Surfaktan berfungsi menjaga kestabilan suatu emulsi agar tetap homogen, dengan cara menurunkan tegangan permukaan. Saat ini, industri yang memproduksi surfaktan di Indonesia masih menggunakan bahan baku yang berasal dari minyak bumi tak terbarukan (surfaktan sintetis). Gliserol monostearat (GMS) merupakan jenis surfaktan yang sering digunakan dan hingga saat ini belum ada pabrik gliserol monostearat yang didirikan di Indonesia. Kegunaan gliserol monostearat dalam industri misalnya sebagai pearlizing agent, emulsifier dan dispersan. Pemilihan proses untuk memproduksi gliserol monostearat perlu dianalisis agar produksi yang dihasilkan lebih optimal. Gliserol monostearat dapat diproduksi melalui dua macam proses, yaitu proses esterifikasi dan transesterifikasi. Pada proses esterifikasi, digunakan bahan baku berupa gliserol dan asam stearat menggunakan katalis asam atau basa. Sedangkan pada proses trans-esterifikasi (gliserolisis), bahan baku yang digunakan yakni trigliserida berupa tristearat dan gliserol menggunakan katalis basa. Dari studi yang telah dilakukan, proses esterifikasi lebih dipilih karena ditinjau dari aspek teknis, aspek operasi dan aspek lingkungan, proses esterifikasi lebih baik daripada proses transesterifikasi.

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The purpose of this paper is to evaluate the characteristics of corrosion protection of stainless steel substrates coated with silica by electrophoresis with pulsed direct current (PDC) and constant direct current (CDC) with anodization. Electrophoresis was carried out using silica sol from sodium silicate solution as an electrolyte solution. Stainless steel functioned as an anode and carbon as a cathode with a constant electrode distance of 2 cm. The amplitude, duty cycle, and anodization effect on stainless steel corrosion protection characteristics were evaluated. The samples were characterized by linear polarization and electrochemical impedance spectroscopy (EIS) to see the characteristics of metal corrosion protection and scanning electron microscopy (SEM) analysis to see the morphology of the coating. This study showed that PDC electrophoresis and CDC accompanied by anodization could obtain silica film with good corrosion protection characteristics (high pore resistance and low admittance). Linear polarization results showed that metal corrosion protection behavior was increased by anodization. Similar results were obtained by EIS analysis which showed that pore resistance increased by anodization. The highest pore resistance obtained by the constant current with anodization is 543 ohms, and the lowest admittance is 0.0217. Corrosion protection characteristics are also influenced by the amplitude and duty cycle during electrophoresis. Silica film with a high pore resistance and a low admittance were obtained at a frequency, amplitude, and duty cycle of 80 Hz, 0.5 volts, and 60%, respectively. The silica film produced by pulsed electrophoresis resulted in better coating characteristics than by constant current with anodization, which is seen from the pore resistance value and its admittance.

AbstrakPenelitian ini mempelajari pengaruh anodisasi terhadap karakteristik perlindungan korosi lapisan silika pada permukaan stainless steel. Anodisasi dilakukan menggunakan larutan asam oksalat dengan memvariasikan waktu anodisasi dan beda tegangan. Elektroforesis dilakukan menggunakan campuran sol silika, isopropanol dan asam asetat dengan perbandingan mol 0,0028 : 0,5048 : 0,1938 selama 10 menit dengan amplitudo 0,5 V, frekuensi 80 Hz dan duty cycle 60%. Uji Particle Size Analyzer (PSA) dilakukan terhadap sol silika. Distribusi ukuran partikel dan zeta potensial yang diperoleh adalah sebesar 3,19 nm dan zeta potensial -31,68 mV. Analisa polarisasi linier dan Electrochemical Impedance Spectroscopy (EIS) dengan larutan NaCl 3,5% serta Scanning Electron Microscopy (SEM) dilakukan terhadap lapisan yang terbentuk pada permukaan stainless steel. Dari hasil analisa diperoleh logam yang telah dianodisasi dan elektroforesis memiliki kemampuan perlindungan korosi lebih baik dibanding logam tanpa perlakuan. Waktu dan beda tegangan saat anodisasi berpengaruh terhadap karakteristik perlindungan korosi lapisan pada logam. Waktu anodisasi optimum diperoleh selama 20 menit dan voltase 10 volt dengan laju korosi sebesar 0,0051 mm/tahun. Untuk uji EIS, nilai admitan dan nilai tahanan pori masing-masing sebesar 0,0010226 Mho dan 1.774 ohm. Hasil SEM menunjukkan bahwa setelah dilakukan anodisasi terbentuk lapisan yang berpori yang nantinya menjadi tempat menempelnya silika pada proses elektroforesis. AbstractThis research studied the effect of anodization on corrosion protection characteristics of silica layer on stainless steel surface. Anodization was carried out using oxalic acid solution by varying the anodization time and the voltage difference. Electrophoresis was carried out using a mixture of silica sol, isopropanol and acetic acid with a mole ratio of 0.0028: 0.5048: 0.1938 for 10 minutes with a constant amplitude, frequency and duty cycle of 0,5 V, 80 Hz and 60%, respectively. The silica sol was characterized by Particle Size Analyzer (PSA). The particle size distribution was obtained at 3.19 nm and zeta potential of -31.68 mV. Linear polarization and Electrochemical Impedance Spectroscopy (EIS) were analyzed by 3.5 % wt NaCl solution and Scanning Electron Microscopy (SEM) used to characterized the layers formed on the stainless steel surface. The result showed that the anodized and electrophorized stainless steel has better corrosion protection capabilities than metal without treatment. The anodization time and voltage difference affected the corrosion protection characteristics of the metal. The optimum anodization time was obtained at 20 minutes and voltage of 10 volts with a corrosion rate of 0.0051 mm / year. For the EIS analysis, the admission value and pore resistance value were 0.0010226 Mho and 1,774 ohm, respectively. SEM results showed that after anodization a porous layer was formed which later becomes the place where silica attaches on the electrophoresis process.