Palladium membrane usually refers to the tubular or sheet metal palladium or palladium alloy. The structure can be divided into two types: self-supporting type and loading type (also called composite membrane). The dense palladium membrane has the only hydrogen penetration. Therefore, the research on palladium membrane is of great significance in hydrogen purification. In addition, because of the unique purification performance of palladium alloy membrane diffusion method, it is incomparable with other physical or chemical methods, and is the main process of hydrogen isotope extraction, separation and purification at present.
Palladium membrane usually refers to the tubular or sheet metal palladium or palladium alloy. The structure can be divided into two types: self-supporting type and loading type (also called composite membrane). The dense palladium membrane has the only hydrogen penetration. Therefore, the research on palladium membrane is of great significance in hydrogen purification. In addition, because of the unique purification performance of palladium alloy membrane diffusion method, it is incomparable with other physical or chemical methods, and is the main process of hydrogen isotope extraction, separation and purification at present.
The mechanical properties of pure palladium are poor, and hydrogen embrittlement problem exists when the temperature is lower than 300 degrees and hydrogen pressure increases rapidly. When the palladium membrane is in contact with hydrogen, hydrogen dissolves into palladium metal to form alpha palladium hydride. If the temperature is low, it may further form palladium hydride beta and increase with the rapid H/Pd ratio, resulting in the expansion of palladium metal, lattice dislocation and stress. When the stress is too large, the film will become brittle and rupture. In order to control the rapid increase of H/Pd ratio, the first step is to increase the temperature or reduce the hydrogen pressure, so as to avoid the formation of palladium hydride beta. In addition, when the palladium membrane starts to work, if the hydrogen raw material is pressurized too fast, it will also lead to a rapid increase in the H/Pd ratio, resulting in the excessive expansion of palladium and hydrogen brittleness. Compared with pure palladium membrane, the H/Pd ratio of palladium alloy membrane is greatly inhibited, so the hydrogen embrittlement problem is solved.
The operating temperature of palladium membrane is generally 300 to 500 degrees centigrade. High temperature is conducive to improving hydrogen permeability, but it will shorten the service life of the membrane, leading to a series of problems such as diffusion between palladium membrane and metal joints and solder materials. Palladium membrane cannot be oxidized at high temperature for long time. Some impurities of hydrogen raw gas can lead to palladium poisoning, which can reduce hydrogen permeability and even damage the membrane. The substances that can cause palladium poisoning include mercury, arsenide, halide, oil vapor, sulfur, phosphorus and dust.
