Mechanical properties and damage constitutive model of sandstone after acid corrosion and high temperature treatments

Aiming at the problem of temperature-mechanics-chemical(T-M-C)action encountered by rocks in underground engineering,sandstone was selected as the sample for acid corrosion treatment at pH 1,3,5 and 7,the acid corrosion treated samples were then subjected to high-temperature experiments at 25,300,600,and 900℃,and triaxial compression experiments were conducted in the laboratory.The experimental results show that the superposition of chemical damage and thermal damage has a significant impact on the quality,wave velocity,porosity and compression failure characteristics of the rock.Based on the Lemaitre strain equivalent hypothesis theory,the damage degree of rock material was described by introducing damage variables,and the spatial mobilized plane(SMP)criterion was adopted.The damage constitutive model can well reflect the stress-strain characteristics of the rock triaxial compression process,which verified the rationality and reliability of the model parameters.The experiment and constitutive model analyzed the change law of mechanical properties of rock after chemical corrosion and high temperature thermal damage,which had certain practical significance for rock engineering construction.

Separation of galena and chalcopyrite using the difference in their surface acid corrosion characteristics

Galena(PbS)and chalcopyrite(CuFeS_(2))are sulfide minerals that exhibit good floatability characteristics.Thus,efficiently separating them via common flotation is challenging.Herein,a new method of surface sulfuric acid corrosion in conjunction with flotation separation was proposed,and the efficient separation of galena and chalcopyrite was successfully realized.Contact angle test results showed a substantial decrease in surface contact angle and a selective inhibition of surface floatability for corroded galena.Meanwhile,the contact angle and floatability of corroded chalcopyrite remained almost unaffected.Scanning electron microscope results confirmed that sulfuric acid corrosion led to the formation of a dense oxide layer on the galena surface,whereas the chalcopyrite surface remained unaltered.X-ray photoelectron spectroscopy results showed that the chemical state of S^(2-)on the surface of corroded galena was oxidized to SO_(4)^(2-).A layer of hydrophilic PbSO4was formed on the surface,leading to a sharp decrease in galena floatability.Meanwhile,new hydrophobic CuS_(2),CuS,and Cu_(1-x)Fe_(1-y)S_(2-z)species exhibiting good floatability were generated on the chalcopyrite surface.Finally,theoretical analysis results were further verified by corrosion–flotation separation experiments.The galena–chalcopyrite mixture was completely separated via flotation separation under appropriate corrosion acidity,corrosion temperature,and corrosion time.A novel approach has been outlined in this study,providing potential applications in the efficient separation of refractory copper–lead sulfide ore.

Efficiency of Chalcone Compounds Inhibitors for Acid Corrosion of Al and Al-3.5Mg Alloy

Corrosion inhibition of Al and Al-3.5Mg alloy by organic compounds, namely chalcones in hydrochloric acid solutions has been investigated by rapid polarization technique and weight loss method. Polarization measurements show that, the inhibitors act cathodically both in case of Al and Al-3.5Mg alloy. It was found from the weight loss measurements that, the inhibition efficiency depends on the substituent in the chalcone compound. The relative inhibitive efficiency of these compounds has been explained on the basis of structure dependent electron donor properties of the inhibitors and the metal inhibitor interaction on the surface. The inhibition efficiency ranges from 16 to 64% for Al and from 30% to 91% for Al-3.5Mg alloy

Concentration Boundary Layer Model of Mortar Corrosion by Sulfuric Acid

A long time immersion experiment of mortar specimens is carried out to investigate their degradation mechanism by sulfuric acid.Water-cement ratios of mortar are ranging from 0.5 to 0.7 and the pH value of sulfuric acid is 3.5 and 4.0 respectively.The pH meter is used to monitor the soak solution and the titration sulfuric acid with given concentration is added to maintain original pH value,through which the acid consumption of mortar is recorded.A theoretical reaction rate model is also proposed based on concentration boundary layer model.The results show that theoretical model fits the experimental results well and the corrosion mechanism can be modeled by a diffusion process accompanied with an irreversible chemical reaction when pH value of soak solution is no less than 3.5.

Benevolent behavior of Kleinia grandiflora leaf extract as a green corrosion inhibitor for mild steel in sulfuric acid solution

The ethanolic extract of Kleinia grandiflora leaves was characterized and tested for its potential anticorrosion properties on mild steel in 1 M H2SO4 medium using mass-loss analysis, potentiodynamic polarization measurements, electrochemical impedance spectroscopy, Fourier-transform infrared spectroscopy, scanning electron microscopy, UV–visible spectroscopy, and X-ray diffraction analysis. The effect of temperature on the corrosion behavior of mild steel was studied in the range of 308 to 328 K. The inhibition efficiency was observed to increase with increasing concentration of the extract. Polarization curves revealed that the Kleinia grandiflora leaf extract is a mixed inhibitor. Impedance diagrams revealed that an increase of Kleinia grandiflora leaf extract concentration increased the charge transfer resistance and decreased the double-layer capacitance. The adsorption process obeys Langmuir＇s model, with a standard free energy of adsorption（ΔGads） of-18.62 k J/mol. The obtained results indicate that the Kleinia grandiflora leaf extract can serve as an effective inhibitor for the corrosion of mild steel in a sulfuric acid medium.

