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Showing 62 results for Corrosion

Lee W.e.,
Volume 1, Issue 3 (9-2004)
Abstract

Penetration and dissolution mechanisms are reviewed for predominantly single-phase oxide, two phase oxide and oxide-carbon composite refractories by liquid silicate slags. Theoretical models of these processes, as well as static (sessile drop, dipping and crucible) and dynamic (rotating finger and rotary slag) experimental tests, along with their practical limitations are considered. Direct (congruent or homogeneous) attack is controlled by the reaction rate at the slag-refractory interface or the rate of diffusive transport of species to it through the slag leading to active corrosion. Indirect (incongruent or heterogeneous) attack is controlled by diffusive transport through the slag or through a new solid phase, which forms at the original slagrefractory interface. This may lead to passive corrosion. Examples of direct and indirect attack in a range of refractory/slag systems are described highlighting the critical influence of the composition and hence viscosity of the local liquid slag adjacent the solid refractory. Penetration and corrosion can be controlled either through the local slag composition via the refractory or the bulk slag or by microstructural control of the refractory by e.g. internal generation of dense layers or external deposition/generation of passive coatings, so-called in situ refractories.
Karaminezhaad M., Maghsoudi A.a., Nozhati R., Sakhaei A.,
Volume 1, Issue 4 (12-2004)
Abstract

A large number of reinforced concrete structures subjected to chloride ions. Two basicapproaches for preventing corrosion of reinforcing steel embedded in concrete are: Increasing theconsolidation of concrete and using different coating on rebars. In present research steel rebarsare coated in different ways: a) 40 µm of zinc electroplated on steel rebar b) Zinc powder withepoxy paste (zinc rich). The rebars were placed in a macrocell design according to ASTM G109-92. Concrete operations were done with mixture designs of high and normal strength concrete.The results show corrosion decrease of zinc coated rebars.
Pakshir M., Amini R.,
Volume 2, Issue 1 (3-2005)
Abstract

Anodes are critical component of cathodic protection systems. As part of this effort, three different anodes were tested in a cathodic protection system that was designed and constructed to prevent further corrosion of reinforced concrete. This anodic system includes an electrically conductive coating composition applied in fluid form over an outer surface of the concrete mix. The composition further includes a predetermined amount of electrically conductive carbon material (coke, carbon black, graphite) uniformly distributed in the epoxy resin (as a binder) whereby the coating composition has a predetermined value of resistively. This investigation attempts to find the best type and optimum content of conductive carbon filler in poxy coating, to ensure optimal anode working parameters for marine environments (basically marine and sewer environments) and if any of the coating systems tested in this study excel over the other. In this study, electric and electrochemical parameters of three layer (with average coating thickness of 300µm) coke-epoxy, carbon black-epoxy and graphite-epoxy conducting paints (with different amount of filler) have been determined during long-term anodic polarization (70 days) in a seawater solution. During this test, on the basis of impedance measurements, the electrical resistances of these coatings have been calculated every 14 days. if conductive paints exhibit good electric and electrochemical stability, they will be attractive for cathodic protection of reinforced concrete.
Dehghanian C., Saremi M., Mohammadi Sabet M.,
Volume 2, Issue 1 (3-2005)
Abstract

The synergistic behavior of molybdate and phosphate ions in mitigating the corrosion of mild steel in simulated cooling water was evaluated performing potentiodynamic polarization and impedance spectroscopy tests. Phosphate and molybdate showed a synergistic effect on corrosion inhibition of steel in simulated cooling water. The observed reduction in anodic and cathodic current densities could be the consequence of incorporation of both phosphate and molybdate ions in forming a protective layer on the surface. The charge transfer resistance of the protective layer formed on steel surface was much greater in presence of both ions in solution than that when each inhibitor used alone.
Moayed M.h.,
Volume 2, Issue 3 (9-2005)
Abstract

