From towering skyscrapers to small and exquisite chronograph watches, glass can be seen everywhere in life.
Before the two sessions of the National People's Congress, Peng Shou, a representative of the National People's Congress, an academician of the Chinese Academy of Engineering, chief engineer of China National Building Materials Group, and president of China National Building Materials Glass New Materials Research Institute, said in an interview with reporters that we must vigorously promote energy conservation and carbon reduction in the glass industry, so that China's glass The industry is "going green".
In fact, glass must not only "go green", but also be expected to "rejuvenate" - as the service time increases, glass will produce aging phenomena, which is usually accompanied by the deterioration of physical, mechanical and other properties. How to "rejuvenate" aging glassy substances and restore their properties has attracted more and more attention from the scientific community in recent years.
At the end of 2022, the team of Jiang Minqiang, a researcher at the Institute of Mechanics of the Chinese Academy of Sciences, revealed a new rejuvenation mechanism for severely aged metallic glasses through research, and deepened the understanding of the rejuvenation of glass structures. The relevant research results were published in the National Natural Science Foundation of China, managed by the National Natural Science Foundation of China. Fundamental Research, a multidisciplinary English-language journal sponsored by
Glass Aging: Slow Transition from Disorder to Order
To make glass "rejuvenate", we must first understand how glass "grows".
Jiang Minqiang introduced that from a microscopic perspective, glass is an amorphous solid with an irregular structure. He gave reporters an example: In crystalline solids such as steel, atoms are like students sitting quietly in a classroom, arranged in an orderly manner and showing regular shapes. In glass, an amorphous solid with an irregular structure, atoms are like students after class, running around on campus, and their arrangement is disordered.
The phenomenon of glass aging is essentially the transformation of glass from a disordered state when it is initially formed to an ordered state. "Generally speaking, the total energy of matter in a disordered state is higher, while in an ordered state, the total energy of matter is lower. As time goes by, glass will gradually transform from a high-energy state to a low-energy state. This The process is generally called glass aging. "Jiang Minqiang explained that if the aging time is long enough, or the aging is accelerated by heating, the glass can even transform into a solid crystal with a regular structure.
Glass aging will affect many properties such as the toughness, optical properties, and electrical conductivity of the glass. It is a phenomenon that people want to delay or even avoid. Therefore, as a process of reversing glass aging, glass rejuvenation has long received widespread attention from scientific researchers.
"Glass rejuvenation is the reverse process of glass aging, that is, the glass whose atoms have become relatively ordered after aging slowly returns to a state of relatively disordered atoms," Jiang Minqiang said. In previous studies on glass rejuvenation, researchers found that rejuvenated glass will release part of the heat enthalpy when it is heated to a certain temperature, and the higher the degree of rejuvenation of the glass, the greater the heat enthalpy released during heating. many. Thermal enthalpy is an important state parameter characterizing the energy of a material system. In layman's terms, enthalpy is the energy released by rejuvenated glass during the heating process.
"Our research shows that the above point of view does not apply to severely aged glass. As the degree of rejuvenation of severely aged glass increases, its heat enthalpy release does not change, or even has no heat enthalpy release at all." Research by Jiang Minqiang's team It shows that the previous views on the aging mechanism of glass are not applicable to severely aged glass, which updates people's understanding of the rejuvenation mechanism of glass structure.
"Unintentional insertion": The research results are unexpected
"Actually, the breakthrough in this research came from an 'unintentional' attempt by our research team." Jiang Minqiang said that the original purpose of this experiment was just to prepare experimental samples. "Our team originally prepared the sample for another experiment. In order to strengthen the scientific nature of the experiment, it is necessary to eliminate the thermal history of the sample and ensure that they have a consistent structure. We performed a low-temperature annealing operation on the glass sample - slowly heating the metallic glass to a certain temperature and maintained for a sufficient time, and then cooled to room temperature at a certain speed. "Then, the research team rejuvenated the severely aged glass through mechanical deformation. The result was unexpected - "We obviously input energy into the glass through mechanical work, so why don't these glasses release heat and become younger?" This is contrary to the previous mainstream view.
