Introduction

Section number 1. Building materials and their behavior under fire conditions.

Topic 1. Basic properties of building materials, research methods and evaluation of the behavior of building materials in a fire.

Topic 2. Stone materials and their behavior in a fire.

Topic 3. Metals, their behavior in a fire and ways to increase resistance to its effects.

Topic 4. Wood, its fire hazard, methods of fire protection and evaluation of their effectiveness.

Topic 5. Plastics, their fire hazard, methods of its research and evaluation.

Topic 6. Rationing of fireproof use of materials in construction.

Section 2. "Building structures, buildings, structures and their behavior in a fire."

Topic 7. Initial information about space-planning and design solutions for buildings and structures.

Topic 8. Initial information about the fire hazard of buildings and building structures.

Topic 9. Theoretical foundations for the development of methods for calculating the fire resistance of building structures.

Topic 10. Fire resistance of metal structures.

Topic 11. Fire resistance of wooden structures.

Topic 12. Fire resistance of reinforced concrete structures.

Topic 13. Behavior of buildings, structures in a fire.

Topic 14. Prospects for improving the approach to determining and standardizing the requirements for fire resistance of building structures.

Introduction

The structure of the discipline, its significance in the process of professional training of the graduate of the institute. Modern trends in design, construction, operation, buildings and structures.

The national economic significance of the activities of firefighters in monitoring the fireproof use of building materials and the use of fire-resistant building structures in the design, construction, reconstruction of buildings and structures.

Section 1. Building materials and their behavior in a fire.

Topic 1. Basic properties of building materials, research methods and evaluation of the behavior of building materials in a fire.

Types, properties, features of the production and use of basic building materials and their classification. Factors affecting the behavior of building materials in a fire. Classification of the basic properties of building materials.

Physical properties and indicators that characterize them: porosity, hygroscopicity, water absorption, water-gas and vapor permeability of building materials.

The main forms of communication of moisture with the material.

Thermophysical properties and indicators characterizing them.

The main negative processes that determine the behavior of inorganic building materials in a fire. Methods for experimental evaluation of changes in the mechanical characteristics of building materials in relation to fire conditions.

Processes occurring in organic materials under fire conditions. Fire-technical characteristics of building materials, methods of their research and evaluation.

Practice 1. Determining the basic properties of some building materials and predicting the behavior of these materials in a fire.

Page 1

Introduction.

Human civilization throughout its development, at least in the material sphere, constantly uses the chemical, biological and physical laws that operate on our planet to satisfy one or another of its needs. http://voronezh.pinskdrev.ru/ dining tables in voronezh.

In ancient times, this happened in two ways: consciously or spontaneously. Naturally, we are interested in the first way. An example of the conscious use of chemical phenomena can be:

Souring of milk used to produce cheese, sour cream and other dairy products;

Fermentation of some seeds such as hops in the presence of yeast to form beer;

Sublimation of pollen of some flowers (poppy, hemp) and obtaining drugs;

Fermentation of the juice of some fruits (primarily grapes), containing a lot of sugar, resulting in wine, vinegar.

Revolutionary transformations in human life were introduced by fire. Man began to use fire for cooking, in pottery, for processing and smelting metals, processing wood into coal, evaporating and drying food for the winter.

Over time, people have a need for more and more new materials. Chemistry provided invaluable assistance in their creation. The role of chemistry is especially great in the creation of pure and ultrapure materials (hereinafter abbreviated as SCM). If, in my opinion, the leading position in the creation of new materials is still occupied by physical processes and technologies, then the production of SCM is often more efficient and productive with the help of chemical reactions. And also there was a need to protect materials from corrosion, this is actually the main role of physico-chemical methods in building materials. With the help of physicochemical methods, physical phenomena that occur during chemical reactions are studied. For example, in the colorimetric method, the color intensity is measured depending on the concentration of a substance, in the conductometric analysis, the change in the electrical conductivity of solutions is measured, etc.

This abstract outlines some types of corrosion processes, as well as ways to deal with them, which is the main practical task of physical and chemical methods in building materials.

Physical and chemical methods of analysis and their classification.

Physicochemical methods of analysis (PCMA) are based on the use of the dependence of the physical properties of substances (for example, light absorption, electrical conductivity, etc.) on their chemical composition. Sometimes in the literature, physical methods of analysis are separated from PCMA, thus emphasizing that a chemical reaction is used in PCMA, but not in physical ones. Physical methods of analysis and FHMA, mainly in the Western literature, are called instrumental, since they usually require the use of instruments, measuring instruments. Instrumental methods of analysis basically have their own theory, different from the theory of methods of chemical (classical) analysis (titrimetry and gravimetry). The basis of this theory is the interaction of matter with the flow of energy.

When using PCMA to obtain information about the chemical composition of a substance, the test sample is exposed to some form of energy. Depending on the type of energy in a substance, there is a change in the energy state of its constituent particles (molecules, ions, atoms), which is expressed in a change in one or another property (for example, color, magnetic properties, etc.). By registering a change in this property as an analytical signal, information is obtained about the qualitative and quantitative composition of the object under study or about its structure.

