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    Chemical synthesis of single-layer graphene by using ball milling compared with NaBH4 and hydroquinone reductants
    (INST ENGINEERING TECHNOLOGY-IET, 2018) Niftaliyeva, Aysel; Pehlivan, Erol; Polat, Safa; Avci, Ahmet
    Graphene materials especially single-layer graphene have been identified as a new generation of nanomaterials having various potential applications in material industries. However, the synthesis procedure of single-layer graphene to improve its quality, size and amount has been still under research for commercial applications. The graphene oxide (GO) is synthesised from graphite by Hummer's spontaneous approach which is the most suitable reaction for a large-scale production. For the single-layer graphene, in this work, GO was exfoliated by using a ball milling in an inert atmosphere. Owing to using ball milling as intermediate treatment degreased oxygen functional groups and number of layers, it facilitates to synthesise graphene. Sodium borohydride (NaBH4) and hydroquinone were used as a reductant for the chemical conversion of the exfoliated GO to graphene. The results showed that due to the strong reduction feature, both reducing agents can be applied in the graphene production. As a preferred reductant, hydroquinone can be successfully applied for the synthesis of the single-layer graphene compared to NaBH4. The obtained graphene particles by two different chemicals were characterised by various analytical techniques. The big difference in the structure of GO and graphene was observed in transmission electron microscope analysis.
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    Fatigue behavior of composite to aluminum single lap joints reinforced with graphene doped nylon 66 nanofibers
    (ELSEVIER SCI LTD, 2018) Polat, Safa; Avci, Ahmet; Ekrem, Mursel
    It is an important approach to prevent the damage mechanisms that cause sudden fractures during fatigue loading in bonding joints by modifying the matrix with nanostructured materials. The aim of this study is to examine the effect of graphene nanoplates (GNPs) doped nylon 66 (N66) nanofiber mats reinforcement on the fatigue life of composite to aluminum single lap joint. For this purpose, 1 wt%, 3 wt% and 5 wt% GNPs doped N66 nanofibers were produced by electrospinning method. The morphological characteristics, chemical bond structures and % crystallinity of these nanofiber mats was investigated by SEM, TEM, FTIR, DSC analysis. The fatigue tests of the bonding joints with single axis periodic cycle loading were performed at five different load levels as 20%, 30%, 40%, 50% and 60% of the maximum shear strength of each samples. Fatigue life of bonding joints was assessed by S-N curves plotted according to the fatigue results. Damage mechanisms of fractured surface in the bonding joints were investigated with the macro and micro images. The results show that, these composite nanofiber mats have increased the fatigue life of bonding joints in all case.