• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.2
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• pp.173-180
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• 2013

Compacted graphite iron(CGI), also known as vermicular graphite iron, is a metal which is gaining popularity in applications that require either greater strength, or lower weight than cast iron. Recently compacted graphite iron has been used for diesel engine blocks. Considering that using in exhaust manifold of the diesel engine, CGI340 was conducted the heat treatment during 1 hour to 96 hours from 873 to 1273 K. Mechanical characteristics were evaluated. The obtained results are as follows; The tensile strength of the heat treated specimens showed overall lower tensile strength than that of the base metal. Tensile strength decreases with increasing of heat treatment time, and the higher heat treatment temperature and the longer time, were more reduced. The fatigue limit by the ultrasonic fatigue test was approximately 130 MPa of base metal, 100 MPa of 1173 K (96 hrs) specimen, respectively. The hardness decreases with increasing heat treatment time, and the higher the heat treatment temperature was lowered hardness distribution. In CGI340, average hardness of nodular graphite was 120 Hv, average hardness of vermicular graphite was 114 Hv. This showed lower hardness than the base structure ferrite. The nodular graphite and vermicular graphite according to the heat treatment temperature and time didn't have a consistent change. However, the grain size of base structure grew with increasing of heat treatment time.

• Clean Technology
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• v.28 no.4
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• pp.293-300
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• 2022

The remarkable mechanical, electrical, and thermal properties of graphene have recently sparked tremendous interest in various research fields. One of the most promising methods to produce large quantities of graphene dispersion is liquid-phase exfoliation (LPE) which utilizes ultrasonic waves or shear stresses to exfoliate bulk graphite into graphene flakes that are a few layers thick. Graphene dispersion produced via LPE can be transformed into graphene ink to further boost graphene's applications, but producing high-quality graphene more economically remains a challenge. To overcome this shortcoming, an advanced LPE process should be developed that uses relatively cheap natural graphite as a graphene source. In this study, a flow-LPE process was used to exfoliate natural graphite to produce graphene that was three times cheaper and seven times larger than synthetic graphite. The optimal exfoliation conditions in the flow-LPE process were determined in order to produce high-quality graphene flakes. In addition, the structural and electrical properties of the flakes were characterized. The electrical properties of the exfoliated graphene were investigated by carrying out an ink formulation process to prepare graphene ink suitable for inkjet printing, and fabricating a printed graphene pattern. By utilizing natural graphite, this study offers a potential protocol for graphene production, ink formulation, and printed graphene devices in a more industrial-comparable manner.

• Journal of the Korea Institute of Building Construction
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• v.24 no.2
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• pp.203-213
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• 2024

This study delves into the mechanical properties of fiber-reinforced cement composites(FRCC) concerning the dispersion method of multi-walled carbon nanotubes(MWCNTs). MWCNTs find utility in industrial applications, particularly in magnetic sensing and crack detection, owing to their diverse properties including heat resistance and chemical stability. However, current research endeavors are increasingly directed towards leveraging the electrical properties of MWCNTs for self-sensing and smart sensor development. Notably, achieving uniform dispersion of MWCNTs poses a challenge due to variations in researchers' skills and equipment, with excessive dispersion potentially leading to deterioration in mechanical performance. To address these challenges, this study employs ultrasonic dispersion for a defined duration along with PCE surfactant, known for its efficacy in dispersion. Test specimens of FRCC are prepared and subjected to strength, drawing, and direct tensile tests to evaluate their mechanical properties. Additionally, the influence of MWCNT dispersion efficiency on the enhancement of FRCC mechanical performance is scrutinized across different dispersion methods.