Leaching Behavior and Corrosion Inhibition of a Rare Earth Carboxylate Incorporated Epoxy Coating System.

While paint coatings act as important barriers to corrosion, defects can lead to localized, rapid metal loss. The addition of corrosion inhibitors that are capable of leaching from a coating to protect the metal surface at a defect can prevent this type of corrosion. This work investigates the release and corrosion protection capabilities of two rare earth (RE) carboxylate inhibitors from an epoxy coating as an initial step to understanding their leaching behavior and interaction with the coating system. Leaching experiments were performed via inductively coupled plasma mass spectroscopy (ICP-MS) analyses of the solutions in which free-standing coatings loaded with varying concentrations of inhibitor compounds had been immersed. Inhibitor release from the epoxy coating was observed to be dependent on initial inhibitor concentration, inhibitor chemistry, and solution pH conditions. The coating systems with greater initial inhibitor loadings showed higher leaching rates, particularly in acidic environments. Following immersion, the absence of characteristic inhibitor peaks in the FTIR spectra of the coatings also confirmed leaching had taken place. Cross-sectional views of the coatings after exposure to the pH 1 environment presented a chloride infusion zone at the coating/solution interface where the inhibitor had leached out. The RE active inhibition provided by the leached RE carboxylate inhibitors was verified by exposure of a coating defect to a chloride contaminated environment.

The effect of treatment temperature on corrosion resistance and hydrophilicity of an ionic liquid coating for Mg-based stents.

Mg alloys are attractive candidate materials for biodegradable stents. However, there are few commercially available Mg-based stents in clinical use because Mg alloys generally undergo rapid localized corrosion in the body. In this study, we report a new surface coating for Mg alloy AZ31 based on a low-toxicity ionic liquid (IL), tributyl(methyl)phosphonium diphenyl phosphate (P1,4,4,4 dpp), to control its corrosion rate. Emphasis is placed on the effect of treatment temperature. We showed that enhancing the treatment temperature provided remarkable improvements in the performances of both corrosion resistance and biocompatibility. Increasing treatment temperature resulted in a thicker (although still nanometer scale) and more homogeneous IL film on the surface. Scanning electron microscopy and optical profilometry observations showed that there were many large, deep pits formed on the surface of bare AZ31 after 2 h of immersion in simulated body fluid (SBF). The IL coating (particularly when formed at 100 °C for 1 h) significantly suppressed the formation of these pits on the surface, making corrosion occur more uniformly. The P1,4,4,4 dpp IL film formed at 100 °C was more hydrophilic than the bare AZ31 surface, which was believed to be beneficial for avoiding the deposition of the proteins and cells on the surface and therefore improving the biocompatibility of AZ31 in blood. The interaction mechanism between this IL and AZ31 was also investigated using ATR-FTIR, which showed that both anion and cation of this IL were present in the film, and there was a chemical interaction between dpp(-) anion and the surface of AZ31 during the film formation.

Potentiostatic control of ionic liquid surface film formation on ZE41 magnesium alloy.

The generation of potentially corrosion-resistant films on light metal alloys of magnesium have been investigated. Magnesium alloy, ZE41 [Mg-Zn-Rare Earth (RE)-Zr, nominal composition approximately 4 wt % Zn, approximately 1.7 wt % RE (Ce), approximately 0.6 wt % Zr, remaining balance, Mg], was exposed under potentiostatic control to the ionic liquid trihexyl(tetradecyl)phosphonium diphenylphosphate, denoted [P(6,6,6,14)][DPP]. During exposure to this IL, a bias potential, shifted from open circuit, was applied to the ZE41 surface. Electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA) were used to monitor the evolution of film formation on the metal surface during exposure. The EIS data indicate that, of the four bias potentials examined, applying a potential of -200 mV versus OCP during the exposure period resulted in surface films of greatest resistance. Both EIS measurements and scanning electron microscopy (SEM) imaging indicate that these surfaces are substantially different to those formed without potential bias. Time of flight-secondary ion mass spectrometry (ToF-SIMS) elemental mapping of the films was utilized to ascertain the distribution of the ionic liquid cationic and anionic species relative to the microstructural surface features of ZE41 and indicated a more uniform distribution compared with the surface following exposure in the absence of a bias potential. Immersion of the treated ZE41 specimens in a chloride contaminated salt solution clearly indicated that the ionic liquid generated surface films offered significant protection against pitting corrosion, although the intermetallics were still insufficiently protected by the IL and hence favored intergranular corrosion processes.

New insights into the fundamental chemical nature of ionic liquid film formation on magnesium alloy surfaces.

