• Journal of the Korean Crystal Growth and Crystal Technology
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• v.30 no.6
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• pp.258-263
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• 2020

Silicon carbide (SiC) fibers mainly fabricated from polycarbosilane, a ceramic precursor, are applied as reinforcing materials for ceramic matrix composites (CMCs) because of their high temperature oxidation resistance, tensile strength, and light weight. In this study, continuous SiC fibers used to fabricate rope-type flexible heating elements capable of generating high-temperature heat (> 650℃). For high-efficiency heating elements, the resistance of SiC fiber rope was measured by 2-point probe method according to the cross-sectional area and length. In addition, the fabrication conditions of rope-type SiC fiber heating elements were optimized by controlling the oxygen impurities and the size of crystal grains present in the amorphous SiC fiber. As a result, the SiC fiber heating element having a resistance range of about 100~200 Ω exhibited an excellent power consumption efficiency of 1.5 times compared to that of the carbon fiber heating element.

• Composites Research
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• v.33 no.6
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• pp.395-400
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• 2020

In this paper, we manufactured silsesquiaznae (SSQZ)-coated carbon nanotube (CNT) surface heating elements, which allowed stable heating at high temperatures. The prepared composite sheet was confirmed by FE-SEM that the SSQZ fully coated the surface of CNT sheet. Furthermore, it was also confirmed that the silicon carbonitride (SiCN) ceramic formed by heat treatment of 800℃ have no defects found and maintain intact structure. The CNT/SiCN composite sheet was able to achieve higher thermal stability than raw CNT sheets in both nitrogen and air atmosphere. Finally, the CNT/SiCN composite sheet was possible to heat up at a temperature of over 700℃ in the atmosphere, and the re-heating was successfully operated after cooling.

• Applied Chemistry for Engineering
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• v.10 no.5
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• pp.690-695
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• 1999

An experimental study for mesophase pitch prepared from coal tar pitch has been carried out to clarify the rheological behaviors in the molten state. The apparent viscosity, shear stress, shear rate, Qunoline insoluble(QI), and softening point(SP) change were investigated especially. The conditions to increase mesophase content during polymerization were heat treatment time of 5 hrs, catalyst concentration of 3% and reaction temperature of $420^{\circ}C$. Apparent viscosity change with increase in temperature of pitches was different according to the heat treatment conditions and apparent viscosity increased with increasing heat treatment temperature, heat treatment time, contents of mesophase, on the contrary, fluidity is decreased. Rheological behavior of molten mesophase pitches at about $270^{\circ}C$ showed Newtonian behavior below $375^{\circ}C$ and non-Newtonian behavior above $270^{\circ}C$, the flow behavior was analyzed with Casson model.

• Journal of the Korean Ceramic Society
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• v.42 no.7 s.278
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• pp.469-474
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• 2005

Activated Carbon Fibers (ACFs) are widely used as adsorbents in technologies related to pollution abatement due to their highly porous structure and large adsorption capacity. The porous structure and surface area of ACFs depends strongly on both the activation processes arid the nature .of the precursors. The chemical activation with hydroxides has recently been, of great interest as it permits the preparation of activated carbon fibers with highly developed porosity. In this work, OXI-PAN fiber used as precursor for the preparation of activated carbon fibers by chemical activation with KOH and NaOH. The affects of several activation conditions on the surface properties, pore size distribution and adsorption capacity of Ag ion and Iodine ion on ACFs studied.

• Composites Research
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• v.30 no.2
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• pp.116-125
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• 2017

The purpose of this study is to develop silicon carbide fiber showing an excellent mechanical properties under highly oxidative conditions at high temperature. Polycarbosilane(PCS) as a preceramic precursor was used for making the SiC fiber. PCS fiber was taken by melt spinning method followed by melting the PCS at $300{\sim}350^{\circ}C$ in N2 gas. The Curing of PCS fiber was carried out in air oxygen chamber, prior to high temperature pyrolysis. Degree of cure was calculated by characteristic peak's ratio of Si-H to $Si-CH_3$ in FT-IR spectra before and after curing of PCS fiber. The properties of SiC fiber was affected greatly by the degree of cure. The SiC fiber produced by controlling fiber tension during heat treatment showed good properties. The SiC fiber exposed to $1000^{\circ}C$ at air from 1 min. up to maximum 50 hrs showed around 60% reduction in tensile strength. We found that large amount of carbon content on the fiber surface after long-term exposure has resulted in lower tensile strength.

