Interfacial Characterization of Epoxy-bonded Maraging Steel

Adhesion phenomena involving polymer-metal interfaces have become a central subject for research and technological development, especially in view of adhesive bonding of metallic components in primary load-bearing structures. Since adhesion implies that some sort of chemical and/or physical interactions take place between the metal adherend and the polymeric adhesive, a great deal of attention has been devoted to identification and characterization of such interactions and to the development of techniques to study them. Among the most widely used methods for interfacial studies are: ESCA (Electron Spectroscopy for Chemical Analysis), AES (Auger Electron Spectroscopy), SIMS (Secondary Ion Mass Spectroscopy), IR spectroscopy, optical microscopy, and electron microscopy.     

Adhesive Bonding of Clean and Oil-Contaminated Electrogalvanized Steel Substrates

The performance of two-part, amidoamine-cured epoxy adhesives on clean and oil-contaminated electrogalvanized steel (EGS) was studied using screening and lap shear tests. On exposure to boiling water, the cured epoxy adhesives with amidoamines having higher amine value delaminated from the clean and oil-contaminated EGS surfaces before those cured with amidoamines having low amine value. The results of X-ray photoelectron spectroscopy (XPS) showed that the adhesives cured with amidoamines having high amine value were unable to displace the oil from the EGS substrate. However, the durability and the strength of the adhesive bonds on the oiled EGS could be improved by adding proper amounts of silane or wetting agent to the adhesive. The preferential adsorption of amino curing agents occurred on the clean EGS surface, confirmed by XPS and reflection absorption infrared spectroscopy, and this decreased the durability of the bonds in boiling water. In addition, from XPS analyses of various specimens, different amounts of cured resins were detected in the adhesive/EGS interfacial regions which affecting the durability of the adhesive bonds. In addition, the amidoamine curing agents may form complexes on the EGS surface.     

新型环氧建筑粘钢胶固化剂的开发和应用研究

粘钢胶属于建筑结构胶的一种,在建筑结构补强中有着极其重要的地位和作用,其配制以环氧胶为主,固化剂在其中起基础核心作用。文章开发了三种新型固化剂,经测试其力学性能均优于市场通用固化剂。选择性能最优的Ⅲ号固化剂配制了环氧粘钢胶,经测试完全达到了建筑加固行业的性能指标,其高强度、高韧性的优异性能预示着良好的应用前景。     

Zinc Coated Steel/Epoxy Adhesive Systems: Investigation of the Interfacial Zone by FTIR Spectroscopy

The present study takes advantage of the ability of Fourier Transform Infrared Spectroscopy (FTIR) for the analysis of ultrathin organic films on metals. FTIR in the reflection mode (IRRAS) is used in order to study the interaction of ultrathin films of dicyandiamide (hardener of most one-pack epoxy resins) with various substrates, model ones such as gold or zinc and industrial ones such as steel and zinc-coated steels.

Pure zinc surfaces and, to a lesser extent, zinc-coated steels are shown to react with dicyandiamide after heating at 180°C, as evidenced by the frequency shift of the absorption band (at about 2200 cm^-1) characteristic for nitrile groups. As real systems consist of thick layers of a fully formulated adhesive cured onto a metallic substrate, the direct investigation of such a buried interphase is no longer possible by FTIR and by most of the known spectroscopies. Some mechanically tested specimens are then analysed, after failure, by FTIR microspectrometry. The spectra obtained, corresponding to the fracture initiation zone which is about 100 μm in diameter, advocate for the presence of an ultrathin layer of modified polymer still covering the substrate.     

Comparison of the Degradation Mechanisms of Zinc-Coated Steel, Cold-Rolled Steel, and Aluminium/Epoxy Bonded Joints

The durability properties of bonded lap shear joints made from an epoxy/dicyandiamide adhesive and zinc, zinc-coated steel, two different aluminium alloys or cold-rolled steel metal coupons have been investigated. The influence of the dicyandiamide content of the adhesive on the durability properties-has been assessed by salt spray testing or by storing the joints in water at 70°C or 90°C for periods of time up to five weeks. The degradation products formed during ageing of the epoxy adhesive in water have been investigated using high performance liquid chromatography (HPLC) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFT). The degradation mechanisms of aluminium/epoxy bonded joints have been thoroughly studied using X-ray photoelectron spectroscopy.

