Preparation and Characterization of KNO3/Diatomite Shape-Stabilized Composite Phase Change Material for High Temperature Thermal Energy Storage

Abstract

Abstract:

A new potassium nitrate (KNO₃)/diatomite shape-stabilized composite phase change material (SS-CPCM) was prepared by the mixing and sintering method. KNO₃ served as the phase change material (PCM) for thermal energy storage, while diatomite acted as the carrier matrix to provide the structural strength and prevent the leakage of PCM. It was found that KNO₃ could be retained 65 wt% into pores and on surfaces of diatomite without the leakage of melted KNO₃ from the SS-CPCM. The calculated filling rate of molten KNO₃ that could enter into the disc-like shape pore of diatomite verified the scanning electronic microscopy images of SS-CPCM. X-ray diffraction and Fourier transform infrared spectroscopy results showed that no reaction occurred between KNO₃ and diatomite, performing good compatibility. According to the differential scanning calorimetry results, after 50 thermal cycles, the phase change temperatures for melting and freezing of SS-CPCM with 65 wt% KNO₃ were changed from 330.23?°C and 332.90?°C to 330.11?°C and 332.84?°C and corresponding latent heats varied from 60.52?J/g and 47.30?J/g to 54.64?J/g and 41.25?J/g, respectively. The KNO₃/diatomite SS-CPCM may be considered as a potential storage media in solar power plants for thermal energy storage.

Key words: Potassium nitrate, Diatomite, Shape-stabilized composite phase change material, Thermal energy storage

Deng Yong,Li* Jinhong,Qian Tingting,Guan Weimin,Wang Xiang. Preparation and Characterization of KNO3/Diatomite Shape-Stabilized Composite Phase Change Material for High Temperature Thermal Energy Storage[J]. J. Mater. Sci. Technol., 2017, 33(2): 198-203.

Figures/Tables 10

Table 1 Physical and thermal properties of inorganic salt compounds

Compound	Specific heat capacity (J/(g K))	Density (g/cm³)	Thermal conductivity (W/(m K))	Melting temperature (°C)	Heat of fusion (J/g)	Volume change (%)
LiNO₃	1.78	2.38	0.58	254	360	21.5
NaNO₂	1.65	2.2	0.53	270	180	16.5
NaNO₃	1.78	2.26	0.51	306	182	10.7
NaOH	0.82	2.13	—	323	170	—
KNO₃	1.43	2.11	0.45	334	100	3.3
KOH	1.17	2.04	0.598	380	149.7	—
Ba(NO₃)₂	0.58	3.23	—	594	209	—
Sr(NO₃)₂	1.00	2.11	—	608	221	—
KCl	1.87	1.98	11.0	771	353	—
NaCl	2.33	2.16	6.24	802	482	—
Na₂SO₄	0.90	2.68	0.598	884	165	—

Table 2 Chemical components of the diatomite sample

Constituent	SiO₂	Al₂O₃	Fe₂O₃	K₂O	CaO	H₂O	MgO	Na₂O	P₂O₅	TiO₂
Ratio (%)	86.82	3.21	1.60	0.56	0.46	0.44	0.43	0.25	0.22	0.15

Fig.1 Schematic diagram of preparation of KNO3/diatomite SS-CPCM

Fig.2 Photographs of SS-CPCM with different ratios of diatomite and schematic of the calculation of filling rate

Fig.3 FT-IR spectra of diatomite, KNO3, and SS-CPCM

Fig.4 XRD patterns of diatomite, KNO3, and SS-CPCM

Fig.5 Effects of KNO3 content on bulk density and apparent porosity of SS-CPCM

Fig.6 SEM images of diatomite (a, c) and SS-CPCM with 65 wt% KNO3 (b, d)

Fig.7 DSC curves of SS-CPCM with 65 wt% KNO3 before and after 50 thermal cycles

Fig.8 Nonlinear relationship between weight loss and thermal cycle numbers

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