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Section 5. Material Science
Adilkhodjaev Anvar Ishanovich, doctor of Technical Sciences, professor Tashkent Institute of Engineers of Railway Transport Mahamataliev Irkin Muminovich, candidate of Technical Sciences, professor, Tashkent Institute of Engineers of Railway Transport Ilyasov Allanazar Torehanovych, basic doctoral student Tashkent Institute of Architecture and Construction E-mail: [email protected]
ON POROSITY PARAMETERS OF CERAMIC BRICKS MADE OF LOW-GRADE RAW MATERIAL USING BURN-OUT ADDITIVES OF AGRICULTURAL PRODUCTION
Abstract: This article presents a classification of methods for controlling the porous structure of materials. It presents the study of experimental data on porosity parameters of ceramic bricks made of optimal composition of a raw mix of various kinds of burn-out additives by the method of mercury porosimetry. Keywords: Mercury porosimetry, brick, porosimeter, porous structure.
Ensuring the high quality of materials and products with a predefined set of properties is impossible without the use of modern and effective methods of structure study.
As is known, physical, mechanical and operational properties of porous materials depend to a large extent on the pores - their type, dispersion, size distribution, number of conditionally-closed ones, etc.
In this regard, the porosity study of the designed composites both at the stages of the development of manufacturing technology and the control of finished products compliance with technical specifications and other normative documents is an urgent task. Despite certain achievements in the production of porous ceramic products and extensive experience in their manufacture, a large-scale introduction is not observed in Uzbekistan and other countries, especially in the manufacture of high porosity material that provides resource and energy savings both in the manufacturing process and in further operation. This is due to the fact that the process of creating new material is associated with the solution of problems of optimization of batch compositions, studying their behavior in shaping the necessary mass, and adjusting the technological redistribution of production. Moreover, it is impossible to guarantee the necessary properties of the final material without carrying out research at the level of structural changes
due to the changes in raw material characteristics, external and internal factors significantly affecting the quality of the composite.
For ceramic bricks, with a porosity of more than 5060%, it is necessary to pay a special attention to the study of the pore space formation, as this characteristic has a significant effect on the energy efficiency of the fencing structures made of these materials.
To solve such a complex problem, the methods are needed that allow measuring not only the pore volume, but also the characteristics of the pore structure, its volume and sizes [1].
By the nature of the impact on material, all methods of controlling porosity are classified into destructive ones (hydraulic, sorption, electromagnetic and ionizing) and nondestructive ones (visual-optical) [2].
The phenomena of capillarity and diffusion are the bases of hydraulic methods. All methods of fluid porosimetry (mercury porosimetry, fluid pyknometry, capillary methods) are based on volume or weight determination of fluid amount filling the pores of material or displaced by it when immersed in fluid. To measure porosity, the sorption methods (the Dubinin's method, the BET method (the one offered by Brunauer, Emmett and Taylor)) based on the phenomenon of gas condensation on open surfaces of adsorbents are widely used.
The advantage of the sorption method is the possibility of reliable determination of such a significant structure parameter as the specific surface area of pores [3; 4]. The electromagnetic method (the method of nuclear magnetic resonance) is a sensitive method for studying the parameters of porosity [5; 6], it allows one to register the pores up to 0.1 nm in size. The ionizing methods (radiographic method and the X-ray observation method) along with the data on basic parameters of porous structure make it possible to conduct a detailed analysis of the closed porosity.
In the visual-optical method, the loupes, endoscopes, microscopes, flexible telescopic devices based on light-emitting diodes are used [7].
The methods mentioned above have their advantages and disadvantages. The main disadvantage ofall methods (except for mercury porosimetry) is a weak registration of macroporosity.
The pore size of composite building materials is generally considered to be more than 0.1 ^m. To describe the macropo-rous structure, a mercury porosimeter is used, as a rule. Modern and effective device for studying macroporous structure parameters is a mercury porosimeter made in Thermo Scientific, of Pascal 240 series, which allows one to determine the main parameters such as: percentage of porosity, pore volume distribution depending on pore size in solid samples, specific pore volume, average pore size, integral and differential specific surface area of material.
The method of mercury porosimetry is based on the fact that fluid, that does not wet a solid object, penetrates
into its pores only when exposed to external pressure. The fluid volume filling the pores is a function of external pressure, which makes it possible to obtain data on the pore size distribution.
This method is based on the fact that an excessive pressure must be applied to induce the non-wetting fluid, its value is related to the pore size by the Washburn equation (l):
R = (-2y cosO)/P (l)
where Y is the surface tension of mercury 0.48 N/m, R is the pores radius, 9 is the contact angle of mercury wetting, 9 ~ 140 and P is the pressure of mercury penetration into the sample.
In the article on the example of obtaining an effective ceramic brick [8], the possibility of using the mercury po-rosimetry method is considered for studying the structure parameters of porosity.
