Numerical simulations of the cathodic delamination of adhesive bonded rubber/steel joints

Cathodic delamination of mechanically loaded rubber/steel adhesive bonds occurs due to bondline degradation (weakening) followed by crack growth under mechanical (here, mostly cleavage) load. In this paper, a mechano-chemical failure criterion is proposed, which couples fracture mechanics principles with the weakening mode of debonding due to environmental effects. The latter is mainly described by electrolyte type, cathodic potential, and temperature and may be analytically described according to the recently introduced [1] analytical model based on liquid-solid reactions and is capable of simulating the weakening mode of bond degradation. This paper extends the model advanced in [1] to where we now account for externally applied mechanical loading (mostly peel mode). Such loads cause already weakened bonds to delaminate thus resulting in physical separation of the rubber from the steel substrate.For the rubber/metal, variable-G, strip blister specimen (SBS) used in this work, progressive delamination proceeds as the applied strain energy release rate, G, decreases from an initial maximum value, G_T0 (of about 2.24 kJ/m² for the most utilized specimen configuration). As the applied G decreases, delamination correspondingly proceeds at progressively slower rates. The fact that delamination rates decrease with increasing delaminated bond lengths has already been established experimentally and simulated using empirical [2] and semi-empirical models [3] but will be simulated numerically in this paper. The model is validated using such experimental data of bond delamination under a variety of cathodic conditions. The validated methodology provides numerical simulations of joint delamination of the SBS under the combined action of mechanical peel loads and cathodic environment.     

Scanning Kelvin Probe Blister test measurements of adhesive delamination – Bridging the gap between experiment and theory

The delamination of an epoxy-adhesive film from a zinc coated steel substrate was studied by means of the electrochemical Height Regulated Scanning Kelvin Probe Blister Test (HR-SKP-BT¹) under controlled atmospheric conditions, applied pressure and interfacial electrode potential. The experimental studies focused on the analysis of the critical environmental water activity that leads to a corrosive delamination process under applied mechanical load and the analysis of the corrosion and delamination mechanisms at the front of delamination. The influence of applied pressure and relative humidity on the increase in the maximum blister height and the delamination rate was measured under constant polarization of the defect. 90° peel-tests were performed in order to correlate the water activity with the resulting peel force. The corrosion products that formed across the delamination front were analyzed by Raman microscopy. Through these HR-SKP-BT studies, a critical value was found for relative humidity for the delamination process. A transition zone was detected in which electrochemical degradation precedes mechanical delamination. In addition to the experimental studies, the critical energy release rates of the blister were calculated in finite element (FE²) simulations so as to enable a better understanding of the delamination of adhesives on metal surfaces. The combined experimental and theoretical studies show that the delamination process is controlled by the interfacial electrochemical reactions at the delamination front and that a transition area of few hundred micrometers exists in which the adhesion strength is lowered by the cathodic oxygen reduction process to a value which can be overcome by the mechanical stress in this area.     

Hydrothermal Cement/Metal Interfaces

We investigated the adherence of two cementitious materials, calcium phosphate cement (CPC) and silica flour-filled class G cement (CGC), to metal substrates, such as cold-rolled steel (CRS), stainless steel (SS), electroplated zinc-coated steel (EZS), and zinc phosphate-coated steel (ZPS) after autoclaving at 200°C. In CPC/metal joints, the γ-AlOOH phase, which segregated from the hydroxyapatite phase of the CPC matrix, was preferentially precipitated on the CRS and SS surfaces and also mixed with the reaction products formed at the interfaces between CPC and EZS or ZPS. Precipitation of γ-AlOOH caused the formation of a weak boundary layer at the interfacial transition zones, thereby resulting in a low shear-bond strength. Although CGC accelerated the rate of corrosion of CRS and SS surfaces, the growth of Fe₂O₃ clusters, formed as the corrosion products of metals at interfaces, aided the anchoring effect of xonotlite crystals as the major phase of CGC matrix, thereby conferring a high shear-bond strength. The EZS and ZPS surfaces were susceptible to alkali dissolution caused by the attack of the high-pH interstitial fluid of CGC pastes to the Zn and zinc phosphate coatings. Thus, the bond strengths of the CGC/EZS and /ZPS joints were lower than those of the joints made with CRS and SS.     