Effects of W and Mo Additions on Wet-dry Acid Corrosion Behavior of Low-Alloy Steels Under Different O_2 Concentrations

Effects of W and Mo additions on wet-dry acid corrosion behavior of low-alloy steels under different O2 concentrations were investigated. The results showed that W and Mo-containing steels presented excellent wet-dry cor- rosion resistance under O2 concentrations of both 1 and 5%. The roles of W and Mo played in increasing corrosion resistance of the steels were different. W could improve the thermodynamic stability of the steel substrate, while Mo could promote the formation of protective rust. Interaction between W, Mo and O2 concentration greatly influenced wet-dry acid corrosion of low-alloy steels. W addition was more effective for depressing charge transfer process at the rust/substrate interface and presented higher enhanced effect on increasing corrosion resistance than Mo under O2 concentration of 1%. Mo was more effective on increasing rust compactness and showed higher enhanced effect on increasing corrosion resistance than W under O2 concentration of 5%.

Corrosion behaviour of 6061 Al-15vol. Pct. SiC composite and its base alloy in sulphuric acid medium

In this paper the corrosion characteristics of Silicon carbide particulate-reinforced 6061 aluminum composite （ 6061 AI/SiCp composite ） and the base alloy are experimentally assessed. The corrosion tests are carried out at different temperatures in the concentration range of 0.01N to 1N sulphuric acid as corrosion media using Tafel extrapolation technique and Electrochemical Impedance Spectroscopy （EIS）. The results obtained from Tafel extrapolation technique and Electrochemical Impedance Spectroscopy are in good agreement. The results show an increase in the corrosion rate with increase in temperature as well as with increase in the concentration of the corrosion media. The thermodynamic parameters like energy of activation are calculated using Arrhenius theory equation and, enthalpy of activation and entropy of activation are calculated using transition state theory equation.

A Study of Eruca vesicaria, Bromelia hemisphaerica and Erythrina americana as Green Corrosion Inhibitors for Carbon Steel in Sulfuric Acid

A study of Eruca vesicaria, Bromelia hemisphaerica and Erythrina americana as eco-friendly corrosion inhibitors for 1018 carbon steel in 0.5 M H2SO4 has been carried out by using weight loss tests, potentiodynamic polarization curves and electrochemical impedance spectroscopy measuremnts. Results have shown that the three extracts performed as good corrosion inhibitors, but the Eruca vesicaria exhibited the best performance followed by Erythrina americana. The three inhibitors formed a protective, passive film which protected the steel from corrosion. This was because they contain antioxidants present in their molecular structure with heteroatoms such as N, C and O like phenols, amino acids, etc., which react with metal and environment to form the protective film.

Corrosion behavior and characteristics of the product film of API X100 steel in acidic simulated soil solution

The short-term corrosion behavior of API X100 steel in an acidic simulated soil was investigated by electrochemical measurements and soaking experiments,followed by corrosion morphology observations and X-ray photoelectron spectroscopy analyses.The results show that X100 steel exhibits an obvious pitting susceptibility in an acidic soil environment.Pits nucleate after approximately 10 h of immersion.Along with the nucleation and growth of the pits,the charge-transfer resistance and open-circuit potential first increase sharply,then decrease slowly,and eventually reach a steady state.The maxima of the charge-transfer resistance and open-circuit potential are attained at approximately 10 h.The evolution of the electrochemical process is confirmed by the analysis of the product film.The product film exhibits a porous and loose structure and could not protect the substrate well.The product film is primarily composed of ferrous carbonate and ferrous hydroxide（Fe（OH）2）.The concentration of Fe（OH）2 in the product film increases from the inside to the outside layer.

