Valter Dolecek

Corrosion Monitoring System Based on Measurement and Analysis of Electrochemical Noise

Abstract A corrosion monitoring system using electrochemical noise measurements and their numerical analysis was developed. Electrochemical noise was measured in a freely corroding system containin...

Electrochemical noise during non-stationary corrosion processes

In the present work, electrochemical noise (EN) was measured in three different types of experimental set-ups in order to obtain and compare various types of corrosion. Simultaneously with EN measurements, a parallel technique was used, regarding the type of experimental set-up: a computer visualization system combined with optical microscopy, or measurements of mechanical changes. In order to distinguish between these corrosion types and to assess corrosion rate, the measured EN signals were analysed by two different techniques: spectral and statistical. On the basis of estimated significant spectral parameters (power spectral densities of current and voltage noise, spectral noise resistance) and statistical parameters (standard deviation, localisation index and noise resistance), the passive state, localized corrosion types and uniform corrosion can be recognized. However, by these parameters it is not possible to distinguish between certain localized corrosion processes: metastable pitting, initiation and growth of stable pits, stress-corrosion cracking. It was ascertained that these corrosion processes exhibit unstable nature, and consequently generated EN signals are usually non-stationary. Since stationarity is required for spectral and statistical analysis, the unstable nature of these processes was recognized as the main reason for unreliable results. It is believed that these types of signal analysis give poor information about corrosion processes which can be easily identified from EN signal itself: transient corrosion processes and transitions between different corrosion processes. Elektrochemisches Rauschen bei nicht-stationaren Korrosionsprozessen In der hier vorgestellten Arbeit wurden elektrochemische Rauschmessungen an drei verschiedenen experimentellen Systemen mit dem Ziel durchgefuhrt, verschiedene Korrosionsformen bestimmen und vergleichen zu konnen. Parallel zu den elektrochemischen Rauschmessungen wurden mechanische Veranderungen erfasst, sowie mikroskopische Untersuchungen mit Hilfe rechnergestutzter Visualisierung durchgefuhrt. Zur Bestimmung der Korrosionsart und der Korrosionsgeschwindigkeit wurden die gemessenen Rauschsignale mittels spektraler und statistischer Methoden analysiert. Anhand bestimmter Spektralparameter (Leistungsdichte des Strom- und Potentialrauschens, spektraler Rauschwiderstand) und statistischer Kenngrosen (Standardabweichung, Lokalisationsindex, Rauschwiderstand) konnte zwischen dem passiven Zustand, lokalen Korrosionsformen und aktiver Korrosion unterschieden werden. Jedoch konnen anhand dieser Parameter verschiedene lokale Korrosionsformen, wie z. B. metastabile Lochkorrosion, stabiles Lochwachstum oder Spannungsrisskorrosion nicht eindeutig voneinander unterschieden werden. Es wurde festgestellt, dass diese Korrosionsprozesse instabiler Natur und demnach auch die daraus resultierenden Rauschsignale nichtstationar sind. Darin liegt auch der Hauptgrund fur die nicht zuverlassigen Ergebnisse, da fur eine spektrale und statistische Analyse Stationaritat der ablaufenden Prozesse erforderlich ist. Die Resultate fuhren zu der Schlussfolgerung, dass diese Formen der Signalanalyse nur durftige Informationen uber die ablaufenden Korrosionsprozesse liefern. Lediglich kurzlebige Korrosionsprozesse und der Ubergang zwischen verschiedenen Korrosionsformen konnen somit identifiziert werden.

Comparative Analysis of Electrochemical Noise Generated During Stress Corrosion Cracking of AISI 304 Stainless Steel

Abstract Electrochemical noise measurements were performed on electrodes made from a sample of AISI 304 (UNS S30400) stainless steel. Potential and current noise were measured under open-circuit co...

Stochastic analysis of current fluctuations during general corrosion of stainless steel in sulfuric acid

Abstract Current fluctuations during general corrosion of stainless steel in sulfuric acid (H2SO4) were studied experimentally and analyzed using a simple electrochemical model. Stochastic behavior...

Interpretation of current noise generation by a simple model

The corrosion process of low carbon steel in natural aerated sulphuric acid was examined by electrochemical noise. Noise was interpreted in the time domain in terms of current fluctuations and amplitude distribution. A simple electrochemical model was used to analyse the electrochemical state of steel surface. Stochastic behaviour of the metal-electrolyte interface in the model was based upon the assumption that the elementary fluctuation sources were related to fluxes of electrons that pass from a metal to electron-acceptor ions in solution. The probability that in a certain time a number of successful electron transfers occur, obeyed the Gaussian distribution. At the corrosion potential, it was possible to estimate the corrosion current density (i corr ) from the number of successful electron transfers.

An Alternative Way to Monitor H2O2 Decomposition in Bleaching Solutions

A new method has been developed for monitoring temperature, pressure, pH, and redox potential during peroxide bleaching of cotton fabrics. The time dependence of pressure in the closed reaction system is supposed to reflect H2O2 decomposition. Pro cess conditions are monitored on-line and compared with results obtained by mangan ometric titration. On-line monitoring results correspond very well with those from titration. The results indicate that the process very much depends on the presence of stabilizer and cotton, but it can be described as a first-order reaction in any case.