• International Journal of Advanced Culture Technology
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• v.8 no.2
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• pp.246-251
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• 2020

Dimethyl Ether(DME) engine use a highly efficient alternative fuel having a great quantity of oxygen and has a advantage no polluting PM gas. The existing DME fuel cam material is a highly expensive carbide alloy, and it is difficult to take a price advantage. Therefore the study of replacing body area with inexpensive steel material excluding piston shoe and contact area which demands high characteristics is needed. The development of WC-Ni base carbide alloy optimal bonding composition technique was accomplished in this study. To check out the influence of bonding temperature and time, bonding characteristics of sintering temperature was experimented. The hardness of specimen and bonding rate were measured using ultrasound equipment. The bonding state of each condition was excellent, and the thickness of mid-layer, temperature and maintaining time were measured. The mid-layer thickness according to bonding temperature and maintaining time were observed with optical microscope. We analyzed the micro-structural analysis, formation of bonding specimen, wafer fabrication and fuel cam abrasion test. Throughout this study, we confirmed that the fuel cam for DME engine which demands high durability against velocity and pressure is excellent.

• Journal of the Korean institute of surface engineering
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• v.52 no.6
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• pp.321-325
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• 2019

Triso-type coating layers of silicon carbide and graphite on UO₂ paticulate nuclear fuel were prepared by using fluidized bed type chemical vapor deposition and self-propagating high temperature synthesis methods to make a coated nuclear fuel of a power plant for hydrogen mass-production. The source and carrier gases were the mixture of methyltrichlorosilane and propane, and inert argon. Chemical analysis and microstructure observation showed that the coated layers were inner graphite, middle silicon carbide and outer graphite. The elastic modulus and nano-hardness of the silicon carbide layer were 503 [GPa] and 36 [GPa], respectively.

• Nuclear Engineering and Technology
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• v.55 no.10
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• pp.3725-3731
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• 2023

Thorium dioxide (ThO₂)-silicon carbide (SiC) composite fuel pellets were fabricated via the spark plasma-sintering (SPS) method to investigate the role of the addition of SiC in enhancing the thermal conductivity of ThO₂ fuel. SiC particles with an average size of 1㎛ in 10 and 15 vol% were used to manufacture the composite pellets. The changes in the composites' densification, microstructure and thermal conductivity were explored by comparing them with pure ThO₂ pellets. The structural and microstructural characterization of the composite pellets has revealed that SPS could manufacture high-quality composite pellets without having any reaction products or intermetallic. The density measurement by the Archimedes principles and the grain size from the electron back-scattered diffraction (EBSD) analysis has indicated that the composites have higher densities and smaller grain sizes than the pellets without SiC addition. Finally, thermal conductivity as a function of temperature has revealed that sintered ThO₂-SiC composites showed an increase of up to 56% in thermal conductivity compared to pristine ThO₂ pellets.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.722-725
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• 2004

An experimental investigation was conducted to investigate the effects of the equivalence ratio and air mass flux on the combustion efficiency in a solid fuel ramjet used fuel grains which were highly loaded with boron carbide. Combustion efficiency increased with increasing equivalence ratio (grain length), and decreasing air mass flux. Higher inlet air temperature produced higher combustion efficiencies, apparently the result of enhanced combustion of the larger boron particles those bum in a diffusion controlled regime. Short grains which considered primarily of the recirculation region produced larger particles and lower combustion efficiencies. The result of the normalized combustion efficiency increased with inlet air temperature, is coincident with the result of the Brayton cycle thermal and the total efficiency relating to the heat input.

• New & Renewable Energy
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• v.9 no.1
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• pp.51-59
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• 2013

Tantalum carbide crystallites which is to be used for $H_2$ fuel cell has been synthesized via a temperature-programmed reduction of $Ta_2O_5$ with pure $CH_4$. The resultant Ta carbide crystallites prepared using two different heating rates and space velocity exhibit the different surface areas. The $O_2$ uptake has a linear relation with surface area, corresponding to an oxygen capacity of $1.36{\times}10^{13}\;O\;cm^{-2}$. Tantalum carbide crystallites are very active for hydrogen production form ammonia decomposition reaction. Tantalum carbides are as much as two orders of magnitude more active than Pt/C catalyst (Engelhard). The highest activity has been observed at a ratio of $C_1/Ta^{{\delta}+}=0.85$, suggesting the presence of electron transfer between metals and carbon in metal carbides.

• Nuclear Engineering and Technology
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• v.48 no.3
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• pp.660-672
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• 2016

In Part I of this paper, the two-temperature homogenized model for the fully ceramic microencapsulated fuel, in which tristructural isotropic particles are randomly dispersed in a fine lattice stochastic structure, was discussed. In this model, the fuel-kernel and silicon carbide matrix temperatures are distinguished. Moreover, the obtained temperature profiles are more realistic than those obtained using other models. Using the temperature-dependent thermal conductivities of uranium nitride and the silicon carbide matrix, temperature-dependent homogenized parameters were obtained. In Part II of the paper, coupled with the COREDAX code, a reactor core loaded by fully ceramic microencapsulated fuel in which tristructural isotropic particles are randomly dispersed in the fine lattice stochastic structure is analyzed via a two-temperature homogenized model at steady and transient states. The results are compared with those from harmonic- and volumetric-average thermal conductivity models; i.e., we compare $k_{eff}$ eigenvalues, power distributions, and temperature profiles in the hottest single channel at a steady state. At transient states, we compare total power, average energy deposition, and maximum temperatures in the hottest single channel obtained by the different thermal analysis models. The different thermal analysis models and the availability of fuel-kernel temperatures in the two-temperature homogenized model for Doppler temperature feedback lead to significant differences.

