High porosity and low thermal conductivity high entropy (Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)C

doi:10.1016/j.jmst.2019.04.006

Abstract

Abstract:

Porous ultra-high temperature ceramics (UHTCs) are promising for ultrahigh-temperature thermal insulation applications. However, the main limitations for their applications are the high thermal conductivity and densification of porous structure at high temperatures. In order to overcome these obstacles, herein, porous high entropy (Zr_0.2Hf_0.2Ti_0.2Nb_0.2 Ta_0.2)C was prepared by a simple method combing in-situ reaction and partial sintering. Porous high entropy (Zr_0.2Hf_0.2Ti_0.2Nb_0.2Ta_0.2)C possesses homogeneous microstructure with grain size in the range of 100-500 nm and pore size in the range of 0.2-1 μm, which exhibits high porosity of 80.99%, high compressive strength of 3.45 MPa, low room temperature thermal conductivity of 0.39 W·m^-1 K^-1, low thermal diffusivity of 0.74 mm²·s^-1 and good high temperature stability. The combination of these properties renders porous high entropy (Zr_0.2Hf_0.2Ti_0.2Nb_0.2Ta_0.2)C promising as light-weight ultrahigh temperature thermal insulation materials.

Key words: Ultrahigh temperature ceramics (UHTCs), High entropy ceramics, (Zr_0.2Hf_0.2Ti_0.2 Nb_0.2Ta_0.2)C, Thermal conductivity, Porosity

Heng Chen, Huimin Xiang, Fu-Zhi Dai, Jiachen Liu, Yiming Lei, Jie Zhang, Yanchun Zhou. High porosity and low thermal conductivity high entropy (Zr_0.2Hf_0.2Ti_0.2Nb_0.2Ta_0.2)C[J]. J. Mater. Sci. Technol., 2019, 35(8): 1700-1705.

Figures/Tables 6

Fig. 1. The linear shrinkage, linear shrinkage rate, TG and DTG curves recorded during the heating of green body of porous HE (Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)C.

Table 1 Porosity, sintered density, theoretical density, radical shrinkage and compressive strength of porous HE (Zr0.2Hf0.2Ti0.2Nb0.2 Ta0.2)C together with those of TiC, NbC, TaC, ZrC [25], HfC [25] for comparison.

Porous UHTCs	Porosity (%)	Sintered density (g·cm^-3)	Theoretical density (g·cm^-3)	Radial shrinkage (%)	Compressive strength (MPa)
(Zr_0.2Hf_0.2Ti_0.2 Nb_0.2Ta_0.2)C	80.99	1.79	9.42	14.21	3.45
NbC	80.13	1.55	7.79 [30]	15.93	5.01
TiC	80.24	0.97	4.91 [31]	24.13	4.39
TaC	82.62	2.52	14.50 [30]	18.56	3.02
ZrC	68.74	2.06	6.59 [31]	21.97	8.28
HfC	77.82	2.82	12.67 [31]	20.30	5.51

Fig. 2. (a) XRD patterns of as-prepared porous HE (Zr0.2Hf0.2Ti0.2Nb0.2 Ta0.2)C and TiC, NbC, TaC, ZrC [25] and HfC [25], (b) SEM micrograph of as-prepared porous HE (Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)C with porosity of 80.99%.

Fig. 3. TEM-EDS analysis of porous HE (Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)C, (a) TEM micrograph, (b)-(f) the corresponding EDS mapping of Zr, Hf, Ti, Nb and Ta elements.

Table 2 Thermal diffusivity (α), specific heat capacity (Cp) and thermal conductivity (κ) of dense (Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)C [21] and porous HE (Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)C prepared in this work.

Temp (^oC)	Dense (Zr_0.2Hf_0.2Ti_0.2Nb_0.2Ta_0.2)C			Porous (Zr_0.2Hf_0.2Ti_0.2Nb_0.2Ta_0.2)C
Temp (^oC)	α (mm² ·s^-1)	C_p (J·mol^-1 ·K^-1)	κ (W·m^-1 ·K^-1)	α (mm² ·s^-1)	C_p (J·mol^-1 ·K^-1)	κ (W·m^-1 ·K^-1)
25	-	-	-	0.74	38.56	0.39
29.5	3.6	24.89	6.45	0.74	38.88	0.40
50.7	3.68	20.98	5.56	0.76	40.28	0.42
70.8	3.73	20.19	5.42	0.76	41.42	0.43
100	-	-	-	0.75	42.60	0.44
200	-	-	-	0.80	44.73	0.49

Fig. 4. (a) Linear shrinkage curve of porous HE (Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)C during its synthesis process and during the second round heat treatment, (b) SEM micrograph of porous HE (Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)C after second round heat treatment, (c) XRD pattern of as-prepared porous HE (Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)C and that after second round heat treatment.

