From towering skyscrapers to small and exquisite wristwatches, the presence of glass can be seen everywhere in life.

　　Before the National Two Sessions, Peng Shou, a representative of the National People's Congress, an academician of the Chinese Academy of Engineering, the chief engineer of China National Building Material Group, and the president of the China National Building Material Group Glass New Materials Research Institute, said in an interview with reporters that it is necessary to vigorously promote energy conservation and carbon reduction in the glass industry, allowing China's glass industry to "go green".

　　In fact, glass not only needs to "go green," but also has the potential to "regain youth"—as the service time increases, glass undergoes aging phenomena, usually accompanied by deterioration in physical and mechanical properties. How to make aged glass-like substances "regain youth" and restore their properties has received increasing attention from the scientific community in recent years.

　　At the end of 2022, a team led by researcher Jiang Minqiang from the Institute of Mechanics of the Chinese Academy of Sciences revealed a new mechanism for rejuvenating severely aged metallic glass through research, deepening the understanding of the rejuvenation of glass structures. The relevant research results were published in the multidisciplinary English journal "Fundamental Research," which is supervised and hosted by the National Natural Science Foundation of China.

　　Glass aging: a slow transition from disorder to order

　　To make glass "regain youth," it is first necessary to understand how glass "ages."

　　Jiang Minqiang introduced that, at the microscopic level, glass is an amorphous solid with a disordered structure. He gave reporters an example: in crystalline solids like steel, atoms are like students quietly sitting in a classroom, arranged in an orderly manner, presenting a regular form. In contrast, in the disordered structure of glass, atoms are like students running around the campus after class, presenting a disordered arrangement.

　　The phenomenon of glass aging essentially represents the transition of glass from an initial disordered state to an ordered state. "Generally speaking, the total energy of a substance in a disordered state is higher, while in an ordered state, the total energy is lower. As time progresses, glass gradually transitions from a high-energy state to a low-energy state, a process commonly referred to as glass aging." Jiang Minqiang explained that if the aging time is long enough, or if aging is accelerated by heating, glass can even transform into a solid crystalline state with a regular structure.

　　Glass aging affects many properties of glass, such as toughness, optical properties, and electrical conductivity, and is a phenomenon that people strive to delay or even avoid. Therefore, as a process to reverse glass aging, glass rejuvenation has long been a focus of researchers.

　　"Glass rejuvenation is the reverse process of glass aging, which means making the relatively ordered atoms of aged glass gradually return to a relatively disordered state." Jiang Minqiang said. In previous studies on glass rejuvenation, researchers found that rejuvenated glass releases a portion of thermal enthalpy when heated to a certain temperature, and the higher the degree of rejuvenation of the glass, the more thermal enthalpy is released during heating. Thermal enthalpy is an important state parameter that characterizes the energy of a material system. In simple terms, thermal enthalpy is the energy released by rejuvenated glass during the heating process.

　　"Our research believes that the above viewpoint does not apply to severely aged glass. For severely aged glass, as the degree of rejuvenation increases, the release of thermal enthalpy does not change, and there may even be no thermal enthalpy released at all." The research of Jiang Minqiang's team indicates that previous views on the mechanism of glass aging do not apply to severely aged glass, updating people's understanding of the mechanism of glass structure rejuvenation.

　　"Unintentional success": Research results are unexpected

　　"In fact, the breakthrough in this research originated from an 'unintentional success' attempt by our research team." Jiang Minqiang said that the initial purpose of this experiment was merely to prepare experimental samples. "Our team originally prepared samples for another experiment. To enhance the scientific nature of the experiment, it was necessary to eliminate the thermal history of the samples to ensure their structural consistency. We performed low-temperature annealing on the glass samples—slowly heating the metallic glass to a certain temperature and maintaining it for a sufficient time, then cooling it to room temperature at a certain speed." Subsequently, the research team rejuvenated this batch of severely aged glass through mechanical deformation. The results were unexpected—"We clearly input energy into the glass through mechanical work, so why did these glasses not release thermal enthalpy and become rejuvenated?" This is contrary to previous mainstream views.