A computational investigation on the molecular structure,electronic properties and intramolecular hydrogen bonding interaction of 1,1,1-trifluoro-4-mercaptobut-3-ene-2-thione in ground and electronic excited state

The hydrogen bond (HB) strength, geometry optimization, vibrational frequencies and several well-established indices of aromaticity in 1,1,1-trifluoro-4-mercaptobut-3-ene-2-thione and its 15 derivatives in two positions, R1 and R2, have been investigated by means of the density functional theory (DFT) method with 6-311++G** basis set in the gas phase. The obtained results show that the HB strength is mainly governed by resonance variations inside the chelate ring induced by the substituent groups. The following substituents have been taken into consideration: NO₂, SCF₃, Ph, PhOCH₃, SCOCH₃, CH₂OCH₃ and CH₂OH. The strongest S–H···S HBs belong to PhOCH₃-substituted system in both positions, whereas NO₂ and H substitutions in R1 and R2 positions, respectively, produce the weakest S–H···S hydrogen bridges. The excited-state properties of intramolecular hydrogen bonding in substituted systems have been investigated theoretically using the time-dependent DFT method. Natural bond orbital analysis is also performed for a better understanding of the nature of intramolecular interactions. The electron density and Laplacian (?²ρ) properties, estimated by atoms in molecule calculations, indicate that the H···S bond possesses low ρ, positive ?² ρ and H_C<0, which are in agreement with the partially covalent character of HBs.     

Electroplating of cobalt from aqueous citrate baths

Electroplating of cobalt onto steel substrates from citrate baths has been investigated under different conditions of bath composition, current density, pH and temperature. A detailed study has been made of the influence of these variables on the potentiodynamic cathodic polarization curves, cathodic current efficiency and the throwing power as well as the throwing index of these baths. The optimum bath composition has been established and it contains: CoSO₄.7H₂O (0·36 mol dm⁻³) trisodium citrate (0·19 mol dm⁻³) and citric acid (0·1 mol dm⁻³) at pH 5·0. The microhardness of cobalt electrodeposited from citrate baths is high and it may be, under certain conditions, two or three times higher than that reported for cobalt electrodeposited from other different baths. The surface morphology of the as-plated cobalt was investigated by using scanning electron microscopy (SEM) while the structure was studied by using X-ray diffraction analysis and anodic stripping voltammetry (ASV) techniques. © 1998 Society of Chemical Industry     

Effect of polyphenylene sulfide containing amino unit on thermal and mechanical properties of polyphenylene sulfide/glass fiber composites

Three kinds of high‐molecular‐weight compatibilizers [copoly(1,4‐phenylene sulfide)‐poly(2,5‐phenylene sulfide amine)] (PPS‐NH₂) containing different proportions of amino units in the side chain) were synthesized by the reaction of dihalogenated monomer and sodium sulfide via nucleophilic substitution polymerization under high pressure. The intrinsic viscosity of the obtained copolymers was 0.354–0.489 dL/g and they were found to have good thermal performance with melting point (T_m) of 271.3–281.0 °C and initial degradation temperature (T_d) of 490.0–495.7 °C. There was an excellent physical compatibility between PPS‐NH₂ and the pure industrial PPS. The results of dynamic mechanical analysis and macro‐ and micromechanical test showed that the selective compatibilizer PPS‐NH₂ (1.0) (1.0% mol aminated ratio) can improve the mechanical and interfacial properties of polyphenylene sulfide/glass fiber (PPS/GF) composite. The macro‐optimal tensile strength, Young's modulus, bending strength, and notched impact strength of 5%PPS‐NH₂ (1.0)/PPS/GF composite raised up to 141 MPa, 1.98 GPa, 203 MPa, and 6.15 kJ/m², which increased 12.8%, 9.4%, 4.1%, and 13.8%, respectively, comparing with the pure PPS/GF composite (125 MPa, 1.81 GPa, 195 MPa, and 5.40 kJ/m², respectively). © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45804.     

