Inhibiting localized corrosion of aluminum and aluminum alloy by rare earth metal compounds : behaviors and characteristics observed using an electrochemically integrated multi-electrode array

An electrochemically integrated multi-electrode array namely the wire beam electrode (WBE) has been used to characterize the behavior of cerium chloride (CeCl3) and lanthanum chloride (LaCl3) in inhibiting localized corrosion of AA2024-T3 and AA1100. CeCl3 has been found to inhibit AA2024-T3 corrosion in 0.005 M sodium chloride (NaCl) solution by suppressing galvanic corrosion activities and by creating a large number of insignificant anodes. It has also been shown to inhibit localized corrosion of AA1100 in 0.5 M NaCl solution by promoting the random distribution of minor anodes. LaCl3 has been found to inhibit localized corrosion of AA2024-T3 at 1000 ppm, although its efficiency dropped significantly when its concentration decreased to 500 ppm. The addition of CeCl3 and LaCl3 to corrosion testing cells at later stages was unable to effectively suppress existing corrosion anodes.

Synthesis and structural properties of Anhydrous Rare Earth Cinnamates, [RE(cinn)3]

Anhydrous rare earth tris(cinnamates) [RE(cinn)3] (RE = La–Lu, Y and Sc and cinnH = trans-cinnamic acid) were prepared by metathesis in water and by direct reaction of the metal with cinnamic acid in a 1,2,4,5-tetramethylbenzene flux at ca. 200 °C. X-ray crystal structure determinations and X-ray powder data show that, in the solid state, the larger lanthanoids (La–Dy) form an isomorphous polymeric series consisting of homoleptic nine-coordinate metal centres bonded to three chelating and bridging tridentate cinnamates. The late REIII cinnamate (RE = Dy, Ho–Lu, Y) complexes also form linear one-dimensional polymeric chains with all RE metal atoms being seven-coordinate. The cinnamates are either bound tridentate bridging in a μ-η2:η1 fashion, or μ-η1:η1syn-syn bidentate bridging. A structural break occurs at dysprosium which has been characterised in both crystallographic forms, and gives solely the late RE form when precipitated at 80 °C. ScIII cinnamate was also isolated as an analytically pure precipitate which was, again, found to be anhydrous in nature. A structural change was identified by powder XRD between the late REIII cinnamates and ScIII cinnamate.

Recent developments in corrosion inhibitors based on rare earth metal compounds

Rare earth organic compounds can provide an environmentally safe and non-toxic alternative to chromates as corrosion inhibitors for some steel and aluminium applications. For steel lanthanum 4-hydroxy cinnamate offers corrosion protection and reduces the susceptibility to hydrogen embrittlement. Recent work has also indicated that it inhibits the corrosion of steel in environments containing high levels of carbon dioxide. For aluminium alloys, cerium diphenyl phosphate provides excellent corrosion inhibition in chloride environments, and reduces susceptibly to stress corrosion cracking. Furthermore, for both steel and aluminium alloys filiform corrosion can be suppressed when rare earth inhibitor compounds are added as pigments to polymer coatings. The levels of inhibition observed are thought to be due to synergistic effects between the rare earth and organic parts of these novel compounds, and are related to the various species that may be present in the complex chemical conditions that develop in solution close to a metal surface. This paper reviews some of the published research conducted by the group at Deakin University over recent years.©2014 Institute of Materials, Minerals and Mining.

Rare earth 4-hydroxycinnamate compounds as carbon dioxide corrosion inhibitors for steel in sodium chloride solution

A series of rare earth 4-hydroxycinnamate compounds including Ce(4OHCin)3, La(4OHCin)3, and Pr(4OHCin)3 has been synthesized and evaluated as novel inhibitors for carbon dioxide corrosion of steel in CO2-saturated sodium chloride solutions. Electrochemical measurements and surface analysis have shown that these REM(4OHCin)3 compounds effectively inhibited CO2 corrosion by forming protective inhibiting deposits that shut down the active electrochemical corrosion sites on the steel surface. Inhibition efficiency was found to increase in the order Ce(4OHCin)3 < La(4OHCin)3 < Pr(4OHCin)3 and with increase in inhibitor concentration up to 0.63 mM. Detailed insights into corrosion inhibition mechanism of these compounds in carbon dioxide environment are also provided.