• Proceedings of the Korean Fiber Society Conference
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• 2003.04a
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• pp.311-312
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• 2003

Activated carbons (ACs) are widely used in adsorption for the removal of gaseous and aqueous pollutants[1]. Although a wide range of carbonaceous materials can be converted into ACs, the coal and lingocellulosic materials are the most commonly used starting materials for the production of commercial ACs. Recently, there are a quite large number of studies regarding the preparation of ACs from various polymeric materials because of high carbon yield and low ash content In this work, ACs are prepared from polystyrene (PS) by chemical activation with potassium hydroxide and the effect of the KOH-to-PS ratio to adsorption of ammonia is investigated. (omitted)

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.19 no.3
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• pp.144-151
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• 2009

Photocatalytic degradation of methylene blue (MB) in aqueous solution was investigated using $TiO_2$ coated on various acid modified activated carbon fiber (ACF). The ACFs/$TiO_2$ composites were prepared from titanium n-butoxide (TNB) as titanium precursor and various acid modified ACFs. The prepared samples are heat treated at 973 K. Then the ACF/$TiO_2$ composites were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX). Moreover, photocatalytic degradation of MB by the ACF/$TiO_2$ composites was determined under UV irradiation. The results shows that the photocatalytic activity of ACF/$TiO_2$ composites ($AT1{\sim}AT4$) prepared with TNB and various acid modified ACF was much better than that of ACF/$TiO_2$ composite (AT) prepared with TNB and non-acid modified ACF, and the effects improved with order of sample AT3 > AT4 > AT1 > AT2.

• Journal of the Korean Applied Science and Technology
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• v.22 no.1
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• pp.43-49
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• 2005

OXI-PAN fibers, Kynol fibers and rayon fibers were used as precursorsfor the preparation of activated carbon fibers (ACFs) by chemical activation with KOH at $800^{\circ}C$. The effects of different precursorfibers and fiber/KOH ratios on the final ACFs are discussed. The precursor fibers used are appropriate for the ACFs in a single stage pyrolysis process. The OXI-PAN fibers which were activated with KOH of 2.0M showed a specific surface area of $2328m^2/g$ however, loosed the fiber shape because of low yields. The Kynol fibers and Rayon fibers showed the high yields but the lower specific surface area of $900m^2/g$ and $774m^2/g$, respectively, at KOH of 1.5M. The OXI-PAN fibers which were activated with KOH of 1.5M have a specific surface area of $1028m^2/g$ and higher micro-pore volumes and lower yields rather than Kynol-1.5 and Rayon-1.5 samples. This phenomenon is because of higher chemical resistance of the Kynol and Rayon fibers rather than OXI-PAN fibers. However, the Kynol fibers were the best precursors on KOH activation at $800^{\circ}C$ considered carbon yields, surface areas and micropore volumes.

• Composites Research
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• v.32 no.6
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• pp.342-348
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• 2019

Development of flame retarding polymer based materials has been studied actively due to the increase in use of polymers. The post treatment of manufactured fibers or the introduction of flame retardant into fibers is representative method for the way to improve the flame retardancy. Among the polymers, polyacrylonitrile (PAN), which is a precursor of carbon fiber, has been widely used for clothes. Due to low flame retardancy of PAN fiber (LOI value: 17~18%), the improvement of flame retardancy of PAN fiber is needed. In this review paper, we report preparation methods for the fabrication of post-treated (oxidization or chemical reaction) flame-retarding PAN fibers and composites composed of PAN and organic/inorganic materials (SiO₂, 2D materials or CNT).

• Journal of Korean Society for Atmospheric Environment
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• v.33 no.1
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• pp.1-10
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• 2017

Adsorption is a plausible technology using solid adsorbents for dry capture of carbon dioxide ($CO_2$). In general, narrow size distribution of tiny pores and surface chemical functionalities of solid adsorbents enhance the adsorption capacity of gaseous $CO_2$ molecules. In order to utilize the advantages of fibrous adsorbents, this work prepared activated carbon nanofibers (ACNFs) via the electrospinning process using a polymer precursor of polyacylonitrile (PAN). The spun fibers were 390 nm to 580 nm in thickness with an average surface area of $27.3m^2/g$. The surface structure was improved by a programmed thermal activation at $800^{\circ}C$ in $CO_2$ atmosphere. It was also found that the nitrogen-groups including pyrrole and pyridine were created during the activation facilitaing the selective adsorption as forming enhanced active sites. The finally obtained adsorption capacities were 2.74 mmol/g for pure $CO_2$ flow and 0.74mmol/g for 3000 ppm.