Innovations in Corrosion and Materials Science (Discontinued) - Volume 7, Issue 2, 2017

Background: Despite much attention of scientists paid to magnesium hydride, methods of its obtaining and properties investigation, the latter still has not found wide applications as a hydrogen material- accumulator for automotive industry. This work provides an overview and comparative analysis of the results studies performed by the authors. This review is directed at the synthesis of magnesium dihydride with low temperature, high kinetics of its dissociation, high hydrogen capacity and cyclic stability. Methods: To reduce the temperature, improve the kinetics of stoichiometric MgH2 hydride decomposition, a range of new mechanical alloys-composites have been synthesized by reactive grinding in hydrogen. By the method of thermal desorption spectroscopy, we studied the influence of alloying elements on the hydrogen-sorption properties, thermal resistance, and the kinetics of hydrogen desorption from the MgH2 hydride phase obtained by mechanical fusion. For the X-ray phase diffraction analysis of specimens, we used a DRON-3M diffractometer. The diffraction patterns were analyzed by Rietveld method using Fullprof software Powder Cell 2.4. Results: It has been established that Al addition to Mg (without addition of Ti, Fe, Ni) does not cause temperature decreasing of the beginning of hydrogen desorption from the MgH2 hydride phase. Very fast desorption kinetics at 300ºC and PH2 = 0,1 MPa were observed for Mg+Me mixture in comparison with the pure Mg, releasing 50% of total hydrogen in 7, 13, 16, 5 and 58 minutes at addition to Mg of 10 wt. % Ni, Fe, Ti, Al, correspondently. Investigated mechanical alloys-composites contain MgH2 hydride phase are able to accumulate from 5 to 6.5 wt. % H2. Conclusion: Analysis of the research results presented in the article allows us to conclude that mechanical treatment of Mg in the presence of the catalyst additives allowed for significant improvement of the kinetics of the desorption process of hydrogen from the hydride phase MgH2. At the same time, its thermodynamic stability, decomposition temperature (at PH2 = 0.1 MPa) remains high for practical use of the mechanical alloys as the hydrogen accumulators for vehicles. However, the performance characteristics of the developed composite materials allow their use at stationary application conditions. As a “high-temperature” hydrogen storage material, magnesium hydride attracts the attention of developers of hydrogen storage systems thermally integrated with hydrogen-oxygen solid oxide fuel cells.

Background: Corrosion monitoring in other words the health checkup of civil infrastructures is an essential survey required for maintaining the service life of concrete structures. In order to avoid the catastrophic failures, corrosion monitoring and effective additional protective measures must be undertaken at the initial stage itself. The in situ corrosion monitoring techniques provide information on the state of condition of reinforcement rods and concrete. For concrete, concrete resistivity measurements, and in situ strength by ultrasonic pulse velocity measurements are discussed. For embedded steel, techniques (i) for identifying corrosion pits and cracks by acoustic emission (ii) for identifying grouted and non-grouted portions of pre stressed steel by radiography (iii) corrosion rate of embedded steel by linear polarization resistance and potentiostatic pulse technique are discussed. Cyclic polarization and potentio dynamic polarization tests were conducted to characterize and evaluate MnO2 sensors. The half-cell potential of MnO2 in concrete is found to be +200 mV Vs SCE. The potential of embedded steel with reference to MnO2 are -315 mV and -525 mV for non-corroding and corroding conditions of embedded steel in concrete. Rebar potential sensors and corrosion rate monitoring probe sensors were embedded in real concrete structures for long-term corrosion monitoring studies. The sensor materials provide information on the corrosion condition of embedded steel during the service life of structures. Corrosion monitoring techniques identify the corrosion hot spot areas; so that repairs and rehabilitation work can be carried out at the right time before substantial damage / collapse occurs in the existing concrete bridges. Methods: The corrosion condition assessment of any civil infrastructures such as marine bridges, double wall concrete nuclear reactors and multi storey buildings, on-shore and offshore concrete structures will be implemented using advanced corrosion monitoring portable equipments. Results: The in situ concrete parameters such as compressive strength obtained from Rebound Hammer test and Ultrasonic Pulse velocity measurements were compared and analyzed for service life prediction. The potential of embedded steel in concrete and corrosion rate of embedded steel in concrete are the key parameters for determining the residual life of concrete structures. The corrosion currents measured from various electro chemical techniques were converted into millimeter per year (mmpy) units and correlated with service life of civil structures. Conclusion: The rebar potential measurements indicate whether the embedded steel exists in the passive or active conditions. The corrosion rate of embedded steel indicates the loss of diameter due to corrosion process. Based on the data collected, the site investigated will be classified as severely corroded and moderately corroded areas. The severely corroded areas will be identified and recommended for repair and rehabilitation to be implemented to enhance the durability of the civil infrastructures.

