• Journal of the Korean Ceramic Society
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• v.46 no.1
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• pp.108-115
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• 2009

In this study, a novel-processing route for producing microcellular zirconia ceramics has been developed. The proposed strategy for making the microcellular zirconia ceramics involves hollow microsphere as a pore former which has extremely low density of $0.025\;g/cm^3$. Effects of hollow microsphere content and sintering temperature on microstructure, porosity, pore distribution, and compressive strength were investigated in the processing of microcellular zirconia ceramics. By controlling the content of hollow microsphere, it was possible to make the porous zirconia ceramics with porosities ranging from 45% to 75%. Typical compressive strength value of microcellular zirconia ceramics with ${\sim}65%$ porosity was over 50 MPa. By adjusting the mixing ratio of large and small zirconia powders, it was possible to control the pore structure from close to open pores.

• Journal of Welding and Joining
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• v.21 no.5
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• pp.540-546
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• 2003

Recently Al alloys are being used gradually for structural materials of transports. In welding of Al alloys used for transports, good weldabilities as well as adequate mechanical properties of the welds should be ensured as structural materials. In this study, the welds formation, macro and microstructural characteristics, generation of defects and hardness distribution in welds of Al alloys of 5083, 6N01 and 7N01 by DCSP- and AC-GTA welding process, were investigated. The deeper penetration was obtained in all welds of the alloys by DCSP-GTAW with He gas, compared with those by using AC-GTAW. The 6N01 alloy showed high susceptibilities to solidification cracking in weld metal and liquation cracking in HAZ of the welding beads of both DCSP- and AC-GTAW process. The cracking ratio of 6N01 alloy was increased with increasing of welding current. The porosity ratios in weld metal of all alloys used were extremely low including all welding conditions of DCSP-GTAW. However, in AC-GTAW process, the porosity ratios of the welds using Ar gas showed much higher values than those using He gas.

• Journal of the Korean Ceramic Society
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• v.50 no.5
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• pp.341-347
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• 2013

Kaolin-based membranes with a pore size of 0.30-0.40 ${\mu}m$ were successfully prepared by a simple pressing route using low-cost starting materials, kaolin and sodium borate. The prepared green bodies were sintered at different temperatures ranging between 900 and $1200^{\circ}C$. The sintered membranes were characterized by X-ray diffraction, mercury porosimetry, scanning electron microscopy, and capillary flowmetry. It was observed that the porosity decreased with an increase in both the sintering temperature and the sodium borate content, whereas the flexural strength increased with an increase in both the sintering temperature and the sodium borate content. The air flow rate decreased with an increase in the sodium borate content. The typical porosity, flexural strength, and specific flow rate of the kaolin-based membrane sintered with 5 wt% sodium borate at $1100^{\circ}C$ were 37%, 19 MPa, and $1{\times}10^{-3}L/min/cm^2$, respectively, at a p of 30 psi.

• Journal of the Korean Ceramic Society
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• v.52 no.3
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• pp.180-185
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• 2015

Low-cost ceramic membrane supports with pore sizes in the range of $0.52-0.62{\mu}m$ were successfully prepared by uniaxial dry compaction method using inexpensive raw materials including kaolin, bentonite, talc, sodium borate, and alkaline-earth oxides in carbonate forms (e.g., $MgCO_3$, $CaCO_3$, and $SrCO_3$). The prepared green supports were sintered at $1000^{\circ}C$ for 8 hr in air. The effect of alkaline-earth oxide additives on the flexural strength of clay-based membrane supports was investigated. The porosity of the clay-based membrane supports was found to be in the range of 33-34%. The flexural strength of the clay-based membrane supports with 1% alkaline-earth carbonates was found to be in the range of 42.8-52.7 MPa. The addition of alkaline-earth carbonates to clay-based membrane supports resulted in large increases (47-80%) in the flexural strength of the membrane supports, compared to that of membrane supports without alkaline-earth carbonates. The typical flexural strength of the clay-based membrane support with 1% $SrCO_3$ was 52.7 MPa at 33.8% porosity.

• Advances in nano research
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• v.15 no.6
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• pp.551-565
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• 2023

Coupled porous curved beams, due to their low weight and high flexibility, have many applications in engineering. This study investigates the vibration behavior of coupled porous curved beams in different boundary conditions. The system consists of two curved beams connected by a mid-layer of elastic springs. These beams are made of various materials, such as homogenous steel foam, and composite materials with PMMA (polymethyl methacrylate) and SWCNT (single-walled carbon nanotube) used as the matrix and nanofillers, respectively. To obtain equivalent material properties, the role of mixture (RoM) was employed, followed by the implementation of the porosity function. The system's governing equations were obtained by employing FSDT and Hamilton's law. To investigate thermal vibration, temperature was implemented as a load in the governing equations. The GDQ method was used to solve these equations. To demonstrate the applicability of the GDQ method in calculating the frequencies of the system and the correctness of the developed program, a validation study was conducted. After validation, numerous examples were presented to investigate the behavior of single and coupled curved beams in various material properties and boundary conditions. The results indicate that the frequencies of the curved beams and the system depend highly on the amount of porosity (n) and the distribution pattern. The system frequencies decreased with an increase in the porosity coefficient. The stiffness of the springs had no effect on the first mode frequency but increased frequencies of other modes in a specific range. The frequencies of the system decreased with an increase in environmental temperature.