In this research pitting Corrosion of a sensitized 316 stainless steel was investigated employing potentiodynamic, potentiostatic techniques. Sensitization process was carried out on as-received alloy by submitting the specimen in electric furnace set at 650°Cfor five hours and then the specimen was quenched 25°C water. Potentiodynamic polarization of as received and sensitized specimens in 1M H2SO4 solution at room temperature and 70°C clearly revealed that the sensitization process has caused a magnificent change on electrochemical behavior of the specimen by changing critical current density for passivation, passivation potential and passive current density. Optical microscopy examination of the specimen surface after oxalic acid electrochemical etching also showed the deterioration of grain boundary of sensitized specimen due to chromium carbide precipitation in compared to as-received one. Several anodic potentiodynamic polarization on rode shaped working electrodes prepared from as-received and sensitized specimen in 3.5% NaCl test solution proved an average ~220 mV drop in pitting potential due to sensitization. Anodic potentiostatic polarization at 400 and 200 mV above corrosion potential also demonstrate the deterioration of pitting resistance of alloy as a result of sensitization. Scanning electron microscopy examination of anodically polarized of sensitized specimen at 700mVprior and after oxalic acid etching revealed large stable pits with lacy cover and also openpits with deep crevice for etched specimens.
Saremi M., Nouri Delavar A., Kazemi M.,
Volume 2, Issue 4 (12-2005)
Abstract

An investigation of the electrochemical noise generation during Stress Corrosion Cracking (SCC) of 70-30 Brass in Mattson's solution was conducted. The fluctuations of potential and current were monitored. The relationship between potential and current fluctuations has been evaluated in time domain and the obtained data has been analyzed in the frequency domain using Power Spectral Density (PSD). It is shown that 70-30 Brass has characteristic noise behavior during SCC that is step-by-step change in current and potential up to the final stage of fracture, and this may be used for SCC monitoring.
Rigaud M., Palco S., Paransky E.,
Volume 3, Issue 1 (6-2006)
Abstract

Wear of various basic refractory materials to substitute to currently used magnesia chrome bricks has been studied, measuring matte and slag penetration and dissolution, through different cup and rotary slag tests. High magnesia with and without impregnation, magnesia graphite, magnesia-alumina spinel with and without impregnation, olivine-magnesia and olivine magnesia- graphite bricks, as well as magnesia-graphite and olivine magnesia castables, have been tested. It has been shown that carbon impregnation and graphite introduction into basic refractories are feasible ways to enhance their corrosion-dissolution and penetration resistance against fayalite as well as calcium-ferrite slags. Olivine-based refractories (castables or bricks) may be considered as viable candidates to use in copper-making furnaces. At this point, evaluation of the thermo-mechanical properties of this new class of materials is still missing.
Oprea G.,
Volume 3, Issue 3 (12-2006)
Abstract

Although the flash smelting technologies use different furnace designs, the refractory linings are exposed to very similar aggressive environments and, as a result, the corrosion analysis results on one type of furnace could be generally applied to other furnaces of similar high temperature processes. Particularities regarding the different chemistries of the pyrometallurgical process and operating parameters of these furnaces could also bring particular aspects to be considered when analyzing the refractory ware and final failure in use. This paper presents a review of the existent experimental. data of corrosion analyses on refractory linings used in two particular flash furnaces for zinc-lead and respectively nickel-copper smelting. Although various modern water cooling systems are generally used to protect the refractory wall linings against corrosion by molten slag and matte, the performance of the refractory roof lining, usually used without water cooling, represents a permanent concern and the object of research studies to extend their life in service. The failure mechanisms analysed in this study are based on postmortem analyses and laboratory corrosion experiments with magnesite-chrome bricks of different chemical and mineralogical compositions. The gaseous atmosphere, usually rich in SO2 and/or CO and various metal fumes, produces irreversible microstructural changes which could shorten the life in service of the refractory lining. The experimental data proved that thermal cycling in SO2/SO3 atmospheres could bring more damage than a continuous use at relatively constant temperature, due to the magnesium and calcium sulphate formation. The laboratory experiments and postmortem analyses showed that that metal fumes at various partial pressure of oxygen would condense as oxides and react inside the pores and at the grain boundaries, contributing to the continuous deterioration of the ceramic matrix of the refractory brick lining. The mechanisms of corrosion, discussed based on laboratory experiments, were confirmed by the postmortem analyses on brick samples used in the industrial flash smelting furnaces.
A. Khavasfar1,, M. H. Moayed2, M. M. Attar3,
Volume 4, Issue 3 (12-2007)
Abstract