Mechanisms of Formation of the Interphase in Epoxy-Amine/Aluminium Joints

Detailed investigations of the interaction of 1,2- diaminoethane with aluminium surfaces have been performed to understand the mechanisms of interphase formation in epoxy-amine/aluminium joints. In particular, it has been shown that both metal bond surface complexes (O-Al … N bonds) and hydrogen-bonded surface complexes (Al-OH … N and C_xO_yH_z … N bonds) can be formed on aluminium surfaces covered with a partly contaminated (hydr)oxide film. However, surface dissolution can only be induced by mononuclear bidentate metal bond surface complexes (chelates), which result from a ligand exchange mechanism between specific hydroxyl sites (η¹- and µ₂-OH) of the surface and the amino terminations of the molecule. The formation of these chelates weakens the trans Al-O bonds and detachment of the ligand-metal complexes can occur. This mechanism is enhanced by the presence of moisture. In practical epoxy-amine/aluminium joints, the interphase can, thus, be formed by migration of these complexes in the liquid polymeric phase before curing is achieved.     

A mechanistic evaluation of cathodic debonding of elastomer to metal bonds

—The durability of adhesively bonded neoprene rubber/metal joints for marine applications is discussed. In order to simulate the local corrosive environment on cathodic surfaces, neat film specimens of various adhesive systems were fabricated and tested in NaOH aqueous solutions resulting in chemical degradation of the polymer accompanied by weight changes. In comparison, neat film specimens exposed to artificial sea water (ASW) showed much smaller changes. The addition of a silane coupling agent to the primer component enhanced the chemical resistance of the free samples considerably. Actual bonded diffusion specimens were also utilized, and it was found that the propagation of a weakened bond obeyed a linear relationship when plotted against the square root of time, suggesting Fickian diffusion. The results suggest that the rate is very sensitive to temperature, the applied cathodic voltage (current), and other accelerating parameters. It was also shown that the use of zinc phosphate-coated steel substrates improves the durability, especially at low cathodic voltages. Stressed specimens were also tested and showed that tensile stresses accelerate bond delamination. The addition of relatively high concentrations of the silane coupling agent was correlated with reduced delamination rates.     

Ag–SiO2 - An optimized braze for robust joining of commercial coated stainless steel to ceramic solid oxide cells

In this study, Ag–SiO₂ was successfully used to join Ce/Co coated AISI 441 stainless steels produced by Sandvik to Solid Oxide Cells. Defect-free and robust joints were obtained at 950 °C when brazing in air. The influence of the chemical composition of the braze and the brazing temperature on the microstructure and mechanical properties of joints was studied. An enhanced interfacial adherence was achieved through the reaction of the SiO₂ in the braze and the Co coating of the steel during the air brazing process. The obtained joints possess excellent mechanical robustness with a fracture energy of 96.5 J/m², and a superior gas tightness (leak rate of 5.4 × 10^?4 sccm cm^?1) compared to the existing brazing systems. Long-term aging in air or the exposure to reducing atmosphere only had minor effects on the measured fracture energy.     

Effect of inter-plies on the short beam shear delamination of steel/composite hybrid laminates

Interlaminar shear test methods (ILS) were implemented to characterize the delamination behavior of asymmetric steel/carbon fiber reinforced plastic (CFRP) hybrids. To improve the delamination behavior thermoplastic inter-plies were inserted between CFRP and steel. Supported by optical strain measurement the maximum shear stress (τ_MAX), the shear stress at interfacial delamination (τ_IF) and the shear stress at large-scale CFRP ply delamination τ_D were evaluated. The significant effect of inter-plies on the adhesion was best reflected by the shear stress value at interfacial delamination. Finite element analysis of the actual shear stress distribution in an asymmetric hybrid sample without inter-ply revealed that the calculated shear strength is just slightly overestimated compared to the standardized evaluation procedure.     

