International Journal of Global Advanced Materials & Nanotechnology

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1 Research Article Scientific Future Group scientificfuture.com International Journal of Global Advanced Materials & Nanotechnology Microhardness of Different-Oxides Nanoceramics Vladimir Lysenko * Institute of Theoretical & Applied Mechanics, Russian Academy of Sciences, Novosibirsk, , Russia * Corresponding author: Vladimir Lysenko, Institute of Theoretical & Applied Mechanics, Russian Academy of Sciences, Novosibirsk, , Russia, vl@itam.nsc.ru Abstract The method of the Spark Plasma Sintering (SPS) was used for formation of the fine-grained ceramics from different nanodimensional alumina powders and powders of other oxides. A comparison of the microhardness of ceramics from various alumina nanopowders was held. The microhardness of ceramics created by SPS method and the conventional way (pressing, then sintering) is compared. The dependence of ceramics microhardness on the average size of its particles was investigated. Besides alumina nanopowders, there were compared microhardness of ceramics from nanopowders of oxides of zinc, copper, titanium, zirconium, tungsten, magnesium, chromium, cobalt, niobium, silicon, iron, yttrium and gadolinium created by SPS and the conventional way. It was determined that for ceramics created by SPS method, the microhardness is considerably larger than the microhardness of ceramics created by the conventional way; at the SPS method the average size of ceramics grains diminishes (to less than 1 micron). Keywords: Microhardness; Nanopowders; Nanoceramics; Oxides Introduction The existence of nanoparticles in structure of materials adds to materials new properties. Many characteristics change. Distinction between nanocrystal and coarsegrained materials in different properties are caused by the small grain size in nanomaterials and by a particular condition of a grain surface in them [1]. The current state of researches on nanoceramics is rather well displayed in [2-5]. Than ceramics grains size less, the ceramics is stronger. But hardly-destroyed agglomerates of nanoparticles are in the nanopowders [6,7] that requires the deployment of new compaction methods (for example, the hot pressing method). The purpose of this work was the creation of the dense and hard ceramics of fine-grained (less than 1 micron) structure by the SPS method from different nanopowders. Materials and Methods Different alumina nanopowders were applied to ceramics creation. The nanopowders of companies Plasmotherm and NskNano (Russia) were used. The sintering was carried out on the Labox Sinter Land facility in Novosibirsk by the SPS (spark plasma sintering) method when impulses of electric current (of 2 ka) pass through in-advance pressed powder. The main 1

