lO2

lO2 is a notation that can denote liquid oxygen, with the lowercase l indicating the liquid phase. In some contexts, it may simply be a typographical variant of O2, the chemical formula for diatomic oxygen. When used to mean liquid oxygen, lO2 refers to the cryogenic liquid obtained by cooling oxygen gas below its boiling point.

Liquid oxygen is the liquid state of diatomic oxygen, formed at temperatures below 90.2 K (-182.95°C) at standard pressure. It appears pale blue and is paramagnetic due to unpaired electrons. It is a dense, highly oxidizing liquid and can greatly accelerate combustion of materials that are normally nonreactive with air. Its properties make it valuable in industrial and aerospace applications, but they also demand careful handling.

Production and storage of lO2 typically involve fractional distillation of air to separate oxygen, followed by condensation into the liquid phase. It is stored in double-walled, highly insulated cryogenic dewars designed to minimize heat gain and vent out gases that form from the liquid’s slight expansion. Equipment handling lO2 requires materials that resist embrittlement and avoidance of oils or fuels nearby, due to the high oxidizing potential of liquid oxygen.

Key properties include its cryogenic temperature range, high oxidizing power, and a critical point around 154.6 K and 5.08 MPa, above which it becomes a supercritical fluid. Common applications are rocket propulsion as an oxidizer, metal and chemical processing, and other industrial processes requiring a robust oxygen source. As with all cryogenic oxidizers, lO2 demands rigorous safety measures to prevent cold burns, material ignition, and pressure-related hazards.