Physicochemical methods for assessing composition and structure. Abstract: Physico-chemical methods for studying building materials

Introduction

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

In ancient times, this process took place in two different ways: consciously, based on accumulated experience, or by chance. 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; fermentation of certain seeds, for example, hops and subsequent production of brewing products; fermentation of the juices of various fruits (mainly grapes, which contain a large amount of sugar), ultimately produced wine products and vinegar.

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

Over time, people have developed a need for more functional materials and products based on them. Their knowledge in the field of chemistry had a huge impact on solving 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 accomplished using chemical reactions [

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

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

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

1. Classification of physical and chemical research methods

Physico-chemical research methods are based on close connection physical characteristics of the material (for example, ability to absorb light, electrical conductivity, etc.) and structural organization material from a chemical point of view. It happens that from physico-chemical methods, purely physical research methods are distinguished as a separate group, thus showing that physico-chemical methods consider a certain chemical reaction, 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 is at odds with the theoretical base chemical research(titrimetric and gravimetric). It was based on the interaction of matter with various energies.

In the course of physical and chemical research, in order to obtain the necessary data on the composition and structural organization of a substance, an experimental sample is exposed to the influence of some kind of energy. Depending on the type of energy in a substance, 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 recording changes in the characteristics of a substance, data is obtained on the qualitative and quantitative composition of the test sample, or data on its structure.

According to the type of influencing energies and the characteristics being studied, physico-chemical research methods are divided in the following way.

Table 1. Classification of physicochemical methods

In addition to those given in this table, there are quite a lot of private physicochemical methods that do not fit this classification. In fact, the most actively used are optical, chromatographic and potentiometric methods for studying the characteristics, composition and structure of a sample [ Galuso, G.S. Methods for studying building materials: educational manual / G.S. Galuzo, V.A. Bogdan, O.G. Galuzo, V.I. Kovazhnkova. – Minsk: BNTU, 2008. – 227 p.].

2. Thermal analysis methods

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

The correspondence law says that a specific thermal effect can be correlated with any phase change in a sample.

And the law of characteristicality states 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 in systems of substances or specific compounds during 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 state of aggregation of a system with its constant chemical composition.

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

Initially, thermal curves for limestone and clayey rocks were obtained by the French chemist Henri Louis Le Chatelier in 1886 - 1887. In Russia, academician N.S. was one of the first to study thermal research methods. Kurnakov (in 1904). Updated modifications of the Kurnakov pyrometer (an apparatus for automatically recording heating and cooling curves) are still used to this day in most research laboratories. Regarding the characteristics under study as a result of heating or cooling, the following methods of thermal analysis are distinguished: differential thermal analysis (DTA) - the change in 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.

During thermal research, several study methods can be used in parallel, each of which records 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 basics 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 by sequentially heating it. So, the crucible is filled with experimental material (sample), placed in an electric furnace, which heats up, and the temperature readings of the system under study begin to be taken using a simple thermocouple connected to a galvanometer.

Registration of changes in the enthalpy of a substance occurs using an ordinary thermocouple. But due to the fact that the deviations that can be seen 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 presented 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 makes it possible to record transformations in the electromotive force (EMF) circuit that appear as a result of an increase in the temperature of the hot junctions of the thermocouple. One hot junction is located in the sample being studied, and the second is located in the 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 – thermocouple hot junction; 6 – cold junction of thermocouple; 7 – galvanometer for fixing the DTA curve; 8 – galvanometer for recording the temperature curve.

If, for the system under study, any transformations that are associated with the absorption or release of thermal energy are frequent, then its temperature indicator in at the moment may be much greater or less than the reference reference substance. This temperature difference leads to a difference in the EMF value and, as a consequence, to a deviation of the DTA curve up or down from zero or the base line. 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. Schematic of simple and differential (DTA) temperature curves.

In fact, 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. X-ray phase analysis methods

X-ray methods for studying building materials are based on experiments in which X-rays are used. This class of research 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 X-ray diffraction technique used to determine the parameters of the unit cell of a substance is called the X-ray diffraction technique. The technique that is followed in the study of phase transformations and the mineralogical composition of substances is called X-ray phase analysis. X-ray phase analysis (XRF) methods have great value when studying mineral building materials. Based on the results of X-ray phase studies, information is obtained about the presence of crystalline phases and their quantities 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 being studied. The methods are based on the fact that each specific crystalline material has a specific x-ray pattern with its own set of diffraction maxima. Nowadays, there is reliable radiographic data on most known to man crystalline substances.

