′-((2-methoxy-naphthalene-1-yl)methylene) pyrimidine-5-carbohydrazide (H5) and

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Abstract

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• 3.1.2 Effect of temperature.
• Comp. Temp. 30 °C 35 °C

Comp.	Conc.
Activation parameters
	ΔH* (kJ mol−1)	−ΔS* (J mol−1 K−1)
	Blank	55.14	57.71	73.30
H4	1 × 10−6	77.74	80.29	3.51
	2 × 10−6	80.47	83.03	4.46
	5 × 10−6	84.73	87.28	17.48
	10 × 10−6	92.90	95.45	42.00
	15 × 10−6	97.17	99.71	54.79
	20 × 10−6	123.16	125.69	132.54
H5	1 × 10−6	76.21	78.76	8.63
	2 × 10−6	80.22	82.77	3.97
	5 × 10−6	83.96	86.51	15.15
	10 × 10−6	89.40	91.94	31.45
	15 × 10−6	93.28	95.83	43.13
	20 × 10−6	111.34	113.88	99.87
H6	1 × 10−6	77.74	80.29	3.51
	2 × 10−6	80.86	83.41	5.74
	5 × 10−6	84.73	87.28	17.48
	10 × 10−6	93.67	96.21	44.42
	15 × 10−6	97.17	99.71	54.79
	20 × 10−6	126.94	129.46	144.61

3.1.2 Effect of temperature.The influence of temperature on the corrosion rates of carbon steel in 1 M HCl and in the presence of gradual inhibitor amounts was considered in the temperature from 30 to 45 °C using the weight loss method. As the temperature rises, the % IE of the added inhibitors slightly increases which is the characteristics of chemisorption, the results were summarized in Table 5.
Table 5 Weight loss results for carbon steel sheets in 1 M HCl solution without and with gradual concentrations of (H4 & H5 & H6) at 30–45 °C

Comp.	Temp.	30 °C		35 °C		40 °C		45 °C
	Conc.	θ	% IE	θ	% IE	θ	% IE	θ	% IE
H4	1 × 10−6	0.537	53.7	0.566	56.6	0.562	56.2	0.583	58.3
	2 × 10−6	0.588	58.8	0.599	59.9	0.605	60.5	0.621	62.1
	5 × 10−6	0.682	68.2	0.697	69.7	0.701	70.1	0.787	78.7
	10 × 10−6	0.783	78.3	0.802	80.2	0.821	82.1	0.838	83.8
	15 × 10−6	0.826	82.6	0.831	83.1	0.852	85.2	0.865	86.5
	20 × 10−6	0.909	90.9	0.924	92.4	0.945	94.5	0.962	96.2
H5	1 × 10−6	0.381	38.1	0.425	42.5	0.444	44.4	0.484	48.4
	2 × 10−6	0.522	52.2	0.548	54.8	0.587	58.7	0.596	59.6
	5 × 10−6	0.587	58.7	0.607	60.7	0.618	61.8	0.623	62.3
	10 × 10−6	0.695	69.5	0.729	72.9	0.744	74.4	0.751	75.1
	15 × 10−6	0.711	71.1	0.735	73.5	0.766	76.6	0.782	78.2
	20 × 10−6	0.883	88.3	0.906	90.6	0.929	92.9	0.926	92.6
H6	1 × 10−6	0.412	41.2	0.452	45.2	0.454	45.4	0.464	46.4
	2 × 10−6	0.501	50.1	0.521	52.1	0.522	52.2	0.582	58.2
	5 × 10−6	0.574	57.4	0.623	62.3	0.685	68.5	0.691	69.1
	10 × 10−6	0.643	64.3	0.645	64.5	0.663	66.3	0.685	68.5
	15 × 10−6	0.802	80.2	0.824	82.4	0.825	82.5	0.844	84.4
	20 × 10−6	0.955	95.5	0.953	95.3	0.952	95.2	0.965	96.5

3. 2Potentiodynamic polarization (PDP) method

The polarization curves for carbon steel in corrosive media having increasing amounts of (H4 & H5 & H6) at 25 °C are illustrated in Fig. 6. kinetic parameters as corrosion current (I_corr), corrosion potential (E_corr), and Tafel slopes (β_a and β_c) were got from the obtained figures and are shown in Table 6 for carbon steel in 1 M HCl corrosive medium with and without gradual concentrations of (H4 & H5 & H6). % IE rises with increasing the concentrations of the compounds. Fig. 6 shows that the I_corr values decrease by the addition of the additives which decreases the carbon steel oxidation. The increase of the concentration of the compounds influences the anodic and cathodic directions of the polarization curves. The increase in the concentrations of additives moved the E_corr values towards the negative values when comparing with the blank. Hence, addition of (H4 & H5 & H6) decrease the carbon steel corrosion and suppress hydrogen release as demonstrated of equal cathodic Tafel curves in Fig. 6. The parallel lines of the Tafel lines after the addition of the (H4 & H5 & H6) indicate that there is no change in the mechanism of both H₂ release and metal consumption processes. In fact, the inhibitor is categorized as cathodic or anodic kind if the moving of corrosion potential in the existence of the inhibitor is ±85 mV from that in the absence of the inhibitor. (H4 & H5 & H6) presence shifts E_corr values to values not exceeded 15 mV, and Tafel slopes of β_a and β_c at 25 °C did not notably changed which indicated that (H4 & H5 & H6) can be categorized as a mixed-type inhibitors.³⁴

	Fig. 6 Potentiodynamic polarization curves for the corrosion of carbon steel in 1.0 M HCl in the absence and presence of altered concentrations of compound (H4) at 25 °C.

Table 6 The effect of concentration of (H4 & H5 & H6) on the corrosion potential (E_corr), corrosion current (I_corr), Tafel slopes (β_a & β_c), corrosion rate (C.R.), surface coverage (θ) and inhibition efficacy (% IE) for the corrosion of carbon steel 1 M HCl at 25 °C^a

C.	Conc.	Icorr, μA cm−2	−Ecorr, mV (vs. SCE)	βa, mV dec−1	βc, mV dec−1	C.R. (mpy)	θ	% IE

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