The aging effects of repeated oxygen plasma treatment on the surface rearrangement and adhesion of LDPE to aluminum

The effects of aging temperature and time on the adhesion properties of oxygen plasmatreated low-density polyethylene (LDPE) were investigated. As the aging temperature and time increased, surface rearrangement and the migration of molecules containing polar functional groups into the bulk were accelerated to the surface to form a hydrophobic surface. The adhesion strength of oxygen plasma-treated LDPE/aluminum joints was measured using a 90° peel test by varying the plasma treatment time and aging temperature. The adhesion strength was constant, regardless of the plasma treatment time. As the aging temperature increased, the adhesion strength of the LDPE/aluminum joints decreased and the locus of failure changed from cohesive to interfacial failure. It was also found that the polar functional groups buried in the bulk could be reoriented to the surface in a polar environment. This study also investigated whether repeated oxygen plasma treatment would increase the concentration of polar functional groups at the surface and reduce the surface rearrangement and the migration of molecules containing polar functional groups during aging. Contact angle measurements and X-ray photoelectron spectroscopy (XPS) showed that repeated oxygen plasma treatments increased the concentration of polar functional groups at the surface. However, the aging time between plasma treatments had a negligible effect on the concentration of polar functional groups at the surface.     

Influence of Mg and Si on the Oxidation of Aluminum

Test materials of pure Al, Al alloyed with 10,50, and 190 ppm Mg, and Al alloyed with 10 ppm Mg + 500ppm Si were oxidized at temperatures ranging from 250 to620°C. The composition and thickness of the oxide film were determined by electronspectroscopy for chemical analysis (ESCA) and Augerspectroscopy. Below the crystallization temperature(400°C) of Al₂O₃,Mg²⁺ is enriched in the interior portion of the oxide. The enrichment of Mg²⁺gives a somewhat thinner oxide compared with the oxideformed on pure Al. Above 400°C, MgO is formed as aseparate phase on the surface of theAl₂O₃. The Si-containing material showed Si⁴⁺ enrichment inthe surface oxide. Mg²⁺ species were notdetectable. Silicon is also strongly enriched in themetal phase just below the metal-oxideinterface.     

Surface Modification of Polymer Films for Improved Adhesion of Deposited Metal Layers

Plasma treatment and vacuum Al deposition on films from biaxially oriented polypropylene is a multistep large scale industrial process, mainly ending up in packaging film laminates. As atmospheric plasma treatment processes suffer from lack of reproducibility, low pressure plasma treatment processes that can be operated in-line with the metal deposition are being developed. Process development is difficult, because the final packaging film laminate has to deliver optimum properties of adhesion as well as of the barrier against oxygen and water vapor permeation. As a typical production run involves tens of thousands to up to one hundred thousand square meters of film, experiments on an industrial scale are expensive, so smaller scale experimental processes are needed, which so far do not match well enough with industrial process characteristics. Moreover, bonding mechanisms between the treated substrate film and the deposited Al layer are not sufficiently understood. This paper describes the sequence in development and optimization of substrate films and plasma treatment that has been performed on an experimental as well as on an industrial scale. A sufficient correlation between experimental and industrial scales was achieved, which helps to perform development and optimization on a small scale before scaling up to industrial processes. However, improvement is still needed both in fundamental understanding of the aluminum–polypropylene interface as well as in experimental equipment and methodology.     

Fracture behavior of an epoxy/aluminum interface reinforced by sol–gel coatings

The strengths of epoxy/aluminum joints reinforced with a zirconium-silicon based sol–gel adhesion promoter were investigated using an ADCB (Asymmetric Double Cantilever Beam) wedge test. The fracture energies and loci of failure of these joints were shown to depend upon the mixity of the normal and shear modes of stress acting at the crack. The ADCB geometry enabled the crack to propagate along the epoxy/aluminum interfaces so that the effect of surface pretreatment and the processing conditions of the adhesion promoter on adhesion strength could be directly evaluated. The dry strength of these joints depends on the thickness of the sol–gel film derived from different concentrations of the precursors. Thinner films are more fully crosslinked and thus give higher adhesion strengths than those obtained with thicker films. The differences in the wet strengths of the sol–gel reinforced joints for various surface pretreatments suggest that the sol–gel films are subject to moisture degradation with certain surface pretreatments. The loci of failure of many of these joints alternate between the sol–gel/aluminum and epoxy/sol–gel interfaces. This behavior is similar to that observed more generally in adhesively-bonded joints tested in DCB (Double Cantilever Beam) geometry. The brittle versus ductile behavior associated with the failure process reveals important information about how the sol–gel films affect the adhesion strength.     

