Evaluation of Nano-Scale ZnO Coatings Prepared via the Sol–Gel Method on Cast Iron Piston Rings: Tribological Performance. EJIITEK [Internet]. 2026 Sep. 27 [cited 2026 Sep. 27];16(2):501-18. Available from: https://e-journal.upm.ac.id/index.php/energy/article/view/energy.v16i2.p501-518