Propagation Stage Of Corrosion Research Articles

New resorbable Ca-Mg-Zn-Yb-B-Au alloys: Structural and corrosion resistance characterization

New resorbable Ca32Mg12Zn38Yb18-2xBxAux (x = 1,2) alloys were designed and prepared in order to verify their use for medical applications as potential short-term implants. Their amorphous structure containing some crystalline phases (CaZn, CaZn2 and MgZn) was determined by X-ray and neutron diffraction and electron microscopy methods. The biocorrosion behavior of the plates was tested by hydrogen evolution measurements, immersion, electrochemical polarization tests, and electrochemical impedance spectroscopy in Ringer's solution at 37 °C. The corrosion analysis was also supplemented by X-ray diffraction, photoelectron, and ICP-AES spectroscopy. The corrosion resistivity measurements revealed that the alloys manifest enhanced corrosion resistance. The corrosion current density for Ca32Mg12Zn38Yb18-2xBxAux (x = 1, 2) alloys were 18.46 and 8.79 μA/cm2, which is lower than for pure Mg (47.85 μA/cm2) and Zn (33.96 μA/cm2). A decreasing tendency for hydrogen to evolve as a function of time was noted. The hydrogen evolution did not exceed 1 ml/cm2 over 1 h and average corrosion rate is calculated as 0.32 g/m2 . h for Ca32Mg12Zn38Yb14B2Au2 alloy after 312 h. The corrosion mechanism of the alloys includes an anodic dissolution, a hydroxide precipitation, corrosion product layer formation and corrosion propagation stage.

The Corrosion Propagation Stage of Stainless Steel Reinforced Concrete: A Review

Stainless steel (SS) reinforcement is increasingly used to control corrosion of reinforced concrete in aggressive marine and deicing salt service. It is well established that the chloride threshold of SS is greater than that of plain steel (PS) rebar, yielding substantially increased duration of the corrosion initiation stage (ti). Much less known, however, is if there is a similar benefit to the duration of the corrosion propagation stage (tP). Thus, credit for increased tP in durability forecasts for SS use tends to be conservatively limited. To reduce that uncertainty, the literature was gleaned for the few instances where SS reinforcement had reached, and preferably completed, the corrosion propagation stage. Particular attention was given to actual structural service experience, outdoor tests, and realistic laboratory conditions. Only a single case of actual service in a structure was found for which tP could be estimated, albeit indirectly. The result suggests a tP of several decades for the case of austenitic Cr-Ni rebar in marine service. Outdoor tests without unnatural acceleration showed a few cases where tP was reached, but only for straight Cr ferritic alloys, which showed some limited improvement over tP for PS. With the additional insight from laboratory tests, it was concluded that SS rebar made with high pitting-resistant grades, and thoroughly descaled, had a positive outlook for propagation stage durations that substantially exceed those of PS rebar. Quantification of that improvement is much in need of further field and laboratory assessment.

Dissolution kinetics of the sulfide-oxide complex inclusion and resulting localized corrosion mechanism of X70 steel in deaerated acidic environment

Dissolution kinetics of the sulfide-oxide complex inclusion and its surrounding matrix of X70 steel in deaerated acidic environment was investigated. The dissolution process can be divided into three stages including the initiation stage, galvanic corrosion stage, and the corrosion propagation stage. Chemical dissolution of CaS generates H2S and deposits, providing the condition for the formation of the galvanic couple in which the occluded micro-pits serve as anode and the surrounding matrix serves as cathode. The presence of CaS and appropriate electrolyte chemistry are indispensable for the formation of galvanic couple, of which the cathode/anode area ratio is about 50.

