Sintering Behavior of Simulating Core FCM Fuel via Hot Oscillatory Pressing

doi:10.15541/jim20230492

Abstract

Abstract:

Fully ceramic micro-encapsulated (FCM) fuel has become the focus of nuclear energy research because of its good inherent safety. In order to overcome the difficulty of SiC matrix densification, this study focused on the sintering behavior of simulating core FCM fuel via hot oscillatory pressing (HOP), taking the advantages of HOP to accelerate mass transfer and reduce sintering temperature. The influence of oscillatory sintering temperature, oscillatory time and oscillatory pressure on the matrix densification behavior was studied, and the results were compared with those of hot pressing (HP). The results indicate that the oscillatory sintering temperature, holding time, and median pressure have important effects on matrix densification, while the amplitude of oscillatory pressure has little effect. Compared with HP, the density of the samples is increased by HOP, and the density of sample sintered at 1850 ℃ via HOP is 99.99%. The grain size of the samples via HOP is smaller, and the grain size of the sample sintered via HOP at 1850 ℃ is (284±4) nm, which is ~27% less than that of the sample sintered via HP at the same temperature. The hardness of the samples sintered via HOP is higher, and the hardness of the sample sintered via HOP at 1850 ℃ is (26.7±0.4) GPa. When the density of sample is 90%, the stress exponent n=1 and activation energy Q=430 kJ/mol are obtained by using the modified constitutive equation of HP. The dominant mechanism of densification is grain boundary sliding, which is accommodated by the grain boundary diffusion.

Key words: fully ceramic micro-encapsulated fuel, SiC matrix, hot oscillatory pressing, densification mechanism

CLC Number:

TL352

HE Zongbei, CHEN Fang, LIU Dianguang, LI Tongye, ZENG Qiang. Sintering Behavior of Simulating Core FCM Fuel via Hot Oscillatory Pressing[J]. Journal of Inorganic Materials, 2024, 39(5): 501-508.

Figures/Tables 14

Fig. 1 Schematic diagram of hot oscillatory pressing

Table 1 Sintering parameters of simulated core FCM fuel via hot oscillatory pressing and hot pressing

No.	T/℃	t/h	σ_m/MPa	σ_a/MPa
HOP-1	1600	1	20	5
HOP-2	1600	2	20	5
HOP-3	1650	1	20	5
HOP-4	1650	2	20	5
HOP-5	1700	1	20	5
HOP-6	1700	2	20	5
HOP-7	1750	0	20	5
HOP-8	1750	1	20	5
HOP-9	1750	2	20	5
HOP-10	1750	2	10	5
HOP-11	1750	2	15	5
HOP-12	1750	2	20	1
HOP-13	1750	2	20	3
HOP-14	1800	2	20	5
HOP-15	1850	2	20	5
HP-1	1700	2	20	0
HP-2	1750	2	20	0
HP-3	1800	2	20	0
HP-4	1850	2	20	0

Fig. 2 Densification curves of samples sintered via hot oscillatory pressing at different temperatures (a) Relative density-time curves; (b) Densification rate-relative density curves

Table 2 Densities and open porosities of samples under different holding time

No.	T/℃	t/h	ρ/(g·cm^-3)	Open porosity/%	ρ_m/(g·cm^-3)
HOP-7	1750	0	2.65	26.57	2.04
HOP-8	1750	1	3.63	3.68	3.00
HOP-9	1750	2	3.75	1.48	3.13

Fig. 3 Densification curves of samples sintered via hot oscillatory pressing under different median pressures

Fig. 4 Densification curves of samples sintered via hot oscillatory pressing at different pressure amplitudes

Fig. 5 XRD patterns of samples sintered via hot oscillatory pressing at different temperatures

Fig. 6 Densification curves of samples sintered via hot oscillatory pressing and hot pressing at different temperatures

Fig. 7 Grain size of samples sintered via hot oscillatory pressing and hot pressing as function of (a) sintering temperature and (b) relative density

Fig. 8 SEM images of fracture surface and grain size distributions of samples sintered at 1850 ℃ (a, c) Hot oscillatory pressing (2 h-(20±5) MPa); (b, d) Hot pressing (2 h-20 MPa)

Fig. 9 Hardness of samples sintered via hot oscillatory pressing and hot pressing as function of (a) sintering temperature and (b) porosity

Fig. 10 Densification rate-effective stress plots of samples sintered via hot oscillatory pressing by taking n=1

Table 3 Similarity between densification rate and effective stress at different stress exponents (n)

T/℃	n=1	n=2	n=3
1700	0.9994	0.9740	0.9476
1750	0.9773	0.9986	0.9874
1800	0.9904	0.9647	0.9528
1850	0.9858	0.9742	0.9695

Fig. 11 Arrhenius relationship curve of samples sintered via hot oscillatory pressing at different temperatures

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