Innovations in Corrosion and Materials Science (Discontinued) - Volume 6, Issue 1, 2016

Background: Natural fiber reinforced polymers are finding enormous applications in fields of automobile and house hold applications due to its distinct advantages over synthetic fiber reinforced polymer composites. In order to meet the escalation in demand of natural fiber reinforced composites, quick and versatile processing methods have to be adopted by the industry. Injection molding, being a promising method for this purpose has been chosen for the present study in order to reinforce short kenaf fibers into polypropylene. Methods: Kenaf fiber reinforced PP based composites having a fiber weight fraction of 30% were fabricated using injection molding process. Mechanical properties and fiber distribution of the developed composites were evaluated in comparison to neat polypropylene and maleic anhydride grafted polypropylene (MAPP). Mechanical properties in terms of flexural and tensile strength of the developed composites were evaluated in accordance to respective ASTM standards. Results: The flexural strength of PP/(30)K composite increased marginally, while the flexural strength of PP/(30)K/(5)MAPP composite was found to be significantly higher than both neat PP and PP/(30)K composite. Tensile strength of PP/(30)K composite is found to deteriorate with the addition of untreated short kenaf fibers. However, the addition of MAPP into the matrix improves the tensile strength of the developed composites. The flexural and tensile modulus of the developed composites also increased significantly compared to neat PP indicating increased stiffness of the developed composites. Morphological investigation of the developed composites revealed uniform distribution of short kenaf fibers throughout the composite and improved interfacial bonding in case of PP/(30)K/(5)MAPP composites resulting in better mechanical properties. Conclusion: Short kenaf fiber reinforced polypropylene composites having fiber weight fraction of 30% were successfully developed through injection molding process. Injection molding process for the fabrication of natural fiber reinforced composites is found to be a viable option and short kenaf fibers also have tremendous potential to be used as a reinforcement in natural fiber reinforced composites.

Background: The integration of chemistry principles with materials science research can lead to the creation of highly stable materials with complex geometries and enhanced functionality. In that view, we designed a hybrid organic-inorganic composite, ethyl cellulose-nickel(II) hydrogen phosphate (EC-NiHPO4) for its efficient electrochemical and biological activity. Methods: The EC-NiHPO4 composite was prepared by sol-gel method and was physically characterized by Fourier transform infrared (FT-IR) spectroscopy, UV-Visible (UV-Vis), and powdered X-ray diffraction. Further, the biological activity by means of anticancer and antimicrobial effects was tested following the treatment of ECNiHPO4 composite at different concentrations. Results: The porosity studies indicated that the pore diameter of the composite to be 395 nm and the X-ray diffraction pattern shows that the crystalline phase greatly enhanced as a result of polymer-inorganic complexation. Further from the electrochemical studies, a change in the material conductivity values with that of electrolyte concentration was observed. Also, the conductivity of EC-NiHPO4 material for the 1:1 electrolyte solution was found to decrease in the order of K+ > Na+ and the material seems to work very well in the pH range of 5-7.5. We also observed significant biological activity by means of anticancer and antimicrobial effects following the treatment of EC-NiHPO4 composite. Conclusion: Our analysis of the EC-NiHPO4 composite demonstrates the conductometric behavior and biological activity of organic-inorganic composites.

Introduction: The world has now discovered in natural fiber reinforced composites, a more eco-friendly alternative. Ever since, the interest in and demand for natural fiber reinforced composites is on the rise. Today, manufacturers in the construction, automotive, and packaging industries, among others are well aware of the worth of plant fiber reinforced composites. In particular, industrial hemp fiber reinforced composites have been gradually replacing fiberglass counterparts for vehicles that are fuel efficient and light weight. This may be attributed to the appealing qualities including their biodegradability and low cost as well as acceptable mechanical properties. Still, there exist certain challenges in the machining of composite products that need to be overcome. Methods: Drilling, an operation for making holes in composite laminates is one of the challenging steps in the production cycle. It is indispensable for ascertaining the assembly of intricate composite products. The present experimental investigation is part of the ongoing attempts to come up with solutions to minimize the drilling induced damage. Experiments have been conducted using a state of the art experimental facility to determine the machining behavior of woven industrial hemp fabric reinforced polypropylene composites. The effect of the processing parameters; feed rate, cutting speed and the drill point geometry has been investigated on the drilling induced damage. The solid carbide drill bits have been used for conducting the experiments. Drilling-induced damage was quantified using stereo microscope. Results: The major form of drilling induced damage is the delamination. Both the peel-up type and the push-down type of mechanisms have been observed for delamination. The push-down type of delamination has been found to be more severe in the current experimental domain. The processing parameters affect the drilling induced damage significantly. The delamination factor shows a strong dependence on the feed rate. The selection of the tool point geometry also influences the drilling induced damage. The Parabolic drill point geometry shows a better drilling behaviour in terms of minimum drilling induced damage. The experimental values indicate close relationship between tool point geometry and the delamination factor. Conclusion: The natural fiber reinforced composite laminates are a viable alternative to the synthetic fiber reinforced composites. The hole making operation in these materials is a perplexing challenge. It can be concluded that the selection of the optimal processing parameters (cutting speed, feed rate) and the drill point geometry can significantly minimize the drilling induced damage. The drill point geometry is the most important parameter and its judicious selection can certainly reduce the rejection rate of composite products with drilled holes.

