Thermal and electrical conductivity and magnetoresistance of graphite films prepared from aromatic polyimide films

Kaburagi, Yutaka; Kimura, Takeshi; Yoshida, Akira; Hishiyama, Yoshihiro

doi:10.7209/tanso.2012.106

Cited by 23 publications

(11 citation statements)

References 16 publications

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“…Relation of κ RT to d 002 shows scattering (Figure a), but σ RT shows better relation with d 002 (Figure b). Between κ RT and maximum transverse magnetoresistance ( Δρ / ρ ) max at 77 K and a magnetic field of 1 T, a relation similar to Figure b was observed . Since both ρ RT / ρ 77K and ( Δρ / ρ ) max are known to be parameters representing the degree of graphitization or crystallinity, the dependence of κ RT on ( Δρ / ρ ) max shows the same trend as that on ρ RT / ρ 77K shown in Figure b: κ RT increases rapidly with increasing crystallinity and tend to saturate in high crystallinity region.…”

Section: Materials With High Thermal Conductivitysupporting

confidence: 64%

“…The κ RT of various highly oriented and highly‐crystallized graphite membranes, commercially available and laboratory‐made, are plotted against electrical conductivity at room temperature σ RT and resistivity ratio ρ RT / ρ 77k in Figure a and b, respectively . Here, the value L a is not useful for the discussion on κ RT , because highly‐crystalline graphites have much larger crystallite size than 100 nm, beyond the limit for accurate determination by X‐ray diffraction.…”

Section: Materials With High Thermal Conductivitymentioning

confidence: 99%

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Thermal Management Material: Graphite

Kaburagi²,

2014

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Graphite has pronounced anisotropy in its properties. Thermal conductivity of graphite crystal is extremely high along its layer plane, as high as 2000 Wm À1 K À1 , much higher than metals, and very low across its layer plane, as low as 7 Wm À1 K À1 . This anisotropy gives high possibility for graphite as thermal management materials. Here, graphite membranes with high thermal conductivity along the surface for heat dissipation and with low conductivity perpendicular to the surface for heat insulation, in addition to graphite foams as container of phase change materials for heat energy storage, are reviewed, particularly referring to the preparations of various graphite materials. Thermal conductivity of diamond crystal is also high, 2500 Wm À1 K À1 , but it is very sensitive for structural defects, but that of graphitic materials is less sensitive for structural defects, suggesting that the latter is more practical for thermal management than the former.(along the layer plane) as %2000 Wm À1 K À1 , [1] much higher than metals, such as Cu and Ag, but very small k RT along the c-axis (perpendicular to the layer plane) as around 6-9 Wm À1 K À1[2] : graphite crystal can be highly conductive along the layer and be highly insulating perpendicular to the layer. This pronounced anisotropy is due to graphite structure, graphite layer consisting of strong s bonding, and parallel stacking of these layers by van der Waals bonding due to the interaction between p-electron clouds on neighboring layers. Diamond crystal, which consists of carbon atoms using sp 3 CÀ ÀC bonding, is isotropic and has the highest value of k RT in solids as %2200 Wm À1 K À1 . [3] Highly graphitized carbon materials exhibit very high thermal conductivities. A highly-oriented pyrolytic graphite (HOPG) is reported to have k RT of 1950 Wm À1 K À1 . [1,4] Recently, graphite films with high thermal conductivity have become commercially available for dissipating heat from electronic devices containing integrated circuits, such as personal computers and mobile phones. [5] The k RT of the commercially available graphite films is reported to be more than 1600 Wm À1 K À1 , more than four times higher than the values of Ag, which is known to have the highest k RT among metals. Carbon/carbon composites prepared from natural graphite flakes by using mesophase pitch as binder, followed by heat treatment at high temperatures, gives k RT of about 650 Wm À1 K À1 , higher than Ag. In order to develop practical materials having k high enough, the preparation of highly oriented and highly crystallized graphite is essential. Flexible graphite sheets prepared from natural graphite via [*] Prof. M. InagakiProfessor Emeritus

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Section: Materials With High Thermal Conductivitysupporting

confidence: 64%

Section: Materials With High Thermal Conductivitymentioning

confidence: 99%

Thermal Management Material: Graphite

Kaburagi²,

2014

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“…We assume that at joins between crystal-grains there exists no significant thermal resistance 4) . The thermal conductivity of the graphite film along the longitudinal direction of the film κ // , denoted as κ corr in the previous study 1) , can be obtained as the average of κ X with a weight of I(ϕ) 3)-7) ;…”

