Innovations in Corrosion and Materials Science (Discontinued) - Volume 9, Issue 1, 2019

Background: Magnesium and magnesium alloys are currently being explored for biodegradable metallic implants. Magnesium’s biocompatibility, low density, and mechanical properties could offer advantages in the development of low-bearing orthopedic prosthesis and cardiovascular stent materials. Objective: Magnesium’s susceptibility to corrosion and increased hydrogen evolution in vivo compromises the success of its potential applications. Various strategies have been pursued to control and subsequently evaluate degradation. Methods: This review provides a broad overview of magnesium-based implant materials. Potential coating materials, coating techniques, corrosion testing, and characterization methods for coated magnesium alloys are also discussed. Results: Various technologies and materials are available for coating magnesium to control and evaluate degradation. Polymeric, ceramic, metallic, and composite coatings have successfully been coated onto magnesium to control its corrosion behaviour. Several technologies are available to carry out the coatings and established methodologies exist for corrosion testing. A few magnesium-based products have emerged in international (European Union) markets and it is foreseen that similar products will be introduced in the United States in the near future. Conclusion: Overall, many coated magnesium materials for biomedical applications are predominantly in the research stage with cardiac stent materials and orthopaedic prosthesis making great strides.

Asphalt binder research papers characterized by X-ray diffraction are reviewed. The Xray results reveal the aromaticity and crystallite size parameters of asphaltene in asphalt binders as reported in the research literature. The research data is discussed in terms of asphalt molecular structure on a length scale, methodology, and petroleum oil fields. Box plots and summary statistics created for each parameter are compared and discussed as they relate to eleven data sets from various asphaltene-crude-oil-geological-regions.

Background: Deceleration of the corrosion rate of Mg by surface chemical method via hydrofluoric acid treatment has a special interest because it is a simple, cost-effective, and efficient method for the coating of interior as well as the exterior part of any size and shape of implant material. However, conversion coating by hydrofluoric acid treatment fails to produce a long-term stable coating of Mg in ionic solutions caused by the formation of cracks on the surface during the process. Consequently, the corrosive ions of the SBF solution enter through the cracks that accelerate the dissolution by local galvanic corrosion. On the above view, we aim to develop a simple strategy for enhancement of corrosion resistance of the hydrofluoric acid treated Mg bioimplant material. Methods: This method is comprised of dip coating of hydrofluoric acid treated Mg sample in the polymethylhydrosiloxane followed by curing at 170°C for 30 min. The samples were characterized by electron probe microanalysis, X-ray photoelectron spectroscopy and electrochemical test. Results: The electrochemical test results reveal that the corrosion rate of the coated Mg sample in the simulated body fluid solution is decreased by more than 8500 times than the bare sample. The long term immersion data indicate that the chemical resistance of the coated Mg sample in the SBF solution even after 25 days is better than the bare Mg metal. Conclusion: Polymethylhydrosiloxane coating is efficient to enhance the corrosion resistance of hydrofluoric acid treated Mg metal in simulated body fluid solution.

Background: Lithium tantalate (LiTaO3) thin film was synthesized and in situ coated on tantalum substrate via anodic oxidation. Methods: The effects of temperature, voltage and time on composition, morphology and hardness of film were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Vickers hardness, respectively. Results: Our results showed that surface hardness of all coated samples has been increased compared with that of pure tantalum. The value of hardness was found to gradually increase with temperature, voltage and reaction time of the coating process. Selected specimens, after coating, were immersed into 10 wt% NaOH solution at 50oC for 96h to explore their anti-corrosion performance. Immersing results indicated that LiTaO3 coated samples have a smaller mass loss and corrosion rate compared to those of pure Ta substrate. Pure tantalum sample and those coated by LiTaO3 thin film were further examined by electrochemical methods including open-circuit potential (OCP), potentiodynamic polarization curves and electrochemical impedance spectra (EIS). Conclusion: We have found that samples coated with LiTaO3 thin film exhibit higher potentials and lower corrosion current densities than those of pure tantalum substrate, according to the results and analysis of OCP curves and potentiodynamic polarization curves. Upon anodic oxidation, samples display higher polarization resistance with higher resistance to corrosion.

Background: Despite the process of rusting being well known, it was uncertain whether rust was contagious or not through temporary contact that is, involving no permanent bonding. Objective: The study investigated whether rust could be transmitted through temporary contact using controls. Methods: Eight rusted steel wool rolls, each less than 3.50 g were staggeringly arranged in groups of four onto two non-rusted steel plates, each measuring 400 x 200 mm, with control cells in between. After 10 days, rust stains formed on the plates and the rolls were removed. The conspicuous stains were monitored every month by means of manual tracing. After six monthly observations, the first month tracings were superimposed onto each respective plate. Results: Although intrinsic rust had formed on the control and experimental cells, the original stains remained constant in shape and size. Conclusion: Rust is probably not transmitted to other metals by simple contact.

Background: Many studies were done to assess the mechanical characteristics of the bandage casts with regards to different specifications of materials under different parameters. Many patents have been designed on the various types of casting materials such as POP, fiberglass and polyester. A recent trend in the patent is to explore a hybrid combination for bandage casts to withstand structural failure, crack formation or deformation. Objective: This study aims to study the effect of impact force on plaster of Paris, fiberglass and hybrid bandage casts. Methods: There different bandage casts were constructed using plaster of Paris, fiberglass and a hybrid combination of plaster of Paris and fiberglass. They were subjected to Charpy impact test, three-point flexural test, and Rockwell B hardness test. Results: The impact characteristics, energy absorption properties, ductility, rigidity, strength, stiffness and indentation hardness of the hybrid bandage cast were found to be greatly influenced from being a composite of two casts and interfaces. It was found that the impact energy capable of being absorbed prior to fracture for the plaster of Paris, fiberglass and hybrid were 1.225 Joules, 11.125 Joules and 6.750 Joules, respectively. Conclusion: Hybrid bandage casts possessed improved impact characteristics compared to plaster of Paris bandage casts and more cost-effectiveness as compared to fiberglass bandage casts.

Background and Objective: The effects of representative solder flux residue weak organic acids on electrochemical migration (ECM) of tin in thin electrolyte layer were studied using a technique based on the coupling of in situ electrochemical measurements and optical observations, as well as ex situ characterizations. Methods and Results: The results showed that the increasing amount of weak organic acid decreased the probability of ECM and dendrites formed were mainly composed of metallic tin. Tin ions reacted with organic compound ions from hydrolysis of weak organic acids to form complexes with electronegativity, which retarded the transfer of tin ions. Some complexes can be oxidized to the insoluble tin oxides on the anode surface and blocked the dissolution of anode during tin ECM. Conclusion: The growth rate of tin dendrite was found to be limited by the dissociation of complexes. Mechanisms involved were proposed to explain the role of weak organic acid in the tin ECM.