Photocolorimetry

Quantitative determination of the concentration of a substance by light absorption in the visible and near ultraviolet region of the spectrum. Light absorption is measured using photoelectric colorimeters.

Spectrophotometry (absorption). A physicochemical method for studying solutions and solids, based on the study of absorption spectra in the ultraviolet (200–400 nm), visible (400–760 nm) and infrared (>760 nm) regions of the spectrum. The main dependence studied in spectrophotometry is the dependence of the absorption intensity of incident light on the wavelength. Spectrophotometry is widely used in studying the structure and composition of various compounds (complexes, dyes, analytical reagents, etc.), for the qualitative and quantitative determination of substances (determination of trace elements in metals, alloys, technical objects). Spectrophotometric instruments – spectrophotometers.

Absorption spectroscopy, studies the absorption spectra of electromagnetic radiation by atoms and molecules of matter in various states of aggregation. The intensity of the light flux as it passes through the medium under study decreases due to the conversion of radiation energy into various forms of internal energy of the substance and (or) into the energy of secondary radiation. The absorption capacity of a substance depends on the electronic structure of atoms and molecules, as well as on the wavelength and polarization of the incident light, layer thickness, concentration of the substance, temperature, and the presence of electric and magnetic fields. Spectrophotometers are used to measure absorbance - optical instruments, consisting of a light source, a sample chamber, a monochromator (prism or grating), and a detector. The signal from the detector is recorded in the form of a continuous curve (absorption spectrum) or in the form of tables if the spectrophotometer has a built-in computer.

1. Bouguer-Lambert law: if the medium is homogeneous and the layer of matter is perpendicular to the incident parallel light flux, then

I = I 0 exp (- kd),

where I 0 and I-intensities, respectively. incident and passed through the light, d-layer thickness, k-coefficient. absorption, which does not depend on the thickness of the absorbing layer and the intensity of the incident radiation. To characterize the absorb. abilities widely use coefficients. extinction, or light absorption; k" = k/2.303 (in cm -1) and optical density A = log I 0 /I, as well as the transmittance value T = I/I 0. Deviations from the law are known only for light fluxes of extremely high intensity (for laser radiation). Coef. k depends on the wavelength of the incident light, because its value is determined by the electronic configuration of molecules and atoms and the probabilities of transitions between their electronic levels. The set of transitions creates an absorption spectrum characteristic of a given substance.

2. Beer's law: each molecule or atom, regardless of the relative location of other molecules or atoms, absorbs the same fraction of radiation energy. Deviations from this law indicate the formation of dimers, polymers, associates, and chemical reactions. interaction of absorbing particles.

3. Combined Bouguer-Lambert-Beer law:

A = log(I 0 /I)=КLC

L – thickness of the absorbing layer of atomic vapor

Absorption spectroscopy is based on the use the ability of a substance to selectively absorb light energy.

Absorption spectroscopy studies the absorption capacity of substances. The absorption spectrum (absorption spectrum) is obtained as follows: a substance (sample) is placed between a spectrometer and a source of electromagnetic radiation with a certain frequency range. A spectrometer measures the intensity of light passed through a sample compared to the intensity of the original radiation at a given wavelength. In this case, the high energy state also has a short lifespan. In the ultraviolet region, the absorbed energy usually turns back into light; in some cases it can induce photochemical reactions. A typical water transmission spectrum taken in an AgBr cuvette about 12 µm thick.

Absorption spectroscopy, which includes infrared, ultraviolet and NMR spectroscopy, provides information about the nature of the average molecule, but, unlike mass spectrometry, does not recognize the different types of molecules that may be present in the analyzed sample.

Paramagnetic resonance absorption spectroscopy is a technique that can be applied to molecules containing atoms or ions with unpaired electrons. Absorption leads to a change in the orientation of the magnetic moment when moving from one allowed position to another. The true absorbed frequency depends on the magnetic field, and therefore, by varying the field, the absorption can be determined from some microwave frequency.

Paramagnetic resonance absorption spectroscopy is a technique that can be applied to molecules containing atoms or ions with unpaired electrons. This leads to a change in the orientation of the magnetic moment when moving from one allowed position to another. The true absorbed frequency depends on the magnetic field, and therefore, by varying the field, the absorption can be determined from some microwave frequency.