The task of quantitative composition is to obtain information about the amount 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. As the amount of any phase increases, its reflection intensity becomes greater. But for polyphase substances, the relationship between the intensity and quantity of this phase is ambiguous, since the magnitude of the reflection intensity of a given phase depends not only on its percentage content, 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 being studied depends on the attenuation values and the number of other phases that are also included in its composition. It follows from this that each technique quantitative analysis must somehow take into account the effect of the attenuation index, as a result of changes 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 studying building materials: textbook / I.A. Makarova, N.A. Lokhova. – Bratsk: Iz-vo BrGU, 2011. – 139 p. ].

Options for obtaining X-ray images are divided, based on the method of recording radiation, into photographic and diffractometric. The use of methods of the first type involves photographic recording of X-ray radiation, under the influence of which 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 studying building materials: guidelines for laboratory work / T.F. Pindyuk, I.L. Chulkova. – Omsk: SibADI, 2011. – 60 p. ].

4. Methods for studying porous structure

Building materials have heterogeneous and quite complex structure. Despite the variety and origin of materials (concrete, silicate materials, ceramics), their structure always contains various pores.

The term “porosity” connects the two most important properties of a material – geometry and structure. The geometric characteristic is the total volume of pores, the size of the pores and their total specific surface area, which determine the porosity of the structure (large-porous material or fine-porous one). Structural characteristics are the type of pores and their distribution by size. These properties vary 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, process production. The most important characteristics are the particle size distribution, binder volume, percentage of moisture in the feedstock, methods of forming the final product, conditions for the formation of the final structure (sintering, fusion, hydration, etc.). Specialized additives, so-called modifiers, have a strong influence on the structure of porous formations. These include, for example, fuel and burn-out additives, which are added to the charge during the production of ceramic products, and in addition to surfactants, they 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 the combination of all types of pores. Porous formations can be randomly located inside a substance, or they can have some 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 or with the external environment. This class of pores is impermeable to gaseous substances and liquids and, as a result, is not considered hazardous. Open channel-forming and dead-end porous formations aquatic environment can be filled in without difficulty. Their filling proceeds according to various patterns and depends mainly on the area cross section 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 never filled due to the presence of air in them. Large porous formations fill very quickly, but air environment, as a result of the low value of capillary forces, water is poorly retained in them.

The volume of water absorbed by a 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 general meaning volume of porous formations. General porosity does not determine the structure of a substance; the principle of pore size distribution and the presence of porous formations of a specific size play an important role here.

Geometric and structural indicators The porosity of building materials differs both at the micro and macro levels. G.I. Gorchakov and E.G. Muradov developed an experimental and computational methodology for identifying the general and group porosity of concrete materials. The basis of the technique is that during the experiment the level of hydration of cement in concrete is determined using quantitative x-ray examination or approximately by the volume of water ω bound in the cement binder that 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 studying building materials: textbook / I.A. Makarova, N.A. Lokhova. – Bratsk: Iz-vo 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 matter by the spatial distribution and intensity 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 atomic structure, radiation with a wavelength on the order of the size of the atom is used.

X-ray diffraction analysis methods are used to study metals, alloys, minerals, inorganic and organic compounds, polymers, amorphous materials, liquids and gases, protein molecules, nucleic acids, etc. X-ray diffraction analysis is the main method for determining the structure of crystals.

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

X-ray diffraction analysis makes it possible to objectively determine the structure of crystalline substances, including complex substances such as vitamins, antibiotics, coordination compounds, etc. A complete structural study of a crystal often allows one to solve purely chemical problems, for example, establishing or clarifying 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. X-ray diffraction analysis also provides valuable information in the study of amorphous and liquid bodies. X-ray patterns of such bodies contain several blurred diffraction rings, the intensity of which rapidly decreases with increasing intensity. Based on the width, shape and intensity of these rings, one can draw conclusions about the features of 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 a spectrum obtained by exposing the material under study x-ray radiation. When irradiated, the atom goes into an excited state, accompanied by the transition of electrons to higher quantum levels. The atom remains 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 with outer shells either they fill the resulting 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. Then, according to the energy and 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 background (bremsstrahlung) radiation and the shape of Compton scattering bands. This takes on special meaning in the case where 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, the presence of crystallization water, polishing quality, spray thickness, etc. Identification is performed based on detailed comparison of spectra. There is no need to know the chemical composition of the sample. Any difference in the compared spectra irrefutably indicates that the sample under study differs from 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 of application: definition heavy metals in soils, sediments, 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 archaeological finds, study of paintings, sculptures, for analysis and examination.

