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Information Seminar Paper

Title

APPLICATION OF 2-MERCAPTOMENZOIMIDAZOLE AS CORROSION INHIBITION OF STAINLESS STEEL IN CITRIC ACID PICKLING PROCESS

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Abstract

 METALS CAN BE IMMERSED INTO SOLUTION OF ACIDS TO REMOVE METAL, METAL OXIDES, HEAT-TRATE SCALE AND FOREIGN METALS. SUCH TREATMENTS GENERALLY LEAVE THE SURFACE CHEMICALLY CLEAN AND READY FOR FURTHER PROCESSING. THE USUAL SOLUTION FOR THE REMOVAL OF SCALE AND FROM IRON AND STEEL PRODUCTS IS HYDROCHLORIC OR SULFURIC ACIDS. THESE ARE USED IN CONCENTRATION RANGES FROM A FEW OUNCES PER GALLON TO VERY CONCENTRATED, DEPENDING ON THE TYPE OF WORK BEING PROCESSED [1]. COMMERCIAL INHIBITORS -AMINES AND NITRATES- ARE COMMON AND ARE OPTIONALLY USED IN THESES PICKLES TO PREVENT OVERETCHING AND TO AVOID PITTING. IN THE OTHER WORDS, INHIBITORS ARE GENERALLY USED IN THESE PROCESSES TO CONTROL THE METAL DISSOLUTION. MOST WELL- KNOWN ACID CORROSION INHIBITORS ARE ORGANIC COMPOUNDS CONTAINING NITROGEN, SULFUR AND OXYGEN ATOMS; NITROGEN-CONTAINING ORGANIC COMPOUNDS ARE KNOWN TO BE EFFICIENT CORROSION INHIBITORS IN ACID SOLUTIONS. AMONG THEM, N-HETEROCYCLIC COMPOUNDS ARE CONSIDERED TO BE THE MOST EFFECTIVE CORROSION INHIBITORS FOR STEEL IN ACID MEDIA [2]. THE USE OF 2-MERCAPTOMENZOIMIDAZOLE (2-MBI) INHIBITOR IS ONE OF THE MOST PRACTICAL METHODS FOR THE PROTECTION OF METALS AGAINST CORROSION DURING THE PICKLING PROCESS AND IT TAKES MORE OF MORE ATTENTION UNTIL NOW [3]. THIS PAPER DISCUSSES THE PICKLING OF STAINLESS STEEL BY THE USE OF 2-MBI INHIBITOR IN THE 2-MBI INHIBITION USE OF CITRIC ACID. THE USE OF CITRIC ACID IS TESTED FOR THE FIRST TIME IN THE ACIDIC PICKLING PROCESS OF STAINLESS STEEL IN 25OC. THE INHIBITIVE ACTIVITY OF 2-MBI IS EXAMINED SUCCESSIVELY VIA ELECTROCHEMICAL TECHNIQUES IN THE RANGE OF 100 TO 1000 PPM. THE METAL SAMPLES WERE PRE-TRATED PRIOR TO THE EXPERIMENTS BY GRINDING WITH EMERY PAPERS (100-40-800-1000); RINSED WITH DISTILLED WATER, DEGREASED IN ALKALINE SOLUTION FOR 45 S, WASHED AGAIN WITH DISTILLED WATER AND DERIDED AT ROOM TEMPERATURE BEFORE USE. THE 6 WT.% CITRIC ACID SOLUTION WERE PREPARED BY THE DISSOLVING OF CITRIC ACID SOLID WITH DISTILLED WATER. IMPEDANCE MEASUREMENTS WERE CARRIED OUT AT THE OPEN CIRCUIT POTENTIAL (EOCP), USING A COMPUTER-CONTROLLED POTENTIOSTATE (PAR EG&G MODEL 273A) AND A FREQUENCY RESPONSE ANALYZER. IN THE CONVENTIONAL THREE-ELECTRODE ASSEMBLY, A PT FOIL AUXILIARY ELECTRODE AND A SATURATED CALOMEL REFERENCE ELECTRODE (SCE) WERE USED. THE SAMPLES WERE IMMERSED IN THE ACIDIC MEDIA CONTAINING THE DIFFERENT CONCENTRATION OF INHIBITOR FOR A TIME PERIOD OF 24 H. THE A.C. FREQUENCY RANGE EXTENDED FROM 100 KHZ TO 10 MHZ, A 5 MV PEAK-TO-PEAK SINE WAVE BEING THE EXCITATION SIGNAL. DATA PROCESSING WAS BASED ON A NON-LINEAR LEAST SQUARES FITTING PROCEDURE AS DESCRIBED ELSEWHERE [4]. FOR THIS PURPOSE, THE ZVIEW (II) SOFTWARE WAS USED AND FOR TRANSFORMING CONSTANT PHASE ELEMENT PARAMETER VALUES INTO VALUES OF IDEALIZED CAPACITANCES, A PROCEDURE OUTLINED IN THE SAME REFERENCE WAS EMPLOYED. THE SAME EQUIPMENT AS FOR THE IMPEDANCE MEASUREMENTS WAS USED LEAVING THE FREQUENCY RESPONSE ANALYZER OUT OF CONSIDERATION. THE POTENTIOSTATIC POLARIZATION CURVES WERE OBTAINED USING A SWEEP RATE OF 1 MV S-1. CORROSION CURRENT DENSITIES WERE OBTAINED FROM THE POLARIZATION CURVES BY TAFEL CURVE SIMULATION. THE RESULTS SHOWED THAT THE ANODIC AND CATHODIC REACTIONS ARE AFFECTED BY THE ADDITION OF 2-MBI. SO, THE 2-MBI ACTS AS A MIXED CONTROLLED INHIBITOR IN CITRIC ACID MEDIA. IT COULD BE OBSERVED THAT THE INHIBITION EFFICIENCY INCREASED WITH INCREASING THE CORROSION INHIBITOR CONCENTRATION AND THE INHIBITION EFFICIENCY SHOWED A MAXIMUM VALUE OF 93.2% AT A CONCENTRATION OF 400 PPM. THE EIS RESULTS CONFIRMED WELL DEFINED TWO TIME CONSTANT AND WERE IN GOOD AGREEMENT WITH POLARIZATION METHOD. IN THE CASE OF 400PPM 2-MBI ADDITION, THE POLARIZATION RESISTANCE (RP) AND CHARGE TRANSFER RESISTANCE (RCT) WERE THE MAXIMUM AMOUNTS AND OBTAINED EQUAL TO 220 AND 2618  W.CM2, RESPECTIVELY.

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