2 difference of the SPS method from the conventional way (pressing, then sintering) is the pulse electric current through a pattern that leads to fast powder heating. This sintering was at the 1400 С maximum temperature and 40 MPa pressure. The heating speed was 100 /min. The obtained-samples diameter was 10 mm, the thickness about 3 mm. The ceramics density was g/cm 3. The ceramics created from nanopowders of oxides of zinc, copper, titanium, zirconium, tungsten, magnesium, chromium, cobalt, niobium, silicon, iron, yttrium and gadolinium was investigated also. The sintering was made on the same Labox Sinter Land facility at different maximum temperatures (from С) and 40 MPa pressure. The samples diameter was 10 mm, the thickness mm. The obtained (at SPS method) ceramics microhardness was compared to the ceramics microhardness obtained in works [8, 11-15] at conventional method using. The microhardness gage PMT-3 was used in this work. Results & Discussion The microhardness of ceramics from different alumina nanopowders are given in Figure 1. The average particles size d and phase structure for each powder (No-its number) is indicated. According to phase structure, the powders by vertical lines in Figure 1 are divided into four classes: 1) δ- and θ-phases, 2) γ-phase, 3) α-phase (corundum), 4) composites on the basis of the Al 2 powders (α-phase). Three clear conclusions follow from this Figure 1: 1. The microhardness of the ceramics created by the SPS method is considerably larger than the microhardness of the ceramics created by the conventional way. 2. The ceramics microhardness strictly depends on the nanopowder phase structure. It increase at change of the powder phase structure in such succession: (1) δ- and θ-phases, (2) γ-phase, (3) α-phase (corundum), (4) composites on the basis of α-phase powders. 3. For the α-phase ceramics, created by the same way (either conventional, or SPS), the ceramics microhardness is larger at the powder-particle average size decreasing. Then, at an electronic scanning microscope of ZEISS EVO- 50WDS-XVP-BU using, the structure of ceramics created by the SPS method was investigated, and the collation was made with the data of scanning electronic microscopy for the ceramics created by the conventional way [8]. The scanning electronic microscopy of the chip of the ceramics (of the density of 3.95 g/cm 3 ), created from the alumina powder (100% α-phase, Plasmotherm, d=185 nm) by the SPS method (at p max =40 MPa, T max =1400 C) is given in Figure 2a. It was compared to scanning electronic microscopy of the ceramics (of the density of 3.9 g/cm 3 ), created by conventional way (at p max =40 MPa, T max =1500 C) from the alumina AKP-50 powder (d=200 nm) [8]. It was found that if the grain size in the ceramics from the AKP-50 is 3-5 microns, the grain size of the ceramics from the Al 2 (α-phase, Plasmotherm ) powder is about 1 micron. Thus the microhardness of the first ceramics was 10 GPa, and of the second one 17 GPa. These data confirm that than the ceramics-grains size is less and the granular structure is more developed, the ceramics is stronger and harder. The alumina powders were used also as a part of compositions. In Figures 2b and 2c the pictures of scanning electronic microscopy of a chip of the ceramics created by the SPS method (at p max =40 MPa, T max =1400 C) from the components: Al 2 (α-phase, d=185 nm, Plasmotherm, 95%), MgO (d=25 nm, 2%) (Figure 2b), and Al 2 (α-phase, d=185 nm, Plasmotherm, 95%), MgO (d=25 nm, 3%), Y 2 (d=32 nm, 2%) (Figure 2c) are presented. They were confronted with the scanning electronic microscopy of the ceramics created from such components: Al 2 (200 nm, 95%), MgO (73 nm, 2%), Al 2 (13 nm, 3%), by the conventional way (pressed at p max =40 MPa and sintered at T max =1500 C) [8]. While the grain size in the composite ceramics on the basis of AKP-50 equals to 3-5 microns, the grain size in the composite ceramics on the basis of Al 2 (α-phase, Plasmotherm ) is about 1 micron. The microhardness of the first ceramics was GPa, and of the second ceramics 21 GPa (with use of Y 2 additives 23 GPa). According to the radiographic research of phase structure, all three samples of the composite ceramics contained the main phase α-al 2 (corundum of rhombohedral modification). Also the ceramics created from the nanopowders of oxides of zinc, copper, titanium, zirconium, tungsten, magnesium, chromium, cobalt, niobium, silicon, iron, yttrium and gadolinium, were explored. The obtained data on the ceramics microhardness are shown in Figure 3. The particles average size and the maximum sintering temperature for each powder (No its number) are given in the Figure. From Figure 3 it follows that the 2