Corrosion Inhibition of Carbon Steel in Hot Hydrochloric Acid Solutions

The dissolution of carbon steel in 5% HCl in the temperature range of 30~90℃ was inhibited by two organic compounds having the general formula: ClR NH2(CH2)n NH2 RCl where R is a benzyl group. The behaviour of these inhibitors in acidic medium were investigated using weight loss method, open circuit potential and linear polarization technique. These inhibitors provided satisfactory corrosion inhibition for carbon steel in hydrochloric acid solutions even at higher temperature and acid concentration (10%). The electrochemical results showed that the polarization resistance (Rp) values increased with increasing inhibitor concentration, also the corrosion current decreased and a higher inhibition efficiency was obtained. The protective properties of these two organic inhibitors were attributed to the chemisorption mechanism

Effects of applied potential on the stress corrosion cracking behavior of 7003 aluminum alloy in acid and alkaline chloride solutions

Potentiodynamic polarization tests and slow strain rate test（SSRT） in combination with fracture morphology observations were conducted to investigate the stress corrosion cracking（SCC） behavior of 7003 aluminum alloy（AA7003） in acid and alkaline chloride solutions under various applied potentials（Ea）. The results show that AA7003 is to a certain extent susceptible to SCC via anodic dissolution（AD） at open-circuit potential（OCP） and is highly susceptible to hydrogen embrittlement（HE） at high negative Ea in the solutions with p H levels of 4 and 11. The susceptibility increases with negative shift in the potential when Ea is less than-1000 m V vs. SCE. However, the susceptibility distinctly decreases because of the inhibition of AD when Ea is equal to-1000 m V vs. SCE. In addition, the SCC susceptibility of AA7003 in the acid chloride solution is higher than that in the alkaline solution at each potential. Moreover, the effect of hydrogen on SCC increases with increasing hydrogen ion concentration.

Erosion–corrosion behavior of austenitic cast iron in an acidic slurry medium

A series of austenitic cast iron samples with different compositions were cast and a part of nickel in the samples was replaced by manganese for economic reason. Erosion–corrosion tests were conducted under 2wt% sulfuric acid and 15wt% quartz sand. The results show that the matrix of cast irons remains austenite after a portion of nickel is replaced with manganese.（Fe,Cr）3C is a common phase in the cast irons, and nickel is the main alloying element in high-nickel cast iron; whereas,（Fe,Mn）3C is observed with the increased manganese content in low-nickel cast iron. Under erosion–corrosion tests, the weight-loss rates of the cast irons increase with increasing time. Wear plays a more important role than corrosion in determining the weight loss. It is indicated that the processes of weight loss for the cast irons with high and low nickel contents are different. The erosion resistance of the cast iron containing 7.29wt% nickel and 6.94wt% manganese is equivalent to that of the cast iron containing 13.29wt% nickel.

Temperature effect on the corrosion and passivation characterization of Ni_(82.3)Cr_7Fe_3Si_(4.5)B_(3.2) alloy in acidic media

The effects of temperature on corrosion and the electrochemical behavior of Ni82.3Cr7Fe3Si4.5B3.2 glassy alloy in HC1,H2SO4,and H3PO4 acids were studied using AC and DC techniques.Impedance data reveal that the susceptibility to localized corrosion increases with increasing temperature.Potentiodynamic polarization curves reveal that the bulk glassy alloy is spontaneously passivated at all the investigated temperature in H2SO4 and H3PO4 solutions.A localized corrosion effect in HCl solution is clearly observed.The apparent activation energies in the regions of Tafel,active,and passive,as well as the enthalpies and entropies of the dissolution process were determined and discussed.The high apparent activation energy（Ea） value for H3PO4 solution in Tafel region is explained by the low aggressivity of PO4^3- ions.

CORROSION INHIBITION OF STEARIC ACID LANGMUIR-BLODGETT MONOLAYERS ON IRON

The Langmuir-Blodgett (LB) technique was used for the first time to study inhibition mechanism. Stearic acid Langmuir-Blodgett (SALB) monolayers showed a good inhibition effect on iron corrosion in neutral environment and the inhibition is mainly based on the blocking effect.

INHIBITIVE ACTION OF INORGANIC COMPOUND ON CORROSION OF ALUMINIUM IN HYDROCHLORIC ACID

The inhibitive action of CaSO_4 towards corrosion of aluminium in 1 mol/L HCl has been inveetigated by using fluorometrio and weight loss techniques.The results show that the inhibitor exhibits an outstanding function of inhibition,especially at higher tempe- ratures,and it was found to be predomiantly of cathodic rate control.Ths mechanism of inhibition and the effect of CdSO_4 on the corrosion kinetics are also discussed.

Corrosion Inhibition of Carbon Steel in Acidic Mediaby Using Actinidia deliciosa(Kiwifruit)Extract

The corrosion inhibition of 1018 carbon steel in 0.5 M H2SO4 by using Actinidia deliciosa (Kiwifruit) peel extract has been investigated by using potentiodynamic polarization curves and electro-chemical impedance spectroscopy. Two kinds of extracts are investigated, one from the tender, and another one from ripe Actinidia deliciosa. Concentrations include 0, 25, 50, 75, and 100 ppm at room temperature. Results indicate that both kind of extracts acted as good corrosion inhibitors, is more efficient in the ripe extract. Corrosion inhibition efficiency increases with increasing its concentration for ripe extract, whereas for the tender Actinidia deliciosa, the higest inhibitor efficiency is obtained by adding 25 ppm and decresaing with a further increase in its concentration. Both extracts improve the passive film properties by decreasing the passive current density values. It is found that the corrosion inhibition is due to the presence of heteroatoms present in Actinidia deliciosa, mainly quercitine, which is physically adsorbed in the steel following a Frumkin type of adsorption isotherm which forms a protective film.

