Corrosion is a serious industrial concern. According to a cost of corrosion study released in 2002, the direct cost of corrosion is approximately $276 billion dollars in the United States approximately 3.1% of their Gross Domestic Product. Key influences on the severity of corrosion include: metal and electrolyte composition, temperature, turbulent flow, and location of attack. In this work, mechanistic models of localized and flow influenced corrosion were constructed and these influences on corrosion were simulated.<p>A rigourous description of mass transport is paramount for accurate corrosion modelling. A new moderately dilute mass transport model was developed. A customized hybrid differencing scheme was used to discretize the model. The scheme calculated an appropriate upwind parameter based upon the Peclet number. Charge density effects were modelled using an algebraic charge density correction. Activity coefficients were calculated using Pitzers equations. This transport model was computationally efficient and yielded accurate simulation results relative to experimental data. Use of the hybrid differencing scheme with the mass transport equation resulted in simulation results which were up to 87% more accurate (relative to experimental data) than other conventional differencing schemes. In addition, when the charge density correction was used during the solution of the electromigration-diffusion equation, rather than solving the charge density term separately, a sixfold increase in the simulation time to real time was seen (for equal time steps in both simulation strategies). Furthermore, the charge density correction is algebraic, and thus, can be applied at larger time steps that would cause the solution of the charge density term to not converge.<p>The validated mass transport model was then applied to simulate crevice corrosion initiation of passive alloys. The cathodic reactions assumed to occur were crevice-external oxygen reduction and crevice-internal hydrogen ion reduction. Dissolution of each metal in the alloy occurred at anodic sites. The predicted transient and spatial pH profile for type 304 stainless steel was in good agreement with the independent experimental data of others. Furthermore, the pH predictions of the new model for 304 stainless steel more closely matched experimental results than previous models.<p>The mass transport model was also applied to model flow influenced CO2 corrosion. The CO2 corrosion model accounted for iron dissolution, H+, H2CO3, and water reduction, and FeCO3 film formation. The model accurately predicted experimental transient corrosion rate data.<p>Finally, a comprehensive model of crevice corrosion under the influence of flow was developed. The mass transport model was modified to account for convection. Electrode potential and current density in solution was calculated using a rigourous electrode-coupling algorithm. It was predicted that as the crevice gap to depth ratio increased, the extent of fluid penetration also increased, thereby causing crevice washout. However, for crevices with small crevice gaps, external flow increased the cathodic limiting current while fluid penetration did not occur, thereby increasing the propensity for crevice corrosion.

Abstract: Concrete cover cracking due to reinforcement corrosion is widely accepted as a limit-state indicator in defining the end of functional service life for existing reinforced concrete (RC) structures undergoing corrosion. Many of the currently available durability prediction models are incapable of providing realistic estimates of remaining service lives of RC structures beyond the corrosion initiation point. Therefore, the need to incorporate the length of the corrosion propagation stage in a comprehensive durability prediction approach has recently received much research attention. Previous research focus however was mostly limited to the case of uniformly corroding reinforcement with only few studies addressing the commonly encountered case of localized rebar corrosion. It was empirically shown in a previous study that localized corrosion can have a mitigating effect on time to concrete cover cracking due to the larger required depth of rebar corrosion penetration (Critical penetration or Xcrit). The present research was focused on developing a model for predicting Xcrit for various degrees of corrosion localization including new cases of highly localized corrosion. Accelerated corrosion testing of controlled anodic regions along axial rebars in sound concrete cylinders suggested that localized corrosion can increase Xcrit by up to about a factor of 10. The effect of corrosion localization on the orientation of corrosion-induced surface cracks was also addressed. Testing of freely corroding pre-cracked RC pipe specimens in a chloride-containing environment indicated that steel corrosion can be localized at intersection regions with the pre-existing cracks and uniformly distributed around the reinforcing steel perimeter. Numerical modeling was undertaken to substantiate the experimentally observed trends on a theoretical basis for various degrees of corrosion localization. A mechanical model was developed to improve understanding of the underlying mechanism responsible for corrosion-induced stresses. A thick-walled multiple-cylinder approach was employed to simulate crack initiation and propagation to account for the residual strength property of concrete after cracking by applying the principles of applied elasticity. For a given concrete cover depth, the amount of Xcrit was shown by modeling to be largely determined by the length of corroding region and the capacity of the induced cracks to accommodate produced rusts. The properties of both concrete-rebar interface and corrosion products were also found to have a significant impact on Xcrit. Based on the model and experimental trends and comparisons with literature data, an improved relationship for the estimation of Xcrit was proposed. An electrochemical model was also formulated to address the possible role of corrosion aggravation due to macrocell coupling in counteracting the mitigating effect of increased Xcrit on time to concrete cover cracking. Findings confirmed that corrosion localization can reasonably be considered a mitigating factor for extending the corrosion propagation stage, and provided more precise quantification to that effect.

