Senterra r200 l

The morphology and structure of GO were characterized by AFM (‘E-Sweep’ of the NanoNavi-Series) and Raman spectroscopy (Senterra R200-L, Bruker). Phase and elemental analyses were performed by XRD (D8 Advance, Bruker) and XPS (AXIS Ultra DLD, Shimadzu-Kratos). The microstructures of the film and composite were observed by SEM (FEI SIRION 200) and TEM (JEOL JEM-2100F). For compressive testing, the obtained samples were cut using a wire electrical discharging machine along the direction both parallel and perpendicular to the layered direction and were polished to cylinder shape with a height of 3.5 mm and a diameter of 2 mm. The compressive testing was conducted using a servo-hydraulic materials testing system (Zwick/Roell Z020) at room temperature at a strain rate of 1 × 10⁻⁴ s⁻¹.

We used Raman spectroscopy to characterize the defect states of graphene in the composite powders (0.8 vol.% C). Both composite powders before and after the ball-milling were probed. Micro-Raman spectroscopy (Senterra R200-L, Bruker) with an excitation wavelength of 633 nm (1.96 eV) was used. A laser beam power of 10 mW and an exposition time of 10 s was employed so as to collect sufficient Raman intensity, as the embedding of unc into metal matrix drastically reduces the carbon signal. Five measurements were taken in each composite powder (i.e., before and after ball-milling) from different areas. The Raman peaks (D, G, and D^’) were fitted with Lorentzian functions with the commercial software Origin 8, and we denote their intensities (height) as I(D), I(G), and I(D’). The I(D)/I(G) ratio was used to estimate the domain size of graphene, following the theory and equation described by our previous work⁴⁴ . For the graphene we used, the crystalline domain size was found to decrease from 1.3 nm to 1.1 nm after ball milling. Since our unc has an average size of ~2.5 nm, this suggests that a large fraction of unc is amorphous.

The morphology and size of as-synthesized Fe₃O₄@graphene NPs were observed with a TEM (Tecnai G2 Spirit Biotwin, FEI) operating at 120 KV. XRD patterns were collected by an X-ray polycrystalline diffractometer (D8 Advance, Bruker). Raman spectra were collected by a dispersive Raman microscope (Senterra R200-L, Bruker). XPS spectra were measured by an X-ray photoelectron spectrometer (AXIS, UltraDLD). Magnetization curves of the Fe₃O₄@graphene NPs were measured by a physical property measurement system (PPMS-9T, Quantum Design). Thermal conductivity of paraffin and paraffin-Fe₃O₄@graphene composite samples was measured by a transient hot bridge analyzer (Linseis THB-1). Optical spectra were measured by a UV-Vis spectrometer (Lambda 950, PerkinElmer) equipped with an integrating sphere. TGA and DSC analysis was conducted in a differential scanning calorimeter (Netzsch 204 F1) and a thermo gravimetric analyzer (Pyris 1) under nitrogen atmosphere with a heating and cooling rate of 5 °C min⁻¹, respectively.

Zeta potential measurements of the dispersed nanocarbons and metal flakes in aqueous solutions were conducted by Zeta potential analyzer (Brookhaven ZetaPlus) and ten data for each sample were measured. Scanning electron microscopy (SEM, Quanta 250, FEI) was used to characterize the morphology of the composite powders. Biology Transmission Electron Microscope (TEM, Tecnai G2 spirit Biotwin, FEI) and Raman spectroscopy (Senterra R200-L, Bruker Optics) with an Ar⁺ laser wavelength of 532 nm were applied to analyze the morphology and defects of dispersed and adsorbed SWCNT, respectively.