Synthesis of monolithic carbon aerogels with high mechanical strength via ambient pressure drying without solvent exchange

doi:10.1016/j.jmst.2020.02.013

Abstract

Abstract:

A simple, fast and cost-effective method for monolithic carbon aerogels (CAs) preparation was proposed through sol-gel polycondensation of resorcinol with formaldehyde in a basic aqueous solution followed by ambient pressure drying without solvent exchange, and carbonization. The microstructure and network strength of CAs were tailored by adjusting the catalyst concentration ([resorcinol]/[sodium carbonate] in the range of 300-2000), water content ([deionized water]/[resorcinol] equals to 17 and 24, respectively), and gelation temperature (T_gel in the range of 30-90°C). Resultantly, the CAs with a wide range of density (0.30-1.13 g/cm ³), high specific surface area (465-616 m ²/g), high compressive strength (6.5-147.4 MPa) and low thermal conductivity (0.065-0.120 W·m ^-1 K ^-1) were obtained in this work. Moreover, the large-sized CAs (100 × 100 × 20 mm ³) can also be prepared by this method since the formed robust skeleton network can resist shrinkage/collapse of pore structure and prevent cracking during drying. The improved mechanical strength and monolithic forming abilities could be mainly attributed to the uniform arrangement of carbon particles and pores, fine particle size, abundant network structure and enhanced particle neck.

Key words: Carbon aerogels, Ambient pressure drying, High mechanical strength, Thermal insulation

Zhi Yang, Jian Li, Xiaojing Xu, Shengyang Pang, Chenglong Hu, Penglei Guo, Sufang Tang, Hui-Ming Cheng. Synthesis of monolithic carbon aerogels with high mechanical strength via ambient pressure drying without solvent exchange[J]. J. Mater. Sci. Technol., 2020, 50: 66-74.

Figures/Tables 15

Table 1 Synthesis parameters and properties of OAs and CAs.

Samples	R/C	W/R	T_gel (°C)	DS (%)	ρ_OA (g/cm³)	CS (%)	ρ_CA (g/cm³)	σ_CA (MPa)	E_CA (MPa)
A1	300	17	30	29.21	0.92	23.14	1.13	126.8	1981.3
A2	500	17	30	22.93	0.71	19.87	0.80	84.3	1170.8
A3	1000	17	30	15.94	0.49	18.92	0.54	27.1	451.7
A4	1500	17	30	6.54	0.38	17.75	0.37	10.8	156.5
A5	2000	17	30	3.48	0.31	17.39	0.30	6.5	135.4
B1	300	24	30	35.73	0.96	23.63	1.12	147.4	2076.1
B2	500	24	30	30.15	0.73	20.55	0.82	124.4	1574.7
B3	1000	24	30	22.16	0.49	18.04	0.51	39.6	545.7
B4	1500	24	30	13.70	0.37	17.64	0.36	8.9	120.3
B5	2000	24	30	-	-	-	-	-	-
C1/A5	2000	17	30	3.48	0.31	17.39	0.30	6.5	135.4
C2	2000	17	45	8.92	0.42	19.08	0.40	11.5	169.4
C3	2000	17	60	10.63	0.43	18.94	0.42	21.4	270.6
C4	2000	17	75	11.86	0.44	18.17	0.46	29.1	323.8
C5	2000	17	90	14.92	0.46	17.64	0.47	38.2	502.6
C3*	2000	17	60	10.35	0.41	18.35	0.42	22.3	258.7
C5*	2000	17	90	14.18	0.47	16.63	0.45	35.4	481.9

Fig. 1. SEM images of CAs-A1-A5 with different catalyst concentrations: (a) R/C?=?300; (b) R/C?=?500; (c) R/C?=?1000; (d) R/C?=?1500; (e) R/C?=?2000.

Fig. 2. Average particle size and maximum pore diameter of CAs-A1～A5.

Fig. 3. Nitrogen adsorption-desorption isotherms (a) and pore size distributions (b) of CAs-A1-A5.

Table 2 Porosity parameters of CAs-A1～A5.

Samples	S_BET (m²/g)	S_mic (m²/g)	S_mes (m²/g)	V_pore (cm³/g)	V_mic (cm³/g)
CAs-A1	465	382	83	0.31	0.17
CAs-A2	616	350	266	0.77	0.16
CAs-A3	589	395	194	1.14	0.18
CAs-A4	555	436	119	0.52	0.20
CAs-A5	558	476	82	0.44	0.22

Fig. 4. Compressive stress-stain curves of CAs-A1-A5.

Fig. 5. SEM images of CAs-B1-B4 with different catalyst concentrations: (a) R/C?=?300; (b) R/C?=?500; (c) R/C?=?1000; (d) R/C?=?1500.

Fig. 6. The average particle size and maximum pore diameter of CAs-B1-B4.

Fig. 7. SEM images of CAs-C1-C5 with different gelation temperatures: (a) Tgel?=?30?°C; (b) Tgel?=?45?°C; (c) Tgel?=?60?°C; (d) Tgel?=?75?°C; (e) Tgel?=?90?°C.

Fig. 8. The average particle size and maximum pore diameter of CAs-C1-C5.

Fig. 9. Schematic models of the influence of gelation temperature on the network structures of hydrogels.

Fig. 10. Compressive stain-stress curves of CAs-C1-C5.

Fig. 11. TEM images of (a) CAs-C1, (b) CAs-C3 and (b) CAs-C5.

Fig. 12. SEM images of (a) CAs-C3* and (b) CAs-C5*.

Fig. 13. Thermal conductivities of CAs with different bulk densities.

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