Measurements ofbrick porosity have been carried out on standard Thermo Scientific CD3 dilatometers at a maximum pressure of 200 MPa induced by the Pascal 240 porosimeter. In experiments a weighted portion of brick of certain mass, placed into a dilatometer to form a vacuum, was used. After the vacuum was created, the dilatometer was filled with mercury and immersed in the compartment of the porosimeter autoclave to produce the porograms. The porosity parameters were calculated automatically using the SOL.ID EVO program and output to the printing device in the form of histograms of the pore radius size distribution in logarithmic scale (Fig. 1).
Figure 1. Example of a histogram of pore size distribution
For comparative studies, 3 series ofsamples made of ceram- acteristics ofbricks of various composition ofbatch, the compo-ic masses (charge) containing the components listed in (Table sitions of clay mass of Bestyuben loamy soil (63%) and Beltau 1) have been taken. After a complex of studies on strength char- zeolite-containing rock (27%) were stated as optimal ones.
Table 1. - Composition of ceramic masses (batch)
Components Measuring units Symbols of batch
Batch -1 Batch -2 Batch -3
Bestyuben loess loamy soil % 63 63 63
Beltau zeolite-containing rock % 27 27 27
Grinded rice straw % 10 - -
Rice husk % - 10 -
Grinded stems of cotton % - - 10
Analysis of obtained quantitative characteristics of the porosity of ceramic shard (Table 2) shows that the most effective is the use of a burn-out additive in the form of grinded stems of cotton. This is confirmed by the fact that the total porosity of ceramic bricks made of batch No. 1 (with addition of rice straw) is 51.04%, batch No. 2 (with addition of rice husk) -49.60%, and batch No. 3 (with addition of cotton stems) -53.09% in the range of pore sizes from 15.000 to 0.0103 ^m. The average density of ceramic brick is 1.3308 g/cm3.
For each series of ceramic samples shown in the diagram (Fig. 2), a qualitative calculation of the porosity parameters was carried out according to the data given in (Table 2).
A study of qualitative characteristics of ceramic shard porosity (Fig. 2) has shown that despite the increased total porosity of samples from ceramic masses with a burn-out additive of grinded stems of cotton, the amount of "dangerous" pores (37.03%) is significantly less than for samples made of batch No.1 (41.76%) and batch No.2 (45.06%). This is apparently due to the peculiarities of structure formation of ceramic masses with a burn-out additive of cotton stems under baking, the essence of these peculiarities is to improve the pore structure of material due to additional number of new formations that contribute to the transition of a certain number of "dangerous" pores to the category of "safe" ones.
Table 2.- Quantitative characteristics of porosity of ceramic bricks samples with various types of burn-out additives
№ Ranges of pore diameters (^m) Average pore diameter (^m) Porosity (%)
burn-out additive burn-out additive
Rice straw Rice husk Cotton stems Rice straw Rice husk Cotton stems
1. 15.0000-10.2221 12.6111 12.6111 12.6111 0.384 0.088 0.031
2. 10.2221-6.9661 8.5941 8.5941 8.5941 0.499 1.235 1.598
3. 6.9661-4.7473 5.8567 5.8567 5.8567 2.048 0.848 2.548
4. 4.7473-3.2351 3.9912 3.9912 3.9912 2.609 0.848 2.901
5. 3.2351-2.2047 2.7199 2.7199 2.7199 3.567 1.168 3.437
6. 2.2047-1.5024 1.8535 1.8535 1.8535 4.563 2.380 4.353
7. 1.5024-1.0239 1.2631 1.2631 1.2631 13.075 7.782 11.608
8. 1.0239-0.6977 0.8608 0.8608 0.8608 12.432 15.610 12.627
9. 0.6977-0.4755 0.5866 0.5866 0.5866 6.355 9.496 7.449
10. 0.4755-0.3240 0.3998 0.3998 0.3998 3.074 4.958 2.881
11. 0.3240-0.2208 0.2724 0.2724 0.2724 1.262 2.441 1.318
12. 0.2208-0.1505 0.1857 0.1857 0.1857 0.569 1.243 0.613
13. 0.1505-0.1026 0.1265 0.1265 0.1265 0.294 0.721 0.321
14. 0.1026-0.0699 0.0862 0.0862 0.0862 0.134 0.394 0.213
15. 0.0699-0.0476 0.0588 0.0588 0.0588 0.052 0.222 0.197
16. 0.0476-0.0325 0.0400 0.0400 0.0400 0.006 0.107 0.227
17. 0.0325-0.0221 0.0273 0.0273 0.0273 0.096 0.050 0.334
18. 0.0221-0.0151 0.0186 0.0186 0.0186 0.027 0.017 0.375
19. 0.0151-0.0103 0.0127 0.0127 0.0127 0.000 0.000 0.064
E 51.04 E 49.60 E 53.09
Figure 2. Diagram of porosity of ceramic bricks samples with various types of burn-out additives
waste into the batch, it is most expedient to use the following ratio of components in the form of grinded cotton stems: loess loamy soils - 63%, zeolite-bearing rock - 27% and grinded cotton stems - ;
Thus, it can be concluded that in order to produce an effective ceramic bricks from low-grade loess loamy soils of the
Bestyuben deposit and zeolite-bearing rocks of the Beltau deposit with an inclusion ofburn-out additives from agricultural
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