D.ch.s. Skvortsov V.G.*, k.ch.s. Michailov V.I.*, k.ch.s. Ershov Ì.À.**,

k.ch.s. Koltsova Î.V.*, k.ch.s. Pylchikova Yu.Yu.*,

Kamaev E.V.*, Bagautdinov À.Ì.*

* The Chuvash State Pedagogical University named I.Ya. Yakovlev

(ChGPU nam. I.Ya. Yakovlev),

Cheboksary, the Russian Federation

** Chuvash State Agricultural Academy (ChSAA),

Cheboksary, the Russian Federation

Inhibitory properties of aliphatic amins and tHEIR borats in neutral environments

The cause of metals’ corrosion is their thermodynamic instability in various environments under the given external conditions.

Iron and steel corrosion in the solutions close to neutral proceeds with oxygen depolarization [1-4]:

Fe ® Fe^2+ + 2 e^– (oxidation of metal) O2 + 2H2O + 4 e^– ® 4OH^– (restoration of the oxygen dissolved in water)

(1) (2)

or totally:

2Fe + O2 + 2H2O ® 2Fe(OH)2.

(3)

In view of formation of 1 mol of substance we shall obtain:

Fe + ½ O2 + H2O ® Fe(OH)2.

(3à)

Change of Guibbs’ energy of reaction (3a) under standard conditions is:

Constant of balance:

or

Calculations show that in the given corrosion environment iron is thermodynamicaly unstable and under standard conditions of balance reaction (3a) is moved much to the right.

The purpose of the our research is to study the influence of the nature of alifatic amins (AA) and their compounds with a boric acid on corrosion electrochemical and corrosion fatigue behaviour of steel 10 (St. 10) and to establish an opportunity of using them as inhibitor for protection of ferrous metals and their alloys in neutral environments against corrosion.

In this connection we have studied the influence of ÀÀ: hexamethylendiamin H₂N(CH₂)₆NH₂ (HMDA), ethylendiamin H₂N(CH₂)₂NH₂ (EDA), diethylamin (C₂H₅)₂NH₂ (DEthA), threbutylamin (C₄H₉)₃N (TBA) and their borats on corrosion electrochemical behaviour and cyclic durability St. 10 in neutral environments using the methods of gravimetry, removals potentionaly dinamical polarizing curves and cyclic loadings. The borats of alifatic amins (BAA): BHMDA, BEDA, BDEthA, BTBA have been obtained by the abore described techniques [5].

According to graviometric data we studied rate of corrosion (r, g/m²×h), inhibitory effect g and protection degree Z. Electrochemical measurements were carried out on the potentiostat P-5848 in potentioanal dinamic mode of polarization. An electrode of comparison was the silverclorid (cl.s.e.) one. Protective action of inhibitory additives were estimated in size of density of an anode current (i_a, mcÀ/sm²) in the field of a passive condition at the potential of polarization j = +0,2  on cl.s.e. The basic characteristics of cyclic durability of metal were defined on values of factor of a stock of cyclic durability on the basis of tests N = 4×10⁶ cycles and cyclic durability N at s=±325,0 ÌPa. The distilled water (background₁) and a solution containing 30 mg/l NaCl + 70 mg/l Na₂SO₄ (background₂) were served as the corrosion active environment. Concentration of additives was 2×10-2 mol/l. All measurements were made at a natural aeration and temperature 20 ± 0,2 ^îÑ. The table shows an average data of three parallel measurements.

The table. Influence AA and BAA on corrosion-electrochemical behavior and the basic characteristics of cyclic durability of St. 10 in neutral environments

The corrosion environment	pH	r×10^3, g/m^2×h	g	Z, %	ia, mcA/sm^2	, MPa	N, cycles
Air						327,0	5,0×10^6®
Background1	6,6	39,37	1,00	0,00	–	200,0	1,5×10^5
At presence
HMDA	11,9	0,82	48,01	97,00	1,6	310,5	1,8×10^6
BHMDA	8,9	0	¥	100,00	0,6	318,5	3,7×10^6
EDA	11,5	0,99	39,77	97,49	2,0	304,5	1,6×10^6
BEDA	8,9	0	¥	100,0	0,9	311,0	2,2×10^6
DEthA	12,0	1,18	33,36	97,00	2,3	298,0	1,5×10^6
BDEtA	8,9	0,42	93,74	98,93	1,8	306,5	1,7×10^6
TBA	11,1	1,43	27,53	96,37	2,5	290,5	1,1×10^6
BTBA	8,7	0,47	83,77	98,81	2,0	297,0	1,4×10^6
Background2	7,0	49,77	1,00	0,00	–	186,0	1,4×10^5
At presence
HMDA	11,9	2,04	24,40	95,90	2,0	281,5	7,5×10^5
BHMDA	8,9	0,28	177,75	99,44	0,7	302,5	1,4×10^6
EDA	11,5	3,17	15,70	93,63	2,4	273,5	6,5×10^5
BEDA	8,9	0,33	150,82	99,34	1,5	289,5	9,0×10^5
DEthA	12,0	3,67	13,56	92,63	2,6	262,5	6,0×10^5
BDEtA	8,9	1,37	36,33	97,23	2,3	274,5	7,5×10^5
TBA	11,1	4,42	11,26	91,12	3,0	258,0	5,0×10^5
BTBA	8,7	1,47	33,86	97,05	2,5	261,0	5,6×10^5

