Showing papers on "Corrosion published in 1997"

Duplex stainless steels : microstructure, properties and applications

Abstract: Developments, grades and specifications Alloy design Microstructure Forming and machining Physical and mechanical properties Corrosion Stress corrosion cracking Welding metallurgy Welding processes Weld properties Non-destructive testing of welds Applications Service experience.

Sol-gel coatings on metals

Abstract: Sol-gel derived films can be deposited on metals to improve their resistance to oxidation and corrosion or to modify their surface properties. However, practical applications are limited by problems intrinsic to sol-gel processing or specific of coating/metal systems. Coatings aimed to improve oxidation and wet corrosion resistance have been the most studied. The results published in the literature show that sol-gel coatings may offer good protection against oxidation. More difficult is to achieve a protection against wet corrosion. An important aspect of the application of the sol-gel method for coating metallic objects is also the deposition technique.

Characteristics of Metals Used in Implants

Abstract: The performance of any material in the human body is controlled by two sets of characteristics: biofunctionality and biocompatibility. With the wide range of materials available in the mid-1990s, it is relatively easy to satisfy the requirements for mechanical and physical functionality of implantable devices. Therefore, the selection of materials for medical applications is usually based on considerations of biocompatibility. When metals and alloys are considered, the susceptibility of the material to corrosion and the effect the corrosion has on the tissue are the central aspects of biocompatibility. Corrosion resistance of the currently used 316L stainless steel, cobalt-chromium, and titanium-based implant alloys relies on their passivation by a thin surface layer of oxide. Stainless steel is the least corrosion resistant, and it is used for temporary implants only. The titanium and Co-Cr alloys do not corrode in the body; however, metal ions slowly diffuse through the oxide layer and accumulate in the...

Industrial applications of CrN (PVD) coatings, deposited at high and low temperatures

Abstract: Industrial applications of CrN (PVD) coatings are entering an expanding but selective range of mass manufactured goods. They may be prepared as single, low and high temperature CrN coatings and double TiN+CrN coatings. In this work, depositions of CrN at high temperatures were performed by a low voltage thermionic arc in a BAI 730M apparatus, while at low temperatures (below 250 °C), the plasma-beam sputtering process in a SPUTRON apparatus was used. We studied the following critical parameters that influence the quality of the coatings and applied the performance tests used in industrial practice: adhesion and scratching coefficient, microhardness, surface topography, oxidation and corrosion resistance. The performance tests were made with the assistance of technicians as well as in 12 Slovenian factories. CrN coatings were deposited at 480 °C for wear and corrosion protection in cold forming and cutting of copper in commutator manufacturing, in forming of aluminium components in automotive production and for surface improvement of moulds (made of H11 steel) in Al-Si die casting under pressure. Deposition temperatures of 180–220 °C, obtained in the SPUTRON apparatus, were required to improve cold forming tools made of alloyed tool steels (e.g. D2 and D3). The lowest obtainable temperature of 140 °C in the SPUTRON gave a CrN coating of high quality for practical use. These coatings were used to protect electrodeposited and electropolished nickel moulds (models) in artificial teeth production. Double TiN+CrN coatings were used as a highly abrasive resistant coating in the production of rotors (in the electromotor industry), and in cold forming and forging in mass manufacturing of screws. The results and performance tests were compared with the available data, mostly published on forming, milling, deep drawing of copper, nickel and titanium and their alloys, and on die casting of aluminium and Al-alloys.

Structure and composition of passive titanium oxide films

Abstract: The thickness and composition of several kinds of titanium oxide films formed on a titanium substrate were determined by surface analysis techniques: X-ray photoelectron spectroscopy, Rutherford back scattering, X-ray diffraction and atomic force microscopy. Most titanium oxide samples were prepared by anodisation, using a galvanostatic procedure. The films were shown to be composed of an amorphous TiO2 outer layer (10–20 nm thick) and an intermediate TiOx layer, in contact with the TiO2 layer and the metallic substrate. The outer layer is sensitive to the environment: its thickness usually decreases with ageing in a corrosive solution. A stabilisation procedure was proposed in order to improve its ability to withstand corrosion.

