Comparative Study of Factors Influencing the Action of Corrosion Inhibitors for Mild Steel in Neutral Solution: III. Sodium Nitrite

Abstract

The action of sodium nitrite as a corrosion inhibitor for mild steel in neutral aqueous solution has been studied in relation to the surface preparation of the steel, the presence of aggressive salts in the solution, and temperature.

Surface preparation of mild steel has little effect on the minimum concentration of nitrite required for protection in distilled water. In solutions containing aggressive anions a linear relation exists between the logarithm of the nitrite concentration and the logarithm of the maximum concentration of aggressive anion that will permit inhibition. In solutions of low nitrite concentration the order of aggressiveness of anions is sulphate > chloride > nitrate; the order changes with increase in nitrite concentration. Corrosion in non-inhibiting nitrite/aggressive anion solutions is frequently of a severely localised form. A 5-fold increase in nitrite requirement for inhibition of abraded mild steel in distilled water is found between 5° and 70°, with a further large, rather indeterminate, increase above 70°.

Of the three inhibitors studied in Parts I-III, chromate and nitrite are slightly moreeffective than benzoate for the protection of an abraded surface, and considerably more so for a grit-blasted surface. In general, nitrite is the most tolerant towards the presence of chloride, but it is the most dangerous if excess chloride is present. The increase in inhibitor requirement with increase in temperature from 5° to 70° is very approximately the same for all three inhibitors, that is, about 5– to 10–fold,with all inhibitors needing much higher concentrations at about 90°.     

Corrosion inhibition of reinforcing steel by using hydrazine hydrate

The effectiveness of hydrazine hydrate as a corrosion inhibitor for reinforcing steel in alkaline media (lime water) has been investigated. It has been found that the critical concentration for inhibition increases with the increase of the aggressive ion concentration. The mechanism of the corrosion inhibition was discussed in terms of competitive adsorption between the aggressive ion and hydrazine at relatively low concentrations of hydrazine. Higher concentrations of hydrazine caused instantaneous passivation of the steel even more readily than that obtained in pure lime water.     

Studies on the pitting corrosion of zinc in aqueous solutions I. Variations of the potential of the zinc electrode in relation to the concentration of the aggressive anion

The way in which the stationary potential of a zinc electrode previously treated with various passivating and inhibiting solutions changes in the present of the chloride, bromide and iodide ions is studied in solutions of potassium chromate, disodium hydrogen phosphate and sodium tungstanate. It is shown that the potential change as a function of the halogenide concentration follows a S shaped curve. The potentials are established after an induction period the duration of which decreases as the concentration of the aggressive anion increases and/or the concentration of the inhibiting anion decreases. A linear relationship is obtained for the maximum permissible concentration of the aggressive anion at a given concentration of the inhibiting anion. This relationship is theoretically derived from the defect resulting from the specifical adsorption of both ions at the metal surface. While e.g. a temperature increase shifts the potential in pure chromate solutions to more positive potentials, thus improving the protective effect, the permissible concentration of the aggressive anion is simultaneously decreased. This phenomenon suggests that in these conditions the desorption of the inhibiting anions is increased.     

Comparative Study of Factors Influencing the Action of Corrosion Inhmitors for Mild Steel in Neutral Solution: II. Potassium Chromate

Abstract

The action of potassium chromate as a corrosion inhibitor for mild steel in neutral aqueous solution has been studied in relation to the surface preparation of the steel, the presence of aggressive salts in the solution, and temperature.

Surface preparation of mild steel has little effect on the minimum concentration of chromate required for protection in distilled water. In solutions containing aggressive anions a linear relation exists between the logarithm of the chromate concentration and the logarithm of the maximum concentration of aggressive anion that will permit inhibition. In solutions of low chromate concentration, up to 10^?1M, the order of aggressiveness of anions is chloride > sulphate > nitrate; the order changes at chromate concentration above 10^?1M to chloride > nitrate > sulphate. Corrosion in non-inhibiting chromate/aggressive anion solutions is always of a localised nature but is usually stifled, thus not leading to ‘dangerous’ attack. A 5-fold increase in chromate requirement for inhibition of abraded mild steel in distilled water is found between 5° and 60°, with a further large, rather indeterminate, increase above 60°.     

Stability of the Oxide Film on Metals in Relation to Inhibition of Corrosion: II* Dual Role of the Anion in the Inhibition of the Corrosion Of Mild Steel

Abstract

It has been found that anions have a dual role in relation to the stability of the oxide film on mild steel. They contribute both to the destruction of the oxide film and to the passivation process in which the film is stabilised. The dependence of these functions on concentratinn differs, so that the aggressive action predominates at low concentrations and the inhibitive action at high concentrations. The change from aggressive action to passivation occurs at a concentration specific to each anion. In many cases at a certain critical concentration either result may ensue. A list is given of anions in order of aggressiveness towards the oxide film.     

