ adsorption on the surface, we provide a meaningful understanding about the gas sensing mechanism.

cond-mat.mtrl-sci↗

arXiv2015

Infrared absorption property of silicon carbide-silica nanocables synthesized by ethanol pyrolysis

A controllable synthesis method for SiC-SiO$_{2}$ nanocables has been proposed. The diameter of SiC core and thickness of SiO$_{2}$ shell were changed by adjusting the flow ratio between Ar dilution gas and ethanol precursor. With increasing the flow, the enhancement of 1137cm$^{-1}$ peak was observed from fourier transform infrared spectroscopy (FTIR) spectra. This peak is considered to be originated from a highly disordered surface structure of SiO$_{2}$ shell which was enhanced with increasing the flow. The FTIR spectra show the 910cm$^{-1}$ peak which is attributed to surface phonon resonance in the nanostructure of SiC exited by p-polarized field component.

cond-mat.mtrl-sci↗