Afriani, Fitri, Evi J, Zaitun, and Yuant Tiandho. “Improvement of Hardness of Hydroxyapatite by the Addition of Silica from Tin Tailings”. Journal of Engineering and Scientific Research 2, no. 2 (December 28, 2020): 85–89. Accessed June 26, 2022. https://jesr.eng.unila.ac.id/index.php/ojs/article/view/48.