Sodium gluconate as corrosion and scale inhibitor of ordinary steel in simulated cooling water

The effect of sodium gluconate anion (SG) on the corrosion and scale inhibition of ordinary steel in simulated cooling water has been studied using weight loss, polarisation curves, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) techniques. SG was studied in concentration from 10⁻⁴ M to 10⁻¹ M. Results obtained reveal that SG perform excellently as corrosion and scaling inhibitor for ordinary steel in simulated cooling water. An increase of SG concentration leads to the increase of the corrosion potential towards the positive direction. The inhibition efficiency was a low temperature dependence. The inhibitor mechanism was treated as an adsorption process according to Langmuir adsorption isotherm. The SEM/EDAX data show that was a corrosion and scale inhibitor.     

Estimate of contributions of polysulfide film and inhibitor to the protection of steel from hydrogen-sulfide corrosion

A method for estimating the contributions of film formed on a corrosive surface in aggressive medium favoring its formation and INKORGAS-T30 inhibitor at the inhibition of corrosion in steel has been proposed. Experimental results obtained by studying the behavior of the St3 carbon steel in mineralized chloride medium (5 wt % NaCl) containing 50–400 mg/l H₂S and the addition of an inhibitor have been presented. Using the polarization resistance method, the protective efficacy of oxide and polysulfide surface films and an inhibitor has been estimated as a function of the duration of the action of the aggressive medium, hydrogen sulfide concentration, and the corrosion inhibitor.     

Inhibitor protection and corrosion monitoring in Benfield installation to purify gas for synthesis

Abstract

The aggressive media in the Benfield processfor preparing gasfor use in synthesis by means of ‘potassium purification’ consist of KHCO₃ + K₂CO₃ solutions having total contents and molar ratios that vary over a very wide range which also contain diethanoloamine. Operating temperatures are typically 70–120°C. Despite the use of inhibitors, intensive corrosion of mild steel walls has been observed in several installations. In laboratory tests performed in simulated Benfield solutions, a relationship has been established between the inhibitor content necessary to suppress active dissolution and pitting corrosion and the total content and molar ratio of the carbonates. These results have been checked and verified in an industrial installation. The corrosion monitoring system applied to critical parts of the equipment allowed the solution composition to be controlled and an inhibitor content appropriate to the composition of the aggressive medium to be maintained. As a result, substantial decreases in corrosion have been achieved, as was confirmed by microscopic examination of disposable electrodes and by the observation of the inner surface of an installation during routine maintenance.     

Role of complexes in inhibition of mild steel by zinc–1-hydroxyethylidene-1, 1-diphosphonic acid mixtures

Abstract

The action of 1-hydrox yethylidene-1, 1-diphosphonic acid (HEDP) in combination with zinc ions as a corrosion inhibitor for mild steel in oxygen containing aqueous solutions has been investigated in relation to the presence of different zinc levels, the presence of aggressive anions, and different pH values. The highest inhibition effect was obtained at a 2·7:1 zinc/HEDP molar ratio, corresponding to 60 ppm zinc, and was associated with a significant anodic effect. In the absence of chloride and with no free forms of the inhibitor components, the zinc-HEDP mixture exhibited good protection over a wide range of pH (6·5-9·5). However, in a weakly acidic medium, protection could not be achieved. Calculations based on the dissociation constants of the HEDP and the stability constants of the possible zinc-HEDP complexes showed that this inhibition can be attributed to the presence of the 2:1 zinc-HEDP complex (Zn₂H_-1L^-) at a sufficient level. It is found that this anionic complex can behave as an anodic, passivating, inhibitor at a concentration as low as 0·00015M (20 ppm zinc-32 ppm HEDP mix ture). This passivity is prevented by the presence of sufficient chloride. The critical chloride concentration in these studies is approximately ten times higher than the complex concentration, in molar terms. It is also found that free phosphonate is aggressive and can prevent passivity due to the preferential formation of soluble iron-HEDP complex. The tolerance of the 2:1 complex to free phosphonate is substantially less than to chloride, approx imately equimolar.     

Corrosion inhibition of steel by sodium sulphite

The corrosion inhibition of steel in a closed system containing sodium sulphite at room temperature has been established. Steady-state potential as well as weight loss measurements indicated that sodium sulphite did not only remove O₂ from the solution but also brought complete cathodic protection. It was found also that sodium sulphite could tolerate the presence of Cl^?, SO₄^2? and S^2?. In case of sulphite—sulphate or sulphite—chloride mixtures a concentration of 5 × 10^?3M Na₂SO₃ was required to tolerate a wide range of concentration of these aggressive ions. A linear relationship was found between log sulphite concentration and log maximum tolerated concentration of sulphide.     

