• Journal of Ceramic Processing Research
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• v.20 no.1
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• pp.63-68
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• 2019

We investigated the effects of Al2O3 addition on (1-x)Li2B4O7-xAl2O3 (LBAO; x = 0, 0.005, 0.01, 0.05, 0.07, and 0.1) glasses. The glasses were synthesized by a conventional melt-quench method. Structural transformations of the LBAO glasses were assessed via X-ray diffraction analysis. Estimations of ΔT, KGS = (Tc-Tg)/(Tm-Tc), activation energy, and the Avrami parameter were performed using differential thermal analysis and differential scanning calorimetry. An interpretation of non-isothermal kinetics of the crystallization process is presented using the modified Ozawa equation. The activation energy E increased from 3.3 to 3.5 eV for the LBAO (x < 0.01) glasses whereas those of the LBAO (x > 0.05) glasses slightly increased from 3.75 to 4.05 eV. The exponent n was estimated to be 3.9 ± 0.1 for the LBAO (x < 0.01) glasses and 3.2 ± 0.02 for the LBAO (x > 0.05) glasses. Microstructural characterization of the glassy and crystalline phases using atomic force microscopy was investigated. The effects of Al2O3 on the LBAO glasses include a decreased nucleation rate in the crystallization process and a significantly reduced crystal size.

• Korean Chemical Engineering Research
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• v.59 no.3
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• pp.305-315
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• 2021

An intermeshing corotating twin screw extruder is mainly used for compounding polymeric materials. Twin screw extruder can adopt modular-type screw configurations, which directly controls the quality and productivity of the products. The types, shapes, and specifications of the screw and kneading elements are summarized, and the effects of screw configuration on the processabiliy of the materials are discussed. The principles of screw configuration universally applied to mass production of general-purpose resins are explained, and the guidelines of screw combination according to the roles of feeding, melt mixing, and metering zones are listed. The strategies of screw combination suitable for various cases, such as side feeding of liquid additives or inorganic fillers, reactive extrusion, devolatilization process, production of products requiring bright color and transparency, and processing of materials with low apparent specific gravity, are presented.

• Textile Coloration and Finishing
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• v.35 no.3
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• pp.159-168
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• 2023

Polyolefin elastomer (POE) is widely used in a variety of applications, particularly in the manufacture of composites, due to its excellent mechanical properties, chemical resistance, and flexibility. However, POE has a high processing temperature, which causes damage to the fiber during the manufacturing process when impregnating the fiber. Therefore, ethylene vinylacetate (EVA), which has a low melting point and excellent adhesion properties, is blended with POE to reduce the processing temperature, and POE-g-MAH (Polyolefin elastomer-grafted-maleic anhydride) is used as a compatibilizer to further improve the POE/EVA blend properties. The compatibility of POE/EVA blends is observed by SEM, and the interaction between each polymer is confirmed by DSC and FT-IR. In addition, the effect of adding the compatibilizer is analyzed through mechanical properties such as tensile strength and elongation. The optimal content of compatibilizer for POE/EVA blends considering physical properties and moldability is sought, and 20 phr is determined to be the most appropriate.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.4
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• pp.314-321
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• 2000

A gap between a $Al_2O_3/Fe$ thermite and lower head vessel is formed in the lower-plenum arrested vessel attack(LAVA) experiment which is the 1st phase study of simulation of naturally arrested vessel attack in vessel(SONATA-IV). The gap measurement using a conventional ultrasonic method would be lack of a reliability due to the structure complexity and the metallurgical grain size change of the lower head HAZ occurred by a thermite $Al_2O_3/Fe$ melt or a $Al_2O_3$ melt at $2300^{\circ}C$. The grain echoes having false signals and lower S/N ratio signals are detected due to a multiple scattering, a mode conversion and an attenuation of a ultrasonic resulted from at the interface of increased grain size zone. In this test, the signals pattern was classified to understand the behavior of the ultrasonic in a multi-layer specimen of solid-liquid-solid of assuming that the thermite and the lower head vessel is immersed. The polarity threshold algorithm of frequency diversity gives us the enhancement about 6dB of the ratio S/N.

• Carbon letters
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• v.11 no.4
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• pp.279-284
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• 2010

Graphene is one of the most promising materials for many applications. It can be used in a variety of applications not only as a reinforcement material for polymer to obtain a combination of desirable mechanical, electrical, thermal, and barrier properties in the resulting nanocomposite but also as a component in energy storage, fuel cells, solar cells, sensors, and batteries. Recent research at Michigan State University has shown that it is possible to exfoliate natural graphite into graphite nanoplatelets composed entirely of stacks of graphene. The size of the platelets can be controlled from less than 10 nm in thickness and diameters of any size from sub-micron to 15 microns or greater. In this study we have investigated the influence of melt compounding processing on the physical properties of a polyamide 6 (PA6) nanocomposite reinforced with exfoliated graphite nanoplatelets (xGnP). The morphology, electrical conductivity, and mechanical properties of xGnP-PA6 nanocomposite were characterized with electrical microscopy, X-ray diffraction, AC impedance, and mechanical properties. It was found that counter rotation (CNR) twins crew processed xGnP/PA6 nanocomposite had similar mechanical properties with co-rotation (CoR) twin screw processed or with CoR conducted with a screw design modified for nanoparticles (MCoR). Microscopy showed that the CNR processed nanocomposite had better xGnP dispersion than the (CoR) twin screw processed and modified screw (MCoR) processed ones. It was also found that the CNR processed nanocomposite at a given xGnP content showed the lowest graphite X-ray diffraction peak at $26.5^{\circ}$ indicating better xGnP dispersion in the nanocomposite. In addition, it was also found that the electrical conductivity of the CNR processed 12 wt.% xGnP-PA6 nanocomposite is more than ten times higher than the CoR and MCoR processed ones. These results indicate that better dispersion of an xGnP-PA6 nanocomposite is attainable in CNR twins crew processing than conventional CoR processing.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.10
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• pp.42-47
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• 2017

