Diffusion controlled corrosion in gas sparged systems

The rate of diffusion - controlled corrosion of the walls of rectangular bubble column and a liquid has been studied with the copper dissolution technique. Variables studied were superficial air velocity, initial height of solution in the column, physical properties of the solution and the presence of suspended solids with different concentrations and different particle size. The rate of diffusion - controlled corrosion in solution free solids was given by the equation J = 0.232 (Fr .Re)-0.22 (L/de)-0.169 while for the presence of suspended solids, the data were correlated by the equation J = 0.171 (Fr .Re)-0.214(L/d p) 0.187 The presence of suspended solids increases the rate of diffusion - controlled corrosion by an amount ranging from 5 to 16 %

Bacteria have transient influences on marine corrosion of steel

The contribution of bacteria to the corrosion mass loss and to pitting of mild steel was observed over 2.5 years using parallel streams of unpolluted natural (biotic) and nominally sterilized (abiotic) Pacific Ocean coastal seawater. As also observed by others, in artificial laboratory exposures, corrosion mass loss within the first few days of exposure was much greater in the biotic stream. However, after only about 10 days the difference in mass losses were gradually reduced and were very similar up to about one year of exposure. Thereafter, the corrosion loss in the biotic stream again became more severe. Pitting corrosion in the biotic stream was more severe from the very first exposure throughout the 2.5 years. Corrosion in both seawater streams exhibited three distinct but transient time-dependent phases. Of these only the first and third obviously involve bacteria. Similar longer-term observations in real seawaters have not been described previously but are generally consistent with some long-term field data. The results show that longer-term corrosion behavior and possible microbial influences cannot be predicted from short-term laboratory observations, even if natural seawater is used

A phase field formulation for dissolution-driven stress corrosion cracking

We present a new theoretical and numerical framework for modelling mechanically-assisted corrosion in elastic-plastic solids. Both pitting and stress corrosion cracking (SCC) can be captured, as well as the pit-to-crack transition. Localised corrosion is assumed to be dissolution-driven and a formulation grounded upon the film rupture-dissolution-repassivation mechanism is presented to incorporate the influence of film passivation. The model incorporates, for the first time, the role of mechanical straining as the electrochemical driving force, accelerating corrosion kinetics. The computational complexities associated with tracking the evolving metal-electrolyte interface are resolved by making use of a phase field paradigm, enabling an accurate approximation of complex SCC morphologies. The coupled electro-chemo-mechanical formulation is numerically implemented using the finite element method and an implicit time integration scheme; displacements, phase field order parameter and concentration are the primary variables. Five case studies of particular interest are addressed to showcase the predictive capabilities of the model, revealing an excellent agreement with analytical solutions and experimental measurements. By modelling these paradigmatic 2D and 3D boundary value problems we show that our formulation can capture: (i) the transition from activation-controlled corrosion to diffusion-controlled corrosion, (ii) the sensitivity of interface kinetics to mechanical stresses and strains, (iii) the role of film passivation in reducing corrosion rates, and (iv) the dependence of the stability of the passive film to local strain rates. The influence of these factors in driving the shape change of SCC defects, including the pit-to-crack transition, is a natural outcome of the model, laying the foundations for a mechanistic assessment of engineering materials and structures

Corrosion of alloy 800H and the effect of surface-applied CeO2 in a sulphidizing/oxidizing/carburizing environment at 700°C

The corrosion behavior of a wrought austenitic Fe-20Cr-32Ni steel, Alloy 800H, was studied in a simulated coal-gasification atmosphere at 700°C for exposure times up to 2500 hr. The influence of preoxidation and CeO2-surface application followed by preoxidation on the corrosion resistance of this material was assessed. The improvement in the corrosion resistance due to preoxidation of the blank material was small, whereas the effect of the CeO2-treatment was significant. This difference is thought to be due to better scale adherence in the case of CeO2-surface application

Study Program for Encapsulation Materials Interface for Low-Cost Solar Array (LSA)

The early validation of a 20 year service integrity for the bonded interfaces in low cost solar arrays is an important requirement in the Low Cost Solar Array ( LSA) project. An atmospheric corrosion model has been developed and verified by five months of corrosion rate and climatology data acquired at Mead, Nebraska LSA test site. Atmospheric corrosion monitors (ACMs) installed at the Mead test site showed that protection of the corroding surface by the encapsulant is achieved independent of climatology variations. A newly designed Mead climatology simulator has been developed in laboratory corrosion studies to clarify corrosion mechanisms displayed by two types of LSA modules at the Mead test site. Controlled experiments with identical moisture and temperature aging cycles showed that UV radiation causes corrosion while UV shielding inhibits LSA corrosion. The implementation of AC impedance as a NDE monitor of environmental aging in solar cell arrays has also been demonstrated

The corrosion of Ni₃Si alloys in sulfuric acid

Hydrogen production from water, the world\u27s most renewable natural resource, can provide an economical and sustainable form of energy for the future. One means to achieve this is with a nuclear reactor-based sulfur-iodine (S-I) thermochemical cycle. Currently there are few materials available, other than precious metals like gold and platinum, that possess the corrosion resistance and mechanical properties required for the sulfuric acid decomposition loop of the S-I process. However, alloys based on Ni₃Si show promise to be a more affordable, corrosion resistant materials option for this technology. In this study, the corrosion behavior of NiSi₂₂ and NiSi₂₀(Nb,Ti)₃ alloys in boiling 70 wt. % sulfuric acid is examined. The mechanism that provides corrosion resistance for these alloys is the formation of an inert SiO₂ surface film which spontaneously grows in oxidizing acid mediums. However, niobium and titanium alloying each have very different effects on the corrosion behavior. The results presented herein indicate that niobium alloying enhances the corrosion resistance of Ni₃Si, whereas titanium alloying has deleterious effects. The changes in corrosion behavior that are imparted by niobium and titanium alloying are linked to the alloy properties, and are the focus of this research --Abstract, page iii

Predictive Peridynamic 3D Models of Pitting Corrosion in Stainless Steel with Formation of Lacy Covers

In this work, the peridynamic corrosion model is used for 3D simulation of pitting corrosion in stainless steel. Models for passivation and salt layer formation are employed to predict detailed characteristics of pit growth kinetic in stainless steels, such as lacy cover formation on top of the pit, and the diffusion-controlled regime at the pit bottom. The model is validated against an experimentally grown pit on 316L stainless steel in NaCl solution. Lacy covers in this model are formed autonomously during the simulation process. They are remarkably similar to the covers observed on top of the real pits

Predictive Peridynamic 3D Models of Pitting Corrosion in Stainless Steel with Formation of Lacy Covers

In this work, the peridynamic corrosion model is used for 3D simulation of pitting corrosion in stainless steel. Models for passivation and salt layer formation are employed to predict detailed characteristics of pit growth kinetic in stainless steels, such as lacy cover formation on top of the pit, and the diffusion-controlled regime at the pit bottom. The model is validated against an experimentally grown pit on 316L stainless steel in NaCl solution. Lacy covers in this model are formed autonomously during the simulation process. They are remarkably similar to the covers observed on top of the real pits