Exploring the inhibition effect of tri-sodium phosphate concentrations on corrosion in Mg-sn-ca-mn anode for magnesium batteries

Figures & data

Figure 1. As cast Mg-5Sn-0.2Ca-0.2Mn (a) SEM micrograph, (b) optical micrograph, (c) EDS spectrum and (d) average grain size distribution.

Figure 2. SEM micrographs and EDS spectrum of as cast Mg-5Sn-0.2Ca-0.2Mn immersed in (a) NaCl, (b) NaCl +0.1 wt.% TSP, (c) NaCl +0.2 wt.% TSP, (d) NaCl +0.3 wt.% TSP.

Figure 3. Corrosion inhibition behaviour.

Table 1. Chemical composition of corroded samples.

	Magnesium	Tin	Calcium	Manganese	Oxygen	phosphate	Sodium
As cast	98.04	1.44	0.23	0.29	-	-	-
NaCl	29.48	0.09	0.02	0	70.42	-	-
0.1 wt. %	28.03	0.11	0.03	0	66.83	2.83	2.17
0.2 wt. %	28.36	0.16	0	0.01	66.88	1.75	2.83
0.3 wt. %	28.19	0.14	0.02	0.03	67.52	1.77	2.33

Figure 4. pH value of Mg alloy immersed in electrolytes for 72 hours.

Table 2. Weight gain of Mg alloy during 72 hours of immersion.

Immersion of as cast sample in electrolytes	Initial Weight [g]	After Immersion [g]	Weight gain [g]
NaCl	1.95	1.9586	0.0086
NaCl +0.1wt. % TSP	2.0721	2.0784	0.0063
NaCl +0.2 wt. % TSP	2.2292	2.2338	0.0046
NaCl +0.3 wt. % TSP	2.4062	2.4133	0.0071

Figure 5. Open circuit potential of Mg alloy with different concentration of TSP.

Figure 6. Nyquist plots of Mg-5Sn-0.2Ca-0.2Mn in different concentration of inhibitor.

Figure 7. Z curves of bode plot for Mg-5Sn-0.2Ca-0.2Mn alloy.

Figure 8. Phase angle of bode plots for Mg-5Sn-0.2Ca-0.2Mn alloy.

Figure 9. Equivalent circuit for short term immersed samples.

Figure 10. Equivalent circuit for 72 hours immersed samples.

Table 3. Open potential circuit results after 200 seconds.

	Vf (V)
NaCl [ST]	−1.62
NaCl +0.1 wt TSP [ST]	−1.626
NaCl +0.2 wt TSP [ST]	−1.62
NaCl +0.3 wt TSP [ST]	−1.616
NaCl [72 h]	−0.3183
NaCl +0.1 wt TSP [72 h]	−0.348
NaCl +0.2 wt TSP [72 h]	−1.582
NaCl +0.3 wt TSP [72 h]	−0.4904

Table 4. EIS results of Mg-Sn-Ca-Mn alloys.

	R1 (ohms)	R2 (ohms)	R3 (ohms)	Yo1	a1	Yo2	a2	W1	C1	L1	R4 (ohms)
NaCl [ST]	37.1	197.6	2.29E + 06	6.14E–05	7.85E–01	-	-	-	1.02E + 04	2.12E–03	-
NaCl + 0.1wt TSP [ST]	36.89	117	329.4	3.67E–05	8.51E–01	-	-	-	179.7	3.04E+03	-
NaCl + 0.2wt TSP [ST]	41.95	293.3	144	7.64E–05	7.24E–01	-	-	-	21.37	5.14E–01	-
NaCl + 0.3wtTSP [ST]	39.94	147	153.8	4.79E–05	8.40E–01	-	-	-	2.37E + 04	200.1	-
NaCl [72h]	53.58	-	-	1.92E–05	7.99E–01	1.91E–03	1	5.91E–04	-	-	323.3
NaCl + 0.1wtTSP [72h]	63.32	-	-	334.2	1.61E–03	7.26E–06	1.86E–02	2.26E–02	-	-	-
NaCl + 0.2wtTSP [72h]	44.9	331.4	413.5	6.19E–05	7.29E–01	-	-	-	3.15E+03	5.32E–01	-
NaCl + 0.3wtTSP [72h]	60.16	-	-	1.07E–04	5.40E–01	7.17E–04	5.34E–01	-4.51E–04	-	-	1.39E + 03

Figure 11. Tafel curves of Mg-5Sn-0.2Ca-0.2Mn for different immersion period in different electrolyte concentrations

Table 5. Corrosion results of Mg-5Sn-0.2Ca-0.2Mn alloys estimated by the tafel extrapolation method.

	Short term Immersion				72 hours Immersion
	NaCl [ST]	NaCl+0.1wt TSP [ST]	NaCl+0.2wt TSP [ST]	NaCl+0.3wt TSP [ST]	NaCl [72h]	NaCl+0.1wt TSP [72h]	NaCl+0.2wt TSP [72h]	NaCl+0.3wt TSP [72h]
Beta A (V/decade)	1.86E–02	1.81E–02	6.33E–02	2.00E–01	1.00E+15	1.00E+15	3.75E–02	6.22E–2
Beta C (V/decade)	1.76E–01	1.17E–01	8.87E–02	2.03E–01	1.59E–01	1.56E–01	1.67E–01	3.91E–2
icorr (μA)	59.1	6.88	5.73	24.2	0.339	0.402	32	0.0609
Ecorr (mV)	−1.560	−1.470	−1.500	−1.500	−0.630	−0.470	−1.500	−0.533
Corrosion Rate (mpy)	142.4	16.57	13.80	58.39	306.1e-3	363.6e-3	77.20	146.7E–3
Rp	1.24E–04	9.90E–04	2.80E–03	1.81E–03	2.03E–01	1.69E–01	4.16E–04	1.71E–1

Table 6. Inhibitor efficiency of trisodium phosphate.

Samples immersed in electrolytes	Inhibitor Efficiency (%)
NaCl + 0.1wt. % [ST]	88.35
NaCl +0.2wt. % [ST]	90.30
NaCl + 0.3wt. % [ST]	59.05
NaCl + 0.1wt. % [72h]	inefficient
NaCl +0.2wt. % [72h]	inefficient
NaCl +0.3wt. % [72h]	82.03

Figure 12. CV curves of Mg alloy in (a) NaCl (b) 0.1wt. % TSP (c) 0.2wt. % TSP (d) 0.3wt. % TSP for short term of immersion.

Figure 13. CV curves of Mg alloy in (a) NaCl (b) 0.1wt. % TSP (c) 0.2wt. % TSP (d) 0.3wt. % TSP for 72 hours of immersion.

Figure 14. Linear sweep voltammetry curves of Mg alloy in different concentrations for ST and 72h.