Processing and properties of silica-bonded porous nano-SiC ceramics with extremely low thermal conductivity

Generally, high thermal conductivity of SiC ceramics is required. However, in some circumstances, low thermal conductivity SiC is also needed, for example, for good thermoelectricity or heat insulation. In this work, the product of pyrolysis of polycarbosilane (PCS) is chosen as raw materials. The microwave sintering process was applied to obtain low thermal conductivity at a relatively low sintering temperature. The microwave sintering processes were performed at 1200 °C under Ar atmosphere with dwelling time of 10, 20 and 30 min. The morphology and phases were analyzed by electric microscopy and X-ray diffraction (XRD), respectively. The thermal diffusivities, specific heat and thermal conductivities were measured by laser-flashed method using a thermal analyzer. The thermal conductivity of samples is within the range from 0.81 to 1.37 W/m•K. The sample with dwelling time of 30 min shows potential for multiple applications, due to its good crystallization in XRD spectra and relatively low thermal conductivity in the considered temperature range. The results also suggest a phase transformation at a dwelling time near 20 min that may have occurred.

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Microstructures and Thermophysical Properties of Polymer Derived SiC/C Composites

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.152-154.86 ◽

2012 ◽

Vol 152-154 ◽

pp. 86-90

Author(s):

Xiao Yi Han ◽

Hai Feng Cheng ◽

Xin Xing ◽

Jun Wang

Keyword(s):

Thermal Conductivity ◽

Raw Materials ◽

Holding Time ◽

X Ray Diffraction ◽

X Ray ◽

Low Thermal Conductivity ◽

Sic Ceramics ◽

Transmission Electron ◽

Thermal Diffusivities ◽

Hot Press Sintering

Polymer derived SiC ceramics usually present a relatively low thermal conductivity for the large porosity and complex phases. In order to obtain condensed SiC ceramic with low thermal conductivity, a preceramic precursor polycarbosilane (PCS) was selected as the raw materials. And hot press sintering processes were performed at 1600 °C under Ar atmosphere with the holding time in the range of 20 to 40 min for consolidation. The microstructures and phases were analyzed by scanning electron microscopy (SEM) with energy disperse X-ray spectroscopy (EDS), X-ray diffraction (XRD) and high-resolution transmission electron microscope (HRTEM). The specific heat, thermal diffusivities and thermal conductivities were measured and investigated from room temperature to 650 °C. A minimum thermal conductivity of 4.13 W•m-1•K-1 was obtained at 650 °C with a holding time of 30 min.

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Structure and Thermoelectric Properties of New Quaternary Tin and Lead Bismuth Selenides, K1+xM4-2xBi7+xSe15 (M = Sn, Pb) and K1+xSn5-xBi11+xSe22

MRS Proceedings ◽

10.1557/proc-626-z8.4 ◽

2000 ◽

Vol 626 ◽

Author(s):

Antje Mrotzek ◽

Kyoung-Shin Choi ◽

Duck-Young Chung ◽

Melissa A. Lane ◽

John R. Ireland ◽

...

Keyword(s):

Thermal Conductivity ◽

Single Crystal ◽

Thermoelectric Properties ◽

Three Dimensional ◽

Structure Type ◽

Narrow Gap ◽

Low Thermal Conductivity ◽

Seebeck Coefficients ◽

Metal Atoms ◽

Anionic Framework

ABSTRACTWe present the structure and thermoelectric properties of the new quaternary selenides K1+xM4–2xBi7+xSe15 (M = Sn, Pb) and K1-xSn5-xBi11+xSe22. The compounds K1+xM4-2xBi7+xSe15 (M= Sn, Pb) crystallize isostructural to A1+xPb4-2xSb7+xSe15 with A = K, Rb, while K1-xSn5-xBi11+xSe22 reveals a new structure type. In both structure types fragments of the Bi2Te3-type and the NaCl-type are connected to a three-dimensional anionic framework with K+ ions filled tunnels. The two structures vary by the size of the NaCl-type rods and are closely related to β-K2Bi8Se13 and K2.5Bi8.5Se14. The thermoelectric properties of K1+xM4-2xBi7+xSe15 (M = Sn, Pb) and K1-xSn5-xBi11+xSe22 were explored on single crystal and ingot samples. These compounds are narrow gap semiconductors and show n-type behavior with moderate Seebeck coefficients. They have very low thermal conductivity due to an extensive disorder of the metal atoms and possible “rattling” K+ ions.

