Department of Mechanical Engineering

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Author: search.filters.author.Makanjuola OkiSubject: search.filters.subject.T

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    Corrosion rates of green novel hybrid conversion coating on aluminium 6061
    (Elsevier, 2020-08-19) Makanjuola Oki; A.A. Adediran; Peter Pelumi Ikubanni; O.S. Adesina; Adekunle Akanni Adeleke; S.A. Akintola; F. Edoziuno; A. Aleem
    The use of chromate conversion coatings have been limited by several protocols as a result of their carcinogenicity and toxicity towards humans and the environment. Searches are ongoing for chromate replacement in coating baths and processes. This paper describes the comparison among the corrosion rates of a novel hybrid conversion coating derived from water extracts of hibiscus sabdariffa calyx in conjunction with ammonium molybdate, a molybdate conversion coating and the so-called chromate conversion coating. Potentiodynamic polarization measurement in 3.5 ​wt% sodium chloride solution was employed in ranking the coatings as sabdariffa molybdate being more corrosion resistant than chromate, which in turn out performed molybdate.
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    Influence of temperature on the chemical compositions and microstructural changes of ash formed from palm kernel shell
    (Elsevier, 2020-09-30) Peter Pelumi Ikubanni; Makanjuola Oki; Adekunle Akanni Adeleke; Adediran, A.A; O.S. Adesina
    This study investigated the characteristics of raw palm kernel shell (raw PKS) and the influence of temperature variation on palm kernel shell ash (PKSA). The PKSA was obtained under different temperature regimes of 900, 1000, and 1100°C. The characterization of the samples was carried out using X-ray Fluorescence (XRF), Fourier Transform Infrared (FTIR), X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) with attached Energy Dispersive X-ray (EDX) facilities. The results showed that moisture and ash contents and the density of raw PKS were 6.56%, 8.86%, and 745 ​kg/m3, respectively. The colour of the pulverized PKS was dark brown, as observed by visual examination based on standard colour gradation. This colour transformed into various shades of brown when PKS was subjected to different temperature regimes to form PKSA. The XRF analysis showed that silica is the main constituent of the raw PKS and PKSA samples. Silica content in the PKSA increased with the rise in the heating temperature. The FTIR and EDX spectra confirmed the predominance of silicon compounds with functional groups associated with silanol and siloxane. Also, XRD analysis revealed that the silica contents in the samples are quartz, while SEM examinations indicated that temperature increases during processing influenced the microstructure through the reduction of pore concentration in the samples. The silica obtained from the PKSA would find applications in metal matrix composites as partial reinforcing materials.
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    Scanning and transmission electron microscopy examinations of composite hybrid chromate and chromate phosphate conversion coatings exposed in hot 100% relative humidity environments
    (Elsevier, 2023-07-20) Peter Pelumi Ikubanni; Makanjuola Oki; Adesoji A. Adediran; Sarah A. Akintola; Adekunle Akanni Adeleke
    Conversion coatings are sine qua non in the finishing of aluminium alloys. They may be put into service without coating of paints. However, for aesthetics in architectural applications, paint overcoat is common. Chromate phosphate coatings are relatively less toxic than chromate which gained the pride of place until recently. Thus, aluminium specimens coated with hybrid chromate/phosphate conversion coatings have been subjected to 100% relative humidity for 480 h at 313K in comparison to chromate coatings and bare aluminium. Scanning electron microscopy examination revealed that initial dried river bed morphologies on coated specimens were obliterated. The friable outer coatings collapsed into the cracks/environment leaving a relatively smooth surface after exposure. Additionally, transmission electron microscopy of sections before and after exposure revealed similar texture and morphological striations nearly parallel to each other throughout the length of the coatings to the metal/coating interface. These were not disrupted as well as the metal/coating interface which remained relatively smooth with no visible corrosion products after exposure. Thus, the coatings formed effective barrier between the substrate and the relatively harsh environment. From EDS, elemental compositions were the same albeit, spectral intensities remained relatively constant after humidity exposure regimes. The coatings are made up of either Cr, O and Al for chromate and Cr, P, O and Al for chromate/phosphate. At deliberately breached regions, the coatings prevented spread of corrosion and paint delamination over the substrates. On the other hand, bare aluminium was decorated with mounds of hydrated aluminium oxide/hydroxide after exposure as revealed in the SEM/TEM.