M. Tech. Metallurgical Engineering / Mild steel is vulnerable to corrosion; this behaviour affects the material strength and electrochemical behaviour during industrial application. Mild steel also has poor tribological resistance; its application for the components of machines, however, requires good tribological property. The cost incurred from equipment failures, properties loss and increased production overheads makes is imperative to enhance mild steel's electrochemical and tribological properties. Electroless nickel plating has found extensive use in various industries attesting to its exceptional properties. The effect of bath parameters on the electroless plating process is of importance as this affects the adhesion, morphological behaviour, electrochemical properties and uniformity of coating. The key aim of this research is: To generally improve the understanding of the effect of electroless binary and ternary alloys on the corrosion and wear resistance of mild steel using weight loss method, potential measurement, linear polarization and tribological sliding wear tests. This work studies the effect of temperature, concentration, deposition time and the inclusion of Tin (Sn) as a third addition to the electroless bath. Corrosion and wear behaviour of the electroless plated mild steel was studied.

No description available.

Concrete is strong in compression; however, it is quite fragile in tension. To overcome this flaw, concrete is frequently reinforced with bars typically made of low grade, low carbon steel. The environment inside of concrete is favorable for steel; unfortunately when passive steel is exposed to chlorides, active corrosion can initiate, resulting in damage to the structure. One source of chloride contamination is through anti-icing agents which are used to inhibit the formation of ice on roadways, ensuring safe driving conditions. This represents a serious concern from both the cost associated with rehabilitation (Canadian infrastructure deficit in 2003 was $125 billion [1]) and as a safety concern to the public. In Canada, 5 million tonnes of road salts are used each year [2], of which Ontario uses 500 to 600 thousand tonnes [3]. As a result, the Ministry of Transportation Ontario (MTO) has requested a study of four frequently used anti-icing agents: 25.5% NaCl, 31.5% MgCl2, 37.9% CaCl2 and 32.6% multi Cl- (12% NaCl, 4% MgCl2 and 16% CaCl2). The objective of the study is two-fold, the first is comparing the effects of the solutions on steel embedded in concrete (high pH environment) and the second is to compare the effects of the anti-icing agents to a variety of construction steels in atmospheric conditions (neutral pH). Macro-cell and micro-cell corrosion in concrete were tested using both modified ASTM G109 prisms and concrete beams with 6 embedded black steel bars. Unfortunately, these tests proved inconclusive; all of the steel remained passive. This was a result of casting a high quality concrete in laboratory conditions which ultimately lead to minimal diffusion of the anti-icing solutions. Therefore, it is recommended that for short term corrosion testing (<2 years), poor quality concrete or cement paste should be used. Micro-cell testing in synthetic concrete pore solution contaminated with the anti-icing solutions was conducted in order to obtain results in the period of the M.A.Sc. program and to directly observe the corrosion. The initial concentration of Cl- in each solution was 0.00% Cl-; this was incrementally increased by 0.005% Cl-/week. Potentiostatic linear polarization to resistance measurements and pH measurements were used to