Determination of the corrosion resistance of low alloyed steels by magnetic method

An innovative method of measuring and control of the steel corrosion rate by changing magnetic characteristics is developed. The impact of heat treatment on the corrosion rate of the samples of high-carbon steels (maximum corrosion loss is observed at a tempering temperature of 400°C) is attributed to the appearance of micro-galvanic pairs (MGP) between the phase components of the material. MGP undergo redistribution under heat treatment thus changing conditions of the galvanic current flow. The structural phase composition, in turn, determines the magnetic properties of steel and correlation between the magnetic properties and corrosiveness. The goal of the study is demonstration of the possibility and expediency of using the magnetic parameters of steel for determination of the steel corrosion rate. A close correlation dependence is observed between the coercive force and the electrochemical potential (relative to the silver chloride electrode) which are direct indicators of the corrosiveness. Case study of a pipeline made of 09G2S steel along which change in the coercive force attained 25% revealed rather high risk of developing micro-galvanic pairs. A rapid method of scanning magnetic parameters is proposed to detect potentially corrosive zones. A multi-parameter approach can be used to solve the problem of the ambiguity of the relationship between the corrosiveness and magnetic parameters. Harmonic decomposition of magnetic hysteresis loops of 45Kh steel samples is used to obtain a number of odd harmonics. Some of them weakly correlate with the corrosion loss, whereas complexes of several harmonics correlate to a greater extent. The results can be used in technical diagnostics and prediction of the corrosion activity of steel structures before their operation. The results can be used in technical diagnostics and forecasting of the corrosiveness of steel structures prior to their operation.

Corrosion of galvanic pairs of Co-Cr alloys with high-copper silver amalgam using Mansfeld formulas

ABSTRACT In the restoration of lost or damaged dental pieces, different alloys are frequently used, leaving the mouth exposed to electrical currents that circulate through saliva and dental fluids. In the present work, electrochemical methods are used to determine the corrosion rate of galvanic pairs of a high copper silver amalgam with Co-Cr dental alloys in artificial saliva. It is observed that when the difference in corrosion potentials of dissimilar alloys are small (less than 100 mVecs), Evans diagrams do not give good results, so the Mansfeld correction formulas must be used. Thus, it is found that the most resistant to corrosion is the pair formed between the amalgam and the bulk Co-Cr alloy (PG1,3) and that the corrosion products released in greater quantity to the electrolyte are those that contain ions of Co, Cr, Ag, Sr and Cu.

EVALUACIÓN DE LA SUSCEPTIBILIDAD A LA CORROSIÓN DE PARES GALVÁNICOS DE AMALGAMAS DE PLATA CON ALEACIONES DENTALES Ni-Cr EN SALIVA ARTIFICIAL USANDO EL MÉTODO DE EVANS Y LAS FÓRMULAS DE MANSFELD

EVALUACIÓN DE LA SUSCEPTIBILIDAD A LA CORROSIÓN DE PARES GALVÁNICOS DE AMALGAMAS DE PLATA CON ALEACIONES DENTALES Ni-Cr EN SALIVA ARTIFICIAL USANDO EL MÉTODO DE EVANS Y LAS FÓRMULAS DE MANSFELD EVALUATION OF THE SUSCEPTIBILITY TO CORROSION OF GALVANIC PAIRS OF AMALGAMS OF SILVER WITH DENTAL ALLOYS OF NI-CR IN ARTIFICIAL SALIVA USING THE METHOD OF EVANS AND THE FORMULAS OF MANSFELD Elvar QuezadaCastillo, Bertha Quezada Alván DOI: https://doi.org/10.33017/RevECIPeru2009.0002/ RESUMEN La corrosión galvánica es un proceso de disolución metálica que se produce cuando dos metales de distinto potencial electroquímico se sumergen en un electrolito, originando corrientes eléctricas entre los metales a través del medio conductor. En la restauración de piezas dentales perdidas o deterioradas se usan frecuentemente diferentes aleaciones, quedando la boca expuesta a corrientes eléctricas que circulan a través de la saliva y los fluidos dentarios. En el presente trabajo se utilizaron el método de Evans y las fórmulas de corrección de Mansfeld para evaluar la susceptibilidad a la corrosión de pares galvánicos de amalgamas de plata con aleaciones dentales Ni-Cr en saliva artificial, encontrándose que los más resistentes son los pares formados entre amalgamas de plata de alto cobre con aleaciones Ni-Cr que contienen berilio, y que los productos de corrosión liberados en mayor cantidad al medio electrolítico contienen iones de Hg, Ag, Ni y Cr. Palabras clave: Aleaciones, amalgamas, corrosión, pares galvánicos, saliva artificial, polarización. ABSTRACT Galvanic corrosion is a process of metallic dissolution that takes place when two metals of different electrochemical potential are submerged in an electrolyte, so originating electrical current between metals through conductor environment. For restoration of lost or deteriorated dental pieces different alloys are used frequently, then mouth is exposed to electrical currents that circulate through the saliva and dental fluids. In the present work the method of Evans and the formulas of correction of Mansfeld were used to evaluate the susceptibility to corrosion of galvanic pairs of amalgams of silver of high copper with Ni-Cr alloys that contain beryllium, and that products of corrosion released in greater amount to electrolytic environment contain ions of Hg, Ag, Ni and Cr. Keywords: Alloys, amalgams, corrosion, galvanic pairs, artificial saliva, polarization.

Corrosion of galvanic pairs of dental alloys copper base with silver amalgams in artificial saliva

ABSTRACT Galvanic corrosion is a metal dissolution process that occurs when two metals of different electrochemical potential are immersed in an electrolyte causing electrical currents between the metals through the conducting medium. To restore lost or damaged teeth, different alloys are used, leaving the mouth exposed to electrical currents that circulate through saliva and dental fluids. In the present work, the potentials and densities of corrosion currents of galvanic pairs of silver amalgams and copper base dental alloys were determined simultaneously using potenciodynamic methods, finding that the most resistant to corrosion are the pairs formed by silver amalgams of high copper and Cu -Zn alloys, and that the corrosion products released in greater quantity in the electrolytic medium are formed by Hg, Cu, Zn and Ni ions.