Principle: After sodium chloride snow melting agent is dissolved in water (snow), its freezing point is at zero degrees. After sodium chloride snow melting agent is dissolved in water, its freezing point is -10°C. The freezing point of salt water is higher than the freezing point of water. Low, so it is difficult to form ice again after the salt is dissolved in the snow water. In addition, after the snow melting agent is dissolved in water, the ion concentration in the water increases, causing the liquid vapor pressure of water to decrease, but the solid vapor pressure of ice remains unchanged. In order to reach the state of solid, liquid, vapor pressure, etc. of the ice-water mixture, the ice melts. This principle also explains why salt water does not freeze easily.
The harm of snow melting agent to the environment:
1. It brings great harm to the green belts and farmland on both sides of the road
Although chlorine salt snow melting agents are easy to melt and remove snow, they are also cheap. However, snow after using snow melting agents often accumulates in green belts or farmland on both sides of the road. After spring, all its salt residues accumulate in farmland and green belts, salinizing the soil and destroying vegetation.
2． Corrosion of roads, bridges and other road facilities
When salt meets water, salt will rise, causing damage to the road bed and making road maintenance more difficult. Chloride salts penetrate into concrete and promote freezing and thawing of concrete. But its most important destructive effect is corrosion of steel bars. When chloride ions reach the surface of the steel bar and exceed a certain amount (critical value), the steel bar that was originally in a passivated state will be activated and corroded.
3. Pollution of groundwater resources
Commonly used snow melting agents are mainly salts. After the salt on the road melts the ice, it flows with the snow water. After salt substances enter the ground, they will inevitably cause pollution to local groundwater resources.