Design of continuous casting machines based on a heat-flow analysis: state-of-the-art review

Abstract

The design of the mould and spray sections of a continuous casting machine for steel has been examined in detail with the aid of a heat-flow mathematical model. The thermal requirements that the design must meet have been established using Experimental data obtained from commercial continuous-casting machines. For the mould, the requirement is the solidification of a sufficiently thick shell; for the sprays, the requirements are the minimization of surface reheating and the maintenance of a reasonably high solidification rate. Correlations are developed which relate the working mould length, casting speed and shell thickness at the mould exit. Design curves are also presented of spray length, spray heat transfer. coefficient and water flux distributions for two sizes of billets. The method by which the theoretical spray water flux distribution can be related to practical spray parameters — spray pressure, nozzle type and arrangement — is also discussed.

Résumé

On a étudié en detail, à l'aide d'un modèle mathématique de l' écoulement de chaleur, la conception du moule et des sections de refroidissement d'une machine de coulée continue pour l'acier. Les exigences thermiques à rencontrer ont été fixées à l'aide de données expérimentales provenant de machines industrielles. Pour Ie moule, l'exigence est la formation d'une carapace solide suffisamment épaisse alors que pour les jets l'exigence consiste en un réchauffement minimal de la surface et le maintien d'un taux de solidification assez élevé. On a développé des corrélations qui relient la longueur effective du maule, le taux de coulée, et l'epaisseur de la carapace à la sortie du moule. L'article inclut des courbes permettant d' établir la longueur de la zone des jets, leur coefficient de transmission de chaleur et les distributions de débit d'eau pour deux dimensions de billettes. Finalement, on discute de la méthode pour relier la distribution du débit théorique d'eau aux paramètres pratiques des jets (pression d'eau aux jets, type et configuration des gicleurs).     

Use of polymeric emeraldine salt for conductive adhesive applications

The wide range of electrical, electrochemical, and optical properties associated with Polyaniline (PANI) and its composites has made them attractive for many industrial applications. In this study, Emeraldine Salt (ES), which is a doped conducting form of PANI, was chemically prepared in situ using the oxidizing agent ammonium persulphate in the presence of aqueous HCl solution. In order to gain insight into the efficiency of electrical conduction in relation to the chemical and viscoelastic behaviors of ES in homogeneous powder and as filler in composite adhesive forms, the interrelationship between their electrical resistivity and morphology was studied. The pressure-dependent electrical conduction behavior of ES powder shows, among other factors, the dependence of electrical resistivity on the intrinsic chemical and viscoelastic properties of powders. In order to obtain electrically conductive composite adhesive forms, a nonconducting nitrocellulose solution based adhesive was filled with as-synthesized ES in the amount 30%, 40%, and 50% by volume, and the effects of filler concentration on the composite's electrical resistivity were investigated. The results of our investigation revealed a typical percolation threshold behavior with a critical concentration of approximately 30% by volume. Finally, single lap joints were made using aluminum and zinc (plated on copper) as well as silver substrates bonded using the ES filled nitrocellulose adhesive developed, and the corresponding electrical and mechanical properties of these bonded interconnections were investigated. A complex redox-reaction mechanism catalyzed by ES filler is thought to be occurring at the boundary layer between the adhesive and the substrate for conversion from semiconductor to insulator of the joints in the cases of aluminum and zinc (plated) substrates.     

Optimum Silane Treatment for the Adhesively Bonded Aluminum Adherends at the Cryogenic Temperature

Aluminum adherends for the adhesive joints at cryogenic application such as LNG (Liquefied Natural Gas) containment tanks were silane treated to improve bond strength of the aluminum joints. The bond strengths of the single-lap joints composed of aluminum adherends and epoxy adhesive were measured with respect to the condition of the silane solution and surface roughness obtained with grit blast. The chemical composition of the silane treated aluminum surface was analyzed by XPS (X-ray photoelectron spectroscopy). Also, contact angles of appropriate liquids on the silane treated aluminum surface were measured with respect to treatment conditions. From the experiments, the optimum treatment conditions for the aluminum adherends were obtained for the adhesive joints at the cryogenic temperature.     