Background: The durability of civil infrastructures is a severe problem faced by Scientists, Engineers and Technologies of 21st Century, due to the increasing pollution of our environments. This paper deals with innovative corrosion protection techniques/technologies to enhance the durability of civil infrastructures. Corrosion resistant rebars manufactured using Cu, P, Ni and Cr are capable of bearing the humid conditions of the coastal areas. TATA TISCON 500D rebars de-signed with diminished levels of impurities like S and P showed better corrosion resistance properties. Compared to CTD rebars, TMT rebars with tempered martensite zone showed improved corrosion re-sistance properties. Cement based coated steel rebars (inhibited cement slurry coated, cement polymer composite coated rebars) found to be more compatible for reinforcement corrosion control, in compari-son to galvinized and epoxy coated rebars. Fly ash, slag or silica fume, blended cements are finer as compared to OPC. The fineness reduced the permeability of blended cement concrete and improved the durability. Ternary blended cements, due to the fineness of the material and increased alumina, silica contents showed improved mechanical properties and better protection for steel in concrete. Owing to the unique molecular structure and high ion exchange capacity, chloride scavengers reduced the corro-sion susceptibility. Epoxy-polyurethane based surface coatings enhanced the durability as barrier type of coatings. Corrosion inhibiting admixtures such as calcium nitrite, citrate and stannate due to the for-mation of an insoluble film enhanced the corrosion resistance properties of reinforcements. Migrating corrosion inhibitors (MCI) based on amino alcohol, amines and nitrites showed superior corrosion resistance properties when compared to admixed inhibitor systems. Depending upon the environmental conditions, the implementation of corrosion protection technologies definitely enhanced the durability of civil infrastructures. Methods: The durability of the civil infrastructures such as National Highway Bridges, Nuclear Reactors, Elevated water tanks, On-shore and Off-shore concrete structures will be enhanced by adopting Innovative Corrosion protection Techniques/ Technologies such as i) Corrosion resistant rebars, ii)Coatings to steel rebars, iii) Blended cements, iv) Chloride scavengers for marine structures and v) Corrosion inhibiting admixtures for fresh structures. For existing structures, the following innovative technologies such as i). Coatings to concrete surface ii). Migrating corrosion inhibitors will be implemented. Results: After adopting the appropriate innovative corrosion protection techniques/technologies, the effect of treated structures will be monitored by conducting NDT techniques. Conclusion: Each and every innovative corrosion protection techniques/technologies have its own merits, demerits and limitations. Proper selection of method of corrosion protection strategies depending upon the environmental conditions can only lead to saving of money and enhancing the durability of civil infrastructures. In order to enhance the service life of civil infrastructures, it is essential to provide additional protective measures.