Background: Stress Corrosion Cracking (SCC) is a sudden and difficult-to-predict severe degradation mode of failure of nuclear, petrochemical, and other industries. This is a review of a development proposal for methodological software for modeling SCC based on: the failure propensity plus a kinetic model link which better describes its evolution. Methods: The basic issues of this methodology are: a) A fixed combination of material-environmental condition is plotted on a potential-pH (Pourbaix) diagram marked with corrosion submodes – which can be originated from literature and/or experimental data. This forms a Knowledge Base (KB) for SCC-Propensity. Fuzzy Logic- a form of multiple valued logic where uncertainties can be considered - can be used to determine the SCC-Propensity zones; b) When the actual corrosion submode of the concerning material-environment is marked, based on new experiments, a feedback should be sent to the KB with the purpose to check the original submode border; c) Over the determined point (or region) in a SCC submode, a proper kinetic model should be chosen (departing for example from a kinetic library model-KB) to adjust the experimental data from the concerning material-environment. Alternatively a new empiric or numeric model can be adjusted; d) The regression quality of the model adjusted should be properly and statistically evaluated, and a feedback should be “fuzzylogically” retrofit its adequacy. Results: The main result is prediction with an adequate statistical regression. Conclusion: In this article the methodology is reviewed with an improving concerning the Pourbaix diagram construction for multielement systems, and at high temperatures.

Background: Organic inhibitors used to reduce the degradation rate of steel structures in acid solution are highly toxic to human and environment. Natural products such as plants or seeds extracts are being investigated as green inhibitor to combat this global environmental threat. A homeopathic medicine, commonly used in preventing gas and acidity problems of human beings is investigated to reduce similar gas and acidity problems of acid steel tank. Methods: The study was conducted, with low carbon steel, in 0.5 to 2 N HCl with variation of drops of homeopathic medicine with constituents: Lycopodium, Robinia, Natrumphos and carboveg. The corrosion rates of test specimens were determined by performing electrochemical polarization tests with computer controlled Gamry machine, with variation of concentration of acids as well as inhibitor. The study of adsorption of inhibitor on metal surface was also conducted and the adsorption isotherm fitting the data was evaluated to under the science of corrosion inhibition. Results: The results shows that increase in inhibitor concentration decreases the rate of degradation. But there is an optimum concentration at which the inhibitor effect is maximum, beyond that the corrosion rate again increases. The adsorption study shows that the mechanism of corrosion inhibitor is due to physical adsorption, following Langmuir and Temkin adsorption isotherms. The metallic surface in acid before and after addition of inhibitor, under optical microscopy, clearly reveals that the corrosion process has been retarded by the adsorption of the inhibitor. Conclusion: A new green inhibitor has come up in a homeopathic medicine in inhibiting the acid corrosion of carbon steel. The percentage of corrosion retardation depends on the concentration of acid as well as the amount of inhibitor added.

Severe localised corrosion has long been considered the main cause for structural integrity loss of steel assets exposed to aggressive marine environments, particularly as caused by pitting corrosion on or around weld zones. The weld heat affected zones for welds in steel structures are known for their higher rate of localized corrosion. The effects of corrosion losses on the structural reliability of welded mild steel, as commonly used within the offshore industry world-wide, are considered for quantifying the long-term loss of structural capacity. Apart from the expected reduction of capacity due to cross-section loss the results show that structural reliability is sensitive to likely nutrient pollution and macro-galvanic effects within the steel matrix. The possibility of localised corrosion being the result of thermal microstructural gradients produced during the welding process is discussed.

