Amorphous materialAlso called amorphous or glassy materials, this is a large class of rigiditysolid, which is comparable to that of crystalline substanceshardnessAnd highCoefficient of viscosity(Usually 10 poise, that is, more than 10 Pa · s, which is typicalfluid10 times the viscosity coefficient of).
Amorphous materialAlso called amorphous orGlassy stateMaterials, which are a large class of rigid solids, have high hardness and high viscosity coefficient comparable to crystalline materials (generally 10 poise, that is, more than 10 Pa · s, 10 times the viscosity coefficient of typical fluids).But its constituentatomThe spatial arrangement of molecules does not exhibit periodicity and translational symmetry, and the long-range order of the crystalline state is destroyed;Only because of the interaction between atoms, it has a short program in a small area of several atomic (or molecular) diameters.Since there is no effective experimental method to accurately determine the atomic structure of amorphous materials, the above definitions are relative.[1]
basic feature
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Amorphous materials have three basic characteristics.
① There are only short programs in the cell, but no long programs;Wave vectorkIt is no longer a good quantum number to describe the state of motion (seeEnergy band of solid）。
③ Any systemAmorphous solidCompared with its corresponding crystalline materials, they are metastable.When the temperature rises continuously, in a very narrow temperature range, there will be obvious structural changes, from amorphous to crystalline. This crystallization process mainly depends on theAtomic diffusion coefficient, interface energy and melting entropy (seeStructural relaxation）。
Material preparation
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There are many methods to prepare amorphous materials, the most common ones are melt quenching and vapor deposition (such asevaporation, ion sputteringglow discharge Etc.).In recent years, new technologies such as ion bombardment, intense laser radiation and high-temperature detonation polymerization have been developed, and they can be produced continuously on a large scale.[2]
Some with sufficient viscosityliquid, which can be obtained after rapid coolingGlassy state。In 1960, P. Duweis and others developed the traditional glass process to metals and alloys by using a high cooling rate to produce corresponding amorphous materials, calledMetallic glassOr glassy metal.When the RF heating coil melts the sample, open the valve, and the pressurized air flow (such as He, N, Ar, etc.) breaks through the polyester membrane, making the sample fromQuartz crucibleThe nozzle at the lower end rapidly sprays onto the cooling copper block, and the cooling speed can reach more than 10K/s to obtain its amorphous state.Except for a few alloys (such as Pd Cu Si, Pd Ni-P, Pt Ni-P, etcAmorphous alloyOf.
It is generally believed that pure metal can not use the cooling rate of 10~10K/s to obtain glassy state from liquid quenching.Therefore, all glassy metals contain two or more components.grossGlassy alloyBoth of them have two components, one of which is a highly metallic element, such as Cu, Ag, Au or transition metal FeCo、Ni、Pd、Pt；The other part is non-metallicMetalloid element, such as 3-valent B, 4-valent C, Si, Ge, and 5-valent P.The total sum of the former accounts for about 70~80at% (atomic percentage), while the latter accounts for about 20at%. Such composition ratio can be explained by the Berner polyhedron model of amorphous solids.The most easily obtained amorphous component is near the eutectic point of the alloy phase diagram, which corresponds to the lowest melting temperature.
Material properties
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As a kind of rigid solid with special structure, metallic glass has higherstrength(e.g. amorphous Fe80B20, breaking strengthσF reaches 37kgf/mm, more than seven times of general structural steel);And the size effect of strength is very small.Its elasticity is also better than that of ordinary metals, and its bending deformation can reach more than 50%.The hardness and toughness are also very high (Vickers hardness HV is generally about 1000~2000).
The corrosion resistance of iron base metal glass with low chromium content (such as Fe27Cr8P13C7) is far better than that of stainless steel.Due to the long-term disorder of atomic arrangement,phononThe contribution to conducted electron scattering is very small, making its resistivity very high, generally 100 μ m at room temperatureΩ·Above cm, the temperature coefficient of resistivity is very small (below ± 10K);It has high residual resistance at 0K.In some casesAmorphous alloyMedium (such as PdSiCr), resistance in resistance temperature curveT=TThere is a minimum value when mT<TM, the resistance increases with the decrease of temperature, similar to theKondo effectThe mechanism is still unclear.
Fifteen kinds of amorphous quench superconducting alloys have been reported. Their superconducting transition temperature is 1.5 ～ 8.71K, which is lower than that of crystalline superconductors. Their characteristics are that their radiation resistance is much stronger than that of crystalline superconductors.Metallic glasses based on transition metals (iron, cobalt, nickel) have excellent soft magnetic properties (seemagnetic material ）, high permeability and low AC loss, far superior to commercial silicon steel sheet, andPermalloyCompared with the coercivity of (Fe4Co96) (P16B6Al3) amorphous alloyHc≈0.13Oe，remanenceBr≈4500G,It is likely to be widely used in highLow frequency transformer(partially replacing silicon steel sheet and permalloy)Magnetic sensor, recording head, magnetic shielding material, etc.
After research, the internal structure of glass has no "spatial lattice" characteristics, but is similar to the structure of liquid.However, the "crystal like regions" cannot move with each other, resulting in no fluidity of the glass.We call this state "amorphous".Strictly speaking, "amorphous solid" does not belong to solid, because solid specifically refers to crystal;It can be regarded as a very viscous liquid.Therefore, the "amorphous state" can be proposed as another state of matter.exceptOrdinary glassIn addition, there are many "amorphous" solids, such as rubber, paraffinNatural resin、asphaltAnd polymer plastics, etc.
Material type
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There are many kinds of amorphous materials. Silica, as well as the mixture of silica and the oxides of Al, Na, Mg, Ca and other elements, constitute the oldest and most important inorganic glass. Some mixtures of Group V A-VI A and Group VII A elements are also easy to obtain their glassy state (such as chalcogenide glass).
In addition to traditional glass and recently rapidly developed metallic glassAmorphous semiconductor, amorphous high polymerAmorphous dielectricAmorphous ionic conductor, etc.
application
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In the past 20 years, amorphous materials have developed rapidly and become a major class of new solid materials due to their excellent physical and chemical properties and extensive technical applications.[1]
