Study of the histidine complex of uranium(IV): synthesis, spectrophotometric, magnetic and electrochemical properties

We synthesized the novel histidine complex of uranium(IV). A 1:3 mole ratio was found between metal and ligand by the mole ratio method, while –NH2 and –COO– groups of histidine behave as coordinating sites. The IR spectra confirmed the lone pair donating or coordinating sites. The elemental analysis confirmed the stoichiometry. The bathochromic shift with an increase in the optical density in the UV-Visible range indicated that the compound and its central metal ion hold uniform electronic charge distribution. The electrochemical results indicated a quasi-reversible (neither completely reversible nor completely irreversible) oxidation of the complex to its uranium(V) product at the platinum working electrode. The quasi-reversible process shows a comparatively slow electron transfer (ET) rate with the heterogeneous electron transfer rate constant ‘ks’ (3.4 ×  10–4 cm s-1) at 50 mV s-1 and 305 ± 0.5 K. The kinetics such as diffusion and charge transfer lead the reaction with an ECE (electrochemical–chemical–electrochemical) mechanism. The thermodynamic parameters of activation such as ΔH*; 4.257 kJ mol–1, ΔS*; -2.519 × 10–3 J mol–1 K–1 and ΔG* 4.26 kJ mol–1 helped to propose an associative mechanism of the electron transfer at the platinum working electrode.                     KEY WORDS: Uranium, Histidine, Spectroscopy, Electrochemistry, Kinetics   Bull. Chem. Soc. Ethiop. 2020, 34(3), 557-569.  DOI: https://dx.doi.org/10.4314/bcse.v34i3.1

Life assessment prognostic modelling for multi-layered coating systems using a multidisciplinary approach

The multi-disciplinary approach has been adopted to model the formation and propagation of blistering effect for evaluation of useful coating life in the multi-layered coating-substrate system. Prognostic model of de-bonding driving force has been formulated as a function of material science, solid mechanics and fracture mechanics properties to estimate critical, safe and fail conditions of the coating-substrate system. The blister growth velocity rate is also included in the developed model to estimate the blister propagation as a function of diffusion-induced stress and residual stress. The proposed prognostic modelling for the formation and propagation of blistering effect are combined to form an assessment model for evaluation of useful coating life of the multi-layered coating-substrate system and validated through experimental observation

Fabrication and characterisation of electrodeposited and magnetron sputtered thin films

The MnO-Zn thin films were fabricated by radio frequency (RF) magnetron sputtering and compared with pulse electrodeposition (PED) Zn thin films, doped with MnO and ZrO nanoparticles. Surface morphology, structural properties, chemical composition and corrosion resistance of these coatings were investigated by using Scanning Electron Microscopic (SEM), X-ray Diffraction (XRD), Energy-dispersive X-ray Spectroscopy (EDS), 3-D Scanning Interferometry and environmental chamber. Surface morphology and degree of crystallinity have different behaviour for differen t deposi tion method. Pulse coated films have polycrystalline structure with high surface roughness (Ra) whereas sputtered films are mono-crystalline with reduced roughness (Ra). Corrosion tests of both RF sputter and PED films revealed that the distribution of corrosion products formed on the surface of sputter films were not severe in extent as in case of electrodeposited coatings. Results showed that the doping of ZrO nano-sized particles in Zn matrix and Mn-Zn composite films significantly improved the corrosion resistance of PED thin films

Fabrication and characterisation of electrodeposited and magnertron-sputtered thin films

The MnO–Zn thin films were fabricated by radio frequency (RF) magnetron sputtering and compared with pulse electrodeposition (PED) Zn thin films, doped with MnO and ZrO nanoparticles. Surface morphology, structural properties, chemical composition and corrosion resistance of these coatings were investigated by using scanning electron microscopy, X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy, 3-D scanning interferometry and environmental chamber. Surface morphology and degree of crystallinity have different behaviours for different deposition methods. Pulse-coated films have polycrystalline structure with high surface roughness (Ra), whereas sputtered films are monocrystalline with reduced roughness (Ra). Corrosion tests of both RF sputter and PED films revealed that the distribution of corrosion products formed on the surface of sputter films were not severe in extent as in case of electrodeposited coatings. Results showed that the doping of ZrO nano-sized particles in Zn matrix and Mn–Zn composite films significantly improved the corrosion resistance of PED thin films. Keywords: Corrosion resistance, electro-deposition, magnetron sputtering, surface analysis, thin films

Corrosion measurement device [PATENT]

This is a novel predictive and prognostic remote probing system invention to monitor corrosion of coating and subsurface. Coatings can be both metallic and non-metallic. The EIS measurement is resistant to interference and has a high corrosion resolution which produces stable and reliable results. Protective properties of a coating can be learned from an impedance spectroscopy obtained via the measurement that reflects changes in the coating and at the interface of coating-substrate system

A model for cathodic blister growth in coating degradation using mesomechanics approach

The paper presents a novel theoretical model of blistering initiation and propagation especially useful for coating life assessment. The focus is on initially circular blisters. A two-part theoretical analysis of blistering is conducted using mesomechanics approach coupling diffusion concepts with fracture mechanics concepts. The diffusion concept is used to treat the corrosive species transport, eventually causing corrosion and blistering, while the fracture mechanics concept is used to treat the blister growth as circular crack propagation. Effects of thickness ratio and modulus ratio on blistering propagation are discussed. A simple criterion is identified which excludes the possibility of widespread blister propagation. Furthermore, a comparative study with the existing blistering models is carried out. Experiments are reported for blistering using a model coating-substrate system, chosen to allow visualisation of interface and to permit coupled (diffusion and residual) stresses in the coating over a full range of interest. The predicted limits from theoretical model are expected to be useful for the manufacturers in the design and deposition of coatings

Corrosion Mechanisms of 304L NAG in Boiling 9M HNO3 Containing Cr (VI) IONS

In this research, mechanisms of end grain corrosion of 304L NAG tubes in boiling 9M HNO3-containing Cr (VI) ions are reported to manage the corrosion of nuclear fuel reprocessing plant components sustainably. Specific heat treatments were applied to as-received specimens to produce phosphorus and/or sulphur intergranular segregation. End grain corrosion on heat-treated specimens and the effect of Cr (VI) concentration on 304L NAG tube [as received] were investigated. It has been reported that an increase in Cr (VI) ions leads to the acceleration of end grain corrosion due to high electrochemical potential. After systematic heat treatments of the 304L NAG specimens, it is concluded that the primary causes of heat-induced end grain corrosion are phosphorus or sulphur segregation to the grain boundaries. The key findings of this research are highly significant in terms of understanding the corrosion mechanisms and controlling the end grain corrosion of NAG steel in boiling HNO3 environment. This research work will help reduce power plant maintenance costs sustainably and will have significant impact on the delivery of long-term, clean, secure and tenable energy