References

[1]	P. Colombo, Science 322 (2008) 381-383.
[2]	G.L. Messing, A.J. Stevenson, Science 322 (2008) 383-384.
[3]	Y.C. Zhou, H.M. Xiang, Z.H. Feng, Z.P. Li, J. Am. Ceram. Soc. 99 (2016) 2110-2119.
[4]	W.G. Fahrenholtz, G.E. Hilmas, A.L. Chamberlain, J.W. Zimmermann, J. Mater. Sci. 39 (2004) 5951-5957.
[5]	H.P. Yuan, J.G. Li, Q. Shen, L.M. Zhang, Int. J. Refract. Metals Hard Mater. 16 (2013) 225-231.
[6]	E. Landi, D. Sciti, C. Melandri, V. Medri, J. Eur. Ceram. Soc. 33 (2013) 1599-1607.
[7]	J.M. Jiang, S. Wang, W. Li, Z.H. Chen, J. Alloys. Compd. 695 (2017) 2295-2300.
[8]	Y.C. Zhou, H.M. Xiang, Z.H. Feng, Z.P. Li, J. Mater. Sci. Technol. 31 (2015) 285-294.
[9]	K. Yada, H. Masaoka, Y. Shoji, T. Tanji, J. Electron Microsc.Tech. 12 (1989) 252-261.
[10]	S.S. Hwang, A.L. Vasiliev, N.P. Padture, Mater. Sci. Eng. A 464 (2007) 216-224.
[11]	F. Monteverde, R. Savino, J. Eur. Ceram. Soc. 27 (2007) 4797-4805.
[12]	F. Monteverde, Corros. Sci. 47 (2005) 2020-2033.
[13]	Y.F. Shi, Y. Meng, D.H. Chen, S.J. Cheng, P. Chen, H.F. Yang, Y. Wan, D.Y. Zhao, Adv. Funct. Mater. 16 (2006) 561-567.
[14]	M. Gasch, D. Ellerby, E. Irby, S. Beckman, M. Gusman, S. Johnson, J. Mater. Sci. 39 (2004) 5925-5937.
[15]	S.R. Levine, E.J. Opila, M.C. Halbig, J.D. Kiser, M. Singh, J.A. Salem, J. Eur. Ceram. Soc. 22 (2002) 2757-2767.
[16]	F. Monteverde, A. Bellosi, L. Scatteia, Mater. Sci. Eng. A 485 (2008) 415-421.
[17]	K. Upadhya, J.M. Yang, W.P. Hoffman, Am. Ceram. Soc. Bull. 76 (1997) 51-56.
[18]	E. Wuchina, E. Opila, M. Opeka, W. Fahrenholtz, I. Talmy, Electrochem. Soc. Interf. 16 (2007) 30.
[19]	W.G. Fahrenholtz, E.J. Wuchina, W.E. Lee, Y.C. Zhou, New Jersey, 2014, pp. 1-5.
[20]	E. Sani, L. Mercatelli, J.L. Sans, L. Silvestroni, D. Sciti, Opt. Mater. 36 (2013) 163-168.
[21]	X.L. Yan, L. Constantin, Y.F. Lu, J.F. Silvain, M. Nastasi, B. Cui, J. Am. Ceram. Soc. 101 (2018) 4486-4491.
[22]	J. Zhou, J. Zhang, F. Zhang, B. Niu, L. Lei, W. Wang, Ceram. Int. 44 (2018) 22014-22018.
[23]	L. Feng, W.G. Fahrenholtz, G.E. Hilmas, Y. Zhou, Scripta Mater. 162 (2019) 90-93.
[24]	B. Ye, T. Wen, K. Huang, C.Z. Wang, Y. Chu, J. Am. Ceram. Soc. (2019), http://dx.doi.org/10.1111/jace.16295.
[25]	H. Chen, H.M. Xiang, F.Z. Dai, J.C. Liu, Y.C. Zhou, J. Mater. Sci. Technol. (2019), To be published.
[26]	X.F. Wang, H.M. Xiang, X. Sun, J.C. Liu, F. Hou, Y.C. Zhou, J. Am. Ceram. Soc. 98 (2015) 2234-2239.
[27]	Q.Q. Guo, H.M. Xiang, X. Sun, X.H. Wang, Y.C. Zhou, J. Eur. Ceram. Soc. 35 (2015) 3411-3418.
[28]	H. Chen, H.M. Xiang, F.Z. Dai, J.C. Liu, Y.C. Zhou, J. Mater. Sci. Technol. (2019), To be published.
[29]	L.E. Toth, Transition Metal Carbides and Nitrides, Academic Press, New York, 1971, pp. 11-14.
[30]	H.O. Pierson, William Andrew, 1996, pp. 82.
[31]	H.O. Pierson, William Andrew, 1996, pp. 56.
[32]	J.H. She, T. Ohji, Mater. Chem. Phys. 80 (2003) 610-614.
[33]	N. Claussen, S. Wu, D. Holz, J. Eur. Ceram. Soc. 14 (1994) 97-109.
[34]	D.D. Jayaseelan, N. Kondo, M.E. Brito, T. Ohji, J. Am. Ceram. Soc. 85 (2002) 267-269.
[35]	Y. Yang, Y. Wang, W. Tian, Z. Wang, C.G. Li, Y. Zhao, H.M. Bian, Scripta. Mater. 60 (2009) 578-581.
[36]	D.B. Miracle, O.N. Senkov, Acta Mater. 122 (2017) 448-511.
[37]	M.H. Tsai, J.W. Yeh, Mater. Res. Lett. 2 (2014) 107-123.