According to the type of perturbation energy and measured property (analytical signal), FHMA can be classified as follows (Table 2.1.1).

In addition to those listed in the table, there are many other private FHMAs that do not fall under this classification.

Optical, chromatographic and potentiometric methods of analysis have the greatest practical application.

Table 2.1.1.

Mankind, throughout its development, uses the laws of chemistry and physics in its activities to solve various problems and satisfy many needs.

In ancient times, this process went in two different ways: consciously, based on accumulated experience, or accidentally. Vivid examples of the conscious application of the laws of chemistry include: souring milk, and its subsequent use for the preparation of cheese products, sour cream and other things; the fermentation of certain seeds, such as hops, and the subsequent manufacture of brewing products; fermentation of the juices of various fruits (mainly grapes, which contain a large amount of sugar), eventually gave wine products, vinegar.

The discovery of fire was a revolution in the life of mankind. People began to use fire for cooking, for the heat treatment of clay products, for working with various metals, for producing charcoal and much more.

Over time, people have a need for more functional materials and products based on them. Their knowledge in the field of chemistry had a huge impact on the solution of this problem. Chemistry played a particularly important role in the production of pure and ultrapure substances. If in the manufacture of new materials, the first place belongs to physical processes and technologies based on them, then the synthesis of ultrapure substances, as a rule, is more easily carried out using chemical reactions [

Using physico-chemical methods, they study the physical phenomena that occur during the course of chemical reactions. For example, in the colorimetric method, the color intensity is measured depending on the concentration of a substance, in the conductometric method, the change in the electrical conductivity of solutions is measured, and the optical methods use the relationship between the optical properties of the system and its composition.

Physico-chemical research methods are also used for a comprehensive study of building materials. The use of such methods allows you to study in depth the composition, structure and properties of building materials and products. Diagnostics of the composition, structure and properties of the material at different stages of its manufacture and operation makes it possible to develop progressive resource-saving and energy-saving technologies [

This paper shows a general classification of physical and chemical methods for studying building materials (thermography, X-ray diffraction, optical microscopy, electron microscopy, atomic emission spectroscopy, molecular absorption spectroscopy, colorimetry, potentiometry) and considers in more detail such methods as thermal and X-ray phase analysis, and also methods for studying the porous structure [ Builder's Handbook [Electronic resource] // Ministry of Urban and Rural Construction of the Byelorussian SSR. URL: www.bibliotekar.ru/spravochnick-104-stroymaterialy.html].

1. Classification of physical and chemical research methods

Physical and chemical research methods are based on the close relationship between the physical characteristics of the material (for example, the ability to absorb light, electrical conductivity, and others) and the structural organization of the material from the point of view of chemistry. It happens that from physicochemical methods, purely physical research methods are distinguished as a separate group, thus showing that a certain chemical reaction is considered in physicochemical methods, in contrast to purely physical ones. These research methods are often called instrumental, because they involve the use of various measuring devices. Instrumental research methods, as a rule, have their own theoretical base, this base diverges from the theoretical base of chemical studies (titrimetric and gravimetric). It was based on the interaction of matter with various energies.

In the course of physical and chemical studies, in order to obtain the necessary data on the composition and structural organization of a substance, an experimental sample is subjected to the influence of some kind of energy. Depending on the type of energy in substances, the energy states of its constituent particles (molecules, ions, atoms) change. This is expressed in a change in a certain set of characteristics (for example, color, magnetic properties, and others). As a result of registering changes in the characteristics of a substance, data are obtained on the qualitative and quantitative composition of the test sample, or data on its structure.

According to the variety of influencing energies and the characteristics under study, physicochemical research methods are divided in the following way.

Table 1. Classification of physical and chemical methods

In addition to those listed in this table, there are quite a few private physico-chemical methods that do not fit into such a classification. In fact, optical, chromatographic and potentiometric methods are most actively used to study the characteristics, composition and structure of the sample [ Galuzo, G.S. Methods for the study of building materials: teaching aid / G.S. Galuzo, V.A. Bogdan, O.G. Galuzo, V.I. Kovazhnkov. - Minsk: BNTU, 2008. - 227 p.].

2. Methods of thermal analysis

Thermal analysis is actively used to study various building materials - mineral and organic, natural and synthetic. Its use helps to reveal the presence of a particular phase in the material, to determine the reactions of interaction, decomposition, and, in exceptional cases, to obtain information about the quantitative composition of the crystalline phase. The possibility of obtaining information on the phase composition of highly dispersed and cryptocrystalline polymineral mixtures without division into polymineral fractions is one of the main advantages of the technique. Thermal research methods are based on the rules of constancy of the chemical composition and physical characteristics of the substance, under specific conditions, and among other things, on the laws of correspondence and characteristic.

The law of correspondence says that a specific thermal effect can be attributed to any phase change in the sample.