In absorption spectroscopy, a molecule in a lower energy level absorbs a photon with frequency v, calculated by the equation, moving to a higher energy level. In a conventional spectrometer, radiation containing all frequencies in the infrared region passes through the sample. The spectrometer records the amount of energy passed through the sample as a function of the frequency of the radiation. Since the sample absorbs only radiation with a frequency determined by the equation, the spectrometer recorder shows uniform high transmittance, except in the region of those frequencies determined from the equation where absorption bands are observed.

Absorption spectroscopy determines the change in the intensity of electromagnetic radiation created by some source, a change that is observed when the radiation passes through a substance that absorbs it. In this case, the molecules of the substance interact with electromagnetic radiation and absorb energy.

The absorption spectroscopy method is used to determine the amount of a gas impurity from the measured area of ​​an individual absorption line, a group of lines, or an entire absorption band in the spectrum of radiation that has passed a certain path in the medium. The measured areas are compared with similar values ​​calculated on the basis of data on absorption spectra obtained in laboratory conditions with dosed quantities of the measured gas.

In absorption spectroscopy, the minimum lifetime required before discernible spectra can be observed increases as the transition energy decreases.

For absorption spectroscopy, a white light source can be used in combination with a spectrograph to obtain a photographically recorded survey spectrum of the absorbing compounds in the reaction system. In other cases, a monochromator with a photoelectric detector can be used to scan the spectral range. Many short-lived intermediates under study have quite high optical absorption due to the presence of an allowed electronic dipole transition to a higher high level energy. In this case, for example, triplet excited states can be observed by their triplet-triplet absorption. IN general case Individual absorption bands have a greater amplitude the narrower they are. As a result of this effect, atoms have allowed absorption lines with particularly large amplitudes. In quantitative absorption measurements, a wavelength is usually selected at which a strong absorption band is observed and is not superimposed by the absorption bands of other compounds.

In absorption spectroscopy, we are limited not so much by the optical properties of the gas under study, heated by a shock wave, as by the properties of the radiation source.

The use of absorption spectroscopy involves the consumption of small quantities of the substance under study.

Kinetic absorption spectroscopy, covering the electronic region of the spectrum, is well known as the main method for monitoring the concentrations of radicals, reactants and end products formed as a result of pulsed photolysis. However, this method has only recently become widely used in many jet discharge installations. Due to low optical densities, scanning the striped spectra of unknowns chemical systems difficult. This method is most suitable for studying radicals whose electronic absorption spectra have been determined quite accurately.

In absorption spectroscopy devices, light from an illumination source passes through a monochromatizer and falls on a cuvette with the substance being studied. In practice, the ratio of the intensities of monochromatic light passing through the test solution and through a solvent or a specially selected reference solution is usually determined.

In the absorption spectroscopy method, a beam of monochromatic light with wavelength A and frequency v passes through a cuvette of length l (in cm) containing a solution of an absorbing compound of concentration c (mol/l) in a suitable solvent.

However, in atomic absorption spectroscopy this light source is still undeservedly little used. The advantage of high-frequency lamps is their ease of manufacture, since the lamp is usually a glass or quartz vessel containing a small amount of metal.

Flame in atomic absorption spectroscopy is the most common method of atomizing a substance. In atomic absorption spectroscopy, the flame plays the same role as in flame emission spectroscopy, with the only difference being that in the latter case the flame is also a means of exciting atoms. Therefore, it is natural that the technique of flame atomization of samples in atomic absorption spectral analysis largely copies the technique of flame emission photometry.

Atomic absorption spectrometry (AAS) method, atomic absorption analysis (AAA) is a method of quantitative elemental analysis based on atomic absorption (absorption) spectra. Widely used in analysis mineral matter to define various elements.

The principle of operation of the method based on the fact that the atoms of each chemical element have strictly defined resonant frequencies, as a result of which it is at these frequencies that they emit or absorb light. This leads to the fact that in a spectroscope, lines (dark or light) are visible on the spectra in certain places characteristic of each substance. The intensity of the lines depends on the amount of substance and its state. In quantitative spectral analysis, the content of the substance under study is determined by the relative or absolute intensities of lines or bands in the spectra.