Background: Corrosion is a crucial worldwide problem that strongly affects natural and industrial environments, in particular affecting land, sea and air transportation vehicles: Cars, trucks, buses, merchant ships, and aircraft. This study describes a corrosion protection technology, based on chemical conversion coatings (CCC), to prevent, avoid or minimize corrosion event. Phosphating, a particular CCC was applied. Methods: Carbon steel pieces were phosphate by immersion in a solution containing phosphoric acid (PA, H3PO4), zinc sulphate, hydrogen peroxide as an oxidant and a Zr salt, a sealing agent. The characteristics of the phosphate layer was determined by Scanning Electron Microscope (SEM), Energy Dispersive X-Ray Spectroscopy (EDS) and Raman Spectroscopy. The phosphate steel was painted with an industrial epoxy paint. Its corrosion resistance was determined by potentiodynamic polarization and by exposure in a saline chamber following the practice recommended in American Society for Testing and Materials (ASTM). Results: The steel specimens were weighed before and after immersion in the phosphating solution, after different immersion times. The weight increases resulting from the formation of the phosphate layer were recorded and are expressed in mg/cm2. The corrosion rates were calculated using the Tafel slopes based on the Stern-Geary equation. The current density i in μA/cm2 units were converted into corrosion rate in mm/y units, applying the Faraday equation. Conclusion: Phosphating is a useful pretreatment, based on a phosphoric acid solution containing additional components to improve the protective capabilities of coating systems that are applied to steel in order to improve its corrosion resistance.

DMR-249A is a High Strength Low Alloy (HSLA) steel, with micro-alloying additions of V, Nb and Ti. The steel is designed to have a predominantly ferritic microstructure, with pearlite content less than 10% by volume. For this structural grade steel used in the construction of the hulls of vessels, the deterioration of strength and structural integrity is a major factor in assets management. This paper discusses comparison of electrochemical corrosion properties of both DMR-249A steel and the welded butt joints fabricated with four different welding processes: Manual process - Shielded Metal Arc Welding (SMAW) and Automatic processes - Submerged Arc Welding (SAW), Flux Cored Arc Welding (FCAW) and Activated Flux Gas Tungsten Arc Welding (A-GTAW). The microstructures exhibited transformation of fine grained equiaxed ferrite structure of DMR-249A base metal to grain boundary ferrite, Windmenstatten ferrite, acicular ferrite, polygonal ferrite and microphases in weld metal. The difference in OCP and corrosion rate observed in the base metal and the four different weld metals was found to be negligible. The base metal (DMR-249A steel) and all weld metals demonstrated similar trends of corrosion within small scatter band establishing that the welding process has not deteriorated the corrosion properties of the base metal. The DMR-249A steel was compared with other ship building steels (ABA and D40S) of Russian origin. The corrosion characteristics of DMR-249A with ABA and D40S steels displayed comparable trends and extent of corrosion.

Background: Excellent corrosion resistant titanium is prone to intense biofilm formation leading to biofouling and biomineralization affecting the heat transfer properties of condenser tubes. This work looks into the possibility of using electroless copper (Cu) plating on tube side of titanium (Ti) condenser for biofouling control. Methods: Electroless copper was coated on anodized Ti specimens and annealed at 450°C. Surfaces of annealed Cu coated Ti specimens were characterized using XRD, AFM, SEM and XPS. Antibacterial activity and long term stability of the electroless Cu coating on Ti were studied after exposure of coating specimens to natural seawater for four months. Biofilm community diversity and copper tolerance of microorganisms were analyzed with Denaturing gradient gel electrophoresis (DGGE) and 2-Dimensional electrophoresis (2-DE). Results: Surface analyses of electroless copper coated titanium specimens with AFM and SEM showed reduction in the microroughness of Cu coated Ti surfaces when compared to anodized Ti surface. XPS spectral analysis showed the shift in binding energy inferring the reduction of the hydroxide to metallic copper in Cu 2p3/2 peaks. Total viable counts and epifluorescence microscopy analyses showed two orders decrease in bacterial counts on electroless Cu coated Ti specimens when compared to as polished control Ti specimens establishing the antibacterial activity. DGGE analysis inferred the differences in the bacterial diversity among Cu coated and as polished Ti surface biofilms. Distinct protein spots in the 2-DE results of electroless copper coated Ti biofilm protein samples indicated copper accumulating proteins in copper resistant bacterial species of biofilm. Conclusion: Biofouling control due to reduced microroughness of the surface and toxic copper ions was established and inferred the stability of copper coating even after four months exposure to sea water.