Spectral analysis of metal. Spectral analysis Spectral analysis of the chemical composition of the metal

The most effective way to determine the chemical composition of metals from the optical emission spectra of atoms and ions of the analyzed sample, excited in a light source.

The light source for optical emission analysis is the plasma of an electric spark or arc, which is produced using an excitation source (generator). The principle is based on the fact that the atoms of each element can emit light of certain wavelengths - spectral lines, and these wavelengths are different for different elements.

In order for atoms to begin emitting light, they must be excited by an electrical discharge. An electrical discharge in the form of a spark in an argon atmosphere can excite a large number of elements. High-temperature (more than 10,000 K) plasma is achieved, capable of exciting even such an element as nitrogen.

In a spark stand between the tungsten electrode and the test sample, sparks occur with a frequency of 100 to 1000 Hz. The spark table has a light channel through which the received light signal enters the optical system. In this case, the light channel and the spark stand are purged with argon. The entry of air from the environment into the spark stand leads to deterioration of the firing spot and, accordingly, to a deterioration in the quality of the chemical analysis of the sample.

The modern optical system is made according to the Paschen-Runge scheme. The spectral resolution of an optical system depends on the focal length, the number of lines of the diffraction grating used, the linear dispersion parameter and the qualified alignment of all optical components. To cover all the necessary emission lines, it is enough to cover the spectral region from 140 to 680 nm. For good visibility of the spectrum, the optical chamber must be filled with an inert gas (high frequency argon) or evacuated.

A device for spectral analysis of metal - M5000 analyzer. As recording elements, modern metal analyzers are equipped with CCD detectors (or PMTs), which convert visible light into an electrical signal, register it and transmit it to a computer. On the monitor screen we observe the concentrations of elements as percentages.

The intensity of the spectral line of the analyzed element, in addition to the concentration of the analyzed element, depends on a large number of different factors. For this reason, it is impossible to theoretically calculate the relationship between line intensity and the concentration of the corresponding element. That is why standard samples that are similar in composition to the sample being analyzed are required for analysis. These standard samples are first exposed (burned) on the device. Based on the results of burning, a calibration graph is constructed for each analyzed element, the dependence of the intensity of the spectral line of the element on its concentration. Subsequently, when analyzing samples, these calibration graphs are used to recalculate the measured intensities into concentrations.

It should be borne in mind that in reality several milligrams of a sample from its surface are analyzed. Therefore, to obtain correct results, the sample must be homogeneous in composition and structure, and the composition of the sample must be identical to the composition of the metal being analyzed. When analyzing metal in foundries, it is recommended to use special molds for casting samples. In this case, the sample shape can be arbitrary. It is only necessary that the sample being analyzed has sufficient surface area and can be clamped in a stand. Special adapters are used to analyze small samples, such as rods or wires.

Advantages of the method:

• Low cost
• Possibility of simultaneous quantitative determination of a large number of elements,
• High accuracy,
• Low detection limits,
• Easy sample preparation

Rostov-on-Don 2014

Compiled by: Yu.V. Dolgachev, V.N. Pustovoit Optical emission spectral analysis of metals. Methodical instructions for laboratory workshop / Rostov-on-Don. Publishing center of DSTU. 2014. – 8 p.

The guidelines are developed for use by students when performing laboratory workshops in the disciplines “Non-destructive methods of testing materials”, “Physical chemistry of nanomaterials”, “Nanotechnologies and nanomaterials” and are intended for the practical development of theoretical concepts about the structure and properties of materials, obtaining skills in analyzing the chemical composition of metals and alloys, .

Published by decision of the methodological commission

Faculty of Mechanical Engineering Technologies and Equipment

Scientific editor, Doctor of Technical Sciences, Professor Pustovoit V.N. (DSTU)

Reviewer: Doctor of Technical Sciences, Professor Kuzharov A.S. (DSTU)

 Publishing center DSTU, 2014

Optical emission spectral analysis of metals

PURPOSE OF THE WORK: To become familiar with the purpose, capabilities, operating principle of the Magellan Q8 spectral analyzer and to perform a chemical analysis of a metal sample.