Atomic spectra (absorption or emission) are obtained by transferring the substance to the vapor state by heating the sample to 1000–10000 °C. A spark or an alternating current arc are used as sources of excitation of atoms in the emission analysis of conductive materials; in this case, the sample is placed in the crater of one of the carbon electrodes. Flames or plasmas of various gases are widely used to analyze solutions.

Advantages of the method:

· simplicity,

· high selectivity,

· little influence of the sample composition on the analysis results.

· Economical;

· Simplicity and accessibility of equipment;

· High performance analysis;

· Availability of a large number of certified analytical methods.

· Literature for familiarization with the AAS method

Limitations of the method– the impossibility of simultaneous determination of several elements when using linear radiation sources and, as a rule, the need to transfer samples into solution.

In the laboratory The HSMA AAS method has been used for more than 30 years. With his help are determined CaO, MgO, MnO, Fe 2 O 3, Ag, trace impurities; flame photometric method - Na 2 O, K 2 O.

Atomic absorption analysis(atomic absorption spectrometry), quantitative method. elemental analysis based on atomic absorption (absorption) spectra.

Principle of the method: Radiation in the range of 190-850 nm is passed through a layer of atomic vapors of samples obtained using an atomizer (see below). As a result of the absorption of light quanta (photon absorption), atoms pass into excited energy states. These transitions in atomic spectra correspond to the so-called. resonant lines characteristic of of this element. A measure of the concentration of an element - optical density or atomic absorption:

A = log(I 0 /I) = KLC (according to the Bouguer-Lambert-Beer law),

where I 0 and I are the intensities of radiation from the source, respectively, before and after passing through the absorbing layer of atomic vapor.

K-proportionality coefficient (electronic transition probability coefficient)

L - thickness of the absorbing layer of atomic vapor

C – concentration of the element being determined

Schematic diagram flame atomic absorption spectrometer: 1-radiation source; 2-flame; 3-monochrome of mountains; 4-photomultiplier; 5-recording or indicating device.

Instruments for atomic absorption analysis- atomic absorption spectrometers – precision, highly automated devices that ensure reproducibility of measurement conditions, automatic introduction of samples and recording of measurement results. Some models have built-in microcomputers. As an example, the figure shows a diagram of one of the spectrometers. The source of line radiation in spectrometers is most often single-element lamps with a hollow cathode filled with neon. To determine some highly volatile elements (Cd, Zn, Se, Te, etc.), it is more convenient to use high-frequency electrodeless lamps.

The transfer of the analyzed object into an atomized state and the formation of an absorbing layer of vapor of a certain and reproducible shape is carried out in an atomizer - usually in a flame or a tubular furnace. Naib. flames of mixtures of acetylene with air (max. temperature 2000°C) and acetylene with N2O (2700°C) are often used. A burner with a slot-like nozzle 50-100 mm long and 0.5-0.8 mm wide is installed along the optical axis of the device to increase the length of the absorbing layer.

Tubular resistance furnaces are most often made from dense grades of graphite. To eliminate vapor diffusion through the walls and increase durability, graphite tubes are coated with a layer of gas-tight pyrolytic carbon. Max. The heating temperature reaches 3000 °C. Less common are thin-walled tubular furnaces made of refractory metals (W, Ta, Mo), quartz with a nichrome heater. To protect graphite and metal furnaces from burning in air, they are placed in semi-hermetic or sealed chambers through which inert gas (Ar, N2) is blown.

The introduction of samples into the absorption zone of a flame or furnace is carried out using different techniques. Solutions are sprayed (usually into a flame) using pneumatic sprayers, less often ultrasonic sprayers. The former are simpler and more stable in operation, although they are inferior to the latter in the degree of dispersion of the resulting aerosol. Only 5-15% of the smallest aerosol droplets enter the flame, and the rest is screened out in the mixing chamber and discharged into the drain. Max. the concentration of solid matter in solution usually does not exceed 1%. Otherwise, intense deposition of salts occurs in the burner nozzle.

