Topic 1: Introduction. Nanocrystalline materials (4:00)

Plan of the lecture

1. Introduction.

2. The concept of nanomaterials.

3. The relevance of Manufacture of nano-and ultrafine materials.

In recent years, the rapid growth of scientific, industrial and commercial interest in a new class of materials, the purpose of which reflected the desire for miniaturization in the practice of construction of various objects. These materials have unusually strong crystal lattice and exhibit unique properties in the CIS called ultrafine materials (UDM), or ultra-systems (UDS), and in Western literature - nanostructured materials (NSM).

Currently, both of these terms are equivalent to this new class of materials referred to the size of the morphological elements of less than 100 nm. On geometrical features of these elements can be divided into volmernye atomic clusters and particles, one-and two-dimensional multilayers, coatings and daminarnye structure, three-dimensional bulk nanocrystalline and nanophase materials.

It is generally accepted that under the UDM or nanomaterials means or deliberately engineered or natural materials, in which one or more sizes are in the range of nanometers. This category also includes the so-called "nano-nano" composites that contain more than one phase, but the phase is less than 100 nm. A large variety of types of UDM with their common feature size allows you to combine them in one term "nanomaterial". It is now widely used ultrafine powders (UDP), which occupy more than 90% of the U.S. market UDM, nanofibers and nanowires, nanofilms and nanocoatings, and start getting more and more application of bulk nanomaterials and nanozernistye nanocrystalline (grain size less than 100 nm) [1 ].

Understanding of nanocrystals has been introduced in the scientific literature in the 80-ies Glyayterom H. (Germany) and, independently, actively developed in Russia ID Morohovym with employees.

In the former Soviet Union a major role in the study of the properties of nanomaterials, the development of new, technology acquisition and use (nanotechnology) played high school.

The relevance of Manufacture of nano-or ultrafine (AP) materials are defined by features of their physical and chemical properties that allow you to create materials with a qualitatively and quantitatively new properties for use in practice. This is due to the fact that the material is of such small size is of great importance quantum mechanics, and it fundamentally alters the mechanical, optical and electrical properties of the substance.

The first studies of nanomaterials have shown that they are changed, compared to conventional materials such fundamental characteristics as the specific heat capacity, elastic modulus, and the diffusion coefficient, magnetic properties, etc. Consequently, we can talk about the state of nanostructured solid, fundamentally different from conventional crystalline or amorphous.

An analysis of theoretical and experimental studies carried out to the end of the 70's, led to the conclusion of a special solid state UD different from traditional and amorphous materials, and a definition of this concept on the basis of physical nature. In this case, the nano-or UD materials include media or materials that are characterized as small size of the morphological elements that it is commensurate with one or more fundamental quantities of the substance (measuring the crystal lattice, etc.)

As the size of the grains or particles become smaller and smaller, an increasing fraction of the atoms is on the boundaries or free surfaces. Thus, when the size of the structural units of 6 nm and thickness of the surface layer one atom almost half of the atoms will be located on the surface. Since the fraction of surface atoms in the UD material is tens of percent, clearly manifested all the features of the surface states, and the division of properties in "bulk" and "surface" becomes, to some extent, arbitrary. The developed surface affects both the lattice and the electronic subsystem.

There are anomalies in the behavior of electrons, quasi-particles (photons, magnons) and other elementary excitations, which result in changes in the physical properties of the DM systems compared to bulk materials.

The behavior of UD materials are often determined by the processes at the grain boundaries. For example, can deform nanoceramics almost long enough to slip through the borders. But "superplasticity" strain is in a strong contrast to the fragile behaviors associated with conventional ceramics. Because of the large number of borders and, as a consequence, this - a lot of short diffusion distances nanometally and ceramics are used as solid-phase binding agent to connect with others (sometimes disparate) coarse-grained materials. It is known [1] that some ceramics have extremely low thermal conductivity. This allows their use as thermal barrier coatings.

Reducing the size of grains of metal from 10 microns to 10 nanometers gives strength increase of about 30 times. Adding to the usual nano powders for pressing the latter leads to a decrease in the pressing temperature, high strength products. With the use of diffusion bonding between the welded parts of a thin layer of suitable composition nanopowders allows welding of dissimilar materials, including some difficult-to-metal alloys with ceramics, as well as to reduce the temperature of diffusion bonding.

Scientific research on the subject has been held for more than 100 years ago. In 1861, chemist T. Graham used the term "colloid" to describe solutions containing particles with a diameter of 1 to 100 nm in the suspension.

The use of colloids can be considered one of the first applications of nanomaterials. Similarly, for a long time used such substances containing ultrafine particles such as aerosols, paint pigments, colorants steklokolloidnye metal particles.

In recent years came into use the concept of nanotechnology. This term refers to the process of obtaining nano-and ultrafine materials and technological processes of instruments, devices, structures using nanomaterials.

Scientific and technical direction to obtain and study the properties of UD materials formed in the former USSR in the 50 years of the twentieth century. In the nuclear industry received UD powders with a particle size of about 100 nm, which have been successfully used in the manufacture of highly porous membranes for the diffusion method of uranium isotope separation. In the 60 years for the Institute of the USSR was developed levitation method for UD powders. In the 70 years through the use of electrical explosion of conductors and plasma fusion range UD powders has been significantly expanded, developed chemical methods for the synthesis of nanopowders of iron and other metals and composites based on them.

In the 1980s, Germany had obtained consolidated nanocrystalline materials.

In the last decade in developed countries formed the scientific and technical direction "Nanoparticles, materials, technologies and equipment," which is the fastest growing in terms of finance in the world.

In 1980, the study of clusters containing less than 100 atoms. In 1985, Smiley and Kroto with a group of Spectrographic found evidence that the C60 carbon clusters (fullerenes) exhibit extraordinary stability. In 1991, S. Iijima reported the study of carbon-graphite tube filaments nanotubes.