Background:Metal surface immersed in natural or industrial waters undergo a sequence of processes in time and space that lead to the formation of biological and inorganic (scaling) deposit adhesion of different microorganisms (bacteria, microalgae, fungi) on the metal surface through extracellular polymeric substances, causing microbiologically influenced corrosion. The biofilm formation and microbiologically influenced corrosion impact on economic interests and after inorganic corrosion they are the most important problems affecting different industries. The eradication of biofilm in the industry is difficult and costly. Technological importance in the thermoelectric industry by biofilm and biofouling formation lies in energy losses in heat exchanger systems. In the oil industry, problems derived from the presence of biofilms as filter plugging, corrosion in structures storage and distribution of fuel are presented. The aim of this work is to show the different industry cases of microbiologically influenced corrosion: jet aircraft fuel storage tanks and distribution plant, steel plant, thermoelectric industry. The evaluation of microbiologically influenced corrosion and the biofilm formation are investigated. Methods: Microbial counts were performed by conventional techniques. The formation of the biofilm and the attack on the metal surface were studied through scanning electron microscopic techniques. Results: Different results were obtained for each of the industrial environments studied. Conclusion:Strategies to evaluate corrosion problems systems are proposed through microbiological and physical-chemical studies.

Background: The energy efficiency of optoelectronic devices in aqueous solutions was derived using a simple mathematical criterion. The criterion was based on calculating the limit of the ratio value of the conductivity of an optoelectronic material in aqueous solution (σs) to the conductivity of the optoelectronic material in air (σair). In other words, the criterion; lim (σs/σair) =1 was applied to determine the energy efficiency of the optoelectronic material in the aqueous solution when σs became equal (decreased) to σair as a function of time of the exposure of the material to the aqueous solution. The values of σs and σair were determined by the electrochemical impedance spectroscopy (EIS). The energy efficiency of an optoelectronic devise, i.e., computer disc(CD) material, was evaluated in distilled water and polluted water with a predetermined period of optoelectronic operations. Methods: The electrochemical impedance spectroscopy (EIS) was used to determine values of σs and σair of the computer disc(CD) material, Al2O3, in distilled water and a polluted water. Results: The energy efficiency of the computer disc(CD) material, Al2O3, was evaluated in distilled water and polluted water with a predetermined period of 12 months. Conclusion: A derived analytical model (lim (σs/σair) =1, as σs → σair) of the energy efficiency of optoelectronic materials was used to Plot; lim (σs/σair) vs. time of exposure of the pure Al, Al2O3, and Al2O3 in air, distilled water, and polluted water, respectively. Therefore, plots of the lim (σs/σair) vs. time of exposure like those of Figs. (2-4) can be standard plots of energy efficiency for different kinds of optoelectronic material.

Background: Aluminum tubes of a refrigerator evaporator were having pitting problems in the field. A failure analysis was performed using a scanning electron microscopy with energy dispersive x-ray analysis. The root cause of the problematic evaporator tubes was identified as the chlorine in a cotton adhesive tape that was used to fasten the evaporator tube to the inner case. The crevice (or pitting) corrosion mechanism occurred on the evaporator tube surface. Methods: A variety of chemical reactions were analyzed. To reproduce the pitting corrosion on the evaporator tube, a parametric accelerated life testing was performed using a 20% saline solution on the evaporator tube that was wetted in the chlorine water. Results: It showed that the evaporator tube was pitted in a place where the cotton tape was attached. The failure modes and mechanisms validated experimentally were identical to those of the problematic refrigerators in field. To modify the problem with the refrigerator evaporator tube, the cotton tape was changed into a generic transparent tape. Conclusions: The reliability of the new design for the cooling enclosure system pitted in field is now expected to have B1 life of over 10 years.