Pitting Corrosion Currents on Steel in Relation to the Concentration of the Inhibitive and Corrosive Anions under Natural Corrosion Conditions

Abstract

The changes with time in the pitting corrosion current density on a steel electrode with the concentration of both the inhibitive anions (CrO₄^2?, HPO₄^2? and WO₄^2?) and aggressive anions (Cl^?, Br^? and I^?) was followed using a simple electrolytic cell. In chromate solutions the pitting corrosion currents started to flow after an induction period, τ, which varied, in one and the same inhibitor solution, with the concentration of the aggressive anion, according to the expression: log τ =a?b log C_agg.

The pitting corrosion currents finally reached steady-state values which depended on the type and concentration of both the inhibitive and corrosive anions. At a constant inhibitor concentration,the corrosion current varied with the concentration of the aggressive anion according to: log i_corr = a_l + b₁ log C_agg, and with constant aggressive ion concentration according to: log i_corr =a₂ - b₂ log C_inh Comparison was made between the experimentally obtained values of a_l (a₂ and b₁ (b₂), and the corresponding computed values. The a₂ values show that the corrosivity of the three aggressive anions decreases in the order: Cl^? > Br^? > I^?; on the other hand the inhibitive efficiency of the inhibiting anions decreases in the order: CrO₄^2? > HPO₄^2? > WO₄^2?.     

The inhibition of mild steel corrosion in phosphoric acid solutions by some N-heterocyclic compounds in the salt form

The effect of some quaternary N-heterocyclic compounds on the corrosion of mild steel in solutions of phosphoric acid (H₃PO₄) has been investigated in relation to the concentration of the inhibitor and acid as well as temperature by various monitoring corrosion techniques. Surface morphology was studied by scanning electron microscopy (SEM). Results obtained revealed that these compounds are good mixed-type inhibitors without changing the mechanism of the corrosion process. In general, at constant acid concentration, inhibitor efficiency increased with concentration of the inhibitor. On the other hand, at constant inhibitor concentration, inhibitor efficiency decreased with concentration of the acid up to a critical concentration above which it started to increase. The studied compounds appeared to function through general adsorption following the thermodynamic-kinetic adsorption isotherm. The thermodynamic parameters were determined and discussed. A quantitative correlation between inhibitor structure and inhibition efficiency was discussed.     

在NaCl溶液中CTAB、SDS和钨酸钠对印刷电路板缓蚀作用研究

采用电化学阻抗和极化曲线法,研究了在NaCl溶液中,钨酸钠、十六烷基三甲基溴化铵(CTAB)及十二烷基硫酸钠(SDS)的单一配方以及其复配对印刷电路板的缓蚀作用.结果表明:CTAB、SDS和钨酸钠各自的单一配方对印刷电路板(PCB)均具有一定的缓蚀作用,其中CTAB浓度为1.0×10-4mol/L,SDS浓度为5.0×10-3mol/L及350 me,/L钨酸钠表现出最佳的缓蚀效率;SDS和钨酸钠属于阳极型缓蚀剂,CTAB为混合型缓蚀剂;当二者复配使用时,浓度为250 ms/L钨酸钠和1.0 x 10-4moL/L CTAB以及300 mg/L钨酸钠和5.0×10-3～moL/L SDS的复配缓蚀剂的缓蚀效果最佳,复配缓蚀剂具有协同效应,并且对印刷电路板的缝隙腐蚀有一定的抑制作用.     

在中性NaCl溶液中工业纯Al孔蚀发展过程的研究

对工业纯Al在中性NaCl溶液中孔蚀的发展过程进行了初步探讨,采用了恒电位阳极极化方法测定了不同浓度的NaCl溶液中和不同极化电位下孔蚀发展的i～t曲线,分析了孔蚀发展前期和后期氯离子浓度和极化电位的影响,借助原子吸收光谱从物质分析的角度对腐蚀产物进行了研究.     

The influence of pH on the inhibition of corrosion of iron and mild steel by sodium silicate

The inhibition of iron and mild steel in solutions of sodium silicate of different concentration and pH has been studied by means of potentiostatic and potentiokinetic polarization measurements. The mechanism of formation of protective layers formed in the presence of inhibitor has been discussed on the basis of experimental measurements and literature data. The difference in the protective action due to the presence of sodium silicate as distinguished from the effect of the alkaline media has been demonstrated. The influence of the metal corrosion products in the formation of the protective layers has also been investigated.     