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.1
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• pp.9-15
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• 2023

The cement is a typical CO₂ emission industry. Manufacturing process improvements and increased use of alternative materials are needed to reduce energy consumption and CO₂ emissions. This study confirmed the basic characteristics of cement hydration by sintering CAF at low temperature as a CO₂ adsorbent material. For the hydration product of the synthetic CAF, crystal phase analysis, porosity, and structural images were confirmed, and the compressive strength was measured. The replacement rate of SCAF was 10, 20, and 100 %, and the compressive strength tended to decrease as the replacement rate increased. In addition, when the SCAF substitution rate is 100 %, the hydration products of the early age are calcium aluminum oxide hydrate (Ca₃Al₂O₆ x H₂O) and calcium iron hydroxide (Ca₃Fe(OH)₁₂), and at substitution rates of 10 and 20 %, CAF compounds other than general cement hydrates brownmillerite was observed. As for the porosity, the pore size increased and the porosity increased with the increase of the replacement ratio. As a result of this study, CAF manufactured by low-temperature sintering seems to be difficult to use alone and general curing for utilization as a CO₂ adsorbing material.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.137-137
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• 2003

Optical amplificator have been used to compensate the losses in the optical signal transmission and processing. Today, there has been increasing demand for the very low cost optical amplifier. Sol-gel offers considerable potential both low cost manufacture, and for great flexibility in materials composition and structure. In addition, the sol-gel process is a very attractive method for producing porous materials with controlled structure. In this work, we present the potoluminescence properties of Er doped A1$_2$O$_3$/SiO$_2$ films. Erbium doped alumina nano sol was prepared by Al(NO$_3$)$_3$.9$H_2O$ and Er(NO$_3$)$_3$.5$H_2O$ through hydrolysis and peptization, and then GPS (3-Glycidoxypropyltrimethoxysilane) was added into Er doped alumina nano sol for organic- inorganic hybridization. Er doped A1$_2$O$_3$/SiO$_2$ film was obtained by spin coating, dip coating and thermal treatment from 30$0^{\circ}C$~120$0^{\circ}C$, and there were crack-free after thermal treatment. The thickness of film was measured SEM, and the porosity of film was characterized by BET and TGA. The crystal phase of Er doped A1$_2$O$_3$/SiO$_2$ were determined by XRD. Finally, the photoluminescence properties of Er doped A1$_2$O$_3$/SiO$_2$ films will be discuss with the consideration of porosity and crystallity.

• Journal of Korea Foundry Society
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• v.31 no.5
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• pp.293-301
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• 2011

Representative magnesium alloys applied to the die-casting are AZ91, AM60, etc., and the application of these alloys is restricted to components operating at moderate temperatures, due to grain boundary siding of ${\beta}$-phase($Mg_{17}Al_{12}$) at temperatures above $120^{\circ}C$. Heat-resistant magnesium alloys such as AE42, AE44 have been developed, but that have been too burdensome to produce because of the expensive rare earth materials. Research work for the development of low-priced heat-resistant magnesium alloy is actively in progress and positive results are being reported. This study aims to investigate the effect of Ca additions on mechanical properties of Mg-4Al-2Sn heat resistant magnesium alloys. Mg-4Al-2Sn alloys with Ca (0wt.%, 0.3wt.%, 0.7wt.%, 1wt.%) have been produced through the die-casting process for the development of low-priced heat-resistant magnesium alloy, and high temperature tensile tests are performed using the specimens. The results showed that mechanical properties of Mg-4Al-2Sn-xCa increased with the addition of Ca up to 0.7wt.% Ca and further addition of Ca deteriorated the mechanical properties of the alloys. A significant amount of porosity was observed at the sample with 1wt%. Ca and the longer freezing range of the alloy was believed to cause the formation of porosity.

• Journal of Sensor Science and Technology
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• v.15 no.3
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• pp.173-178
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• 2006

Silica aerogel with ultra low density and high porosity has been focused on versatile application due to its fascinating properties. Ambient drying process of waterglass, in this study was researched to fabricate a crack-free monolith body in the point view of cost effective way. Wet gel was obtained by removing of $Na^{+}$ ions in waterglass, which contains 8 wt% of $SiO_{2}$. Xylene, which has a low vapor pressure, was used as a solution substitutor to prevent the formation a cracks during drying. Various surface modifiers like as hexamethyldisilazane (HMDSZ), trimethylchlorosilane (TMCS), methyltriethoxylsilane (MTES), methyltrimethoxysilane (MTMS) and phenyltriethoxysilane (PTES) were used in order to improve hydrophobicity of the waterglass Silica aerogel. Some physical properties of the surface modified aerogels were investigated by FT-IR, TGA, BET and SEM. Hydrophobicity and hydrophilicity of Silica aerogel is attributed to the Si-OH bond and the non-polar C-H bond groups on the surface of aerogel. Crack-free waterglass aerogel with >90 % of porosity, 17 nm of pore size and <0.15 $g/cm^{3}$ of density was prepared. HMDSZ and TMCS are effective as a surface modifier

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.262-267
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• 2007

In this paper, we study about wear properties for the metal matrix composites fabricated by low pressure infiltration process. Metal fiber preform reinforced aluminum alloy composite were fabricated by low pressure casting process under 0.4MPa. Infiltration condition was changed the pressure infiltration time of 1 s, 2 s and 5 s under a constant pressure of 0.4MPa. The molten alloy completely infiltrated the FeCrSi metal perform regardless of the increase in the pressure acceleration time. However, the infiltration time at the pressure acceleration time of 1s was shorter than at the pressure acceleration time of 2s or 5s. The FeCrSi/A366.0 composite was investigated the porosity. The porosity is reducing as the pressure acceleration time compared with the pressure acceleration time of 2s and 5s. The FeCrSi/A366.0 composites were investigated the wear resistance. FeCrSi/A366.0 composite at pressure acceleration time of 1s has excellent wear resistance.