The work is devoted to the development of process fluids based on synergistic mixtures of surfactants and corrosion inhibitors for the electric-spark mechanical method steel surfaces preparing using electric grinders.
The use of individual representatives of inhibitors and surfactants usually does not allow to obtain high efficacy. More effective are mixtures, the composition of which is characterized by a synergism in the action of their components.
Nowadays, studies devoted to elucidating the mechanism of action of highly effective synergistic mixtures of metal corrosion inhibitors and surfactant compositions, same as related to the uncertainty of if effectiveness influence on the nature of components, as well as concerning the ratio of their concentrations in solutions remain developed insufficiently. The influence of additives on the qualitative characteristics of the prepared surfaces and energy costs of the process are also studied insufficiently.
Such situation requires to develop research aimed on the increasing the corrosion resistance of metals during their postoperative period of storage, and also on improving of its protective properties after the paints and varnishes application.
To prevent an occurrence of corrosion processes during electrospark machining of steel, technological fluids specifically containing synergistic mixtures of corrosion inhibitors with different mechanism of action oxide and salt passivation or adsorption were developed, their effectiveness depends on the ratio of components and is characterized by an extremum where attained maximum level of inhibitory effect of additives on the kinetics of electrochemical corrosion processes of steel and full protection is achieved.
Anticorrosive efficiency of synergistic mixtures of the passivator oxide action (sodium nitrite) and the salt action (sodium silicate) depend on the nature of the components, the mechanism of their action, and also on the ratio of its molar concentrations constituting in synergistic mixtures and is characterized by a synergistic extremum of inhibitory action at a ratio of sodium nitrite concentrations and sodium silicate, as 1:2.
The results of polarization studies of the electrochemical behavior of steel have revealed an advantage of the inhibitory efficiency of the synergistic compositions compared to the efficiency of individual components, and is confirmed by the existence of a passivation zone in a wide range of potentials (0.8-1 V) and by minimum values of the full passivation (1-2*10-6 A/cm2) current density, which indicates the comprehensive corrosion protection of steel.
The introduction of such process fluids into the processing zone allows the treatment energy costs reducing by 30–40% and increasing the surface cleanliness class by 3 and more units due to the surface plasticization effect (Rehbinder effect).
Synergistic mixtures of surfactants contain molecules with oppositely charged functional groups, between which the forces of mutual attraction arise that allows to achieve high surface activity at the phase boundaries: air - liquid and liquid - metal. It was found that a decrease of the surface tension in aqueous solutions of the developed surfactant mixtures at the air-liquid interface and a decrease in the microhardness of steel at the liquid-metal interface have a similar nature and demonstrate efficiency extremes with a similar ratio of molar concentrations of anionic and cationic active components of order 1:1.
The thermodynamic characteristics of the formation of an adsorption layer surfactant at the interface of the aqueous solution-air were determined. It is shown that the dependences of surface tension, changes in entropy and enthalpy on the ratio of molar concentrations of cationic and anion active surfactants have a parallel extreme character, and the positive value of ΔS> 0 indicates that the driving force of the direct adsorption process is the entropy factor. The electro-spark treatment with a galvanized brush allows to apply zinc protectors to the metal surface, which, together with the synergistic mixtures of inhibitors, demonstrate the phenomenon of additivity and provide almost one hundred percent corrosion protection of steel even in strong corrosive media (3% NaCl), and enlarges the period of postoperative storage.
Especially high rates of steel surfaces protection are obtained using a galvanized brush with the subsequent application of a paint and varnish coating, where the effect of mutual reinforcement (synergism) between the sacrificial electrochemical protection with a paint coating is realized. Due to the formation of zinc hydroxide inside the paint coating, the ohmic resistance is enlarged, the adhesion and protective properties of paint coatings are improved.
Keywords: corrosion, mild, surfactants, adsorption, synergistic mixtures of surfactants, microhardness of steel, synergism.