Typically, preparing samples for all types of X-ray fluorescence analysis is not difficult. To conduct a highly reliable quantitative analysis, the sample must be homogeneous and representative, have a mass and size not less than that required by the analysis technique. Metals are ground, 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 heterogeneity). 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 of S. a. - spectroscopy of atoms and molecules, it is classified according to the purposes of analysis and types of spectra (see Optical spectra). Atomic S. a. (ACA) determines the elemental composition of a sample from the atomic (ion) emission and absorption spectra; molecular S. a. (MSA) - molecular composition of substances based on molecular spectra of absorption, luminescence and Raman scattering of light. Emission S. a. produced by 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 using the absorption spectra of electromagnetic radiation by the analyzed objects (atoms, molecules, ions of matter in various states of aggregation). Atomic spectral analysis(ASA) Emission ASA consists of the following main processes:

selection of a representative sample reflecting the average composition of the analyzed material or the local distribution of the determined elements in the material;
introducing a sample into a radiation source, in which evaporation of solid and liquid samples, dissociation of compounds and excitation of atoms and ions occur;
converting their glow into a spectrum and recording it (or visual observation) using a spectral device;
interpretation of the obtained spectra using tables and atlases of spectral lines of elements.

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

Quantitative ASA is 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 an 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 into vapor in an atomizer (flame, graphite tube, stabilized RF or microwave discharge plasma). In AAA, light from a source of discrete radiation, passing through this vapor, is attenuated, and by the degree of attenuation of the intensities of the lines of the element being determined, its concentration in the sample is judged. AAA is carried out using 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 large concentrations of elements in samples. AAA successfully replaces labor-intensive and time-consuming chemical analysis methods without being inferior to them in accuracy.

In AFA, atomic pairs of the sample are irradiated with light from 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 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 HF and microwave lamps). To carry out isotopic spectral analysis of most elements, high-resolution instruments are required (for example, the Fabry-Perot standard). Isotopic spectral analysis can also be carried out using the electronic vibrational spectra of molecules, measuring isotopic shifts of bands, which in some cases reach significant values.

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 using ASA methods. Quantometers are used to carry out operational (within 2-3 minutes) control during melting in open-hearth and converter production. In geology and geological exploration, about 8 million analyzes are performed per year to evaluate deposits. ASA is used for environmental protection and soil analysis, in forensics and medicine, seabed geology and the study of the composition of the upper atmosphere, in isotope separation and determining the age and composition of geological and archaeological objects, etc.

Infrared spectroscopy

The IR method includes obtaining, studying and applying emission, absorption and reflection spectra in the infrared region of the spectrum (0.76-1000 microns). ICS is mainly concerned with the study of molecular spectra, because The majority of vibrational and rotational spectra of molecules are located in the IR region. The most widespread study is the study of IR absorption spectra that arise when IR radiation passes through a substance. In this case, energy is selectively absorbed at those frequencies that coincide with the rotation frequencies of the molecule as a whole, and in the case of a crystalline compound, with the vibration frequencies of the crystal lattice.

The IR absorption spectrum is probably a unique physical property of its kind. There are no two compounds, with the exception of optical isomers, with different structures but the same IR spectra. In some cases, such as polymers with similar molecular weights, the differences may be almost imperceptible, but they are always there. In most cases, the IR spectrum is a “fingerprint” of a molecule, which is easily distinguishable from the spectra of other molecules.

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

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

The liquid substance is most often removed as a thin film between caps of NaCl or KBr salts. The solid is most often removed as a paste in petroleum jelly. 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 recording IR spectra of solid and liquid samples. Spectral range – 4000…200 cm-1; photometric accuracy ± 0.2%.

Absorption analysis of visible and near ultraviolet region

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

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, a substance absorbs radiation of only a certain wavelength, while light of a different wavelength passes through the solution. Therefore, in the visible region of light, the color of a solution perceived by the human eye is determined by the wavelength of 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 simply called Beer's law. It is based on two laws:

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

In T. a. it is possible to record the so-called heating (or cooling) curves of the sample under study, i.e. change in temperature of the latter over time. In the case of k.-l. phase transformation in a substance (or mixture of substances), a plateau or kinks appear on the curve. The method of differential thermal analysis (DTA) is more sensitive, in which the change in temperature difference DT is recorded over time between the sample under study and a comparison sample (most often Al2O3), which does not undergo this no transformations within the temperature range.

Differential thermal analysis(DTA) has greater sensitivity. It records the change in time of the temperature difference DT between the sample under study and a comparison sample (most often Al2O3), which does not undergo any transformations in a given temperature range. The minima on the DTA curve (see, for example, Fig.) correspond to endothermic processes, and the maxima to exothermic processes. Effects recorded in DTA, m.b. caused by melting, changes in the crystal structure, 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.

Mat. The relationships between the peak area on the DTA curve and the parameters of the device and the sample make it possible to determine the heat of transformation, the activation energy of the phase transition, some kinetic constants, and conduct a semi-quantitative analysis of mixtures (if the DH of the corresponding reactions is known). Using DTA, the decomposition of metal carboxylates, various organometallic compounds, and oxide high-temperature superconductors is studied. This method was used to determine the temperature range for the conversion of CO into CO2 (during the afterburning of automobile exhaust gases, emissions from thermal power plant pipes, etc.). DTA is used to construct phase diagrams of the state of systems with different numbers of components (physical-chemical analysis), for qualities. evaluation of samples, e.g. when comparing different batches of raw materials.

