• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.37 no.4
• /
• pp.267-274
• /
• 2024

Hydrogen embrittlement fracture poses a challenge in ensuring the structural integrity of materials exposed to hydrogen-rich environments. This study advances our comprehension of hydrogen-induced fracture through an integrated numerical modeling approach. In addition, it employs a ductile fracture model named the Gurson-cohesive model (GCM) and hydrogen diffusion analysis. GCM is employed as a fracture model that combines the Gurson model to illustrate the continuum damage evolution and the cohesive zone model to describe crack surface discontinuity and softening behavior. Moreover, porosity and stress triaxiality are considered as crack initiation criteria . A hydrogen diffusion analysis is also integrated with the GCM to account for hydrogen enhanced decohesion (HEDE) mechanisms and their subsequent impacts on crack initiation and propagation. This framework considers the influence of hydrogen on the softening behavior of the traction-separation relationship on the discontinuous crack surface. Parametric studies explore the sensitivity to diffusion properties and hydrogen-induced fracture properties. By combining numerical models of hydrogen diffusion and the ductile fracture model, this study provides an understanding of hydrogen-induced fracture and thereby contributes significantly to the ongoing efforts to design materials that are resilient to hydrogen embrittlement in practical engineering applications.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2010.02a
• /
• pp.236-236
• /
• 2010

알루미늄 자체에 대한 질화 기술의 어려움 때문에 현재까지는 AlN 분말을 이용한 소결 공정을 통하여 주요 부품의 제작이 되어 왔으며. Al 질화 기술보다는 아노다이징과 같은 표면 산화 공정 또는 도금과 같은 기술이 선호되어 왔다. 알루미늄 질화 기술이 잘 사용되지 않았던 이유는 알루미늄 표면에 2 5 nm 두께로 존재하는 치밀한 산화층의 높은 안정성 때문에 질화반응이 어렵기 때문이다. 이 알루미늄 산화물의 안정성은 질화물에 비교하여 5 배까지 높으며, 이런 경향은 온도가 높아짐에 따라 더욱 커지기 때문이다. 특히, 알루미늄의 낮은 기계적 물성을 향상시키기 위해서는 충분히 깊은 두께로 형성되어야 할 필요성이 높으나 알루미늄에 대한 질소의 고용도가 거의 없고 확산 계수가 매우 낮기 때문에 충분히 두꺼운 질화층의 형성이 어렵기 때문이다. 결국, 알루미늄 질화가 가능하기 위해서는 표면의 산화층을 없애야 하며, 알루미늄이 AlN이 되려는 속도는 $Al_2O_3$를 만드려는 속도보다 매우 느리므로, 잔존 산소량을 최소화 할 필요성이 있어서 고진공 분위기에서 처리되어야 한다. 일반적으로 알루미늄 질화를 위해서는 $10^{-6}\;torr$ 이하의 고진공도의 챔버가 필요하며 고순도의 반응 가스를 사용하여야 한다. 그러나 이러한 고진공하에서는 낮은 이온밀도 때문에 신속질화가 기존의 공정시간인 20시간동안, AlN층이 5um이하로 형성되었다. 본 연구에서, 알루미늄의 질화에 있어서, 표면층에 높은 전류를 걸어주어, 용융상태로 만들어주는 것이 좋다는 연구 결과를 얻었으며, 이를 토대로 신속질화를 위하여 전류밀도(전력량)에 따라 알루미늄 질화층의 형성 정도를 연구하였다. SEM, EDS, XRD등을 통해 Al의 표면에 플라즈마 질화를 통해 Al에 질소의 함유량이 증가하는 것을 확인하였으며 광학현미경을 통해 질화층의 두께와 표면조직을 확인하였다. Al 시편의 표면을 효과적으로 활성화할 수 있는 $400^{\circ}C$ 이상의 온도에서 전류밀도(전력량)와 시간의 변화에 따라 질화층이 효과적으로 형성되는 조건과 시간에 따라 두께가 증가하는 경향을 확인할 수 있었다. 이러한 신속 질화 공정을 통해 2시간 이내의 질화를 통해 40um이상의 AlN층을 형성할 수 있었다.

• Applied Chemistry for Engineering
• /
• v.33 no.6
• /
• pp.636-645
• /
• 2022

In this study, we investigated the adsorption characteristics of methyl orange (MO), an anionic dye, on ginkgo shell-based activated carbon (AC). For this purpose, ACs (GS-1, GS-2, and GS-4) with different textural properties were prepared using ginkgo shells and potassium hydroxide (KOH), a representative chemical activating agent. The correlation between the textural characteristics of AC prepared and the mixing ratio of KOH was investigated using nitrogen adsorption/desorption isotherms. The MO adsorption equilibrium experiment on the prepared ACs was conducted under different pH (pH 3~11) and temperature (298~318 K) conditions, and the results were investigated by Langmuir, Freundlich, Sips and temperature-dependent Sips equations. The feasibility of the MO adsorption treatment process of the prepared AC was also investigated using the dimensionless Langmuir separation factor. The heterogeneous adsorption properties of MO for the prepared AC examined using the adsorption energy distribution function (AED) were closely related to the system temperature and textural characteristics of AC. The kinetic results of the batch adsorption performed at different temperatures can be satisfactorily explained by the homogeneous surface diffusion model (HSDM), which takes into account the external mass transfer, intraparticle diffusion, and active site adsorption. The relationship between the activation energy value obtained by the Arrhenius plot and the adsorption energy distribution function value was also investigated. In addition, the adsorption process mechanism of MO on the prepared AC was evaluated using Biot number.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.4 no.3
• /
• pp.210-222
• /
• 1994