The performances of the bonded joints under a pure corrosive environment have been found to be little influenced by the quantity of dicyandiamide in the adhesive. When the bonded joints were aged in hot water, the stability of the interface toward an excess of dicyandiamide directly followed the sensitivity of the oxide layer at high pH values. Optimal durability properties without peel strength losses of the adhesive were aehieved both with zinc and aluminium-coated substrates by reducing the quantity of dicyandiamide in the epoxy adhesive by 20% (the initial dicyandiamide content in the commercial adhesive being ca. 9%, with respect to the epoxy resin).     

彩涂板用环氧底漆的研制

采用正交实验法分析了各种因素对环氧底漆性能的影响,从而确定出最佳配方,制得漆膜具有明显硬度和耐溶剂性能及附着力极佳的产品。     

Stress Analysis and Failure Properties of Carbon-Fibre-Reinforced-Plastic/Steel Double-Lap Joints

The present paper considers the strength of CFRP/steel double-lap joints loaded in tension. A detailed stress analysis has been conducted of the shear and transverse tensile stresses in the joint, using an elastic-plastic model for the rubber-modified epoxy adhesive. The results of this analysis have been combined with the measured properties of the materials forming the joint in order to predict quantitatively the failure strengths of the various joint designs studied. There was good agreement between the theoretically predicted and experimentally measured strengths. These studies have led to a highly efficient design being developed.     

环氧粘合剂粘接聚四氟乙烯板/不锈钢的耐温性研究

考察了经表面化学活化的3种纯聚四氟乙烯(PTFE)板和1种聚苯酯填充PTFE板在室温和高温下的拉伸性能,用两类环氧粘合剂DG–3S和JF205–1对这4种PTFE板与不锈钢进行了粘接,研究了室温和高温下这两种粘合剂的粘接效果。结果表明,4种活化PTFE板经高温老化后的拉伸性能变化不明显;室温下两种环氧粘合剂对4种PTFE板与不锈钢的粘接性能均良好,但DG–3S粘合剂不适合高温下对PTFE板/不锈钢的粘接,经耐热改性的JF205–1粘合剂在300℃下的粘接性能则较好;JF205–1粘接聚苯酯填充PTFE板/不锈钢的实际粘接性能较好且具有高的耐磨性能和抗蠕变性,在满足实际粘接要求的情况下可应用于制造发动机零部件。     

Ultrasonically-Induced Interfacial Changes

The ultrasonic wirebond failure mechanism associated with interfacial changes in a thin-film device was studied. The thin-film device was fabricated on a ferrite substrate and composed of a gold layer on top with titanium, nickel-iron and aluminum oxide underneath. The chemical changes at the nickel-iron/aluminum oxide interface, induced by the transfer of ultrasonic energy through the gold and the titanium layers were investigated by Auger electron spectroscopy. The applied ultrasonic energy promoted preferential migration of iron to the interface resulting in weakening of the bond between the nickel-iron and its adjacent aluminum oxide layer.     

聚氨酯-环氧树脂复合体系的制备及性能研究

利用甲苯二异氰酸酯（TDI）与聚醚多元醇N-330及聚四氢呋喃二元醇（PF-15）为原料,制得了结构不同的聚氨酯预聚体。进一步将其与环氧树脂（E-51与E-20）进行接枝反应,最后加入固化剂双氰胺,制成了一系列环氧树脂-聚氨酯（EPR-PU）复合体系。详细考察了环氧树脂与聚氨酯预聚体的结构及用量、触变剂白碳黑的用量对EPR-PU体系性能的影响。结果表明,当原料组成的质量比为m（E-51）∶m（E-20）∶m（PU-D）∶m（PU-A）=3∶2∶0.06∶0.54时,所得EPR-PU体系同时具有较高的剪切、剥离及断裂强度。     

Ultrasonically-Induced Interfacial Changes

The ultrasonic wirebond failure mechanism associated with interfacial changes in a thin-film device was studied. The thin-film device was fabricated on a ferrite substrate and composed of a gold layer on top with titanium, nickel-iron and aluminum oxide underneath. The chemical changes at the nickel-iron/aluminum oxide interface, induced by the transfer of ultrasonic energy through the gold and the titanium layers were investigated by Auger electron spectroscopy. The applied ultrasonic energy promoted preferential migration of iron to the interface resulting in weakening of the bond between the nickel-iron and its adjacent aluminum oxide layer.     