Reliability of deteriorating rc slab bridges

Abstract: Reinforced concrete (RC) bridges deteriorate with time. This results in reduction of their resistance, and, consequently, of their reliability. Corrosion of embedded reinforcing steel is one of the main causes of deterioration. The paper presents a method for reliability assessment of RC slab bridges with corroded reinforcement. The method includes a traffic load model, a corrosion model, and a nonlinear finite element structural model. Two types of corrosion--general corrosion, including spalling and debond between concrete and the corroded reinforcement, and localized corrosion--are considered. Reliability is estimated in terms of the reliability index using the first-order reliability method. Uncertainties associated with material properties, geometry, loads, and corrosion parameters are taken into account. A sensitivity analysis of a simple span bridge is carried out to examine the influence of these uncertainties on the bridge reliability. Reliability assessment of a deteriorated three-span continuous bridge illustrates the application of the method.

Corrosion Mechanisms and Products of Copper in Aqueous Solutions at Various pH Values

Abstract: The corrosion behavior of copper in aqueous solutions of different pH values was investigated using electrochemical and surface analysis methods. It was shown that the corrosion mechanism changed with pH and was associated with morphology of the surf ace films formed. In solution of pH 3, the copper surface was covered with porous corrosion products of cuprous oxide (Cu2O). Corrosion was controlled predominately by diffusion in solution. In solutions of pH 4 to pH 5, formation of cubic Cu2O on the copper surface provided a diffusion barrier to copper dissolution. The anodic process was controlled by a mixed diffusion of copper ions in oxide films and in solution. In solutions of pH 6 to pH 9, the oxide films (Cu2O) became more protective. Diffusion in the oxide films became a rate-determining step of anodic dissolution. In pH 10 solution, a thin, compact Cu2O film formed, and spontaneous passivation was observed. At pH 12 and pH 13, analysis by x-ray photoelectron spectroscopy (XPS) and scanning ...

Some Aspects of the Hot Corrosion of Thermal Barrier Coatings

Abstract: This paper reviews the hot corrosion of zirconia-based thermal barrier coatings for engine applications. Emphasis is placed on understanding the chemical reactions, and such other mechanisms as can be iden-tified, that cause corrosive degradation of the thermal barrier coating. The various approaches taken to improve the hot corrosion resistance of thermal barrier coatings are also briefly described and critiqued.

Corrosion and Passivity of Ti-13% Nb-13% Zr in Comparison to Other Biomedical Implant Alloys

Abstract: Corrosion and passivation of solution-treated (ST), solution-treated and aged (STA), and diffusion-hardened (DH) variants of Ti-13% Nb-13% Zr (Ti-13-13) were examined in a simulated physio...

Reliability of Reinforced Concrete Girders Under Corrosion Attack

Abstract: Reinforcement corrosion is a major problem for many reinforced concrete structures. Currently, most reliability-based studies of reinforced concrete structures do not account for the effects of corrosion. The authors of this paper present a reliability-based approach to the design of reinforced concrete bridge girders that are under corrosion attack. Reserve and residual reliability constraints are satisfied via the proposed approach. The approach is based on the American Association of State Highway and Transportation Officials (AASHTO) standard specifications for highway bridges and on data of chloride corrosion of steel in concrete. Initially, the authors investigate the effects of corrosion on both moment and shear reliabilities. Then, a reliability-based design approach based on minimization of total material cost including corrosion effects is proposed. Several design examples are provided to demonstrate the approach. The authors conclude by suggesting and illustrating a reliability-based design approach based on minimization of expected lifetime cost including corrosion effects and cost of failure consequences.

