H. Dafalla

Novel hybrid epoxy silicone materials as efficient anticorrosive coatings for mild steel

Novel hybrid-sol–gel materials (C1–C5) based on silica–epoxy composite resins were successfully prepared by coupling different aminosilanes with DER736 epoxy resin, followed by an in situ sol–gel process, and finally introducing the urethane moieties to the final coatings. This research has emphasized the effect of changing the type of aminosilane on the properties of the prepared hybrid coatings. Three different aminosilanes were examined and their reaction parameters with the epoxy and the trialkoxysilanes were carefully optimized in order to avoid fast gelation and to obtain the desired properties of the hybrid coatings. The prepared organic–inorganic hybrid coatings were loaded and cured on mild steel panels and characterized for FTIR, NMR, TGA, water contact angles (WCA), nanoindentation hardness, pull-off adhesion, SEM, EIS and polarization studies. The results revealed that the coatings prepared from the trialkoxysilanes APTMS and MTMS (C4) demonstrate the best mechanical, anticorrosion and adhesion properties on mild steel substrates as compared to all other coatings in a 3.5 wt% NaCl medium. Electrochemical impedance spectroscopy (EIS) results indicated a corrosion resistance value for this coating in the range of 106 Ω cm2 after 10 days of continuous immersion in the saline medium. The SEM observations suggest that coatings produced from the other aminosilanes, APT-PDMS and APM–DMS are inhomogeneous and have some defects which have ultimately affected their barrier protection properties.

Surface mechanical characterization of sputtered nickel using nanoindentation

The surface of carbon steel (CS) samples was deposited with pure Ni for the durations of 2, 5 and 10 minutes using DC magnetron sputter deposition process. The aim was to examine the microstructure and surface mechanical properties of Ni coatings. Field emission scanning electron microscope coupled with an energy dispersive x-ray spectrometer and x-ray diffractometer were used to undertake materials characterization. Instrumented nanoindentation hardness, elastic modulus, adhesion and coefficients of friction of coatings were evaluated. Nickel coatings obtained were relatively uniform, continuous and adherent for all deposition times. Thickness of Ni coatings increased with deposition times. Coatings with lower deposition times showed relatively higher nanohardness, elastic modulus and creep which is thought to be due to its lower thickness. Coatings were found to crack and delaminate at relatively low applied normal force during micro-scratch testing. Coefficient of friction values of coatings was comparable with that found in the literature.

Corrosion Behavior of Coarse- and Fine-Grain Ni Coatings Incorporating NaH2PO4.H2O Inhibitor Treated Substrates

Plain carbon steel substrates were treated with NaH2PO4.H2O inhibitor for 24 hours and coated with Ni using dc and pulse electrodeposition in standard Watt’s bath. The effect of dc and pulse electrodeposition, on the microstructure and corrosion properties of Ni coatings in 3.5 wt% NaCl solution was studied. The effect of inhibitor on the deposition process and corrosion behavior was also examined. Materials characterization was performed using field emission scanning electron microscopy, cross-sectional scanning transmission electron microscopy, atomic force microscopy, x-ray diffraction and nanoindentation. Experimental results indicated that pulse electrodeposition produced fine grained Ni coatings that showed lower corrosion rate compared to coarse grained dc electrodeposited Ni. Pre-treatment of substrates with inhibitor did not adversely affect the deposition process and adherent Ni coatings were readily developed. The results showed that pulse electrodeposition could be used to produce hard corrosion resistant Ni coatings while the inhibitor treatment yielded enhanced corrosion protection by providing a protective buffer layer between the Ni coating and the substrate.

Microstructural study of NiCrAlY electrodeposits

Pulse electrodeposition technique was used to co-deposit Ni with NiCrAlY powder on Ni-based high temperature alloy substrate. Pure nickel anode was immersed in a standard Watt’s bath containing fine particles of NiCrAlY powder that were entrapped during electrodeposition to form a NiCrAlY electrodeposit on cathode specimen surface. Diffusion heat treatment was conducted in argon at ≈1150°C and the samples were oxidized at 1000°C in air. Scanning and transmission electron microscopy coupled with energy dispersive X-ray spectroscopy and X-ray diffraction were used to characterize the microstructure and identify the phases. Pulse electrodeposition resulted in dense and fine-grained deposit with the formation of Al2O3 oxide at the coating surface after exposure to high temperature.