Thermal evaporation of dry solution residues is the main method of introducing samples into tube furnaces. In this case, samples are most often evaporated with inner surface ovens; the sample solution (volume 5-50 μl) is injected using a micropipette through the dosing hole in the wall of the tube and dried at 100°C. However, samples evaporate from the walls with a continuous increase in the temperature of the absorbing layer, which causes instability of the results. To ensure a constant oven temperature at the time of evaporation, the sample is introduced into a preheated oven using a carbon electrode (graphite cell), graphite crucible (Woodriff oven), metal or graphite probe. The sample can be evaporated from a platform (graphite trough), which is installed in the center of the furnace under the dosing hole. As a result it means. If the temperature of the platform lags behind the temperature of the furnace, which is heated at a rate of about 2000 K/s, evaporation occurs when the furnace reaches an almost constant temperature.

To introduce solid substances or dry residues of solutions into the flame, rods, threads, boats, crucibles made of graphite or refractory metals are used, placed below the optical axis of the device, so that the sample vapor enters the absorption zone with the flow of flame gases. In some cases, graphite evaporators are additionally heated by electric current. To exclude fur. To prevent loss of powdered samples during the heating process, cylindrical capsule-type evaporators made of porous graphite are used.

Sometimes sample solutions are treated in a reaction vessel with reducing agents present, most often NaBH 4 . In this case, Hg, for example, is distilled off in elemental form, As, Sb, Bi, etc. - in the form of hydrides, which are introduced into the atomizer with a flow of inert gas. To monochromatize radiation, prisms or diffraction gratings are used; in this case, a resolution of 0.04 to 0.4 nm is achieved.

In atomic absorption analysis, it is necessary to exclude the overlap of the radiation of the atomizer with the radiation of the light source, to take into account a possible change in the brightness of the latter, spectral interference in the atomizer caused by partial scattering and absorption of light by solid particles and molecules of foreign components of the sample. For this they use various techniques, eg. the source radiation is modulated with a frequency to which the recording device is tuned approximately; a two-beam scheme or an optical scheme with two light sources (with discrete and continuous spectra) is used. max. An effective scheme is based on Zeeman splitting and polarization of spectral lines in an atomizer. In this case, light polarized perpendicularly is passed through the absorbing layer magnetic field, which makes it possible to take into account non-selective spectral interference reaching values ​​of A = 2 when measuring signals that are hundreds of times weaker.

The advantages of atomic absorption analysis are simplicity, high selectivity and little influence of the sample composition on the analysis results. The limitations of the method are the impossibility of simultaneous determination of several elements when using linear radiation sources and, as a rule, the need to transfer samples into solution.

Atomic absorption analysis is used to determine about 70 elements (mainly sample metals). Gases and some other nonmetals whose resonance lines lie in the vacuum region of the spectrum (wavelength less than 190 nm) are also not detected. Using a graphite furnace, it is impossible to determine Hf, Nb, Ta, W and Zr, which form low-volatile carbides with carbon. The detection limits of most elements in solutions during atomization in a flame or in a graphite furnace are 100-1000 times lower. The absolute detection limits in the latter case are 0.1-100 pg.

The relative standard deviation under optimal measurement conditions reaches 0.2-0.5% for a flame and 0.5-1.0% for a furnace. In automatic operating mode, the flame spectrometer allows analyzing up to 500 samples per hour, and the spectrometer with a graphite furnace allows up to 30 samples. Both options are often used in combination with pre-treatment. separation and concentration by extraction, distillation, ion exchange, chromatography, which in some cases makes it possible to indirectly determine some non-metals and organic compounds.

Atomic absorption analysis methods are also used to measure some physical properties. and physical-chemical quantities - diffusion coefficient of atoms in gases, temperatures gas environment, heat of evaporation of elements, etc.; to study the spectra of molecules, study processes associated with the evaporation and dissociation of compounds.

The properties of materials are largely determined by its composition and pore structure. Therefore, to obtain materials with desired properties, it is important to have a clear understanding of the processes of structure formation and emerging formations, which is studied at the micro- and molecular-ion level.

The most common physicochemical methods of analysis are discussed below.