Derivatography- a comprehensive method of chemical research. and physical-chemical processes occurring in a substance under conditions of programmed temperature changes.

Based on a combination of differential thermal analysis (DTA) with one or more physical. or physical-chemical 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, the change in the mass of the sample (liquid or solid) is recorded. This makes it possible to immediately unambiguously determine the nature of processes in a substance, which cannot be done using data from DTA alone or other thermal methods. In particular, an indicator of phase transformation is the thermal effect, which is not accompanied by a change in the mass of the sample. A device that simultaneously records thermal and thermogravimetric changes is called a derivatograph. In a derivatograph, the operation of which is based on a 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 dependences at once (see, for example, Fig.): the temperature difference between the sample under study and the standard, which does not undergo transformations, on time t (DTA curve), changes in mass Dm on temperature (thermogravimetric curve), rate of change mass, i.e. derivative dm/dt, from temperature (differential thermogravimetric curve) and temperature from time. In this case, it is possible to establish the sequence of transformations of the substance and determine the number and composition of intermediate products.

Chemical methods analysis

Gravimetric analysis based on determining the mass of a substance.
During gravimetric analysis, the substance being determined 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 is used to determine, for example, the content of water of crystallization in crystalline hydrates.
Gravimetric analysis is one of the most universal methods. It is used to define almost any element. Most gravimetric techniques use direct determination, where the component of interest is isolated from the mixture being analyzed and weighed as an individual compound. Part of the elements periodic table(for example, compounds of alkali metals and some others) are often analyzed using indirect methods. In this case, two specific components are first isolated, converted into gravimetric form and weighed. One or both of the compounds are then 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 imperfect methods of separation and isolation of the analyzed component. The advantages of the gravimetric method also include the absence of any standardization or calibration using standard samples, which are necessary in almost any other analytical method. To calculate the results of gravimetric analysis, knowledge only of molar masses and stoichiometric ratios is required.

The 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 solution being analyzed to determine the equivalence point. The titrimetric method of analysis is based on measuring the volume of a reagent of a precisely known concentration spent on the reaction of interaction with the substance being determined. This method is based on the accurate measurement of the volumes of solutions of two substances that react with each other. Quantification using the titrimetric method of analysis, it is performed quite quickly, which makes it possible to carry out several parallel determinations and obtain a more accurate arithmetic average. 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, titrimetric analysis methods are divided into the following groups: the method of neutralization or acid-base titration; oxidation-reduction method; precipitation method and complexation method.

Acoustic methods are based on recording the parameters of elastic vibrations excited in a controlled structure. Oscillations are usually excited in the ultrasonic range (which reduces interference) using a piezometric or electromagnetic transducer, an impact on the structure, and also when the structure of the structure itself changes due to the application of a load.

Acoustic methods are used to monitor continuity (detection of inclusions, cavities, cracks, etc.), thickness, structure, physical and mechanical properties (strength, density, elastic modulus, shear modulus, Poisson's ratio), and study of fracture kinetics.

By frequency range Acoustic methods are divided into ultrasonic and sound, according to the method of excitation of elastic vibrations - into piezoelectric, mechanical, electromagnetoacoustic, self-excitation during deformations. During non-destructive testing, acoustic methods record the frequency, amplitude, time, mechanical impedance (attenuation), and spectral composition of vibrations. Longitudinal, shear, transverse, surface and normal acoustic waves are used. The oscillation emission mode can be continuous or pulsed.

To the group acoustic methods includes shadow, resonant, pulse-echo, acoustic emission (emission), velosymmetric, impedance, free oscillations.

The shadow method is used for flaw detection and is based on the establishment of an acoustic shadow formed behind a defect due to reflection and scattering of an acoustic beam. The resonance method is used for flaw detection and thickness gauging. With this method, the frequencies that cause vibration resonance across the thickness of the structure under study are determined.

The pulse method (echo) is used for flaw detection and thickness gauging. An acoustic pulse reflected from defects or surfaces is detected. The emission method (acoustic emission method) is based on the emission of waves of elastic vibrations by defects, as well as sections of the structure under loading. The presence and location of defects and stress levels are determined. acoustic material flaw detection radiation

The velosymmetric method is based on fixing vibration rates, the influence of defects on the speed of wave propagation and the wave path length in the material. The impedance method is based on the analysis of changes in wave attenuation in the defect zone. In the free vibration method, the frequency spectrum of natural vibrations of a structure is analyzed after a blow is applied to it.

