is also called amorphous or glassy state, this is a kinds of rigid solid, has compared with crystalline material is of high hardness and high viscous coefficient (
Is in commonly 10 piece, or more than 1 t. seconds, is typical of the viscous coefficient of fluid 10 times)
But its constituent atoms, molecules of space arrangement not periodic and translational symmetry, the long process of the crystalline;
Just due to the correlation function between the atoms, make it in a few atoms (
The diameter of the small area with a short program.
Because up to now, there is no any effective experimental method can accurately determine the atomic structure of amorphous materials, the above definition is relative.
Three basic characteristics of amorphous materials.
(1) only exist in the area between the short program, with no long program;
Wave vector k is no longer a good quantum number (describe the motion
See solid band)
(2) its electron diffraction, neutron diffraction and X-ray diffraction diagram is composed of wide halo and diffuse ring;
Using an electron microscope can't see any formed by grain boundary, crystal defect yan lining of contrast.
(3) any system of amorphous solid compared to corresponding crystalline materials, are metastable.
When the continuous heating, in a very narrow temperature zone, can produce significant structure change, from amorphous to crystalline state, the crystallization process mainly depends on the atomic diffusion coefficient and interface of materials can be and the melting entropy.
A lot of methods for preparation of amorphous materials, the most common is the melt quenching and from gas phase deposition (
Such as evaporation, ion sputtering, glow discharge, etc. )
In recent years and the development of the ion bombardment, strong new technology, such as laser radiation and high temperature implosion and has set up a large-scale continuous production.
Some have enough liquid viscosity, the rapid cooling can obtain the glassy state.
In 1960, P.
Du wes and others using the high cooling rate, the traditional craft of glass to metal and alloys, made the corresponding amorphous materials, called state metal metal or glass.
When rf heating coil sample melting, open the valve, pressure air (
As He, N, Ar, etc. )
Break the polyester film, make the samples from quartz crucible bottom nozzle jet rapidly to cooling copper, cold speed can reach more than 10 k/s, in order to obtain the amorphous.
In addition to a few relatively easy to form a glassy state alloy (
Such as Pd -
P, Pt -
P, etc. )
Outside, most of the metallic glass cooling rate is quite high, generally in 10 ~ 10 k/s, within 50 microns thickness, also have made first amorphous thin particles within dozens of micrometers, pressed again caking of amorphous alloy.
It is generally believed that pure metal can't use the current reach 10 ~ 10 k/s cooling speed, by liquid quenching glass state.
So, now all of the glassy state metal containing two or more group of yuan.
Most of the glassy state alloy has two components, part is gold properties of elements, such as Cu, Ag, Au or transition metal Fe, Co, Ni, Pd, Pt;
Non-metallic, class, the other part is the metal elements, such as the price of 3 B, 4 price of C, Si, Ge, 5 P.
The sum of the former accounted for about 70 ~ 80 at % (
The atomic percentage)
, which accounts for about 20 at %, the ratio of components available amorphous solid 'ear polyhedral model is explained.
Is most likely to get the amorphous component in near eutectic alloy phase diagram, the corresponding lowest melting temperature.
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