Palladium is the fifth cycle Ⅷ clan members of platinum group elements, transition metal palladium is silvery white, soft, good ductility and plasticity, forging, rolling and drawing. The massive metal palladium can absorb large amounts of hydrogen gas, making the volume expand significantly, become brittle and even break into fragments. It is a chemical element found in the platinum mine by British chemist wollaston in 1803. It is an indispensable key material in aerospace, aviation and other high-tech fields as well as automobile manufacturing.
Industrial production may be made by dry process from ore; The by-products produced in the process of copper and nickel production from copper and nickel sulfide ores can also be obtained by wet smelting. The residual components of nickel and copper were extracted as raw materials by wet method. The residue was extracted by adding wang shui for extraction and filtration. Ammonia and hydrochloric acid were added to the filtrate for reaction to form ammonium chloropaluronate precipitation. After refining and filtration, ammonium chloropaluronate was reduced with hydrogen gas to make about 99.95% palladium products.
Usually rolled from palladium alloy, can be made into film (called palladium membrane) and film tube (called palladium tube). The film thickness is usually 50~100 microns. It is mainly used for purifying hydrogen, and its principle is solution-diffusion mode. The driving force of diffusion is the difference of hydrogen partial pressure on both sides of the membrane. Under the 300-500 ℃, the raw material of hydrogen pressure ventilation with one side of the membrane, a hydrogen molecule in the first place in the membrane surface chemical adsorption and dissociated into hydrogen, which formed in the dissolved palladium alloy hydride, small size of hydrogen in palladium alloy lattice clearance, can move freely. Driven by the concentration gradient, the hydrogen atom diffuses to the other side of the membrane and precipitates out. In addition to hydrogen and its isotopes, no other gases can pass through the palladium membrane, so the palladium membrane can be used to obtain ultra-high purity hydrogen. The rate at which hydrogen permeates palladium membrane is related to temperature, membrane thickness, and hydrogen content difference between two sides of the membrane. The increase of temperature, the increase of plasma P and the decrease of film thickness will increase the hydrogen permeability. However, high temperature will increase energy consumption and reduce the physical strength of the film. Therefore, temperature control usually at about 400 ℃. Some impurities can lead to membrane poisoning, reduce the hydrogen permeability of the membrane, and even damage the membrane. Substances that can cause palladium poisoning include mercury, arsenide, halide, oil vapor, sulfur, ammonia and dust. Palladium alloys can be made into tubes (called palladium tubes) or membranes (called palladium membranes).
An alloy of palladium and other elements, consisting mainly of:
(1) palladium gold alloy pd-au alloy, which contains more than 20% gold Au, is not soluble in nitric acid, and is used to manufacture chemical utensils because of its high melting point and high corrosion resistance; Alloys containing 20% pd-30 %Au are used to make artificial fiber drawing dies.
(2) palladium silver alloy Pd - Ag alloy, silver containing less than 50% Ag alloy corrosion resistance is close to palladium, add gold and platinum can improve the performance of the alloy with 50% Ag and 10% of Pt or Pd Au - Ag alloy can be used to make optical instrument corrosion resistant parts and watch case.
(3) palladium iridium alloy pd-ir alloy, which can significantly improve the corrosion resistance of Pd. Pd-ir alloy is used as an electrical contact point.
