High Temperature Resistant Calcium-doped Silica Aerogels with Enhanced Thermal Insulation via Sol-Gel Hydrothermal Route

doi:10.15541/jim20250113

Abstract

Abstract:

Silica aerogel has broad applications in the field of high-temperature thermal insulation due to its low density, low thermal conductivity and high stability. However, its thermal insulation performance deteriorates significantly at elevated temperatures exceeding 600 ℃, primarily due to the collapse of pore structure. Meanwhile, the shielding capacity of SiO₂ aerogel to the infrared radiation at high temperature is rather low due to the intrinsic properties of SiO₂. Herein, a strategy for improving the high-temperature stability and infrared shielding properties of SiO₂ aerogel via Ca doping was explored. Calcium-doped silica aerogel (CSA) powders were prepared by Sol-Gel, hydrothermal, and ambient pressure drying (APD) techniques using water glass and anhydrous calcium chloride as precursors and trimethylchlorosilane as a hydrophobic modifier. The effects of Ca/Si molar ratio in the precursor and hydrothermal conditions (temperature and pH) on the crystalline properties, microscopic morphology and pore structure of CSAs were investigated. The results show that the Ca/Si molar ratio and hydrothermal treatment have significant effects on the microstructure and heat resistance of CSAs in the temperature range of 400-1000 ℃. The samples sintered at 1000 ℃ have a high specific surface area of 100.1 m²/g and a pore volume of 0.8705 cm³/g, indicating that the CSA has good heat resistance. One-side insulation tests at temperatures up to 600 ℃ show that the sample with a Ca/Si molar ratio of 1.0 has the best insulation performance, with a cold surface temperature of 450 ℃, which is 27 ℃ lower than that of the pure silica aerogel.

Key words: silica aerogel, calcium doping, high-temperature resistance, hydrothermal, ambient pressure drying

CLC Number:

TQ424

LI Hao, QI Yuan, GAO Xiangdong, ZHANG Xingxing, WANG Jinmin. High Temperature Resistant Calcium-doped Silica Aerogels with Enhanced Thermal Insulation via Sol-Gel Hydrothermal Route[J]. Journal of Inorganic Materials, 2026, 41(2): 262-272.

Figures/Tables 14

Fig. 1 Schematic illustration of the preparation process of hydrothermal CSA (HCSA) by the Sol-Gel, hydrothermal and APD method

Table 1 Experimental parameters of the aerogel powders

Sample	Ca/Si molar ratio	Temperature/℃	pH^*
PSA	0	-	-
HPSA	0	180	5-6
CSA-0.4	0.4	-	5-6
HCSA-0.4	0.4	120	5-6
	0.4	140	5-6
	0.4	160	5-6
	0.4	180	5-6
	0.4	200	5-6
HCSA-0.6	0.6	180	5-6
HCSA-0.8	0.8	180	5-6
HCSA-1.0	1.0	180	5-6
	1.0	180	7-8
	1.0	180	9-10
	1.0	180	12-13
HCSA-1.2	1.2	180	5-6
HCSA-1.5	1.5	180	5-6

Fig. 2 Packing densities of different samples (a) PSA and CSA-0.4 under different hydrothermal conditions; (b) HCSA-0.4 at different hydrothermal temperatures and HCSA-1.0 at different hydrothermal pH; (c, d) HCSA sintered at different temperatures for 2 h

Fig. 3 XRD patterns of the PSA, HPSA, CSA-1.0, and HCSA-1.0 samples

Fig. 4 (a-d) SEM images of (a) PSA, (b) HPSA, (c) CSA-1.0, and (d) HCSA-1.0; (e) Elemental mappings and (f) EDS spectrum of HCSA-1.0

Fig. 5 (a) TEM image, (b) SAED pattern and (c) HRTEM image of the as-prepared HCSA-1.0; (d) TEM image, (e) SAED pattern and (f) HRTEM image of HCSA-1.0 sintered at 1000 ℃ for 2 h

Fig. 6 Pore structure of HCSA-1.0 sintered at different temperatures (a) Adsorption-desorption isotherms; (b) Pore size distributions (evaluated from desorption isotherm); (c) Specific surface area and pore volume; (d) Average pore size

Fig. 7 SEM images of HCSA-1.0 samples sintered at (a) 400, (b) 600, (c) 800, and (d) 1000 ℃

Fig. 8 TG-DSC curves of (a) PSA and (b) HCSA-1.0

Fig. 9 (a) Flat heating furnace test device; (b) Schematic diagram of a home-made device for measuring thermal insulation properties; (c) Plots of temperature variation of the flat heating furnace test; (d) Specific extinction coefficients of PSA and HCSA-1.0 in infrared band Colorful figures are available on website

Fig. S1 Low resolution SEM image used for EDS mapping test

Fig. S2 Photographs of PSA (a) and HCSA-1.0 (b) samples calcined at 1000 ℃

Fig. S3 TEM images of HCSA-1.0 calcined at 1000 ℃ (a) Fringe of a large particle; (b) A small particle

Fig. S4 XRD patterns of HCSA-1.0 sintered at different temperatures

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