Factors Affecting the Durability of Ti-6Al-4V/Epoxy Bonds

Factors influencing the durability of Ti-6Al-4V/epoxy interphases were studied by determining chemical and physical properties of Ti-6Al-4V adherend surfaces and by characterizing the strength and durability of Ti-6Al-4V/epoxy bonds.

Ti-6Al-4V adherend surfaces were oxidized either by chemical etch or anodization. Four principal pretreatments were studied: chromic acid anodization (CAA), sodium hydroxide anodization (SHA), phosphate fluoride acid etch (P/F) and TURCO basic etch (TURCO). The oxides were characterized by SEM, STEM, profilometry, contact angles and XPS.

All adhesive bonding was carried out using a structural epoxy, FM-300U. Both lap shear and wedge test samples were tested in hot, wet environments. The results lead to the conclusion that the interfacial area between the adhesive and adherend is the primary factor affecting bond durability.     

Interfacial Characterization of Silicon Nitride Powders

The composition of the surface and the behavior in aqueous suspensions of three silicon nitride powders were investigated using electron spectroscopy for chemical analysis (ESCA), potentiometric titrations, leaching experiments, and electrophoretic mobility. ESCA shows that the as-received powders have a surface-layer composition similar to that identified as an intermediate state between silica and silicon oxynitride. The original differences in pH_iep between the three powders disappears by aging the powders. The common pH_iep of 6.8 ± 0.3 for the three powders is interpreted as the equilibrium pH_iep for silicon nitride in aqueous suspensions.     

Surface and Interfacial Studies of Plasma-Modified Composite Surfaces

Model epoxy and bismaleimide compounds in thin film form were used to simulate epoxy and bismaleimide composite surfaces, in order to study compositional changes and interfacial reactions induced by oxygen plasma treatment. X-ray photoelectron spectroscopy (XPS) and infrared reflection-absorption spectroscopy (IR-RAS) were used to probe chemical changes which occurred. XPS and IR-RAS were found to be complementary techniques in determining the nature of functional groups incorporated into surfaces by plasma treatment. IR-RAS analysis of the model surfaces following exposure to a liquid epoxy resin revealed that while adsorption of the liquid epoxy occurred on both plasma-treated and nonplasma-treated surfaces, the oxygen plasma-treated surface alone was capable of initiating ring-opening reactions in the epoxy. However, this effect was not observed unless immediate contact was made between the plasma-treated surface and the liquid epoxy resin, illustrating the short-lived reactivity of the functional groups on the plasma-treated surface.     

Silanisation of adhesively bonded aluminium alloy AA6060 with γ-glycidoxypropyltrimethoxysilane. I. Durability investigation

The wedge test was used to determine the durability of adhesively bonded joints of pretreated aluminium alloy AA6060 in a hydrothermal environment. Testing of joints bonded with the one-component epoxy adhesive XD4600 showed that the durability was higher for surfaces that were grit-blasted with alumina than for alkaline etched, FPL-etched, and sulphuric acid anodised surfaces. All these surfaces performed much better than those abraded with ScotchBrite®. It was discovered that increased surface roughness improved the durability, while increased surface contamination reduced the durability of the bonded joints. On a very rough surface such as the grit-blasted, the effects of surface contamination were more than outweighed by the effects of surface roughness. Treatment of some of the pretreated surfaces with a 1% aqueous solution of γ-glycidoxypropyltrimethoxysilane significantly improved the durability, but the ranking between the pretreatments was the same as before the silane treatment. The silane treatment also reduced the initial crack lengths of the wedge test specimens. The best performance was seen by the grit-blasting plus silane treatment, which performed much better than the well-established FPL-etch.     

Study of the nature of interaction of EPDM-40 rubber with an epoxy adhesive

—The mechanism of improving the adhesion of ethylene-propylene rubber to an epoxy adhesive has been studied. The basic factor that improves the rubber adhesion is the formation of chemical bonds between polymer networks of the substrate and the adhesive by reaction of epoxy groups of the adhesive with oxygen-containing groups of the oxidized surface layer of rubber.     