The influence of rare earth mercaptoacetate on the initiation of corrosion on AA2024-T3 Part II: The influence of intermetallic compositions within heavily attacked sites

Localised corrosion is typical on AA2024-T3 due to intermetallic particles embedded in the alloy. The effect of intermetallic compositions on corrosion are not yet fully understood. EPMA data on AA2024-T3 surfaces before and after a 16. min immersion, analyses the influence of intermetallic clustering on the severity attack at local sites. While sites with a high number of domains and a large S-phase surface area typically lead to severe attack, maximising these features did not always lead to severe corrosion attack. Cerium or praseodymium mercaptoacetate inhibited corrosion ring formation. The common trends observed from such attack sites was also discussed.

Investigation of corrosion inhibition mechanisms of rare-earth mercaptoacetate inhibitors on AA2024-T3

 Corrosion inhibition mechanisms on the aerospace alloy, AA2024-T3, was investigated for the inhibitor combination of rare earth metals and mercaptoacetate. The inhibitor demonstrated synergistic protection for AA2024-T3 from localised corrosion. It is intended to be a more environmentally friendly alternative to toxic chromate-based inhibitors.

The influence of rare earth mercaptoacetate on the initiation of corrosion on AA2024-T3 Part I: average statistics of each intermetallic composition

De-alloying of S-phase in AA2024-T3 in the presence chlorides, is well-known. However, it is unclear how rare earth mercaptoacetate inhibitors affect this process when immersed in a 0.1. M NaCl solution. This paper analyses data obtained using EPMA on AA2024-T3 surfaces before and after a 16. min immersion period. Cerium and praseodymium mercaptoacetate inhibited the de-alloying process of S-phase particles. Although no significant change in composition was observed for cathodic intermetallics, each appeared to participate in local corrosion reactions as evidenced by the development of surface oxides. Clustering between S-phase and one of the Cu-containing intermetallic domains was also evident.

Rare earth 3-(4′-hydroxyphenyl)propionate complexes

The reaction of lanthanoid chlorides or nitrates with sodium 3-(4′-hydroxyphenyl)propionate (Na4hpp) in methanol or water has yielded complexes [La4(4hpp)12(H2O)6]·4H2O·MeOH (1), [Ce2(4hpp)6(H2O)3]·(H2O)·2.5(EtOH) (2a) (after crystallization from ethanol), [Ho(4hpp)3(H2O)2] (5), [Er(4hpp)3(H2O)2]·1.5(H2O) (6), and [Lu(4hpp)3]·H2O crystal composition (7), as well as heterobimetallics [NaCe2(4hpp)7(H2O)2]·3(H2O) (2b), [NaPr2(4hpp)7(H2O)2]·3(H2O) (3), and [NaNd2(4hpp)7(H2O)(MeOH)]·(H2O)·3(MeOH) (4). The structures of homometallic complexes 1, 2a, 6, and 7 reveal one-dimensional coordination polymers and vividly illustrate the effect of lanthanoid contraction with a decline in coordination numbers in the series from 9-11 (1), 9,10 (2a), 8 (6) to 7 (7) through variations in carboxylate coordination and ligation of water. Bimetallic complexes 2a and 4 each exhibit five different carboxylate binding modes as well as coordination of the 4-OH substituent of 4hpp to sodium thereby linking 1D polymer chains into a 2D network with both 9 and 10 coordinate Ln atoms and 6 coordinate sodium. Bulk products after drying lose solvent of crystallization in some cases (2a, 6), or exchange MeOH for water (4). X-ray powder diffraction indicates that bulk 2b and 3 are isotypic, as are bulk 5 and 6. In contrast to the excellent corrosion protection of lanthanum 4-hydroxycinnamate, compound 1 is ineffective in preventing the corrosion of mild steel, thereby establishing the importance of the -CHCH- structural unit of the former in its anti-corrosion properties. However the flexible -CH2-CH2- chain of the 4hpp ligand enables the crystal engineering of its lanthanoid complexes in a wide variety of structures as well as effective crystallization for structure determination, whereas the analogous 4-hydroxycinnamates have so far evaded structural characterization except for Ln = La, Ce owing to crystallization problems.

