• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.350-352
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• 2009

The effect of porosity on the high-cycle fatigue properties of Al-Si-Mg casting aluminum alloys was investigated in this study. Microstructure examination, tensile and high-cycle fatigue test were conducted on both Al-Si-Mg casted (F) and heat-treated (T6) conditions. Porosity characteristics on the fracture surfaces of fatigue-tested samples were examined using SEM and image analysis. The microstructure observation results showed that eutectic Si particles were homogeneously dispersed in the matrix of the Al-Si-Mg casting alloys, but there were porosities formed as cast defects. The high-cycle fatigue results indicated that the fatigue strength of the 356-T6 alloy was higher than that of the 356-F alloys because of the significant reduction in volume fraction of pores by heat treatment. The SEM fractography results showed that porosity affected detrimental effect on the fatigue life: 80% of all tested samples fractured as a result of porosity which acted as the main crack initiation site. It was found that fatigue life decreased as the size of the surface pore increased. A comparison was made between surface pore and inner pore fur its effect on the fatigue behavior. The results showed that the fatigue strength with the inner pores was higher than that of the surface pore.

• Carbon letters
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• v.28
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• pp.24-30
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• 2018

Coke aggregates and carbon artifacts were produced to investigate the interactions of coke and pitch during the kneading process. In addition, the kneading ratio of the coke and binder pitch for the coke aggregates was controlled to identify the formation of voids and pores during carbonization at $900^{\circ}C$. Experiments and thermogravimetric analysis revealed that carbon yields were improved over the theoretical yield calculated by the weight loss of the coke and binder pitch; the improvement was due to the binding interactions between the coke particles and binder pitch by the kneading process. The true, apparent, and bulk densities fluctuated according to the kneading ratio. This study confirmed that an excessive or insufficient kneading ratio decreases the density with degradation of the packing characteristics. The porosity analysis indicated that formation of voids and pores by the binder pitch increased the porosity after carbonization. Image analysis confirmed that the kneading ratio affected the formation of the coke domains and the voids and pores, which revealed the relations among the carbon yields, density, and porosity.

• Journal of the Microelectronics and Packaging Society
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• v.23 no.4
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• pp.57-61
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• 2016

Thick film sealing glass paste is required for cell packaging of NaS based battery for energy storage system, to join the beta-alumina electrolyte tube and the alpha-alumina battery cell cap components. This paper presents the effect of the particle sizes of seal glass powder and the sealing temperatures on the microstructure of the glass sealants was investigated. It was found that the larger in the particle size of seal glass powder, the smaller the pore volume and the number of pores in a unit area. Also, the number of pores decreased with increasing the sealing temperatures while the pore size was increased. This result enables the control of porosity, pore distribution and number of pores in a microstructure of glass sealing component by proper selection of glass powders particle size and sealing temperature.

• Journal of Welding and Joining
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• v.30 no.5
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• pp.46-50
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• 2012

This study was carried out to investigate the effect of welding parameters such as shielding gas compositions welding voltage and welding current on the pore formation in the weld beads of galvanized steel pipes produced with gas metal arc welding. The porosity was evaluated and rated by metallography and radiographic test in terms of weight percentage, number and distribution of pores in weld beads. The porosity increased with increasing welding voltage and current, in which Ar gas produced the most porosity while $Ar+5%O_2$ generated the least porosity. It was found that the porosity could be reduced by selection of the proper gas mixture composition such as $Ar+5%O_2$ and $Ar+10%CO_2$ and by using current (130~150A) and voltage(16~20V).

• Journal of the Korean Ceramic Society
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• v.25 no.5
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• pp.532-540
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• 1988

Even the finest cement as having a specific surface area of 6.000~8.500$\textrm{cm}^2$/g (Blaine) is to convert into low-porosity hardened cement paste by the use of appropriate plasticizer. In this study, tests were carried out on such a special cement mix(fineness of 6.000$\textrm{cm}^2$/g, Ca-lignosulfonate plus k2CO3 as plasticizer and W/C=0.25) in comparison with ordinary Portland cement. Owing mainly to the high fineness of the cement powder and the low water-to-cement ratio, the hardened low-porosity cement paste showed a very tight microstructure, the pore texture of which consisted of micropores and wide pores only of small radii. The consequence of such mix was hence that the low-porosity special cement had excellent properties of early-high and very high strengths as compared to ordinary Portland cement. Its volume change when dried in the air or re-wetted, exhibited superor behaviour as well.

• Journal of Powder Materials
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• v.21 no.4
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• pp.266-270
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• 2014

Metal foams have a cellular structure consisting of a solid metal containing a large volume fraction of pores. In particular, open, penetrating pores are necessary for industrial applications such as in high temperature filters and as a support for catalysts. In this study, Fe foam with above 90% porosity and 2 millimeter pore size was successfully fabricated by a slurry coating process and the pore properties were characterized. The Fe and $Fe_2O_3$ powder mixing ratios were controlled to produce Fe foams with different pore size and porosity. First, the slurry was prepared by uniform mixing with powders, distilled water and polyvinyl alcohol(PVA). After slurry coating on the polyurethane(PU) foam, the sample was dried at $80^{\circ}C$. The PVA and PU foams were then removed by heating at $700^{\circ}C$ for 3 hours. The debinded samples were subsequently sintered at $1250^{\circ}C$ with a holding time of 3 hours under hydrogen atmosphere. The three dimensional geometries of the obtained Fe foams with an open cell structure were investigated using X-ray micro CT(computed tomography) as well as the pore morphology, size and phase. The coated amount of slurry on the PU foam were increased with $Fe_2O_3$ mixing powder ratio but the shrinkage and porosity of Fe foams were decreased with $Fe_2O_3$ mixing powder ratio.

