Chloride-rich Environments Research Articles

Role of Tartaric Acid on the Anodizing and Corrosion Behavior of AA 2024 T3 Aluminum Alloy

Tartaric acid is added to sulfuric acid anodizing baths to generate porous anodic film that provides corrosion resistance to practical aerospace alloys and reduces the environmental impact of the traditional chromic acid anodizing process. Here, a fundamental study on the effects of the addition of tartaric acid to the sulfuric acid anodizing electrolyte has been undertaken. During anodizing, it was evident that tartaric acid does not significantly affect the mechanism of porous film growth, but it reduces the growth rate of the porous anodic film. After anodizing, in acidic environments, it may reduce the dissolution rate of a previously formed oxide. Furthermore, it was found that in a nearly neutral, chloride-rich environment, tartaric acid limits the anodic reaction of aluminum dissolution at concentrations in the hundreds of ppm range. The previous suggests that the good anticorrosion performance of alloys anodized in the presence of tartaric acid is due to residues of tartaric acid in the pore solution.

Analysis of Chloride Penetration into the Corner Zone of Concrete Structure Member

Chloride penetration into concrete is the main cause of steel corrosion in concrete structures exposed to chloride-rich environments. In general, conditions on the diffusion process are dominant among various penetration mechanisms, such as ionic diffusion, capillary sorption, and so on. In recent analysis of current literature, chloride diffusion is as a simplified one-dimensional diffusion process. However, for the rebar in the corner zone of concrete beam, the diffusion belongs to a two-dimensional diffusion. Based on a galerkin finite element method, a two-dimensional diffusion differential equation is built and solved numerically and the different chloride concentration is compared to one dimensional diffusion and two-dimensional diffusion process. The service life of concrete structure members under two-dimensional chloride penetration is predicted by compared with a critical threshold chloride concentration. Compared with general one-dimensional chloride attack, the service life is considerably reduced in a corner zone due to two-dimension penetration.

Experimental determination of the hydrothermal solubility of ReS2 and the Re-ReO2 buffer assemblage and transport of rhenium under supercritical conditions.

To understand the aqueous species important for transport of rhenium under supercritical conditions, we conducted a series of solubility experiments on the Re–ReO2 buffer assemblage and ReS2. In these experiments, pH was buffered by the K–feldspar–muscovite–quartz assemblage; in sulfur-free systems was buffered by the Re–ReO2 assemblage; and and in sulfur-containing systems were buffered by the magnetite–pyrite–pyrrhotite assemblage. Our experimental studies indicate that the species ReCl40 is dominant at 400°C in slightly acidic to near-neutral, and chloride-rich (total chloride concentrations ranging from 0.5 to 1.0 M) environments, and ReCl3+ may predominate at 500°C in a solution with total chloride concentrations ranging from 0.5 to 1.5 M. The results also demonstrate that the solubility of ReS2 is about two orders of magnitude less than that of ReO2. This finding not only suggests that ReS2 (or a ReS2 component in molybdenite) is the solubility-controlling phase in sulfur-containing, reducing environments but also implies that a mixing process involving an oxidized, rhenium-containing solution and a solution with reduced sulfur is one of the most effective mechanisms for deposition of rhenium. In analogy with Re, TcS2 may be the stable Tc-bearing phase in deep geological repositories of radioactive wastes.

The anticorrosion ability of titanium nitride (TiN) plating on an orthodontic metal bracket and its biocompatibility.

