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The study of the effects of flavanoid derivatives as corrosion inhibitors for zinc and aluminium metals in sulphuric and hydrochlorine acids
Full text linkMSc (Chemistry)Departrment of ChemistryIn this study, the corrosion inhibition potentials of three flavonoid derivatives namely Naringenin (NRNG), Morin hydrate (MNHD) and 6-Hydroxyflavone (6-HFN) for zinc and aluminium metals was investigated using gravimetric analysis, electrochemistry, and surface characterization techniques in three aggressive acidic environments of 0.5 M and 1.5 M hydrochloric acid and 1.5 M sulphuric acid at a temperature range from 30 – 60°C. All the three inhibitors managed to inhibit the corrosion of zinc and aluminium metals from the acid attack by adsorption of their molecules onto the metals surface. The adsorption of the inhibitors onto the zinc metals was found to be both physisorption and chemisorption. However, in the presence of aluminium metals, the inhibitors were found to adsorb through physisorption only. The experimental data obtained from gravimetric analysis obeys Langmuir adsorption isotherms. Atomic Absorption Spectroscopy (AAS) was used to find the concentration of the metal ions leached into the solution after gravimetric analysis in the absence and presence of the inhibitors. The lowest concentration was obtained when the three inhibitors were used in the presence of sulphuric acid in zinc, which suggest that the inhibitors managed to inhibit the metal dissolution to a much greater extent as compared to when the acid was used alone. Fourier Transform Infrared Spectroscopy (FTIR) was utilised to understand the functional groups that disappeared or formed during the adsorption process of the inhibitor’s molecules on the metals surface. The Ar - OH functional group was the worst affected since only 6-hydroxyflavone was the only inhibitor to retain it after gravimetric analysis in the presence of hydrochloric acid. The C=C functional group of the aromatic ring was retained by all the inhibitors in all the metals studied. A two-dimensional (2D) and three-dimensional (3D) microscopy was also used to study the extent to which the metals were damaged by the acid and the type of corrosion that resulted thereafter, in the absence and presence of the three inhibitors. The results obtained from Potentiodynamic Polarization (PDP) indicated that the compounds are mixed-type inhibitors. The results from PDP also indicated that the use of three flavonoid derivatives compounds as corrosion inhibitors managed to significantly reduce the corrosion current densities for the cathodic and anodic half reactions, which indicate that, the dissolution and cathodic reduction of the hydrogen ions were inhibited. The order of the inhibition efficiency at 1.8x10-3 M for the maximum temperature (60°C) was 6-HFN (86.54 and 77.24 %) ˃ MNHD (81.37 and 73.30 %) ˃ NRNG (78.07 and 72.47 %) for zinc metals in sulphuric acid and hydrochloric acid, and NRNG (91.48) ˃ 6-HFN (90.12) ˃ MNHD (81.59) for aluminium metals in hydrochloric acid. In Electrochemical Impedance Spectroscopy (EIS), the charge transfer resistance increased with an increase in inhibitors concentration, while the constant phase element was found to decrease with an increase in inhibitors concentration. This observation is an indication that the inhibitors adsorbed onto the metal surface
and formed a film layer protecting the metal from corrosion. The percentage inhibition efficiency of Electrochemical Impedance Spectroscopy (%IEEIS) was found to correlate with those obtained from PDP, AAS and gravimetric measurements.NR
Investigation of UV-Induced geometrical isomerisation of helichrysum kraussii extracts and their inhibition potentials for acid corrosion of mild steel, zinc and aluminium
No full textMNPDPCDepartment of ChemistryCorrosion is the destruction of material due to chemical or electrochemical processes. Corrosion can be controlled by using corrosion inhibitors. Recently, plants have been explored as possible green corrosion inhibitors because they are environmentally friendly, easy to dispose, easily accessible and cheaper to extract or convert to inhibitors. Plant's metabolites or chemical constituents undergo geometrical isomerisation under the influence of UV light radiation. These changes might affect the extract's ability to inhibit corrosion. In this study, the effect of the UV light radiation on the Helichrysum kraussii (H. kraussii) plant extract was investigated through comparison with the non-UV-radiated H. kraussii plant extracts for mild steel, zinc and aluminium metal