And the law of characteristicity says that thermal effects are individual for each chemical substance.

The main idea of ​​thermal analysis is to study the transformations that occur under conditions of increasing temperature indicators in systems of substances or specific compounds in various physical and chemical processes, according to the thermal effects accompanying them.

Physical processes, as a rule, are based on the transformation of the structural structure, or the state of aggregation of the system with its constant chemical composition.

Chemical processes lead to the transformation of the chemical composition of the system. These include directly dehydration, dissociation, oxidation, exchange reactions, and others.

Initially, thermal curves for limestone and clay rocks were obtained by the French chemist Henri Louis Le Chatelier in 1886-1887. In Russia, one of the first to study the method of thermal research was Academician N.S. Kurnakov (in 1904). Updated modifications of the Kurnakov pyrometer (an apparatus for automatically recording heating and cooling curves) are still used in most research laboratories to this day. Regarding the studied characteristics as a result of heating or cooling, the following methods of thermal analysis are distinguished: differential thermal analysis (DTA) - the change in the energy of the sample under study is determined; thermogravimetry - mass changes; dilatometry - volumes change; gas volumetry - the composition of the gas phase changes; electrical conductivity - electrical resistance changes.

In the course of thermal research, several methods of study can be applied simultaneously, each of which captures changes in energy, mass, volume, and other characteristics. A comprehensive study of the characteristics of the system during the heating process helps to study in more detail and more thoroughly the fundamentals of the processes occurring in it.

One of the most important and widely used methods is differential thermal analysis.

Fluctuations in the temperature characteristics of a substance can be detected during its sequential heating. So, the crucible is filled with experimental material (sample), placed in an electric furnace, which is heated, and they begin to measure the temperature indicators of the system under study using a simple thermocouple connected to a galvanometer.

Registration of the change in the enthalpy of a substance occurs with the help of an ordinary thermocouple. But due to the fact that the deviations that are fashionable to see on the temperature curve are not very large, it is better to use a differential thermocouple. Initially, the use of this thermocouple was proposed by N.S. Kurnakov. A schematic representation of a self-registering pyrometer is shown in Figure 1.

This schematic image shows a pair of ordinary thermocouples, which are connected to each other by the same ends, forming the so-called cold junction. The remaining two ends are connected to the apparatus, which allows you to fix the transformation in the electromotive force (EMF) circuit, resulting from an increase in the temperature of the hot junctions of the thermocouple. One hot junction is located in the studied sample, and the second one is located in the reference reference substance.

Figure 1. Schematic representation of a differential and simple thermocouple: 1 - electric furnace; 2 - block; 3 – experimental sample under study; 4 - reference substance (standard); 5 – hot junction of thermocouple; 6 – cold junction of thermocouple; 7 - galvanometer for fixing the DTA curve; 8 - galvanometer for fixing the temperature curve.

If, for the system under study, some transformations are frequent that are associated with the absorption or release of thermal energy, then its temperature index at the moment can be much higher or lower than that of the reference reference substance. This temperature difference leads to a difference in the value of the EMF and, as a result, to the deviation of the DTA curve up or down from zero, or the baseline. The zero line is the line parallel to the x-axis and drawn through the beginning of the DTA curve, this can be seen in Figure 2.

Figure 2. Scheme of simple and differential (DTA) temperature curves.

In fact, quite often after the completion of some thermal transformation, the DTA curve does not return to the zero line, but continues to run parallel to it or at a certain angle. This line is called the baseline. This discrepancy between the base and zero lines is explained by different thermophysical characteristics of the studied system of substances and the reference substance of comparison [].

3. Methods of X-ray phase analysis

X-ray methods for studying building materials are based on experiments in which X-ray radiation is used. This class of studies is actively used to study the mineralogical composition of raw materials and final products, phase transformations in the substance at various stages of their processing into ready-to-use products and during operation, and, among other things, to identify the nature of the structural structure of the crystal lattice.

The technique of X-ray studies used to determine the parameters of the elementary cell of a substance is called the X-ray diffraction technique. The technique, which is followed in the course of studying phase transformations and the mineralogical composition of substances, is called x-ray phase analysis. Methods of X-ray phase analysis (XRF) are of great importance in the study of mineral building materials. Based on the results of X-ray phase studies, information is obtained about the presence of crystalline phases and their quantity in the sample. It follows from this that there are quantitative and qualitative methods of analysis.

The purpose of qualitative X-ray phase analysis is to obtain information about the nature of the crystalline phase of the substance under study. The methods are based on the fact that each specific crystalline material has a specific X-ray pattern with its own set of diffraction peaks. In our time, there are reliable x-ray data on most of the crystalline substances known to man.

