Preparation of high solid content stable yttrium sol for lost wax casting by chelation method

This study presents a malic-acid-mediated chelation strategy for preparing high-solid-content, aggregation-resistant yttrium sols tailored for titanium–aluminide investment casting. By systematically tuning the molar ratios of YCl 3 , Y(OH) 3 , and malic acid, the coordination structure and colloidal stability were clarified. Under optimal conditions (YCl 3 :Y(OH) 3  = 10:2; Y(OH) 3 :malic acid = 1:2), malic acid coordinated with yttrium through combined monodentate and bidentate modes, forming stable five- and six-membered chelate rings that effectively suppressed hydrolysis. The optimized sol achieved a solid content of 26.70 % with a zeta potential of 27 mV. In contrast, acetic, oxalic, and acrylic acids predominantly formed monodentate complexes, resulting in inferior stability. A critical solid-content threshold was identified, beyond which rapid gelation occurred. To enhance sol uniformity and mitigate the adverse effects of residual chloride ions during shell fabrication, the sol was dialyzed for 30 min in a pH 3.5 malic acid solution. After dialysis, the sol retained a solid content above 24 %, exhibited a zeta potential of 27.3 mV, and showed uniformly distributed spherical particles with an average size of 75 nm, confirming excellent stability and suitability for investment casting applications.