Can metals be made into glass? You'll never think of its applications

Produced by: Science Popularization China

Author: Yao Bingnan, Wang Junqiang (Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences)

Producer: China Science Expo

What are glassy materials? Some people may say, isn't it just a cup or a window? That's right, in addition to these, common candles, rubber, optical fibers, etc. are also glassy materials. What are their characteristics? Unlike crystalline materials with neatly arranged atoms, these materials have long-range disordered and short-range ordered atomic structures .

Schematic diagram of the atomic structure of crystals and glasses. The left picture is a crystal and the right picture is a glass.

(Image source: Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences)

If the crystal structure is compared to an orderly queue, the glass structure is more like a crowd on the street. Disorder breeds infinite possibilities. Glassy materials have a series of very valuable properties, such as isotropy, metastability, high strength, high elasticity, corrosion resistance, and wear resistance. It is precisely because of these good properties that it is not only widely used in construction, automobiles, household goods, etc., but also a key material in cutting-edge fields such as information communication, aerospace, etc.

The glassy materials mentioned above are all non-metallic. Can the metal materials that we can see everywhere in our daily life be made into glassy materials? The answer is yes. This material is metallic glass, also called amorphous alloy.

Amorphous alloys in different forms

(Image source: Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences)

Generally speaking, we can quickly cool the high-temperature metal melt that has not yet crystallized, such as Fe-based alloys, Co-based alloys, Fe-Ni alloys, etc., by spinning a belt to obtain metallic glass materials. Its microstructure is not like common metals with neatly arranged atoms, but like glass, the atoms are arranged in a disordered manner. This special structure gives it many unique properties, such as excellent soft magnetic properties, mechanical properties, chemical properties, etc., so it is applied to various fields such as power electronics, information communication, transportation, energy, etc.

Metallic glass has high saturation magnetic induction intensity, high magnetic permeability and low coercive force. Electronic components made of it have a more miniaturized and lightweight structure and low loss, which is of great significance for achieving energy conservation and emission reduction.

Electronic components

(Photo source: Veer Gallery)

For example, compared with traditional materials, metallic glass can reduce no-load losses by 70-80% when used in distribution transformers. Moreover, metallic glass can also be made into iron cores for use in high-speed motors. Especially in medium and high frequency applications, the iron core loss of traditional silicon steel motors increases sharply. After replacing them with metallic glass, the motor operating efficiency can generally be increased to more than 95%, or even up to 98%, with obvious energy-saving advantages.

Application of metallic glass - distribution transformer

(Photo source: Veer Gallery)

With the advent of the 5G era, metallic glass also plays an important role.

Applying metallic glass to wireless charging technology can significantly increase charging power by taking advantage of its high magnetic permeability. This is because there are countless small magnets dispersed in the internal structure of the material, which we call magnetic domains .

The magnetic domain structure of metallic glass is relatively regular, but the magnetic domain structure of crystal is not only chaotic, but also has different directions. When an external magnetic field acts, the grain boundary of the crystal is like a wall that hinders the movement of the magnetic domain; metallic glass, because it has no grain boundary, dislocation, etc. , is easy to form regularly arranged magnetic domains in a large range, is sensitive to external magnetic fields, and exhibits high magnetic permeability characteristics .

Therefore, adding metal glass to magnetic induction wireless charging is like adding a condenser to concentrate the magnetic flux lines that were originally divergent in space. The receiving coil will receive more magnetic signals, charging faster and more efficiently.

At present, metallic glass has been successfully applied to mobile phones, smart watches and electric vehicles, becoming one of the most critical materials for wireless charging technology.

Wireless charging for electric vehicles

(Photo source: Veer Gallery)

In fact, the application prospects of metallic glass are not limited to the above. It is precisely because of its various wonderful properties that the "eighteen martial arts" demonstrated by this magical material far exceeds our imagination.

Metallic glass has high strength . For example, the fracture strength of cobalt-based bulk metallic glass is as high as 6.0 GPa, and the fracture strength of iron-based metallic glass can reach 3.6 GPa, which is several times that of general structural steel.

Metallic glass has high elasticity , and its elastic limit is several to dozens of times that of ordinary crystal alloys. Using zirconium-based metallic glass to make the hitting head of a golf club can transfer nearly 99% of the energy to the ball, and its hitting distance is 1.3 times farther than that of an ordinary club. The high elasticity of metallic glass can also be used to make various space application parts, such as harmonic gears used as reducers for spacecraft mechanical arm joints, and elastic porous metal rubbers used for shock absorption.

Metallic glass is a functional material that can be used to clean water pollution, store energy and evolve hydrogen, providing new ideas for solving environmental pollution and energy storage problems. For example, iron-based, magnesium-based, aluminum-based and other metallic glasses can degrade azo dye solutions, and their fading rate is dozens or even thousands of times that of the corresponding crystalline alloys. Metallic glass can be prepared into nanoporous composite structures through dealloying, thereby greatly improving the transport properties of ions and electrons, and ultimately increasing the specific capacitance. This high energy storage density nanoporous material is expected to be used as a flexible self-supporting supercapacitor electrode. Metallic glass has high catalytic activity for hydrogen evolution and is an ideal independent catalytic electrode.

Effect diagram of aluminum-based amorphous alloy degrading azo dye solution

(Image source: PP Wang, JQ Wang*, H. Li, H. Yang, JT Huo, JG Wang, C. Chang, X. Wang, RW Li, G. Wang**. Fast decolorization of azo dyes in both alkaline and acidic solutions by Al-based metallic glasses[J]. Journal of Alloys and Compounds, 701(2017)759-767.)

Metallic glass is a magnetic refrigeration material with a wide operating temperature range, large magnetic entropy change and strong refrigeration capacity. For example, a new magnetic refrigeration material developed can achieve refrigeration from 50K to room temperature, with a refrigeration capacity of more than 1000Jkg-1, and has broad potential application value in refrigerators, freezers, low-temperature refrigeration equipment, cryo-electron microscopes and other fields.

Schematic diagram of metallic glass magnetic refrigeration materials and their potential applications

(Image source: JQ Feng, YH Liu, JH Sui, AN He, WX Xia, WH Wang, JQ Wang**, JT Huo*. Giant Refrigerant Capacity in Gd-based Amorphous/Nanocrsytalline Composite Fibers[J]. Materials Today Physics, 2021, 100528.)

The emergence of metallic glass has a revolutionary significance for the field of human materials science. In the future, it will continue to shine in the fields of energy, life and health, national defense and military industry. The road ahead is long and arduous, but I will continue to explore. Only unremitting struggle can provide the inexhaustible driving force and long-term hope for the continuous development of new materials in my country!

References:

【1】Wang Weihua. The nature and properties of amorphous matter[J]. Progress in Physics, 2013, 33(5): 177-351.