On the table one can see, that steel intensively suffers from corrosion in background electrolits. Clorid- and sulfate-ions noticeably accelerate corrosion process. Introduction ÀÀ in corrosion environments essentially reduces value r and i_a and raises size and N, and BAA possess greater inhibitor ability than corresponding ÀÀ. According to their inhibitory abilities alifatic amins settle down in a following decreasing order: HMDA > EDA > DEthA > TBA.

Results of corrosion measurements, electrochemical researches and corrosion fatigue tests perfectly correspond with each other.

Experimental data show, that the presence of amins and their borates makes corrosion environment more alcalic (see the table). It leads in to the fact that sufficient concentration of hydroacid-ions in electrolyte makes the passive oxide formation possible without external anode polarization which is proved by the data of thermodynamic calculations:

Fe + 2OH^– « FeO + H2O + 2e^–. DG^0=[–244,300+(–237,240)]–2(–157,335) = –166,870 kJoul/mol. èëè	(4)
3Fe + 8OH^– « Fe3O4 + 4H2O + 8e^–. DG^0=[–1014,200+4(–237,240)]–8(–157,335) = –704,480 kJoul/mol. èëè	(5)
2Fe + 6OH^– « Fe2O3 + 3H2O + 6e^–. DG^0=[–740,300+3(–237,240)]–6(–157,335) = –508,010 kJoul/mol. èëè	(6)

However it is necessary to note that there is no direct correlation between inhibitory action of additives and the size of pH environments. Anticorrosive properties of amins depend on their nature. Efficiency of amin action may be connected with their ability to adsorption due to interaction of non divided electronic atomic pairs of nitrogen with vacant d-orbital atoms of iron. Monoamins have one center of adsorption and diamins –have two. Therefore HMDA and EDA, containing two atoms of nitrogen, possess higher adsorption and inhibitory characteristics in comparison with DEthA and TBA. It is necessary to consider a spatial structure of amin molecules. The configurations of diethylamin and threbutylamins, as well as ammonia, represent a trigonal pyramid, that stericaly complicates adsorptions. In case of diamins the arrangement of nitrogen atoms admits their simultaneous link to a surface of iron, i.e that the adsorption-active centers are not complicated spatially. Therefore they form stronger links with metal that leads to the strengthening of their inhibitory ability in comparison with monoamins. According to [6] ocsoborats form dis soluble connections on metal. The increase of inhibitory abilities BAA may be explained by the formation of a stronger protective film the surface of a metal, formed by means of donor-acceptor ties through n-doublets of nitrogen atom and borats-ions hemobsorbtion.

Thus, AA and BAA can be used as inhibitory additives for protection of ferrous metals and their alloys against corrosion in neutral environments.

The literature:

1. Zhuk N.P. Course of corrosion and protection of metals. – Moscow: Metallurgy, 1968. – 408 p.

2. Skorchelletti V.V. Theoretical basis of metals corrosion. – Leningrad: Chemistry, 1973. – 264 p.

3. Ulig G.G., Revi R.U. Corrosion and struggle against it. Introduction in a corrosion science and technics: Trans. from English / Editor. A.M. Suhotins. – Leningrad: Chemistry, 1989. – 456 p.

4. Michailov V.I., Skvortsov V.G. Basis of corrosion and metal protection. P.1. – Cheboksary: Chuvashgospeduniversitet, 2004. – 241 p.

5. Skvortsov V.G Interaction's of a boric acid and borats with organic derivatives of ammonia // J. Inorgan. Chem. – 1986. – Vol. 31. – N 12. – P. 3163–3172.

6. Rosenfeld I.L. Ingibitory of corrosion. – Moscow: Chemistry, 1977. – 352 p.