[China Aluminum Network] The chemical composition of aluminum alloy ingots is determined by chemical analysis and spectrochemical analysis. The chemical analysis method has the advantages of high analysis accuracy, unaffected by the state of the sample, and simple equipment. It is the basic analysis method for aluminum alloys, but the test operation is complicated and the test time is long, which is not suitable for the pre-furnace analysis on the production line.
Spectrochemical analysis is an instrumental analysis method for determining the composition of a substance based on its spectrum, referred to as spectral analysis. The commonly used analytical instrument is a spectrometer. Its characteristics are: analysis speed, analysis process is simple. Simultaneous analysis of many elements and the analysis of trace elements up to 0.01%.
1. Chemical Analysis Chemical analysis is a method that uses chemical analysis methods to determine the chemical composition of an alloy. The sample processing, separation techniques, and masking methods involved also fall within the scope of chemical analysis. GB/T6987-2001 "Aluminum and aluminum alloy chemical analysis method" measured a total of 22 elements, there are 32 analytical methods, some of which are used in two or more methods for analysis. The main application of the standard of chemical analysis methods are: heavy (mass) method, volumetric method, photometry, ion selective electrode method, complexation method, redox method, atomic absorption spectrometry. Each analytical method specifies the scope of application, method summary, analytical procedures, and expression of analytical results. It also specifies the reagents, equipment, and sample processing required for the test. Chemical analysis is an arbitration test method for inspecting the chemical composition of ingots.
Second, instrument analysis method Instrument analysis method is the use of more complex or special equipment, through the measurement of certain physical and physical chemical properties of the material parameters and changes to determine the chemical composition of the substance, component content and chemical structure. With the development of science and technology, the proportion of instrumental analysis in analytical chemistry continues to grow, and has become an important pillar of modern analytical chemistry. Instrumental analysis is more intelligent, efficient, and diversified. However, the use of instrumental analysis methods to analyze the composition of aluminum alloys still has certain limitations, mainly because the accuracy of detection is not high. Although the analysis of low-content components can meet the requirements, the accuracy of the tests such as titration analysis and heavy (mass) measurement cannot be achieved for the analysis of macro-components. Therefore, in the selection of detection methods, the requirements for analysis accuracy should be fully considered. In addition, prior to instrumental analysis, the sample is usually chemically pretreated (eg, enriched, removed from interfering impurities, etc.); at the same time, instrumental analysis generally requires calibration with standards, and many standards require chemical analysis. Method to calibrate.
The instrumental analysis method widely used in the analysis of the chemical composition of aluminum alloys is the optical analysis method, in which the spectral analysis method is a common optical analysis method. Spectral analysis is based on the characteristics of the material spectrum to study the chemical composition, structure and presence of substances, involving various electromagnetic spectrum, can be broken down into atomic emission spectrometry, atomic absorption spectrometry, infrared and Raman spectroscopy analysis method.
1 Atomic emission spectrometry 1) Principle Atomic emission spectrometry can analyze more than 70 elements. This method is often used for qualitative, semi-quantitative, and quantitative analysis. Under normal circumstances, the detection limit for components below 1% can reach 1×10-6 (ppm) with an accuracy of about ±10%, and the linear range is about 2 orders of magnitude, but if an inductively coupled plasma is used The body (ICP) as a light source can reduce the detection limit of certain elements to (10-3 to 10-4)×10-6, with an accuracy of ±1 % or less, and the linear range can be extended to 7 orders of magnitude.
Atomic emission spectrometry determines the chemical composition of a substance based on the spectrum emitted by the atom. Different substances consist of atoms of different elements, and atoms contain a closely packed atomic nucleus surrounded by constantly moving electrons. Each electron is at a certain energy level and has a certain amount of energy. Under normal circumstances, the atom is in a stable state and its energy is lower. This state is called the ground state. However, when an atom is affected by external energy (such as heat energy, electric energy, etc.), the atom acquires energy by colliding with the adjusting movement of gaseous particles and electrons, causing the electrons in the outer layer of the atom to jump from the ground state to a higher energy level. The atoms in this state are called excited states. One of the outer electrons in an atom transitions from the ground state to infinity, which is the binding force that leaves the nucleus and makes the atom an ion. This process is called ionization. The energy required for an atom to lose an outer electron to become an ion is called the first-order ionization potential. When the applied energy is greater, the ions can be further ionized into secondary ions (losing two electrons) or tertiary ions (losing three outer electrons), and have corresponding ionization potentials. The outer electrons in these ions can also be excited, and the required energy is the excitation potential of the corresponding ion.
The process of atomic emission spectrometry can be simply described as that the sample is transformed into the outer electron excitation of the gaseous atom to a high energy state under the influence of external energy, and when the energy transitions from a higher energy level to a lower energy level, the atom Excess energy will be released to emit characteristic lines. The generated radiation is subjected to dispersion and spectrophotometry by a spectrograph apparatus, and recorded on a photosensitive plate in the order of wavelengths, so that a regular spectrum line, ie, a spectrum diagram, can be presented, and qualitative or quantitative analysis can be performed based on the obtained spectrum diagram.
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