• Proceedings of the Korean Vacuum Society Conference
• /
• 1998.02a
• /
• pp.135-136
• /
• 1998

By the ion bombardment the original discrete layered structure is damaged and a uniformly mixed layer is formed by the intermixing of the films. Immediately after this dynamic cascade mixing a structure of this mixed layer is likely to be a mixture of randomly distributed atoms. Subsequently the mixed layered structure becomes a non-equilibrium structure such as the metastable pphase because the kinetic energies of the incident ions rappidly dissippate and host atoms within the collision cascade region are quenched from a highly energetic state. The formation of the metastable transition metal alloys using ion-beam-mixing has been extensively studied for many years because of their sppecific ppropperties that differ from those of bulk materials. in ion-beam-mixing the alloy or comppound is formed due to the atomic interaction between different sppecies during ion bombardment. in this study the metastable pphase formed by ion-beam-mixing pprocess is comppared with equilibrium one by arc-melting method by GXRD and XAS. Therfore we studied the fundamental characteristics of charge redistribution uppon alloying and formation of intermetallic comppounds. The multi-layer films were depposited on a wet-oxidized Si(100) substrate by sequential electron beam evapporation at a ppressure of less than 5$\times$10-7 Torr during depposition. These compprise 4 ppairs of Co and ppt layers where thicknesses of each layer were varied in order to change the alloy compposition.

• Korean Chemical Engineering Research
• /
• v.55 no.6
• /
• pp.731-744
• /
• 2017

Triplet-triplet annihilation upconversion (TTA-UC) is a special photochemical process that converts low energy photons to higher energy photon via combination of organic chemicals which fulfill specific energetic criteria. TTA-UC has been known as attractive technology that is able to enhance energy conversion efficiency of the photonic devices based on sunlight, which is achieved by conversion of wasted low energy photons in solar spectrum into higher energy photon. In the present paper, we introduced the photochemical mechanism and characteristics of TTA-UC phenomenon, which is yet unfamiliar to the domestic academia, and investigated recent research status, application, and future research directions of TTA-UC technology.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.21 no.6
• /
• pp.39-48
• /
• 2017

In this study, combustion modeling of ZPP and $BKNO_3$ mainly used in the PMD industries has been performed. Saint Robert's law, energy conservation equation, and the Noble-Abel equation of the state have been used for governing equations. The results of pressure obtained from established combustion models and actual CBT have been compared. In the case of ZPP, the model has predicted a pressure curve similar to that of the experimental results, but $BKNO_3$ has showed that the maximum pressure of the model is greater than the experiment at small chamber volume. For these gaps, the probability of $BKNO_3$ unburning has been considered.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2017.05a
• /
• pp.172-178
• /
• 2017

Thermal property is one of the important characteristic in the field of energetic materials. As the energy material is released during decomposition, DSC(Differential Scanning Calorimetry) is frequently used for the thermal analysis. In case of the dynamic DSC measurements, thermal dynamic change like melting is prevented from the thermal property measurements. And due to the predicting kg scale, the conditions of the heat exchange with the environment significantly is changed. In this study, As the method to resolve the problem, we predict the thermal aging property using the AKTS thermokinetic program from DSC measurements which performed isothermal method. Predicting the thermal aging properties from ARC(Accelerating Rate Calorimetry) measurement, we compare two results.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.22 no.2
• /
• pp.66-73
• /
• 2018

A computational fluid dynamics simulation of pyrotechnic material combustion inside a cylindrical closed vessel was carried out using the Eulerian-Lagrangian method. The 5th order upwind WENO scheme and the improved delayed detached eddy turbulence model were implemented to capture shock waves. The flow structure was analyzed inside the cylindrical vessel with a pressure sensor installed at the side wall center. The analysis revealed that the pressure oscillated because of the shock wave vibration. Additionally, the simulation results with four different sensor tab depths implied that, inside the sensor tab, eddies were generated by the excessively large gap between the sensor diaphragm and the side wall. These eddies caused irregularity to the measured time-pressure curve, which is an undesirable characteristic.

