Maglev train is a kind of high-speed high-tech means of transportation. Some countries such as China, Germany, Japan, etc. are developing it as fast transportation and means of transportation in big cities and between cities in the region. The world's first commercial maglev train is a maglev line from Shanghai Longyang Road Station in the west to Pudong International Airport in the east. The total length is 33km, the design speed is 431km/h, and the whole journey takes only 7 minutes. The technology used is provided by Germany. It has been operating safely for nearly 20 years, proving that the technology is excellent. Later, China planned to build the Shanghai-Hangzhou maglev line, which was planned to be put into operation before the 2010 Shanghai World Expo but was stranded due to various reasons. The total length of the Shanghai-Hangzhou Line is about 175km, of which the mainline of the Zhejiang section is about 105km long. The entire line is elevated, with Shanghai Station, Jiaxing Station, and Hangzhou East Station. The Shanghai-Hangzhou maglev line is a line between the suburbs of the city, with a normal operating speed of 450km/h and a normal maximum operating speed of ≤200km/h in the central urban area.
Maglev train is a kind of high-tech transportation using magnetic pole repulsion and attractive force, that is, the repulsive force makes the train float and the attractive force drives the train. The maglev train is equipped with superconducting magnets, and the bottom of the railway is equipped with coils. After the power is turned on, the polarity of the magnetic field generated by the ground coil is always the same as that of the electromagnet on the train. There are also coils on both sides of the rails, and the alternating current turns the coils into electromagnets, which interact with the magnets on the train to move the train forward. The main material for making superconducting magnets is titanium-niobium (Ti-Nb) alloys.
In 1801, British chemist C. Hatchett discovered an element when analyzing ore, named Columbium. In 1844, the German chemist H. Rose discovered a metal element similar to tantalum and named it Niobium after the daughter of tantalum (Niobe). In 1866, an element of columbium and niobium was identified. In 1951, the International Union of Pure and Applied Chemistry unified the name as niobium. The superconducting transition critical temperature of niobium is 9.25K, the thermal neutron absorption cross-section of the atom is 1.1 barn, and the standard electrode potential is Nb/Nb5+0.96V. The chemical properties of niobium and tantalum are very similar, and both are very stable chemical elements. Niobium does not react too much corrosive media in cold or slightly hot conditions, and dense niobium oxidizes significantly in the air only when the temperature is greater than 200 °C. The main physical properties of niobium (see table):
The physical and chemical properties of niobium and tantalum are similar, and they are mostly symbiotic in natural minerals. Most of the niobium ores in the world have a grade of 0.2% to 0.6%, and the standard niobium concentrate obtained after beneficiation has a grade of 50% to 65% (Nb, Ta) 2O5. The world's proven niobium ore reserves are 6.9 million tons. The extraction of niobium mainly includes processes such as decomposition of concentrate, separation of tantalum and niobium, preparation of compounds and metals, and refining. The industrial production methods of niobium include carbothermal reduction, sodium thermal reduction, and aluminothermic reduction.
Niobium is used in the iron and steel industry in the form of ferroniobium, and its consumption accounts for more than 85% of the world's total. It is mostly used in carbon steel and high-strength low-alloy steel. The main function of niobium in steel is to control the size and distribution of desolubilized niobium carbide to improve the wear resistance, corrosion resistance, grain refinement, and precipitation strengthening of steel, thereby improving the performance of steel. The superconductors formed by niobium and titanium, tin, zirconium, aluminum, germanium alloys, or metal compounds are of great significance. An indispensable material for train superconducting magnets, without niobium-titanium alloy superconducting materials, high-speed trains cannot float or run forward.
The biggest advantage of the high-speed maglev train is its high speed and fully automatic operation. The speed is ≥550km/h, so it is stable and noise-free; the line occupies less area, the magnetic field strength is low, and the energy consumption is low. The facilities are configured according to the fire protection standard of the aircraft, so the ride is smooth, comfortable, and extremely safe. A high-power linear synchronous motor is installed in the track, so the power of the high-speed maglev train comes from the track, which has high acceleration and braking ability; the turning radius is small, and the climbing ability is strong.
The Ti-Nb binary phase diagram is shown below, Nb is infinitely dissolved in β-Ti, forming a continuous solid solution. The solid solubility of Nb in α-Ti increases with decreasing temperature, and there are solid solutions α-Ti and β-(Ti, Nb).
