Browsing by Author "S. Kolawole"

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    UNTRADITIONAL SYNTHESIS OF BORON-CONTAINING SUPERHARD AND REFRACTORY MATERIALS - A REVIEW
    (Global journal of Engineering, Design & Technology, 2013) B. Agyei-Tuffour; E. Annan; E. R. Rwenyagila; E. Ampaw; E. Arthur; Kabiru Mustapha; S. Kolawole; W. O. Soboyejo; D. D. Radev
    Boron-containing ceramics find large application in production of superhard and high-temperature materials with application in nuclear and aerospace techniques, military industry etc. The synthesis methods are decisive for the complexity of chemical, morphological and technological properties of these materials. The traditional high-temperature synthesis methods have some disadvantages leading to inconstancy of the product composition due to the boron evaporation, degradation of the furnace materials and contamination of the products, high energy losses etc. Here we show the advantages of some untraditional synthesis methods like direct mechanical synthesis and self propagating high-temperature synthesis (SHS) in the production of titanium diboride (TiB2), zirconium diboride (ZrB2) and production of dense boron carbide (B4C) based materials. Using SEM, TEM, XRD and analytical chemical methods, it was shown that diborides of titanium and zirconium have appropriate properties for production of dense ceramic materials. Using the method of mechanically-assisted sintering high-dense B4C-based ceramic materials was obtained. It was shown that the mechanical properties of materials obtained by pressureless sintering are close or overcome the corresponding properties of boron carbide densified by the method of hot pressing. The possibility to produce B4C-based ceramics with controlled properties was also shown.
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    Untraditional synthesis of Ni-based alloys for medical application
    (ARPN Journal of Engineering and Applied Sciences, 2013-04) B. Agyei-Tuffour; E. Annan; E. R. Rwenyagila; E. Ampaw; E. Arthur; Kabiru Mustapha; S. Kolawole; W. O. Soboyejo; M. I. Marinov; D. D. Radev
    Due to the combination of excellent mechanical properties, high chemical stability and appropriate biocompatibility, the Ni-based alloys find large application in implantology and dentistry. The traditional metallurgical synthesis methods of these alloys have some difficulties leading to inconstancy of the composition, degradation of properties and escalation of the product price. Here we show how to overcome the disadvantages of the traditional methods of synthesis and production of Ni-based alloys for medical application using combination of mechanochemical and powder-metallurgical routes. The structural properties of the products were studied using SEM/TEM and XRD methods. It was shown that the mechanically assisted synthesis allows obtaining nanosized Ni-Ti alloy with mean particle size of 20-30 nm at significantly lower temperature in comparison with the traditional metallurgical high-temperature alloying. It was also shown that after 40 hours of intense mechanical treatment of the starting Ni and Ti powders, a direct synthesis of Ni-Ti alloy proceeds. The product has excellent sinterability which allows producing bodies with controlled structural properties appropriate for application in implantology. Using standard mechanical tests and structural examinations it was demonstrated that the Ni-Cr dental alloys obtained by mechanically assisted sintering and casting possess excellent mechanical, technological and aesthetic properties. These alloys are suitable as dental restoration materials and production of porcelain veneered constructions like crowns and bridges using the so called metal-to-ceramic technique.