1. Basic theoretical concepts

1.1. Purpose of optical emission spectral analysis

Today, chemical composition analysis has found wide application in many sectors of the national economy. The quality, reliability, and durability of the product largely depend on the composition of the alloy used. The slightest deviation from the specified chemical composition can lead to a negative change in properties. A particular danger is that this deviation may be visually invisible and, as a result, indeterminable without special instruments. Human senses do not make it possible to analyze such parameters of a metal as its composition or the grade of alloy used. One of the devices that allows you to obtain the necessary information about the chemical composition of the alloy is an optical emission spectrometer.

An optical emission spectrometer is used to measure the mass fraction of chemical elements in metals and alloys and is used in analytical laboratories of industrial enterprises, in workshops for the rapid sorting and identification of metals and alloys, as well as for the analysis of large structures without compromising their integrity.

1.2 Operating principle of the optical emission analyzer

The operating principle of the spectrometer is based on measuring the radiation intensity at a certain wavelength of the emission spectrum of atoms of the analyzed elements. The radiation is excited by a spark discharge between the auxiliary electrode and the analyzed metal sample. During the analysis process, argon flows around the object under study, making it more visible for study. An emission spectrometer records the intensity of radiation and, based on the data obtained, analyzes the composition of the metal. The content of elements in the sample is determined by calibration relationships between the intensity of emission radiation and the content of the element in the sample.

The spectrometer consists of a spectrum excitation source, an optical system, and an automated control and recording system based on an IBM-compatible computer.

The spark spectrum excitation source is designed to excite the emission light flux from a spark between the sample and the electrode. The spectral composition of light is determined by the chemical composition of the sample being studied.

Currently, the most optimal layout of the optical system is considered to be based on the Paschen-Runge scheme (Fig. 1).

Rice. 1 Optical system according to the Paschen-Runge scheme

When atoms excited by a glow discharge move to a lower orbit, they emit light. Each emitted wavelength is characteristic of each atom that emitted it. The light is focused at the entrance slit of the spectrometer and split into a concave holographic grating according to wavelengths. After this, through precisely positioned output slits, the light enters the photomultiplier tube corresponding to the element.

To ensure good transparency, the optical chamber must be evacuated. In addition, the system must be independent of external conditions (temperature and air pressure). Currently, stationary optical spectrometers are thermally stabilized with an accuracy of tenths of a degree.

The process of measuring and processing output information is controlled from a built-in IBM-compatible computer using a special software package. The program configures the device, constructs calibration curves based on the analysis of standard samples, optimizes its parameters, controls the spectrometer modes, processes, saves and prints measurement results.

1.3 Installation of Magellan Q8

Qantron Magellan (Magellan Q8) is an optical emission analyzer with vacuum optics from Bruker (Fig. 2). Allows you to determine the chemical composition of alloys based on iron (steel and cast iron), copper (bronze, brass, etc.) aluminum (duralumin, etc.). The installation is equipped with sensors that determine the percentage of elements such as carbon, nitrogen, phosphorus, sulfur, vanadium, tungsten, silicon, manganese, chromium, molybdenum, nickel, aluminum, cobalt, copper, niobium, titanium, tin, boron, iron, zinc , tin, beryllium, magnesium, lead.

Calibration of the installation is carried out using calibration samples of various steels, cast irons, bronze, aluminum alloys. The accuracy of determining the chemical composition of alloys is up to hundredths of a percent.

Rice. 2. Installation of Magellan Q8

Analysis of metals and alloys

Analysis of metals and alloys solves the problem of determining the elemental composition of metals and their alloys using analytical methods. The main purpose is to check the alloy grade or type and compositional analysis of various alloys (quantitative analysis).

• wave dispersive analysis,
• emission analysis,
• X-ray fluorescence analysis,
• assay analysis.

