Application of ToF-SIMS surface analysis to tribochemistry in metal forming processes

Tribochemical properties are an essential component of the efficiency of metal forming lubricants. Their understanding, a basis for the selection of adequate additives, heavily relies on surface analytical techniques. In the last ten years, we have applied time-of-flight secondary ion mass spectroscopy (ToF-SIMS) to the analysis of the reactions of strip surfaces with typical additives of cold strip rolling and deep drawing lubricants. Data analysis procedures have been evolved to perform semi-quantitative comparisons. Analytical results performed on laboratory simulation tests and on real-size processes are compared. Examples of competition and synergies between different additives in a single lubricant are described.     

Specific control of cell–material interactions: Targeting cell receptors using ligand-functionalized polymer substrates

Cells respond to their environment in complex and sometimes poorly understood ways. Protein, peptide and synthetic peptidomimetic ligands may all be used to stimulate cells via receptor signaling, using interactions that are often highly specific. Polymer substrates that present these ligands provide a promising way to control cell development, both for applications in biotechnology and for fundamental studies of cell biology. Here we review a large range of techniques that have been employed to create and characterize ligand-functionalized substrates, with a particular focus on techniques that allow specific and consistent stimulation.     

Effect of acidic etching and fluoride treatment on corrosion performance in Mg alloy AZ91D (MgAlZn)

Fluoride activation of Mg AZ91D die-cast alloy surfaces by ammonium fluoride pre-treatment is an important procedure in industry. The procedure forms a fluoride rich layer on the surface enabling the formation of coatings in a uniform manner during further treatments. The present study explores the time dependence of the sequential two-step pre-treatment process – acid etching in H₂SO₄ (first step) and steeping in NH₄F (second step) – on the corrosion properties of AZ91D alloy. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) show the α phase to be selectively etched via a “peeling-off” mechanism that eventually leads to the undercutting and undermining of the β-phase network. After ammonium fluoride treatment, variations in structure and chemical composition of the fluoride rich layer were shown to depend on the underlying phase of the alloy surface by SEM and time-of-flight secondary-ion-mass-spectroscopy (ToF-SIMS). After step 1 (acid etching), electrochemical impedance spectroscopy (EIS) in 3.5% NaCl solution indicates greater charge transfer resistance (R_t) for samples of greater exposed β surface area. This greater R_t increases after step 2 (NH₄F steeping). Furthermore, the corrosion protection properties of F-coated AZ91D can be significantly enhanced by optimizing the durations of the two pre-treatment steps. Indeed, over extension of the duration of either step 1 or step 2 leads to deterioration of the overall corrosion resistance.     

Electrochemical behavior of current collectors for lithium batteries in non-aqueous alkyl carbonate solution and surface analysis by ToF-SIMS

Several metals (Cu, Fe, Al, Ti, and Cr) as current collector for lithium-ion battery were investigated to understand their electrochemical behavior and passivation process in a non-aqueous alkyl carbonate solution containing LiPF₆ salt. From cyclic voltammetric study, it was found that Cu and Fe metals were dissolved into the electrolyte below 4 V vs. Li/Li⁺. Alternatively, Al and Ti were stable up to 5 V vs. Li/Li⁺. Their scratched surfaces at 5 V vs. Li/Li⁺ were polarized in a transient mode and it was found that the surfaces were passivated during the polarization test. Formed passive film was composed of two hybrid layers: outer layer by metal (Al and Ti) fluoride and inner by metal oxide, as confirmed by time-of-flight secondary ion mass spectroscopy. Presence of HF in the electrolyte was indispensible to form the metal fluoride layer on the oxide layer. The outer fluoride layer would protect the inner oxide layer and metal substrate from HF attack, bringing about satisfactory corrosion resistance under lithium-ion battery environment.     

Aliphatic hyperbranched polyesters based on 2,2-bis(methylol)propionic acid—Determination of structure, solution and bulk properties

Due to their highly branched structure and the large number of functional groups hyperbranched polymers possess unique properties that make them interesting for uses in a wide variety of applications. Some of the most widely investigated hyperbranched polymers are the polyesters based on 2,2-bis(methylol)propionic acid. In this paper we present the results of characterization studies of hyperbranched polyesters based on 2,2-bis(methylol)propionic acid which show that they are very complex products with a multidimensional distribution of various properties. The influence of the synthesis conditions on the structure and molar-mass characteristics of hyperbranched polyesters as well as the findings that allow a thorough understanding of the structure-property relationships are reviewed in detail.     

Interphase Chemistry: The Synergy of Surface Analysis,Surface Adsorption and Adhesion

The formation of an interphase zone at the junction between an organic system, such as an adhesive or coating, and an inorganic substrate is considered. Drawing on experimental work for a fully-formulated photocured resin and theoretical models for a simple homopolymer it is shown that such a feature may be the result of preferential adsorption (for a multicomponent system) or conformational changes in the case of a homopolymer. Guidelines for the recognition, cause and prediction of such layers are provided, and their possible effects on the strength and durability of the organic/inorganic couple are discussed. It is suggested that the consideration of these phenomena at the design stage of a new resin may provide a route to optimise hydrolytic stability. The behaviour of an interphase zone of this type as a weak boundary layer is also considered.     

镍黄铁矿与长石的相互作用及其对它们浮选分离的影响

在用优先浮选分离南非Merensky矿石中的铂族金属和贱金属与硅酸盐脉石时，铂族金属和贱金属的损失较大。进入精矿中的主要硅酸盐脉石矿物是辉石和长石，另外一类脉石矿物是滑石和绿泥石。大量的这类矿物进入精矿中，使得精矿品位降低，因而增加了精矿运输和冶炼费用。长石是天然亲水矿物，它的浮选需要活化。本工作研究了捕收剂（异丁基钠黄药）的吸附、硫酸铜活化和离子在矿物表面上的分布对这种矿石浮选选择性的影响。研究了在合成镍黄铁矿、天然长石和1：1的矿物混合物表面上可能发生的化学反应。在所研究的pH范围内，Zeta电位测定和ToF-SIMS分析结果表明，在镍黄铁矿表面上有黄原酸离子和铜离子存在时，黄原酸离子不吸附在长石表面上。可用不同铜组分和黄原酸组分之间的反应，以及在不同pH范围内矿物的Zeta电位来解释这些试验结果。