Dielectric response features and oxygen migration on rare earth modified lead titanate ferroelectric ceramics

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Hydrothermal rare earth elements mineralization in the Barra do Itapirapua carbonatite, southern Brazil: behaviour of selected trace elements and stable isotopes (C, O)

The Bura do Itapira pua carbonatite is located in southern Brazil and belongs to the Cretaceous Ponta Grossa alkaline-carbonatitic province related to the opening of the South Atlantic. The carbonatite complex is emplaced in Proterozoic granites and is mainly composed of plutonic magnesio- to ferrocarbonatite, with smaller amounts of subvolcanic magnesiocarbonatite. Hydrothermal alteration of the carbonatite has led to the formation of quartz, apatite, fluorite, rue earth fluorocarbonates, barite and sulfides in variable proportions. Trace element data, delta(13)C and delta(18)O are presented here, with the aim of better understanding the geochemical nature of hydrothermal alteration related to rare earth elements (REE) mineralization. The non-overprinted plutonic carbonatite shows the lowest REE contents, and its primitive carbon and oxygen stable isotopic composition places it in the field of primary igneous carbonatites. Two types of hydrothermally overprinted plutonic carbonatites can be distinguished based on secondary minerals and geochemical composition. Type I contains mainly quartz, rare earth fluorocarbonates and apatite as hydrothermal secondary minerals, and has steep chondrite normalized REE patterns, with Sigma(REE+Y) of up to 3 wt.% (i.e., two orders of magnitude higher than in fresh plutonic samples). In contrast, the Type II overprint contains apatite, fluorite and barite as dominant hydrothermal minerals, and is characterized by heavy REE enrichment relative to the fresh samples, with flat chondrite normalized REE patterns. Carbon and oxygen stable isotope ratios of Types I and II are elevated (delta(18)O + 8 to + 12 parts per thousand; delta(13)C - 6 to - 2 parts per thousand) relative to the fresh samples. Hydrothermally overprinted carbonatites exposed to weathering show even higher delta(18)O values (delta(18)O 13 to 25 parts per thousand) but no additional REE enrichment. The subvolcanic carbonatite has anomalously high delta(13)C of up to + 1 parts per thousand, which suggests crustal contamination through interaction with carbonate-bearing metasediments. (C) 1999 Elsevier B.V. B.V. All rights reserved.

Biosorption and desorption of lanthanum(III) and neodymium(III) in fixed-bed columns with Sargassum sp.: Perspectives for separation of rare earth metals

Rare earth (RE) metals are essentials for the manufacturing of high-technology products. The separation of RE is complex and expensive; biosorption is an alternative to conventional processes. This work focuses on the biosorption of monocomponent and bicomponent solutions of lanthanum(III) and neodymium(III) in fixed-bed columns using Sargassum sp. biomass. The desorption of metals with HCl 0.10 mol L-1 from loaded biomass is also carried out with the objective of increasing the efficiency of metal separation. Simple models have been successfully used to model breakthrough curves (i.e., Thomas, Bohart-Adams, and Yoon-Nelson equations) for the biosorption of monocomponent solutions. From biosorption and desorption experiments in both monocomponent and bicomponent solutions, a slight selectivity of the biomass for Nd(III) over La(III) is observed. The experiments did not find an effective separation of the RE studied, but their results indicate a possible partition between the metals, which is the fundamental condition for separation perspectives. (C) 2012 American Institute of Chemical Engineers Biotechnol. Prog., 2012