The corrosion resistance of zinc-nickel composite coatings

Purpose: The aim of this work was to estimate the corrosion resistance of composite Zn+Ni and (Ni-Zn+Ni)/Zn coatings by salt spray test, electrochemical methods and grazing incidence X-ray diffraction (GIXD) method. Design/methodology/approach: The corrosion resistance properties of zinc-nickel coatings in 5% NaCl solution were investigated by salt spray test in 5% NaCl solution and electrochemical methods. Using Stern method the corrosion potential - Ecorr, corrosion current density - icorr, and polarization resistance - Rp. have been determined as a measure of corrosion resistance. Phase composition of the corrosion products was determined by X-ray diffraction using Bragg-Brentano and grazing incidence X-ray diffraction (GIXD) methods. Findings: The corrosion resistance of zinc-nickel coatings is dependent on Ni content and it grows with the increase in Ni percentage in the coatings. The higher corrosion resistance could be attributed to the presence of intermetallic Ni2Zn11 phase. The maximum protective ability is reached for the coatings above 40% Ni, where the content of this phase is the highest. The results of salt spray test exhibit the appearance of white rust corrosion, which is characteristic for zinc oxidation process. The main component of corrosion products was Zn5(OH)8Cl2ּ H2O phase. The products related to the nickel or steel substrate corrosion process were not found. The application of the GIXD technique has allowed to determine the changes in the phase composition of the corrosion products in the zinc and zinc-nickel coatings versus the penetration depth of the X-ray radiation. The presence of corrosion products on the electrode surface results in further improve in their protective ability and the limiting of the corrosion processes

Nanoniejednorodności materiałów a efekt małokątowego rozpraszania promieni rentgenowskich i neutronów

The presence of nanoscale heterogeneities significantly affect the physical, chemical and mechanical properties of materials. This monograph focuses on the applications of small angle X-ray (SAXS) and neutron (SANS) scattering methods for the studies of such materials. The theoretical aspects of these methods for two-phase systems — that is the scattering object as well as the surrounding medium – are given. The effect obtained from different scattering systems is described. This systems involve the particle type as well as more complex, disordered ones. Investigation possibilities of SAXS and SANS methods for metallic materials and for porous materials are presented. The following metallic materials are analyzed: — precipitation hardened alloys on the aluminum, nickel, magnesium and iron matrices, — metallic glasses, — metals hardened by inert oxidation, — metals with defect structure, — electrodeposited metals. The methods based on the scattering effect are particularly applicable in the studies of porous materials owing to their intensive scattering effect. Moreover it is difficult to test them with the use of electron microscopy methods. The scattering effects from different porous silica materials as well as porous carbonation materials are analyzed. The heterogeneous catalysts studied using the anomalous small angle X-ray scattering (ASAXS) method are given as an example of the investigations of three- -phase materials

Magnetic nanoparticles in MCM-41 type mesoporous silica

Structural phase transformations and magnetic properties of mesoporous MCM-41 template modified with iron and nickel salts were studied by nitrogen physisorption, X-ray diffraction, Mossbauer spectroscopy and transmission electron microscopy. The FeNi-oxide or the bimetallic crystal structure is formed for low and high Ni concentrations, respectively. The average size of nanoparticles is about 10 nm. About 70% of particles exist in a superparamagnetic state at room temperature