Mechanisms of corrosion in surface layers at solid-solution interfaces

This review is focussed on solids in the broad categories of oxides, both simple (e.g. binary) and complex (e.g. silicates, aluminosilicates, titanates), and sulfides as ceramics, minerals and surface coatings. Mechanisms of surface reaction, corrosion and leaching associated with protons, hydroxide, water and simple cations and anions are considered. A variety of mechanisms that have some generality in determining the kinetics and reaction products at the solid-solution interfaces is illustrated. The focus of the experimental studies is on the surface layers; their development, distribution of species, depth and control. Mechanisms discussed and illustrated include: diffusion; protonation and ion transfer to solution; lattice reaction; ion exchange (leaching); precipitation; surface oxidation; surface reconstruction; intergranular films and grain boundaries. Theoretical models for the first four mechanisms are presented.     

Development of novel materials through interface engineering

The impact of interfaces in the processing and properties of polycrystalline material is briefly discussed. The local properties of the interfacial layer are considered in terms of composition, structure and related properties that differ substantially from those of the bulk phase. It has been postulated that novel materials with desired properties for specific industrial applications may be processed through interface engineering rather than through bulk chemistry. This paper considers the impact of interfaces on the properties of materials for technological applications, such as electrochemical devices for reduction of greenhouse gases, through energy conversion and environmental monitoring. The procedures that may be applied for the modification of interfacial chemistry are considered.     

Controlling Fusion and Aggregation in Polymersome Dispersions

The effects of addition of poly(ethylene oxide) (PEO) to poly(ethylene oxide)₁₆‐block‐poly(butylene oxide)₂₂ (EB1) polymersome dispersions has been studied. Aggregation and membrane fusion between polymersomes were observed with great control of the outcome by varying PEO molecular weight. Small‐scale fusion of 2 to 3 polymersomes was seen with low‐molecular‐weight PEO, whilst large‐scale aggregation occurred above a critical PEO molecular weight of 4 000 Da. The resulting highly porous EB1‐PEO aggregate shows great promise for applications in cell entrapment for transport and delivery, and as a three‐dimensional scaffold for use in tissue engineering.

     

Generation of a stable surface concentration of amino groups on silica coated onto titanium substrates by the plasma enhanced chemical vapour deposition method

This report describes the amino functionalisation of the surface of plasma enhanced chemically vapour deposited silica films (PECVD-SiO₂), which were coated onto titanium substrates. Amino groups were linked to PECVD-SiO₂ via 3-aminpropyl triethoxysilane (APTES). We showed that the APTES functionalised PECVD-SiO₂ surfaces contained a high packing density of amino groups (67-92 NH₂ groups per nm²), indicative of a multilayered and highly cross-linked APTES film. 65-66% of the original surface concentration of APTES was retained on the PECVD-SiO₂ surface after incubation under physiological conditions, indicating that APTES films are relatively stable on PECVD-SiO₂ in these environments. The stability of the amino groups obtained on PECVD-SiO₂ in this study is much higher compared to other hydroxyl-bearing materials, such as titanium. Therefore, PECVD-SiO₂ films may find use as functional biomaterial coatings and as intermediate adhesion layers in silanisation processes.     

A Multi‐Method Investigation of Mathematics Motivation for Elementary Age Students

This paper presents the results of a multi‐method study examining elementary students with high self‐reported levels of mathematics motivation. Second‐ through fifth‐grade students at a Title One school in the southeastern United States completed the Elementary Mathematics Motivation Instrument (EMMI), which examines levels of mathematics motivation across three subscales: (a) Math Anxiety, (b) Self‐Efficacy, and (c) Value of Math. Results from this quantitative phase were used to identify a sample for a qualitative phase examining how students who report high levels of motivation perceive mathematics. The resulting qualitative phase utilized a phenomenological design to explore mathematics motivation for a particular set of students in a fifth‐grade setting. Findings indicate that elementary students with high mathematics motivation value mathematics as a present and future oriented discipline and value teachers that deemphasize testing as a measure of success.     

One-Step Ring Opening Metathesis Block-Like Copolymers and their Compositional Analysis by a Novel Retardation Technique

Using a one-step synthetic route for block copolymers avoids the repeated addition of monomers to the polymerization mixture, which can easily lead to contamination and, therefore, to the unwanted termination of chain growth. For this purpose, monomers ( M1 – M5 ) with different steric hindrances and different propagation rates are explored. Copolymerization of M1 (propagating rapidly) with M2 (propagating slowly), M1 with M3 (propagating extremely slowly) and M4 (propagating rapidly) with M5 (propagating slowly) yielded diblock-like copolymers using Grubbs’ first ( G1 ) or third generation catalyst ( G3 ). The monomer consumption was followed by ¹H NMR spectroscopy, which revealed vastly different reactivity ratios for M1 and M2 . In the case of M1 and M3 , we observed the highest difference in reactivity ratios (r₁=324 and r₂=0.003) ever reported for a copolymerization method. A triblock-like copolymer was also synthesized using G3 by first allowing the consumption of the mixture of M1 and M2 and then adding M1 again. In addition, in order to measure the fast reaction rates of the G3 catalyst with M1 , we report a novel retardation technique based on an unusual reversible G3 Fischer-carbene to G3 benzylidene/alkylidene transformation.     

Adjoint Methods for the Infinity Laplacian Partial Differential Equation

To study fine properties of certain smooth approximations ${u^\varepsilon}$ to a viscosity solution u of the infinity Laplacian partial differential equation (PDE), we introduce Green??s function ${\sigma^\varepsilon}$ for the linearization. We can then integrate by parts with respect to ${\sigma^\varepsilon}$ and derive various useful integral estimates. We are, in particular, able to use these estimates (i) to prove the everywhere differentiability of u and (ii) to rigorously justify interpreting the infinity Laplacian equation as a parabolic PDE.     

A neutron monitor for in-situ real-time determination of transuranics in a processed waste effluent stream

A pilot plant operation at the Savannah River Site will remove ⁹⁰Sr, ¹³⁷Cs, and transuranics from a high-level liquid waste stream prior to encapsulation in a Saltstone Facility. Monitors are required to determine the concentrations of all radionuclides, including transuranics, in real-time on this processed waste stream. A neutron counter used to measure the concentration of each actinide isotope present in the stream is described. The neutron counter assembly consists of nested annular layers of shielding, reflectors, detectors, and moderators. On-line, live-time system control and calibration is provided by a time-tagged neutron source embedded in the moderator assembly.