• Journal of the Korean Ceramic Society
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• v.35 no.4
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• pp.399-405
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• 1998

The effect of each factor on the porosity and mean pore size of cordierite(2Mg$.$2{{{{ {Al}_{2 } {O }_{3 } }}$.$5{{{{ {SiO}_{2 } }}) ceram-ics which have been mainly used for hot gas filter was investigated by using orthogonal array. The poros-ity was observed to increase with the content of graphite added as pore-forming material and decrease with increasing talc size. The effects of the other factors the graphite size sintering temperature and hold-ing time at sintering temperature were observed to be small relatively. In case of mean pore size the ef-fect of talc size on the mean pore size of cordierity was investigated to be the largest. The mean pore size was observed to increase with increasing talc size.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.611-612
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• 2006

In a manufacturing technique of the sintered filter, pressureless sintering method has good permeability, it is not need the binder and lubricant used on compacting process, so it has little contamination and it is easy to control the pore size and shape but the mechanical strength is low relatively and it is difficult that parts of complicate form are manufactured. In the case of manufacturing the filter by press and sintering method, in order to be satisfactory characteristic of un-pressed filter, in this study sintered metal filter fabricated by using 30-40mesh stainless steel 316L powder and additive agents. Porosity and structure of pores, permeability and mechanical strength of the sintered filter were investigated with the variation sintering conditions. Porosity was nearly constant about $60{\sim}70%$, density, permeability and mechanical strength were changed markedly with quantity of additive materials and sintering conditions.

• Journal of Welding and Joining
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• v.10 no.3
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• pp.1-12
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• 1992

A literature review was conducted to survey informations available on the welding metallurgy of aluminum alloys and its effect on fusion weldability, especially on solidification cracking and pore formation. Solidification cracking behavior of Al weld is a complicate matter as compared to other high alloys, where a relatively simple Fe-X(most detrimental elements S, P, B, Si, etc) binary diagram can be successfully applicable. Both additive and synergistic effects of elements should be considered together. A same element play a different role from system to system. Porosity, caused by hydrogen contamination of the weld is one of the most troublesome welding problems. The primary sources of hydrogen are believed to be an absorbed moisture on the filler metal or base metal and in the shielding gas. It is extremely important that reliable quality-control procedures be employed to eliminate all possible sources of hydrogen contamination. Selection of proper process and parameters is sometimes more important than controlling of alloying elements in order to make a defect-free weld.

• Journal of the Korean Ceramic Society
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• v.45 no.1
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• pp.65-68
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• 2008

A simple pressing process using zirconia and microbead for fabricating porous zirconia ceramics is demonstrated. Effects of microbead content and sintering temperature on microstructure, porosity, compressive and flexural strengths were investigated in the processing of porous zirconia ceramics using microbead as a pore former. By controlling the microbead content and the sintering temperature, it was possible to produce porous zirconia ceramics with porosities ranging from 43% to 70%. Typical compressive and flexural strength values at ${\sim}50%$ porosity were ${\sim}150\;MPa$ and ${\sim}35\;MPa$, respectively.

• Journal of Welding and Joining
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• v.34 no.4
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• pp.48-54
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• 2016

The use of Zn coated steel has increased in the automotive industry due to its excellent corrosion resistance. Conventionally the BIW(body-in-white) structure and the hang-on parts have been made of Zn coated steel and more recently Zn coated steel began to be applied in the chassis parts. During gas metal arc (GMA) welding of the chassis part, lap fillet joint used to be adopted but spatter generation and porosities are most important concerns. In the industrial applications, an intentional joint gap was made to avoid the weld defects but it is not easy to control the size of joint gap. In this research, gas tungsten arc (GTA) is combined with GMA welding where GTA precedes GMA. As pulsed arc was adopted as GMA, GTA was oscillated along the longitudinal direction by pulsing GMA, but the arc oscillation did not disturb the molten droplet transfer of GMA welding. By increasing the distance between GTA and GMA, the length of weld pool increased and porosity could be reduced. Moreover porosity in the welds was fully removed when the distance between two arcs was 15 mm.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.1
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• pp.41-48
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• 2017

