研究目的
To fabricate highly homogenized reduced graphene oxide/alumina metacomposites with low percolation threshold and adjustable negative permittivity using freeze-drying and spark plasma sintering methods.
研究成果
Freeze-drying effectively improved the dispersion of GO in Al2O3, leading to highly homogeneous RGO/Al2O3 metacomposites with a low percolation threshold of 14.31 wt% and adjustable negative permittivity. Negative permittivity was achieved at lower RGO contents compared to dry grinding methods, with transitions from negative to positive permittivity at specific frequencies due to LC resonance. This method shows promise for fabricating metacomposites with tailored electromagnetic properties.
研究不足
The study is limited to specific GO and Al2O3 materials and sintering conditions; scalability and cost of freeze-drying and SPS methods may be constraints. Further optimization for industrial applications and comparison with other dispersion methods could be explored.
1：Experimental Design and Method Selection:
The study used freeze-drying to improve dispersion of GO in Al2O3 powders, followed by spark plasma sintering to reduce GO to RGO and form metacomposites. This was compared to previous dry grinding methods.
2：Sample Selection and Data Sources:
GO sheets (1–5 μm, thickness 0.8–1.2 nm, purity >99%) and Al2O3 powders (purity 99.99%, particle size <30 nm) were purchased. Distilled water was used for all experiments.
3：8–2 nm, purity >99%) and Al2O3 powders (purity 99%, particle size <30 nm) were purchased. Distilled water was used for all experiments. List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: Equipment includes ultrasonic treatment apparatus, liquid nitrogen for freezing, freeze-dryer, spark plasma sintering system (Dr Sinter 1020 SPS), FESEM (Hitachi SU-70), XRD (Rigaku Dmax-rc), Raman spectrometer, and Precision Impedance Analyzer (Agilent E4991A) with 16453A dielectric test fixture.
4：Experimental Procedures and Operational Workflow:
GO was dispersed in distilled water via ultrasonic treatment for 5 hours. Al2O3 powders were added, ultrasonically treated for 1 hour, frozen with liquid nitrogen, and freeze-dried to produce composite powders. These were sintered by SPS at 1550°C with a heating rate of 150°C/min for 5 min in vacuum (≤6 Pa) under 50 MPa pressure. Samples were polished to 15 mm × 2 mm size.
5：Data Analysis Methods:
Microstructures were analyzed using FESEM, phase composition by XRD, structural defects by Raman spectroscopy. Dielectric properties (ε′, ε′′, tan δ, σac, Z′′) were measured from 10 MHz to 1 GHz using formulas based on capacitance, resistance, and reactance measurements.
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Field Emission Scanning Electron Microscope
SU-70
Hitachi
Used to observe microstructures of composite powders and metacomposites.
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X-ray Diffractometer
Dmax-rc
Rigaku
Used to characterize phase composition of metacomposites.
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Precision Impedance Analyzer
E4991A
Agilent
Used to analyze dielectric properties of metacomposites.
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Dielectric Test Fixture
16453A
Agilent
Used with the impedance analyzer for dielectric property measurements.
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Graphene Oxide
Sheet size 1–5 μm, thickness 0.8–1.2 nm
Nanjing JCNANO. INC
Used as a conductive filler to fabricate metacomposites with negative permittivity.
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Al2O3 Powders
Particle size <30 nm
Hangzhou Wanjing New Material Co. Ltd
Used as the matrix material in the metacomposites.
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Spark Plasma Sintering System
Dr Sinter 1020 SPS
Sumitomo Coal Mining Co.
Used for sintering the composite powders to form metacomposites.
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Raman Spectrometer
Incident radiation 532 nm
Used to investigate structural defects of metacomposites.
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