When using ultrasonic method Emitters and receivers (or seekers) are used to excite and receive ultrasonic vibrations. They are made of the same type and represent a piezoelectric plate 1 placed in a damper 2, which serves to dampen free vibrations and protect the piezoelectric plate (Fig. 1).

Rice. 1. Designs of finders and their installation diagrams:

a - diagram of a normal finder (oscillation emitter or receiver); b -- finder circuit for inputting ultrasonic waves at an angle to the surface; c -- diagram of a two-element finder; d -- coaxial position of emitters and receivers during end-to-end sound; d - the same, diagonal; e - superficial sounding; g -- combined sounding; 1 -- piezoelectric element; 2 -- damper; 3 -- protector; 4 -- lubricant on the contact; 5 -- sample under study; 6 -- body; 7 -- conclusions; 8 - prism for introducing waves at an angle; 9 -- dividing screen; 10 -- emitters and receivers;

Ultrasonic waves are reflected, refracted and subject to diffraction according to the laws of optics. These properties are used to capture vibrations in many methods. non-destructive testing. In this case, a narrowly directed beam of waves is used to study the material in a given direction. The position of the oscillation emitter and receiver, depending on the purpose of the study, may be different in relation to the structure under study (Fig. 1, d-g).

Numerous devices have been developed that use the above methods of ultrasonic vibrations. In practice construction research The devices used are GSP UK14P, Beton-12, UV-10 P, UZD-MVTU, GSP UK-YUP, etc. The “Beton” and UK devices are made with transistors and are distinguished by their low weight and dimensions. UK instruments record the speed or time of propagation of waves.

Ultrasonic vibrations in solids are divided into longitudinal, transverse and surface (Fig. 2, a).

Rice. 2.

a - ultrasonic longitudinal, transverse and surface waves; b, c -- shadow method (defect outside the zone and in the sounding zone); 1 -- vibration direction; 2 -- waves; 3 -- generator; 4 -- emitter; 5 -- receiver; 6 -- amplifier; 7 -- indicator; 8 test sample) 9 -- defect

There are dependencies between the oscillation parameters

Thus, the physical and mechanical properties of the material are related to the vibration parameters. Non-destructive testing methods use this relationship. Let's look at simple and widely used methods ultrasonic testing: shadow and echo method.

The defect is determined using the shadow method as follows(see Fig. 2, b): generator 3, through emitter 4, continuously emits vibrations into the material under study 8, and through it into vibration receiver 5. In the absence of a defect 9, vibrations are perceived by receiver 5 almost without attenuation and are recorded through amplifier 6 by an indicator 7 (oscilloscope, voltmeter). Defect 9 reflects part of the oscillation energy, thus shading receiver 5. The received signal decreases, which indicates the presence of a defect. The shadow method does not allow determining the depth of the defect and requires bilateral access, which limits its capabilities.

Flaw detection and thickness testing using the pulse echo method is carried out as follows (Fig. 3): generator 1 sends short pulses through emitter 2 to sample 4, and the waiting scan on the oscilloscope screen allows you to see the sent pulse 5. Following the sending of the pulse, the emitter switches to receiving reflected waves. The bottom signal 6 reflected from the opposite side of the structure is observed on the screen. If there is a defect in the path of the waves, then the signal reflected from it arrives at the receiver earlier than the bottom signal. Then another signal 8 is visible on the oscilloscope screen, indicating a defect in the design. The depth of the defect is judged by the distance between the signals and the speed of propagation of ultrasound.

Rice. 3.

a - echo method without defect; 6 - the same, with a defect; in determining the depth of the crack; g - determination of thickness; 1 -- generator; 2 - emitter; 3 -- reflected signals; 4 - sample; 5 - sent impulse; 6 - bottom impulse; 7 defect; 8 -- average impulse; 9 - crack; 10 - half-waves

When determining the depth of a crack in concrete, the emitter and receiver are located at points A and B symmetrically relative to the crack (Fig. 3, c). Oscillations from point A to point B come along the shortest path ACB = V 4No + a2;

where V is speed; 1H - time determined experimentally.

When flaw detection of concrete using the ultrasonic pulse method, through sounding and longitudinal profiling are used. Both methods allow you to detect a defect by changing the speed value longitudinal waves ultrasound when passing through the defective area.

The through-sounding method can also be used in the presence of reinforcement in concrete, if it is possible to avoid direct intersection of the sounding route with the rod itself. Sections of the structure are sounded sequentially and points are marked on the coordinate grid, and then lines of equal speeds - isospides, or lines of equal time - isochores, by examining which it is possible to identify a section of the structure on which there is defective concrete (zone of low speeds).