3 24 22 δ+θ γ α composite Hv, GPa Figure 1: Microhardness of the ceramics from various alumina nanopowders. -The ceramics created by the conventional method [8], -the ceramics created by the SPS method. The used alumina nanopowders: 1- A (plasmochemical), mix of δ- and θ-phases, d=300 nm (Siberian Chemical Plant) 2- Aluminum Oxide C, γ-phase, d=13 nm (Degussa [Evonik Industries AG], Germany) 3- Al 2, mix γ-(80%), δ-and θ-phases, d=25 nm (NskNano) 4- B, γ-phase, d=33 nm (ITAM-INPh of SB RAS) 5- AM-21, α-phase, d=4000 nm (Sumitomo Chemical, Japan) 6- Al 2, mix of α-phase (34%), δ-phase and θ-phase, d= nm (Plasmotherm) 7- Al 2 nanofibres, mix of α-phase (95%) and θ-phase, d= nm (NskNano) 8- Al 2, α-phase (95%), θ-phase (5%), d= nm (NskNano) 9- AKP-50, α-phase, d=200 nm (Sumitomo Chemical, Japan) 10- AKP-60, α-phase, d=177nm (Sumitomo Chemical, Japan) Al 2, α-phase (100%), d=185 nm (Plasmotherm) 11- composite: Al 2 (α-phase, d=185/200 nm, 98%, Plasmotherm, AKP-50), MgO (d=25/73 nm, 2%) 12- composite: Al 2 (α-phase, d=185 nm, Plasmotherm, 95%), MgO (d=25 nm, 3%), Y 2 (d=32 nm, 2%) microhardness of the ceramics created by the SPS method, is considerably larger than the microhardness of the ceramics created by the conventional way. In Figure 4a the picture of scanning electronic microscopy of a chip of the ceramics of yttrium oxide created by the SPS method at T max =1500 C from the same yttrium oxide powder as in work [12], in which the ceramics was created at T max =1500 C by the conventional way. According to the electronic-microscopy photos, the average size of yttrium oxide grains is about 10 microns. For the obtained yttriumoxide ceramics, the microhardness was about 11 GPa. From Figure 4a (for the ceramics created by the SPS way) it follows that the yttrium-oxide ceramics are rather well sintered. According to the photos, the average size of yttrium-oxide grains created by the SPS method, is less than 5 microns while this size at the conventional ceramicspreparation way was about 10 microns. Respectively the microhardness of the ceramics from yttrium oxide created by the SPS method was 15.5 GPa, against 11 GPa for Y 2 ceramics created by the conventional way. When using SPS method, in a sample of zinc-oxide ceramics at Т max =1500 C (Figure.4b) the ceramics grains had the size of 2-5 microns, in ceramics of iron oxide at Т max =800 C 1 micron and less, in ceramics of silica at 3

4 (a) (c) Figure 2: The scanning electronic microscopy of a chip of the ceramics created by the SPS method: a) From the alumina powder (α-phase, d=185 nm, Plasmotherm); b) from the components: Al 2 (α-phase, d=185 nm, 98%), MgO (d=25 nm, 2%), c) from the components: Al 2 (α-phase, d=185 nm, 95%), MgO (d=25 nm, 3%), Y 2 (d=32 nm, 2%). (b) Т max =1000 C 300 nm (Figure 4c), and in ceramics of niobium oxide Nb 2 O 5 at Т max =800 C nm (Figure.4d). Conclusion Investigations on obtaining by the Spark Plasma Sintering (SPS) method the fine-grained ceramics from different nanopowders of alumina and other oxides are carried out. A comparison of microhardness of the ceramics created from nanopowders of 14 oxides was executed. It is found that at alumina nanopowders using: (1) The microhardness of the ceramics created by the SPS method is considerably larger than the microhardness of the ceramics created by the conventional way; at the SPS method the average size of the grains of ceramics diminishes (to less than 1 micron), (2) The ceramics microhardness strictly depends on the nanopowder phase structure. It increase at change of the powder phase structure in such succession: (1) δ- and θ-phases, (2) γ-phase, (3) α-phase (corundum), (4) composites on the basis of α-phase powders, (3) For the α- phase ceramics, created by the same way (either conventional, or SPS), the ceramics microhardness is larger at the powder-particle average size decreasing, (4) At the SPS method for the composite samples, the fine-grained, dense, strong ceramics with the microhardness up to 23 GPa is created. From the nanopowders of different oxides, the dense and hard ceramics with the fine-grained (less than 1 micron) structure is created by the SPS method. For ceramics created from nanopowders of different oxides by SPS method, the microhardness is considerably larger than the microhardness of ceramics created by the conventional way. References 1. Moiseev I, Klimov D. Discussion of problems of nanotechnology. Messenger of the Russian Academy of Sciences. 2003; 73(7): Zhou Xinzhang, Hulbert D. Superplasticity of zirconiaalumina-spinel nanoceramic composite by spark plasma sintering of plasma sprayed powders. Materials Science and Engineering A. 2005; 39:

