Abstract:

Five NaNO₃/diatomite composite phase change materials (CPCM) for thermal energy storage with different mass content of diatomite were prepared using the mixing and sintering method. Diatomite and NaNO₃ were employed as carrier material and phase change material respectively. The compressive strength, thermal properties, microscopic morphology, photoelectron spectroscopy and thermal analysis were carried out. The compressive strength of the CPCM was enhanced with the mass fraction of diatomite increasing from 30% to 35% and 40% and showed brittle characteristic. When the mass fraction of diatomite reached 45% and 50%, the NaNO₃/diatomite CPCM performed the paddy behavior. The DSC characterization results revealed that diatomite had little effect on the latent heat and phase-change temperature of NaNO₃. The obtained results of LFA tests showed that the thermal conductivity of the CPCM decreased with the increase of the temperature. At the given temperature, the thermal conductivity of the NaNO₃/diatomite CPCM showed upward trend with the mass fraction of diatomite increases. It was also observed that the enhancing rate of the thermal conductivity was eight times larger when increasing the mass fraction of diatomite increased from 30% to 35% compared with the mass fraction increasing from 35% to 50%. Compared with pure NaNO₃, with the diatomite mass fraction increasing from 30% to 50%, the average specific heat capacity of the NaNO₃/diatomite CPCM performed the upward and downward trend within the room temperature-phase transition and the end of the phase transition-the highest temperature range. The SEM and EDS results showed that the NaNO₃/diatomite CPCM have dense structure with NaNO₃ adsorbed uniformly inside the diatomite. The desirable compressive strength and thermal properties of the NaNO₃/diatomite CPCM can be achieved by optimizing the mass ratio of diatomite. The NaNO₃/diatomite CPCM with 35% (mass) diatomite behaved superior overall performance according to the work in this paper.

Key words: diatomite, NaNO₃, composites, phase change, compressive strength, thermophysical properties, adsorption

摘要：

采用混合烧结工艺，通过改变硅藻土载体材料的质量分数制备5种不同参数的NaNO₃/硅藻土复合相变储热材料（CPCM）样品，并对其进行抗压强度测试、热物性测试、能谱表征、微观形貌观察及热性能分析。当硅藻土质量分数从30%增加到35%和40%时，样品抗压强度随之增加，表现出脆性材料特征，当达到45%和50%时，则表现出塑性材料特征。硅藻土的加入和混合烧结处理对NaNO₃的相变几乎没有影响。样品的热导率随温度升高而降低，在同一温度条件下，样品热导率均随硅藻土质量分数的升高基本呈上升趋势，但从30%增加到35%时，热导率的增幅大于从35%增加到50%时热导率的增幅，前者约为后者的8倍。与NaNO₃相比，样品在常温-相变前温度段和相变结束-最高温度段的平均比热容随硅藻土质量分数变化均出现先下降后上升的变化。硅藻土质量分数为35%时，样品内部结构致密，NaNO₃充分均匀吸附于硅藻土的分离独立小单元中。硅藻土质量分数为35%时样品具有较好的抗压强度和储热效果。

关键词: 硅藻土, NaNO₃, 复合材料, 相变, 抗压强度, 热物性, 吸附