The task of the quantitative composition is to obtain information about the number of specific phases in polyphase polycrystalline substances; it is based on the dependence of the intensity of diffraction maxima on the percentage of the phase under study. With an increase in the amount of any phase, its intensity of reflections becomes greater. But for polyphase substances, the relationship between the intensity and amount of this phase is ambiguous, since the magnitude of the reflection intensity of this phase depends not only on its percentage, but also on the value of μ, which characterizes how much the X-ray beam is attenuated as a result of passing through the material under study. . This attenuation value of the material under study depends on the attenuation values ​​and the amount of other phases that are also included in its composition. From this it follows that, each method of quantitative analysis must somehow take into account the effect of the attenuation index, as a result of a change in the composition of the samples, which violates the direct proportionality between the amount of this phase and the degree of intensity of its diffraction reflection [ Makarova, I.A. Physico-chemical methods for the study of building materials: study guide / I.A. Makarova, N.A. Lokhov. - Bratsk: From BrGU, 2011. - 139 p. ].

The options for obtaining radiographs are divided, based on the method of registration of radiation, into photographic and diffractometric. The use of methods of the first type involves the photo registration of X-rays, under the influence of which the darkening of the photographic emulsion is observed. Diffractometric methods for obtaining X-ray patterns, which are implemented in diffractometers, differ from photographic methods in that the diffraction pattern is obtained sequentially over time [ Pindyuk, T.F. Methods for the study of building materials: guidelines for laboratory work / T.F. Pindyuk, I.L. Chulkov. - Omsk: SibADI, 2011. - 60 p. ].

4. Methods for studying the porous structure

Building materials have a heterogeneous and rather complex structure. Despite the variety and origin of materials (concrete, silicate materials, ceramics), there are always various pores in their structure.

The term "porosity" links the two most important properties of a material - geometry and structure. The geometric characteristic is the total pore volume, pore size and their total specific surface, which determine the porosity of the structure (large-pore material or fine-pore material). Structural characteristic is the type of pores and their size distribution. These properties change depending on the structure of the solid phase (granular, cellular, fibrous, etc.) and the structure of the pores themselves (open, closed, communicating).

The main influence on the size and structure of porous formations is exerted by the properties of the feedstock, the composition of the mixture, and the technological process of production. The most important characteristics are particle size distribution, binder volume, percentage of moisture in the feedstock, methods for shaping the final product, conditions for the formation of the final structure (sintering, fusion, hydration, and others). Specialized additives, the so-called modifiers, have a strong influence on the structure of porous formations. These include, for example, fuel additives and burnout additives, which are introduced into the composition of the charge during the production of ceramic products, and besides this, surfactants are used both in ceramics and in cement-based materials. The pores differ not only in size, but also in shape, and the capillary channels they create have a variable cross section along their entire length. All pore formations are classified into closed and open, as well as channel-forming and dead-end.

The structure of porous building materials is characterized by a combination of all types of pores. Porous formations can be randomly located inside the substance, or they can have a certain order.

Pore ​​channels have a very complex structure. Closed pores are cut off from open pores and are in no way connected with each other and with the external environment. This class of pores is impermeable to gaseous substances and liquids and, as a result, does not belong to dangerous ones. The open channel-forming and dead-end porous formations can be easily filled by the aquatic environment. Their filling proceeds according to various schemes and depends mainly on the cross-sectional area and the length of the pore channels. As a result of ordinary saturation, not all porous channels can be filled with water, for example, the smallest pores less than 0.12 microns in size are not filled due to the presence of air in them. Large porous formations fill up very quickly, but in the air, as a result of the low value of capillary forces, water is poorly retained in them.

The volume of water absorbed by the substance depends on the size of the porous formations and on the adsorption characteristics of the material itself.

To determine the relationship between the porous structure and the physicochemical characteristics of the material, it is not enough to know only the general value of the volume of porous formations. The general porosity does not determine the structure of the substance; the principle of pore size distribution and the presence of porous formations of a specific size play an important role here.

The geometric and structural indicators of the porosity of building materials differ both at the micro level and at the macro level. G.I. Gorchakov and E.G. Muradov developed an experimental-computational technique for identifying the total and group porosity of concrete materials. The basis of the technique lies in the fact that during the experiment the level of cement hydration in concrete is determined using a quantitative X-ray study or approximately by the volume of water bound by the cement binder ω, which did not evaporate during drying at a temperature of 150 ºС: α = ω/ ω max .

The volume of bound water with complete hydration of cement is in the range of 0.25 - 0.30 (to the mass of uncalcined cement).

Then, using the formulas from table 1, the porosity of concrete is calculated depending on the level of cement hydration, its consumption in concrete and the amount of water [ Makarova, I.A. Physico-chemical methods for the study of building materials: study guide / I.A. Makarova, N.A. Lokhov. - Bratsk: From BrGU, 2011. - 139 p. ].

Substance analysis methods

X-ray diffraction analysis

X-ray diffraction analysis is a method for studying the structure of bodies using the phenomenon of X-ray diffraction, a method for studying the structure of a substance by distribution in space and intensities of X-ray radiation scattered on the analyzed object. The diffraction pattern depends on the wavelength of the X-rays used and the structure of the object. To study the atomic structure, radiation with a wavelength of the order of the size of an atom is used.

