R. M. Latanision

Hot corrosion in gas turbine components

Abstract The macroscopic and microscopic characteristics as well as the proposed mechanisms of Type I (high-temperature) and Type II (low-temperature) hot corrosion are reviewed. Two case histories of gas turbine blade failures are presented. Different practical approaches to minimize hot corrosion are described.

Electrochemical migration tests of solder alloys in pure water

Abstract Electrochemical migration (ECM) tests on solder alloys were conducted by applying constant voltage with a power supply or sweeping the voltage at a constant rate with a potentiostat. Distilled water was used as the test environment. Time to short and short voltage were the measure of ECM susceptibility. Similar results were obtained in both test methods. In SnPb alloy system, pure lead showed the highest susceptibility. Alloys with 5–60%Sn showed similar high susceptibility. Further addition of tin lowered the susceptibility and pure tin had the lowest susceptibility. Dendrites grew from cathode and reached to the anode. The composition of dendrites of Sn 40Pb alloy was enriched in lead. Some tin base solder alloys without lead were more resistant to ECM than Sn40Pb alloy. Pure indium, In−48Sn and In−50Pb alloys were found to be immune to ECM in pure water. Large anodic dissolution rate seems to be responsible to high ECM susceptibility.

A study of corrosion initiation on polyimide coatings

Abstract The protective properties of thin polyimide (PI) films on aluminum and iron metallic substrates were studied using a.c. and d.c. electrochemical techniques. The effects of storage time, film thickness, and the synergistic effect of temperature (80°C) and relative humidity (85%) on the lifetime of the PI were investigated. The results obtained can be summarized as follows: (i) early failure was observed for the PI/AI samples tested directly after curing, while extended lifetime was observed for samples stored in a desiccator for 2 months before testing, (ii) early failure was also observed for the PI/Fe samples even after storage in a desiccator before testing, (iii) the lifetime increases by increasing the film thickness, and (iv) temperature and relative humidity (RH) dramatically affect failure. A mathematical model is presented to relate coating failure to salt uptake by the PI. By applying this model to the experimental findings, an estimate of the heterogeneities or defects in the PIs is given.

Corrosion behavior of advanced titanium-based alloys made by three-dimensional printing (3DPTM) for biomedical applications

New Ti–5Ag and Ti–5Ag–35Sn (wt.%) alloys were designed and synthesized by three-dimensional printing (3DPTM) through liquid-phase sintering or liquid-tin infiltration, respectively. The corrosion behavior of these alloys as well as of pure titanium was studied by means of short- and long-term open-circuit potential and potentiodynamic measurements during immersion in a saline solution at body temperature, as well as by Auger electron spectroscopy (AES). Due to its relatively low porosity level and the presence of silver, the Ti–5Ag alloy sintered at 1300°C exhibited good passivation behavior. However, the Ti–5Ag–35Sn alloy, while exhibiting improved dimensional stability, suffered from a deteriorated corrosion resistance.

Electronic Properties and Defect Structure of Fe and Fe-Cr Passive Films ✫

Abstract The electronic properties of passive films on Fe-Cr alloys were determined by the photoelectrochemical technique. Measurement of the flat band potential for the passive films on the different alloys indicated that the film is doped increasingly n-type as the Cr concentration in the base alloy is increased. This doping is due to a Cr oxide with Cr in the 4+ or 6+ valence state. The concentration of this doping species increases as the concentration of Cr in the Fe-Cr alloy is increased. The n-type doping has the effect of decreasing the number of oxygen vacancies in the Fe-Cr passive film. Since oxygen vacancies are the mobile point defect species in the Fe-Cr passive film, decreasing this species decreases the oxygen vacancy flux and ultimately the passive film growth kinetics. The contribution of film dissolution and cation transmission through the passive film was also analyzed. Film dissolution was shown to be the major contribution to the passive current density.