Abstract: The performance of an Imidazoline based commercial corrosion inhibitor in CO2 corrosion of a gas-well tubing steel was studied by employing Electrochemical Impedance Spectroscopy (EIS) technique. Inhibitor performance was investigated by means of its efficiency at various concentration and also its behavior at various exposure time. EIS results showed that inhibitor interaction to the electrode surface obeys Lungmuir adsorption isotherm. Interpretation of some parameters such as Rct, Rpf, Cdl, and Cpf associated to the equivalent circuit fitted to the experimental rsults showed that not only inhibitor efficiency and surface coverage improve by increasing in inhibitor concentration in the solution but also at constant inhibitor concentration both surface coverage and efficiency improve with exposure time and reach to their highest value after 4 hours.
A. Ahmadi,, H. Sarpoolaky,, A. Mirhabibi, F. Golestani-Fard,
Volume 4, Issue 3 (12-2007)
Abstract

Abstract: Dolomite based refractories are widely used in Iranian steelmaking plants. In the present research, wear and corrosion of refractories used in steel-making converter lining in Esfahan Steel Company was studied. Post-mortem analysis of refractories clarified that the wear started with oxidation of carbon followed by chemical corrosion. Iron oxide from slag reacted with calcia, resulting in formation of low melting phase, and subsequent washout process, caused the refractory corrosion onset from the hot face. In addition, the effect of aluminum as an anti-oxidant and graphite on the corrosion resistance of refractory was investigated. Tar-dolomite samples containing different amount of graphite (0, 4, 7, and 10 wt. %) were prepared in order to study their physical properties, before and after coking. SEM micrographs employed to analyze the microstructures to determine the effect of graphite and antioxidant on corrosion behavior of the refractory. Results showed that oxidation process of carbon in the system was hindered and improved corrosion resistance by introducing graphite and antioxidant into the refractory composition.
H. Fattahi, M. H. Shariat,
Volume 5, Issue 1 (3-2008)
Abstract

Abstract: In chloride salt solutions, titanium alloys exhibit reasonably high pitting potentials as high as +10 V (vs. Ag/AgCl) at room temperatures. On the other hand, anodic pitting potentials are significantly lower in bromide solutions. In this study, pitting corrosion of commercially pure titanium in aqueous NaBr solution of 0.1 M concentration at room temperature was studied and the effect of an external magnetic field oriented both parallel and perpendicular to electrode surface was investigated. Cyclic potentiodynamic and potentiostatic polarization tests were carried out. Anodic breakdown potential of +1.45 V (vs. Ag/AgCl) obtained in the absence of magnetic field, decreasing to +1.11 V in the presence of a 0.05 T parallel magnetic field. The perpendicular magnetic field actually did not affect the breakdown potential. Applying of an external magnetic field, independent of its orientation, shifted the repassivation potential approximately 150 mV in the positive direction. SEM microscopy observations of sample surfaces indicated that applying of magnetic field results in some variations in the pit shapes and their sizes.
M. Rezvani, B. Eftekhari Yekta, V. K. Marghussian,
Volume 5, Issue 1 (3-2008)
Abstract

Abstract: The application of inexpensive materials such as copper, zinc, lead, iron and steel slag in manufacturing of glass and glass-ceramic products in construction industry, lining materials as anti-corrosion and anti-abrasion coatings in metals and etc, has led to considerable progress in glass technology in recent years. The composition of slag glass-ceramics is mainly located in the SiO2-Al2O3-CaO-MgO system, in which one of the most important problems is the lack of bulk crystallization. To resolve the above-mentioned problem, the crystallization behavior of various compositions containing different nucleating agents Cr2O3 , Fe2O3 and TiO2 in the single, double and triple forms were studied by differential thermal analysis (DTA).The precipitated crystalline phases was determined by the X-ray diffractometry and the micro-structural analysis was studies using the SEM micrographs. The three point bending strength, micro-hardness and the chemical resistance of the best composition were determined. According to the results, the resulted glassceramic had a better specification than the stoneware floor tiles and the porcelain one, which are considered as the two important competitors for it.
C. Dehghanian, Y. Mirabolfathi Nejad,
Volume 5, Issue 1 (3-2008)
Abstract