Metals, alloys, minerals, inorganic and organic compounds, polymers, amorphous materials, liquids and gases, molecules of proteins, nucleic acids, etc. are studied by the methods of X-ray diffraction analysis. X-ray diffraction analysis is the main method for determining the structure of crystals.

When examining crystals, it gives the most information. This is due to the fact that crystals have a strict periodicity in their structure and represent a diffraction grating for X-rays created by nature itself. However, it also provides valuable information in the study of bodies with a less ordered structure, such as liquids, amorphous bodies, liquid crystals, polymers, and others. On the basis of numerous already deciphered atomic structures, the inverse problem can also be solved: the crystalline composition of this substance can be established from the X-ray pattern of a polycrystalline substance, for example, alloy steel, alloy, ore, lunar soil, that is, a phase analysis is performed.

X-ray diffraction analysis makes it possible to objectively establish the structure of crystalline substances, including such complex ones as vitamins, antibiotics, coordination compounds, etc. A complete structural study of a crystal often makes it possible to solve purely chemical problems, for example, establishing or refining the chemical formula, type of bond, molecular weight at a known density or density at a known molecular weight, symmetry and configuration of molecules and molecular ions.

X-ray diffraction analysis is successfully used to study the crystalline state of polymers. Valuable information is also provided by X-ray diffraction analysis in the study of amorphous and liquid bodies. X-ray diffraction patterns of such bodies contain several blurred diffraction rings, the intensity of which rapidly decreases with increasing magnification. Based on the width, shape, and intensity of these rings, conclusions can be drawn about the features of the short-range order in a particular liquid or amorphous structure.

X-ray diffractometers "DRON"

X-ray fluorescence analysis (XRF)

One of the modern spectroscopic methods for studying a substance in order to obtain its elemental composition, i.e. its elemental analysis. The XRF method is based on the collection and subsequent analysis of the spectrum obtained by exposing the material under study to X-rays. When irradiated, the atom goes into an excited state, accompanied by the transition of electrons to higher quantum levels. An atom stays in an excited state for an extremely short time, on the order of one microsecond, after which it returns to a quiet position (ground state). In this case, electrons from the outer shells either fill the formed vacancies, and the excess energy is emitted in the form of a photon, or the energy is transferred to another electron from the outer shells (Auger electron). In this case, each atom emits a photoelectron with an energy of a strictly defined value, for example, iron, when irradiated with X-rays, emits photons K? = 6.4 keV. Further, respectively, according to the energy and the number of quanta, the structure of the substance is judged.

In X-ray fluorescence spectrometry, it is possible to conduct a detailed comparison of samples not only in terms of the characteristic spectra of elements, but also in terms of the intensity of the background (bremsstrahlung) radiation and the shape of the Compton scattering bands. This is of particular importance when the chemical composition of two samples is the same according to the results of quantitative analysis, but the samples differ in other properties, such as grain size, crystallite size, surface roughness, porosity, humidity, presence of water of crystallization, polishing quality, deposition thickness, etc. The identification is carried out on the basis of a detailed comparison of the spectra. There is no need to know the chemical composition of the sample. Any difference between the compared spectra irrefutably indicates the difference between the test sample and the standard.

This type of analysis is carried out when it is necessary to identify the composition and some physical properties of two samples, one of which is a reference. This type of analysis is important when looking for any differences in the composition of two samples. Scope: determination of heavy metals in soils, precipitation, water, aerosols, qualitative and quantitative analysis of soils, minerals, rocks, quality control of raw materials, production process and finished products, analysis of lead paints, measurement of concentrations of valuable metals, determination of oil and fuel contamination , determination of toxic metals in food ingredients, analysis of trace elements in soils and agricultural products, elemental analysis, dating of archaeological finds, study of paintings, sculptures, for analysis and examination.

Usually sample preparation for all types of X-ray fluorescence analysis is not difficult. To conduct highly reliable quantitative analysis, the sample must be homogeneous and representative, have a mass and size not less than that required by the analysis procedure. Metals are polished, powders are crushed to particles of a given size and pressed into tablets. Rocks are fused to a glassy state (this reliably eliminates errors associated with sample inhomogeneity). Liquids and solids are simply placed in special cups.

Spectral analysis

Spectral analysis- a physical method for the qualitative and quantitative determination of the atomic and molecular composition of a substance, based on the study of its spectra. Physical basis S. and. - spectroscopy of atoms and molecules, it is classified according to the purpose of analysis and the types of spectra (see Optical spectra). Atomic S. a. (ACA) determines the elemental composition of the sample by atomic (ionic) emission and absorption spectra, molecular S. a. (ISA) - the molecular composition of substances according to the molecular spectra of absorption, luminescence and Raman scattering of light. Emission S. a. produced according to the emission spectra of atoms, ions and molecules, excited by various sources of electromagnetic radiation in the range from?-radiation to microwave. Absorption S. a. carried out according to the absorption spectra of electromagnetic radiation by the analyzed objects (atoms, molecules, ions of a substance in various states of aggregation). Atomic spectral analysis (ASA) Emission ASA consists of the following main processes:

1. selection of a representative sample that reflects the average composition of the analyzed material or the local distribution of the elements to be determined in the material;
2. introduction of a sample into a radiation source, in which evaporation of solid and liquid samples, dissociation of compounds and excitation of atoms and ions occur;
3. conversion of their glow into a spectrum and its registration (or visual observation) using a spectral device;
4. interpretation of the obtained spectra using tables and atlases of the spectral lines of the elements.