A New Metal–Organic ZnII Supramolecular Assembled via Hydrogen Bonds and N···N Interactions as a New Precursor for Preparation Zinc(II) Oxide Nanoparticles, Thermal, Spectroscopic and Structural Studies

A new 1D supramolecular involving two different ligands, {[Zn(GB)₂]·(μ-bpe)₃} _n (ClO₄)_2n ·nH₂O (GB = 2-guanidinobenzimidazole and bpe = 1,2-bis(4-pyridyl)ethylene, has been synthesised, characterized by elemental analysis, IR-, ¹H NMR-, ¹³C NMR spectroscopy. The thermal stability of compound {[Zn(GB)₂]·(μ-bpe)₃} _n (ClO₄)_2n ·nH₂O was studied by thermal gravimetric and differential thermal analyses. The single crystal X-ray analysis shows that the complex is a one-dimensional polymer involving macrocycle rings as a result of non-covalent bridging bpe ligands via N–H···N and N···N interactions, N–H···bpe···bpe···H–N, with the basic repeating {[Zn(GB)₂](μ-bpe)₃}(ClO₄)₂·H₂O units and by connecting [Zn(GB)₂]²⁺ nodes. ZnO nanoparticles were obtained by calcination of compound {[Zn(GB)₂]·(μ-bpe)₃} _n (ClO₄)_2n ·nH₂O at 500 °C in air. The nanoparticles were characterized by X-ray diffraction and scanning electron microscopy.     

Inhibition of corrosion-driven organic coating disbondment on galvanised steel by smart release group II and Zn(II)-exchanged bentonite pigments

Bentonite pigments exchanged with either zinc or group II cations are characterised as inhibitors of corrosion-driven cathodic disbondment of model polyvinylbutyral (PVB) coatings adherent to the intact zinc surface of hot dip galvanised steel. An in situ scanning Kelvin probe (SKP) technique is used to quantify rates of coating delamination as a function of pigment volume fraction (?_pt) and draw up a ranking order of inhibitor efficiency. Group II cation-exchanged bentonites show a moderate degree of inhibition, where rates of coating disbondment are reduced by up to 60-70% compared to the unpigmented case. In contrast, bentonite pigments containing exchangeable Zn²⁺ ions are markedly more effective, and no delamination is observed over periods of up to 24 h when ?_pt ≥ 0.1. The efficiency of in-coating Zn²⁺ is attributed to the ability to block underfilm cathodic oxygen reduction by reinforcing a pre-existing zinc (hydr)oxide layer.     

Mechanical and tribological properties of diamond-like carbon films prepared on steel by ECR-CVD process

Diamond-like carbon (DLC) films were prepared on AISI 440C steel substrates at room temperature by the electron cyclotron resonance chemical vapor deposition (ECR-CVD) process in C₂H₂/Ar plasma under different conditions. In order to prevent the inter-diffusion of carbon and improve the adhesion strength of DLC films, functionally gradient Ti/TiN/TiCN/TiC supporting underlayers were deposited on the steel substrates in advance. Using the designed interfacial transition layers, relatively thick DLC films (1–2 μm) were successfully prepared on the steel substrates without delamination. By optimizing the deposition parameters, DLC films with hardness up to 28 GPa and friction coefficients lower than 0.15 against the 100Cr6 steel ball were obtained. In addition, the specific wear rates of the films were found to be extremely low (∼10⁻¹⁷ m³/Nm). The friction-induced graphitization mechanism of DLC was confirmed by micro-Raman analysis.     