Ionic liquids (ILs) based on trihexyltetradecylphosphonium coupled with either diphenylphosphate or bis(trifluoromethanesulfonyl)amide have been shown to react with magnesium alloy surfaces, leading to the formation a surface film that can improve the corrosion resistance of the alloy. The morphology and microstructure of the magnesium surface seems critical in determining the nature of the interphase, with grain boundary phases and intermetallics within the grain, rich in zirconium and zinc, showing almost no interaction with the IL and thereby resulting in a heterogeneous surface film. This has been explained, on the basis of solid-state NMR evidence, as being due to the extremely low reactivity of the native oxide films on the intermetallics (ZrO2 and ZnO) with the IL as compared with the magnesium-rich matrix where a magnesium hydroxide and/or carbonate inorganic surface is likely. Solid-state NMR characterization of the ZE41 alloy surface treated with the IL based on (Tf)2N(-) indicates that this anion reacts to form a metal fluoride rich surface in addition to an organic component. The diphenylphosphate anion also seems to undergo an additional chemical process on the metal surface, indicating that film formation on the metal is not a simple chemical interaction between the components of the IL and the substrate but may involve electrochemical processes.

Influenza A induced rhabdomyolysis resulting in extensive compartment syndrome.

This is a case of influenza A induced rhabdomyolysis resulting in extensive compartment syndrome and acute renal failure in a 10-year-old child. The patient required fasciotomies in all four extremities. Even after fasciotomies were performed, the muscle tissue continued to swell, suggesting a primary myositis. This case emphasizes the importance of considering the diagnosis of compartment syndrome in patients with influenza infection and severe myalgia.

Pseudoparalysis of the lower extremity in an infant.

We describe a case of septic arthritis of the knee in an afebrile, well-appearing four-month-old female. She had been evaluated previously for lower extremity disuse attributed to antecedent trauma. Her physical examination was remarkable only for limitation of extension of the affected leg at the knee. Emergency physicians should understand the physical examination findings suggesting joint effusion and the need to consider osteomyelitis/septic arthritis in children less than one year of age with pseudoparalysis.

Torsional and angular deformities.

A general understanding of the cause and natural history of rotational and angular malalignment of the lower extremity allows accurate differentiation between pathologic and physiologic conditions. One can then educate the involved and often concerned family and proceed with observational management of physiologic conditions as spontaneous improvement of alignment can be expected. Aside from treatment for resistant metatarsus adductus, other forms of treatment, such as special shoes, casts, or braces, are rarely beneficial and have no proven efficacy. Persistent deformity beyond skeletal maturity is unusual and rarely causes significant functional disability. In rare cases of severe residual deformity, operative correction is the only effective treatment.

Long-term effects of dietary calcium on risk markers for colon cancer in patients with familial polyposis.

There is conflicting evidence regarding the benefit of calcium in prevention of colon cancer. Patients who have undergone ileorectal operations for familial polyposis can be useful to study hypotheses on prevention of colon cancer. In this study we evaluated the effect of long-term calcium supplementation on risk markers of colon cancer. Thirty-one patients with familial polyposis, after subtotal colectomy, were randomized to group A, which received placebo, and group B, which received 1200 mg of calcium daily. Intervention lasted 9 months, in which they underwent four 3-monthly evaluations that included food records, fecal pH, calcium and bile acids, and rectal biopsy for thymidine labeling. Age, height, weight, macronutrients, and dietary fiber were comparable in both groups. More women were in the group that received placebo. Fecal pH, weight, and bile acid levels were similar before intervention and remained unchanged. Fecal calcium levels were similar before intervention and increased in the calcium group throughout the study (p less than 0.05). Labeling index of placebo and calcium groups was similar before intervention (4.8 and 6.1, respectively). After 3 months it was reduced in both groups (3.1 and 4.4, respectively; p less than 0.05). After 6 months it was reduced only in the calcium group (3.4; p less than 0.05). After 9 months it did not differ from the starting point (3.4 and 4.0, respectively). In a long-term intervention study with a homogenous group of patients with familial polyposis, supplemental dietary calcium did not affect mucosal risk factors for colon cancer.

A model study of fecapentaenes: mutagens of bacterial origin with alkylating properties.

Fecapentaene-14 and -12 are directly acting mutagens that do not require metabolic activation. Their unusual structure suggests a possible mechanism of action. A carbocation that is formed by the addition of an electrophilic species (such as a proton) to the enol ether is most probably the reactive species. A series of model enol ethers with conjugated systems of various lengths was prepared, and a correlation between mutagenicity and increasing reactivity of derived carbocations was found. The glycerol moiety does not play a crucial role in the overall reactivity of the fecapentaenes.

Glycogen depletion and lactate responses in freestyle wrestling.

Metabolic responses to international freestyle wrestling were investigated in six university wrestlers, four of whom were studied on two separate occasions. Lactate concentration in venous blood averaged 10.5 mM after the six minute bouts, while blood pH was (p less than 0.01) reduced to 7.063 +/- 0.061 (mean +/- S.D.) after wrestling. Glycogen concentration in biopsy samples from the vastus lateralis muscle was lower by 10.0 +/- 4.4 mmoles glucose units/kg wet muscle weight (p less than 0.01) after, compared to before wrestling. Evaluation of glycogen utilization in individual muscle fibre types using the periodic acid Schiff histochemical stain revealed that glycogen depletion, although modest, was similar in ST, FTa and FTb fibres. These data demonstrate that wrestling involves significant anaerobic metabolism, and that the vastus lateralis muscle is significantly involved in wrestling performance.