This stage ends qualitative ASA. The most effective is the use of sensitive (the so-called "last") lines that remain in the spectrum at the minimum concentration of the element being determined. Spectrograms are viewed on measuring microscopes, comparators, and spectroprojectors. For a qualitative analysis, it is sufficient to establish the presence or absence of analytical lines of the elements being determined. By the brightness of the lines during visual viewing, one can give a rough estimate of the content of certain elements in the sample.

Quantitative ACA carried out by comparing the intensities of two spectral lines in the spectrum of the sample, one of which belongs to the element being determined, and the other (comparison line) - to the main element of the sample, the concentration of which is known, or to the element specially introduced at a known concentration ("internal standard").

Atomic absorption S. a.(AAA) and atomic fluorescent S. a. (AFA). In these methods, the sample is converted to vapor in an atomizer (flame, graphite tube, plasma of a stabilized RF or microwave discharge). In AAA, light from a source of discrete radiation, passing through this vapor, is attenuated, and the degree of attenuation of the intensities of the lines of the element being determined is used to judge its concentration in the sample. AAA is carried out on special spectrophotometers. The AAA technique is much simpler compared to other methods, it is characterized by high accuracy in determining not only small, but also high concentrations of elements in samples. AAA successfully replaces labor-intensive and time-consuming chemical methods of analysis, not inferior to them in accuracy.

In AFA, the atomic vapors of the sample are irradiated with the light of a resonant radiation source and the fluorescence of the element being determined is recorded. For some elements (Zn, Cd, Hg, etc.), the relative limits of their detection by this method are very small (10-5-10-6%).

ASA allows measurements of the isotopic composition. Some elements have spectral lines with a well resolved structure (for example, H, He, U). The isotopic composition of these elements can be measured on conventional spectral instruments using light sources that produce thin spectral lines (hollow cathode, electrodeless RF and microwave lamps). For isotopic spectral analysis of most elements, high-resolution instruments (for example, a Fabry-Perot etalon) are required. Isotopic spectral analysis can also be carried out using the electronic-vibrational spectra of molecules, by measuring the isotopic shifts of the bands, which in some cases reach a significant value.

ASA plays a significant role in nuclear technology, the production of pure semiconductor materials, superconductors, etc. More than 3/4 of all analyzes in metallurgy are performed by ASA methods. With the help of quantometers, operational (within 2-3 minutes) control is carried out during melting in open-hearth and converter industries. In geology and geological exploration, about 8 million analyzes per year are performed to evaluate deposits. ASA is used for environmental protection and soil analysis, forensic science and medicine, seabed geology and the study of the composition of the upper atmosphere, in the separation of isotopes and determining the age and composition of geological and archaeological objects, etc.

infrared spectroscopy

The IR method includes the acquisition, study and application of emission, absorption and reflection spectra in the infrared region of the spectrum (0.76-1000 microns). ICS deals mainly with the study of molecular spectra, since in the IR region, most of the vibrational and rotational spectra of molecules are located. The most widely used is the study of IR absorption spectra arising from the passage of IR radiation through a substance. In this case, energy is selectively absorbed at those frequencies that coincide with the rotational frequencies of the molecule as a whole, and in the case of a crystalline compound, with the vibrational frequencies of the crystal lattice.

The IR absorption spectrum is probably a unique physical property of its kind. There are no two compounds, except for optical isomers, with different structures but identical IR spectra. In some cases, such as polymers with similar molecular weights, the differences may not be noticeable, but they always exist. In most cases, the IR spectrum is the "fingerprint" of the molecule, which is easily distinguishable from the spectra of other molecules.

In addition to the fact that absorption is characteristic of individual groups of atoms, its intensity is directly proportional to their concentration. That. measurement of absorption intensity gives, after simple calculations, the amount of a given component in the sample.

IR spectroscopy finds application in the study of the structure of semiconductor materials, polymers, biological objects and living cells directly. In the dairy industry, infrared spectroscopy is used to determine the mass fraction of fat, protein, lactose, solids, freezing point, etc.

The liquid substance is most often removed as a thin film between NaCl or KBr salt caps. The solid is most often removed as a paste in liquid paraffin. Solutions are removed in collapsible cuvettes.

spectral range from 185 to 900 nm, double-beam, recording, wavelength accuracy 0.03 nm at 54000 cm-1, 0.25 at 11000 cm-1, wavelength reproducibility 0.02 nm and 0.1 nm, respectively	The device is designed for taking IR - spectra of solid and liquid samples. Spectral range – 4000…200 cm-1; photometric accuracy ± 0.2%.

