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Dense and solid fine-grained ceramics (microhardness of 16 GPA and grain size of 1µ) based on nanoscale titan dioxide powder was prepared by spark plasma sintering (SPS) method.
Теги: ceramics fine-grained ceramics microhardness nanopowder sps method sps-метод titanium dioxide диоксид титана керамика мелкозернистая керамика микротвердость нанопорошок
INTRODUCTION
Different properties of the nanocrystalline and coarse-grained materials depend not only on small size grains of nanocrystalline material but also on the special state of their surface or grain boundaries [1].
Manufacturing of small grain size ceramics made of nanoscale powder is one of the ways to develop modern nanotechnologies. It is assumed that such nanoceramics will have some special properties (e.g., superplasticity [2]) as compared with the ceramics made of coarse-grained material.
It is well known that the smaller the ceramics grains are and the more developed their grain structure is, the harder and more solid the ceramics is. At the same time the stable and hard-to-break agglomerates of nanoparticles used for ceramics manufacturing [3] are present in nanopowders, and it is necessary to apply non-standard methods for their compaction (for example, the hot-pressing method).
The current state of research in nanoceramics made of different nanopowders is sufficiently well described in [4–6] and in the author’s works [7–16].
In this paper we present the research in ceramics prepared of titanium dioxide nanopowder.
Usually, titanium dioxide is used in the manufacturing industry for production of paints, protective coatings, abrasives and polishing. It plays an important role in optics as a photocatalyst and lens coating that retains ultraviolet radiation.
Titanium dioxide is increasingly used for environmental protection, e.g., in sewage water treatment and in air filters. Besides, it is applied in construction materials, glass and mirrors manufacturing and disposal of the chemical rocket warheads.
This substance is also used in fiber optics and radioceramics production, as a filler in polymer materials for aircraft and automobile industries, when producing chemical fibers, plastics, printing paints, in cosmetics (sun-protection, bleaching and moisture-protective creams and in paper industry).
This work is aimed at production of dense and solid ceramics with fine grain (about 1µ) structure made of nanodisperse titanium dioxide powder by SPS method.
RESEARCH METHODS
For this research chosen was the titanium dioxide (TiO2) nanopowder produced by "PlazmoTherm", a Russian company (they synthesize powders in the thermal plasma flow generated in electrical discharge). Fig.1 shows an image of titanium dioxide nanopowder obtained by electron microscopy.
The average size of particles equals d ≈ 90 nm, and their specific surface is S ≈ 16 m2/g.
The powder has had following properties: CAS number – 13463-67-7, purity – 99,5%, phase ratio anatase/rutile 50 : 50, white colour, spherical form of particles, polydisperse powder. Distribution of particles by sizes is close to logarithmically normal function.
Agglomeration of the powder was accomplished with the aid of Labox "Sinter Land" installation in Lavrentyev Institute of Hydrodynamics of SB RAS using the SPS method (hot-pressing together with the spark plasma sintering) when electrical pulses were applied to the previously hot-pressed powder (in these experiments strength of electrical current reached 2 kA at applied voltage of 3–4 V).
The SPS method differs from the traditional pressing (when pressing and sintering are carried out sequentially) by applying pulsed electric current directly to a sample in order to heat the powder rapidly and preserve, to a considerable extent, its micro-structural parameters in the consolidated material. Hot-pressing was accomplished at the maximum temperature of 1,100 °С and 40 MPa pressure. The heat rate was equal to 100 "/min without any exposure at the maximum temperature. Ceramic chippings were studied with ZEISS EVO-50WDS-XVP-BU electron scanning microscope in the Khristianovich Institute of Theoretical and Applied Mechanics, SB RAS, after spraying a gold layer on them. The micro-hardness of all ceramic samples was studied with PMT-3 microhardness tester.
RESULTS AND CONCLUSIONS
The diameter and thickness of the obtained samples are 9.6 mm and 3.2 mm, correspondingly.
Electron scanning microscopy of the ceramic chippings shows that grain sizes of the obtained ceramics is about 1 µ, in other words, the SPS method enabled to obtain the fine-grain solid ceramics.
The micro-hardness of the obtained ceramics appears to be very high (Hv = 16 GPa).
For the sake of comparison: the microhardness of the ceramics prepared by the traditional method [17] (by sequential pressing and sintering) from the nanodispersed TiO2 powder with particle size of 78 nm when sintering at maximum temperature of 1600 °С was 9 GPa while the microhardness of coarse ceramics prepared by the traditional method from coarse TiO2 powder (particle size exceeds 4000 nm) was equal to 4 GPa only.
Thus, the fine-grained (grain size is about 1 µ) dense and solid ceramics with microhardness of 16 GPa made of nanoscale titanium dioxide (TiO2) was prepared by SPS method.