A New Ti-5Ag Alloy for Customized Prostheses by Three-dimensional Printing (3DP™)

Three important considerations in the fabrication of customized cranio-maxillofacial prostheses are geometric precision, material strength, and biocompatibility. Three-dimensional printing (3DP™) is a rapid part-fabrication process that can produce complex parts with high precision. The aim of this study was to design, synthesize by 3DP™, and characterize a new Ti-5Ag (wt%) alloy. Silver nitrate was found to be an appropriate inorganic binder for the Ti powder-based skeleton, and the optimum sintering parameters for full densification were determined. The hardness of the Ti-5Ag alloy was shown to be much higher than that of a pure titanium sample. Potentiodynamic measurements, carried out in saline solution at body temperature, showed that the Ti-5Ag alloy had good passivation behavior, similar to that of pure titanium. It is concluded that the Ti-Ag system may be suitable for fabrication of customized prostheses by 3DP™.

An X-ray photoelectron spectroscopy study of chromium-metalloid alloys—III

X-ray photoelectron spectroscopy has been used to examine the surface of a series of Cr100-xPx alloys (x = 0, 7, 13, 28) following a variety of electrochemical treatments in 1 mol1 H2SO4. At oxidizing potentials the passivating effect of the surface film formed on Cr100−xPx, is similar to that found on chromium. Semi-quantitative analysis indicates a minor amount of oxidized phosphorus in the passive film formed on Cr87P13, while a much larger concentration of oxidized phosphorus is found in the passive film on Cr72P28 and Cr93P7. Phosphorus is also slightly enriched in the metallic state beneath the oxide-based film. The thickness of the passivating overlayer is a monotonie function of the growth potential. At reducing potentials the surface of Cr72P28 is enriched in both oxidized and metallic phosphorus via selective dissolution of chromium. This layer inhibits further chromium dissolution and simultaneously accelerates proton reduction. The coupling of these reactions is responsible for spontaneous passivation of Cr100-xPx in reducing acids.

An Overview of the Current Understanding of Corrosion in SCWO Systems for the Destruction of Hazardous Waste Products

Summary During the Workshop on Corrosion in SCWO Systems held at MIT in 1993 the attendees recognized the potential for corrosion to restrict the commercialization of SCWO for aggressive waste streams. At that time, the group consensus was that a material of fabrication universally applicable to all sections of a SCWO system was extremely unlikely [8]. As presented in this review, while the database for the potential materials of fabrication for SCWO systems has increased significantly since then, the group consensus apparently still holds. The corrosion of the materials of fabrication remains a serious concern and a significant amount of research remains to be carried out to identify materials or methods to reduce degradation within all sections to an acceptable level.

The effect of composition on the performance of epoxy paints

Water-diffusion coefficient water solubility and oxygen permeability measurements have been performed on free-standing membranes of epoxy-based organic coatings for different values of paint composition. Concomitant direct (d.c.) and alternating (a.c.) current measurements were carried out on coated mild steel in order to investigate the protection exhibited by the coatings in neutral aerated 0.5 M NaCl. A general model has been used to analyse the a.c. data in terms of reactions occurring during the interaction of the coated metal with the aggressive environment. A correlation between transport properties of free films and the protective properties of paints has also been attempted. No relationship was found between the water permeability and the coating performance over exposure time, whereas the oxygen permeability seems to be responsible for coating effectiveness at later stages. The electrical resistivity of the coatings and its dependence on both the composition and water content has been related to early failures.

A photoelectrochemical study of the passive film on chromium

Abstract The photoelectrochemical behaviour of the passive film on chromium has been studied in H 2 SO 4 solution. The results show that photoelectrochemical techniques can be applied to very thin passive films of relatively low quantum efficiency. The positive photocurrent seen in the passive domain indicated an n-type behaviour. The photocurrent response was analysed as a function of wavelength and electrode potential. The presence of inclusions in the chromium samples was found to have significant influence on the photoresponse.