Tài liệu hạn chế xem trước, để xem đầy đủ mời bạn chọn Tải xuống
1
/ 357 trang
THÔNG TIN TÀI LIỆU
Thông tin cơ bản
Định dạng
Số trang
357
Dung lượng
6,26 MB
Nội dung
[...]... their geometrical form and the dimensionality of structural elements from which they consist The main types of nanocrystalline materials as regards the dimensionality are cluster materials, fibrous materials, films and multilayer materials, and also polycrystalline materials whose grains have 1 Nanocrystalline Materials &RDUVH JUDLQHG PDWHULDOV 3DUWLFOH JUDLQ VL]H µP a[ 6XEPLFURFU\VWDOOLQH... smaller than 10 nm When examining the properties of superfine materials, it is necessary to take into account not only their structure and composition but also dispersion Polycrystalline superfine materials with a mean grain size of 300 to 40 nm are referred to as submicrocrystalline, and those with a mean grain size of less than 40 nm as nanocrystalline The conditional classification of materials on... example, radiowave- Fig 1.3 The first encounter with nanomaterials causes the same surprise as these buildings in the modern style, designed by F.O’Gehry in Düsseldorf (Germany) 3 Nanocrystalline Materials absorbing ceramic materials, whose matrix is characterised by the random distribution of fine-dispersion metallic particles, are used in aviation industry Whisker single crystals and polycrystals (fibres)... (1.1) 11 Nanocrystalline Materials takes place spontaneously at temperatures 800–1000 K lower than the temperature of the reaction between normal coarse-grained oxides Hybrid nanocomposites of the metal–polymer type are produced by forming nanoparticles in a specially prepared polymer matrix [42, 43] Polymer composites with metallic nanoparticles are used as electrically conducting film composite materials,. .. and complicated broken contours (Fig 1.3) However, after some time it becomes obvious that it is possible to live in such an unusual building and that it may even be interesting This also relates to the nanocrystalline state, i.e it is unusual but it may be interesting to work with it The difference between the properties of small particles and the properties of bulk materials has been known for a relatively... SP Fig 1.1 Classification of substances and materials on the basis of particle (grain) size D Clusters (0D) Nanotubes, filaments and rods Films and layers (2D) (1D) Space network (3D) Fig 1.2 Types of nanocrystalline materials: 0D (zero-dimensional) clusters; 1D (one-dimensional) nanotubes, filaments and rods; 2D (two-dimensional) films and layers; 3D (three-dimensional) polycrystals comparable size... strength of steel wire They are used as fillers for light composite materials for aerospace applications Carbon fibres and graphite whiskers are relatively thick (approximately 1–10 µm) and are not nanomaterials, but their production and applications were the first step on the path to the development of carbon nanomaterials After discovery in 1984–1985 of a new allotropic modification of carbon, i.e... nanotubes (Fig 1.6); this structure is referred to as the Y-junction carbon nanotube Synthesis was carried out by chemical deposition from the gas phase (CVD): pyrolysis of acetylene with subsequent 5 Nanocrystalline Materials Fig 1.6 Model of a carbon Y-nanotube growth of Y-nanotubes was carried out at a temperature of 920 K in branching nanochannels of the aluminium matrix Cobalt, being a growth catalyst,... lecture “The stateof-art synthesis techniques for carbon nanotubes and nanotubesbased architecture” P Ajayan told about silicon carbide nanotubes produced on an Al 2 O 3 substrate At the 2nd NASA Advanced 7 Nanocrystalline Materials Materials Symposium “New Directions in Advanced Materials Systems” (May 29–31, 2002, Cleveland, Ohio), D Larkin presented a report “High temperature nano-technology: silicon carbide... bonds with the carrier It is evident that as the number of atoms that are in contact with the carrier increases, the effect of the carrier on catalytic activity becomes stronger It is clear that the 9 Nanocrystalline Materials effect of the carrier is relatively small for large particles but increases and becomes quite strong with a decrease in the particle size Metallic alloys (for example, alloys . light composite materials for aerospace applications. Carbon fibres and graphite whiskers are relatively thick (approximately 1–10 µm) and are not nanomaterials, but their production and applications. infirm Delight The Truth’s superb surprise” After Emily Dickinson Preface In 1998 the monograph Nanocrystalline Materials: Preparation and Properties” by A. I. Gusev was published by Ural Division. SMALL PARTICLES 131 4.1. ELECTRON MICROSCOPY 132 4.2. DIFFRACTION 137 4.3. SUPERPARAMAGNETISM, SEDIMENTATION, PHOTON CORRELATION SPECTROSCOPY AND GAS ADSORPTION 151 References 156 vi 5. PROPERTIES