Absorption analysis of the visible and near ultraviolet region

On the absorption method of analysis or the property of solutions to absorb visible light and electromagnetic radiation in the ultraviolet range close to it, the principle of operation of the most common photometric instruments for medical laboratory research - spectrophotometers and photocolorimeters (visible light) is based.

Each substance absorbs only such radiation, the energy of which is capable of causing certain changes in the molecule of this substance. In other words, the substance only absorbs radiation of a certain wavelength, while light of a different wavelength passes through the solution. Therefore, in the visible region of light, the color of the solution perceived by the human eye is determined by the wavelength of the radiation not absorbed by this solution. That is, the color observed by the researcher is complementary to the color of the absorbed rays.

The absorption method of analysis is based on the generalized Bouguer-Lambert-Beer law, which is often called simply Beer's law. It is based on two laws:

1. The relative amount of energy of the light flux absorbed by the medium does not depend on the intensity of the radiation. Each absorbing layer of the same thickness absorbs an equal proportion of the monochromatic light flux passing through these layers.
2. The absorption of a monochromatic flux of light energy is directly proportional to the number of molecules of the absorbing substance.

Thermal analysis

Research method fiz.-chem. and chem. processes based on the registration of thermal effects accompanying the transformation of substances under conditions of temperature programming. Since the change in enthalpy? H occurs as a result of most physical. processes and chem. reactions, theoretically the method is applicable to a very large number of systems.

In T. a. you can fix the so-called. heating (or cooling) curves of the test sample, i.e. temperature change over time. In the case of k.-l. phase transformation in a substance (or a mixture of substances), a platform or breaks appear on the curve. The method of differential thermal analysis (DTA) has a higher sensitivity, in which the change in the temperature difference DT between the test sample and the reference sample (most often Al2O3) that does not undergo in this no transformations in the temperature range.

In T. a. you can fix the so-called. heating (or cooling) curves of the test sample, i.e. temperature change over time. In the case of k.-l. phase transformation in a substance (or a mixture of substances), a platform or kinks appear on the curve.

Differential thermal analysis(DTA) is more sensitive. It registers in time the change in the temperature difference DT between the test sample and the reference sample (most often Al2O3), which does not undergo any transformations in this temperature range. The minima on the DTA curve (see, for example, Fig.) correspond to endothermic processes, while the maxima correspond to exothermic ones. Effects registered in DTA, m. b. due to melting, a change in the crystal structure, the destruction of the crystal lattice, evaporation, boiling, sublimation, as well as chemical. processes (dissociation, decomposition, dehydration, oxidation-reduction, etc.). Most transformations are accompanied by endothermic effects; only some processes of oxidation-reduction and structural transformation are exothermic.

In T. a. you can fix the so-called. heating (or cooling) curves of the test sample, i.e. temperature change over time. In the case of k.-l. phase transformation in a substance (or a mixture of substances), a platform or kinks appear on the curve.

Mat. the relationship between the area of ​​the peak on the DTA curve and the parameters of the device and sample make it possible to determine the heat of transformation, the activation energy of the phase transition, some kinetic constants, and to carry out a semi-quantitative analysis of mixtures (if the DH of the corresponding reactions are known). With the help of DTA, the decomposition of metal carboxylates, various organometallic compounds, oxide high-temperature superconductors is studied. This method was used to determine the temperature range of CO to CO2 conversion (during the afterburning of automobile exhaust gases, emissions from CHP pipes, etc.). DTA is used to construct phase diagrams of the state of systems with a different number of components (phys.-chemical analysis), for qualities. sample evaluations, e.g. when comparing different batches of raw materials.

Derivatography- a complex method for the study of chem. and fiz.-chem. processes occurring in a substance under conditions of a programmed temperature change.

Based on the combination of differential thermal analysis (DTA) with one or more physical. or fiz.-chem. methods such as thermogravimetry, thermomechanical analysis (dilatometry), mass spectrometry and emanation thermal analysis. In all cases, along with transformations in the substance that occur with a thermal effect, a change in the mass of the sample (liquid or solid) is recorded. This makes it possible to immediately unambiguously determine the nature of the processes in a substance, which cannot be done using DTA data or other thermal methods alone. In particular, the thermal effect, which is not accompanied by a change in the mass of the sample, serves as an indicator of the phase transformation. A device that simultaneously registers thermal and thermogravimetric changes is called a derivatograph. In the derivatograph, which is based on the combination of DTA with thermogravimetry, the holder with the test substance is placed on a thermocouple freely suspended on the balance beam. This design allows you to record 4 dependencies at once (see, for example, Fig.): the temperature difference between the test sample and the standard that does not undergo transformations on time t (DTA curve), the change in mass Dm on temperature (thermogravimetric curve), the rate of change masses, i.e. derivative of dm/dt, temperature (differential thermogravimetric curve) and temperature versus time. In this case, it is possible to establish the sequence of transformations of a substance and determine the number and composition of intermediate products.