monitor the corrosion on a weekly basis. The results of this test showed that MgCl2 has the most detrimental effects due to the drop in pH (from 13.5 to 9.1) caused by Mg replacing Ca in Ca(OH)2 to form the less soluble Mg(OH)2. The transition from passive to active corrosion initiated at 0.7, 0.4-0.9, 0.6 and 0.6% Cl- for NaCl, MgCl2, CaCl2 and multi Cl-, respectively. The active corrosion current densities were 11mA/m2 for NaCl, CaCl2 and multi Cl-, whereas MgCl2 had active corrosion rates of ~100 mA/m2. One bar exposed to CaCl2 showed corrosion rates as high as 600 mA/m2. This was a result of crevice corrosion between the shrink fitting and the rebar. Once the expansive corrosion products broke through the shrink fitting and ample supply of oxygen became available, allowing the corrosion rates to spike dramatically. The following steels were tested directly in the diluted solution in a cyclic corrosion chamber: stainless steels: 304L, 316LM, 2101, 2205, 2304, XM28; corrosion resistant steel reinforcing bars (rebar): galvanized rebar, guard rail (galvanized plate steel) and MMFX; carbon steels: black steel rebar, box girder, drain, weathering steel. The reinforcing bars were virgin steels whereas the remaining steels were components from the field. The testing regime followed SAE J2334 using the anti-icing solutions diluted to 3% by wt. Cl- as the immersion liquid. Unfortunately, the mutli Cl- solution was not tested due to time constraints. The mass change per unit area was measured every five cycles. All stainless steels exposed to all anti-icing solutions exhibited similar changes in mass per unit area, less than 10 g/m2. All plain carbon steels including weathering steel exhibited mass changes per unit area of more than 1000 g/m2 with some variability between the various anti-icing solutions and steel types, although the black steel rebar typically outperformed the other carbon steels. The corrosion products of MMFX were non-adherent, resulting in inconclusive results. The galvanized layer on the guard rail, which had been exposed to the environment in service, proved to be more protective than the fresh zinc coating on the galvanized rebar. When exposed to the MgCl2 solution, the mass change of both new and used galvanized steels was comparable to that found in the stainless steels. When exposed to NaCl solutions, the galvanized guard rail also exhibited this trend, whereas the new galvanic coating did not, suggesting that with exposure to the atmosphere a galvanic coating will protect the steel against NaCl. In all cases galvanized steel exposed to CaCl2 solutions exhibited mass changes per unit area of less than 100 g/m2 this is considered moderate, as this value is one order of magnitude higher than the stainless steels and one order of magnitude lower than the carbon steels exposed to the same test. It is recommended that galvanic coatings be utilized in areas heavily exposed to anti-icing solutions. The weathering steel offers no advantages over carbon steels when directly exposed to anti-icing solutions. Furthermore, in areas with high amounts of exposed galvanized steel, CaCl2 should be avoided. Between the four solutions tested, NaCl solutions are recommended as the anti-icing agents that, overall, causes the least amount of damage to both the reinforcing steel in concrete and to exposed metallic components. NaCl is followed by multi Cl- and CaCl2. Even though MgCl2 causes less damage when directly exposed to carbon steels and galvanized steels than CaCl2, it is much easier to repair external components than internal components. Therefore, MgCl2 is not recommended.

