ANTI-CORROSION PROPERTIES OF CARBOXYLIC ACID IN WATER-GLYCOL SOLUTIONS

ANTI-CORROSION PROPERTIES OF CARBOXYLIC ACID IN WATER-GLYCOL SOLUTIONS

Research article

Bashkirceva N. Y.¹, Sladovskya O. Y.², Ovchinnikova Y. S.³, Vagapov B.R.⁴

^1,2,4 Kazan National Research Technological University, Kazan, Russia

³«Bulgar-syntez» Ltd., Kazan, Russia

 

Abstract

Sodium salts of carboxylic acids were investigated to evaluate the corrosion properties of the water-glycol solutions. Corrosion tests were performed by methods of gravimetry and galvanostatic dissolution with metals used in cooling systems. The compositions of anticorrosion systems and their concentration that provide the most effective inhibition of metals were determined.  

Key words: water-glycol solution, corrosion inhibitors, carboxylic acids, properties, researching.  

Modern techniques requires a large range of liquid heat carriers and working bodies with specific complex of rheological, thermal, anticorrosion and other properties. However, the choice of the basis for the creation of such fluids from the chemical and petrochemical industry products is extremely difficult because of the large number of requirements to them. Sometimes these requirements are mutually exclusive.

The water is the cheapest coolant used in heat exchangers, heating and cooling internal combustion engines having a set of thermophysical properties. Low freezing point of water is a significant disadvantage that limits its application. Freezing point of water can be reduced by adding inorganic salts, glycerin, monobasic alcohols (methanol, ethanol, isopropyl).

However, in continuous contact with metal element of thermally conductive systems brine and water-alcohol mixtures cause corrosion. Under conditions of high temperature and constant circulation of coolant corrosion processes are amplified many times. In this regard, any coolant must contain in its composition anticorrosion systems.

This paper presents research on the effectiveness of inhibitory complexes based on carboxylic acid salts for water-glycol solutions. Sodium salt of benzoic acid, lauric acid, succinic, adipic and sebacic acid in the concentration range of 0.25 - 2.5% were studied. Corrosion tests were performed in 50% vol. aqueous solution ethylene glycol according to methods of gravity and galvanostatic dissolution of metals.

Corrosion activity was assessed against the following materials: aluminum (type 3003), steel (SAE 1010), copper (electrolytic), brass (Cu-70, Zn-30), cast iron, solder (Pb-70, Sn-30). Data about corrosion losses of test metals in experimental solutions of salts are given in Table 1.  

Table 1 - Corrosion losses of metals in water-glycol solutions of sodium salts

Salt concentration, %	The loss in weight, mg
	solder	copper	brass	aluminum	steel	cast iron
1	2	3	4	5	6	7
Sodium succinate
0,25	10,7	7,1	5,8	5,0	2,2	3,1
0,5	4,1	7,0	2,6	5,1	1,7	2,6
0,75	3,2	4,4	2,5	4,9	0,5	1,1
1,0	2,8	4,1	2,4	5,2	0,4	0,9
1,5	2,0	2,4	2,5	5,5	0,3	0,2
2,0	1,7	2,2	2,4	5,9	0,1	0,1
2,5	1,6	1,5	1,9	6,1	0,0	G
Sodium adipate
0,25	11,8	5,0	5,0	1,8	5,4	6,9
0,5	4,5	5,0	4,9	1,9	2,8	4,0
0,75	3,3	4,2	3,4	3,5	2,0	3,1
1,0	2,4	2,9	3,0	4,5	1,5	2,3
1,5	2,3	2,1	2,8	4,4	0,2	0,4
2,0	0,7	1,4	2,8	4,5	0,1	0,3
2,5	0,6	0,9	2,7	4,8	0,1	0,1
Sodium sebate
0,25	7,4	5,4	5,2	4,0	6,9	4,1
0,5	7,0	4,2	2,9	4,5	6,8	4,0
0,75	4,6	3,2	2,7	5,9	5,7	2,9
1,0	2,7	0,8	1,4	6,8	3,2	2,6
1,5	0,7	0,1	0,1	7,4	0,1	1,2
2,0	0,6	0,1	0,1	8,2	0,1	1,2
2,5	0,5	0,0	0,0	8,8	0,1	0,9
Sodium laurate
0,25	16,9	6,0	5,5	5,4	18,8	20,5
0,5	12,4	6,0	5,1	5,4	9,0	10,7
0,75	7,2	4,9	4,6	4,9	8,2	10,2
1,0	4,7	4,6	2,3	4,2	6,6	6,8
1,5	2,4	3,3	2,3	3,5	4,7	6,8
2,0	2,1	3,0	2,2	3,3	4,6	6,7
2,5	2,0	2,9	2,2	2,9	4,4	6,2

It is well known that the carboxylate anions of dibasic organic acids are effective complexing agents for a wide range of metals. Therefore, the protective mechanism of action of salts of dicarboxylic acids is associated with the formation of sparingly soluble chelate compounds on the surface of all studied metals except aluminum and its alloys [1]. Neutral aluminum octahedral complexes {[(СН2)nС2О4]³Al}^3¯ are insoluble in water, but readily soluble in most organic solvents, including alcohols. This, apparently, prevents the formation on the surface of aluminum and its alloys effective protective films.

On the contrary, when we used sodium laurate as a corrosion inhibitor, there was a significant reduction in the corrosion loss of aluminum. This is most likely due to the formation on the surface of poorly soluble in water-glycol solution of aluminum laurate.

