Graphene Nanosheets (GNs) addition on the Palm Oil Fuel Ash (POFA) based geopolymer with KOH activator

Graphene Nanosheets (GNs) have been successfully added to the palm oil fuel ash (POFA) based geopolymer with KOH activator to improve the geopolymer compressive strength. The graphene was synthesized using turbulence assisted shear exfoliation (TASE) method and identified using Raman spectroscopy. The influence of concentrations and weight percent of graphene against the compressive strength, porosity, and morphological properties were investigated. The crystallinity phases of geopolymer and graphene were also identified using XRD. Raman spectroscopy revealed that graphene produced by TASE method had ≥ 3 layers (graphene nanosheets, GNs). Furthermore, Raman maping constructed by the intensity D band showed the graphene had different atomic arrangements at the edge (armchair and zigzag). The compressive strength and the porosity tests showed that increasing the concentration and the weight percent of graphene increased the compressive strength and reduced the porosity. The highest compressive strength and the lowest porosity (10.8 MPa and 5.92%, respectively) were exhibited by the geopolymer synthesized using 0.7 wt% graphene with concentrations of 30 mg/ml. The SEM micrographs indicated that the graphene reduced the porosity of geopolymers with a pores fulfilling mechanism due to of very small of graphene nanosheets size (~60 - ~80 nm)

Formation kinetics of sol-gel derived LiFePO4 olivine analyzed by reliable non-isothermal approach

The formation kinetics of LiFePO4 Olivine synthesized through sol-gel route has been studied by non-isothermal approach. LiFePO4 precursors were prepared by mixing lithium dihydrogen phosphate (LiH2PO4) and iron (III) citrate (C6H5FeO7) and subsequently calcined in an Argon atmosphere at temperatures ranged from of 300–900 °C to form LiFePO4 products. Thermal behaviors of calcination process were analyzed by thermogravimetry (TGA) and differential scanning calorimetry (DSC) simultaneously, while the mineralogical properties of LiFePO4 were characterized using X-ray diffractometer (XRD). The kinetic parameters were determined by Ozawa–Flynn–Wall (OFW), Kissinger, and Kissinger-Akahira-Sunose (KAS) methods, and the reaction mechanism model was evaluated by Coats–Redfern approach. The results indicated that the reaction model of LiFePO4 formation agreed with the three-dimensional diffusion mechanism. The temperature had an essential role in the synthesis of LiFePO4. The optimum calcination temperature was 700 °C where this condition produced LiFePO4 Olivine with high degree of crystallinity, better lattice parameters and phase purity