V. Z. Abdrakhimov, I. V. Kovkov ANALYSIS OF PHASE STRUCTURE OF THE CERAMIC BRICK OF OVER FIVE HUNDRED YEARS

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1 UDC Samara Academy of State and Municipal Management D. Sc. in Engineering, Prof. of Dept. of Cadastre and Geoinformation Technologies V. Z. Abdrakhimov Russia, Samara, tel.: ; Ph. D. in Engineering, Prof. of Dept. of Cadastre and Geoinformation Technologies I. V. Kovkov Russia, Samara, tel.: ; V. Z. Abdrakhimov, I. V. Kovkov ANALYSIS OF PHASE STRUCTURE OF THE CERAMIC BRICK OF OVER FIVE HUNDRED YEARS Statement of the problem. Problems of durability of constructions and buildings and decreasing expenses for their major repairs are rather actual and determined by the scales of industrial, housing and individual construction. The aim of the given research is using the Mossbauer spectroscopy to establish electron microscopic and x-ray phase methods of the phase structure analysis of brick of over 500 years, as it is the phase structure that mainly defines the operational properties of products. Results. The research showed that in the brick of the Nizhniy Novgorod Kremlin, mullite instead of finest needles crystallizes as isometric grains, short and long prismatic crystals. Mossbauer spectra of absorption showed that in the studied ceramic brick, hematite was found on the surface, while magnetite was in the internal layer. Conclusions. Based on the research made, it is assumed that clay was used in the production of brick which contained not less than 15 % of Al 2 O 3, 5 to 8 % of Fe 2 O 3 8 to 10 % of СаО and 2 to 5 % of R 2 O. The research showed as well that either ceramic brick burnt at the temperature of no less than 1050 о С was used in the construction of the Nizhny Novgorod Kremlin, or alkaline and alkaline-earth additives were introduced into the masses. Keywords: Mossbauer spectroscopy, phase structure, a microscope, the Nizhny Novgorod Kremlin, x-ray phase analysis, mullite, isomorphism, solid solutions, hematite, magnetite. Introduction The problem of the phase content is given a lot of prominence in the physical chemistry of silicates as the phase content is vital to the operation properties of products [1 2]. 36

2 Issue 4 (16), 2012 ISSN Mullite is one of the minerals that commonly occur in burned ceramic [3]. Its enhanced density, fire, chemical and mechanical resistance characteristics were a major draw for researchers seeking to obtain the synthetical mullite and study its structure [3 6]. The content of mullite has long been the subject of discussions resulting in the researchers arguing that the content of mullite varies from 2Al 2 O 3 SiO 2 to 3Al 2 O 3 2SiO 2 [3, 7]. Until recently the researchers have not yet agreed to how mullite is formed in ceramic materials. We concur that the study of the physical and mechanical processes in ceramic materials should be conducted in conjunction with the study and analysis of the historical experience in this area as well as with the study of architectural monuments made of the material under investigation. One of these is the Ensemble of the Nizhegorodsky Kremlin that had been under construction from 1500 to Fig. 1. Nizhegorodsky Kremlin (Koromyslova Tower) It is noteworthy that the quality of the Rus made brick has been invariably high. Peter Alensky who was on a visit to Moscow in the 16 th century wrote that bricks in that country were unsurpassed and Moscovites reached great excellence in making them [8]. However, 37