Chemical methods of analysis

Gravimetric analysis based on the determination of the mass of a substance.
In the course of gravimetric analysis, the analyte is either distilled off in the form of some volatile compound (distillation method), or precipitated from solution in the form of a poorly soluble compound (precipitation method). The distillation method determines, for example, the content of water of crystallization in crystalline hydrates.
Gravimetric analysis is one of the most versatile methods. It is used to define almost any element. Most gravimetric techniques use direct determination, when a component of interest is isolated from the analyzed mixture, which is weighed as an individual compound. Some elements of the periodic system (for example, compounds of alkali metals and some others) are often analyzed by indirect methods. In this case, two specific components are first isolated, converted into gravimetric form and weighed. Then one of the compounds or both are transferred to another gravimetric form and weighed again. The content of each component is determined by simple calculations.

The most significant advantage of the gravimetric method is the high accuracy of the analysis. The usual error of gravimetric determination is 0.1-0.2%. When analyzing a sample of complex composition, the error increases to several percent due to the imperfection of the methods for separating and isolating the analyzed component. Among the advantages of the gravimetric method is also the absence of any standardization or calibration according to standard samples, which are necessary in almost any other analytical method. To calculate the results of gravimetric analysis, only the knowledge of molar masses and stoichiometric ratios is required.

Titrimetric or volumetric method of analysis is one of the methods of quantitative analysis. Titration is the gradual addition of a titrated solution of a reagent (titrant) to the analyzed solution to determine the equivalence point. The titrimetric method of analysis is based on measuring the volume of a reagent of exactly known concentration, spent on the reaction of interaction with the analyte. This method is based on the precise measurement of the volumes of solutions of two substances that react with each other. Quantitative determination using the titrimetric method of analysis is quite fast, which allows you to carry out several parallel determinations and obtain a more accurate arithmetic mean. All calculations of the titrimetric method of analysis are based on the law of equivalents. According to the nature of the chemical reaction underlying the determination of the substance, the methods of titrimetric analysis are divided into the following groups: the method of neutralization or acid-base titration; oxidation-reduction method; precipitation method and complex formation method.

Based on the analysis of the optical spectra of atoms and molecules, spectral optical methods for determining the chemical composition of substances have been developed. These methods are divided into two: the study of the emission spectra of the substances under study (emission spectral analysis); study of their absorption spectra (absorption spectral analysis, or photometry).

When determining the chemical composition of a substance by the method of emission spectral analysis, the spectrum emitted by atoms and molecules in an excited state is analyzed. Atoms and molecules pass into an excited state under the influence of high temperatures achieved in a burner flame, in an electric arc or in a spark gap. The radiation thus obtained is decomposed into a spectrum by a diffraction grating or prism of a spectral device and is recorded by a photoelectric device.

There are three types of emission spectra: line, striped and continuous. Line spectra are emitted by excited atoms and ions. Striped spectra arise when light is emitted by hot pairs of molecules. Continuous spectra are emitted by hot liquid and solid bodies.

Qualitative and quantitative analysis of the composition of the material under study is carried out along the characteristic lines in the emission spectra. To decipher the spectra, tables of spectral lines and atlases with the most characteristic lines of the elements of the periodic system of Mendeleev are used. If it is necessary to establish only the presence of certain impurities, then the spectrum of the substance under study is compared with the spectrum of a reference substance that does not contain impurities. The absolute sensitivity of spectral methods is 10 -6 10 -8 g.

An example of the application of emission spectral analysis is the qualitative and quantitative analysis of reinforcing steel: the determination of impurities of silicon, carbon, manganese and chromium in the sample. The intensities of the spectral lines in the test sample are compared with the spectral lines of iron, the intensity of which is taken as a standard.

Optical spectral methods for studying substances also include the so-called flame spectroscopy, which is based on measuring the radiation of a solution introduced into the flame. This method determines, as a rule, the content of alkali and alkaline earth metals in building materials. The essence of the method lies in the fact that the solution of the test substance is sprayed into the zone of the flame of a gas burner, where it passes into a gaseous state. Atoms in this state absorb light from a standard source, giving line or striped absorption spectra, or they themselves emit radiation that is detected by measuring photoelectronic equipment.

The method of molecular absorption spectroscopy allows obtaining information about the mutual arrangement of atoms and molecules, intramolecular distances, bond angles, distribution of electron density, etc. In this method, when visible, ultraviolet (UV) or infrared (IR) radiation passes through a condensed substance, partial or complete absorption of radiation energy of certain wavelengths (frequencies). The main task of optical absorption spectroscopy is to study the dependence of the intensity of light absorption by a substance on the wavelength or oscillation frequency. The obtained absorption spectrum is an individual characteristic of the substance and, on its basis, qualitative analyzes of solutions or, for example, building and colored glasses are carried out.