Abstract: Despite having a number of advantages, reinforced concrete can suffer rebar corrosion in high–chloride media, resulting in failure of reinforced concrete structures. In this research the corrosion inhibition capability of the mixture of calcium and ammonium nitrate of steel rebar corrosion was investigated in the simulated concrete pore solution. Cyclic polarization and Electrochemical Impedance Spectroscopy (EIS) techniques were applied on steel concrete pore solution containing 2 weight percent sodium chloride (NaCl). Results show that such mixtures had higher inhibition efficiency than calcium nitrate alone. The optimum concentration of the inhibitor mixture was determined to be 45 mgr/lit.
K. Ghanbari Ahari,
Volume 5, Issue 1 (3-2008)
Abstract

Abstract: Thermodynamic computational packages MTDATA and FactSage have been used to carry out calculations on the variation with temperature of the phases precipitated on cooling in both oxidising and reducing conditions of a typical ladle slag composition, in the temperature range 1700 - 900°C. The current coverage of the databases associated with the computational packages is discussed in relation to their application to slag - refractory interaction and the validity of the results is compared with some relevant experimental data and phase equilibrium studies
William L. Headrick,, Alireza Rezaie, William G. Fahrenholtz,
Volume 5, Issue 2 (6-2008)
Abstract

gasification (BBLG). One particularly harsh application is linings for gasifiers used in the treatment of black liquor (BL). Black liquor is a water solution of the non-cellulose portion of the wood (mainly lignin) and the spent pulping chemicals (Na2CO3, K2CO3, and Na2S). Development of new refractory materials for the black liquor gasification (BLG) application is a critical issue for implementation of this technology. FactSage® thermodynamic software was used to analyze the phases present in BL smelt and to predict the interaction of BL smelt with different refractory compounds. The modeling included prediction of the phases formed under the operating conditions of high temperature black liquor gasification (BLG) process. At the operating temperature of the BLG, FactSage® predicted that the water would evaporate from the BL and that the organic portion of BL would combust, leaving a black liquor smelt composed of sodium carbonate (70-75%), potassium carbonate (2-5%), and sodium sulfide (20-25%). Exposure of aluminosilicates to this smelt leads to significant corrosion due to formation of expansive phases with subsequent cracking and spalling. Oxides (ZrO2, CeO2, La2O3, Y2O3, Li2O, MgO and CaO) were determined to be resistant to black liquor smelt but non-oxides (SiC and Si3N4) would oxidize and dissolve in the smelt. The other candidates such as MgAl2O4 and BaAl2O4 were resistant to sodium carbonate but not to potassium carbonate. LiAlO2 was stable with both sodium carbonate and potassium carbonate. Candidate materials selected on the basis of the thermodynamic calculations are being tested by sessile drop test for corrosion resistance to molten black liquor smelt. Sessile drop testing has confirmed the thermodynamic predictions for Al2O3, CeO2, MgO and CaO. Sessile drop testing showed that the thermodynamic predictions were incorrect for ZrO2.
S.r. Allahkaram, R. Shamani,
Volume 6, Issue 1 (3-2009)
Abstract

Abstract: Due to the expansion of high voltage Alternating Current (AC) power transmission lines and cathodically protected buried pipelines, it is becoming more and more difficult to construct them with enough safe distances between them. Thus, the pipelines are frequently exposed to induced AC interferences, which result in perturbation of Cathodic Protection (CP) due to AC corrosion. To study the above criterion, an experimental set up was used with coupons exposed to simulated soil solutions, while under both CP and AC induced condition for which an AC+DC power supply was utilized. The experiments were carried out in several simulated soil solutions corresponding to several soil samples collected from various regions along a buried pipeline with overhead parallel high voltage power transmission line. The results indicated that AC corrosion depends strongly on the composition of the soil.
S.r. Allahkaram, R. Shamani,
Volume 6, Issue 2 (6-2009)
Abstract

