Method of determining heat resistance of bentonite clay

FIELD: physics.

SUBSTANCE: method of determining heat resistance of bentonite clay is characterised by that, a nomograph which reflects dependency of temperature of the second endothermal effect and heat resistance of bentonite clay from contained structural iron is constructed first. For this purpose samples of bentonite clay from known deposits are analysed. The samples are tested in a derivatograph. Derivatograms with differential thermo-weighted (DTW) and differential thermal (DT) curves are obtained, from which temperature of the second endothermal effect is determined depending on structural iron contained in the samples. Heat resistance of the samples is determined depending on structural iron contained in the samples. From the said two curves, the said nomogram is constructed, which is then used for subsequent determination of heat resistance of the analysed bentonite clay; a wet ground up sample is tested in a derivatograph by heating followed by drying. Derivatograms with differential thermo-weighted and differential thermal curves are obtained, from which temperature of the second endothermal effect is determined and heat resistance of the analysed bentonite clay is determined from the said nomogram.

EFFECT: cutting on time and simplification of the process of determining heat resistance.

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The invention relates to test equipment and in particular to methods of testing materials for resistance.

Well-known methods of testing materials for resistance are the ways in which the specimens are subjected to several successive thermal cycles, periodically produce control samples for the parameters of the elastic properties and fatigue characteristics, and heat resistance is judged by the number of cycles until the occurrence of cracks in the sample (ed. St. USSR №1345097, CL G01N 3/60, publ. 1987.10.15; ed. St. USSR №1645883, CL G01N 3/60, publ. 1991.04.30; ed. St. USSR №1696966, CL G01N 3/60, publ. 1991.12.07).

The disadvantage of the methods is the low reliability of evaluation of heat resistance materials, working in conditions of one-sided surface heating due to insufficiently accurate reproduction characteristics of the heating of the material.

There is a method of testing materials for resistance to heat, which consists in the fact that the surface of the test sample material is subjected to cyclic thermal effects, including heating and subsequent cooling, as well as produce a control surface of the test sample material, and thermal stability of a material is judged by the number of cycles of thermal influence to the emergence of cracks in said surface, after cooling from the surface of sample mother of the La periodically remove a layer of material thickness, the corresponding intensity of wear of the material during the operation, and the control surface of the test sample of material is carried out after removing the layer of material from the surface of the sample after a specified number of cycles of exposure to heat or after each cycle (patent RF №2117274, CL G01N 3/60, G01N 3/56, publ. 1998.08.10).

The method allows testing materials for resistance at temperature and intensity of material removal from the surface, corresponding to the operating conditions, more accurate prediction of the material behavior during operation. However, the method is tedious and time consuming.

There is a method of determining thermal stability of structural ceramic materials, including manufacturing prismatic samples, creating a thermal shock by cycle heating-cooling and subsequent determination of the loss of physical and mechanical properties of the samples with respect to their values prior to thermal shock, the samples made with a lateral incision, simulating the crack and not containing at the vertex of the induced defects, and without an incision, and the resistance is determined by the values of the relations

(1*1C/K1C)•100% and σ12,

where To*1ccritical intensity factor strain the sample after thermal shock;

To1c- the average value of the critical stress intensity factor of the samples to thermal shock;

σ1- tensile strength Flexural notched specimen after thermal shock;

σ2- the average value of the tensile strength Flexural specimens without notch to thermal shock (RF patent No. 2131403, CL SW 35/00, publ. 1999.06.10).

There is a method allows to reduce the errors of determination of heat resistance while reducing the number of test samples, to eliminate the influence factor of the volume of the test sample to the heat resistance, and also to quantify the resistance patterns of ceramics to initiate thermal cracking, and its sensitivity to defects resulting from thermal shock.

The disadvantage of this method is the inability to directly determine thermal stability of ceramic materials and to directly determine the relevance of the material on this parameter GOST.

The closest technical solution to the invention is a method for determining thermal stability of bentonite clay, described in GOST 28177-89 "molding Clay bentonite. General technical conditions". Moscow, Publishing house of standards, 1989, p.4-8.

According to GOST method of determining thermal stability based on the determination of loss of compressive strength in a wet SOS is the right after heating the clay.

