The differences between the nanocrystalline and coarse-grained materials in the elastic, damping, strength, thermal, electrical, magnetic and diffusion properties are caused by not only grain size but also by a particular state of surfaces or boundaries in nanocrystalline materials . One of the areas of nanotechnology is the creation of ceramics from nanosized powders with very small grain size. It is assumed that along with the properties of ceramics produced from coarse-grained materials, nanoceramics will have some unique properties, such as superplasticity .
It is known that the smaller is the grain size and the more developed is the structure, the stronger and harder will be ceramics. However, nanopowders, used to produce ceramics, include stable agglomerates of nanoparticles  that requires the use of unconventional methods of compacting, for example, hot pressing.
Current status of research of nanoceramics manufactured of different nanopowders shown in papers [4–6] and others, including the author's papers [7–19]. The next step was the study of ceramics manufactured of tin dioxide nanopowder.
Tin oxides are used as catalyst in antistatic coatings, in sensitive layers of gas sensors, optoelectronic devices, resistors, liquid crystal displays, as a pigment in ceramic glazes, paints and enamels, in the production of thermally and chemically resistant glass, as an abrasive material in "fine-tuning" of the surface of optical glass, as luminescent material in lighting equipment.
The purpose of this study is to create dense and solid ceramics with fine-grained (less than a micron) structure of the nano-dispersed powder of tin dioxide using the method of SPS.
Studies performed with use of nanopowder of tin dioxide SnO2, which was manufactured by the Russian company "Plasmotek" by synthesis in thermal plasma generated by the electrical discharge. Fig.1 shows the SEM-image of this nanopowder.
The powder had the following properties:
•average particle size d = 60 nm; •specific surface area S = 18 m2/g; •the CAS number 18282-10-5; •purity of 99.7%; •color – white; •spherical shape of particles; •polydispersed structure; •the distribution function of the particle size is close to lognormal. The sintering of the powder was carried out on the Sinter Land Labox equipment in the Lavrentyev Institute of Hydrodynamics of SB RAS by spark plasma method (hot pressing using a spark plasma sintering), when a pulse of electric current pass through a pre-compacted powder. The main difference between SPS and the traditional pressing (sequential pressing and sintering) is that the pulsed electric current acts directly on the sample that contributes to the rapid heating and preservation of much of its microstructural parameters in the consolidated material. During the experiments, at a voltage of 3–4 V current strength was up to 2 kA. The pressing was conducted at a maximum temperature of 600°C and a pressure of 40 MPa. The heating rate was maintained at 100°C/min, without holding at the maximum temperature.
The choice of the value of the maximum temperature was due to the fact that at T > 600°C began to release oxygen, the more intense, the higher was the temperature, and after 1400°C in the matrix remained fragments of tin.
The microhardness of samples of ceramics was investigated using tester PMT-3. Using digital scanning microscope ZEISS EVO-50WDS-XVP-BU (Khristianovich Institute of Theoretical and Applied Mechanics of SB RAS) and atomic force microscope NT-MDT Solver P47 were investigated chips of ceramics with gold coating. X-ray study of the obtained ceramics was performed using a diffractometer HZG-4.
Results and discussion
The diameter and thickness of obtained ceramics samples was 9.7 mm and 2.6 mm, and the density of ceramics – 4.1 g/cm3.
X-ray examination showed that the sample of ceramics is a tin dioxide SnO2 (77-448) with tetragonal structure, space group P42/mmm (No.136) and the sizes of the lattice a = 4,7391 Å and c = 3,1869 Å.
Images of scanning electron and atomic force microscopy of the chip of the sample (fig.2 and fig.3) show that the grain size range is from 200 to 800 nm.
The microhardness of ceramics obtained at Tmax = 600°C was Hv = 2.8 GPa.
Thus, using the method of spark plasma sintering and nano-sized powder of tin dioxide was created fine-grained (200 to 800 nm), dense, durable ceramics with a hardness of about 3 GPa.
The work was supported by SB RAS (project III.23.4.1). The author is grateful to A.Anisimov, V.Mali, V.Amelkin, G.Pozdnyakova and D. Korneeva for help. ■