Corrosion and Inhibition Effects of Mild Steel in Hydrochloric Acid Solutions Containing Organophosphonic Acid

Table 2

Corrosion rates with respect to concentration of Fe(II), Fe(III), and total Fe(II + III) for mild steel in 10% HCl without inhibitor using voltammetric and polarographic methods.

(a) DPP mode

Time	Fe(II)		Fe(III)		Total Fe(II + III)
	Conc*	CR**	Conc*	CR**	Conc*	CR**
(1) 5 min	5.91	2.37	8.23	3.31	14.14	5.69
(2) 10 min	6.13	1.23	9.89	1.99	16.02	3.22
(3) 20 min	7.93	0.79	11.21	1.12	19.14	1.92
(4) 1 h	12.16	0.40	12.55	0.42	24.17	0.83
(5) 2 h	15.98	0.26	16.81	0.28	32.78	0.55
(6) 24 h	50.57	0.07	56.17	0.07	107.28	0.15

(b) DPASV mode

Time	Fe(II)		Fe(III)		Total Fe(II + III)
	Conc*	CR**	Conc*	CR**	Conc*	CR**
(1) 5 min	5.92	2.38	8.24	3.31	14.16	5.70
(2) 10 min	6.15	1.23	9.87	1.98	16.02	3.22
(3) 20 min	7.93	0.79	11.21	1.12	19.11	1.92
(4) 1 h	12.16	0.40	12.50	0.42	24.57	0.82
(5) 2 h	15.98	0.26	16.80	0.28	32.78	0.55
(6) 24 h	50.57	0.07	56.17	0.07	107.28	0.15

∗Corrosion concentration × 10² milligram.
**Corrosion rate × 10² milligram centimeter⁻² hour⁻¹.