A self-balanced electrochemical model for corrosion of reinforcing steel bar in considering the micro-environments in concrete

Based on the electrochemical mechanism of steel corrosion, an improved electrochemical model was established to numerically simulate the corrosion of reinforcement in concrete under marine environment. The corrosion potential distribution and current density of corroded reinforcement were deduced from the corresponding micro-environments on the surface of steel bar, including oxygen, chloride ions, temperature and relative humidity. The equilibrium of gaseous oxygen and dissolved oxygen in pore solution was considered in the model. And the diffusion of invasion mediums in cement matrix and interfacial transition zone (ITZ) were also taken into account. The anode and cathode areas on the surface of steel bar was determined by the time-varying distribution of chloride ions rather than a fixed ratio to achieve the self-balance between macrocell and microcell corrosion. The simulation results agree well with the experimental data. The numerical analysis indicates that the growth of environmental chloride ions concentration will enhance the non-uniformity of chloride ions distribution, but does not contribute much to the increase of maximum rust layer thickness on steel surface. In the propagation stage of corrosion, oxygen concentration is a key factor in controlling corrosion reactions compared to chloride ions. Moreover, environment temperature has a positive effect on both the range of active areas on surface of steel rebar and rust layer thickness.

Corrosion propagation in cracked reinforced concrete, toward determining residual service life

Durability of reinforced concrete (RC) is influenced by cracks, providing paths for ingress of corrosion agents and early corrosion initiation. The corrosion propagation stage has in recent years been the focus of investigation, however, mainly focused on a single crack and reinforcement bar. This study focuses on chloride‐induced corrosion in three reinforcement layouts with a single or two transverse cracks kept at a constant crack width in flexure. The 27 beams were subjected to cyclic ponding with chloride aqueous solution for 36 weeks, and corrosion rate and potential measured weekly. The results indicate that the corrosion rate of RC members is influenced by crack spacing and reinforcement quantity. In current practice, corrosion initiation indicates end of service life. However, corrosion initiation is quick in cracked regions. It is proposed here to base the residual structural service life on the corrosion rate in the propagation phase, and a limit state of a threshold loss of reinforcing steel. In addition, crack spacing and reinforcement density are to be considered in the prediction of residual service life.

Cr-modified low alloy steel reinforcement embedded in mortar for two years: Corrosion result of marine field test

This paper describes a study of the corrosion behavior of Cr-modified steel reinforcement exposed at marine splash zone for a period of two years. The corrosion behavior was analyzed by the weight loss method, optical and electron microscopy, and X-ray photoelectron spectroscopy. The Cr-modified reinforcement exhibited high corrosion resistance in the actual marine environment. The protection mechanism of the Cr-modified reinforcement at the corrosion propagation stage was that Cr improved the protective quality and buffering ability of the rust layer against aggressive species, by increasing the Fe2+ and OH− content within the iron oxides and improving the compact degree of the rust layer.