Kinetics and mechanism of the hydrogen discharge on Ti in HCl-DMSO solutions

The kinetics of hydrogen discharge in solutions of HCl-DMSO is investigated within 10^?3 1 N HCl concentrations, in the presence of KClO₄ as supporting electrolyte. The cathodic slope is 0·120 V/decade for all solutions. The electrochemical reaction order with respect to the hydrogen ion concentration at E = ?0·6 V is found to be 0·52. The stoichiometric number is practically equal to 2. The experimental activation energy is 11·2 kcal/mole.The cathodic process is interpreted with the discharge reaction as rate determining step, followed by the adatom recombination reaction.     

Zinc(II)-bound thiolate complexes-containing cysteine derivatives modeling of methionine synthase alkylating enzyme

The reaction of thioimidazolylborate-zinc(II)-perchlorate complex [Tt^xyly·Zn? OClO₃] 1 (Tt^xyly=hydrotris[N-xylyl-thioimidazolyl]borate) with cysteine and its derivative N-acetyl cysteine and S-methyl cysteine leads to the formation of three new monomeric and dimeric thiolate complexes: [Tt^xyly·Zn? Cys? Zn·Tt^xyly] 2, [Tt^xyly·Zn? Cys(NAc)? Zn·Tt^xyly] 3, and [Tt^xyly·Zn? Cys(SMe)] 4. The attachment of the cysteine derivatives to the Tt·Zn unit serves as structural models for the active site of methionine synthase. Methylation of the coordinated thiolate in the dinuclear zinc(II) complex 2 with methyl iodide appears to occur intramolecularly at the zinc-bound thiolates, forming methyl thioether-containing zinc(II) complex [Tt^xyly·Zn? Cys(SMe)] 4 and iodo complex [Tt^xyly·Zn? I] 5 with a clean second-order reaction of k=1.0×10^?5 M^?1 s^?1.     

Effect of interfacial microstructure evolution on the peeling strength and fracture of silicon nitride/oxygen-free copper foil joints brazed with Ag-Cu-TiH2 filler

Gas-pressure sintered silicon nitride (Si₃N₄) ceramic was brazed to oxygen-free copper (OFC) foil using 20.22 ± 0.93 mg/cm² of Ag-Cu-TiH₂ filler at 875 ^◦C for 0.5 h. The effect of TiH₂ content on the 3D morphology, including the cross-section microstructure and etched surface morphology of Si₃N₄ ceramic/OFC foil joints, was analyzed. An evolution model of the interfacial microstructure for joints was proposed based on 3D morphological analysis. The reaction between the brazing alloy and Si₃N₄ ceramic formed the interfacial reaction layer and the inside reaction zones during brazing. The growth mechanism of the interfacial reaction layer was discussed in detail. The peeling test was used to evaluate the bonding strength of the Si₃N₄ ceramic/OFC foil joints, and the optimum peeling strength of 25.1 N/mm was achieved at 5 wt% TiH₂ content. The interfacial microstructure of the joints changed with TiH₂ content, leading to different main fracture mechanisms and corresponding peeling strengths.     

Hydrometallurgical Recovery of Zinc from Fine Blend of Galvanization Processes

Abstract

In many factories, which are working in the field of steel industry, there are galvanization units in which steel products are galvanized for corrosion protection. About 15% of the total amount of the used zinc are accumulated as zinc ash and dust at the surface of molten zinc bath and in the chimney respectively. In a previous work, zinc was successfully recovered from the coarse ash by applying pyrometallurgical processing. In this work, zinc fine blend (of fine ash and flue dust) was hydrometallurgically treated using sulfuric acid. Two alternative techniques were applied for producing zinc sulfate salt or pure zinc metal. In the first technique, the salt was separated from the leach solution as zinc sulfate hydrate (ZnSO₄ · H₂O). It was crystallized by concentrating the leach liquor to a density of 1.52 g/cm³. The purity of the produced zinc sulfate was 99.5%. In the second technique, the leach solution has been purified with respect to the soluble impurities using precipitation. The electrowinning technique was applied for producing a pure zinc metal from the purified solution. Electrolysis was performed at ambient temperature (25–28°C) with current density (c.d.) of 40 mA · cm^?2. The recovery of zinc proceeds down to a concentration of 50 g · l^?1 with acceptable cathodic current efficiency of 96.5%, and energy consumption for the electrolysis step of 2.75 KWh/Kg. The zinc purity in the deposit obtained from the electrolysis was 99.9%.     

