Pengaruh kombinasi ekstrak daun Physalis angulata daun ciplukan dan daun Cassia angustifolia daun jati cina sebagai inhibitor ramah lingkungan dengan perbandingan 50:50 pada baja karbon API 5L diinvestigasi. Pengujian dilakukan dalam lingkungan HCl 1M. Pengujian yang dilakukan meliputi polarisasi potensiodinamik, kehilangan berat, dan EIS. Senyawa antioksidan diinvestigasi melalui pengujian FTIR. Sesuai dengan pengujian FTIR, senyawa antioksidan yang terkandung pada kombinasi ekstrak ini adalah flavonoid. Variabel yang digunakan adalah konsentrasi inhibitor, yaitu 10 ml, 30 ml, dan 50 ml. Diketahui bahwa semakin tinggi konsentrasi yang diberikan, maka semakin tinggi kemampuan inhibitor dalam menginhibisi permukaan baja dimana efisiensi inhibitor paling tinggi didapatkan dengan konsentrasi 50 ml. Kombinasi ekstrak daun ciplukan dan daun jati merupakan inhibitor jenis campuran yang lebih dominan ke katodik. Metode adsorpsi inhibitor ini mengikuti adsorpsi isotherm Langmuir dengan tipe adsorpsi fisika atau physisorption.

---

The effect of combination of Physalis angulata leaf and Cassia angustifolia leaf extract as green inhibitor with a 50:50 ratio for API 5L steel was investigated. This experiment was carried in 1M HCl solution by using different concentrations as variables which is 10 ml, 30 ml, and 50 ml inhibitor extracts. This experiment was evaluated using potentiodynamic polarization, EIS, and weight loss. The antioxidant compound was investigated using FTIR and was found to be flavonoid. It was found that the capability of the inhibitor to inhibit the steel surface from the environment increases with increasing concentration, which 50 ml concentration is found to have the best efficiency of all concentrations. Combination of physalis angulata leaf and cassia angustifolia leaf extract is found to be a mixed type inhibitor with predominant cathodic effectiveness. The adsorption of this inhibitor on the steel surface was predominantly through physisorption and obeyed Langmuir adsorption isotherm.