• Journal of Powder Materials
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• v.25 no.5
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• pp.408-414
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• 2018

This study investigates the microstructure and wear properties of cermet (ceramic + metal) coating materials manufactured using high velocity oxygen fuel (HVOF) process. Three types of HVOF coating layers are formed by depositing WC-12Co, WC-20Cr-7Ni, and Cr3C2-20NiCr (wt.%) powders on S45C steel substrate. The porosities of the coating layers are $1{\pm}0.5%$ for all three specimens. Microstructural analysis confirms the formation of second carbide phases of $W_2C$, $Co_6W_6C$, and $Cr_7C_3$ owing to decarburizing of WC phases on WC-based coating layers. In the case of WC-12Co coating, which has a high ratio of $W_2C$ phase with high brittleness, the interface property between the carbide and the metal binder slightly decreases. In the $Cr_3C_2-20CrNi$ coating layer, decarburizing almost does not occur, but fine cavities exist between the splats. The wear loss occurs in the descending order of $Cr_3C_2-20NiCr$, WC-12Co, and WC-20Cr-7Ni, where WC-20Cr-7Ni achieves the highest wear resistance property. It can be inferred that the ratio of the carbide and the binding properties between carbide-binder and binder-binder in a cermet coating material manufactured with HVOF as the primary factors determine the wear properties of the cermet coating material.

• Nuclear Engineering and Technology
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• v.47 no.5
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• pp.608-616
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• 2015

The migration of silver (Ag) in silicon carbide (SiC) and $^{110m}Ag$ through SiC of irradiated tristructural isotropic (TRISO) fuel has been studied for the past three to four decades. However, there is no satisfactory explanation for the transport mechanism of Ag in SiC. In this work, the diffusion coefficients of Ag measured and/or estimated in previous studies were reviewed, and then pre-exponential factors and activation energies from the previous experiments were evaluated using Arrhenius equation. The activation energy is $247.4kJ{\cdot}mol^{-1}$ from Ag paste experiments between two SiC layers produced using fluidized-bed chemical vapor deposition (FBCVD), $125.3kJ{\cdot}mol^{-1}$ from integral release experiments (annealing of irradiated TRISO fuel), $121.8kJ{\cdot}mol^{-1}$ from fractional Ag release during irradiation of TRISO fuel in high flux reactor (HFR), and $274.8kJ{\cdot}mol^{-1}$ from Ag ion implantation experiments, respectively. The activation energy from ion implantation experiments is greater than that from Ag paste, fractional release and integral release, and the activation energy from Ag paste experiments is approximately two times greater than that from integral release experiments and fractional Ag release during the irradiation of TRISO fuel in HFR. The pre-exponential factors are also very different depending on the experimental methods and estimation. From a comparison of the pre-exponential factors and activation energies, it can be analogized that the diffusion mechanism of Ag using ion implantation experiment is different from other experiments, such as a Ag paste experiment, integral release experiments, and heating experiments after irradiating TRISO fuel in HFR. However, the results of this work do not support the long held assumption that Ag release from FBCVD-SiC, used for the coating layer in TRISO fuel, is dominated by grain boundary diffusion. In order to understand in detail the transport mechanism of Ag through the coating layer, FBCVD-SiC in TRISO fuel, a microstructural change caused by neutron irradiation during operation has to be fully considered.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2018.11a
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• pp.114-115
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• 2018

To develop an effective shielding material for spent fuel that emits fast neutrons is necessary. In this study, thermal neutron and fast neutron shielding performance of polyethylene coated boron carbide-incorporated cement paste was quantitatively analyzed by Monte Carlo N-Particle transport code (MCNP) simulations. As the results of the simulations, fast neutrons were effectively shielded through large quantity of hydrogen and boron elements in polyethylene and boron carbide.

• Journal of the Korean Society of Propulsion Engineers
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• v.8 no.2
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• pp.95-101
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• 2004

An experimental investigation was conducted to investigate the effects of the equivalence ratio and air mass flux on the combustion efficiency in a solid fuel ramjet used fuel grains which were highly loaded with boron carbide. Combustion efficiency increased with increasing equivalence ratio (grain length), and decreasing air mass flux. Higher inlet air temperature produced higher combustion efficiencies, apparently the result of enhanced combustion of the larger boron particles those burn in a diffusion controlled regime. Short grains which considered primarily of the recirculation region produced larger particles and lower combustion efficiencies. The result of the normalized combustion efficiency increased with inlet air temperatures coincident with the result of the Brayton cycle thermal and the total efficiency relating to the heat input.