Sulfur Versus Non-Sulfur Containing Polyimide Adhesives for Bonding Steel

Due to their superior thermal and chemical stability, polyimides are often used as adhesives in harsh environments. This study examines the effect on bond strength of thioether sulfur in the polyimide backbone. Bonds were made using steel that was believed to catalyze the oxidation of sulfur. In addition, non-sulfur containing polyimides with similar T_g were also studied for comparison. The polymer/metal interface was studied using both the T-peel and wedge tests. No apparent effect was observed in the T-peel test with steel where the T-peel strengths of non-sulfur and sulfur containing polyimides were similar. In the wedge test, however, the sulfur-containing BDSDA/ODA bonded to steel had the smallest initial crack length of 34 mm. However, the BTDA/APB bonds tested in a dry environment had the smallest crack growth. The sulfur-containing BTDA/ASD performed best of the bonds tested in a wet environment. Metal-catalyzed oxidation of sulfur was observed to take place in the steel case, but not to an extent to have a noticeable effect on peel strength.     

The Adhesive Bonding of Steel with Polysulfone

The bonding of cold rolled steel with polysulfone, a thermoplastic adhesive has been studied. The single lap shear strength of bonded samples where the substrate was gritblasted was 40% lower than for the case where the substrate was hydrothermally oxidized. Both surface preparations resulted in diminished lap shear strength on exposure to high humidity conditions. However, the hydrothermally oxidized substrates resulted in more durable bonds.     

Improvement of the Durability of Zinc-Coated Steel/Epoxy Bonded Joints

The durability properties of bonded lap shear joints made from an epoxy/dicyandiamide adhesive and hot-dipped galvanized (G2F) or electroplated-phosphated (EZ2) steel have been investigated. The degradation mechanisms have been studied after three accelerated ageing tests: the “cataplasme humide” (“C.H.T.”), immersion (“I.T.”), and salt spray (“S.S.T.”) tests. X-ray photoelectron spectroscopy (XPS) analysis of fracture surfaces after ageing have shown that anodic dissolution of the zinc-coating is responsible for debonding in all cases and that intergranular corrosion phenomena account for poorer performances of the hot-dipped galvanized substrate during “C.H.T.” and “I.T.” Silane coupling agents were successfully used as primers on both substrates to increase the hydrolytic stability of the metal/adhesive interface. XPS results indicate that both the interfacial dissolution of the phosphate coating of EZ2 and intergranular corrosion of G2F are delayed for silane-primed specimens. The observed improvements do not appear to depend on the nature of the silane coupling agents. Alkylsilanes have been found to perform as well as silanes having a group capable of reacting with the epoxy/dicyandiamide system.

Additional tests were carried out in view of the possible application of organosilane reagents as additives in corrosion-protective oils. Good durability properties have been obtained by priming the metal coupons with a standard oil/silane mixture prior to bonding.

When corrosion was the controlling degradation mechanism as is the case during the salt spray test, silane treated specimens did not generally perform better than control specimens.     

Improvement of the Durability of Zinc-Coated Steel/Epoxy Bonded Joints

The durability properties of bonded lap shear joints made from an epoxy/dicyandiamide adhesive and hot-dipped galvanized (G2F) or electroplated-phosphated (EZ2) steel have been investigated. The degradation mechanisms have been studied after three accelerated ageing tests: the “cataplasme humide” (“C.H.T.”), immersion (“I.T.”), and salt spray (“S.S.T.”) tests. X-ray photoelectron spectroscopy (XPS) analysis of fracture surfaces after ageing have shown that anodic dissolution of the zinc-coating is responsible for debonding in all cases and that intergranular corrosion phenomena account for poorer performances of the hot-dipped galvanized substrate during “C.H.T.” and “I.T.” Silane coupling agents were successfully used as primers on both substrates to increase the hydrolytic stability of the metal/adhesive interface. XPS results indicate that both the interfacial dissolution of the phosphate coating of EZ2 and intergranular corrosion of G2F are delayed for silane-primed specimens. The observed improvements do not appear to depend on the nature of the silane coupling agents. Alkylsilanes have been found to perform as well as silanes having a group capable of reacting with the epoxy/dicyandiamide system.

Additional tests were carried out in view of the possible application of organosilane reagents as additives in corrosion-protective oils. Good durability properties have been obtained by priming the metal coupons with a standard oil/silane mixture prior to bonding.

When corrosion was the controlling degradation mechanism as is the case during the salt spray test, silane treated specimens did not generally perform better than control specimens.