Corrosion Propagation of Reinforcing Steel in High Performance Concrete

The Florida Department of Transportation (FDOT) has been using high performance concrete since the late 1980s early 1990s. Some of the older bridge structures (assuming 1990 as the completion year) are reaching 35 year of age, and depending on the concrete cover thickness (those with thinner covers), and the diffusivity of the concrete, corrosion of the reinforcement might initiate in a few years on some of these structures. The corrosion propagation stage of carbon steel rebar in high performance concrete might last longer than the typically five years usually attributed for carbon steel rebar in concrete with type I/II Portland cement as the only cementitious material. It is well known that reinforcement corrosion typically initiates at a later time on specimens in which the concrete contains supplementary cementitious materials such as fly ash, silica fume, slag or a combination of these materials when compared to reinforced concrete with no cementitious materials of the same w/cm ratio, cementitious content, and concrete cover. There are some reports[1-2] that indicate that the chloride threshold is lower on concrete with supplementary cementitious materials, particularly for concrete with high fly ash content (i.e., 50%); thus, this needs to be considered when modeling service life. There are several reports[3-4]that indicate that the corrosion rate of carbon steel rebar embedded in high performance concrete is lower when compared to rebar corroding on concrete with no supplementary cementitious materials. This observation in part can be attributed to the higher concrete electrical resistivity for concrete with supplementary cementitious materials when comparing concretes with similar moisture content. It is possible that there are reduced macrocell effects. The higher resistivity is in part due to pore refinement and higher tortuosity that develop with time on concrete structures with supplementary cementitious materials. In this investigation chlorides were driven into reinforced concrete specimens via an electro-migration method, as a way to accelerate chloride transport and allow corrosion to initiate after a short period of time. Mature (samples prepared in 2008) and recently prepared (April/2016) reinforced concrete samples were used in this investigation to gain additional insight on the corrosion propagation stage. The cementitious in the concrete of the older samples: 1) ordinary portland cement (OPC), 2) OPC and 20% fly ash, and 3) OPC, 20% fly ash and 8% silica-fume. Recent concrete samples contained 1) OPC and 50% slag or 2)OPC and 20% fly ash composition. All specimens had a w/cm ratio of .41 and 390 kg/m3 of cementitious material. The older specimens had either a single rebar embedded or four rebars (# 5 rebar/2 inch cover). Recently prepared samples had one rebar (#3 rebar/0.75 inch cover). Solution reservoirs ranged from one inch to 4 inches in length, as a way to vary the anode length. Rebar potential was used to determine if corrosion had initiated. The corrosion propagation was monitored via linear polarization measurements, solution resistance measurements, and rebar potentials. The corrosion propagation monitoring ranged from 300 days to several years. 1. M.D.A. Thomas and J.D. Matthews, “Chloride penetration and reinforcement corrosion in marine-exposed fly ash concretes”. In: Malhotra VM, editor, Third CANMET/ACI International Conference on Concrete in a Marine Environment, ACI SP-164, Detroit: American Concrete Institute; p. 317-38 1996 2. F. Presuel-Moreno, M. Paredes, “16 Years’ Exposure Of Fly Ash And Silica Fume Concretes On Salt Induced Reinforcing Steel Corrosion: Corrosion Potential, Resistivity And Diffusivity”, International Conference in Durability of Concrete, Trondheim, Norway, June 18-21, 2012 (Proceeding published on USB/Electronic form) 3. C Andrade, C Alonso “Test methods for on-site corrosion rate measurement of steel reinforcement in concrete by means of the polarization resistance method” Materials and Structures, v37 p623, 2004 4. W. Morris, A. Vico, M. Vázquez, “Chloride induced corrosion of reinforcing steel evaluated by concrete resistivity measurements” Electrochemica Acta, V 49 pp4447–4453 2004

Impacts of Global Warming and Sea Level Rise on Service Life of Chloride-Exposed Concrete Structures

Global warming will increase the rate of chloride ingress and the rate of steel corrosion of concrete structures. Furthermore, in coastal (atmospheric marine) zones, sea level rise will reduce the distance of concrete structures from the coast and increase the surface chloride content. This study proposes a probabilistic model for analyzing the effects of global warming and sea level rise on the service life of coastal concrete structures. First, in the corrosion initiation stage, an improved chloride diffusion model is proposed to determine chloride concentration. The Monte Carlo method is employed to calculate the service life in the corrosion initiation stage; Second, in the corrosion propagation stage, a numerical model is proposed to calculate the rate of corrosion, probability of corrosion cracking, and service life. Third, overall service life is determined as the sum of service life in the corrosion initiation and corrosion propagation stages. After considering the impacts of global warming and sea level rise, the analysis results show that for concrete structures having a service life of 50 years, the service life decreases by about 5%.

