Can You Freeze Liquid Nitrogen?

You can freeze liquid nitrogen into a solid state by lowering the pressure in a vacuum chamber or by significantly reducing its temperature below -346°F (-210°C). When liquid nitrogen transitions into solid nitrogen under specific controlled conditions, it can be used for cryogenic applications across industries. 

In this guide, we’ll explore the science behind freezing liquid nitrogen. We’ll go over the methods used to achieve this transformation and why it matters for certain specialized applications.

The Science of Freezing Liquid Nitrogen

Liquid nitrogen maintains extremely cold temperatures between -320°F and -346°F under normal atmospheric pressure. To freeze it into its solid state, you need to cool it below the freezing point of -346°F (-210°C). 

Doing so requires specialized equipment and techniques because these temperatures are far colder than anything encountered in everyday life.

When liquid nitrogen reaches its freezing point, it transforms into a solid that resembles white, crystalline ice. The molecular motion slows dramatically, causing the fluid to solidify into a rigid structure.

Unlike water ice, solid nitrogen is extremely fragile and will immediately begin transforming back to liquid if the temperature rises even slightly.

Vacuum Freezing Method

The most practical method for freezing liquid nitrogen involves using a vacuum chamber to lower the pressure.  When placed in the chamber, liquid nitrogen evaporates quickly due to the reduced pressure.

This evaporation process pulls heat energy from the remaining liquid, further cooling it. As the pressure drops to about 12.5% of atmospheric pressure, the temperature of the liquid nitrogen falls until it reaches its freezing point.

At this point, the liquid nitrogen transforms into solid nitrogen, appearing as a white, snow-like substance in the vacuum chamber.

The solid nitrogen created this way is extremely unstable at normal atmospheric pressure and will quickly revert to liquid when the vacuum is released.

High-Pressure Techniques

Another way to create solid nitrogen is to apply extremely high pressures to nitrogen gas or liquid.

Under sufficient pressure, nitrogen molecules can be forced into various solid configurations, including a cubic gauche structure that forms at pressures exceeding 110 GPa.

These high-pressure solid nitrogen forms have unique properties that differ from those created through vacuum freezing. However, these techniques require specialized high-pressure equipment not commonly available outside of advanced research facilities.

Natural Occurrences of Solid Nitrogen

Interestingly, solid nitrogen exists naturally in our solar system, particularly on Pluto.

Pluto’s surface temperature hovers around 40K (-387°F) – well below nitrogen’s freezing point – allowing for vast nitrogen ice glaciers to form. These glaciers on Pluto can be several kilometers thick and flow like glaciers on Earth, though much more slowly due to the extreme cold.

NASA’s New Horizons mission revealed that these nitrogen ice formations create a remarkable “cosmic lava lamp” effect as they slowly convect due to Pluto’s internal heat.

Similar processes may occur on Neptune’s moon Triton, where nitrogen geysers have been observed erupting from the surface.

Solid Nitrogen’s Industrial Applications and Key Considerations

For most industrial applications (including those in California’s manufacturing and healthcare sectors) liquid nitrogen is used instead of solid nitrogen due to its beneficial properties.

Specifically, liquid nitrogen is far more practical for cooling, freezing, and preserving materials because of its relative stability compared to solid nitrogen.

In industrial settings, preventing unintentional freezing of liquid nitrogen is actually more important than intentionally creating solid nitrogen. If liquid nitrogen lines or storage vessels experience unexpected pressure drops, solid nitrogen can form and potentially block flow paths.

This is why properly designed cryogenic systems include features to prevent the conditions that would lead to solid nitrogen formation.

Solid Nitrogen: Possible but Not Feasible

While liquid nitrogen can be frozen into solid nitrogen under specific conditions of extremely low temperature or in a vacuum environment, this process has limited practical applications outside of specialized research. 

Still, understanding the phase transitions of nitrogen expands our scientific knowledge. It also helps ensure the safe and effective use of liquid nitrogen in its many industrial, medical, and research applications.