Corrosion of steels and irons immersed in natural seawater for up to 600 years

Marine immersion corrosion observations for archaeological and other data, including from shipwrecks, wrought iron anchors and cast iron bridge piers are used to estimate corrosion losses in natural unpolluted coastal and near-coastal seawaters for exposures up to about 600 years. Empirical functions for the development of corrosion loss with time were then developed, standardized to 20˚C mean seawater temperature. The resulting slightly non-linear corrosion loss trend, represented by a modified form of the power law, is consistent with Phase 4 of the previously proposed bi-modal corrosion model. These observations support the notion that the rate of long-term corrosion is controlled by outward diffusion, through the rust layers, of gaseous hydrogen generated by the cathodic hydrogen evolution reaction under predominantly anaerobic corrosion conditions. The power-law trend also provides good extrapolation from shorter- term data. For practical purposes for exposures < 100 years in seawaters with mean temperature around 20˚C, a linear model, with longer-term corrosion rate 0.06 mm/y at 20˚C, is sufficiently accurate.

The Interdiffusion Behavior of NiCoCrAlYHf Coating Deposited by Arc Ion Plating on Carburized Ni-Based Single Crystal Superalloy

In the present study, arc ion plating (AIP) was used to prepare a NiCoCrAlYHf coating (HY5 coating) on a carburized third-generation single-crystal superalloy DD10. The interdiffusion behavior of the carburized superalloy with an HY5 coating was investigated for a 1000 h oxidation time at 1100 °C. Carburization enhanced the interfacial bonding force and improved the microstructure of the NiCoCrAlYHf coating. An interdiffusion zone (IDZ) formed after a 300 h oxidation time, and the formation of a carburized layer effectively suppressed an inward diffusion of cobalt, aluminium, and chromium to the DD10 superalloy as well as an outward diffusion of nickel and refractory elements for instance rhenium and tungsten to the HY5 coating that occurred in static air at 1100 °C. The roles of the carburized layer in affecting thermal cyclic oxidation and element interdiffusion were studied. Subsequently, a modified form of the Boltzmann–Matano analysis was used to present the interdiffusion coefficients of aluminium.

ARL3 Mediates BBSome Ciliary Turnover by Promoting Its Outward Diffusion through the Transition Zone

Ciliary receptors and their certain downstream signaling components undergo intraflagellar transport (IFT) as BBSome cargoes to maintain their ciliary dynamics for sensing and transducing extracellular stimuli inside the cell. Cargo laden BBSomes shed from retrograde IFT at the proximal ciliary region above the transition zone (TZ) followed by diffusing through the TZ for ciliary retrieval, while how the BBSome barrier passage is controlled remains elusive. Here, we show that the BBSome is a major effector of the Arf-like 3 (ARL3) GTPase in Chlamydomonas. Under physiological condition, ARL3GDP binds the membrane for diffusing into and residing in cilia. Following a nucleotide conversion, ARL3GTP dissociates with the ciliary membrane and binds and recruits the IFT-detached and cargo (phospholipase D, PLD)-laden BBSome at the proximal ciliary region to diffuse through the TZ and out of cilia. ARL3 deficiency impairs ciliary signaling, e.g. phototaxis of Chlamydomonas cells, by disrupting BBSome ciliary retrieval, providing a mechanistic understanding behind BBSome ciliary turnover required for ciliary signaling.

High Temperature Oxidation Behaviors of BaO/TiO2 Binary Oxide-Enhanced NiAl-Based Composites

High temperature lubricating composites have been widely used in aerospace and other high-tech industries. In the actual application process, high temperature oxidation resistance is a very importance parameter. In this paper, BaO/TiO2-enhanced NiAl-based composites were prepared by vacuum hot-press sintering. The oxidation resistance performance of the composites at 800 °C was investigated. The composites exhibited very good sintered compactness and only a few pores were present. Meanwhile, the composite had excellent oxidation resistance properties due to the formation of a dense Al2O3 layer which could prevent further oxidation of the internal substrate; its oxidation mechanism was mainly decided by the outward diffusion of Al and the inward diffusion of O. The addition of BaO/TiO2 introduced more boundaries and made the Kp value increase from 1.2 × 10−14 g2/cm4 s to 3.3 × 10−14 g2/cm4 s, leading to a slight reduction in the oxidation resistance performance of the composites—although it was still excellent.

Microstructure and Oxidation Behavior of NiCoCrAlY Coating With Different Sm2O3 Concentration on TiAl Alloy

In order to improve the oxidation resistance of TiAl alloys, NiCoCrAlY coatings with different amounts of Sm2O3 were prepared by laser cladding on TiAl alloys. The microstructure and oxidation behavior of the coatings were investigated by isothermal oxidation tests at 900°C. The results indicated that the grains of the coatings were refined by Sm2O3. The fine grain reduced the crack sensitivity of the doped coatings and promoted the transformation of θ-Al2O3 to α-Al2O3. Therefore, the internal oxidation of the coatings and the growth rate of the oxide films were reduced. The segregation of Sm at grain boundary inhibited the outward diffusion of Ti, thus reducing the excessive oxidation of Ti. In addition, the oxidation mechanism of the coating was changed from simultaneous diffusion of Al and O to predominant inward diffusion of O. The oxidation resistance of the doped coatings was significantly improved. However, excessive Sm2O3 is detrimental to the improvement of the oxidation resistance. The oxidation resistance of 3 wt% Sm2O3 is the best.