On the effectiveness of inhibiting metals from water-glycol solutions corrosion studied salts of carboxylic acids can be arranged in the following sequence:

for non-ferrous metals (solder, copper, brass)

sebate > adipate > succinate > laurate

for ferrous metals (steel, cast iron)

succinate > adipate > sebate > laurate

for aluminum

laurate > adipate > succinate > sebate

From the data in Table. 1, we can see that with increasing length of the hydrocarbon chain of dicarboxylic acids protective effect of salts increases in respect of non-ferrous metals and decreases in respect to for ferrous metals (cast iron). In the water-glycol solution containing 2.0% sodium sebate protection degree of solder, copper and brass is about 96 - 97% (for succinate - 91% in the case of solder and 25 - 30% for copper and brass), and protection degree of iron for similar solutions of sodium succinate is 99.7% (for sebate - 96.5%).

The study of the corrosion behavior of metals in combinations of solutions of sodium salts of dicarboxylic acids showed (Table 2) that the most significant positive synergetic effects for all tested metals are in the mixture of sodium succinate and sebate. In the study of other combinations corrosion losses of metal in these mixtures are not lower than in solutions of individual salts at the same concentration.

Table 2 - Corrosion behavior of metals in 2% water-glycol solutions of salts of dicarboxylic acids in their mass ratio 1:1.

*- there are the data about corrosion losses of metal in 2% solutions of the individual salts in the bottom line.  

Cooling systems of internal combustion engines are polymetallic contact systems such as aluminum-steel-cast iron and copper-brass-solder. In this regard, the influence of water -glycol solutions of sodium salts of dicarboxylic acids on the corrosion behavior of metals was studied in these polymetallic contact systems. The results of corrosion tests are presented in Table 3.  

Table 3 - The rate of corrosion of metals in contact systems of water-glycol solution of sodium salts of dicarboxylic acids

Sodium salts concent-ration	Corrosion rate, mg
	solder			copper			brass
	succiniс acid	adipic acid	sebacic acid	succinic acid	adipic acid	sebacic acid	succinic acid	adipic acid	sebacic acid
solder-copper-brass system
0	0,435*			0,080			0,085
0,25	0,288	0,290	0,185	0,178	0,125	0,135	0.14	0,125	0,130
0,5	0,105	0,112	0,130	0,175	0,125	0,105	0,065	0,092	0,073
0,75	0,080	0,083	0,105	0,110	0,105	0,080	0,063	0,085	0,068
1,0	0,070	0,060	0,068	0,100	0,073	0,020	0,060	0,075	0,035
1,5	0,050	0,057	0,018	0,061	0,053	0,005	0,063	0,070	0,005
2,0	0,043	0,018	0,015	0,055	0,035	0,004	0,060	0,070	0,003
2,5	0,040	0,015	0,013	0,038	0,022	0,000	0,056	0,066	0,000
aluminum-steel-cast iron system
	aluminum			steel			cast iron
0	0,108			0,553			0,865
0,25	0,125	0,045	0,100	0,055	0,135	0,175	0,075	0,173	0,103
0,5	0,128	0,048	0,112	0,043	0,070	0,170	0,065	0,100	0,100
0,75	0,123	0,088	0,148	0,013	0,050	0,145	0,028	0,078	0,073
1,0	0,130	0,113	0,170	0,010	0,038	0,080	0,023	0,058	0,065
1,5	0,138	0,110	0,185	0,007	0,005	0,002	0,005	0,010	0,030
2,0	0,148	0,113	0,205	0,002	0,002	0,002	0,002	0,008	0,030
2,5	0,150	0,117	0,220	0,000	0,002	0,002	0,000	0,002	0,022

*- boldface indicates values of corrosion rates of metals that do not meet in GOST 28084 (rates of corrosion loss of metal in accordance with GOST 28084: solder - 0.2, for the other metals - 0.1 mg) [2].  

The investigated salts of dicarboxylic acids in concentrations 0.5-0.75% reliably prevents corrosion of the solder, brass and cast iron, and with increasing concentrations up to 1.0% - of copper and steel. At the same time they initiate corrosion of aluminum, except for sodium adipate, which is in the concentration range of 0.25-0.75%, slightly reduces the corrosion losses of the this metal. Increasing the concentration of sodium succinate from 1.5 to 2.5% almost not impact on the corrosion losses of base metals, while using similar concentrations of sodium adipate can significantly reduce the rate of corrosion of copper and solder (almost four times). Sodium sebate completely inhibits corrosion of copper and brass (protection degree up to 100%), and significantly of solder (97%). Increasing the concentration of the studied salts in water-glycol solutions to 2.0% almost completely prevents the corrosion of steel samples (99.7%). For the cast iron by using sodium succinate value of the protection degree is 99.8%, and in the case of sodium adipate and sodium sebate - 99.1 and 96.5%, respectively. A further increasing of the salt content of dicarboxylic acid has almost no effect on the corrosion losses of tested metals.

Thus, the results of researches on definition of corrosive effects of water-glycol solutions of sodium salts of carboxylic acids in the test specimens, we found that the most effective anticorrosion systems contain sodium succinate and sodium sebate.

Comparison of experimental data obtained in the study of protective properties of examined corrosion inhibitors in water-glycol solutions showed that anticorrosion systems based on carboxylic and dicarboxylic acids exhibit high protective properties with respect to all of the metals and this systems can be used to develop antifreeze formulations.

The results presented in this paper were obtained under financial support of the Ministry of Education and Science of Russia of integrated projects implemented under the RF Government Decree № 218.

References

1. Skorchelletti V.V. Theoretical basis of the corrosion of metals. L.:Chemistry, 1973.

2. State standard ofUSSR, Low-freezing cooling fluids. General specifications. GOST 28084-89, M.: Publishing house of standards, 1989.