Influence of water immersion on the single-lap shear strength of aluminum joints bonded with aluminum-powder-filled epoxy adhesive

Durability of adhesively-bonded aluminum joints was investigated by measuring the joint strength using the single-lap shear test before and after exposure to distilled water and seawater. Fractured specimens were examined by photography and scanning electron microscopy to determine the failure modes. Addition of Al particles as much as 50 wt% did not cause any significant decrease in adhesive joint strength. Moreover, varying the Al filler content in the adhesive did not have a significant effect on adhesive behavior in either of the two environments studied. The unexposed adhesive joints failed almost completely in a cohesive (in the adhesive) failure mode. Some decrease in strength was observed in adhesive joints after exposure to both distilled water and seawater for 6 months. The decrease in adhesive joint strength was more significant for specimens immersed in distilled water than those immersed in seawater, probably due to the higher amount of moisture in the adhesive in distilled water than in seawater, as observed in a related moisture diffusion study. The joints exposed to distilled water or sea water failed in more than one mode. The interior part of the adhesive lap area failed in a cohesive mode while an adhesion failure mode was observed near the edges of the adhesive lap area, which is believed to be a result of moisture diffusion through the edges.     

The Effect of Different Surface Pretreatment Methods on Nano-adhesive Application in High Strength Steel and Aluminum Bonding

Epoxy adhesives (single and two components) modified with SiO₂ nano-particles were used in this investigation to glue aluminum alloy and also two types of high strength steel (dip-galvanized steel DP 600 and micro-alloyed steel ZStE340). To improve the adhesion between metal surfaces and adhesives, the metal surfaces were pretreated with: a self-indicating pretreatment (SIP^*); corundum blasting; corundum blasting + a SIP coating; and a Pyrosil^® treatment + SurALink^® primer (PG 15 for epoxy adhesive). A single-lap shear tension test, done in accordance to DIN EN 1465, was used to determine the adhesive strength. Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray spectroscopy (EDX) analysis were used to analyze fractures that took place in the samples. The results showed that the adhesion strength of glued samples, containing the nano-particles modified adhesive, had significantly higher strength than unmodified ones. Pretreatment of the metal surfaces affected the adhesion, using nano-adhesives, only slightly. The adhesive strength values for single component epoxy resins were higher than those for two component epoxy resins. It was found that steel samples fractured adhesively at the steel surfaces. Aluminum treated samples indicated after pretreatment an increase in adhesive strength and the fracture occurred adhesively at the aluminum surfaces. Aluminum glued with two-component adhesives and pretreated with corundum blasting plus a SIP coating showed a mixed fracture mode; adhesively at the aluminum surface and cohesively in the adhesive layer.     

Effect of Processing Conditions on Adhesion Performance of a Sol–Gel Reinforced Epoxy/Aluminum Interface

The Boeing sol–gel process (Boegel-EPII) is a surface preparation method for metallic substrates for adhesive bonding and painting applications. This paper describes an investigation into the effect of processing conditions on adhesion strength and durability of a sol–gel reinforced, rubber toughened epoxy/aluminum joint. Using an asymmetric double cantilever beam (ADCB) wedge test, the adhesion performance of the sol–gel reinforced epoxy/aluminum joint in a humid environment was measured as a function of sol–gel processing conditions. The sol–gel drying time, concentration and drying humidity all have an effect on adhesion performance. Prolonged drying led to a decrease in fracture energies. The critical and threshold fracture energies show different trends as sol–gel concentration varies, and better adhesion performance was observed for sol–gel dried at higher humidity compared to lower humidity. The failure modes and mechanisms were studied by XPS and SEM. Analysis of locus of failure revealed that the observed trends for adhesion performance can be explained in terms of interdiffusion of the sol–gel film and epoxy. The diffusion of the epoxy into the sol–gel layer is hypothesized to strongly depend on the degree of condensation of the sol–gel film and is directly affected by the sol–gel processing conditions.