The longitudinal profiling method allows for flaw detection when the emitter and receiver are located on the same surface (flaw detection of road and airfield coatings, foundation slabs, monolithic floor slabs, etc.). This method can also determine the depth (from the surface) of corrosion damage to concrete.

The thickness of the structure with unilateral access can be determined by the resonance method using commercially available ultrasonic thickness gauges. Longitudinal ultrasonic vibrations are continuously emitted into the structure from one side (Fig. 2.4, d). Wave 10 reflected from the opposite face goes in the opposite direction. When the thickness H and the half-wave length are equal (or when these values are multiplied), the direct and reflected waves coincide, which leads to resonance. The thickness is determined by the formula

where V is the speed of wave propagation; / -- resonant frequency.

The strength of concrete can be determined using an IAZ amplitude attenuation meter (Fig. 2.5, a), operating using the resonance method. The vibrations of the structure are excited by a powerful speaker located at a distance of 10-15 mm from the structure. The receiver converts the vibrations of the structure into electrical vibrations, which are shown on the oscilloscope screen. The frequency of forced oscillations is smoothly changed until it coincides with the frequency of natural oscillations and resonance is obtained. The resonance frequency is recorded on the generator scale. A calibration curve is first constructed for the concrete of the structure being tested, from which the strength of the concrete is determined.

Fig.4.

a - general view of the amplitude attenuation meter; b - diagram for determining the frequency of natural longitudinal vibrations of the beam; c -- diagram for determining the frequency of natural bending vibrations of the beam; g -- circuit for testing shock method; 1 - sample; 2, 3 -- emitter (exciter) and receiver of vibrations; 4 -- generator; 5 --amplifier; 6 -- block for recording the frequency of natural oscillations; 7 -- starting system with a counting pulse generator and a microsecond watch; 8 -- shock wave

When determining the frequencies of bending, longitudinal and torsional vibrations, sample 1, exciter 2 and vibration receiver 3 are installed in accordance with the diagrams in Fig. 4, b, f. In this case, the sample must be installed on the supports of the stand, the natural frequency of which is 12 - -15 times the natural frequency of the element being tested.

The strength of concrete can be determined by the impact method (Fig. 4, d). The method is used when the length of the structure is sufficiently long, since low frequency vibrations does not allow for greater measurement accuracy. Two vibration receivers are installed on the structure with a sufficiently large distance between them (the base). The receivers are connected through amplifiers to the starting system, counter and microstopwatch. After striking the end of the structure, the shock wave reaches the first receiver 2, which turns on the time counter 7 through the amplifier 5. When the wave reaches the second receiver 3, the time counting stops. Velocity V is calculated by the formula

V = -- where a is the base; I-- time of passing the base.

Purpose of the work: 1. Familiarize yourself with the basic methods for studying the properties of building materials.

2. Analyze the basic properties of building materials.

1. Determination of the true (absolute) density of the material

(pycnometric method) (GOST 8269)

To determine the true density, crushed building materials are taken: brick, limestone crushed stone, expanded clay gravel, they are crushed, passed through a sieve with a mesh of less than 0.1 mm, and a sample weighing 10 g each (m) is taken.

Each sample is poured into a clean, dried pycnometer (Fig. 1) and distilled water is poured into it in such an amount that the pycnometer is filled to no more than half its volume, then the pycnometer is shaken, wetting all the powder, placed in a sand bath and the contents are heated. until boiling in an inclined position for 15-20 minutes to remove air bubbles.

Rice. 1 – Pycnometer for determining the true density of the material

Then the pycnometer is wiped, cooled to room temperature, distilled water is added to the mark and weighed (m 1), after which the pycnometer is emptied of its contents, washed, filled to the mark with distilled water at room temperature and weighed again (m 2). A table is drawn in the notebook in which the masses of each material and subsequent calculations are entered.

The true density of the material is determined by the formula:

where is the mass of the powder sample, g;

Weight of pycnometer with sample and water after boiling, g;

Weight of pycnometer with water, g;

The density of water is 1 g/cm3.

2. Determination of the average density of a sample of the correct geometric shape (GOST 6427)

It is better to determine the average density from the same materials - bricks, a piece of limestone and expanded clay gravel. The volume of samples of regular geometric shape (brick) is determined by geometric dimensions in accordance with the drawing, measured with an error of no more than 0.1 mm. Each linear dimension is calculated as the arithmetic mean of three measurements. Samples must be dry.

Sample volume irregular shape determined by the displaced water by dropping a piece of limestone or gravel into a measuring cylinder filled with water, which sinks, with a mark on the volume of the displaced fluid. 1ml=1cm 3.

Rice. 1 – Measurement of linear dimensions and volume of a sample

prisms cylinder

Average density determined by the formula:

where is the mass of the dry sample, g;

Sample volume, cm3.

