Decomposition performance and kinetics analysis of magnesium hydroxide regulated with C/N/Ti/Si additives for thermochemical heat storage

MgO/Mg(OH)2 is a potential thermochemical material with high heat density and stable characteristics. Four additives including Carbons, Carbides, Nitrides and Titanates were selected for modification. The decomposition behavior and kinetics analysis were both investigated. It is found that Titanates has a catalytic effect, and the tested energy storage density can be increased to 971 J/g. The spectral absorption of candidate material with 6% graphite can reach to more than 50% and 6% CaTiO3 has an extremely high absorption in the short wave segment. In microscopic morphology, Mg(OH)2 particles sintered at high temperature will form adhesion agglomeration. Due to the special microstructures of candidate materials, agglomeration phenomenon is effectively alleviated and the candidate materials with 6% graphite or CaTiO3 are both ideal modified materials. The optimized mechanism of modified material with 6% CaTiO3 was illustrated by model. To investigate the kinetics mechanism, the model of non-isothermal decomposition was developed. The activation energies of pure material, sample with 6%graphite and sample with 6%CaTiO3 are 141 kJ/kg, 113 kJ/kg and 122 kJ/kg respectively. The shape factor polynomials and kinetic governing equations were obtained. According to the established kinetics equations, the heating processes at 8 K, 12 K and 25 K/min were predicted. The study can provide a necessary kinetics reference for the numerical calculation of thermochemical heat storage.

Automated summary

The potential thermochemical material MgO/Mg(OH)2 was modified with four additives and its decomposition behavior and kinetics were studied. It was found that CaTiO3 had a catalytic effect and increased the energy storage density to 971 J/g. Additionally, adding 6% graphite to the candidate material resulted in spectral absorption of more than 50%. The study provides necessary kinetics reference for numerical calculation of thermochemical heat storage.