Background: Corrosion of carbon steel in ocean water is dependent on several parameters, such as, chemistry of seawater, temperature, and pH. Its chemistry is also not fixed but varies from one geographical location to another as well as along the depth from surface to sea bed. The fact causes unpredictable corrosion failures of marine steel structure that leads to economic losses, oil spilling, environment pollution and accidents. This is because; corrosion mechanisms are complex with high degrees of interaction among the corrosion species, products and metallurgies. Methods: For better understanding of the mechanisms of the effects of co existences of these parameters and prediction of the unpredictable life of the structures, ANN model was developed using 170 sets of experimental data, varying the corrosion influencing parameters SO42-, Cl-, HCO3-,CO32-, CO2, O2, pH and temperature as input and the corrosion current as output. About 60% of experimental data were used to train the model, 20% for testing and 20% for validation. The model was developed by programming in Matlab. Results: 80% of the validated data could predict the corrosion rate correctly. Corrosion rates predicted by the ANN model are displayed in 3D graphics which show many interesting phenomenon of the conjoint effects of multiple variables that might throw new ideas of mitigation of corrosion by simply modifying the chemistry of the constituents. The model could predict the corrosion rates of some real systems. Conclusion: It can be summarized that corrosion of carbon steel in aqueous marine environment is strongly influenced by various anions present in sea water, pH and temperature. The conjoint effect of two or more parameters jointly shows interesting phenomenon that even with high Cl- content the corrosion rates can be lower in the presence of high concentration of carbonate and sulfate.

Background: Corrosion of materials is a natural phenomenon that is a cause of concern as it has incurred a total damage of billions of dollars to many industries. Many ways of overcoming the corrosion problem such as inhibitors, anodic protections, cathodic protections and coatings are developed. Natural products such as plant extract, amino acids, proteins, and biopolymers have been reported to be efficient corrosion inhibitors. Plant extracts are viewed as rich source of naturally synthesized chemical compounds that can be extracted by simple procedures with low cost. These natural extracts are analogous to the synthetic organic inhibitors and are being proven to work as much as their synthetic counterparts. Methods: The initial weight of the mild steel specimens was measured using 4 digit model Dewyer SI-234. The initial weight of the coated mild steel specimens was measured. Weight loss experiments were carried out by immersing the coated mild steel specimens in HCl, H2SO4 and HNO3 acids after cleaning and weighing. A medium sized leaf of an Indian Aloe vera is taken and peeled and collected 50ml of the extract. The stem of the banana plant was collected from a local market. The sheets of the stem were separated, crushed in a grinder and the sap is extracted. The sap is stored in the freezer at 18 °C for further use. About 500 gms leaves of the Henna were collected from the garden. It is then cleaned and washed in distilled water. Leaves were blended to batter and the extracts were filtered out. Results: The surface morphology of the corroded mild steel sample is examined under colonial microscope and pictured by a mobile camera. The pictures reveal that the corrosion occurred, and the acids affected the inhibitor layer. Calculated data from the experiment are plotted using the Igor software. Weight loss of the mild steel without any inhibitor by acids is plotted against time. This plot reveals that HCL corrodes more than HNO3 than H2SO4, proving that HCL is more corrosive on Mild Steel Sample. HNO3 corrodes the sample from the 48th hour corroding about ~7 grams. The weight loss of the sample with Aloe Vera extract on various acids. From the plot aloe vera shows more resistance towards HNO3 than HCL and less protection towards H2SO4. The weight loss of the sample with banana sap extract on various acids. It shows the best protection against HNO3. Conclusions: Inhibition efficiency of the aloe vera, Banana sap and the henna extract are found to be higher than the other green inhibitors ranging from 70% to 98% against HNO3, H2SO4 and HCL. Henna extract is found to be more efficient than the rest. Relative corrosion resistance calculated from the corrosion rate is found to be outstanding. Relative corrosion resistance calculated from the corrosion rate is found to be outstanding. The green inhibitor reported in this work is found to be an excellent replacement of the chemical coating present today. These green inhibitors are ecofriendly, nontoxic, leading to zero pollution thus certainly needed for this generation.

Background: Results of a study on the initial stage of corrosion damage of carbon steel in 0.5mol/l NaCl by high-precision Coulometric Registration of Corrosion Products (CRCP) of the metal surface and in the corrosive medium are reported. Methods: During the measurements, the method of coulometric determination of corrosion products developed by the authors was used. Result: An accurate quantitative determination of “initiation phase of corrosion” allowed to find a correlation between the early stage of the process and its subsequent development of corrosion.