5 Hv, GPa c) Figure 3: Microhardness of the ceramics from different oxides nanopowders. the ceramics created by the conventional way, the ceramics created by the SPS method, the coarse-grained (d>4-5 micron) ceramics created by the conventional way. The used oxides nanopowders: 1- SiO 2, d=25 nm (ITAM-INPh of SB RAS), T max =1500 C, T max =1000 C [9] 2- ZnO, d=70 nm (Plasmotherm), T max =1200 C 3- Fe 3 O 4, d=18 nm (ITAM-INPh of SB RAS), T max =900 C [10] 4- CuO, d=140 nm (ITAM-INPh of SB RAS), T max =800 C [11] CuO, d=80 nm (Plasmotherm), T max =900 C 5- Cr 2, d=110 nm (Plasmotherm), Т max =800 С 6- Gd 2, d=54 nm (ITAM-INPh of SB RAS), T max =1500 C [12] 7- CoO, d=40 nm (Plasmotherm), Т max =600 С 8- W, d=140 nm (ITAM-INPh of SB RAS), T max =1100 C [13] W, d=60 nm (Plasmotherm), T max =800 C 9- MgO, d=25 nm (Plasmotherm), T max =1600 C 10- Nb 2 O 5, d=60 nm (Plasmotherm), Т max =800 С 11- TiO 2 (brookite), d=78 nm (ITAM-INPh of SB RAS), T max =1600 C [14] TiO 2 (anatase/rutile), d=90 nm (Plasmotherm), T max =1100 C 12- Al 2 (AKP-50), d=200 nm (Sumitomo Chemical, Japan), T max =1500 C [8] Al 2, d=185 nm (Plasmotherm), T max =1400 C 13- Y 2, d=32 nm (ITAM-INPh of SB RAS) ( T max =1500 C, [12]; this work, T max =1400 C) 14- ZrO 2 (91%, d=20 nm) + MgO (9%) (Siberian Chemical Plant), T max =1500 C [15] ZrO 2, d=70 nm (Plasmotherm), T max =1500 C 3. Physicochemistry of ultradisperse systems (edited by Petrunin V). Theses of the V Russian Conference, Ekaterinburg, Russia, October 9-13, Nanoparticles, Nanostructures & Nanocomposites. Book of Abstracts of the Topical meeting of the European Ceramics Society, St. Peterburg, Russia, July 5-7, Nanostructures: Physics and Technology. Proceedings of 16 th International Symposium, Novosibirsk, Russia, June 25-29, Antsiferov V, Perelman V. Mechanics of processes of pressing of powder and composite materials. Moscow. 2001;

6 (b) (c) (a) (c) (a) (b) (d) Figure 4: The scanning electronic (a-c) and atomic-force (d) microscopy of a chip of the ceramics created by the SPS method from nanopowders of: (a) yttrium oxide, (b) zinc oxide, (c) silica, (d) niobium oxide. 7. Bae C, Bardakhanov S. Ceramic Preparation of Nano- and Micropowder. Abstracts of the 9th Intern. Symp. on Metastable, Mechanically Alloyed and Nanocrystalline Materials, Seoul, Korea, Bardakhanov S, Kim A, Lysenko V. Structure and properties of nanoceramics on the basis of alumina powder. Nanoindustry. 2009; 14(2): Anisimov A, Bardakhanov S. Influence of sintering conditions on structure and property of ceramics from nanodimensional silica powders. Bulletin of NSU. Physics series. 2013; 8(1): Lysenko V, Gorev V. Obtaining and properties of ceramics from nanopowder of iron oxide. Bulletin of NSU. Physics series 2013; 8(1): Bardakhanov S, Lysenko V. Ceramics obtaining from nanopowder of copper protoxide and its properties. Materials science questions. 2010; (3): Bardakhanov S, Lysenko V. Structure and properties of ceramics on the basis of nanodisperse powders of gadolinium oxide and yttrium oxide. Physical mesomechanics. 2008; 11(5): Bardakhanov S, Lysenko V. Receiving and properties of nanopowder of tungsten oxide and ceramics from it. Science and technologies in the industry. 2009; (4): Bardakhanov S, Kim A, Lysenko V. Properties of the ceramics obtained from nanodisperse powders. Inorganic materials. 2009; 45(3): Bardakhanov S, Emelkin V, Lysenko V. Obtaining and properties of ceramics from zirconium dioxide 6

7 nanopowder. Physics and chemistry of glass. 2009; 35(5): Copyright: Lysenko. This is an Open Access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 7