The characteristics of flows, temperatures, and concentrations of oxygen are numerically studies in the Czochralski furnace with a uniform axial magnetic field. Important governing factors to the flow fields include buoyancy, thermocapillarity, centrifugal force, magnetic force, diffusion and segregation coefficients of the oxygen, evaporation coefficient in the form of SiO, and ablation rate of crucible wall. With an assumption that the flow fields have reached the steady state, which means that two velocity components in the meridional plane and circumferential velocity, temperatures, electric current intensity become non-transient, then unsteady concentration field of oxygen has been analyzed with an initially uniform oxygen concentration. Oxygen transports due to convection and diffusion in the Czochralski flow field and oxygen flux through the growing crystal surface has been investigated.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.18 no.7
• /
• pp.71-76
• /
• 2019

The diffusion of the drug component of the inflammatory patch into the living tissue was analyzed by laser induced plasma spectroscopy (LIBS). Calcium element, which is a diffusion catalyst of the drug in the inflammatory analgesic patch, is transferred into the body through the diffusion process of the substance. The test pieces used in the experiment are pig skin tissues which are similar to human skin. As a result, the diffusion coefficient D of the calcium element was found to be average $8.24{\times}10^{-2}({\mu}m^2/s)$. Experimental results showed that the most influential factors on the diffusion of materials were temperature variables.

• Journal of the Korea Concrete Institute
• /
• v.13 no.3
• /
• pp.277-284
• /
• 2001

Hardened concrete contains pores of varying types and sizes, and therefore the transport of air through concrete can be considered. The rate of permeability will not only depends on the continuity of pores, but also on the moisture contents in concrete and finishing material on concrete. Also it knows that the durability of reinforced concrete structure is concerned with air permeability which effects on the carbonation occurred by invasion of CO2 gas and the corrosion of steel bar occurred by O$_2$. In this paper, the effects of curing conditions and finishing materials on carbonation and air permeability are investigated according to the accelerated carbonation test. As results, carbonation velocity and air permeability are effected by curing conditions and finishing materials, and air permeability coefficient is effected by moisture content. Also the relationship between carbonation velocity coefficients and air permeability coefficients has been quite well established.

• Journal of Korean Society of Environmental Engineers
• /
• v.22 no.4
• /
• pp.775-784
• /
• 2000

Nitrate dry deposition fluxes were directly measured using knife-leading-edge surrogate surface (KSS) covered with greased strips and a water surface sampler (WSS). The average gaseous flux ($8.3mg/m^2/day$) was much higher than the average particulate one ($3.0mg/m^2/day$). The best fit gas phase mass transfer coefficient (MTC) of $HNO_3$ was obtained by linear regression analysis between measured gaseous flux containing nitrogen compounds and measured ambient $HNO_3$ concentration. The result showed that the MTCs of $HNO_3$ were approximately two times higher than those of $SO_2$. Especially, during the ozone action day, measured gaseous fluxes containing nitrogen compounds were much higher than those ones calculated as the product of measured ambient $HNO_3$ concentration and gas phase MTC of $HNO_3$, which is calculated from MTC of $SO_2$ using Graham's diffusion law. This result indicated that other nitrogen compounds except $HNO_3$ contributed to gaseous flux containing nitrogen compounds into the water surface sampler. The theoretical calculations suggest the contributions of nitrous acid ($HNO_2$) and PAN to the gaseous dry deposition flux of nitrogen containing compounds to the WSS.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.19 no.5
• /
• pp.67-74
• /
• 2015

RC (Reinforced Concrete) structures are considered as cost-benefit and durable however performances of structural safety and durability are degraded due to steel corrosion. Service life in RC structure is differently evaluated due to different local environmental conditions even if it is exposed to the same chloride attack. In the paper, 25 concrete cores from field investigation are obtained from 4 RC columns with duration of 3.5~4.5 years exposed to sea water. Through total chloride content measurement, surface chloride contents and apparent diffusion coefficients are evaluated. Service life of the target structure is estimated through deterministic method based on Fick's $2^{nd}$ Law and probabilistic method based on durability failure probability, respectively. Probability method is evaluated to be more conservative and relatively decreased service life is evaluated in tidal zone and splash zone over 40.0 m. Chloride penetration behavior with coring location from sea level and the present limitations of durability design method are investigated in the paper.

• Journal of Korean Society of Environmental Engineers
• /
• v.37 no.11
• /
• pp.642-648
• /
• 2015

Oak wood based activated carbon was modified with surface impregnation of $Fe^{3+}$ and $Al^{3+}$ metal ions mixture for enhancements of phosphate adsorption capacity in aqueous solution. The phosphate adsorption capacity of the prepared metal impregnated carbon (MC) was about 8 times higher than that of the original activated carbon (OC). Adsorption equilibrium capacities of the phosphate increased with increasing system temperature. The adsorption equilibrium isotherm of phosphate on the prepared MC could be represented by the Langmuir equation. Thermodynamic parameters also indicated that adsorption system was spontaneous and endothermic reaction. The internal diffusion coefficient was measured to analyze the adsorption behavior and kinetic rate. To determine the internal diffusion coefficient, pore diffusion model (PDM) was employed and the result was in good agreement with experimental data.

• Applied Chemistry for Engineering
• /
• v.5 no.3
• /
• pp.385-394
• /
• 1994

Numerical solutions were obtained to the model equations for various of the parameters characterizing the pore structure, effective internal diffusion, and the chemical reaction constant. The conversion was decreased with the cause of pore closure at the surface of reacting particles, reduction of porosity, surface area of reaction and effective diffusion coefficient in the solid with the progress of reaction. Total conversion was strongly dependent on the local conversion at surface. According to the decreasing of impregnated concentration of the copper oxide and the increase of the flue gases concentration, total conversion was increased. The conversion was affected by gas flow rate and pore size distribution in the reacting solid.