Typically, an orthodontic metal bracket is made from stainless steel. It has been shown that such metal may corrode in an acid- and chloride-rich environment. The purpose of the current study was to investigate a titanium nitride (TiN) ion-plated stainless steel orthodontic bracket's anticorrosion properties and compare its biocompatibility with that of non-TiN-plated brackets. The stainless-steel brackets studied here were tested in acidic artificial saliva. The plated metal bracket was produced by the titanium nitride (TiN) ion-plating method. The TiN-plating on the bracket surface was demonstrated to be successful by EDX analysis. The quantity of metallic-ion release under test immersion solutions was analyzed by atomic absorption spectrophotometry. Both TiN- and non-TiN-plated brackets may release detectable ions into the test solution, including nickel, chromium, manganese, copper, and iron (ferric). The anticorrosion ability of the plated bracket was analyzed by means of inductively coupled plasma atomic emission spectroscopy. The results revealed that the TiN-plated metal bracket did not increase the anticorrosion ability of the standard bracket. The biocompatibility of the TiN plating versus the standard bracket material resulting from bracket immersion in the test solution revealed no toxicity on U2OS cells using a methylthiazole tetrazolium (MTT) colorimetric assay. Clearly, the search for an improved technique for enhancing the anticorrosion ability of the normal metal orthodontic bracket should be continued.

High-performance cement matrices based on calcium sulfoaluminate–belite compositions

Cement clinkers with a mineralogy based on 4CaO·3Al2O3·SO3, Ca2SiO4 (belite) and C2(A,F) (ferrite) are made in China: annual production is >106 tons/year. This cement is interground with 16–25% gypsum. The product has very rapid strength gain and examples removed from service in seawater are found to give remarkable protection to embedded steel after 14 years service in the intertidal zone. The chemistry and physics of sulfoaluminate cement hydration are described. Self-desiccation is more readily achieved in ettringite-rich cements than in traditional OPC formulations. It is concluded that the self-desiccated state, once achieved, is very difficult to resaturate and that the dry internal environment is partly responsible for the virtual absence of corrosion of embedded steel, even in chloride-rich environments.

Chloride stress corrosion cracking of precipitation hardening S.S. impellers in centrifugal compressor. Laboratory investigations and corrective actions

17-4 PH, precipitation hardening stainless steel (ASTM A 705 Grade 630), is widely employed in several industrial fields because of its favourable combination of excellent mechanical properties and good corrosion resistance. An important application of 17-4 PH is the construction of centrifugal compressor impellers, where performance benefits from the steel's high mechanical resistance even when it is necessary to limit hardness, for example, as per NACE MR0175, to avoid devastating sulphide stress cracking phenomena in sour environments. Nevertheless, there has been a case in which impellers made of 17-4 PH have been subject to failures. It was a centrifugal compressor employed in a gas lifting service in which the fluid entrained water with a high level of salinity. Laboratory failure analysis attributed the damage to chloride stress corrosion cracking phenomena and was followed by a study on the behaviour of 17-4 PH in chloride-rich environments and on the action to take to avoid damage causing forced outages and loss of production.

Modelling of chloride diffusion into surface-treated concrete

Chloride penetration into concrete is the main cause of the corrosion of steel in concrete structures exposed to chloride-rich environments. As a preventive or remedial method, surface treatments on concrete have been increasingly applied to both new and existing concrete structures to combat this problem. Ion diffusion is regarded as the dominant chloride transport process for structures constantly immersed in water. So far, knowledge of how a surface treatment reduces chloride diffusion is limited and the relationship between chloride diffusion resistance and surface treatment parameters, such as thickness, porosity and diffusion coefficient, has not been quantitatively identified. To gain an insight into the protective mechanism of surface treatments, a theoretical study of chloride diffusion through surface-treated concrete is required. This work proposes a unified physical model for all types of surface treatment and the concept of water-percolated porosity. The influences of surface treatment and substrate properties on chloride diffusion are studied using a finite difference model. Results indicate that chloride diffusion is controlled by both the surface treatment and the substrate. A surface treatment can significantly reduce the chloride concentration at the concrete surface, but this interfacial concentration increases with time. Hence the chloride profile in the concrete substrate does not obey Fick's law with a constant concentration boundary condition. If Fick's law is applied to such a surface-treated concrete, a diffusion coefficient, termed a pseudo diffusion coefficient, of less than the true diffusion coefficient of the substrate material is obtained.