• Proceedings of the Korea Concrete Institute Conference
• /
• 2002.10a
• /
• pp.549-554
• /
• 2002

In Powder System, SCC demands high dosage of superplasticizer and a lage amout of powder for suitable fluidity and viscosity. Okamura's method of most representative mixing design method in SCC of Powder-System is unfavorable economically because of using a large amount of powder. In addition, many ready-mixed concrete plants do not use his mix design method and procedure due to complexity for practical application. Therefore, Nan Su proposed more simple mix design method than Okamura's. It had an advantage in simplicity in practical application and required a smaller amount of powders compared with Okamura's method. This paper proposed an optimal mixture proportion of SCC with consideration of Nan Su's method. The new and modified mix design method required a smaller amount of powder than that of Nan Su's. To check the properties of SCC, considered with the requirements specified by the Japanese Society of Civil Engineering.(JSCE)

• Journal of the Korean Ceramic Society
• /
• v.32 no.6
• /
• pp.710-718
• /
• 1995

The new forming method, Pressureless Powder Packing Forming Method was applied to the manufacturing of reaction sintered SiC. After the experiments of vibratory powder packing and binder infiltration, the abrasive SiC powder of which mean size is 45${\mu}{\textrm}{m}$ was selected to this forming method. Uniform green bodies with porosity of 45% and narrow pore size distribution could be formed by this new forming method. Also, complex or varied cross-sectional shapes could be easily manufactured through the silicone rubber mould used in this forming method. Maximum 15 wt% amorphous carbon was penetrated into green body by multi impregnation-carbonization cycles. And reaction-bonded SiC was manufactured by infiltration of SiC-carbon shaped bodies with liquid silicon.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09a
• /
• pp.435-435
• /
• 2006

• Journal of Powder Materials
• /
• v.12 no.1
• /
• pp.30-35
• /
• 2005

An aluminum powder compact consolidated by a powder-in sheath rolling (PSR) method was severely deformed by accumulative roll-bonding (ARB) process. The ARB process was performed up to 8 cycles at ambient temperature without lubrication. Optical microscope and transmission electron microscope observations revealed that microstructure of the ARB-processed Al powder compact is inhomogeneous in the thickness direction. The ultra-fine subgrains often reported in the ARB-processed bulky materials were also developed near surface of the Al powder compacts in this study. Tensile strength of the ARB-processed Al powder compact increased at the 1st cycle, but from the 2nd cycle it rather decreased slightly.

• Journal of the Korean Ceramic Society
• /
• v.27 no.2
• /
• pp.274-282
• /
• 1990

SnO2 powder was prepared by hydroxide method and oxalate method. In hydroxide method, the pH dependence of powder characteristics was investigated by using buffer solution. As increasing the pH of solution, SnO2 powder size was decreased because nucleation rate was inctreased by more supersaturation of solution. Also, we found that the powder by our method has larger specific surface area in comaprison with other method. And the degree of agglomeration of precipitate with the change of precipitation temperature was investigated in oxalate method. The SnC2O4 was angular shape precipitate, and the size of the SnC2O4 was increased with the increase of precipitation temperature in methanol solvent.

• Journal of Powder Materials
• /
• v.14 no.6
• /
• pp.362-366
• /
• 2007

Magnesium and magnesium alloys are promising materials for light weight and high strength applications. In order to obtain homogeneous and high quality products in powder compaction and powder forging processes, it is very important to control density and density distributions in powder compacts. In this study, a model for densification of metallic powder is proposed for pure magnesium. The mode] considers the effect of powder characteristics using a pressure-dependent critical density yield criterion. Also with the new model, it was possible to obtain reasonable physical properties of pure magnesium powder using cold iso-state pressing. The proposed densification model was implemented into the finite element method code. The finite element analysis was applied to simulating die compaction of pure magnesium powders in order to investigate the density and effective strain distributions at room temperature.

• Korean Journal of Materials Research
• /
• v.30 no.3
• /
• pp.149-154
• /
• 2020

A powder-in-sheath rolling method is applied to the fabrication of a carbon nano tube (CNT) reinforced copper composite. A copper tube with outer diameter of 30 mm and wall thickness of 2 mm is used as sheath material. A mixture of pure copper powder and CNTs with a volume content of 3 % is filled in a tube by tap filling and then processed to an 93.3 % reduction using multi-pass rolling after heating for 0.5 h at 400 ℃. The specimen is then sintered for 1h at 500 ℃. The relative density of the 3 vol%CNT/Cu composite fabricated using powder in sheath rolling is 98 %, while that of the Cu powder compact is 99 %. The microstructure is somewhat heterogeneous in width direction in the composite, but is relatively homogeneous in the Cu powder compact. The hardness distribution is also ununiform in the width direction for the composite. The average hardness of the composites is higher by 8Hv than that of Cu powder compact. The tensile strength of the composite is 280 MPa, which is 20 MPa higher than that of the Cu powder compact. It is concluded that the powder in sheath rolling method is an effective process for fabrication of sound CNT reinforced Cu matrix composites.

• Journal of Powder Materials
• /
• v.21 no.2
• /
• pp.93-96
• /
• 2014

Cobalt coated tungsten carbide-cobalt composite powder has been prepared through wet chemical reduction method. The cobalt sulfate solution was converted to the cobalt chloride then the cobalt hydroxide. The tungsten carbide powders were added in to the cobalt hydroxide, the cobalt hydroxide was reduced and coated over tungsten carbide powder using hypo-phosphorous acid. Both the cobalt and the tungsten carbide phase peaks were evident in the tungsten carbide-cobalt composite powder by X-ray diffraction. The average particle size measured via scanning electron microscope, particle size analysis was around 380 nm and the thickness of coated cobalt was determined to be 30~40 nm by transmission electron microscopy.

• Journal of Powder Materials
• /
• v.13 no.6 s.59
• /
• pp.415-420
• /
• 2006

Nanostructured metallic materials are synthesized by bottom-up processing which starts with powders for assembling bulk materials or top-down processing starting with a bulk solid. A representative bottom-up and top-down paths for bulk nanostructured/ultrafine grained metallic materials are powder consolidation and severe plastic deformation (SPD) methods, respectively. In this study, the bottom-up powder and top-down SPD approaches were combined in order to achieve both full density and grain refinement without grain growth, which were considered as a bottle neck of the bottom-up method using conventional powder metallurgy of compaction and sintering. For the powder consolidation, equal channel angular pressing (ECAP), one of the most promising method in SPD, was used. The ECAP processing associated with stress developments was investigated. ECAP for powder consolidation were numerically analyzed using the finite element method (FEM) in conjunction with pressure and shear stress.

• Journal of the Korea Concrete Institute
• /
• v.16 no.3 s.81
• /
• pp.303-310
• /
• 2004

The purpose of this study was to investigate the effect of using method and replacement ratio of limestone powder and water-cement ratio on the compressive strength and the resistance to sulfate attack of mortar incorporating limestone powder as fundamental study to use limestone powder as an addition for concrete. As a results, The method using limestone powder as a part of cement showed decrease of the compressive strength of mortar. The strength of mortar incorporating limestone powder almost decided upon unit cement content. It was recognized that the method replacing limestone powder as a part of cement was effective to decrease the heat of hydration in concrete. The method using limestone powder as a part of fine aggregate showed the considerable increase of the strength and resistance to sulfate attack of concrete. Furthermore, it was recognized that the method using limestone powder as a part of fine aggregate were effective materials as an addition for concrete in view of the improvement of strength and resistance to sulfate attack.