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Extremely Low Thermal Conductivity of Graphene Nanoplatelets Using Nanoparticle Decoration

ES Energy & Environments ◽

10.30919/esee8c139 ◽

2018 ◽

Cited By ~ 6

Author(s):

Lin Qiu ◽

◽

Pu Guo ◽

Hanying Zou ◽

Yanhui Feng ◽

...

Keyword(s):

Thermal Conductivity ◽

Graphene Nanoplatelets ◽

Low Thermal Conductivity

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A Novel Poly(Ionic Liquid) as the Thermal Insulating Material

Recent Innovations in Chemical Engineering (Formerly Recent Patents on Chemical Engineering) ◽

10.2174/2405520413666200207114107 ◽

2020 ◽

Vol 13 (3) ◽

pp. 241-247

Author(s):

Wenxin Wei ◽

Guifeng Ma ◽

Hongtao Wang ◽

Jun Li

Keyword(s):

Thermal Conductivity ◽

Ionic Liquid ◽

Glass Transition ◽

Transition Temperature ◽

Glass Transition Temperature ◽

Flame Resistance ◽

Insulating Material ◽

Low Thermal Conductivity ◽

Thermal Insulating ◽

Poly Ionic Liquid

Objective: A new poly(ionic liquid)(PIL), poly(p-vinylbenzyltriphenylphosphine hexafluorophosphate) (P[VBTPP][PF6]), was synthesized by quaternization, anion exchange reaction, and free radical polymerization. Then a series of the PIL were synthesized at different conditions. Methods: The specific heat capacity, glass-transition temperature and melting temperature of the synthesized PILs were measured by differential scanning calorimeter. The thermal conductivities of the PILs were measured by the laser flash analysis method. Results: Results showed that, under optimized synthesis conditions, P[VBTPP][PF6] as the thermal insulator had a high glass-transition temperature of 210.1°C, high melting point of 421.6°C, and a low thermal conductivity of 0.0920 W m-1 K-1 at 40.0°C (it was 0.105 W m-1 K-1 even at 180.0°C). The foamed sample exhibited much low thermal conductivity λ=0.0340 W m-1 K-1 at room temperature, which was comparable to a commercial polyurethane thermal insulating material although the latter had a much lower density. Conclusion: In addition, mixing the P[VBTPP][PF6] sample into polypropylene could obviously increase the Oxygen Index, revealing its efficient flame resistance. Therefore, P[VBTPP][PF6] is a potential thermal insulating material.

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High thermal conductivity of pure dense SiC ceramics prepared via HTPVT

Functional Materials Letters ◽

10.1142/s1793604719500322 ◽

2019 ◽

Vol 12 (03) ◽

pp. 1950032 ◽

Cited By ~ 2

Author(s):

Yuchen Deng ◽

Yaming Zhang ◽

Nanlong Zhang ◽

Qiang Zhi ◽

Bo Wang ◽

...

Keyword(s):

Thermal Conductivity ◽

Silicon Carbide ◽

Grain Size ◽

Phase Composition ◽

Room Temperature ◽

Vapor Transport ◽

Physical Vapor Transport ◽

Growth Substrate ◽

Sic Ceramics ◽

Evolution Of Microstructure

Pure dense silicon carbide (SiC) ceramics were obtained via the high-temperature physical vapor transport (HTPVT) method using graphite paper as the growth substrate. The phase composition, the evolution of microstructure, the thermal diffusivity and thermal conductivity at RT to 200∘C were investigated. The obtained samples had a relative density of higher than 98.7% and a large grain size of 1[Formula: see text]mm, the samples also had a room-temperature thermal conductivity of [Formula: see text] and with the temperature increased to 200∘C, the thermal conductivity still maintained at [Formula: see text].

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