Thermochemical Heat Storage Properties of Mechanical Activated Co۳O۴-۵ wt. % Al۲O۳ and Co۳O۴-۵ wt. % Y۲O۳ Composite Powders

The main problem of cobalt oxide as a thermochemical heat storage material is its slow re-oxidation kinetics. In addition, redox (reduction and oxidation) behavior of as-received Co۳O۴ is degraded with increasing the number of redox cycles. To overcome this drawback, Al۲O۳ and Y۲O۳ were added to Co۳O۴ and  effect of mechanical activation time (۲, ۴, ۸, and ۱۶ h) on the redox behavior (weight change value/rate, redox reversibility, reduction and re-oxidation values, and particle morphologies) of Co۳O۴-۵ wt.% Al۲O۳ and Co۳O۴-۵ wt. % Y۲O۳ composites was investigated using thermogravimetry method. The composites were studied by SEM, EDS, and X-ray map analyses before and after redox reactions. Results showed that increasing the mechanical activation time improves the redox kinetics of Co۳O۴-۵wt. % Al۲O۳ in comparison with as-received Co۳O۴. Although, the alumina-containing samples, activated in short time showed the better redox kinetics than samples activated in long time. It was found that increasing the activation time to more than ۸ h for alumina-containing samples reduces the redox kinetics due to decreasing the positive effect of Al۲O۳ in controlling the particle size growth and sintering. In the case of Co۳O۴-۵wt. % Y۲O۳, an increase in activation time generally reduced the redox kinetics. As a result, redox reactions in a ۱۶ h-activated Co۳O۴-۵wt.% Y۲O۳ composite was completely stopped. In addition, results showed that weak performance of Co۳O۴-۵ wt. % Y۲O۳ is related to intensive sintering and growth of cobalt oxide particles during redox reactions

کلیدواژه ها:

Cobalt oxide ، Redox reactions ، Reversibility ، Thermochemical heat storage ، Mechanical activation