XUE JING, W. “Ultrasonic Assisted Synthesis of Nano-Sized NaY Zeolite Composite from Metakaolin by Hydrothermal Method”. Asian Journal of Chemistry, vol. 21, no. 9, Mar. 2010, pp. 7041-8, https://asianpubs.org/index.php/ajchem/article/view/12218.