corrosion in 1.0 M HCl and H2SO4 at 30-60 ℃. This investigation was made possible by using techniques such as gravimetric weight loss analysis, Liquid chromatography-mass spectrometry (LCMS), Fourier transform infrared spectroscopy (FTIR), electrochemical analysis, contact angle, Scanning electron microscopy (SEM), Energy dispersive spectroscopy (EDS), and quantum molecular dynamic simulations. LCMS confirmed the formation of geometrical isomerisation when the H.kraussii extract was exposed to UV radiation. From the gravimetric analysis data, the corrosion rate (CR) was calculated and found to be decreasing with an increase in the concentration of the inhibitor extracts, with the highest concentration (1500ppm) at 30 ℃ having a corrosion rate of 3.92x10-4 and 1.70x10-4 g.cm2.h-1 for UV-radiated and non-radiated extract in 1.0 M H2SO4 for mild steel, respectively. Similar trends have been observed for the zinc and aluminium metals in HCl and H2SO4 solutions. The percentage inhibition efficiency (%IE) was found to increase with the increase in the two extract concentrations in the acidic media. In the presence of non-radiated extract, the % IE for mild steel in 1.0 M HCl was found to be 99.601% for 1500 ppm at 30 ℃. However, in the presence of UV-radiated H. kraussii extract, it was found to be 98.007%. The activation energy (Ea) values were found to increase with an increase in the concentration of both extract inhibitors. This suggests that the corrosion inhibition process of the three studied metals is through physisorption. The values of the change in Gibbs free energy (Δ) for both the extracts were found to be negative, indicating that the reaction between the inhibitor molecules and the metal surface was spontaneous. From the electrochemical impedance spectroscopy (EIS), the semi-circle diameter for mild steel and zinc metals and the circle diameter for the aluminium metal in the Nyquist plot was found to increase with an increase in the inhibitor concentration. The charge transfer resistance (Rct) values were found to increase with an increase in the extract inhibitor concentrations. For mild steel in 1.0 M H2SO4, the Rct values
ranged between 8.751-26.52 Ωm2 and 10.20-26.41 Ωm2 for the UV-radiated and non-radiated extract, respectively. The introduction of the two extract inhibitors in the HCl and H2SO4 solution managed to reduce the corrosion current density (icorr) for mild steel, zinc and aluminium metals. The icorr values for mild steel in 1.0 M H2SO4 ranged between 397.202 -1395.884 mA.cm-2 and 343.358 – 1572.977 mA.cm-2 for the UV-radiated and non-radiated extracts. FTIR performed on the coated mild steel, zinc, and aluminium surface showed functional groups such as C=C, O-H, and N-H for both extracts, which are known to be functional groups of the most effective corrosion inhibitors. Contact angles were used to study the surface morphology of the metals, and it was observed that introducing the extract inhibitors in aggressive solutions changed the metal's surface from hydrophilic to hydrophobic surface. Computational simulations have been studied to demonstrate the most conceivable adsorption arrangements or configurations between the metal surface and the inhibitor. Parallel configuration of the inhibitor molecules on the metal surface was found to be the best configuration, giving high adsorption energy. SEM showed that introducing the two extract inhibitors in the acidic solution protected the metal surface from developing deep pits caused by the acid attack. EDS showed that corrosion took place on the metal surface and that the extract inhibitors were adsorbed on the metal surface based on the functional groups such as oxygen, calcium and nitrogen obtained on the metal surface. X-ray diffraction showed the presence of oxide on the metal surface confirming that the corrosion process took place. Based on the results obtained, it was found that the non-radiated H. kraussii extract was found to be more effective in inhibiting the corrosion of mild steel, zinc and aluminium metals in 1.0 M HCl and H2SO4 than the UV-radiated H. kraussii extract. This suggests that the UV radiation decreases the inhibition efficiency of the H. kraussii extract as an efficient corrosion inhibitor for mild steel, zinc and aluminium metals in 1.0 M HCl and H2SO4. Therefore, it is recommended that the H. kraussii extract be used only as a corrosion inhibitor for mild steel, zinc, and aluminium metals in 1.0 M HCl and H2SO4 in its original state without being exposed to UV radiation
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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