3 there have been some changes as the time went on. In the late 1950s and the early 1960s the USSR Party and Government set out the construction of panel houses as these houses unlike the brick ones took not so long to construct and were much more cost-effective [9]. The quality of ceramic brick starting from the 60s had seen a decline. There were lots of 4 and 5-storeyed houses constructed with the use of low-labelled brick 75 (there is currently no such label according to GOST requirements). Presently the durability of ceramic brick 75 (underfiring in most cases) which is Soviet-made is on average a bit over 50 years [8 9]. The problems of durability of structures and buildings and reduction in their maintenance costs needs to be addressed and are determined by the scale of industrial, housing and private construction. The objective of the ongoing research is to reveal the phase content of brick of over 500 years using the Mossbauer spectroscopy, electron and microscopic and X-ray phase methods of analysis. 1. The experimental part The study of structure transformations of iron compounds in the sample under investigation was carried out by nuclear gamma-resonance spectroscopy (NGRS) as in [10 12]. The γ- radiation source was 57 Со and Rh. The isomer shift was defined in relation to natrium nitroprusside. The speed of the source varied in the range of mm/sec. The cylindershaped samples ( m) cut from the brick of the Nizhegorodsky Kremlin were the subject of the research. The ceramic samples had the zoning that was more distinctive near the centre. The surface of the samples is light-cherry with a darker middle. In order to define the differences between the transformations of ferrous compounds across the section of ceramics, the surface and the middle of the sample were separated. The absorbers were made of them with the state and nature of the iron ion distribution studied in each. The Mossbauer spectra of the samples are shown in Fig. 2. The depth of the resonance line, its location in relation to the speed scale and extra thin structure is indicative of increasing Fe 2 О 3 content in the averaged sample (see Fig. 2а). According to the values of isometric shift and quadrupole splitting of the Mossbauer spectrum of the samples under investigation the position of iron ions in them are related to the position of Fe 2+ ions in the structure of ferrous montmorillonite of nontronite type [10 13]. 38

4 Issue 4 (16), 2012 ISSN N Fe 2 O 3 A B FeO Fe 2 O 3 Fe 2 O 3 Fe 3 O V. 10 3, м/с b c а V. 10 3,м/с Fig. 2. Mossbauer spectra of absorption: а averaged (from the interior and exterior layers); b surface layer; c interior layer: А hematite, B magnetite; N number of count pulses in the duct, V rate of footage The calculation of the area of the spectrum douplets showed that ferrous compounds on the surface of the surveyed sample with the predominantly oxidizing medium are largely represented by hematite (see Fig. 2b) and with magnetite in the centre (see Fig. 2c). Hematite is the lowest temperature iron oxide and can thus be formed in the low temperature area (of less than 500 о С) [1 2, 14]. Magnetite Fe 3 O 4 takes the immediate position and can thus form in a reducing medium which dominates the middle of the samples due to partial burning off of the organic substances (carbon): 3Fe 2 O 3 + СО = 2Fe 3 O 4 + СО 2, 39

5 3Fe 2 O 3 + С = 2Fe 3 O 4 + СО, or due to the splitting or oxidization of ferrous oxide FeO at the temperatures of less than 570 о С: 4FeO = Fe + Fe 3 O 4. The air diffusion into the central layers of ceramics is hampered and firing gives rise to a reducing medium due to burning of the organics in the lack of oxygen. The particular process of mineral formation of ceramic materials in a reducing medium is caused by a transformation of ferrous compounds at relatively low temperatures (of about 950 о С) into the liquid phase as the resulting oxide of bivalent iron FeO is an active fusing agent. A low temperature formation of the liquid phase is conducive to the reaction of the formation of spinel, herzinite and mullite [1 2, 13 14]. According to the equilibrium diagram iron and oxygen make up three stable oxides: Fe 1-х, Fe 3 O 4 and Fe 2 O 3 [9 10, 13 14]. The process of reduction of iron from the oxides according to the principle of higher oxides shifting to the lower ones takes place as follows Fe 2 O 3 Fe 3 O 4 FeO Fе. As it takes place according to the diagram of Fe-О there are not only low oxides and metal arising in the system but also solid solutions [1 2, 10 14]. During the reduction of Fe 2 O 3 to FeO the molecular concentration of iron oxide becomes twice as large, which causes a significant drop in the fusion temperature of the system accompanied by the formation of gaseous reaction products [1 2, 10 14]. These factors considerably contribute to the formation of a strong and porous structure of ceramics. The papers [10 13] indicate that the high quality of iron oxide is conducive to crystallization of mullite at the early stages of firing ( о С) of ceramic brick. Fig. 3 shows mullite crystals that were observed by us and the authors of [14] in the surveyed samples of the Nizhegorodsky Kremlin. Ceramic materials under firing are prone to isomorphism, i. e. they make up solid solutions or another way to call them is mixed crystals, which contributes to a great variety of silicate contents. The physical properties of solid solutions and sizes of an elementary cell tend to change 40

