Corrosion mechanisms of steel concrete moulds in contact with a demoulding agent studied by EIS and XPS

The behaviour of E24 mild steel was studied by XPS analysis and electrochemical impedance spectroscopy (EIS) in a filtered solution of cement (pH 13), and an alkyl N-aminodiphosphonate aqueous solution called Aquadem^® (7?pH?13). XPS results showed that the corrosion products developed in both media consisted of Fe₂O₃, covered by a very thin layer of goethite. The thickness of this oxide layer was estimated to be 3 nm. XPS analysis also demonstrated the adsorption of Aquadem^® on the outer layer of FeOOH for pH lower than the zero charge pH of goethite (7.55). From XPS and EIS results, physical models of the E24 steel/electrolyte interface are proposed as a function of pH. For 11?pH?13, the steel is covered by a passive film, while for pH?10, pitting corrosion takes place. At pH 7, an additional mass transport phenomenon must be taken into account. The fitting procedure provided values for several physical parameters (electrolyte resistance, passive film resistance), from which the film capacitance and the dielectric constant of the oxide layer were calculated.     

The isoxazolidines: the effects of steric factor and hydrophobic chain length on the corrosion inhibition of mild steel in acidic medium

Several new isoxazolidines having varying degree of steric environment and hydrophobic chain length, prepared efficiently using single-step nitrone cycloaddition reactions, are tested for corrosion inhibition of mild steel in 1 M and 5 M HCl at 50-70 °C range by gravimetric and electrochemical methods. All compounds have shown very good corrosion inhibition efficiency (IE%) in acidic solution. Steric crowding around the nitrogen centres and hydrophobic chain lengths as well as increase in temperature (in the presence of the inhibitor in the higher concentration range 100-400 ppm) are found to increase the inhibition efficiency of the isoxazolidines. Thermodynamic parameters (ΔG°_ads, ΔH°_ads, ΔS°_ads) for the adsorption process and kinetic parameters for the metal dissolution (or hydrogen evolution) reaction in the presence of one of the isoxazolidines were determined. Experimental results agree with the Temkin adsorption isotherm. The inhibition of corrosion in 1 M HCl, influenced by both physi- and chemi-sorption, was found to be under mixed control, but predominantly under cathodic control.     

Inhibiting effects of some mercapto-triazole derivatives on the corrosion of mild steel in 1.0 M HCl medium

The effect of some mercapto-triazole derivatives synthesized in the laboratory containing different hetero atoms and substituents in the organic structures on the corrosion and hydrogen permeation of mild steel in 1.0 M HCl was investigated by weight loss and various electrochemical techniques. Results obtained reveal that all the mercapto-triazole derivatives perform excellently as corrosion inhibitors for mild steel in 1.0 M HCl. Potentiodynamic polarization studies have shown that all these compounds suppress both the anodic and cathodic process and they behave as mixed-type inhibitors. Double layer capacitance and charge transfer resistance values were derived from Nyquist plots obtained from AC impedance studies. Changes in impedance parameters are indicative of the adsorption of these compounds on the metal surface. The inhibition efficiency mainly depends on the nature of the investigated compounds. The values of the inhibition efficiency calculated from these techniques are in reasonably good agreement. The extent of reduction of hydrogen permeation current through mild steel surface was studied by the hydrogen electropermeation technique. The adsorption of these compounds on mild steel surface is found to obey Langmuir adsorption isotherm. The free energy of adsorption for inhibiting process was determined on the basis of Langmuir adsorption isotherm.     

Existence results for impulsive differential inclusions with nonlocal conditions

In this paper, we shall establish sufficient conditions for the existence of mild solutions for nonlocal impulsive differential inclusions. On the basis of the fixed point theorems for multivalued maps and the technique of approximate solutions, new results are obtained. Examples are also provided to illustrate our results.     

数列极限在实际中的应用

数列极限是一类重要的极限,在经济和数学领域中发挥着重要的作用。以举例的方式介绍数列极限在现实生活中的应用,包括几何中计算曲线所围图形的面积．求二次方程的数值解,购房按揭贷款分期还款问题,及连续复利问题。     

Phytochemical screening and corrosion inhibitive behavior of Pterolobium hexapetalum and Celosia argentea plant extracts on mild steel in industrial water medium

Preliminary phytochemical screening was carried out for methanolic extracts of Pterolobium hexapetalum (PH) and Celosia argentea (CA). Methanolic extracts of PH and CA were studied as corrosion inhibitors for mild steel in industrial water medium using mass loss and electrochemical techniques. The adsorption of both PH and CA extracts on mild steel surface followed Langmuir isotherm. The electrochemical impedance spectroscopy (EIS) measurements showed that the charge transfer resistance increases with increasing concentration of extracts. Various thermodynamic parameters were evaluated and discussed. Scanning electron microscopy (SEM) was used to analyze the surface adsorbed film. Further, antioxidant activity of the plant extracts was determined and correlated with the results obtained with inhibition efficiency.     

