Archaeologists restoring iron artifacts recovered from marine shipwrecks face a persistent threat: chloride-induced corrosion. When iron remains submerged in seawater for centuries, it absorbs chloride ions, which accumulate deep within the metal's porous corrosion layers. Upon excavation and exposure to atmospheric oxygen and moisture, these entrapped chlorides react to form hydrochloric acid. This acid rapidly accelerates the oxidation of the remaining iron, a destructive cycle known as 'weeping' that can reduce solid artifacts to dust within years.
Traditional conservation methods, such as washing in sodium carbonate baths, often fail because they cannot penetrate the deepest pores to extract the stubborn chlorides. To address this, conservators developed subcritical water treatment. By heating water to temperatures between and under high pressure, they maintain the water in a liquid state while dramatically altering its physical properties. Specifically, this high-temperature, high-pressure environment reduces the water’s surface tension and viscosity. Consequently, the treated water penetrates the microscopic pores of the iron artifact far more effectively than water at room temperature. Once inside the deepest pores, the subcritical water rapidly dissolves and carries away the trapped chloride ions, thereby halting the cycle of acidic corrosion and stabilizing the artifact for long-term display.
According to the passage, why is subcritical water able to penetrate the microscopic pores of an iron artifact more effectively than room-temperature water?
- ATraditional conservation washing methods have already removed the outermost corrosion layers.
- BThe subcritical environment increases the surface tension and viscosity of the trapped chloride ions.
- The high-temperature, high-pressure conditions decrease the viscosity and surface tension of the water.Answer
- DThe penetration of the liquid water into the deepest pores lowers the surrounding pressure and temperature.