Preparation And Properties Investigation Of Calcium Chloride Hexahydrate/expanded Graphite Composite As Shape-stabilized Phase Change Materials

Phase change materials use latent heat during phase change process to store and release energy,controlling the temperature of surrounding environment.As typical inorganic phase change materials,salt hydrates have advantages of low price,high heat storage density,large latent heat,high thermal conductivity,non-toxic and non-flammable and so on,thus they are potential materials for energy storage applications.However,they also have some shortages of supercooling,phase separation and solid-liquid phase change leakage,which restrict the large-scale application of them.Shape-stabilized composites combine phase change materials with adsorbent matrix to make the shape of phase change materials stable,which can keep soild shape during heat storage process,avoiding leakage of solid-liquid phase change leakage and improve supercooling and phase separation to some extent.In this paper,we used calcium chloride hexahydrate?CaCl₂·6H₂O,CCH?as phase change material,whose phase change temperature is close to room temperature.And with porous expanded graphite?EG?and industrial crushed expanded graphite powder?EGp?as adsorbent matrices,prepared CCH/EG and CCH/EGp shape-stabilized composite phase change materials.Then,surfactant OP-10 and nucleating agent SrCl₂·6H₂O were added for modification of the composites.The phase structures,thermal properties,microstructures,seal properties,supercooling,thermal conductivities and cycle stabilities of the composites were characterized by XRD,DSC,SEM,heating test,cooling curves,thermal conductivity tests,etc.Finally,phase change materials,with simple preparation process,good properties and low cost composite were obtained.1.CCH/EG and CCH/EGp composite phase change materials were prepared by vacuum impregnation method,XRD showed that there were physical adsorption and no new substance generated,and cooling curves showed that the supercooling degree were still large.2.The addition of surfactant OP-10 can effectively increase the binding ability of CaCl₂·6H₂O to matrix and improve the sealing ability of the composites.The contact angle test showed that the optimum amount of OP-10 is 5 wt%.The results of sealing test showed that the optimum amount of CaCl₂·6H₂O combined with EG is 90 wt%,the optimum amount of CaCl₂·6H₂O combined with EGp is 80 wt%,and the addition of OP-10 did not reduce the supercooling degree of the composites.3.The addition of nucleating agent SrCl₂·6H₂O significantly reduced the supercooling degree.The supercooling degree of OSr-CCH/10EG and OSr-CCH/20EGp were within 3 ^oC and 1.5 ^oC during 100 thermal cycles and the latent heat of them were dropping by 9.38%and 5.13%respectively,showing good cycle stabilities.The thermal conductivities of the composites significantly increased in comparision with CaCl₂·6H₂O,decreased after being modified by OP-10 and SrCl₂·6H₂O.The thermal conductivity of OSr-CCH/10EG was 4.092 W/m·K,4.27-fold higher than CaCl₂·6H₂O.Meanwhile,the thermal conductivity of OSr-CCH/20EGp was 3.523 W/m·K,3.68-fold higher than CaCl₂·6H₂O.