No abstract

Infiltration and deposition of CaSO 4 in thermal barrier coatings (TBC) in addition to the CMAS deposits was found in many occasions on real aviation engines. The source and role of CaSO 4 on the degradation of TBC is not well understood. CaSO 4 containing CMAS was synthesized and a systematic study of its role on the CMAS infiltration behavior in EB-PVD 7YSZ is presented in this work. Its influence on the melting and crystallization behavior of CMAS was studied with the help of differential scanning calorimetry. The decomposition of CaSO 4 into CaO and SO 3 was observed at 1050°C in laboratory air under the presence of CMAS using mass spectroscopy and in situ high-temperature XRD. The same amount of CaO is brought into the CMAS system by means of adding CaCO 3 , which will eventually decompose into CaO and CO 2 at 700°C. CMAS infiltration tests were carried out at different temperatures with and without CaSO 4 /CaCO 3 and the results demonstrate that the sulfur has no direct effect on the aggressiveness of the anhydrite containing CMAS with regard to its infiltration behavior in EB-PVD 7YSZ at high temperatures. The extra amount of calcia added to CMAS that is introduced by the evaporating species is responsible for enhanced infiltration of the deposits into the TBC.

No abstract

The coupling reactions of polyethylene glycol (PEG) with two different nano-carbonaceous materials, graphene oxide (GO) and expanded graphene oxide (EGO), were achieved by amide bond formations. These reactions yielded PEGylated graphene oxides, GO-PEG and EGO-PEG. Whilst presence of the newly formed amide links (NH-CO) were confirmed by FTIR stretches observed at 1732 cm−1 and 1712 cm−1, the associated Raman D- and G-bands resonated at 1311/1318 cm−1 and 1584/1595 cm−1 had shown the carbonaceous structures in both PEGylated products remain unchanged. Whilst SEM images revealed the nano-sheet structures in all the GO derivatives (GO/EGO and GO-PEG/EGO-PEG), TEM images clearly showed the nano-structures of both GO-PEG and EGO-PEG had undergone significant morphological changes from their starting materials after the PEGylated processes. The successful PEGylations were also indicated by the change of pH values measured in the starting GO/EGO (pH 2.6–3.3) and the PEGylated GO-PEG/EGO-PEG (pH 6.6–6.9) products. Initial antifungal activities of selective metallic nanomaterials (ZnO and Cu) and the four GO derivatives were screened against Candida albicans using the in vitro cut-well method. Whilst the haemocytometer count indicated GO-PEG and copper nanoparticles (CuNPs) exhibited the best antifungal effects, the corresponding SEM images showed C. albicans had, respectively, undergone extensive shrinkage and porosity deformations. Synergistic antifungal effects all GO derivatives in various ratio of CuNPs combinations were determined by assessing C. albicans viabilities using broth dilution assays. The best synergistic effects were observed when a 30:70 ratio of GO/GO-PEG combined with CuNPs, where MIC50 185–225 μm/mL were recorded. Moreover, the decreased antifungal activities observed in EGO and EGO-PEG may be explained by their poor colloidal stability with increasing nanoparticle concentrations.