The petrographic method is used to study various materials: cement clinker, cement stone, concrete, glass, refractories, slag, ceramics, etc. The light microscopy method is aimed at determining the optical properties characteristic of each mineral, which are determined by its internal structure. The main optical properties of minerals are refractive indexes, double refractive power, axiality, optical sign, color, etc. There are several modifications
of this method: polarization microscopy is intended for studying samples in the form of powders in special immersion devices (immersion liquids have certain refractive indices); transmitted light microscopy - for studying transparent sections of materials; reflected light microscopy of polished sections. Polarizing microscopes are used to carry out these studies.

Electron microscopy is used to study fine crystalline mass. Modern electron microscopes have a useful magnification of up to 300,000 times, which makes it possible to see particles with a size of 0.3-0.5 nm (1 nm = 10’9 m). Such deep penetration into the world of small particles was made possible by the use of electron beams in microscopy, whose wavelengths are many times shorter than visible light.

Using an electron microscope, you can study: the shape and size of individual submicroscopic crystals; processes of crystal growth and destruction; diffusion processes; phase transformations at heat treatment and cooling; mechanism of deformation and destruction.

IN lately raster (scanning) electron microscopes are used. This is a device based on the television scanning principle. thin beam electrons (or ions) on the surface of the sample under study. A beam of electrons interacts with matter, as a result of which a number of physical phenomena arise; by recording radiation sensors and sending signals to a kinescope, a relief picture of the image of the sample surface is obtained on the screen (Fig. 1.1).

X-ray analysis is a method for studying the structure and composition of a substance by experimental study X-ray diffraction in this substance. X-rays are the same transverse electromagnetic oscillations as visible light, but with shorter waves (wavelength 0.05-0.25 10"9 m). They are obtained in an X-ray tube as a result of the collision of cathode electrons with the anode at a large difference potentials. The use of X-ray radiation for the study of crystalline substances is based on the fact that its wavelength is comparable to the interatomic distances in the crystal lattice of the substance, which is a natural diffraction grating for X-rays.

Each crystalline substance is characterized by its own set of specific lines on the x-ray diffraction pattern. This is the basis for qualitative X-ray phase analysis, the task of which is to determine (identify) the nature of the crystalline phases contained in the material. The powder X-ray diffraction pattern of a polymineral sample is compared either with the X-ray diffraction patterns of the constituent minerals or with tabulated data (Figure 1.2).

68 64 60 56 52 48 44 40 36 32 28 24 20 16 12 8 4

Rice. 1.2. X-ray images of samples: a) cement; b) cement stone

X-ray phase analysis is used to control raw materials and finished products, to monitor technological processes, as well as for flaw detection.

Differential thermal analysis is used to determine the mineral-phase composition of building materials (DTA). The basis of the method is that the phase transformations occurring in the material can be judged by the thermal effects accompanying these transformations. During physical and chemical processes of transformation of a substance, energy in the form of heat can be absorbed or released from it. With the absorption of heat, for example, processes such as dehydration, dissociation, and melting occur - these are endothermic processes.

The release of heat is accompanied by oxidation, the formation of new compounds, and the transition from an amorphous to a crystalline state - these are exothermic processes. The instruments for DTA are derivatographs, which record four curves during the analysis process: simple and differential heating curves and, accordingly, mass loss curves. The essence of DTA is that the behavior of a material is compared with a standard - a substance that does not experience any thermal transformations. Endothermic processes produce depressions in thermograms, and exothermic processes produce peaks (Fig. 1.3).

Spectral analysis is a physical method of qualitative and quantitative analysis of substances, based on the study of their spectra. When studying building materials, infrared (IR) spectroscopy is mainly used, which is based on the interaction of the substance under study with electromagnetic radiation in the infrared region. IR spectra are related to the vibrational energy of atoms and the rotational energy of molecules and are characteristic for determining groups and combinations of atoms.

Spectrophotometer devices allow you to automatically record infrared spectra (Fig. 1.4).

a) cement stone without additives; b) cement stone with additive

In addition to these methods, there are others that allow one to determine the special properties of substances. Modern laboratories are equipped with many computerized installations that allow multifactorial complex analysis of almost all materials.