• East Asian Economic Review
• /
• v.26 no.1
• /
• pp.49-91
• /
• 2022

Recent years have witnessed renewed interest in Africa and public diplomacy has emerged as the vital tool being used to cultivate these relations. China has been leading in pursuing stronger economic partnership with Africa while middle powers such as Korea are also intensifying engagement with the continent. While previous studies have analyzed the implications of China's activities in Africa on advanced powers, none has examined them from the paradigm of middle powers. This study fills this gap by assessing China's activities in Africa, their economic engagement and implications for Korea's interest in Africa. The analysis is qualitative based on secondary data from various sources and literature. The study shows that China's public diplomacy strategy involves a high degree of innovation and has evolved to encompass new tools and audiences. China has institutionalized a cooperative model that permeates many aspects of governance institutions in Africa, enabling it to strengthen their relations. This could also be helping China to adjust faster leadership transitions in Africa. Whereas the US is still the most influential country in Africa, China is influential in economic policies and has outstripped the US in infrastructure diplomacy. This could be because African policy makers align more with China's economic model than the US' mainstream economics. Chinese aid to Africa has been diversified to social sectors that are more responsive to the needs of Africa. Trade and investment relations between China and Africa have deepened, but so does trade imbalance since 2010. China mainly imports natural resources and raw materials from Africa. But this product portfolio is not different from Korea and the US. China's energetic insertion in Africa using various strategies has significant implications for countries with ambitions in Africa. Korea can achieve its ambitions in Africa by focusing resources in areas it can leverage its core strengths-such as education and vocational training, environmental policy and development cooperation.

• Clean Technology
• /
• v.15 no.4
• /
• pp.233-238
• /
• 2009

Supercritical fluid processes have gained great attention as a new and environmentally-benign method of preparing the microparticles of energetic materials like explosives and propellants. In this work, RDX (cyclotrimethylenetrinitramine) was selected as a target explosive. The microparticle formation of RDX using supercritical anti-solvent (SAS) recrystallization process was performed and the effect of operating variables on the size and morphology of prepared particles was observed. N,N-Dimethylformamide was used as organic solvent for dissolving the RDX. The size of the RDX particles decreased remarkably up to less than $10\;{\mu}m$ by SAS recrystallization. In the range of operating conditions of the SAS process studied in this work, the finest RDX particles were obtained at 313.15K, 150 bar, and 15wt% RDX concentration in feed solution.

• Journal of The Korean Association For Science Education
• /
• v.36 no.1
• /
• pp.103-112
• /
• 2016

The purpose of this study is to investigate secondary science teacher's concepts of good science teaching. To do these, I have developed a questionnaire composed of 32 good teachings on education content, instructional method, instructional environment and atmosphere and assessment categories. 136 secondary science teachers have participated in the questionnaire and were requested to show agreement. Additionally, they were requested to describe the best science teachings that they have experienced. Results are as follows: First, the best science teaching that science teachers thought is a teaching that is in full accord with students' level in education content category, a teaching with an energetic interaction in instructional method category, a teaching in a trustful atmosphere in instructional environment and atmosphere category, a teaching in which students could learn something through a teaching-related assessment in assessment category. Second, secondary science teachers thought that a self-directed learning, a differentiated instruction and a teaching with diverse materials are not important factors in good science teaching. Third, there is a difference between good teaching that secondary science teachers have conceived and good teaching that they have experienced. It shows that science teachers did not precisely understand what good science teaching is. Additionally, I discussed the need of finding a case on good science teachings and a support of an interaction-focused teaching.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.38 no.6
• /
• pp.525-538
• /
• 2014

Safety of reactive systems is one of the most important research areas in the field of weapon development. A NoGo response or at least a low-order explosion should be ensured to prevent unexpected accidents when the reactive system is impacted by high-velocity projectile. We investigated the shock-induced detonation of cased reactive systems subject to a normal projectile impact to the cylindrical surface based on two-dimensional hydrodynamic simulations using the I&G chemical rate law. Two types of energetic materials, namely LX-17 and AP-based solid propellant, were considered to compare the dynamic responses of the reactive system when subjected to the threshold impact velocity. It was found that shock-to-detonation transition phenomena occurred in the cased LX-17, whereas no full reaction occurred in the propellant.

• Clean Technology
• /
• v.22 no.3
• /
• pp.190-195
• /
• 2016

The thermal decomposition of waste energetic materials such as TNT, RDX and composition B in a commercial rotary kiln has previously been carried out. As part of the demilitarization process, the thermal decomposition of homogeneous double base propellant (DB) used in M8 and consisting predominantly of nitrocellulose and nitroglycerine is examined with respect to a number of operating conditions. A single condensed phase reaction with 4 species and 365 gas phase reactions and 59 species are considered. Simulation results show the sensitivity of the thermal decomposition of DB with temperature and velocity. At relatively low velocity with constant inlet hot air temperature, temperature in the rotary kiln was found to be highest, 953 K and 1300 K for cases 3 and 6 respectively. Illustrating that optimum operating temperature can be achieved by controlling the inlet velocity without additional cooling systems.