Wijaya, A., J. W. Soedarsono, and A. P. Laksana. “Study of Mixing Purple Sweet Potato and Turmeric Extract As Green Corrosion Inhibitor for API-5L in NaCl 3.5% Environment”. Jurnal Pendidikan Teknologi Kejuruan, vol. 4, no. 4, Nov. 2021, pp. 140-5, doi:10.24036/jptk.v4i4.21823.