The method consists in the following. Two hinge clay placed in two varicella bowl, smooth surface clay layer in bowls, put the past in pre-heated to a temperature of 550°C muffle furnace and maintained there for 1 hour. After annealing the bowl kept in a desiccator until reaching room temperature, the average mixing calcined clay and selected a sample mass of 100 g Consistently prepare a mixture of 2 kg mass from the source and calcined clay and continue the test for determining the limit of compressive strength in the wet state. To do this, prepare a mixture of sand (95 parts), clay (5 parts) and water, mix it in a covered container for 20 minutes a sample is Taken mixed with compaction of not less than 60%. Then continue stirring the mixture in the blender with the lid open, every 1-2 min to determine the rate of sealability, and compressive strength as natural drying of the mixture. The test stops after strength reduction mixture. The samples are produced in a metal sleeve on laboratory impact-testing machine triple blow of cargo. The prepared samples have on the device for determining the compressive strength in the wet state on three samples. For the limit of compressive strength in the wet state arithmetic mean of the results of the three is definitely the response to when the compressive strength is greatest. Thermal stability (T) is calculated by the formula

,

where σ1- the limit of compressive strength in the wet state according to the test results calcined clay, PA (kgf/cm2);

σ2- the limit of compressive strength in the wet state according to the test results of the original clay, PA (kgf/cm2).

Determination of thermal stability of a method of GOST takes at least a day and requires a large number of instruments and devices, such as a device for determining the compressive strength in the wet state, laboratory Koper with a cylindrical sleeve, laboratory scales, laboratory mixers, muffle furnace with thermostat, desiccator, porcelain varicella bowl. The error in determining thermostability according to GOST is ± 1-2%.

The task to be solved by the invention, is to reduce the time and simplify the process of determining the heat stability and conformity to the values of GOST, as well as increasing the reliability of the received data.

The problem is solved by the fact that according to the proposed method of determining thermal stability of bentonite clay test shredded wet clay sample is carried out in derivatograph heating, soprovojdali is by its drying, getting derivatograph with differential thermovisual (DTG) and differential thermo analytical (DTA) curves, and the temperature determined by the temperature of the second endothermic effect on these curves, using nomograms, consisting of two axes of ordinates indicating the temperature of the second endothermic effect and the value of thermostability according to GOST, shared x-axis denoting the content of structural iron in clays, and two experimental curves constructed.

Figure 1 presents a nomogram to determine heat stability.

Figure 2 - derivatograph thermal analysis of bentonite Voronezh field.

Thermogravimetric analysis of materials, which consists in testing the crushed wet sample in derivatograph by heating, accompanied by his dehydration, obtaining thermovisual TG, differential thermovisual DTG and differential thermo analytical DTA curves and the determination of the characteristic kinks - endothermic effects on the curves of thermal images, which characterizes the change in temperature of the sample during the test, the well known (see, for example, patent RF №2312328, CL G01N 25/56, publ. 2007.07.20).

However, this analysis is intended only to determine the amount of water fractions and the corresponding C is achene moisture content of the sample and is not applicable to determine thermal stability of clay materials, for example bentonites.

The inventive method consists in the following: natural Comby bentonite grated to a powder. For the analysis uses a sample of about 500 mg, which is placed in a crucible, and then the latter is placed in a derivatograph on a torsion balance.

Derivatograph automatically records 2 curves: differential thermovisual (DTG) and differential thermo analytical (DTA) curves.

The effects in the form of corresponding peaks in the last two curves coincide on the scale of temperature. For example, the peak at 600°C on the curve (DTG) necessarily coincides in position with respect to an axis of the temperature peak on the DTA curve, since this reaction takes place with absorption of heat. Well-known way to determine the temperature of the second endothermic effect of the investigated clay (see, for example, Hoelen. Introduction to theory of thermal analysis. M., Izd-vo "Nauka", 1964; Ax N, Ogorodova L.P., Melchakova L.V. Thermal analysis of minerals and inorganic compounds. M., Izd-vo Mosk. University, 1964; pots B.C., Timashev CENTURIES, Savel'ev V.G. Methods of physicochemical analysis wygesic substances. M., publishing house of the Higher school, 1981).

Based on a large statistical material we found that bentonite when the value of the second endothermic effect within the interval 680-720, will have a temperature not less is it 1 according to GOST.

Structural iron was determined by the us energy dispersive method using an electron microscope of high resolution. The number specified in at.%. In the research process with application of complex methods (x-ray, IR spectroscopy, electron microscopy high resolution), it was found that addition of iron in the octahedral layer on the heat resistance is also influenced by such factors as the degree of imperfection of the structure and position of hydroxyl (TRANS-CIS-position). However, the trivalent cation of iron present in the octahedra, plays a major role.