No.	Material	P, %
	brick
	limestone
	expanded clay
	sq. sand

3. Determination of material porosity (GOST 12730.4)

Knowing the true density and average density of brick, limestone, expanded clay gravel, determine the porosity of the material P, %, using the formula:

where is the average density of the material, g/cm 3 or kg/m 3 ;

True density of the material, g/cm3 or kg/m3.

The comparative densities of different materials are given in Appendix A. The results are entered into the table.

4. Determination of bulk density (GOST 8269)

Bulk material (sand, expanded clay gravel, crushed stone) in a volume sufficient to carry out the test is dried to a constant weight. The material is poured into a pre-weighed measuring cylinder (m) from a height of 10 cm until a cone is formed, which is removed with a steel ruler flush with the edges (without compaction) moving towards you, after which the cylinder with the sample is weighed (m 1).

Rice. 3. Funnel for determining the bulk density of sand

1 – funnel; 2 – supports; 3 – damper

Bulk density of material determined by the formula:

where is the mass of the graduated cylinder, g;

Mass of the measuring cylinder with attachment, g;

Volume of graduated cylinder, l.

The results are entered into the table.

5. Determination of voidness (GOST 8269)

The voidness (V is empty,%) of a bulk material is determined by knowing the bulk and average density of the bulk material using the formula:

where is the bulk density of the material, kg/m3;

Average density of the material, kg/m3.

The average density of quartz sand is not determined; it is accepted as true - 2.65 g/cm 3 .

6. Determination of material moisture (GOST 8269)

A sample of the material in the amount of 1.5 kg is poured into a vessel and weighed, then dried to a constant weight in an oven (this must be done in advance). To determine humidity in a lesson, you can do the opposite: weigh an arbitrary amount of dry sand in a vessel and wet it arbitrarily, weigh it again, getting and.

Humidity W,%, is determined by the formula:

where is the mass of the wet sample, g;

Dry mass of sample, g.

To determine water absorption, three samples of any shape measuring from 40 to 70 mm or a brick are taken and the volume is determined. Clean the samples from dust with a wire brush and dry to a constant weight. Then they are weighed and placed in a vessel with water at room temperature so that the water level in the vessel is at least 20 mm above the top of the samples. The samples are kept in this position for 48 hours. After which they are removed from the water, moisture is removed from the surface with a wrung-out damp soft cloth, and each sample is weighed.

Water absorption by mass Wab,%, is determined by the formula:

Water absorption by volume W o,%, is determined by the formula:

where is the dry mass of the sample, g;

Mass of the sample after saturation with water, g;

Volume of the sample in its natural state, cm3.

Relative density is defined as:

The coefficient of saturation of the material with water is determined:

Having calculated all the indicators with the teacher, the student receives an individual assignment based on the variants of test No. 1 problems.

7. Determination of compressive strength (GOST 8462)

Compressive strength is determined on cubes of sizes 7.07 × 7.07 × 7.07 cm, 10 × 10 × 10 cm, 15 × 15 × 15 cm and 20 × 20 × 20 cm. Bricks and beams are first tested for bending strength (8), then the halves are tested in compression.

To determine the compressive strength, samples of regular geometric shape (beams, cubes, bricks) are examined, measured and tested on a hydraulic press. Place the sample in the center of the base plate and press it with the top plate of the press, which should fit tightly along the entire edge of the sample. During testing, the load on the sample must increase continuously and evenly. The highest compressive load corresponds to the maximum pressure gauge reading during the test.

When testing the compressive strength of cubes, the top face of the cube should become the side face to eliminate unevenness.

Ultimate compressive strength R compressed, MPa, for concrete cube samples is determined by the formula:

where is the maximum breaking load, kN;

Cross-sectional area of the sample (arithmetic mean of the areas of the upper and lower faces), cm 2.

8. Determination of bending strength. (GOST 8462)

The tensile strength in bending is determined on samples - beams using the MII-100 universal machine, which immediately gives readings of the strength weight in kg/cm 2 or on brick using a hydraulic press using rollers according to the scheme proposed in Figure 5. Tests of the strength of the brick must be shown, then the compressive strength of the halves (9) and the brand of brick must be determined.

Rice. 4 – MII-100 testing machine for determining bending strength

Fig. 5 – Scheme of bending strength test

Ultimate bending strength R bend, MPa, is determined by the following formula:

Distance between support axes, cm;

Sample width, cm;

Sample height, cm.

Material
brick
beam
cube

9. Determination of the structural quality coefficient (specific strength of the material)

Enter the calculation results into the table.

Security questions

1. What are the main properties of building materials, which ones are important for structural materials?

2. What densities are determined for building materials, and how?

3. What is true density? Why is it defined?

4. What is bulk density? How is it determined and why?

5. To determine the average density, what volume do you need to know? How to determine the volume of a piece of crushed stone?

