Thermal conductivity of fiber and opacifier loaded silica aerogel composite

Hu, Zhang; Fang, Wenzhen; Wang, Xian; Li, Yueming; Tao, Wen‐Quan

doi:10.1016/j.ijheatmasstransfer.2017.08.006

Cited by 67 publications

(21 citation statements)

References 53 publications

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“…The effective model can be used to predict and to optimize the thermal conductivity of aerogel composite. However, the reliability also relies on the effective model [ 18 ], the solid thermal conductivity of components at different temperature (which is difficult to determine accurately at nanoscale), and extinction coefficient. Therefore, the evaluation of thermal insulation performance should be conducted at various temperatures.…”

Section: Resultsmentioning

confidence: 99%

“…The adding of an opacifier inevitably enhances solid conductivity. The solid thermal conductivity of SiC is much larger than that of ZrO 2 while the extinction coefficient of SiC is much higher than that of ZrO 2 [ 18 ]. Since the overall effect of doping with an opacifier depends on the temperature, samples 2, 8, and 13 are selected and measured from 25 to 750 °C at constant pressure in nitrogen atmosphere and compared with fiber mat-aerogel (sample 16) and fiber mat (sample 17).…”

Section: Resultsmentioning

confidence: 99%

“…Sample 16 is fiber mat synthesized with aerogel and sample 17 is pure fiber mat. The material density is determined by measuring the volume of material with regular shape and its weight after being dried at 150 °C in the hygrothermostat for more than 12 h. The densities of bulk ZrO 2 , SiC and SiO 2 are 5.89 g/cm 3 , 3.22 g/cm 3 and 2.1 g/cm 3 , respectively [ 18 ]. With the known mass fractions, densities of components and apparent material density, the volume fractions of components can be calculated.…”

Section: Experimental Investigationmentioning

confidence: 99%

“…In addition, due to the size effect of solid skeletons, the solid thermal conductivity is also smaller than that of bulk materials [ 7 , 13 ]. Many studies have been conducted to reveal the heat transfer mechanisms of aerogels [ 14 ], to measure, to predict and to optimize the thermal conductivity of aerogels and their composite [ 15 , 16 , 17 , 18 , 19 , 20 ].…”

Section: Introductionmentioning

confidence: 99%

“…Pure silica aerogel is very fragile and nearly transparent to the infrared spectrum over the range of 3–8 μm, in which most thermal radiation is transported [ 21 ]. Therefore, reinforced fibers and opacifiers are doped with silica aerogel to enhance their mechanical properties and extinction ability to thermal radiation [ 16 , 18 , 21 , 22 , 23 ]. To obtain better thermal insulation property at high temperature, experimental characterization on the thermal conductivity and microstructure of the aerogel composite are conducted in the present study.…”

Section: Introductionmentioning

confidence: 99%

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Experimental Characterization of the Thermal Conductivity and Microstructure of Opacifier-Fiber-Aerogel Composite

Zhang

et al. 2018

Molecules

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Due to their high-porosity, nanoporous structure and pores, aerogel materials possess extremely low thermal conductivity and have broad potential in the thermal insulation field. Silica aerogel materials are widely used because of their low thermal conductivity and high temperature resistance. Pure silica aerogel is very fragile and nearly transparent to the infrared spectrum within 3–8 μm. Doping fibers and opacifiers can overcome these drawbacks. In this paper, the influences of opacifier type and content on the thermal conductivity of silica fiber mat-aerogel composite are experimentally studied using the transient plane source method. The thermal insulation performances are compared from 100 to 750 °C at constant pressure in nitrogen atmosphere among pure fiber mat, fiber mat-aerogel, 20% SiC-fiber mat-aerogel, 30% ZrO2-fiber mat-aerogel and 20% SiC + 30% ZrO2-fiber mat-aerogel. Fiber mat-aerogel doped with 20% SiC has the lowest thermal conductivity, 0.0792 W/m·K at 750 °C, which proves that the proper type and moderate content of opacifier dominates the low thermal conductivity. The pore size distribution indicates that the volume fraction of the micropore and mesopore is also the key factor for reducing the thermal conductivity of porous materials.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Experimental Investigationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Experimental Characterization of the Thermal Conductivity and Microstructure of Opacifier-Fiber-Aerogel Composite

Zhang

et al. 2018

Molecules

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Hollow‐Structured Materials for Thermal Insulation

2018

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Heating and cooling represent a significant portion of overall energy consumption of our society. Due to the diffusive nature of thermal energy, thermal insulation is critical for energy management to reduce energy waste and improve energy efficiency. Thermal insulation relies on the reduction of thermal conductivity of appropriate materials that are engineerable in compositions and structures. Hollow‐structured materials (HSMs) show a great promise in thermal insulation since the existence of high‐density gaseous voids breaks the continuity of heat‐transport pathways in the HSMs to lower their thermal conductivities efficiently. Herein, a timely overview of the recent progress in developing HSMs for thermal insulation is presented, with the focus on summarizing the strategies for creating gaseous voids in solid materials and thus synthesizing various HSMs. Systematic analysis of the documented results reveals the relationship of thermal conductivities of the HSMs and the size and density of voids, i.e., reducing the void size below ≈350 nm is more favorable to decrease the thermal conductivity of the HSMs because of the possible confinement effect originated from the nanometer‐sized voids. The challenges and promises of the HSMs faced in future research are also discussed.

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