Band 26, Heft 2-3

ABSTRACT Some confusion exists in the literature between different nomenclatures and units related to the equations of chemical potential, Einstein's relation, mobility, Fick's laws, and stress-assisted diffusion. Moreover, sometimes these concepts are simplified and important parameters are overlooked in textbooks, thus providing students with insufficient knowledge. This paper is aimed at gathering the most important equations, nomenclature and units in a systematic way. A critical discussion is made on the issues that tend to introduce confusion.

ABSTRACT Thermal-spray coatings are widely used in marine structures including offshore pipelines without external cathodic protection (CP). Al, Zn and Zn-Al thermal-spray coatings protect steel by acting both as barrier coatings and as sacrificial anodes at local defects where corrosion would otherwise occur. Zn provides better galvanic protection whereas Al is better as a less-reactive barrier layer. Zn-Al alloys appear to combine the protective properties of both Zn and Al. Although further research is required in order to specify the optimal alloy compositions for specific applications, 85% Zn-15% Al alloy is widely used. The best long-term protection is provided by suitably primed, sealed, and painted thermal-spray coatings. Thermal-spray coatings of acceptable structures and properties can be produced by flame spraying (wire or powder), arc spraying or plasma processing. However, due to economical reasons low melting point metals and their alloys are sprayed either by arc or flame. Surface preparation is considered to be a key factor in the production of uniform high quality coatings with maximum bond strength. Also of equal importance are the control of process facilities, equipment selection, and quality of consumable material for applying thermal-spray coatings. Well-bonded, relatively dense, sealed coatings have the ability to provide effective long term corrosion protection (10-20 years), with minimum periodic maintenance. Standards for evaluating thermal spray coatings have recently been developed.

ABSTRACT Corrosion behavior of the most important metallic materials – mainly used in orthopaedic implants – is summarized. A focus of this review is on the comparison of the susceptibility of the different alloys (especially Ti base alloys and Co-Cr alloys) to corrosion. A short discussion on influence of surface modification on the corrosion performance of biomaterials is included. Critical factors to be considered in the experimental investigation of the corrosion behavior in view of the biomedical applications are summarized. Recent investigations on the possible exploitation of materials with a low corrosion resistance for biodegradable implants are summarized.

ABSTRACT Hydrogen evolving in corrosion processes in the water containing technological media enters the steel and accumulates there. The possibility of hydrogen induced deterioration of metal and thus the hazard for industrial installations increase in the course of exploitation and affects the estimated life time. The continuous (for 20 years) measurement of hydrogen absorption, corrosion and deposition rates in different locations of the Fluidal Catalytic Cracking, Distillation and Desulphurization units of the Polish Refinery that are under inhibitor protection showed that the correlations between the above parameters differed in the same installation, due to the variation in the technological process. The susceptibility of ferrite-pearlite steels that have been in service for up to 240,000 hrs in different boilers and electric power stations of Poland, Ukraine and Syria to hydrogen induced blistering cracking (HIBC) has been described by critical cathodic polarization causing irreversible change of the microstructure, evaluated in hydrogen permeation tests. The decrease in the resistance to the HIBC in the course of exploitation has been correlated with the change of the structure in the course of service. Since the hydrogen charging of boiler pipes has been determined by the quality of the formed magnetite layer, a special method has been elaborated to determine the mechanical adhesion and the protection ability (penetration porosity) of the magnetite layer. The obtained results confirm the possibility of applying the above techniques to monitor the state of steel and to predict the residual lifetime of equipment.