Preparation and property enhancement of magnesium nitrate hexahydrate-lithium nitrate eutectic/expanded graphite composite phase change materials

doi:10.19799/j.cnki.2095-4239.2021.0361

Abstract

Abstract:

Magnesium nitrate hexahydrate-lithium nitrate eutectic phase change materials were successfully prepared by melting blending method with different mass percentage of lithium nitrate. The eutectic point of magnesium nitrate hexahydrate-lithium nitrate eutectic salt is around 85∶15 mass ratio. The phase transition temperature and latent heat of eutectic phase change materials were 72.46 ℃ and 193.7 kJ/kg by differential scanning calorimeter. The exothermic platform of eutectic salt was obvious and the supercooling degree was less than 1.5 ℃ by step cooling curve. X-ray diffraction test showed that there was no chemical reaction between magnesium nitrate hexahydrate and lithium nitrate in eutectic salt. After several cold and hot cycles, the eutectic salt has good stability with little change of phase transition temperature and no phase separation phenomenon. In order to improve the photothermal properties of eutectic phase change materials, expanded graphite was added to improve the photothermal properties of the materials due to their weak light absorption. The phase change materials obtained in this work have suitable phase change temperature, high latent heat value, it solves the problem that the phase change temperature of magnesium nitrate hexahydrate mismatches the heating end temperature area and has good light absorption capacity, which can be used as candidate materials in the field of solar clean heating system with the radiator at the end of building heating.

Key words: phase change material, magnesium nitrate hexahydrate, lithium nitrate, expanded graphite

CLC Number:

TK 124

Enda CI, Hui WANG, Xiaoqing LI, Ying ZHANG, Zhenying ZHANG, Jianqiang LI. Preparation and property enhancement of magnesium nitrate hexahydrate-lithium nitrate eutectic/expanded graphite composite phase change materials[J]. Energy Storage Science and Technology, 2022, 11(1): 30-37.

Figures/Tables 11

Fig. 1

Fig. 2

Fig. 3

Fig. 4

Table 1

Fig. 5

Fig. 6

Table 2

Solid-liquid density and volume expansion rate of the sample 3"

$V l$ /mL	$V ˉ l$ /mL	$ρ l$ /(g/cm³)	$V s$ /mL	$V ˉ s$ /mL	$ρ s$ /(g/cm³)	$? V$ /%
40.1	40	1.57	37	37	1.72	9.38
40			37
39.9			37

Table 2

Fig. 7

Fig. 8

Fig. 9

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样品	相变起始温度/℃	相变峰值温度/℃	相变潜热/(kJ/kg)
六水硝酸镁	74.98/90.21	76.14/92.72	160.60
样品1	70.82	73.95/85.36	164.23
样品2	71.58	75.04	172.99
样品3	72.46	74.26	193.70

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