Section: Thermal Conductivity Of Graphite Crystal-grain In the Basal mentioning

confidence: 99%

“…In Table 1, the values of the interlayer spacing d 002 , resistivity ratio ρ RT / ρ 77 K and the magnetoresistance data at 77 K and in a magnetic Table 1 Interlayer spacing d 002 , ratio of electrical resistivity at room temperature to that at 77 K ρ RT / ρ 77 K for the samples obtained in the previous study 1) and magnetoresistance data for the samples at 77 K and in field of 1 T; Table 2 Electrical and thermal conductivities along graphite film σ //,RT and κ // for samples at room temperature obtained in the previous study 1) . Conductivities in basal plane ‾ σ G,RT and ‾ κ G evaluated by Eqs.…”

Section: General Aspects Of Thermal Conductivity In the Basal Plane Omentioning

confidence: 99%

“…In the previous study, we prepared highly-crystalized graphite films using carbonized films derived from commercially available aromatic polyimide films and using rectangular samples of these graphite films, commercially available graphite films and sheets, and a thincleaved commercially available pyrolytic graphite plate. Thermal conductivities and also electrical conductivities along the longitudinal direction of each sample were measured at room temperature 1) .…”

Section: Introductionmentioning

confidence: 99%

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Crystal-grain size, phonon and carrier mean free paths in the basal plane, and carrier density of graphite films prepared from aromatic polyimide films

Hishiyama

Yoshida

Kaburagi

2012

TANSO

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The electrical and thermal conductivities in the basal plane of graphite films prepared from aromatic polyimide films were evaluated with reference to previously measured electrical and thermal conductivities along their longitudinal directions at room temperature with the aid of magnetoresistance anisotropy measurement at 77 K. The average crystal-grain size of each graphite film was obtained from the relation between thermal conductivity and grain size originally derived by Klemens and Pedraza. It was found that at room temperature the crystal-grain boundary scattering of phonons could dominantly occur for crystal-grains with sizes smaller than ∼520 nm or the average d 002 value of grains larger than ∼0.3357 nm. When the grain size exceeds the intrinsic phonon mean free path in a single graphite crystal, i.e. ∼1760 nm, or the average d 002 value of the crystal-grains is less than ∼0.3357 nm, the three phonon process in thermal conduction becomes dominant. The mean free paths of carriers were found to be much shorter than those of phonons and it was shown that at 77 K grain sizes smaller than ∼220 nm could cause boundary scattering of carriers. The total carrier density at 77 K evaluated from the magnetoresistance and electrical conductivity data shows a decrease from the value of a single crystal of graphite as the crystallinity of the graphite film is reduced. a) Professor Emeritus, Tokyo City University: 4-41-6 Nakanokami-cho, Hachioji-shi,

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Anisotropically Oriented Carbon Films with Dual‐Function of Efficient Heat Dissipation and Excellent Electromagnetic Interference Shielding Performances

Tan

Chen

Cheng

et al. 2022

Adv Funct Materials

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The rapid development of next‐generation portable electronic devices urgently requires dual‐functional materials that possess both efficient heat dissipation and outstanding electromagnetic interference (EMI) shielding performances. In this study, anisotropically oriented carbon films with high thermal conductivity and excellent EMI shielding properties are prepared through an innovative glucose hydrogel‐controllable carbonization method. The horizontal alignment of nanocrystalline graphite results in oriented structures with an extremely high in‐plane thermal conductivity of 439.9 W m−1 K−1, exhibiting a more effective heat‐dissipating capacity on smartphones than their commercial graphite counterparts. Additionally, owing to multiple internal reflections arising from the oriented structures, the films exhibit an EMI shielding effectiveness (SE) of 21.72 dB at an ultrathin thickness of 480 nm in the X‐band and an extraordinarily high absolute shielding effectiveness (SSE/t) of 275 883 dB cm2 g−1, significantly outperforming most of the reported synthetic materials. Furthermore, the flexibility, high mechanical strength, and stability of the films are demonstrated and therefore show promising application prospects. This study offers a facile yet feasible strategy for preparing dual‐functional materials to address the heat emission and EMI problems of advanced electronic devices in a more economical and environmentally friendly manner.

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Thermal and electrical conductivity and magnetoresistance of graphite films prepared from aromatic polyimide films

Cited by 23 publications

References 16 publications

Thermal Management Material: Graphite

Thermal Management Material: Graphite

Crystal-grain size, phonon and carrier mean free paths in the basal plane, and carrier density of graphite films prepared from aromatic polyimide films

Anisotropically Oriented Carbon Films with Dual‐Function of Efficient Heat Dissipation and Excellent Electromagnetic Interference Shielding Performances

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