Efek inhibisi korosi dan sifat-sifat adsorpsi oleh ekstrak kulit buah kakao (Theobroma cacao) pada baja lunak (mild steel) dalam larutan asam 1,5M HCl telah dipelajari menggunakan teknik konvensional metode berat hilang pada variasi waktu, konsentrasi dan suhu. Parameter-parameter termodinamika seperti energi aktivasi, entalpi, entropi dan perubahan energi bebas dihitung. Polarisasi elektrokimia telah dievaluasi untuk memastikan jenis inhibitor. Spektra infrared dan GCMS dilakukan untuk mengetahui senyawa ekstrak yang berperan dalam proses inhibisi. Morfologi permukaan sampel diamati dengan menggunakan scanning electro microscopy dengan energy dispersive X-ray spectroscopy (SEM-EDX) . Keseluruhan hasil penelitian menunjukkan bahwa ekstrak polar kulit buah coklat dapat digunakan sebagai inhibitor korosi yang efektif pada baja karbon di lingkungan 1,5M HCl dengan pencapaian efisiensi inhibisi terkorosi sebesar 96.26% (weight loss) dan 92.08% (Tafel) pada konsentrasi ekstrak 2,5% selama768 jam. Mekanisme inhibisi adalah adsorpsi chemiadsorpsi berdasar tingginya nilai entalpi dan energi bebas.Effisiensi Inhibisi diketahui meningkat dengan peningkatan konsentrasi dari ekstrak serta menurun dengan peningkatan suhu. Kurva polarisasi menunjukkan inhibitor ini berperilaku sebagai inhibitor campuran dengan dominan pada inhibisi katodik. Ekstrak diadsorpsi oleh permukaan mild steel mengikuti model adsorpsi isotherm Langmuir. Kondisi permukaan mild steel menunjukan terjadinya adsorpsi di permukaan membentuk lapisan tipis di permukaan logam. Penambahan ekstrak kulit buah kakao ke dalam larutan HCl sangat efektif untuk mengurangi serangan korosi di permukaan mild steel. Kata kunci: Korosi, Inhibitor, Theobroma cacao, Mild steel, Potensiodinamik Corrosion Inhibition Efficiency Mild Steel in Acid Media with Inhibitor Peels Extract of Cacao (Theobroma cacao)ABSTRACT Inhibition and adsorption properties of Theobroma cacao peel polar extract addition on corrosion inhibition efficiency of 0.3%C mild steel in hydrochloric acid solution for various exposuring time, extract concentration and working temperature were investigated using weight loss test method. Electrochemical polarization test was also conducted to confirm the effectiveness of inhibition. Infrared spectrum of the samples was also evaluated to reveal compounds of the extract which controll the inhibition process. Morphology and local composition of sample surfaces were respectively examined by scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX). Thermodynamic parameters such as energy activation, enthalpy, entropy and change in the free energy were then determined using related data. The results show that the inhibition efficiency increases significantly up to 96.3% (by weight loss method) and 92.08% (Tafel) with the increase of TCPE content. The optimum efficiency is obtained at extract concentration of 2,5% for exposuring time of 768h. However, the efficiency decreases slightly with increasing working temperature in the range of 303K-323K. The polarization curve shows the inhibitor behaves as a mixed inhibitor with the dominant cathodic inhibition. The adsorption model is found to obey Langmuir adsorption isotherm. Surface condition is improved due to the adsorption and then formation of thin layer film protection in the surface of the steel. The addition of extract of cacao peels into HCl is effective to minimize corrosion attack on the mild steel. Key words: Corrosion, inhibitor, Theobroma cacao peel, Mild steel, Potensiodinamic
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