Influence of Electrolyte Layer Thickness and pH on the Initial Stage of the Atmospheric Corrosion of Iron

Abstract: Cathodic polarization curves for the reduction of oxygen and protons on platinum and iron electrodes under thin electrolyte layers (X{sub f}: 1 mm to 10 {micro}m) were measured to elucidate the effects of the thickness and the pH of the electrolyte layer on the initial atmospheric corrosion stage of iron. A limiting current was exhibited on the cathodic polarization curves under neutral electrolyte layers containing 0.1 to 2 M NaCl, which was inversely proportional to the thickness of the electrolyte layer down to approximately 20 {micro}m. This result indicates that oxygen diffusion through the electrolyte layer is the rate-determining step (rds) for the oxygen reduction process. Meanwhile the limiting current under still thinner layers (X{sub f}: 10 to 20 {micro}m) was independent of the thickness, where an oxygen dissolution step at the air/electrolyte interface is the rds because of the considerably higher diffusion rate under such very thin electrolyte layers. AC impedance corrosion monitoring of iron for the period of 4 h was performed under electrolyte layers of different thickness (X{sub f}: 1 mm to 10 {micro}m) and pH (pH 3.0, 4.0, and 5.7). The results indicated that the corrosion rate showed a maximum at an electrolyte thickness of 20more » to 30 {micro}m in all cases, and the effect of pH on the atmospheric corrosion rate was negligible, except for cases wherein a relatively thick electrolyte layer (>1 mm) was present for a short exposure period (<1 h). This can be attributed to a neutralization of the electrolyte due to corrosion reaction because of the extremely limited amount of electrolyte present.« less

Laboratory Studies and Calculations on the Influence of Crack Width on Chloride-Induced Corrosion of Steel in Concrete

Abstract: To clarify the corrosion mechanism and the dominant influencing variables, especially the influence of crack width, laboratory tests were performed on cracked reinforced concrete beams. Test results and a mathematical model were then used to calculate the effect of crack distance and the effect of a crack width limitation by reducing the rod diameters on the steel removal rates due to chloride-induced corrosion.

Corrosion Protection of Copper by a Self‐Assembled Monolayer of Alkanethiol

Abstract: A self-assembled monolayer of 1-dodecanethiol (DT) was formed on a copper surface pretreated using different methods. The corrosion protection abilities of the monolayer were evaluated in an air-saturated 0.51 M NaCl solution using various techniques including electrochemical impedance spectroscopy, polarization, coulometry, weight loss, and X-ray photoelectron spectroscopy. It was found that the corrosion resistance of the monolayer was improved markedly by using a nitric acid etching method. A minimum concentration of 10{sup {minus}4} M DT was needed to form a protective monolayer. The DT-monolayer retarded the reduction of dissolved oxygen and inhibited the growth of copper oxide in the NaCl solution. In comparison with other inhibitors, such as benzotriazole (BTA) and mercapto-benzothiazole (MBT), the DT-monolayer showed much better corrosion resistance in aqueous solution.

Use of Polyaniline and Its Derivatives in Corrosion Protection of Copper and Silver

Abstract: This study examines the use of spin-applied conjugated polymers such as polyanilines for corrosion and dissolution protection of silver and copper. In particular, attention is given to the protection that these polymers provide under conditions of an applied potential and at elevated temperature. These particular conditions are those in which current inhibitors such as benzotriazole do not provide acceptable protection for the metal. A number of polyaniline derivatives are studied, including the unsubstituted parent polymer and the substituted poly-o-phenetidine both nondoped and doped, with several different protonic acids. The polymers are readily soluble in organic solvents and can be applied as thin coatings onto the metal surface. The corrosion protection of the resulting structure is determined by electrochemical and inductively coupled plasma techniques using water as an electrolyte and under varied conditions in which the material is processed and doped. The poly-o-phenetidine is found to adhere well to the metal surface and provides exceptional protection both under an applied potential and at elevated temperature.

