Influence of silane-based treatment on adherence and wet durability of fusion bonded epoxy/steel joints

Three layers polyolefin coatings are widely used in Europe to protect pipelines against corrosion. Loss of adhesion at a fusion bonded epoxy (FBE)/steel interface has occasionally been observed even on pipelines without external defects. Silane-based surface pre-treatments are developed to improve adhesion with limited impact on the environment unlike usual chromate conversion pre-treatments; however the mechanisms involved in silane action need to be more deeply understood. The application process of silane surface treatment implies a series of key parameters of which optimization is imperative to form a silane layer with good properties at the interface. This paper studies the influence of the cure temperature and the pH of an aminosilane based pre-treatment on adhesion strength and durability via single lap shear tests. SEM/EDX, FT-IR and XPS analyses are used to characterize the silane and silane/epoxy structures. Silane pretreatment improved the FBE joints durability and appears as a relevant solution to replace the usual chromate conversion pretreatments. The joints pretreated at pH 10.6 had better durability than at pH 4.6. This was related to the formation of a bridge across the silane/epoxy interface at pH 10.6, whereas, at pH 4.6, formic acid reacts with amino groups of silanes, limiting the reaction between amino groups and epoxy.     

Thermal and mechanical behavior of poly(vinyl butyral)‐modified novolac epoxy/multiwalled carbon nanotube nanocomposites

The effects of poly(vinyl butyral) (PVB) and acid‐functionalized multiwalled carbon nanotube modification on the thermal and mechanical properties of novolac epoxy nanocomposites were investigated. The nanocomposite containing 1.5 wt % PVB and 0.1 wt % functionalized carbon nanotubes showed an increment of about 15°C in the peak degradation temperature compared to the neat novolac epoxy. The glass‐transition temperature of the novolac epoxy decreased with increasing PVB content but increased with an increase in the functionalized carbon nanotube concentration. The nanocomposites showed a lower tensile strength compared to the neat novolac epoxy; however, the elongation at break improved gradually with increasing PVB content. Maximum elongation and impact strength values of 7.4% and 17.0 kJ/m² were achieved in the nanocomposite containing 1.5 wt % PVB and 0.25 wt % functionalized carbon nanotubes. The fractured surface morphology was examined with field emission scanning electron microscopy, and correlated with the mechanical properties. The functionalized carbon nanotubes showed preferential accumulation in the PVB phase beyond 0.25 wt % loading. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43333.     

The performance of epoxy coatings containing polyaniline (PANI) nanowires in neutral salt,alkaline, and acidic aqueous media

PANI/epoxy coatings have great promise applications in the industry as the metal corrosion protection coating, and their performance directly determines the life span of the coating and equipment durability. In this study, the performance of epoxy coatings with and without PANI nanowires immersed in 12 wt% NaCl, 5 wt% HCl, and 5 wt% NaOH solutions at different temperature were investigated for the first time. The performance and the degradation reactions of the coating cooperated with PANI nanowires were characterized by the variety of techniques and methods, including ultraviolet–visible spectrophotometry (UV–vis), field emission scanning electron microscopy (SEM), Attenuated Total Reflectance-Fourier transform Infrared spectroscopy (ATR-FTIR), and thermogravimetric analysis (TGA). The experiment results indicated that the failure mechanism of the different coatings varied with the different temperatures and solutions. Electrochemical impedance spectra (EIS) results showed that an appropriate content of PANI nanowires improve the protection performance of epoxy coatings in 12 wt% NaCl, 5 wt% HCl, and 5 wt% NaOH solutions, which is attributed to the passivation ability and shielding effect of PANI nanowires.     

Improvement in microstructure and mechanical properties of Ti(C,N) cermet prepared by two-step spark plasma sintering

A fine grained Ti(C, N) cermet tool material was prepared by two-step spark plasma sintering. Microstructure evolution and densification mechanisms of Ti(C, N) during spark plasma sintering were studied. Effect of two-step sintering process and Ni content on microstructure and mechanical properties were also investigated. The critical activated densification temperature of Ti(C, N) is about 1300?℃, and the rapidest densification rate takes place at 1300?℃~1400?℃. Grains are in the size of 1?µm when the Ti(C, N) cermet was prepared by two-step spark plasma sintering. The optimal flexural strength, fracture toughness and Vickers hardness are 1094?±?42?MPa, 7.2?±?0.5?MPa?m^1/2 and 18.3?±?0.4?GPa, respectively. The Ti(C, N) cermets containing more content of Ni have higher toughness, which is due to the remarkable toughening effect of crack bridging by large grains.     