Corrosion inhibition by tungstate in aqueous solutions and its application to coal–water slurries

Abstract

Corrosion rates of AISI 1010 steel both in the presence and absence of sodium tungstate as inhibitor were determined in chloride–sulphate solutions of concentrations typical of water used in coal plants. Corrosion rate data of AISI 1010 steel as a function of pH and sodium tungstate concentration showed that 100 ppm tungstate at pH 8·5 gave 87% inhibition. When associated with other chemical species in a binary or multicomponent system the inhibitor efficiency rose to 99%. Results obtained with sodium tungstate alone or in association with hydroxyethylidene diphosphonic acid (HEDP) and zinc sulphate are presented and discussed. The application of tungstate inhibitor in coal–water slurries has been explored.     

Electrolytic Codeposition of Nickel and Phosphorus from Methanesulfonate Electrolyte

The characteristics of Ni–P alloy electrodeposition from a methanesulfonate electrolyte have been investigated. It has been found that the phosphorus content of the alloy increases with increasing the concentration of sodium hypophosphite in the electrolyte and reducing the electrodeposition current density. A mechanism of codeposition of nickel and phosphorus has been suggested. It is shown that phosphorus was formed by electrochemical reduction of hypophosphite anions and their disproportionation at a catalytically active surface of a nickel cathode. It has been shown quantitatively that the most likely path for the formation of phosphorus through the electrochemical mechanism is the direct electrochemical reduction of a hypophosphite anion to atomic phosphorus. The rate of phosphorous formation from hypophosphite anions is dependent on the concentration of hydrogen ions in the near-electrode layer. Therefore, the phosphorus content of the coatings obtained from the methanesulfonate electrolyte is slightly decreased as compared with that from the sulfate electrolyte which exhibits higher buffering properties. It has been revealed that codeposition of nickel and phosphorus reduces the kinetic difficulties of electrochemical reduction of the nickel ions. This might be due to an increased near-electrode concentration of nickel hydroxyl complexes discharging at the cathode, which is the result of an increased near-electrode pH caused by the reactions involving hypophosphite anions and hydrogen ions.     

Electrochemical methods for evaluating inhibitors of steel corrosion in concrete

Abstract

Electrochemical methods were used to evaluate sodium phosphate and sodium nitrite as inhibitors for the corrosion of steel in saturated calcium hydroxide solution containing chloride ions. The studies included immersion, potentiodynamic, potentiostatic, and galvanostatic tests. The results obtained from these methods were in good agreement. They show that sodium nitrite is an anodic inhibitor which is not effective if its concentration is lower than that of the chloride ions. Sodium phosphate acts as an anodic inhibitor if its concentration is higher than 0·6 times the chloride concentration. It is totally effective when its concentration equals the chloride concentration.     

Influence of Movement and Temperature on the Corrosion of Mild Steel IV. Inhibition by sodium metaphosphate glass

Abstract

A study has been made of the influence of small additions of sodium metaphosphate glass (a sodium polyphosphate) on the corrosion of mild steel in a solution of 25 ppm sodium chloride at flow velocities of 1·2, 20 and 200 cm/sec. The inhibitor efficiency is found to depend on the concentration, the rate of flow and the presence of small concentrations of calcium ion. Small additions of metaphosphate glass can actually stimulate corrosion of mild steel at low flow velocities in the absence of calcium although in the presence of cqlcium they have a small but beneficial effect. The efficiency of inhibition increases with increase in flow velocity.

The inhibition is produced by a visible film largely of a colloidal nature the amount of product becoming smaller when the corrosion rate is lowered. Potential measurements have shown that polyphosphate acts mainly as an anodic inhibitor in the absence of calcium and as a cathodic inhibitor in its presence. Stimulation can occur owing to the complexing power of metaphosphate glass and its depolarising action at the anode.     

Limits determination of toleration of aggressive anions by a certain passivator on zinc surface

The open circuit potentials of Zn electrode were followed as a function of time in different concentrations Na₂B₄O₇ solutions until steady-state, E_st., values were attained. The potential shifts immediately towards positive values, indicating film thickening and repair. The effect of addition of NaCl, NaBr and NaI as aggressive agent on the steady-state potential of a Zn electrode previously equilibrated in a passivating borate solution was also established. For each Na₂B₄O₇ concentration, the variation in the potential with the quantity of aggressive anions follows an S-shaped relationship. The new potentials are established after an induction period which decreases with the increase in the concentration of the aggressive anion, C_agg., and/or decreases in that of the passivator anion, C_pass.. The concentration, C_agg., that can be tolerated by a certain concentration of the passivator anion, C_pass., is given by the relation: log C_pass. = k + n log C_agg., where k and n are constants. This is derived on the basis of competitive adsorption of both types of anion and the structure of the double layer at the metal/solution interface. The implications of the equations are briefly discussed.