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Pyun, Hyung-Chick,Kim, Jae-Rok,Lee, Kyung-Hee Korean Nuclear Society 1972 Nuclear Engineering and Technology Vol.4 No.1
A study on the preparation of wood-plastic combinations by gamma-ray induced polymerization is carried out. In monomer impregnation, the rates and amounts are determined for various woods. The polymerization rates of various monomers and monomer mixtures impregnated mainly domestic woods are studied varying the total gamma-dose and gamma-dose rates. The obtained data indicate that; 1) in impregnation of monomer, populus deltoides is the fastest in rate, and the most impregnated in amount 2) the general trends of polymerization of monomers ill woods is in the order of vinyl acetate--methyl metacrylate--styrene, ranging from 3 to 15 Mard of total does in rate of 4$\times$10$^4$rad/hr., thus vinyl acetate or methyl metacrylate is suitable monomer in view of polymerization rate, 3) the successful woods in combination with monomer are pinus rigida and pinus densiflora in view of polymerization rate, 4) the monomers in woods are more easily polymerized under the conditions of moderately lower does rate, 2.1$\times$10$^4$rad/hr.
Boosted thermal conductance of polycrystalline graphene by spin-coated silver nanowires
Lee, Woorim,Kihm, Kenneth David,Lee, Woomin,Won, Phillip,Han, Seonggeun,Lim, Gyumin,Pyun, Kyung Rok,Ko, Seung Hwan Elsevier 2019 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.134 No.-
<P><B>Abstract</B></P> <P>Spin-coated silver nanowires (AgNWs) on graphene show a significantly improved thermal conductance of the composite in comparison with pristine graphene with no nanowires. CVD-synthesized graphene is transferred onto an 8-nm thin TEM grid substrate, and AgNWs (average diameter 150-nm and average length 30-μm) are chemically grown from an AgNO<SUB>3</SUB> reagent solution. The AgNW bridging overrides the negative effect of the grain boundary scattering of the electron/phonon energy carriers propagating in the polycrystalline CVD graphene and ultimately enhances the grain-to-grain heat transport by widening their passages. This boosting contribution of AgNWs is quantitatively assessed by measurement of thermal conductance for synthesized AgNW/graphene composite samples. The Raman thermometry measurement locations are selected to be beside a single AgNW (G-1), two AgNWs (G-2), and three or more AgNWs (G-3), so that the effect of AgNW density can be examined. The average enhanced thermal conductance values for the three AgNW-laid graphene samples are 319.27 nW/K, 343.66 nW/K, and 455.26 nW/K, respectively.</P> <P><B>Highlights</B></P> <P> <UL> <LI> CVD synthesized graphene composites with spin-coated silver nanowires (AgNWs). </LI> <LI> Raman thermometry to measure the thermal sheet conductance <SUB> G S </SUB> of the composite. </LI> <LI> AgNWs widen the transport passages and for both phonons and electrons. </LI> <LI> AgNWs composites show the 113% enhancement in <SUB> G S </SUB> compared to pristine graphene. </LI> </UL> </P>
Two orders of magnitude suppression of graphene's thermal conductivity by heavy dopants (Si)
Lee, Woorim,Kihm, Kenneth David,Kim, Hong Goo,Lee, Woomin,Cheon, Sosan,Yeom, Sinchul,Lim, Gyumin,Pyun, Kyung Rok,Ko, Seung Hwan,Shin, Seungha Elsevier 2018 Carbon Vol.138 No.-
<P><B>Abstract</B></P> <P>The in-plane thermal conductivity ( <SUB> k S i G </SUB> ) of silicon-doped graphene (SiG) was greatly suppressed primarily due to increased phonon scattering associated with the large mass difference of Si from its host C atoms. For SiG as supported on an 8 nm-thick SiO<SUB>2</SUB> substrate, the measured <SUB> k S i G </SUB> represents progressive decrease and saturation with the increase of Si dopants concentration, showing more than an order-of-magnitude reduction from that of supported pristine graphene (PG) and nearly two order-of-magnitude reductions when compared with suspended PG at about 2% doping concentration. The enhanced graphene-substrate conformity through thermal annealing in a vacuum additionally lowers <SUB> k S i G </SUB> from that of ambient annealing. The substitutional Si dopants tend to suppress the contribution of temperature-sensitive phonons with long mean free paths and weaken the temperature dependence of <SUB> k S i G </SUB> . The presence of Si dopants seems to allow for faster attainment of thermal equilibrium between different heat carriers due to the reduced phonon mean free paths. We believe that SiG holds the possibility of exclusively controlling the thermal properties of graphene, since the substitutional dopants do not violently destruct the hexagonal lattice structure of graphene and may possibly have minimal effects on graphene's electrical properties.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Effect of graphene-substrate conformity on the in-plane thermal conductivity of supported graphene
Kim, Hong Goo,Kihm, Kenneth D.,Lee, Woomin,Lim, Gyumin,Cheon, Sosan,Lee, Woorim,Pyun, Kyung Rok,Ko, Seung Hwan,Shin, Seungha Elsevier 2017 Carbon Vol.125 No.-
<P>Measuring the thermal conductivity k(g) of supported graphene is inherently complicated due to uncertainties associated with the heat dissipation into the substrate. We innovate the use of an ultra-thin 8-nm SiO2 substrate to alleviate these uncertainties and thus improve the accuracy of optothermal Raman technique to measure k(g) of supported graphene. As a result, we present an extensive k(g) database for a wide temperature range from 325 K to 575 K. Furthermore, we have found that the thermal conductivity of supported graphene before annealing is close to that of suspended graphene at 3000 W m(-1) K-1, which is attributable to graphene 'suspension' lightly on the substrate roughness, and then progressively decreases over repeated thermal annealing. We elaborate on this annealing-induced kg to occur mainly because of the thermally enhanced graphene-substrate conformity and interfacial scattering by probing the Raman spectroscopic characterization of charge carrier density in graphene and the thermal expansion mismatching strain between graphene and substrate. Repeated thermal annealing also expedites the depletion of intercalated impurities to reduce the graphene-substrate separation distance, which acts to further reduces k(g), ultimately to its lower bound under vacuum-annealing. Therefore, manipulating the thermo-mechanical affiliation can offer an alternative route to control the in-plane thermal conductivity of supported graphene. (C) 2017 Elsevier Ltd. All rights reserved.</P>