This result left the research team confused. In order to solve the mystery, in addition to measuring the thermal enthalpy, the research team also measured the high-temperature (450K-750K) and low-temperature (1.9K-100K) specific heat of the glass sample, and then investigated the atomic vibration information and topological structure information of the glass. "During the experiment, the research team found that although the parameter of enthalpy release before glass transition remained unchanged in some cases, the effective enthalpy change during glass transition and the low-temperature specific heat of atoms reflected However, the two physical quantities of the vibrational Bose peak will change accordingly," Jiang Minqiang further explained, "This shows that thermal enthalpy release is not the only physical quantity that reflects the rejuvenation of glass."
When talking about why the heat enthalpy release remains unchanged, Jiang Minqiang once again explained with a vivid example: "If we place a small ball in the recess of the 'concave' shaped plane, the small ball will naturally remain stationary. This kind of stability The state is like that of severely aged glass. And if we tilt this 'concave' shaped plane at some angle, although the height of the concave, that is, the energy level of the glassy material remains almost unchanged, the state of the glass represented by the small ball will remain the same. It will become unstable, and the phenomenon of glass rejuvenation will occur."
Research results show that, in addition to previous mainstream views, glass rejuvenation can be directly reflected in the release of heat enthalpy, that is, an increase in energy level, or it can also be reflected in the tilt of the energy surface, that is, through the rearrangement of local structure. The free volume is redistributed in space. "This is the new mechanism for rejuvenation of severely aged glassy materials that we discovered." Jiang Minqiang said.
Expanding scenarios: providing a broad application space
This study also found that as the glass enters a stable flow state, the above three physical parameters characterizing rejuvenation will each tend to saturation values, thus for the first time experimentally determining that the upper limit of glass structure rejuvenation is the "frozen" steady-state flow. state.
If we use water as an analogy, glass that becomes liquid at high temperatures is like water, while glass that solidifies at low temperatures is like ice. "The limit of rejuvenating the glass structure is to suddenly freeze the high-temperature glass liquid through extremely rapid cooling, thus forming a material state similar to 'frozen running water'." Jiang Minqiang explained, "In this case, the glass will appear in a solid state. Maintaining a material structure that is almost the same as a liquid, its fluidity will reach the limit of current understanding."
The new mechanism of rejuvenation of glassy substances revealed in this study not only allows us to better understand the causes and processes of glass aging from a physical perspective, but also has huge potential application space in promoting the batch rejuvenation of aged glass. . "The research team is currently communicating with companies engaged in glass production or research and development, trying to find a good combination point to promote the technology to the market."
In addition, Jiang Minqiang also discovered that the new mechanism revealed in this study is also expected to be applied in the preparation of advanced metal materials.
"Generally speaking, the strength and toughness of metal materials cannot be compatible with each other. As the strength increases, the toughness will decrease, and vice versa." Jiang Minqiang said, "How to overcome this inherent inverted relationship is to prepare both Strength and toughness of advanced metal materials must be faced."
High-strength metal materials generally have very low total energy levels at the microscopic level. If energy is input through heating and other methods, trying to improve the toughness of metal materials by increasing the total energy level often requires extremely high energy investment, which is almost impossible to achieve.
"If we can use the new mechanism discovered in this study to adjust the energy surface angle of metallic materials when the total energy level is low, we can increase the disorder of the atoms while maintaining the same macroscopic strength, thus enhancing the Toughness of metal materials. Through this method, we can effectively avoid huge energy input and greatly reduce the cost of preparing high-strength metal materials. "Jiang Minqiang said that his team is currently trying to achieve decisive breakthroughs. It provides new ideas to solve the long-standing irreconcilable contradiction between the strength and toughness of metal materials.