Using capillary electrophoresis to study the chemical conditions within cracks in aluminum alloys

The environment-assisted cracking (EAC) susceptibility of some aluminum alloys used for airplane structural components currently limits their use in the peak strength condition. Understanding the mechanism of EAC will facilitate the development of crack-resistant alloys with optimum mechanical properties. One component towards understanding the fundamental processes responsible for EAC is a comprehensive knowledge of the chemical conditions within cracks. The present work uses capillary electrophoresis (CE) to quantify the crack chemistry in order to provide insight into the nature of the mechanism controlling cracking. The highly restricted geometry of cracks in metals means that a crack typically contains less than 10 μl of solution. The high mass sensitivity combined with the inherently robust nature of CE makes it an ideal analytical technique for this application. Complicating factors in the accurate determination of the crack environment include high levels of sodium present from the test solution. Low sample volume and analyte matrix complexity necessitated the development of specific sampling, extraction and analysis methods. Analysis of the crack solutions in EAC-susceptible material revealed high levels of Al³⁺, Mg²⁺, Zn²⁺, and Cl⁻ near the crack tip. Cations arise from the anodic dissolution of the alloy, whereas chloride ingress from the external environment occurs to maintain solution electroneutrality within the crack. In contrast, EAC-resistant material exhibited significantly lower concentrations of dissolution products.     

BECOOL: Ballooning eigensolver with COOL finite elements

An incompressible variational ideal ballooning mode equation is discretized with the COOL finite element discretization scheme using basis functions composed of variable order Legendre polynomials. This reduces the second order ordinary differential equation to a special block pentadiagonal matrix equation that is solved using an inverse vector iteration method. A benchmark test of BECOOL (Ballooning Eigensolver using COOL finite elements) with second order Legendre polynomials recovers precisely the eigenvalues computed by the VVBAL shooting code. Timing runs reveal the need to determine an optimal lower order case. Eigenvalue convergence runs show that cubic Legendre polynomials construct the optimal ballooning mode equation for intensive computations.     

Reconstructing bulk isotope ratios from compound‐specific isotope ratios

Carbon isotope analysis by bulk elemental analysis coupled with isotope ratio mass spectrometry has been the mainstay of δ¹³C analyses both at natural abundance and in tracer studies. More recently, compound‐specific isotope analysis (CSIA) has become established, whereby organic constituents are separated online by gas or liquid chromatography before oxidation and analysis of CO₂ for constituent δ¹³C. Theoretically, there should be concordance between bulk δ¹³C measurements and carbon‐weighted δ¹³C measurements of carbon‐containing constituents. To test the concordance between the bulk and CSIA, fish oil was chosen because the majority of carbon in fish oil is in the triacylglycerol form and ～95% of this carbon is amenable to CSIA in the form of fatty acids. Bulk isotope analysis was carried out on aliquots of oil extracted from 55 fish samples and δ¹³C values were obtained. Free fatty acids (FFAs) were produced from the oil samples by saponification and derivatised to fatty acid methyl esters (FAMEs) for CSIA by gas chromatography/combustion/isotope ratio mass spectrometry. A known amount of an internal standard (C15:0 FAME) was added to allow analyte quantitation. This internal standard was also isotopically calibrated in both its FFA (δ¹³C = ?34.30‰) and FAME (δ¹³C = ?34.94‰) form. This allowed reporting of FFA δ¹³C from measured FAME δ¹³C values. The bulk δ¹³C was reconstructed from CSIA data based on each FFA δ¹³C and the relative amount of CO₂ produced by each analyte. The measured bulk mean δ¹³C (SD) was ?23.75‰ (1.57‰) compared with the reconstructed bulk mean δ¹³C of ?23.76 (1.44‰) from CSIA and was not significantly different. Further analysis of the data by the Bland‐Altman method did not show particular bias in the data relative to the magnitude of the measurement. Good agreement between the methods was observed with the mean difference between methods (range) of 0.01‰ (?1.50 to 1.30). Copyright © 2010 John Wiley & Sons, Ltd.     

Cluster and Molecular Mechanical Analysis of Cobalt(III) 14-Membered Macrocyclic Complexes

The configurational distribution of all the cobalt(III) complexes containing a 14-membered tetra-aza macrocyclic backbone in the Cambridge Structural Database was determined by cluster analysis, and the reason for some of the complexes adopting their configuration was established by molecular mechanics.     

Regeneration studies on solid acids for batch reactor. Alkylation of isobutane with 2-butene

The regeneration of solid acid catalysts used in alkylation was studied using cal-ad. It was found that an acid site strength of −ΔH=32 kcal/mol is needed to catalyze the reaction.     

Self‐Assembly of MXene‐Surfactants at Liquid–Liquid Interfaces: From Structured Liquids to 3D Aerogels

2D transition metal carbides and nitrides (MXenes), a class of emerging nanomaterials with intriguing properties, have attracted significant attention in recent years. However, owing to the highly hydrophilic nature of MXene nanosheets, assembly strategies of MXene at liquid–liquid interfaces have been very limited and challenging. Herein, through the cooperative assembly of MXene and amine‐functionalized polyhedral oligomeric silsesquioxane at the oil–water interface, we report the formation, assembly, and jamming of a new type MXene‐based Janus‐like nanoparticle surfactants, termed MXene‐surfactants (MXSs), which can significantly enhance the interfacial activity of MXene nanosheets. More importantly, this simple assembly strategy opens a new platform for the fabrication of functional MXene assemblies from mesoscale (e.g., structured liquids) to macroscale (e.g., aerogels), that can be used for a range of applications, including nanocomposites, electronic devices, and all‐liquid microfluidic devices.