Suherman, Suherman, et al. “Synthesis and Characterisation of Biolubricants Castor Oil (Ricinus Communis L.) Using a Homogeneous Catalyst for Hydraulic Engine Applications”. Jurnal Rekayasa Mesin, vol. 20, no. 2, Aug. 2025, pp. 217-28, doi:10.32497/jrm.v20i2.6669.