• Advances in materials Research
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• v.5 no.4
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• pp.279-298
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• 2016

Present disquisition proposes an analytical solution method for exploring the buckling characteristics of porous magneto-electro-elastic functionally graded (MEE-FG) plates with various boundary conditions for the first time. Magneto electro mechanical properties of FGM plate are supposed to change through the thickness direction of plate. The rule of power-law is modified to consider influence of porosity according to two types of distribution namely even and uneven. Pores possibly occur inside FGMs due the result of technical problems that lead to creation of micro-voids in these materials. The variation of pores along the thickness direction influences the mechanical and physical properties. Four-variable tangential-exponential refined theory is employed to derive the governing equations and boundary conditions of porous FGM plate under magneto-electrical field via Hamilton's principle. An analytical solution procedure is exploited to achieve the non-dimensional buckling load of porous FG plate exposed to magneto-electrical field with various boundary condition. A parametric study is led to assess the efficacy of material graduation exponent, coefficient of porosity, porosity distribution, magnetic potential, electric voltage, boundary conditions, aspect ratio and side-to-thickness ratio on the non-dimensional buckling load of the plate made of magneto electro elastic FG materials with porosities. It is concluded that these parameters play remarkable roles on the dynamic behavior of porous MEE-FG plates. The results for simpler states are confirmed with known data in the literature. Presented numerical results can serve as benchmarks for future analyses of MEE-FG plates with porosity phases.

• Korean Journal of Materials Research
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• v.2 no.2
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• pp.85-94
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• 1992

The size, morphology and distribution of pores which affect on the physical properties of thermal barrier coatings were investigated to find the relationship with spraying parameters. The plasma-sprayed zirconia coatings contained numerous micropores as well as macropores which were appeared as spherical and irregular pores, and cracks. The pore formation process and its characteristics were varied with spraying distance. Porosity itself was varied with spraying parameters such as spray gun current, gas flow rate and the gas used(Ar or $N_2). The Porosity of coatings was ranged from 10 to 18% with the variation of spraying conditions. The relative hardness measured by the scratch test, showed strong dependence on the porosity of coatings rather than spraying parameters.

• Advances in nano research
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• v.8 no.1
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• pp.83-94
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• 2020

An analytical formulation and solution process for the buckling analysis of porous magneto-electro-elastic functionally graded (MEE-FG) beam via different thermal loadings and various boundary conditions is suggested in this paper. Magneto electro mechanical coupling properties of FGM beam are taken to vary via the thickness direction of beam. The rule of power-law is changed to consider inclusion of porosity according to even and uneven distribution. Pores possibly occur inside FGMs due the result of technical problems that lead to creation of micro-voids in these materials. Change in pores along the thickness direction stimulates the mechanical and physical properties. Four-variable tangential-exponential refined theory is employed to derive the governing equations and boundary conditions of porous FGM beam under magneto-electrical field via Hamilton's principle. An analytical model procedure is adopted to achieve the non-dimensional buckling load of porous FG beam exposed to magneto-electrical field with various boundary conditions. In order to evaluate the influence of thermal loadings, material graduation exponent, coefficient of porosity, porosity distribution, magnetic potential, electric voltage and boundary conditions on the critical buckling temperature of the beam made of magneto electro elastic FG materials with porosities a parametric study is presented. It is concluded that these parameters play remarkable roles on the buckling behavior of porous MEE-FG beam. The results for simpler states are proved for exactness with known data in the literature. The proposed numerical results can serve as benchmarks for future analyses of MEE-FG beam with porosity phases.

• Journal of Powder Materials
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• v.21 no.1
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• pp.34-38
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• 2014

Cu-Ni alloys with unidirectionally aligned pores were prepared by freeze-drying process of CuO-NiO/camphene slurry. Camphene slurries with dispersion stability by the addition of oligomeric polyester were frozen at $-25^{\circ}C$, and pores in the frozen specimens were generated by sublimation of the camphene during drying in air. The green bodies were hydrogen-reduced at $300^{\circ}C$ and sintered at $850^{\circ}C$ for 1 h. X-ray diffraction analysis revealed that CuO-NiO composite powders were completely converted to Cu-Ni alloy without any reaction phases by hydrogen reduction. The sintered samples showed large and aligned parallel pores to the camphene growth direction, and small pores in the internal wall of large pores. The pore size and porosity decreased with increase in CuO-NiO content from 5 to 10 vol%. The change of pore characteristics was explained by the degree of powder rearrangement in slurry and the accumulation behavior of powders in the interdendritic spaces of solidified camphene.