Corrosion and protection characteristics of zinc and manganese phosphate coatings

Abstract: The corrosion and protection characteristics of zinc and manganese phosphate coatings in aqueous solutions are investigated by means of physical methods and electrochemical measurements. The results show that the insulation property of zinc phosphate coating is better than that of manganese phosphate, but the porosity of the former is inferior to that of the latter. The anodic current of coated samples decreases and polarization resistance increases compared to the substrate. The corrosion of phosphated steel exhibits the characteristics of no diffusion in acidic solution, a finite-length diffusion in neutral medium, and a semi-infinite diffusion in alkahne solution. Chemical dissolution is the primary form in the failure of phosphate coatings, which is induced by the electrochemical corrosion of the substrate. The protection ability of phosphate coatings mainly depends on their barrier performance.

Oxidation behavior of several chromia-forming commercial nickel-base superalloys

Abstract: Several commercially available Ni-base superalloys were exposed isothermally in air at temperatures between 750° and 1000°C and also under cyclic conditions at 1000°C. The kinetics of oxidation were determined and the scales were analyzed by electron microscopy and X-ray diffraction. Thin adherent chromia-rich scales formed on the alloys at 750°C after 1000 hr. Although Waspaloy showed the lowest weight gain in this test, it also showed the deepest internal corrosion due to oxidation of the grain-boundary carbides. At temperatures up to 1000°C the external scales were also chromia-rich but there was greater internal corrosion. Titanium in the alloys oxidized, diffusing through the chromia scale to form faceted rutile (TiO2) grains at the surface as well as forming TiO2 and TiN internally. The amount of rutile at the oxide surface increased with temperature and alloy Ti concentration. Alumina formed as discrete internal oxides below the chromia scale, although Astroloy when oxidized isothermally at 1000°C developed a semicontinuous internal layer of alumina due to its higher Al content. Under cyclic conditions Astroloy formed a thicker, less-protective scale of transition oxides probably due to its lower Cr content.

The relationship between electrochemical behaviour and in-service corrosion of WC based cemented carbides

Abstract: In long-life applications, the corrosion properties of cemented carbides can have a large influence on overall performance. Cemented carbides with improved corrosion resistance have been developed and are now commercially available. The understanding of the corrosion behaviour has been mostly empirical and satisfying explanations of the relationship between the electromechanical behaviour and in-service corrosion have been lacking. In this paper, the electromechanical behaviour of WC-Co is modelled using the behaviour of pure WC and Co(W,C) alloys, according to a linear rule of mixtures. By comparing WC-Co with WC-Ni(Cr,Mo) in both normal sulphuric acid and a synthetic mine water, it is shown that the behaviour of the two grades is inherently different. WC-Co exhibits a ‘pseudo-passivity’ during electro-mechanical tests but corrodes actively in industrial applications. In contrast, WC-Ni( Cr,Mo) passivates and the rate of corrosion can be several orders of magnitude lower than that of WC-Co.

Corrosion resistance for biomaterial applications of TiO2 films deposited on titanium and stainless steel by ion-beam-assisted sputtering.

Abstract: The high corrosion resistance and good biocompatibility of titanium and its alloys are due to a thin passive film that consists essentially of titanium dioxide. There is increasing evidence, however, that under certain conditions extensive titanium release may occur in vivo. An ion-beam-assisted sputtering deposition technique has been used to deposit thick and dense TiO2 films on titanium and stainless steel surfaces. In this study, using the following measurements these TiO2 films have been investigated in a phosphate-buffered saline solution: (1) open-circuit potential versus time of exposure, (2) electrochemical impedance spectroscopy, (3) potentiodynamic polarization, and (4) Mott-Schottky plot. A higher electrical film resistance, lower passive current density, and lower donor density (in the order of 10(15) cm-3) have been measured for the sputter-deposited oxide film on titanium in contrast to the naturally formed passive oxide film on titanium (donor density in the order of 10(20) cm-3). The improved corrosion protection of the sputter-deposited oxide film can be explained by a low defect concentration and, consequently, by a slow mass transport process across the film. As opposed to TiO2 on titanium, a deviation from normal n-type semiconducting Mott-Schottky behavior was observed for TiO2 on stainless steel.