Fine polymeric fibers have been gaining interest from the energy harvesting/storage, tissue, and bioengineering industries because of advantages such as the small diameter, high porosity, permeability, and similarities to a natural extracellular matrix. Electrospinning is one of the most popular methods used to fabricate polymeric fibers because it is not as limited in regards to the materials selection, and it does not require expensive or complex equipment. However, electrospun fibers have a severe aerodynamic instability because the small diameter fibers are able to pass through the atmospheric layer when there is a high electric field. As a result, electrospun fibrous mats have serious difficulties with controlling its shape and geometric properties. In this study, a hybrid nano/microfibrous mat is presented that is fabricated using electrospinning with two different solvent-based PCL solutions. This provides control of the fiber diameter, mat porosity, and mechanical properties. Various hybrid fibrous mats were fabricated after an experimental investigation of the effects of solvent on fiber diameter. It was then demonstrated that the mechanical properties and porosity of the fabricated various hybrid mats could be successfully controlled.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.2
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• pp.329-340
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• 1997

A passive control of interaction of condensation shock wave / boundary layer for reducing the strength of condensation shock was conducted experimentally in a 2.5 * 8 cm$^{2}$ indraft type supersonic wind tunnel. The effects of following factors on passive control were investigated: 1) the thickness of porous wall, 2) the diameter of porous hole, and 3) the orientation of porous hole. On the other hand, the location of nonequilibrium condensation region and condensation shock wave was controlled by regulation of the stagnation conditions. Surface static pressure measurements as well as Schlieren observations of the flow field were obtained, and their effects were compared with the results the cases of without passive control. It was found that thinner porous wall, smaller porous hole and FFH orientation for the same cavity size and porosity of 12% are more favourable than the cases of its opposite.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.47 no.2
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• pp.17-23
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• 2015

Natural cellulose hydrogel membrane cannot be directly used for cell encapsulation because it has many large pores on the surface that immune biomolecules are able to penetrate into easily. For the reason, alginate was used for the control of pore size of the cellulose hydrogel membrane. The surface morphology of cellulose/alginate nanocomposite confirmed the successful control of the porosity of the membrane. The permeability of the cellulose/alginate nanocomposite was decreased but mechanical properties were increased compared with the bacterial cellulose membrane. The cellulose/alginate nanocomposite could be used for the functional membrane as a promising biomedical material in the future.

• The Journal of Advanced Prosthodontics
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• v.2 no.4
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• pp.117-121
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• 2010

PURPOSE. The present study was intended to evaluate the effect of soldering techniques with infrared ray and gas torch under different gap distances (0.3 mm and 0.5 mm) on the tensile strength and surface porosity formation in Ni-Cr base metal alloy. MATERIALS AND METHODS. Thirty five dumbbell shaped Ni-Cr alloy specimens were prepared and assigned to 5 groups according to the soldering method and the gap distance. For the soldering methods, gas torch (G group) and infrared ray (IR group) were compared and each group was subdivided by corresponding gap distance (0.3 mm: G3 and IR3, 0.5 mm: G5, IR5). Specimens of the experimental groups were sectioned in the middle with a diamond disk and embedded in solder blocks according to the predetermined distance. As a control group, 7 specimens were prepared without sectioning or soldering. After the soldering procedure, a tensile strength test was performed using universal testing machine at a crosshead speed 1 mm/min. The proportions of porosity on the fractured surface were calculated on the images acquired through the scanning electronic microscope. RESULTS. Every specimen of G3, G5, IR3 and IR5 was fractured on the solder joint area. However, there was no significant difference between the test groups (P > .05). There was a negative correlation between porosity formation and tensile strength in all the specimens in the test groups (P < .05). CONCLUSION. There was no significant difference in ultimate tensile strength of joints and porosity formations between the gas-oxygen torch soldering and infrared ray soldering technique or between the gap distance of 0.3 mm and 0.5 mm.

• Transactions of Materials Processing
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• v.28 no.1
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• pp.21-26
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• 2019

Direct Laser Melting (DLM) of $Ti-xTiH_2$ (mixing ratio x = 2, 5, 10 wt.%) blended powder is characterized by producing porous titanium parts. When a high energy laser is irradiated on a $Ti-TiH_2$ blended powder, hydrogen gas ($H_2$) is produced by the accompanying decomposition of the $TiH_2$ powder, and acts as a pore-forming and activator. The hydrogen gas trapped in a rapidly solidified molten pool, which generates porosity in the deposited layer. In this study, the effects of a $TiH_2$ mixing ratio and the associated processing parameters on the development of a porous titanium were investigated. It was determined that as the content of $TiH_2$ increases, the resulting porosity density also increases, due to the increase of $H_2$ produced by $TiH_2$. Also, porosity increases as the scan speed increases. As fast solidified melting pools do not provide enough time for $H_2$ to escape, the faster the scan speed, the more the resulting $H_2$ is captured by the process. The results of this study show that the mixing ratio (x) and laser machining parameters can be adjusted to actively generate and control the porosity of the DLM parts.