The role of the ratio (PEG:PPG) of a triblock copolymer (PPG‐b‐PEG‐b‐PPG) in the cure kinetics,miscibility and thermal and mechanical properties in an epoxy matrix

The aim of this study was to evaluate the role of different poly(ethylene glycol):poly(propylene glycol) (PEG:PPG) molar ratios in a triblock copolymer in the cure kinetics, miscibility and thermal and mechanical properties in an epoxy matrix. The poly(propylene glycol)‐block‐poly(ethylene glycol)‐block‐poly(propylene glycol) (PPG‐b‐PEG‐b‐PPG) triblock copolymers used had two different molecular masses: 3300 and 2000 g mol^?1. The mass concentration of PEG in the copolymer structure played a key role in the miscibility and cure kinetics of the blend as well as in the thermal–mechanical properties. Phase separation was observed only for blends formed with the 3300 g mol^?1 triblock copolymer at 20 wt%. Concerning thermal properties, the miscibility of the copolymer in the epoxy matrix reduced the T_g value by 13 °C, although a 62% increase in fracture toughness (K_IC) was observed. After the addition of PPG‐b‐PEG‐b‐PPG with 3300 g mol^?1 there was a reduction in the modulus of elasticity by 8% compared to the neat matrix; no significant changes were observed in T_g values for the immiscible system. The use of PPG‐b‐PEG‐b‐PPG with 2000 g mol^?1 reduced the modulus of elasticity by approximately 47% and increased toughness (K_IC) up to 43%. Finally, for the curing kinetics of all materials, the incorporation of the triblock copolymer PPG‐b‐PEG‐b‐PPG delayed the cure reaction of the DGEBA/DDM (DGEBA, diglycidyl ether of bisphenol A; DDM, Q3‐4,4′‐Diaminodiphenylmethane) system when there is miscibility and accelerated the cure reaction when it is immiscible. All experimental curing reactions could be fitted to the Kamal autocatalytic model presenting an excellent agreement with experimental data. This model was able to capture some interesting features of the addition of triblock copolymers in an epoxy resin. © 2018 Society of Chemical Industry     

Microstructure and mechanical properties of Ti(C,N)-based cermets fabricated by in situ carbothermal reduction of TiO2 and subsequent liquid phase sintering

Ti(C,N)-based cermets were prepared by in situ carbothermal reduction of TiO₂ and subsequent liquid phase sintering in one single process in vacuum. The densification behavior, phase transformation, and microstructure evolution of the cermets were investigated by DSC, XRD, SEM, and EDX. The results showed that the carbothermal reduction of TiO₂ was completed below 1250 °C, and Ti(C,N)-based cermets with refined grains were obtained after sintered at 1400 °C for 1 h by this method. The hard phase of the cermets mainly exhibited white core/gray rim structure, in great contrast to the typical black core/gray rim structure of hard phase in traditional cermets. Ti(C,N)-based cermets prepared by this novel method showed excellent mechanical properties with a transverse rupture strength of 2516±55 MPa, a Rockwell hardness of 88.6±0.1 HRA, and a fracture toughness of 18.4±0.7 MPa m^1/2, respectively.     

Phase behavior of temperature‐ and pH‐sensitive poly(acrylic acid‐g‐N‐isopropylacrylamide) in dilute aqueous solution

Several different composition temperature‐ and pH‐sensitive poly(acrylic acid‐g‐N‐isopropylacrylamide) (P(AA‐g‐NIPAM)) graft copolymers were synthesized by free‐radical copolymerization utilizing macromonomer technique. The phase behavior and conformation change of P(AA‐g‐NIPAM) in aqueous solutions were investigated by UV–vis transmittance measurements, fluorescence probe, and fluorescence quenching techniques. The results demonstrate that the P(AA‐g‐NIPAM) copolymers have temperature‐ and pH‐sensitivities, and these different composition graft copolymers have different lower critical solution temperature (LCST) and critical phase transition pH values. The LCST of graft copolymer decreases with increasing PNIPAM content, and the critical phase transition pH value increases with increasing Poly(N‐isopropylacrylamide) (PNIPAM) content. At room temperature (20°C), different composition of P(AA‐g‐NIPAM) graft copolymers in dilute aqueous solutions (0.001 wt %) have a loose conformation, and there is no hydrophobic microdomain formation within researching pH range (pH 3 ～ 10). In addition, for the P(AA‐g‐NIPAM) aqueous solutions, transition from coil to globular is an incomplete reversible process in heating and cooling cycles. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Development of a model for the anodic behavior of T60 titanium in chlorinated and oxygenated aqueous media. Application to the specific conditions of hydrothermal oxidation (1 MPa<pressure<30 MPa, 20 °C<temperature<400 °C)

This work evaluates the anodic electrochemical behavior of titanium metal in hydrothermal oxidation conditions (up to 400 °C and 28 MPa) in chlorinated media in order to estimate the supercritical water oxidation reactors reliability for the treatment of less than 10% organic-waste waters. The titanium room temperature dissolution mechanism in chlorinated acidic medium (pH<0) is not fundamentally modified by oxygen. Deduced from the ‘current-potential’ and ‘valence-potential’ curves, it is based on four crucial elementary steps leading to two branches: a so-called active branch corresponding to a trivalent dissolution (its effect is inversely proportional to the pH), and a passive branch (TiO₂ oxide formation with a very limited tetravalent dissolution). In hydrothermal oxidation (pH>1), only the second branch is effective. The titanium protection is directly related to the oxide stability in high pH systems. The mechanism model is expressed in terms of ‘current-potential’ laws, which provide kinetic parameters using optimization calculations. The different elementary steps reaction rates were estimated as well as the evolution of the reaction intermediates coverage ratios with the potential. The quantification of each elementary step was performed to understand and/or orient the materials behavior according to different factors (pH, chloride ions contents, potentials…).