To investigate the temporal influence of thermal ageing on the thermal conductivity of bentonite buffer material under high temperature conditions

MX80 bentonite powder was pretreated at 100 ℃ and 200 ℃ for durations of 0

15

30

60

90

120 days. The thermal conductivity of the compacted bentonite samples after pretreatment was measured using the thermal probe method

and the temporal influence was analyzed. The microscopic mechanism underlying the temporal influence on thermal conductivity of bentonite samples was revealed through particle size analysis

X-ray diffraction and thermogravimetric analysis tests. The experimental results indicate that: 1) After high-temperature aging (100 ℃ and 200 ℃)

the thermal conductivity of bentonite samples decreased significantly with increasing thermal aging time t

demonstrating a significant temporal effect. A sharp decline was observed from 0 to 15 days

followed by stabilization after 30 days. The effect was more pronounced at 200 ℃ compared to 100 ℃. 2) High temperatures (100 °C and 200°C) result in the gradual desorption of various forms of water

thinning of the bound water film

and a reduction in the particle size of bentonite samples. Additionally

at 200°C

some montmorillonite minerals in the samples transform into sodium mica. These microstructural evolutions are consistent with the temporal influence observed in the thermal conductivity of the samples. 3)The fundamental reason for the temporal influence of thermal aging on the thermal conductivity of bentonite materials is as follows: At 100 °C

as thermal aging time t increases

the temperature effects lead to the gradual desorption of various forms of water

thinning of the bound water film

reduction in particle size

decrease in solid volume

and increase in gas volume

while the mineral composition remains unchanged. At 200 °C

as the thermal aging time t increases

the aforementioned temperature become more pronounced

and the high temperature causes some montmorillonite minerals to transform into sodium mica

which exhibits a lower thermal conductivity .