Abstract: The risks of alternating current (AC) corrosion and overprotection increasingly demand new criteria for
cathodically protected pipelines. To assess the risk of AC corrosion, new cathodic protection (CP) criteria have been
proposed based on DC/AC current densities measurements using coupons. The monitoring system designed for this
project was based on the instant-off method, with steel coupons simulating coating defects on a buried pipeline. The
problems associated with the instantaneous off-potential measurements have been attributed to a non-sufficient time
resolution. In present study, it has been possible to determine the de-polarisation of steel coupon within a few
milliseconds after disconnecting the coupon from the DC/AC power source, by increasing data acquisition rate. For
this, a monitoring system was developed in order to measure the IR-free potential together with the DC/AC current
densities. The monitoring system was utilized for both laboratory experiments and site survey to study the mechanism
and the condition of AC corrosion, its mitigation and more importantly to define new CP criteria.


A. Davoodi, J. Pan,ch. Leygraf, Gh. R. Ebrahimi, M. Javidani,
Volume 6, Issue 3 (9-2009)
Abstract

Abstract: Localized corrosion of aluminum alloys is often triggered by intermetallic particles, IMP’s. To understandthe role of IMP’s in corrosion initiation of EN AW-3003, efforts were made to combine nano-scale ex-situ analysis ofthe IMP’s by SEM-EDS, SKPFM and in-situ AFM monitoring of the localized attack in chloride containing solution.The results showed that two distinct types of eutectically-formed constituent IMP’s exist the -Al(Mn,Fe)Si and theAl(Mn,Fe) phases. However, the exact chemical composition of the IMP’s varies with the particles size. Volta potentialdifference of surface constituents revealed that IMP’s have a higher Volta potential compared to the matrix, indicatingthe cathodic characteristic of the IMP’s. Noticeably, the boundary regions between the matrix and IMP’s exhibited aminimum Volta potential probably the sites for corrosion initiation. Localized corrosion attack monitored by in-situAFM clearly showed the trench formation occurrence around the large elongated IMP’s in the rolling direction.
Arash Yazdani, Mansour Soltanieh, Hossein Aghajani,
Volume 6, Issue 4 (12-2009)
Abstract

Abstract: In this research plasma nitriding of pure aluminium and effect of iron elemental alloy on the formation and growth of aluminium nitride was investigated. Also corrosion properties of formed AlN were investigated. After preparation, the samples were plasma nitrided at 550oC, for 6, 9 and 12 h and a gas mixture of 25%H2-75%N2. The microstructure and phases analysis were investigated using scanning electron microscopy and X-ray diffraction analysis. Moreover corrosion resistance of samples was investigated using polarization techniques. The results showed that only a compound layer was formed on the surface of samples and no diffusion zone was detected. Dominant phase in compound layer was AlN. Scanning electron microscopy results showed that nitride layer has particulate structure. These nitrided particles have grown columnar and perpendicular to the surface. It was also observed that the existence of iron in the samples increases the nitrogen diffusion, thus growth rate of iron containing nitrides are higher than the others. Corrosion tests results showed that formation of an aluminium nitride layer on the surface of aluminium decreases the corrosion resistance of aluminium significantly. This is due to elimination of surface oxide layer and propagation of cracks in the formed nitride layer
A. m. Hadian, B. Nazari,
Volume 7, Issue 3 (8-2010)
Abstract

  ABSTRACT

Dolomite refractories have a good production potential in Iran due to the existence of high-quality dolomite ore in many regions of the country, particularly in Isfahan and Hamedan. The basic problem associated with the production and use of this type of refractories is inherent tendency to hydration of calcined dolomite. One of the methods to overcome this problem is to increase the amount of magnesia in doloma. This study focuses on the use of Iranian dolomite to produce magnesia –doloma (mag-dol) refractory with high resistance to hydration and corrosion. It was found that addition of 20wt% magnesite to dolomite would result in capsulating of CaO by MgO that protects doloma from further hydration

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