High Temperature Oxidation Behavior of an Equimolar Cr-Mn-Fe-Co High-Entropy Alloy

The oxidation behavior of an equimolar Cr-Mn-Fe-Co high-entropy alloy (HEA) processed by 3D laser printing was investigated at 700 °C and 900 °C. The oxidation kinetics of the alloy followed the parabolic rate law, and the oxidation rate constant increased with the rising of the temperature. Inward diffusion of oxygen and outward diffusion of cations took place during the high-temperature oxidation process. A spinel-type oxide was formed on the surface, and the thickness of the oxide layer increased with the rising of experimental temperature or time. The exfoliation of the oxide layer took place when the test was operated at 900 °C over 12 h. During oxidation tests, the matrix was propped open by oxides and was segmented into small pieces. The formation of loose structures had great effects on the high-temperature oxidation resistance of the HEA.

Microstructure of Aluminide Coatings Modified by Pt, Pd, Zr and Hf Formed in Low-Activity CVD Process

In the present article the doping of aluminide coatings by Pt/Pd as well as Hf or Pd using industrial processes was developed. The different combinations of doping elements were tested as well as their influence on chemical composition of coatings was initially investigated. The Pt and Pd and both Pt + Pd was electroplated on the surface of the MAR M247 nickel superalloy. The Zr or Hf was doped during low activity CVD aluminizing process using industrial Bernex BPX Pro 325S system. The conducted research showed that Pt and Pd formed the (Ni, Pd, Pt) Al solid solution in the outer additive layer. The higher concentration of palladium in the near surface and in the whole additive layer was detected. The platinum was presented below the surface of aluminide coating. The Zr or Hf was detected mainly in the diffusion zone. The low concentration of Zr (about 0.1 wt.%) in the outer zone was observed. The hafnium was detected mainly in the diffusion zone but in the outer additive layer a small concentration of this element was measured. The obtained results showed that formation of three elements (Pd, Pt) + Zr or Hf modified aluminide coating using proposed technology is possible. The structure of all obtained aluminide coatings was typical for a low-activity, high temperature (LAHT) formation process mainly by outward diffusion of Ni from base material.

Surface protective layers of iron aluminides developed on medium carbon steel by the hot-dip aluminizing (HDA) process

The investigation in this paper is based on the existence of carbon content and its role in the formation of Fe-Al intermetallic layer in unalloyed carbon steel C45 with a carbon content of 0.44 wt.%. Several sophisticated techniques such as PFIB SEM equipped with EDS and EBSD, GD-OES were employed for the in-depth surface analysis. The results of the metallographic examination reveal that the carbon would appear and could be well detected at the interface between the solidified aluminum and the solid iron-base steel substrate and got also incorporated in the top aluminum layer. Furthermore, due to the dissolution and outward diffusion of iron into the liquid aluminum melt during the HDA process, plus its involvement in the formation of the solid intermetallic surface layer, thus the carbon atoms gaining higher chemical affinity there will also be more likely to form carbide precipitates of different kinds like Fe3AlC and AlC inside these developing surface layers on the C45 type steel during the process of hot-dip aluminizing at 700 °C.

Selective Loading and Prolonged Release of 5-Fluorouracil in the Nanoconfined Interlayer Space of Montmorillonite

Montmorillonite was used as a carrier for the anticancer drug 5-fluorouracil (5FU). The selective loading of 5FU into the nanoconfined interlayer space of montmorillonite was achieved by rinsing off the weakly bonded 5FU from the external surface. The 5FU loading content in montmorillonite was 3.2 mass%. The intercalated 5FU was in an amorphous state and might be arranged as a roughly vertical monolayer in the interlayer space of montmorillonite. The intercalated 5FU showed a high thermal stability due to the protection of the montmorillonite layers. The release profiles of the intercalated 5FU were well fitted with the modified Korsmeyer-Peppas model. The montmorillonite exhibited a prolonged release of 5FU due to the restriction of the outward diffusion of intercalated 5FU. The 5FU/montmorillonite system has promising potential for oral administration for colonspecific delivery.

The formation of zinc coatings in nanocrystallised zinc powders

The kinetics of and mechanism for galvanising low-carbon steel (0.2% C) were examined in powder media which were pre-treated to obtain a fine nanostructured ZnO layer on the surface of zinc powder particles. The effective diffusion coefficient of Zn atoms through the ZnO shell was estimated to be in the order of 1·10-10 m2·s-1. The contribution of the Zn-gas evaporation/condensation microprocesses, which could occur in relation to the above diffusion through a nanostructured surface layer, was evaluated with numerical calculations in the temperature range of 550–950 K and for an average particle size of ZnO up to 100 nm. Our results suggest that the outward diffusion of metallic zinc takes place from the core of powder microparticles across the nano-grain boundaries of their modified surface layer, and can be further intensified by the presence of other inter-phase defects, such as nano-porosity.