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The dense and durable ceramics with microhardness up to 13 GPA was created on the basis of nanopowder of magnesium oxide with use of spark plasma sintering (SPS).
The creation of ceramics using nanosized powders with preservation of very small grain size is one of the areas of nanotechnology. It is known that the smaller the grain size is and the stronger the granular structure is developed, the stronger and harder ceramics is. However, the nanopowders for ceramics manufacturing contain stable agglomerates of the nanoparticles [1], which require non-standard methods of compaction, such as hot compression.
Current state of researches in the field of creation of nanoceramics with the use of different nanopowders is adequately represented in the papers [2–4] and others, including papers of the author [5–17]. At the next stage, it is advisable to study the ceramic of magnesium oxide nanopowder.
Magnesium oxide is used in the production of high-quality ceramics as an additive in raw materials, in creation of refractory fiber and materials, in paper production, as a fuel additive, in the manufacture of fungicides, in electronics and optics, for cleaning oil, in medicine and pharmaceuticals, as a filler in rubber production, as a very fine abrasive for cleaning surfaces (in particular, in electronics industry), as a protective coating for plasma displays. The aim of this study was the creation of dense and hard ceramics using the SPS and nanopowder of magnesium oxide.
Experimental conditions
The nanopowder of magnesium oxide MgO produced by Russian company "PlasmoTerm" (powders are synthesized in thermal plasma flow generated in an electrical discharge) was used in the study. Fig. 1 shows electron microscopy of this nanopowder.
The average particle size of the initial polydisperse powder was d=25 nm, and specific surface area was S=60 m2/g. Distribution of particle sizes was close to log-normal. Other properties of the powder: CAS number is 1309-48-4; purity of 99.6%; white color; spherical particle shape; explosion- and fire-safe.
The sintering of the powder was carried out using the Sinter Land Labox equipment at the Lavrentyev Institute of Hydrodynamics SB RAS by spark plasma sintering, when the pulses of electric current pass through the pre-compacted powder. In these experiments the current was up to 2 kA at a voltage of 3–4 V. The main difference between SPS and traditional pressing (consecutive compression and sintering) is bringing the pulse electric current directly to the sample that contributes to the rapid heating of the powder and preservation of its microstructural parameters in the consolidated material. The compression was carried out at maximum temperatures of 1500°С and 1600°С and at pressure of 40 MPa. The heating rate was typically 100°С/min (no holding at maximum temperature).
The microhardness of all ceramic samples was determined using PMT-3 microhardness tester. Using the electronic scanning microscope ZEISS EVO-50WDS-XVP-BU in ITAM SB RAS the chips of the ceramics after deposition of a gold layer were studied. HZG-4 diffractometer was used for roentgenography of obtained ceramics.
Results and conclusions
The diameter and thickness of obtained samples of ceramics were of 10 mm and of 1.2–1.5 mm respectively, and the density of ceramics was of 2.9 g/cm3.
Roentgenography of obtained ceramics showed that the sample is periclase (magnesium oxide) MgO (87-651) with a cubic structure, space group of Fm-3m (No. 225) and the lattice size a=4,216 Å.
Fig.2 shows scanning electron microscopy of the chip of ceramics with Tmax=1500°C. It is seen that the grain size is about 10 μm, and the dense ceramics was created using SPS. Ceramics obtained at Tmax=1600°C has a high microhardness Hv=12.4 GPa.
Thus, a dense and strong ceramics with microhardness up to 13 GPa was created on the basis of nanopowder of magnesium oxide with use of spark plasma sintering. ■
The project is supported by SB RAS (project III.23.4.1). The author expresses gratitude to A.Anisimov, V.Mali, V.Emelkin, G.Pozdnyakov and D.Korneev for help.
Current state of researches in the field of creation of nanoceramics with the use of different nanopowders is adequately represented in the papers [2–4] and others, including papers of the author [5–17]. At the next stage, it is advisable to study the ceramic of magnesium oxide nanopowder.
Magnesium oxide is used in the production of high-quality ceramics as an additive in raw materials, in creation of refractory fiber and materials, in paper production, as a fuel additive, in the manufacture of fungicides, in electronics and optics, for cleaning oil, in medicine and pharmaceuticals, as a filler in rubber production, as a very fine abrasive for cleaning surfaces (in particular, in electronics industry), as a protective coating for plasma displays. The aim of this study was the creation of dense and hard ceramics using the SPS and nanopowder of magnesium oxide.
Experimental conditions
The nanopowder of magnesium oxide MgO produced by Russian company "PlasmoTerm" (powders are synthesized in thermal plasma flow generated in an electrical discharge) was used in the study. Fig. 1 shows electron microscopy of this nanopowder.
The average particle size of the initial polydisperse powder was d=25 nm, and specific surface area was S=60 m2/g. Distribution of particle sizes was close to log-normal. Other properties of the powder: CAS number is 1309-48-4; purity of 99.6%; white color; spherical particle shape; explosion- and fire-safe.
The sintering of the powder was carried out using the Sinter Land Labox equipment at the Lavrentyev Institute of Hydrodynamics SB RAS by spark plasma sintering, when the pulses of electric current pass through the pre-compacted powder. In these experiments the current was up to 2 kA at a voltage of 3–4 V. The main difference between SPS and traditional pressing (consecutive compression and sintering) is bringing the pulse electric current directly to the sample that contributes to the rapid heating of the powder and preservation of its microstructural parameters in the consolidated material. The compression was carried out at maximum temperatures of 1500°С and 1600°С and at pressure of 40 MPa. The heating rate was typically 100°С/min (no holding at maximum temperature).
The microhardness of all ceramic samples was determined using PMT-3 microhardness tester. Using the electronic scanning microscope ZEISS EVO-50WDS-XVP-BU in ITAM SB RAS the chips of the ceramics after deposition of a gold layer were studied. HZG-4 diffractometer was used for roentgenography of obtained ceramics.
Results and conclusions
The diameter and thickness of obtained samples of ceramics were of 10 mm and of 1.2–1.5 mm respectively, and the density of ceramics was of 2.9 g/cm3.
Roentgenography of obtained ceramics showed that the sample is periclase (magnesium oxide) MgO (87-651) with a cubic structure, space group of Fm-3m (No. 225) and the lattice size a=4,216 Å.
Fig.2 shows scanning electron microscopy of the chip of ceramics with Tmax=1500°C. It is seen that the grain size is about 10 μm, and the dense ceramics was created using SPS. Ceramics obtained at Tmax=1600°C has a high microhardness Hv=12.4 GPa.
Thus, a dense and strong ceramics with microhardness up to 13 GPa was created on the basis of nanopowder of magnesium oxide with use of spark plasma sintering. ■
The project is supported by SB RAS (project III.23.4.1). The author expresses gratitude to A.Anisimov, V.Mali, V.Emelkin, G.Pozdnyakov and D.Korneev for help.
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