Ministry of Education of the Kyrgyz Republic

Ministry of Education of the Russian Federation

Kyrgyz-Russian Slavic University

Faculty of Architecture Design and Construction

Abstract

On the topic :

“The role of physical and chemical research methods in building materials”

Completed by: Mikhail Podyachev gr. PGS 2-07

Checked by: Dzhekisheva S.D.

Plan

1. Introduction…………………………………………………………………….……p. 3

4. Characteristics of corrosion processes in building materials…. pp. 9-13

5. Physico-chemical methods for studying corrosion in building materials………………p. 13-15

6. Methods for protecting building materials from corrosion………………………p. 15

7. Results of corrosion research based on physicochemical methods………p. 16-18

8. Innovative methods of corrosion research…………………………p. 18-20

9. Conclusion……………………………………………………………………p. 20

10. References……………………………………………………………page 21

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.

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 certain 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 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 the creation of new materials, in my opinion, the leading position is still occupied by physical processes and technology, then obtaining SSM 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 physico-chemical methods in building materials. With the help of physico-chemical 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 the 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 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.

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

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

Electric product weight chemical reaction

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, luminescence analysis, turbidimetry, nephelometry)

Spectral

The same, in the X-ray region of the spectrum =10-8...10-11 m

X-ray photoelectron, Auger spectroscopy

Relaxation times and chemical shift

Nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopy

Temperature

Thermal analysis

Thermal

Thermogravimetry

Amount of heat

Calorimetry

Enthalpy

Thermometric analysis (enthalpimetry)

Mechanical properties

Dilatometry

Energy of chemical and physical (van der Waals forces) interactions

Electrical conductivity Thermal conductivity Ionization current

Gas, liquid, sediment, ion exchange, gel permeation chromatography

Chromatographic

Compared to classical chemical methods, FCMAs are characterized by a lower detection limit, time and labor intensity. FCMAs make it possible to carry out analysis at a distance, automate the analysis process and perform it without destroying the sample (non-destructive analysis).

According to the methods of determination, direct and indirect FCMA are distinguished. In direct methods, the amount of a substance is found by directly converting the measured analytical signal into the amount of a substance (mass, concentration) using the coupling equation. In indirect methods, an analytical signal is used to determine the end of a chemical reaction (as a kind of indicator), and the amount of the analyte that has reacted is found using the law of equivalents, i.e. according to an equation not directly related to the name of the method.

Based on the method of quantitative determination, a distinction is made between non-reference and reference instrumental methods of analysis.

Without reference methods, they are based on strict laws, the formulaic expression of which makes it possible to recalculate the intensity of the measured analytical signal directly in the amount of the substance being determined using only tabular values. Such a pattern can be, for example, Faraday’s law, which makes it possible to calculate the amount of the analyte in a solution during coulometric titration based on the current and time of electrolysis. There are very few non-standard methods, since each analytical determination is a system of complex processes in which it is impossible to theoretically take into account the influence of each of the many operating factors on the result of the analysis. In this regard, certain techniques are used in analyzes that allow these influences to be experimentally taken into account. The most common technique is the use of standards, i.e. samples of substances or materials with precisely known content of the element being determined (or several elements). When carrying out the analysis, the analyte of the test sample and the standard is measured, the data obtained are compared, and the content of this element in the analyzed sample is calculated from the known content of the element in the standard. Standards can be manufactured industrially (standard samples, normal steels) or prepared in the laboratory immediately before analysis (comparison samples). If chemically pure substances (impurities less than 0.05%) are used as standard samples, then they are called standard substances.

In practice, quantitative determinations using instrumental methods are carried out using one of three ways: calibration function (standard series), standards (comparison) or standard additions.

When working according to the calibration function method, using standard substances or standard samples, a number of samples (or solutions) containing different but precisely known quantities of the component being determined are obtained. This series is sometimes called the standard series. Then this standard series is analyzed and the sensitivity value K is calculated from the data obtained (in the case of a linear calibration function). After this, the intensity of the analytical signal A in the object under study is measured and the amount (mass, concentration) of the desired component is calculated using the coupling equation /> or found using the calibration graph (see Fig. 2.1.1).