6. Which density has the greatest numeric expression for the same material, which is the smallest? Why?

7. For what materials is voidness determined, how does it differ from porosity? Compare the true, average, and bulk densities of quartz sand, brick, expanded clay gravel or crushed limestone.

8. What is the relationship between total porosity and density? What is porosity?

9. What porosity can the material have? How can it be determined?

10. Does porosity affect the moisture content of a material? What is humidity?

11. How does humidity differ from water absorption? What properties can be judged by knowing water absorption?

12. How to determine the water saturation coefficient? What does it characterize?

13. How to determine the softening coefficient? What is its significance for air and hydraulic binders?

14. Will water and gas permeability change with a change in density, how? At what type of porosity do these indicators increase?

15. Does the amount of porosity affect the amount of swelling and shrinkage of the material? What is the shrinkage of cellular concrete and what is the shrinkage of heavy concrete?

16. Is there a connection between the density of a material and thermal conductivity? What materials protect better from the cold? What density material are walls built from? residential buildings?

17. Does moistening the material affect the thermal conductivity coefficient? Why?

18. What is the coefficient of linear thermal expansion for concrete, steel, granite, wood? When does it matter?

19. Is it possible to use materials with Kn = 1 for the manufacture of road surface slabs? Why?

20. How does porosity differ from voidness, and what formula is used to determine these indicators?

21. Are there materials whose true density is equal to the average?

22. Why do pores form in bricks? Does the method of brick molding affect their number?

23. How do we increase porosity in artificial stone, why?

24. What causes shrinkage, which materials have it more: dense or porous?

25. Does shrinkage depend on the water absorption of the material? What water in the structure of the material does not evaporate?

26. On what samples is the strength of binders, mortars and concrete determined, by what formula is the strength calculated, in what units?

27. On what indicators does strength depend, and in which structures is it maximum?

28. Why do some materials have greater flexural strength, while others have less compressive strength? What are such materials called?

29. What characteristics does frost resistance depend on?

30. What is called specific surface area? Does moisture depend on this characteristic?

Laboratory work No. 4

Gypsum binders

Purpose of the work: 1. Familiarize yourself with the basic properties of building gypsum.

2. Analyze the main properties of building gypsum.

Page 1

Introduction.

Throughout its development, human civilization, at least in the material sphere, constantly uses chemical, biological and physical laws operating 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;

The fermentation of certain seeds, such as hops, in the presence of yeast to produce beer;

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

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

Fire brought revolutionary changes in human life. Man began to use fire for cooking, in pottery production, for processing and smelting metals, processing wood into coal, evaporating and drying food for the winter.

Over time, people began to need 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 SHM). 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 synthetic materials is often more efficient and productive with the help of chemical reactions. And also there was a need to protect materials from corrosion; this, in fact, is the main role of physical and chemical methods in building materials. Physicochemical methods are used to study physical phenomena that occur during chemical reactions. For example, in the colorimetric method, the color intensity is measured depending on the concentration of the substance; in the conductometric analysis, the change in the electrical conductivity of solutions is measured, etc.

IN this essay Some types of corrosion processes are outlined, as well as ways to combat them, which is the main practical task of physical and chemical methods in building materials.

Physico-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 FCMA, thereby emphasizing that FCMA uses a chemical reaction, while physical methods do not. Physical methods of analysis and PCMA, mainly in Western literature, are called instrumental, since they usually require the use of instruments and measuring instruments. Instrumental methods of analysis generally 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 sample under study is exposed to some type of energy. Depending on the type of energy in a substance, a change occurs 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 disturbance energy and the measured property (analytical signal), FCMA 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.

Greatest practical application have optical, chromatographic and potentiometric methods of analysis.

Table 2.1.1.

Type of disturbance energy	Property being measured	Method name	Method group name
Electron flow (electrochemical reactions in solutions and on electrodes)	Voltage, potential	Potentiometry	Electrochemical
	Electrode polarization current	Voltamperometry, polarography
	Current strength	Amperometry
	Resistance, conductivity	Conductometry
	Impedance (AC resistance, capacitance)	Oscillometry, high-frequency conductometry
	Amount of electricity	Coulometry
	Mass of electrochemical reaction product	Electrogravimetry
	Permittivity	Dielcometry
Electromagnetic radiation	Wavelength and intensity of the spectral line in the infrared, visible and ultraviolet parts of the spectrum =10-3 .10-8 m	Optical methods (IR spectroscopy, atomic emission analysis, atomic absorption analysis, photometry, luminescent analysis, turbidimetry, nephelometry)	Spectral
	The same, in the X-ray region of the spectrum =10-8 .10-11 m	X-ray photoelectron, Auger spectroscopy