Tantalum, niobium metals and alloys in the gas impurities such as oxygen, hydrogen, nitrogen, and carbon and sulfur in the metal due to their behavior and analysis methods and other gases have many similarities, so in analytical chemistry is often included in the "metal gas". The main forms of gas in metal are molecular gas adsorbed on the metal surface, water and solid solution formed by the interaction with metal such as oxide, hydride, nitride and carbide.
(1) instrument calibration
More advanced gas analysis instrument, and sensitivity analysis are high degree of automation, but these instruments are mostly USES the relative analysis method, it is based on the signal value of the gas under test and the gas content in comparison with the signal value of known, on the basis of instrument testing accuracy relies on the calibration of standard material: calibration methods mainly have three.
1) calibration of gas gauge because most of the gas analysis instruments are equipped with calibration function of gas gauge, the operation is relatively convenient. It should be noted that the selected gas standard should be certified by the state metrology and have a composition certificate. The content range of gas should be consistent with that of the gas to be measured, and the commonly used gas should be marked with H2, CO2+SO2, CO2+N2+Ar, etc. Compared with the standard sample (CRM) calibration, gas calibration can avoid the blank error caused by melting samples, but cannot calibrate the whole process of the analysis procedure.
2) the standard sample calibration shall be conducted with the approved standard sample (CRM) with the same material as the sample to be tested and the content of the gas to be tested is close to that of the sample to be tested. This method can compensate the systematic errors caused by gas release and adsorption. This method is easy to operate and is often recommended by some international organizations for standardization. However, it is often difficult to obtain a suitable standard sample. In this case, it is necessary to select the standard sample whose material properties and contents are as close as possible to the sample to be tested through experiments. The instrument may also be calibrated by alternative authoritative methods of analysis of different principles.
3) pure material calibration: calibration instruments and methods for high purity materials are often adopted in the world. For example, carbon analysis was calibrated with Na2CO3, BaCO3, and C12H22O11. Calibration of sulfur analysis with BaSO4 or sulfur; The oxygen analysis was calibrated with Ta2O5 and Nb2O5. Nitrogen analysis was calibrated with TiN. Note that the purity of these substances must be confirmed by the country or industry with a content certificate, and the weighing scales should be accurate to at least 0.01mg.
