Influence of particle Size and Ammonia on Thermochemical Properties of Ca(OH)2@SiO2 Nano-Composites

Abstract

Energy crises in one of the main issues for under developing countries in current era. Scientist and researchers have shifted their focus on renewable energy resources. Wind energy, Hydropower, Ocean Energy, Bio Energy and Thermal Energy etc are some of the main examples of sustainable energy resources. Thermal energy can be a promising candidate as sustainable, less expensive and environment friendly energy source. Thermo- Chemical Energy Storage is an efficient method to resolve the storing problem of the thermal energy in high density. Due to its structure and higher thermal stability, the cyclic process of Ca(OH)2 & CaO is one of the best available cycles for high density thermal energy storage. At the same time the effects of agglomeration and inhomogeneity of particles can reduce thermal efficiency as well as mass and heat transport. This study is proposed to see a comparative effect between nano and micro level silica coated Ca(OH)2 particles. Silica coating can prevent early conversion of calcium hydroxide to calcium oxide, and it can also resist the conversion of calcium hydroxide to calcium carbonate. At high temperature , around 410°C to 425°C, when we got conversion of calcium hydroxide to calcium oxide, we get high chances of getting calcium silicate formation in normal atmosphere. We avoid the formation of calcium carbonate at this stage because of inert atmosphere provided during applicational testing. In start we have purchase sigma ducson micro sized calcium hydroxide particles. Due to low surface to volume ration, we got low reactivity of these particles with air. This was the major reason of not finding calcium carbonate in these particles. On the other side, silica coating was also done on synthesized nanoparticles in lab from sole gel method. These particles attain higher surface to volume ratio. This results higher surface to volume ration that results in higher reactivity with air. Resultantly it shows 8-10% calcium carbonate weight loss in synthesized nanoparticles in TGA-DSC. In XRD, a clear result for larger sized particles for proper hexagonal structure got observed. But in case of nanoparticles, these same peaks were found with some extra peaks for calcium carbonate formation. This distorts the pure crystal structure of calcium hydroxide mixed with calcium carbonate. In SEM analysis, we see the morphological difference between nano and micro sized particles. The surface to volume ration describes the difference in agglomeration and shape change in pure calcium hydroxide. In case of carbonate formation, they didn’t exhibit round and spherical share. The EDX analysis shows almost same ratios in elemental analysis in pure and different levels of coating. FTIR show the intensity wise presence of different functional groups in all respective samples. Similarly, RAMAN Spectroscopy used to find same analysis by scattering iv of laser from different functional groups. TGA-DSC was used for applicational testing under an inert atmosphere created by nitrogen. The percentage weight loses at different stages while having different heating rates. All conversions from one to another shows weight lose according to respective presence of specific compound that gets break down at that temperature. DSC analyses were used to find heat of enthalpy calculations, which further help in finding out activation energy. Specific values of activation energy guide us about differentiating between different compounds break down at same temperature. The effect of catalyst got studied for the formation composite ions and their effect got studied in all different characterization techniques. While applicational testing, the combine effect of ammonia and broken ethyl groups from TEOS plays a vital role in quality or sustainability of coating silica over agglomerated and or larger size single particles. By changing heating rates and comparing all the catalytic sample with the other samples without catalyst and same percentage of coating, we can separate out the effect of catalytic activity of ammonia and behaviour of silica in the presence or absence of ammonia. In future plans, we want to enhance electrical conductivity as well. After making composite of calcium hydroxide with any conductive material, we will coat it with silica to see increment in both electrical and thermal conductivity. Secondly we want to form a set-up, where we can recycle our samples for as many cycles as many possible. This will lead us to one of the possible samples as the most suitable for larger scale energy storage.