Mechanisms of gelation induced by laser irradiation for CaO powder dispersed in ethanol – Formation of calcium acetate and its role in gelation

Our recent study of gelation induced by laser ablation of CaO powders dispersed in ethanol proposed that CaO particle size composition would be an important factor affecting gelation because gelation is brought about by mixing a colloid composed of laser-fragmented particles and a raw CaO colloid. The present work was conducted to clarify this point. Results showed that, differing from our assumption, laser-fragmented particles are not necessary for gelation because gelation occurred even when laser-fragmented particles were removed from a laser-irradiated colloid before mixing it with a raw CaO colloid. Moreover, findings revealed that acetic acid generated by laser-induced oxidation of ethanol causes gelation, as confirmed by the fact that gelation also occurred when a proper amount of acetic acid was added to a raw CaO colloid. Results also revealed that nanofibers composed of calcium acetate hydrate play an important role in the gel structure formation. Results demonstrated that the gel structure and composition can be controlled simply by adjusting the amount of acetic acid without laser irradiation, suggesting that the results obtained from this study are useful as a newly developed and simple method of preparing calcium gel with various structures.