Can High Activity Calcium Oxide Be Used As A Heat Source？

In the fast-paced modern life, self-heating food has emerged as a popular choice for outdoor trips, overtime commutes, and home emergency use, thanks to its convenient feature of "heating up instantly with water, no open flame or power supply required". The core supporting this hassle-free experience is the heat-generating source inside the self-heating packet. Among various options, calcium oxide (commonly known as quicklime) has become the primary heat-generating raw material in the vast majority of commercial self-heating packets, leveraging its unique chemical properties.

The reason why calcium oxide serves as the core heat source of self-heating packets lies in its vigorous exothermic reaction when in contact with water, which releases a substantial amount of heat. This is a typical exothermic reaction, with the chemical equation as follows:

CaO + H₂O = Ca(OH)₂ + A large amount of heat

The product of this reaction, calcium hydroxide (commonly known as slaked lime), is a stable alkaline substance that does not produce toxic or harmful gases, thus laying a solid foundation for the safety of self-heating food.

Although calcium oxide is the core heat source, industrial self-heating packets do not use pure calcium oxide. This is because the reaction of pure calcium oxide with water is overly violent, leading to concentrated heat release that may cause local overheating and even scald the container. Additionally, the reaction duration is relatively short, failing to meet the heating time requirements for food. Therefore, self-heating packets typically adopt a composite formula with calcium oxide as the main component and multiple ingredients as supplements, where each component plays its dedicated role to collectively optimize the heating performance.

Core Heat-Generating Agent: Calcium Oxide

As the "backbone" of the formula, calcium oxide generally accounts for 50%–70% of the total mass of the self-heating packet. Its quality directly determines the basic heat-generating capacity of the packet. High-purity calcium oxide (usually ≥90%) with uniform particle size is preferred to ensure reaction stability and heat release efficiency.

Auxiliary Heat-Generating Agents: Boosting Temperature and Extending Duration

To compensate for the short heating duration of pure calcium oxide, a small amount of metal powders (e.g., aluminum powder, magnesium powder) are added as auxiliary heat-generating agents. These metal powders further react with calcium hydroxide (produced by the reaction of calcium oxide and water) and residual water, releasing additional heat. This not only increases the peak heating temperature but also extends the heating duration from around 10 minutes (with pure calcium oxide) to 20–30 minutes, which is more suitable for heating food.

Water-Retaining and Sustained-Release Agents: Regulating Reaction Rate

To prevent overly violent reactions and ensure a continuous supply of water for the reaction, porous materials such as diatomite, vermiculite, and bentonite are incorporated as water-retaining and sustained-release agents. These materials possess strong adsorption capacity, which allows them to absorb water in the packet (or water added by users) and release it slowly, enabling a steady reaction between calcium oxide and water and avoiding local overheating. Meanwhile, their porous structure also acts as a heat dissipation buffer, reducing the risk of scalding.

Core Advantages of Calcium Oxide as the Heat Source for Self-Heating Packets

Compared with other potential heat-generating materials (e.g., iron powder, magnesium strips, concentrated sulfuric acid), calcium oxide offers irreplaceable advantages in self-heating packet applications, which is the key reason for its dominant position:

Low Cost and Abundant Reserves

High Heat Release Efficiency and Strong Adaptability

High Safety and Environmental Friendliness