In this study,we conducted an injection molding analysis of metal powder materials for the development of flanges, which are necessary adapters for optical communication. The metal powder injection molding process is a technique for producing an injection molded article having a complicated shape by mixing ceramic or stainless powder and binders. It is used to produce products which require complex processing technology or for which the productivity is low. The purpose of this study is to minimize the manufacturing processing of products which are manufactured through existing mechanical processing procedures. For the injection molding analysis, we mixed stainless STS316 metal powder with binders at a ratio of 6 to 4 to make molding materials consisting of granular pellets. Then, three-dimensional modeling and meshing were carried out to obtain the optimal injection molding analysis conditions(molding temperature, melting temperature, injection time, injection temperature, injection pressure, packing time and cooling time). As a result of the analysis, it was discovered that the inlet became available 13.29 seconds after the first injection. Also, as the flowing and packing in the melt through the sprue, runner and gate were stable, it is expected that good molds can be manufactured.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.11
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• pp.1437-1446
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• 2000

A numerical analysis on the freeze coating process of a non-isothermal finite dimensional plate with a binary alloy is performed to investigate the growth and decay behavior of the solid and the mushy layer of the freeze coat and a complete procedure to calculate the process is obtained in this study. The continuously varying solid and mushy layers are immobilized by a coordinate transform and the resulting governing differential equations are solved by a finite difference technique. To account for the latent heat release and property change during solidification, proper phase change models are adopted. And the convection in the liquid melt is modeled as an appropriate heat transfer boundary condition at the liquid/mushy interface. The present results are compared with analytic solutions derived for the freeze coating of infinite dimensional plates and the discrepancy is found to be less than 0.5 percent in relative magnitude for all simulation cases. In addition the conservation of thermal energy is checked. The results show that the freeze coat grows proportional to the 1.2 square of axial position as predicted by analytic solutions ar first. But after the short period of initial growth, the growth rate of the freeze coat gradually decreases and finally the freeze coat starts to decay. The effects of various non-dimensional processing parameters on the behavior of freeze coat are also investigated.

• Resources Recycling
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• v.17 no.2
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• pp.46-54
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• 2008

It is well known that PCB (Printed Circuit Board) is a complex mixture of various metals. In this study, pyro-metallurgical process was investigated to extract valuable metallic components from the PCB scrap. PCB scrap was shredded and oxidized to remove plastic materials, and then, quantitative analysis were made. 15 mass %$Al_2O_3-45$ mass %CaO-40 mass %$SiO_2$ and 32 mass %$SiO_2-20$ mass %$Al_2O_3-38$ mass %CaO-10 mass %MgO, were chosen as basic slag compositions which are determined based on the quantitative analysis of PCB scrap. During experiments a super kanthal rotating furnace was used to melt and separate metallic components. Moreover the revolution effect on was the recovery of valuable metals from PCB scrap also investigated.

• Journal of Powder Materials
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• v.27 no.2
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• pp.103-110
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• 2020

Aluminum (Al) - based powders have attracted attention as key materials for 3D printing because of their excellent specific mechanical strength, formability, and durability. Although many studies on the fabrication of 3D-printed Al-based alloys have been reported, the influence of the size of raw powder materials on the bulk samples processed by selective laser melting (SLM) has not been fully investigated. In this study, AlSi10Mg powders of 65 ㎛ in average particle size, prepared by a gas atomizing process, are additively manufactured by using an SLM process. AlSi10Mg powders of 45 ㎛ average size are also fabricated into bulk samples in order to compare their properties. The processing parameters of laser power and scan speed are optimized to achieve densified AlSi10Mg alloys. The Vickers hardness value of the bulk sample prepared from 45 ㎛-sized powders is somewhat higher than that of the 65 ㎛m-sized powder. Such differences in hardness are analyzed because the reduction in melt pool size stems from the rapid melting and solidification of small powders, compared to those of coarse powders, during the SLM process. These results show that the size of the powder should be considered in order to achieve optimization of the SLM process.

• Korean Journal of Materials Research
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• v.8 no.7
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• pp.584-590
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• 1998

The microstructures of finely distributed Si-phases in $\beta$-$FeSi_2$ thermoelectric matrix, were produced by heat-treating the melt-cast ingots of single $\alpha$-$Fe_2Si_5$ phase at 730~85$0^{\circ}C$ for 4~20 hours, or by resistance-hot-pressing the mechanically alloyed powders ordinarily consisting of $\varepsilon$-FeSi and Si phases at 760~85$0^{\circ}C$ for 10 minutes of composition. $(Fe_{0.98}Mn_{0.02})_xSi_2(x{\leq$}1) The size and interspacing of dispersed Si-phases were able to control within a range of 0.05~0.27$\mu\textrm{m}$ and 0.2~0.6$\mu\textrm{m}$ by variations of heat treatment temperature and sintering temperature as well as the composition. respectively. The dispersion of Si- phases was expected to be effective for the reduction of thermal conductivity responsible for the increment of thermoelectric figure of merit.