In modular hip implants, micro-motion, which leads to fretting corrosion at the head/neck and neck/stem interfaces, has been identified as a major cause of early revision in hip implants, particularly those with heads larger than 32mm. It has been found that the type of fluid used to simulate the fretting corrosion of biomedical materials is crucial for the reliability of laboratory tests. Therefore, to properly understand and effectively design against fretting corrosion damage in modular hips, there is the need to replicate the human body environment as closely as possible during in-vitro testing and validation. In this work, corrosion behavior of CoCrMo in 0.14 M NaCl, phosphate buffered saline (PBS) and clinically relevant simulated body fluid (sbf) is carried out. Also, fretting corrosion studies of the CoCrMo alloy in a clinically relevant novel simulated body fluid (sbf) environment is studied. The presence of phosphate ions in PBS accounted for the higher corrosion rate when compared with 0.14 M NaCl and sbf environment. Despite the low and comparable corrosion rates in 0.14 M NaCl and sbf, the nature of the protective passive film formed in sbf shows the suitability of the novel sbf for future corrosion and fretting corrosion analysis. Finally, the influence of micro-motion at the modular head/neck and neck/stem interfaces on the concentration of metallic ions that goes into the synovial fluid and surrounding tissues is reported.

Thesis (M.S.)--University of Hawaii at Manoa, 2005. / Includes bibliographical references (leaves 120-121). / xii, 282 leaves, bound ill. (some col.) 29 cm

Thesis (Ph. D.)--Murdoch University, 1991.

Thesis (Ph. D.)--University of Florida, 1983. / Description based on print version record. Typescript. Vita. Includes bibliographical references (leaves 240-242).

Les carburants BtL (Biomass to Liquid) font partie des carburants alternatifs au pétrole dits de seconde génération car synthétisés à partir de biomasse solide (contenant de la lignocellulose). Le procédé de fabrication de tels carburants par voie thermochimique repose sur deux étapes successives : la gazéification de la biomasse suivie par un procédé de Fisher-Tropsch. Certains éléments contenus dans la biomasse comme les sels alcalins peuvent se retrouver après l’étape de gazéification et être à l’origine d’attaques sous forme de sels fondus et ainsi endommager les infrastructures. Le travail réalisé dans ce manuscrit consiste à simuler la corrosion de parois d’échangeur thermique en présence de sulfate et chlorure de sodium sous atmosphère de gazéification (CO/H2/CO2) très faiblement oxydante (~ 10−18 bar). Afin de comparer les résultats à ceux issus de la bibliographie, les essais ont également été conduits sous atmosphère fortement oxydante (Ar/O2). Les essais réalisés sur alliage chrominoformeur, HR-120 (38Ni-34Fe-25Cr) à une température de 900°C en présence de sulfate de sodium en milieu faiblement oxydant ont mise en évidence une corrosion de type catastrophique localisée et réversible de l’alliage. Le comportement de l’alliage aluminoformeur, 214 (76Ni-16Cr-4Al) apparaît plus protecteur dans des conditions similaires. En présence de chlorure de sodium, les deux alliages se comportent d’une manière totalement identique : corrosion catastrophique en milieu fortement oxydant et impact du sel négligeable sous atmosphère faiblement oxydante. Un chapitre remède prometteur a été développé en fin de manuscrit. / BTL (biomass to liquid) is an innovative process to synthesize second generation bio-gasoline from wood and farm residues. This process includes a gasification step in order to generate the synthetic gas (syngas) which is subsequently transformed into gas oil by the Fisher Tropsch process. Alkaline salts (mainly potassium and sodium sulphates and chlorides) are present in the biomass and can induce detrimental high temperature corrosion of the refractory alloys where they can condensate as a liquid phase. In this work, we simulate high temperature corrosion of heat exchanger tubes in presence of sulphate and sodium chloride under gasification environment (CO/H2/CO2), consider as weakly oxidizing (~ 10−18 bar). To compare the results with those from the literature, tests were also conducted under highly oxidizing atmosphere (Ar/O2). Results with the chromia-forming alloy HR-120 (38Ni-34Fe-25Cr) at 900°C with sodium sulfate under low oxygen partial pressure shows reversible localized catastrophic oxidation. The behavior of the alumina-forming alloy 214 (76Ni-16Cr-4Al) appears more protective under similar conditions. In presence of sodium chloride, the behavior of the two alloys is identical. Indeed, with oxidizing atmosphere corrosion became totally catastrophic while the impact of sodium chloride was insignificant under gasification atmosphere.