X-ray fluorescence analysis

Portable X-ray fluorescence spectrometer for analysis of metals and alloys

Spectrum displaying alloy Al, Fe, Ti

XRF analysis is carried out by exposing the metal to X-rays and analyzing the fluorescence using modern electronics to achieve good measurement accuracy.

Advantages of the method:

• Non-destructive analysis.
• It is possible to measure many elements with high accuracy.

Alloy identification is achieved by identifying the unique combination of several elements within specified compositional ranges. Accurate quantitative analysis is achieved by using appropriate corrections to the inter-element influence matrix.

The analyzed material is exposed to X-ray fluorescence within a few seconds. Atoms of elements in a material become excited and emit photons with energies specific to each element. The sensor separates and stores photoelectrons received from the sample into energy regions and, based on the total intensity in each region, determines the concentration of the element. The energy region corresponding to the elements , , , MS , , , , , , , , , , , , , , , , , can be analyzed effectively.

The RF analyzer consists of a central processor, an X-ray tube, a detector, and an electronic memory that stores calibration data. In addition, the memory is also used to store and process alloy grade data and other coefficients related to various special operating modes.

As is correct, control over the study is carried out through a computer program based on a hand-held portable computer (PDA), which provides the user with an image of the spectrum and the obtained element content values.

After the analysis, the values ​​are compared with a database of steel grades and the closest grade is searched.

Emission method

Emission method: One of the main sources of random error in measurements of relative impurity concentrations in emission spectral analysis is the instability of the parameters of the spectrum excitation source. Therefore, to ensure the emission of impurity atoms from the sample and their subsequent optical excitation, a low-voltage spark, the so-called C, R, L - discharge is used. In this case, two parameters are stabilized on which the processes of emission and optical excitation depend - voltage and energy in the discharge circuit. This ensures low standard deviation (RMS) of measurement results. A special feature of the emission method is the quantitative determination of light elements in iron-based alloys (analysis of sulfur, phosphorus and carbon in steel). There are several types of devices for emission analysis based on the spark and air-arc methods or their combination.

Assay method

Assay method: Assay melting is based on the physical and chemical laws of metal reduction, slag formation and wetting with molten substances. The main stages of assay analysis using the example of an alloy of silver and lead:

• Sample preparation
• Mixing
• Crucible melting for lead alloy
• Pouring lead alloy into iron molds for cooling
• Separation of lead alloy (werkbley) from slag
• Werkbley cupellation (lead removal)
• Removing a bead of precious metals and weighing it
• Quartering (adding silver, if necessary)
• Treating the bead with dilute nitric acid (dissolving silver)
• Gravimetric (weight) determination of silver

see also

Wikimedia Foundation.

2010.

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A metal analyzer allows you to quickly and accurately check the composition of an alloy or its type. This is important in many industrial sectors. Most often, secondary raw materials are analyzed in this way. This is due to the fact that it is impossible for even an experienced specialist to perform such a procedure at random. The device in question is also called a spectrometer.

Purpose

Using a metal analyzer, you can reliably determine the composition of the copper alloy and the percentage of foreign inclusions in it. In addition, it is possible to determine the nickel content of stainless steel. In this case, the raw material under study does not need to be sawed or its structure disturbed in any other way. The device will be useful for those who work with ferrous scrap. It also helps to identify the presence of heavy metals in the alloy, which ensures safe operation and compliance with the required standards.

Kinds

The analyzer of metals and alloys is a complex high-tech device, the creation of which at home is very problematic. There are two types of these devices:

• Laser modifications, operating on the principle of optical emission.
• X-ray option, determining readings using x-rays.

Stationary analogues are aimed at large warehouses and bases for receiving and processing scrap metal. For example, the M-5000 model is a compact modification that can fit on a table. The device is used primarily in secondary metallurgy production. Reviews from experts confirm that such a device optimally combines quality and price indicators.

Optical emission models

The optical emission metal analyzer is used in the study of various structures, workpieces, parts and ingots. The spark or air arc analysis method is used. In the first case, some evaporation of the metal alloy is noted.