　　This result left the research team puzzled. To unravel the mystery, in addition to measuring thermal enthalpy, the research team also measured the high-temperature (450K—750K) and low-temperature (1.9K—100K) specific heat of the glass samples, further examining the atomic vibration information and topological structure information of the glass. "During the experiment, the research team found that although in some cases the thermal enthalpy release parameter before the glass state transition remained unchanged, the effective thermal enthalpy change during the glass state transition and the atomic vibration Bose peak reflected by the low-temperature specific heat would change accordingly." Jiang Minqiang further explained, "This indicates that thermal enthalpy release is not the only physical quantity reflecting glass rejuvenation."

　　When discussing why the thermal enthalpy release remained unchanged, Jiang Minqiang used a vivid example to explain: "If we place a small ball in the concave part of a 'U' shaped plane, this small ball will naturally remain still. This stable state is akin to severely aged glass. However, if we tilt this 'U' shaped plane at some angle, although the height of the concave part, which is the energy level of the glass state material, remains almost unchanged, the state represented by the small ball will become unstable, leading to the phenomenon of glass rejuvenation."

　　The research results indicate that, in addition to the previously mainstream view that glass rejuvenation can be directly reflected in the release of thermal enthalpy, which is the increase in energy level, it can also be reflected as the tilting of the energy surface, which is the redistribution of free volume in space through local structural rearrangement. "This is the new mechanism of rejuvenation for severely aged glass state material that we discovered," Jiang Minqiang stated.

　　Expanding scenarios: providing broad application space

　　This research also found that as glass enters a stable flow state, the three physical parameters representing rejuvenation will each tend to saturation values, thus experimentally determining that the upper limit of glass structure rejuvenation is the 'frozen' steady-state flow state for the first time.

　　If we use water as a comparison, the glass formed in high temperature as a liquid is like water, while the glass solidified at low temperature is like ice. "The limit of glass structure rejuvenation is to suddenly freeze the high-temperature glass liquid through rapid cooling, thus forming a material state similar to 'frozen flowing water.'" Jiang Minqiang explained, "In this case, the glass will maintain a material structure almost identical to the liquid state beneath its solid surface, and its fluidity will reach the limits of current understanding.

　　The new mechanism of rejuvenating glassy materials revealed by this research not only allows us to better understand the physical essence of the causes and processes of glass aging, but also has great potential application space in promoting the mass renewal of aged glass. "The research team is currently communicating with companies engaged in glass production or R&D, striving to find a good point of integration to push the technology to market."

　　In addition, Jiang Minqiang also found that the new mechanism revealed by this research is expected to be applied in the preparation of advanced metal materials.

　　"Generally speaking, the strength and toughness of metal materials cannot be achieved simultaneously. As the strength increases, the toughness decreases, and vice versa." Jiang Minqiang stated, "How to overcome this inherent inverted relationship is a problem that must be faced in the preparation of advanced metal materials with both strength and toughness."

　　High-strength metal materials generally have a very low total energy level at the microscopic level. If energy is input through methods such as heating, attempting to improve the toughness of metal materials by increasing the total energy level often requires extremely high energy input, which is almost impossible to achieve.

　　"If we can use the new mechanism discovered in this research to adjust the energy surface angle of metal materials at a lower total energy level, we can enhance the atomic disorder while maintaining the macroscopic strength unchanged, thereby improving the toughness of the metal materials. Through this method, we can effectively avoid huge energy input and greatly reduce the cost of preparing high-strength and tough metal materials." Jiang Minqiang stated that his team is currently continuing to try, striving to achieve a decisive breakthrough and provide new ideas for solving the long-standing irreconcilable contradiction between the strength and toughness of metal materials.