Electrochemical corrosion behavior of bulk ultra-fine grained Fe-Ni-Cr alloy

The corrosion behavior of bulk ultra-fine grained（UFG） Fe-Ni-Cr alloy prepared by equal-channel angular pressing technique was investigated in 0.25 mol/L Na2SO4＋0.05 mol/L H2SO4 solution by electrochemical measurements.As compared to the coarse grained（CG） counterpart,the UFG alloy exhibits an acceleration of the active dissolution and a shrunk passive region with a higher passive current.The Mott-Schottky analysis in conjunction with the point defect model indicates mat the donor diffusion coefficient in the passive films of the UFG sample increases greatly to one magnitude order higher and the donor density is slightly lower than that of the CG sample.

Effect of aqueous extract of leaves of Morinda tinctoria on corrosion inhibition of aluminium surface in HCl medium

The effect of Morinda tinctoria(MT) leaves extract on the corrosion inhibition of Al in acid medium was studied. The inhibition studies were carried out on Al in 0.5 mol/L HCl with the extract of leaves of MT using mass loss and electrochemical techniques. Parameters, such as concentration of the inhibitor, concentration of the acid, temperature and concentration of halide ions, were varied and optimized. Increase of the temperature and concentration of acid can decrease the performance of the inhibitor. Thermodynamic parameters show that the physisorption of the inhibitor molecules on Al surface obeys Langmuir isotherm.

Effect of Cl^-Concentration on the Corrosion Behavior of 16Mn Steel in Saturated H2S/CO2 Solution

The corrosion behavior of 16Mn steel was studied in saturated H2S or H2S/CO2 solutions containing different Cl^-concentrations at 80℃.The microstructure and chemical composition of the corrosion products were investigated through scanning electron microscopy,energy-dispersive X-ray spectroscopy,EPMA,and X-ray diffraction.Results showed that the corrosion rate decreased with increasing Cl^-concentration in saturated H2S or H2S/CO2 solution at pH 4.Conversely,the corrosion rate increased with increasing Cl^-concentration in saturated H2S solution at pH 6.The relative H^＋concentration decreased because of the increase of Cl^-concentration at pH 4,and Cl^-acted as a catalyst in the corrosive medium at pH 6 because the net H^＋concentration decreased obviously compared with the condition at pH4.Cl^-promoted the formation of Fe-deficient iron sulfide at pH 4,and the opposite effect was observed in the nearly neutral solution.The corrosion rate increased firstly with increasing Cl^-concentration and then decreased in the saturated H2S/CO2solution at pH 6.The corrosion products were mainly composed of two kinds of iron sulfide.Sulfide FeS（1-x） was a kind of tetragonal crystal,whereas the other was the hexagonal/monoclinic iron sulfide Fe（1-x）S.The corrosion film that was mainly composed of FeS（1-x） did not confer a protective effect on the base metal.The atomic ratio of Fe/S was more than 1 for FeS（1-x）.The appearance of sulfide FeS（1-x） resembled a square block or small,needlelike,flocculent particles.The atomic ratio of Fe/S was less than 1 for Fe（1-x）S,and the corrosion film mainly composed of Fe（1-x）S conferred some protective property on the base metal.The sulfide FeS（1-x） exhibited a long claviform morphology with a hexagonal or quadrilateral cross-sectional shape.

Effect of interstitial carbon and nitrogen on corrosion of FeCoCrNi multi-principal element alloys made by selective laser melting

The corrosion behaviors of selective laser melted(SLMed)FeCoCrNi multi-principal element alloys(MPEAs)with carbon or nitrogen addition in 0.5 M H_(2)SO_(4) solution were investigated.Both C and N ad-dition refined the grains and introduced a heterogeneous structure in SLMed FeCoCrNi MPEA,but they had opposite effects on the corrosion behavior.The doped carbon participated as nano-sized carbides in SLMed MPEA,and localized galvanic corrosion occurred,degrading the corrosion resistance.The doped nitrogen was gathered with chromium and formed CrN chemical clusters in SLMed MPEA,and a protec-tive passive film with a higher Cr_(2)O_(3)/Cr(OH)_(3) ratio formed,which improved corrosion resistance.