The comparison method (standards) is applicable only for the linear calibration function. The determination of this component is carried out in a standard sample (standard substance) and obtain

Then they are determined in the analyzed object

Dividing the first equation by the second eliminates sensitivity

and calculate the result of the analysis

The method of standard additions is also applicable only to the linear calibration function. In this method, a sample of the test object is first analyzed and // is obtained, then a known amount (mass, volume of solution) of the component being determined is added to the sample and after analysis,

By dividing the first equation by the second, K is eliminated and a formula is obtained for calculating the results of the analysis:

The spectrum of a substance is obtained by influencing it with temperature, electron flow, light flow (electromagnetic energy) with a certain wavelength (radiation frequency) and other methods. At a certain amount of impact energy, a substance is able to go into an excited state. In this case, processes occur that lead to the appearance of radiation with a certain wavelength in the spectrum (Table 2.2.1).

The emission, absorption, scattering or refraction of electromagnetic radiation can be considered as an analytical signal, information-carrying about the qualitative and quantitative composition of a substance or its structure. The frequency (wavelength) of the radiation is determined by the composition of the substance under study, and the intensity of the radiation is proportional to the number of particles that caused its appearance, i.e. quantity of a substance or component of a mixture.

Each of the analytical methods usually does not use the full spectrum of a substance, covering the wavelength range from X-rays to radio waves, but only a certain part of it. Spectral methods are usually distinguished by the range of spectral wavelengths that are working for a given method: ultraviolet (UV), X-ray, infrared (IR), microwave, etc.

Methods that operate in the UV, visible and IR ranges are called optical. They are most used in spectral methods due to the comparative simplicity of the equipment for obtaining and recording the spectrum.

Atomic emission analysis (AEA) is based on the qualitative and quantitative determination of the atomic composition of a substance by obtaining and studying the emission spectra of atoms that make up the substance.

Pi AEA, the analyzed sample of the substance is introduced into the excitation source of the spectral device. In the source of excitation, this sample is subjected to complex processes consisting of melting, evaporation, dissociation of molecules, ionization of atoms, excitation of atoms and ions.

Excited atoms and ions through very short time(~10-7-108s) spontaneously return from an unstable excited state to a normal or intermediate state. This leads to the emission of light with frequency  and the appearance of a spectral line.

The general scheme of atomic emission can be represented as follows:

A + E  A*  A + h

The degree and intensity of these processes depends on the energy of the excitation source (ES).

The most common IWs are: gas flame, arc and spark discharges, inductively coupled plasma (ICP). Their energy characteristic can be considered temperature.

Quantitative AEA is based on the relationship between the concentration of an element and the intensity of its spectral lines, which is determined by the Lomakin formula:

where I is the intensity of the spectral line of the element being determined; c - concentration; a and b are constants.

The values ​​of a and b depend on the properties of the analytical line, IV, and the ratio of the concentrations of elements in the sample, therefore the dependence /> is usually established empirically for each element and each sample. In practice, the method of comparison with a standard is usually used.

For quantitative determinations, the photographic method of recording the spectrum is mainly used. The intensity of the spectral line obtained on a photographic plate is characterized by its blackening:

where S is the degree of blackening of the photographic plate; I0 is the intensity of light passing through the unblackened part of the plate, and I - through the blackened part, i.e. spectral line. The measurement of spectral line blackening is carried out in comparison with the background blackening or in relation to the intensity of the reference line. The resulting blackening difference (S) is directly proportional to the logarithm of the concentration (c):

With the three-standard method, the spectra of three standards with known elemental contents and the spectrum of the analyzed sample are photographed on one photographic plate. The blackening of the selected lines is measured. A calibration graph is constructed from which the content of the elements being studied is determined.

In the case of analyzing objects of the same type, the constant graph method is used, which is built using a large number of standards. Then, under strictly identical conditions, the spectrum of the sample and one of the standards is taken. Using the spectrum of the standard, they check whether the graph has shifted. If there is no shift, then the unknown concentration is found using a constant graph, and if there is, then the magnitude of the shift is taken into account using the spectrum of the standard.