The working medium of the devices under consideration is argon. To change the operating mode of the device, it is enough to replace the nozzle on a special sensor. The chemical composition of the alloy is recognized and recorded using an optical spectrometer.

There are several research modes, namely:

• Determination of metal grade using a special table.
• Comparison of the reference spectrum with an analogue of the alloy under study.
• A “yes-no” function that determines the specified characteristics of the raw material.

This device works with ferrite, aluminum, titanium, copper, cobalt, tool alloys, as well as low alloy and stainless steel.

X-ray fluorescence options

This type of metal analyzer consists of light-sensitive elements that can detect more than 40 substances. Reviews from experts note the fast operation of these devices, as well as the monitoring without compromising the integrity of the analyzed object.

Due to their compactness and low weight, the devices in question are easy to use and equipped with a housing protected from moisture. The software makes it possible to set user standards, enter the required parameters and connect a printer with subsequent printing of the received information.

A feature of such analyzers is that they cannot detect elements with atomic numbers below 11. Therefore, they are not suitable for detecting carbon in cast iron or steel.

Peculiarities

The optical emission type metal composition analyzer has the following capabilities:

• The device is able to detect even minor inclusions of foreign mixtures, which is important when testing ferrous metals for the presence of phosphorus, sulfur and carbon.
• High measurement accuracy makes it possible to use the device for certification analysis.
• The unit is offered with a pre-loaded program, which makes it difficult to check the alloy for the introduction of unknown inclusions that are not included in the software list.
• Before starting the inspection, the object must be processed with a file or a grinding wheel to remove the top layer of dirt or dust.

Features of X-ray metal spectral analyzers:

• These devices are not as accurate, but are quite suitable for working with scrap and sorting alloys.
• The device is versatile. Allows you to detect all elements available in its range.
• The surface of the object under study does not need to be carefully treated; it is enough to remove rust or paint.

Portable metal analyzer

The devices under consideration are divided into three types:

1. Stationary option.
2. Mobile models.
3. Portable versions.

Stationary models are located in special rooms, occupy a large area, produce ultra-precise results, and have wide functionality.

Mobile analogues are portable or mobile devices. They are most often used in factories and quality control laboratories.

The portable metal and alloy analyzer is the most compact and can be held in one hand. The unit is protected from mechanical influences and can be used in field conditions. This device is suitable for people looking for raw materials using a metal detector.

Advantages

Portable models operate in the same way as their stationary counterparts. The average weight of the device is from 1.5 to 2 kilograms. Judging by user reviews, in certain areas such a device becomes the best option. The device is equipped with a liquid crystal screen, which displays information about the composition of the object under study.

The unit is capable of accumulating and storing information, including research results and photographs. The analyzer accuracy is about 0.1%, which is sufficient for use in the recycling industry.

Using a portable model, you can analyze large and complex structures, pipes, ingots, small parts, as well as workpieces, electrodes or shavings.

Manufacturers

Among the most famous companies producing metal chemical composition analyzers are the following companies:

• Olympus Corporation. This Japanese corporation specializes in the production of photographic equipment and optics. Analyzers from this company are popular due to their high quality. Consumer reviews only confirm this fact.
• Focused Photonics Inc. The Chinese manufacturer is one of the world leaders in the production of various devices for monitoring various environmental parameters. The company's analyzers are distinguished not only by their high quality, but also by their affordable price.
• Bruker. The German company was created over 50 years ago. It has representative offices in almost one hundred countries. Devices from this manufacturer are distinguished by high quality and a wide selection of models.
• LIS-01. The device is of domestic production. It was released by a scientific division whose office is located in Yekaterinburg. The main purpose of the device is sorting scrap, diagnosing alloys during incoming and outgoing inspection. The device is an order of magnitude cheaper than its foreign analogues.

In their reviews, users speak positively about the MIX5 FPI model. It is powerful and has the ability to accurately detect heavy metals. The device is easy to use: just press one button and wait for the test results. In high-speed mode this will take no more than 2-3 seconds.

