In 1884, scientist Karol Olszewski observed solid nitrogen for the first time, a major discovery that unveiled the mystery of nitrogen. The study of solid nitrogen still attracts widespread attention in the academic community, not only because of its application in scientific research, but also because it plays an important role in the composition of celestial bodies in the outer solar system.
Solid nitrogen is an important component of extraterrestrial bodies at low temperatures and low pressures; at high temperatures and high pressures, it is a powerful explosive with an energy density exceeding that of other non-nuclear materials.
Olszewski's experimental method is quite simple but very creative: he first liquefied hydrogen by evaporating liquid nitrogen, and then used the low temperature of liquid hydrogen to cool the nitrogen to make it solid. This process enabled him to produce the coldest nitrogen temperature ever recorded at that time, 48 K (about -225°C), setting a world record. To this day, the technology for generating solid nitrogen in the laboratory still follows a similar process, evaporating liquid nitrogen in a vacuum.
Solid nitrogen has a significant distribution in nature and can even be found on the surfaces of Pluto and Neptune's satellite Triton. Solid nitrogen was first directly observed at Pluto by the spacecraft New Horizons in 2015, while a similar phenomenon was confirmed at Triton by Voyager 2 in 1989. At these low temperatures, solid nitrogen is relatively volatile and can sublime and form an atmosphere or condense back into nitrogen frost. Solid nitrogen flows at lower pressures than other materials, and when it accumulates, it takes on the form of a glacier, which makes people marvel at the properties of solid nitrogen.
New Horizons observed water ice "floating" on Pluto's surface, leaving viewers surprised by the behavior of solid nitrogen.
Solid nitrogen exhibits different properties at different pressures and temperatures. At standard atmospheric pressure, the melting point of nitrogen is 63.23 K. Nitrogen is an element that exists in many solid forms, and the properties of these forms that melt and sublime under high pressure have attracted extensive research. What is even more noteworthy is that solid nitrogen exhibits amazing energy density under high pressure, which makes it valued in the field of energy materials.
Solid dinitrogen exists in the form of N2 molecules at room temperature and medium pressure. When the temperature drops below 35.6 K, nitrogen can transform into the α phase and start to polymerize at a pressure of 50 GPa. Higher pressure conditions promote the transformation of solid nitrogen into nitrogen crystals with different structures [such as cubic and hexagonal nitrogen]. These different crystal structures have significant variations in both physical and chemical properties.
The existence of nitrogen in solid form has aroused great interest in its stability and reactivity in extreme environments, especially those on non-Earth bodies.
The properties of solid nitrogen make it an important direction for future research, especially in the application of energy materials and deepening theoretical physics. With the development of science and technology, solid nitrogen may play a key role in space exploration or other scientific and technological fields. Scientists are constantly exploring the diversity of solid nitrogen and its potential applications, hoping that this seemingly ordinary element can demonstrate extraordinary performance in future scientific research.
How will the research on solid nitrogen affect our understanding and application of matter in the future?