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Spark plasma sintering of alumina nanopowders produced by electrical explosion of wires
© An et al. 2015
Received: 31 July 2015
Accepted: 27 September 2015
Published: 6 October 2015
Alumina nanopowders produced by electrical explosion of wires were sintered using the spark plasma sintering technique. The results of XRD analysis show that the main phase in the compacted nanopowders is α-Al2O3. According to the SEM observations, the sintered alumina nanopowder consists of micron-sized faceted grains and nano-sized necked grains. The increase in sintering temperature resulted in a higher density of the sintered powders: from 78.44 to 98.21 % of theoretical density.
For ceramic technologies, it is important to obtain ultrafine microstructure that ensures improved physical and physic-mechanical properties: hardness, wear resistance, mechanical and optical properties. Over the last decade, spark plasma sintering has become a powerful technique to produce high quality ceramics including nanostructured ceramics (Bordia and Olevsky 2010; Angerer et al. 2006; Suárez et al. 2013; Monnier et al. 2015; Huang and Nayak 2014). Alumina has attracted great interest and is one of the most used materials in various applications. These materials display excellent properties: high strength, good chemical durability and excellent electrical insulating properties. They can be used as translucent ceramics (Wei 2005; Mao et al. 2008), thermal insulation (Xu et al. 2015), catalysts (Nartova et al. 2015; Gündüz and Dogu 2015), biomedical implant (Deville et al. 2003) etc.
In this work, spark plasma sintering (SPS) is considered as a promising fabrication way. The SPS technique has some advantages with respect to usual sintering methods: higher heating rates and local temperature gradients, particular local temperature distributions. The problem to be solved in the study is how the SPS parameters (pressure, temperature) are related to the product characteristics (size, morphology, porosity). One of the interesting methods for fabrication of alumina nanopowders is electrical explosion of wires (Yavorovskii 1996). The objective of this work was to study processes of densification during spark plasma sintering of alumina nanopowders produced by electrical explosion of wires (EEW) in the gaseous mixture of argon and oxygen at a pressure of 1.5 atm. The authors wanted also to explore polymorph transformations during spark plasma sintering of alumina nanopowders.
Results and discussion
This research work consisted of four main stages: fabrication of alumina nanopowders by electrical explosion of aluminum wires, characterization of as-prepared nanopowders, spark plasma sintering of alumina nanopowders and their characterization. The specific feature of these experiments is the use of alumina nanopowders produced by electrical explosion of wires.
The method of electrical explosion of aluminum wires in the mixture of argon and oxygen was used for the preparation of alumina nanopowders. For this work aluminum wires having the diameter of 0.35 mm were employed. The wire (l = 65 mm) was input in the explosion chamber using a special feeding mechanism. The following parameters of electrical explosion were used: working gas pressure—1.5 atm, voltage—24 kV, capacity—2.3 µF, and inductance—0.72 µH. The BET analysis results showed that the specific surface area of as-prepared nanopowder was 20 m2/g.
Densification parameters of alumina nanopowder sintered at different temperatures by the SPS technique
Absolute density ρ, g/cm3
Relative density ρ, %
Alumina nanopowders were sintered using the spark plasma sintering technique. The samples were sintered at a pressure of 40 MPa and a temperature of 1400, 1500 and 1600 °C. The SPS processes support essential the densification processes. The increase in the sintering temperature leads to a higher density of sintered alumina nanopowder: the relative density increased from 78.44 to 98.21 %. Sintering resulted in polymorph transformation of the initial alumina nanopowder (a mixture of γ-Al2O3 and δ-Al2O3) into pure α-Al2O3.
Nanopowders produced by EEW reveal higher chemical reactivity (An et al. 2010), unusual physicochemical properties (An et al. 2011), can be used for fabrication of nanostructured compounds (Bozheyev et al. 2014) and for other applications (An and Irtegov 2014). In the present work, alumina nanopowders produced by electrical explosion of alumina wires were used in the experiments of spark plasma sintering.
A Shimadzu 7000S X-ray diffractometer with CuKα radiation (λ = 1.54 Å) was used for X-ray phase and structural analysis. A JSM-7500FA scanning electron microscope (JEOL, Japan) was used to observe the morphology and structure of the synthesized nanopowders.
VA carried out the main conception and the main SPS experiments, participated in the analysis and interpretation of data. AK carried the main SPS experiments and participated in the analysis and interpretation of data. CdI participated in the analysis and interpretation of data and have given final approval of the version to be published. All authors read and approved the final manuscript.
This work was supported under the state assignment of the Ministry of Education and Science of Russia for 2014–2016 (research work No. 361). The authors would like to thank the Nano-Center at Tomsk Polytechnic University for the XRD and TEM analyses.
Compliance with ethical guidelines
Competing interests The authors declare that they have no competing interests.
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