With quantitative AEA, the error in determining the base content is 1-5%, and the impurity content is up to 20%. The visual method of recording the spectrum is faster, but less accurate than the photographic one.

Based on the hardware design, it is possible to distinguish AEAs with visual, photographic and photoelectric registration and measurement of the intensity of spectral lines.

Visual methods(registration with the eye) can only be used to study spectra with wavelengths in the region of 400 - 700 nm. The average spectral sensitivity of the eye is maximum for yellow-green light with a wavelength of  550 nm. Visually, it is possible to establish with sufficient accuracy the equality of the intensities of lines with the nearest wavelengths or determine the brightest line. Visual methods are divided into styloscopic and stylometric.

Styloscopic analysis is based on a visual comparison of the intensities of the spectral lines of the analyzed element (impurity) and nearby spectral lines of the main element of the sample. For example, when analyzing steels, the intensities of the spectral lines of impurities and iron are usually compared. In this case, previously known styloscopic features are used, in which the equality of the intensity of the lines of a certain analytical pair corresponds to a certain concentration of the analyzed element.

Steeloscopes are used for express analysis, which does not require high accuracy. 6-7 elements are determined in 2-3 minutes. The sensitivity of the analysis is 0.01-0.1%. For analysis, both stationary steeloscopes SL-3... SL-12 and portable SLP-1... SLP-4 are used.

Stylometric analysis differs from styloscopic analysis in that the brighter line of the analytical pair is weakened using a special device (photometer) until the intensities of both lines are equal. In addition, stylometers allow the analytical line and the comparison line to be brought closer together in the field of view, which significantly increases the accuracy of measurements. Stylometers ST-1... ST-7 are used for analysis.

The relative error of visual measurements is 1 – 3%. Their disadvantages are the limited visible spectrum, tediousness, and lack of objective documentation of the analysis.

Photographic methods are based on photographic recording of the spectrum using special spectrograph instruments. The working area of ​​spectrographs is limited to a wavelength of 1000 nm, i.e. They can be used in the visible region and UV. The intensity of spectral lines is measured by the degree of blackening of their image on a photographic plate or film.

Construction materials and products used in construction, reconstruction and repair of various buildings and structures, divided into natural and artificial, which in turn are divided into two main categories: the first category includes: brick, concrete, cement, timber etc. They are used in the construction of various building elements (walls, ceilings, coverings, floors). To the second category - special purposes: waterproofing, thermal insulation, acoustic, etc. The main types of building materials and products are: stone natural building materials from them; inorganic binders and organic; forest materials and products made from them; hardware. IN depending on the purpose, conditions of construction and operation of buildings and structures, appropriate building materials are selected, which have certain qualities and protective properties from exposure to them from different external environments. Taking these features into account, any construction the material must have certain construction and technical properties. For example, the material for the external walls of buildings should have the least thermal conductivity

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 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. 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 to 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 valuable metal concentrations, 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 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:

1. selection of a representative sample reflecting the average composition of the analyzed material or the local distribution of the determined elements in the material;
2. 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;
3. converting their glow into a spectrum and recording it (or visual observation) using a spectral device;
4. 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 methods of analysis, 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 individual groups of 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 the mass fraction of 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 skimmed off as a paste in Vaseline oil. 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

The principle of operation of the most common photometric devices for medical applications is based on the absorption method of analysis or the property of solutions to absorb visible light and electromagnetic radiation in the close ultraviolet range. 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:

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 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.

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), plateaus or kinks appear on the curve.

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.

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), plateaus or kinks appear on the curve.

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, they study the decomposition of metal carboxylates, various organometallic compounds, oxide high temperature superconductors. 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 quality. sample evaluations, 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, whereby the component of interest is isolated from the mixture being analyzed and weighed as an individual compound. Some elements of the 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 complex composition the error increases to several percent due to the imperfection of methods for separating and isolating 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 precise measurement volumes of solutions of two substances reacting with each other. Quantitative determination using the titrimetric method of analysis 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.

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 the 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 a drying 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 by wrung out wet 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 compressive strength, samples of regular geometric shape (beams, cubes, bricks) are inspected, 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 – Bending strength test diagram

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 numerical 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, what is that 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.

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