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Effect of Post-Heat-Treatment on Various Characteristics of Commercial Pitch-Based Carbon Fibers
Sung-Bong Yoon,Chae-Wook Cho,Dong-Hwan Cho,Jong-Kyoo Park,Jae-Yeol Lee 한국탄소학회 2007 Carbon Letters Vol.8 No.2
In this study, commercially available pitch-based carbon fibers of general grade were post-heat-treated using a boxtype high temperature furnace at 1800℃, 2000˚, 2200℃, and 2400℃, respectively. The fundamental characteristics of each heat-treated carbon fibers were investigated in terms of chemical composition, morphology, thermal stability, X-ray diffraction, single filament tensile test, and electrical resistivity. The result showed that the fiber properties were significantly influenced by the post-heat-treatment, indicating the greater effect with increasing treatment temperature. The carbon contents, thermal stability, and tensile properties of the carbon fibers used here were further increased by the post-heat-treatment, whereas the d-spacing between graphene layers and the electrical resistivity were reduced with increasing post-heat-treatment temperature.
Dynamics and Mechanism of Flame Retardants in Polymer Matrixes: Experiment and Simulation
Yoon, Donghwan,Jung, Hyun Tae,Kwon, Gyemin,Yoon, Yeoeun,Lee, Minsoo,Bae, Imhyuck,Joo, Beom Jun,Kim, Mansuk,Lee, Sun Ae,Lee, Jihye,Lee, Yeonhee,Cho, Eunseog,Shin, Kwanwoo,Sung, Bong June American Chemical Society 2013 The journal of physical chemistry. B, Condensed ma Vol.117 No.28
<P>We investigate the dynamics and the mechanism of flame retardants in polycarbonate matrixes to explore for a way of designing efficient and environment-friendly flame retardants. The high phosphorus content of organic phosphates has been considered as a requirement for efficient flame retardants. We show, however, that one can enhance the efficiency of flame retardants even with a relatively low phosphorus content by tuning the dynamics and the intermolecular interactions of flame retardants. This would enable one to design bulkier flame retardants that should be less volatile and less harmful in indoor environments. UL94 flammability tests indicate that even though the phosphorus content of 2,4-di-<I>tert</I>-butylphenyl diphenyl phosphate (DDP) is much smaller with two bulky tertiary butyl groups than that of triphenyl phosphate (TPP), DDP should be as efficient of a flame retardant as TPP, which is a widely used flame retardant. On the other hand, the 2-<I>tert</I>-butylphenyl diphenyl phosphate (2-<I>t</I>BuDP), with a lower phosphorus content than TPP but with a greater phosphorus content than DDP, is less efficient as a flame retardant than both DDP and TPP. Dynamic secondary ion mass spectrometry and molecular dynamics simulations reveal that the diffusion of DDP is slower by an order of magnitude at low temperature than that of TPP but becomes comparable to that of TPP at the ignition temperature. This implies that DDP should be much less volatile than TPP at low temperature, which is confirmed by thermogravimetric analysis. We also find from Fourier transform infrared spectroscopy that Fries rearrangement and char formation are suppressed more by DDP than by TPP. The low volatility and the suppressed char formation of DDP suggest that the enhanced flame retardancy of DDP should be attributed to its slow diffusivity at room temperature and yet sufficiently high diffusivity at high temperature.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpcbfk/2013/jpcbfk.2013.117.issue-28/jp400114x/production/images/medium/jp-2013-00114x_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp400114x'>ACS Electronic Supporting Info</A></P>
A Design of the Frequency Synthesizer for UWB Application in 0.13 µm RF CMOS process
Sung-Kyu Jung,Jin-Kyung Kim,Ji-Hoon Jung,Kang-Yoon Lee,Chul Nam,Bong-Hyuk Park,Sang-sung Choi 대한전자공학회 2007 ITC-CSCC :International Technical Conference on Ci Vol.2007 No.7
This paper describes a 3 to 5㎓ frequency synthesizer for MB-OFDM UWB application using 0.13um CMOS process. The frequency synthesizer operates in the band group1 whose center frequencies are 3432㎒, 3960㎒, and 4488㎒. To cover the overall frequencies of group 1, an efficient frequency planning minimizing a number of blocks and the power consumption are proposed. And, a high-frequency VCO and prescaler architecture are also presented in this paper. A new coarse tuning scheme that utilizes the MIM capacitance and the varactor is proposed to expand the VCO tuning range. The single PLL and two SSB-mixers consume 75㎽ from a 1.5V supply. The VCO tuning range is 500㎒. The simulated phase noise of the VCO is -110㏈c/Hz at 1㎒ offset. The die area is 3 × 2㎟.