Effect of Climate Change on Service Life of High Volume Fly Ash Concrete Subjected to Carbonation—A Korean Case Study

The increase in CO2 concentrations and global warming will increase the carbonation depth of concrete. Furthermore, temperature rise will increase the rate of corrosion of steel rebar after carbonation. On the other hand, compared with normal concrete, high volume fly ash (HVFA) concrete is more vulnerable to carbonation-induced corrosion. Carbonation durability design with climate change is crucial to the rational use of HVFA concrete. This study presents a probabilistic approach that predicts the service life of HVFA concrete structures subjected to carbonation-induced corrosion resulting from increasing CO2 concentrations and temperatures. First, in the corrosion initiation stage, a hydration-carbonation integration model is used to evaluate the contents of the carbonatable material, porosity, and carbonation depth of HVFA concrete. The Monte Carlo method is adopted to determine the probability of corrosion initiation. Second, in the corrosion propagation stage, an updated model is proposed to evaluate the rate of corrosion, degree of corrosion for cover cracking of concrete, and probability of corrosion cracking. Third, the whole service life is determined considering both corrosion initiation stage and corrosion propagation stage. The analysis results show that climate change creates a significant impact on the service life of durable concrete.

すきま腐食進展過程に対するすきま内電位／電流密度分布の数値解析的考察

すきま腐食進展過程に対するすきま内電位／電流密度分布の数値解析的考察

Effect of Grain Size on the Corrosion Resistance of Friction Stir Welded Mg Alloy AZ31B Joints

The objective of this study was to clarify the effect of grain size on the corrosion rate across friction stir welded AZ31B joints when exposed in aqueous NaCl solutions. Grain size variations were achieved by preparing welded joints using AZ31B in different tempers. Single potentiodynamic polarization measurements made on the isolated base metal and stir zone in 0.6 M NaCl solution revealed no significant difference between the anodic kinetics, but revealed an apparent difference between the cathodic kinetics. The attempt to correlate extracted corrosion current density (icorr) values to grain size (d−0.5) revealed that the slope coefficient was insignificantly different from zero, meaning that no meaningful correlation exists (albeit during the corrosion propagation stage). Scanning vibrating electrode technique (SVET) measurements across an intact AZ31B-O welded joint revealed that grain size had a more complex effect on the anodic and cathodic kinetics of the filiform-like corrosion exhibited in 0.86 M NaCl solution. Grain size had an effect on filament initiation as it consistently occurred on the surface of the base alloy (coarser-grained structure). In contrast, grain size had no effect on filament propagation as the anodic and cathodic kinetics were unaffected when moving from the base metal (coarser-grained surface) across the stir zone (finer-grained surface).

The influence of platinum on the oxidation and sodium sulfate induced hot corrosion of NiAl diffusion coatings

Oxidation and corrosion properties at 900°C of two coatings, one containing platinum and the other platinum-free, on IN792 were investigated. During the corrosion exposures, sodium sulfate salt was situated in the furnace together with the coated specimens. The temperature of the salt was kept above its melting point but lower than the temperature of the coating i.e. 900°C. The exposure times ranged from 100 to 1000 h. The formed oxide scales were studied by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy and scanning transmission electron microscopy techniques. It is shown that the presence of Pt improves the protective properties of the coating against corrosion. The propagation stage of corrosion on the platinum-free coating is reached already after 100 h of exposure. On the other hand the scale formed on the platinum-rich samples still appeared to be protective even after 500 h. The details concerning structure and chemistry of the scales formed are presented and discussed.

Zinc Sulfate Reactions in Hot Corrosion

To further understanding of the potential effects of zinc containing contaminants or fuel additives in gas turbine hot corrosion, the corrosion of (a gas turbine blade coating alloy) spray coated with 50 mole percent was compared with that of spray coated with alone at 700° and 850°C in air containing controlled partial pressures. Thermobalance experiments showed that delayed initiation of low temperature (700°) hot corrosion of , but did not significantly change the total amount of corrosion, nor inhibit LTHC once the propagation stage of corrosion was reached. At 850°, gave somewhat more corrosion than pure , presumably because allowed formation of a liquid sulfate phase. Molten was shown to follow regular solution behavior at 850°, with the standard free energy for formation of in being −9.34 kcal/mol. The overall results suggest that zinc would be of doubtful benefit as an inhibitor for gas turbine hot corrosion.