Volatile inhibitors of atmospheric corrosion of ferrous and nonferrous metals I. Physical and chemical aspects of selection of starting reagents and synthetic routes

Abstract

The paper discusses the relationship between the physicochemical and electronic characteristics of various metals and molecular parameters of inhibitors that allows a better prediction of the efficiency of volatile inhibitors of atmospheric corrosion (VIACs) of ferrous and nonferrous metals. The high efficiency of commercial VNKh-L inhibitors based on Schiff and Mannich bases as VIACs is substantiated. It is demonstrated by analyzing the main molecular characteristics that products of complex condensation of nitrogen-containing compounds with aldehydes can serve as highly efficient VIACs. Key words: physical and chemical aspects; volatile inhibitors; atmospheric corrosion; ferrous and nonferrous metals; Schiff and Mannich bases.Received: August 10, 2012August 10, . doi: 10.17675/2305August 10, -6894-2012 According to the current concepts adopted by most researchers [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16], the efficiency of a volatile inhibitor of atmospheric corrosion (VIAC) generally depends on the pressure of its saturated vapor (P 0 ) at a given temperature, the diffusivity (D) determined by the molecular mass, and the minimum protective concentration (C min ) in water with respect to a metal to be protected. The first two factors, unlike the third one, are independent of the metal nature. The minimum protective concentration depends on the properties of an inhibitor as well as on the metal nature. The mere existence of such a term as "radius of VIAC protective action" can prove that diffusion of an inhibitor across the air layer from the surface of evaporation to the surface of a water film on the metal is the slowest step [7]. Otherwise, the efficiency of VIAC would be independent of the thickness of the air layer [9][10][11][12][13].A detailed analysis of the plot of the efficiency of VIAC vs. D and P 0 , which has been performed for inhibitors used to preserve metallic parts in the last 40-50 years [1, 9-13, 15, 17], revealed that the vapor pressure of a "perfect" VIAC should range from 1·10 -6 to

Volatile inhibitors of atmospheric corrosion of ferrous and nonferrous metals. IV. Application of the VNKh-L-408 inhibitor in an electrostatic field

“…This confirms our previous conclusion that the general concept of evaluating the adsorbability of chemical compounds on metals and, hence, their inhibitive properties based on the general electronic characteristics of compounds and metals (ionization potentials, "resonance" potentials, and electron work functions) fails in accurate prediction of the inhibitive effects of chemical compounds on various metals [5].…”

“…This series differs from that of the atmospheric corrosion inhibition factors [5] as well as from the series of the metals arranged by melting points, stability of hydroxo complexes, first ionization potentials, Nechaev's "resonance" potentials, and electron work functions, which were discussed in [5,6] in the context of possible prediction of the inhibitive properties of organic compounds.…”

“…In [5], we have demonstrated that the high protective effect of the inhibitor on steel, copper, and aluminum is accounted for by the fact that the ionization potentials of the N atoms and the ring -electrons are close to the "resonance" potentials of the metals and their oxides. For zinc, the ionization potentials of those atoms are close only to the "resonance" potential of oxidized zinc; for cadmium (in the form of oxide), adsorption bonds between the metal surface and the inhibitor are formed by the O atoms, while the N heteroatoms cannot be involved in these bonds.…”

Volatile inhibitors of atmospheric corrosion of ferrous and nonferrous metals. V. Study of the adsorption of inhibitors on steel from an aqueous electrolyte solution

“…The parameters given in the tables include: mol/dm 3 ;   is the inhibition factor for atmospheric corrosion in an environmental chamber [5,6];  Z is the protective value (%) in solution calculated by the standard formula from corrosion current data in a blank experiment and in the presence of the inhibitor (C inh = 10 -2 mol/dm 3 );  i is the corrosion current (A) at adsorption completion time t and C inh = 10 -2 mol/dm 3 . The corrosion current in a blank experiment is 50 A;  t is the adsorption completion time (s).…”

Corrosion protection of flanges and valves

“…are often are not effective in combating the atmospheric conditions encountered at many industrial sites. Volatile corrosion inhibitors (VCI) have been used in packaging to protect metal parts during storage, handling and transportation for many years, dating back to the original patents for VCI film [1][2][3][4][5][6][7][8][9]. This VCI technology was selected and has been combined with barrier films to develop a flange, valve and welded joints protection system (FPS), which provides an effective corrosion protection solution against aggressive industrial environments [6].…”