The review of sodium acetate trihydrate

Introduction

Sodium acetate trihydrate (SAT) is a hydrated salt with a phase transition temperature of 58°C and a latent heat value of 266kJ/kg. Due to its stable phase transition temperature, high latent heat of phase transition, non-toxicity, non-corrosion and good economy, The application is more extensive. However, as an inorganic phase change material, it also has the problems of large undercooling, poor phase separation and poor circulation effect. Choi Wenlong et al. used the nucleating agent method, vibration method and stirring method to eliminate the supercooling degree of sodium acetate trihydrate through experimental methods [1]. By adding different kinds of additives and nucleating agents, Wang Zhiping found that adding 5% disodium hydrogen phosphate dodecahydrate and 3% sodium carboxymethyl cellulose to sodium acetate trihydrate can effectively make the material annealed. cooling down to 2.02°C and prevent phase separation [2]. TAKAHIRO et al. added 1% sodium pyrophosphate as a nucleating agent to sodium acetate trihydrate, and the supercooling degree was reduced to less than 5 °C. After multiple cycle experiments, the material still had good heat storage performance [3].

 Supercooling characteristics of sodium acetate trihydrate

The chemical formula of Sodium acetate trihydrate is NaCH₃COO.3H₂0. Sodium acetate trihydrate is a promising heat storage material (m.p:58°C, heat of fusion, AHf~s:252 kJ/ kg (60.3 cal/g)[1]. This salt melts incongruently, producing anhydrous NaCH₃COO. Besides, the salt can supercool heavily. Consequently, two problems of this hydrate, supercooling and phase separation, must be solved before practical use as a latent heat storage material. Supercooling characteristics of NaCH3COO. 3H20 are similar to those of Na₂SEO₃.5H₂0 and CaC₁₂.6H₂0. During nucleation, the chemical potential of water must increase, as the water molecules rearrange themselves into the surroundings of the solid hydrate, because the chemical potential of water in crystalline state, Ixc, is higher than that in the supercooled melt, Ixm. The difference of the chemical potential (A IXH₂0 = IXc -- IX,.) may be considered a rough measure of the barrier to nucleation. Infrared spectroscopic characteristics of these molten hydrates have been clarified by us recently[4]. 

Application of Sodium acetate trihydrate in composite phase change materials

The composite phase  change material  was formed by expanded graphite  (EG)  with porous mesh structure and sodium acetate trihydrate (SAT) as the substrate [5]. The effects of EG on the properties of  SAT  were  studied  by  using  scanning  electron  microscope,  temperature  data  logger,  differential scanning  calorimeter,  and  Hot  Disk  thermal  constant  analyzer  etc.  The  results  showed  that  the  EG could  not  reduce  the  degree  of  supercooling  of  SAT,  but  it  could  largely  improve  the  thermal conductivity  of  the  material.  EG  had  little  effect  on  the  latent  heat  value  and  phase  transition temperature  of  SAT.  EG  could  reduce  the  phase  separation  of  SAT  and  improve  its  durability. Compared  to  the  pure  SAT,  the  degree  of  supercooling  of  composite  PCM  (7%  EG+1%  disodium hydrogen  phosphate  +  SAT)  was  reduced  by  49℃.  Thermal  conductivity  of  the  composite  PCM  was doubled. Latent heat and phase transition temperature of the composite PCM were basically the same. After 50 cycles, the change of latent heat of  composite  PCM  was kept  within 1.4%,  which had great 
potential in thermal storage. As the picture 1 showed, there is ET/SAT composite material on SEM.

Picture 1 EG/SAT composite material [5]

Reference

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