In conclusion

As practice and consumer reviews show, metal and alloy analyzers are quite in demand not only in the industrial sector, but also in small companies and among individuals. Finding a suitable option on the modern market is quite simple. You just need to consider the range of use of the device and its capabilities. The cost of such devices varies from several thousand rubles to 20-25 thousand dollars. The price depends on the type of device, its functionality and manufacturer.

GUIDE TECHNICAL MATERIALS

from 08.09. 1980 No. 11-10-4/1601 introduction date established from 01.10.1980

These technical guidelines apply to chemical and physical methods for studying the chemical composition of basic and welding materials used in chemical and petroleum engineering (except for shielding gases).

Establish standard methods for studying materials with different bases, methods for calculating results and safety precautions.

RD RTM 26-366-80

GUIDE TECHNICAL MATERIAL

ACCELERATED AND MARKING METHODS
CHEMICAL AND SPECTRAL ANALYSIS
BASIC AND WELDING MATERIALS IN
CHEMICAL AND PETROLEUM EQUIPMENT BUILDING

SPECTRAL METHODS FOR ANALYSIS OF STEEL

This technical guidance material applies to monitoring the chemical composition of carbon, alloy, structural and high-alloy steels, as well as weld materials for the main marking and alloying elements using the method of spectral analysis.

1. GENERAL REQUIREMENTS FOR ANALYSIS METHODS

1.2. The state of delivery of standards (which are used as GSO ISO TsNIIChM, as well as secondary production SOPs) and samples must be the same.

1.3. The masses of standards and samples should not differ significantly and should be at least 30 g.

1.4. The sharpness of the surface of standards and samples should be Rz20.

2. PHOTOGRAPHIC METHODS

2.1. Determination of chromium, nickel, manganese, silicon in carbon steels.

2.1.1. Purpose

The method is intended for the determination of chromium, nickel, manganese, silicon in steel grades St. 3, Art. 5 and others according to GOST 380-71, in steel grades 20, 40, 45 and others according to GOST 1050-74.

Medium dispersion quartz spectrograph type ISP-22, ISP-28 or ISP-30.

Arc generator type DT-2.

Spark generator type IG-3.

Microphotometer MF-2 or MF-4.

Spectroprojector PS-18.

Grinding machine with electrocorundum wheels, grain size No. 36-64.

Set of files (for sharpening standards and samples).

A device or fixture for sharpening metal and carbon electrodes.

Sets of GSO ISO TsNIIChM - 12; 53; 76; 77 and their replacements.

Permanent rod electrodesÆ from 6 to 8 mm from electrolytic copper grade M- I according to GOST 859-78 and rodsÆ 6 mm from spectrally pure grade C coals 1, C 2, C 3.

“Spectral” photographic plates, type I, II.

Hydroquinone (paradioxybenzene) according to GOST 19627-74.

Sodium sulfite (sodium sulfite) crystalline according to GOST 429-76.

Metol (para-methylaminophenol sulfite) according to GOST 5-1177-71.

Anhydrous sodium carbonate according to GOST 83-79.

Ammonium chloride according to GOST 3773-72.

Sodium sulfate (sodium thiosulfate) according to GOST 4215-66.

A layer of 1 mm is removed from the end surface of the steel sample using an emery wheel, then the sample is sharpened with a file, the surface quality must be no less than Rz20. Copper electrodes are sharpened to a 90° cone, rounded with a radius of 1.5 to 2.0 mm. Carbon electrodes are sharpened into a truncated cone with a platform diameter of 1.0 to 1.5 mm. The light source is focused onto the slit of the spectral apparatus using a quartz condenser with a focal length of 75 mm or a three-lens lighting system. The lenses are installed at the distances specified in the spectrograph data sheet. The slit width of the spectral apparatus is from 0.012 to 0.015 mm.

2.1.4. Spectrum excitation source

An alternating current arc (DG-2 generator) and a high-voltage spark (IG-3 generator) are used as sources of spectrum excitation. The main parameters of the discharge circuit are given (in table).

Table 1

AC arc

table 2

High voltage spark