Microstructure and properties of functional magnesium titanate ceramic joint brazed by bismuth-borate glass

Bismuth-borate glass braze (Bi25) with low melting point was utilized to braze magnesium titanate ceramic (MTC) in this work. The interfacial reaction between MTC and bismuth-borate glass braze made a well brazing possible. First, the Zn atoms from the glass seam substituted Mg atoms from MTC forming the phase (Zn,Mg)₂TiO₄ of lamellar morphology, which reacted with [BiO₆] (or [BiO₃]) from glass seam and then generated Bi₄Ti₃O₁₂ of granular and sheet-like morphologies. The Mg²⁺ deriving from the reactions above reacted with [SiO₄] unit from glass seam and generated Mg(SiO₃) of granular and stripe-like morphologies. The shear strength increased first and then decreased with the increase of brazing temperature constantly. It reached a maximum value of 72 MPa at 725 °C. The dielectric loss tangent of joints always tended to zero at high frequency, and the dielectric constant of joints brazed at 750 °C was closest to that of base MTC itself.     

Microstructure evolution of SiC/SiC joints during ultrasonic-assisted air bonding using a Sn–Zn–Al alloy

Direct soldering of SiC ceramic in air at 230 °C was achieved using a Sn–9Zn–2Al alloy assisted by ultrasonic wave within seconds. Experimental results indicated that a sound metallurgical bond was formed between the SiC ceramic and Sn–9Zn–2Al alloys. The dependence of interfacial microstructure evolution on ultrasonic action duration time was investigated. Two types of interfacial structures at the interface were observed as the ultrasonic action duration time increased. An amorphous SiO₂ layer was identified at the interface for ultrasonic exposures of 1 s, which was the oxide layer formed on the SiC ceramic surface during heating. A layer of amorphous alumina with a thickness of ~ 6.8 nm formed at the interface under ultrasonic action for over 4 s. The shear strength of joints could reach up to 44 MPa. The formation of the alumina layer at the interface was attributed to the redox reaction of Al from the filler metal and SiO₂ on the SiC ceramic surface under the action of ultrasonic waves. The rapid interfacial reaction was principally induced by the acoustic cavitation and streaming effects at the liquid/solid interface.     

Development of a new thermoplastic laminate system

In this investigation an all-olefin thermoplastic laminate was developed and characterized. Commingled glass-fiber polypropylene (PP) composite was used as skin and HDPE (PE) foam with closed cells as core. Infra-red heating was used for melting the surfaces of the substrates for surface fusion bonding with a cold press. Two tie-layer films, viz., ethylene-propylene copolymer (EPC) and HDPE/elastomer blend were used as hot-melt adhesives for bonding the substrates. Singlelap shear joints were prepared from PP composite and PE foam adherends with a bonding area of 25.4 mm × 25.4 mm to determine the bond strength. EPC tie-layer adhesive provided higher bond strength (2.68 × 10⁶ N/m²) to the all-olefin laminate than that based on HDPE/elastomer blend (1.93 × 106 N/m²). For EPC tie-layer-based laminates, a mixed mode of failure was observed in the failed lap shear samples: about 40% was cohesive failure through the tie-layer, and the rest of failure was interfacial, either at PP composite or PE foam surfaces. Environmental scanning electron micrographs (ESEM) revealed that in the process of surface fusion bonding, PE foam cells in the vicinity of interphase (800-μm-thick) were coalesced with high temperature and pressure. No macro-level penetration of the tie-layer melt front into the foam cells was observed. As the surface morphology of foam was altered due to IR surface heating and the PP composite bonding side had a resin-rich layer, the bonding situation was closer to that between two polymer film surfaces.