Corrosion inhibition of mild steel using Novel Bis Schiff’s Bases as corrosion inhibitors: Electrochemical and Surface measurement

Purpose: The aim of the present investigation is to evaluate the corrosion inhibiting properties of four novel synthesize compounds namely N¹,N^1′-(1,4-phenylene)bis(N⁴-(4-nitrobenzylidene)benzene-1,4-diamine) SB-I, N¹,N^1′-(1,4-phenylene)bis(N⁴-benzylidenebenzene-1,4-diamine) SB-II, N¹,N^1′-(1,4-phenylene)bis(N⁴-(4-methylbenzylidene)benzene-1,4-diamine) SB-III, N¹,N^1′-(1,4-phenylene)bis(N⁴-(4-methoxybenzylidene)benzene-1,4-diamine) SB-IV for mild steel in 1 M HCl. Corrosion inhibitors find wide application in industries during pickling of steel, descaling and oil well acidization. Inhibitors have attracted great attention due to cost effectiveness and simplicity of the methods. Method: Different experimental techniques such as weight loss, open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization were used to evaluate the corrosion inhibition performance of SBs for mild steel in acid solution. After the corrosion experiments, the surface morphology of metal surface in the absence and presence of SBs were studied by scanning electron microscopy (SEM) and Atomic force microscopy (AFM). Findings: The corrosion inhibition efficiency of SBs for mild steel are 71.42% (SB-I), 89.52 (SB-II), 92.85 (SB-III), 96.19 (SB-IV). Tafel polarization revealed that all the SBs behaved as mixed-type inhibitor but predominantly of cathodic type. The inhibition actions of these Schiff base molecules blocked the electrode surface by means of adsorption of the inhibitor molecule on metal surface, obeying the Langmuir adsorption isotherm. SEM/AFM studies of the metal surfaces confirm the protection of metal surface in presence of inhibitor as compared to the damaged surface in blank acid solution.     

Comparative studies on the electrochemical and physicochemical behaviour of three different benzimidazole motifs as corrosion inhibitor for mild steel in hydrochloric acid

This paper examines the anticorrosion characteristics of three different benzimidazole derivatives towards mild steel in 0.5?M hydrochloric acid at temperature ranges from 303 to 323?K. The benzimidazole derivatives used for the screening studies are 2-(2-methyl-1H-benzimidazol-1-yl) acethydrazide (EMBAH), 2-(2-ethyl-1H-benzimidazol-1-yl) acethydrazide (EEBAH) and 2-(2-propyl-1H-benzimidazol-1-yl) acethydrazide (EPBAH). The corrosion inhibition was investigated by weight loss, electrochemical impedance spectroscopy and potentiodynamic polarization studies. The adsorption interaction between metal and inhibitor followed Langmuir adsorption isotherm. The Gibb’s free energy values clarify the spontaneous nature of adsorption process. The temperature dependence of inhibition efficiency was explained by considering thermodynamic parameters of adsorption and kinetic parameters of corrosion. These inhibitors showed good efficiency at lower as well as moderately higher temperatures. Quantum chemical calculations were done using DFT at the B3LYP/6-31G¹ level to study the electronic properties of the molecules for correlating the inhibitive effect and molecular structure.     

Mild oxidative degradation of spent auricularia auricular substrate and molecular composition of carboxylic acids in the resulting soluble portion

Spent auricularia auricular substrate(SAAS) was oxidatively degraded with aqueous hydrogen peroxide(AHPO)/acetic anhydride(AAH) to produce carboxylic acids(CAs) under mild conditions. The results show that up to 53.6% of the organic matter in SAAS was converted to the soluble species(SSs). In total 122 CAs were detected in the SSs by the analysis with a gas chromatograph/mass spectrometer, which can be classified into 29 group components, mainly being aliphatic acids and along with small amount of aromatic acids. Among the aliphatic acids, normal alkanedioic acids are the most abundant. The detected aromatic acids include benzoic acids,phthalic acids, trimellitic acids, pyromellitic acids, and their derivatives. The synergistic oxidation and the released ·OH, CH_3COO·, and HOO· induced by AHPO/AAH play crucial roles in oxidatively degrading SAAS.     

Wear behaviour of steel coatings produced by friction surfacing

Friction surfacing was performed to produce multi-layer coatings of AISI 1024, AISI 1045 and AISI H13 over mild steel substrates where a continuous joining was achieved between adjacent layers and between the clad and the substrate. Microscopic and hardness characterization revealed the presence of bainitic and martensitic microstructures which influenced the hardness of the coatings. The study aimed to determine which material combination was more wear-resistant. The analysis suggested that AISI 1024 presents the least wear, both in terms of friction coefficient and wear rate. This is due to the formation of adherent protective oxide layer which is not present in both the AISI 1045 and AISI H13 steels.