The gaseous impurities in tantalum, niobium and alloys include oxygen, hydrogen, nitrogen, etc., while carbon and sulfur are often listed as "gases in metals" in analytical chemistry because of their similar behavior in metals and analysis methods and other gases. The forms of gas in metal are mainly molecular gas adsorbed on the metal surface, water and solid solutions such as oxides, hydrides, nitride and carbides generated by interaction with metal.
There are vacuum melting method, vacuum thermal extraction method, inert atmosphere melting method, Kjeldahl method, high-frequency induction heating - infrared absorption method, tubular resistance furnace heating - coulomb method, neutron activation method, spectrometric method and mass spectrometry method. The development of material resistance has promoted the continuous upgrading of analytical instruments, and more advanced, more reliable and more sensitive methods are constantly emerging, such as inert atmosphere melting - infrared absorption method or thermal conductivity method, high-frequency induction heating infrared absorption method and other methods to gradually replace the vacuum melting and vacuum thermal extraction method. Various types of gas analysis instruments produced by LECO of the United States, HORIBA of Japan, Leybold-Heraeus of Germany and ELTRA of Germany are widely used in China. Domestic gas analysis instrument manufacturers (such as Shanghai Decai Instrument Company, Beijing Iron and Steel Research Institute, Beijing Analysis instrument Factory and Wuxi High-speed instrument Factory, etc.) also produce a variety of gas analysis instruments to meet user requirements. E{The higher the degree of automation of the pre-analytical instruments, the more convenient the setting and selection of test conditions, there is no difficulty for the general analyst. However, the two technical problems of instrument calibration and the reduction of blank value are worthy of attention.
In inert atmosphere F, the sample in graphite crucible is melted with co-solvent at high temperature. Oxygen and excess carbon in the sample generate CO and a small amount of CO2. CO is oxidized into CO2 by rare earth copper oxide, which is then brought into the infrared detector by carrier gas (ship).
The standard sample for calibration may be the industry-approved oxygen standard sample of tantalum and niobium, or the American NBS or equivalent steel standard sample (note: the high specific volume tantalum powder has a large specific surface area. It is easy to absorb oxygen and water, so it is not suitable to be used as standard sample. The sample weight is 0.05 ~ 0.15g, the blank value is no more than 3 g. The foil coated nickel blue is used as flux. The foil was cleaned with acetone, and the amount of nickel flux was at least 8 times that of the sample to effectively reduce the melting point and accelerate gas precipitation. Method Applicable scope: 0.005% - 0.5%.