The percentage of structural iron determines the qualitative indicators of bentonite clay. The lower the iron content, the higher thermal properties of clays, such as the temperature of the second endothermic effect and thermostability.

We have investigated over 100 samples of bentonite clay every currently known deposits, by definition, the second endothermic effect and heat stability according to GOST and received their average values. The data we used to construct nomograms, which is a two axis of ordinates indicating the temperature of the second endothermic effect and the value of thermostability according to GOST, ABSU the x-axis, denoting the content of structural iron in clays, and two experimental curves constructed, one (1) of which displays the temperature dependence of the second endothermic effect curves DTG and DTA from the content of the structural iron bentonite clay known deposits, and the second (2) shows the dependence of thermal stability of clays according to GOST from the content of the structural iron in the same clays (figure 1).

To use the nomogram simple. The temperature value of the second endothermic effect T lay on the ordinate axis with temperature, spend a horizontal line to the intersection with the first curve (1). Then spend a vertical line to the intersection with the second curve (2), and then a horizontal line to the intersection with the ordinate axis, thus obtaining the value of thermostability according to GOST.

The method is illustrated by the following example.

Sample natural bentonite lump Voronezh field with the content of N2About-7-11 and H2O+5-8 wt.% grated to a powder. With multiple batches of 500 mg conduct thermal studies on derivatograph brand OD-102 automatic recording 2 curves: differential thermovisual DTG curve and differential thermo analytical DTA curve. The precision of the assay of 0.3 mg. due To the fact that in the bentonites studied qui the statement has a significant amount of iron, up to 10% (for the studied bentonite is characterized by a high iron content (8-12%)), which can oxidize when heated, the samples were removed at various modes of the oxygen potential: in air and in nitrogen atmosphere.

The uniformity of the heating furnace is provided program management, which is set at the rate of 5°C/min

Curves are recorded by derivatograph as a function of the determined values with time (figure 2).

The resulting derivatograph typical mineral of the montmorillonite group, with intense dual low-temperature weight loss (100-300°C, a maximum of 100-150°C, remove adsorbed, packet and solvation of water), with the effect of the removal of structural water (500-555°C) and a weak exothermic effect at 800-900°C.

Get the average value for multiple hanging the temperature of the second endothermic effect associated with the removal of a hydroxyl group, within 555°C (total weight loss 12-20%).

Next, using the nomogram (figure 1), find the value of thermostability according to GOST investigated clay.

For this purpose, the temperature scale of the second endothermic effect of the delay obtained in derivatograph temperature of 555°C, hold the line, parallel to the scale of the content in the bentonite structural iron, to the intersection with the first curve 1. From the obtained point do the Oia, parallel to the temperature scale of the second endothermic effect, to the intersection with the second curve 2. From the obtained point spend a line parallel to the scale of the content in the bentonite structural iron, to the intersection with the scale values of the heat stability according to GOST. To determine the temperature, which is equal to the test sample 0,42%

The same results are obtained regardless of are natural bentonite or benthopelagic.

The error in the determination of the heat stability of the proposed method is comparable with the error of the standard and is ±1-2%.

Determination method of GOST takes at least a day and requires complex and expensive devices. Definition the same way thermogravimetric analysis takes 2 hours with the appropriate fairly common device - derivatograph.

The method for determining thermal stability of bentonite clays, characterized by the fact that pre-build a nomogram showing the dependence of the temperature of the second endothermic effect and thermal stability of bentonite clay on the content of structural iron, to do this, examine samples of bentonite clays known deposits, the samples tested in derivatograph by heating, accompanied by their drying, get derivatograph to trim Antialias thermovisual (DTG) and differential thermal (DTA) curves, which determine the temperature of the second endothermic effect depending on contained in samples of structural iron, as well as determine thermal stability of the samples depending on the contained structural iron mentioned two dependencies are built above the nomogram used for subsequent determinations of thermal stability of the studied bentonite clay; to determine thermal stability of the studied bentonite clay crushed wet sample experience in derivatograph by heating, followed by its drying, get derivatograph with DTG and DTA curves, which determine the temperature of the second endothermic effect and referred to the nomogram to determine thermal stability of the studied bentonite clay.



 

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