The author is grateful to A.G. Anisimov, V.I.Mali and V.A.Emelkin for their assistance in the presented work.
Different properties of the nanocrystalline and coarse-grained materials depend not only on small size grains of nanocrystalline material but also on the special state of their surface or grain boundaries [1].
Manufacturing of small grain size ceramics made of nanoscale powder is one of the ways to develop modern nanotechnologies. It is assumed that such nanoceramics will have some special properties (e.g., superplasticity [2]) as compared with the ceramics made of coarse-grained material.
It is well known that the smaller the ceramics grains are and the more developed their grain structure is, the harder and more solid the ceramics is. At the same time the stable and hard-to-break agglomerates of nanoparticles used for ceramics manufacturing [3] are present in nanopowders, and it is necessary to apply non-standard methods for their compaction (for example, the hot-pressing method).
The current state of research in nanoceramics made of different nanopowders is sufficiently well described in [4–6] and in the author’s works [7–16].
In this paper we present the research in ceramics prepared of titanium dioxide nanopowder.
Usually, titanium dioxide is used in the manufacturing industry for production of paints, protective coatings, abrasives and polishing. It plays an important role in optics as a photocatalyst and lens coating that retains ultraviolet radiation.
Titanium dioxide is increasingly used for environmental protection, e.g., in sewage water treatment and in air filters. Besides, it is applied in construction materials, glass and mirrors manufacturing and disposal of the chemical rocket warheads.
This substance is also used in fiber optics and radioceramics production, as a filler in polymer materials for aircraft and automobile industries, when producing chemical fibers, plastics, printing paints, in cosmetics (sun-protection, bleaching and moisture-protective creams and in paper industry).
This work is aimed at production of dense and solid ceramics with fine grain (about 1µ) structure made of nanodisperse titanium dioxide powder by SPS method.
RESEARCH METHODS
For this research chosen was the titanium dioxide (TiO2) nanopowder produced by "PlazmoTherm", a Russian company (they synthesize powders in the thermal plasma flow generated in electrical discharge). Fig.1 shows an image of titanium dioxide nanopowder obtained by electron microscopy.
The average size of particles equals d ≈ 90 nm, and their specific surface is S ≈ 16 m2/g.
The powder has had following properties: CAS number – 13463-67-7, purity – 99,5%, phase ratio anatase/rutile 50 : 50, white colour, spherical form of particles, polydisperse powder. Distribution of particles by sizes is close to logarithmically normal function.
Agglomeration of the powder was accomplished with the aid of Labox "Sinter Land" installation in Lavrentyev Institute of Hydrodynamics of SB RAS using the SPS method (hot-pressing together with the spark plasma sintering) when electrical pulses were applied to the previously hot-pressed powder (in these experiments strength of electrical current reached 2 kA at applied voltage of 3–4 V).
The SPS method differs from the traditional pressing (when pressing and sintering are carried out sequentially) by applying pulsed electric current directly to a sample in order to heat the powder rapidly and preserve, to a considerable extent, its micro-structural parameters in the consolidated material. Hot-pressing was accomplished at the maximum temperature of 1,100 °С and 40 MPa pressure. The heat rate was equal to 100 "/min without any exposure at the maximum temperature. Ceramic chippings were studied with ZEISS EVO-50WDS-XVP-BU electron scanning microscope in the Khristianovich Institute of Theoretical and Applied Mechanics, SB RAS, after spraying a gold layer on them. The micro-hardness of all ceramic samples was studied with PMT-3 microhardness tester.
RESULTS AND CONCLUSIONS
The diameter and thickness of the obtained samples are 9.6 mm and 3.2 mm, correspondingly.
Electron scanning microscopy of the ceramic chippings shows that grain sizes of the obtained ceramics is about 1 µ, in other words, the SPS method enabled to obtain the fine-grain solid ceramics.
The micro-hardness of the obtained ceramics appears to be very high (Hv = 16 GPa).
For the sake of comparison: the microhardness of the ceramics prepared by the traditional method [17] (by sequential pressing and sintering) from the nanodispersed TiO2 powder with particle size of 78 nm when sintering at maximum temperature of 1600 °С was 9 GPa while the microhardness of coarse ceramics prepared by the traditional method from coarse TiO2 powder (particle size exceeds 4000 nm) was equal to 4 GPa only.
Thus, the fine-grained (grain size is about 1 µ) dense and solid ceramics with microhardness of 16 GPa made of nanoscale titanium dioxide (TiO2) was prepared by SPS method.
The author is grateful to A.G. Anisimov, V.I.Mali and V.A.Emelkin for their assistance in the presented work.
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