6 Issue 4 (16), 2012 ISSN along with the concentration of the solved substance. The crystal shape remains until a certain concentration is reached 1, 2, 15. As shown in Fig. 3g short-prism mullite forms in the surveyed samples. As solid solutions of replacement occur, there is mullite of various chemical content in the samples. a) b) d) c) e) Fig. 3. Mullite: а large crystals of fused mullite in the form of long prisms (light going through with the analyzer, 300); b the same with the analyzer; c needle mullite in the operating zone of shamote from the steel teeming ladle (light going through, 250); d a chip of fire clay in steel (light reflected, 300); e needle mullite in the glass phase (light going through, 200) 41

7 f) g) Fig. 3 (end). Mullite: f original flaky mullite ( 24000); g pseudomorphoses of glass with short-prism mullite ( 35000) Fe 3+ ions replace Al , 15. The introduction of iron oxides causes crystallization of mullite in the form of isometric grains, short and long prism crystals instead of finest needles (see Fig. 3g) [3, 13, 15]. The position of cations and anions in the grid is most stable at its minimum potential energy which is achieved if only spheres of opposite charged ions interact. As the spheres of anions interact, the structure is less stable and if the spheres of anions and cations do not interact, the structure is not stable [1 2, 13, 15]. The ratio of the radius of the cation to that of the anion R k /R a results in the lower boundary of this coordination number as well as a reduction in this ratio can make the structure unstable. Following the geometrical considerations, the most stable structures can be determined 1 2, 13, 15 : R 3+ Fe /R 2- O = (0.67/1.36) m = m is stable in relation to R 3+ Al /R 2- O = (0.57/1.36) m = m. 3+ Hence the replacement of R Fe to R 3+ Al promotes a more stable structure with the ratio R Fe /R O corresponding to the coordination number 6. This coordination number corresponds to octahedron. 42

8 Issue 4 (16), 2012 ISSN The X-ray phase content of the surveyed bricks was performed on a diffract meter ДРОН 6 using СоКα-radiation with the table with the sample rotating at 1 degree/min. X-ray diffraction pattern of the powder indicates the typical intensive lines (d/n = 0.136; 0.197; 0.245; 0.333; and nm) of quartz, the line (d/n = 0.138; and nm) was due to a crystallbite, the lines (d/n = 0.152; 0.211; 0.220; and nm) to mullite, the lines (d/n = and nm) to tridymite, the lines (d/n = and nm) to magnetite, the lines (d/n = 0.224; 0.233; and nm) to the anorthite, the lines (d/n = 0.265; and nm) to hematite, the lines (d/n = 0.280; and nm) to wollastonite. The increased content of the glass phase in the surveyed brick is indicated by the correlation of integral areas of amorphous halo and diffraction reflections on X-ray diffraction patterns [1, 2, 13, 15]. Conclusions Mossbauer spectra of absorption showed that the surface of the surveyed brick is largely dominated by hematite and the interior layer by magnetite. The X-ray diffraction pattern and electron and microscopic analysis revealed mullite in the Nizhegorodsky brick in the form of numerous submicroscopic and short-prism crystals which is central to the physical and mechanical properties of ceramic brick. Based on the performed research we can assume that in the manufacturing of brick clay with the content of Al 2 O 3 of no less than 15 %, Fe 2 O 3 from 5 to 8 %, СаО 6 10 % and R 2 O 2 5 %. Besides the research showed that in the construction of the Nizhegorodsky Kremlin ceramic brick was used that was fired at the temperature of less than 1050 о С containing alkaline and alkaline-earth additives. References 1. G. V. Kukolev, Chemistry of Silicon and Physical Chemistry of Silicates (Moscow, 1966) [in Russian]. 2. A. A. Pashenko, A. A. Masnikov, U. A. Masnikova, et al., Physical Chemistry of Silicates (Moscow, 1986) [in Russian]. 43

9 3. Ye. S. Abdrahimova, V. Z. Abdrahimov, Synthesis of Mullite from Technical Raw Material and Pyrophyllite, Journal of Inorganic Chemistry, 2007, vol. 52, N 3, pp A. I. Avgustinik, Ceramics (Leningrad, 1975) [in Russian]. 5. Ye. S. Abdrahimova, V. Z. Abdrahimov, On the Issue of Mullite, Journal of Refractories and Technical Ceramics, 2006, N 3, pp Ye. S. Abdrahimova, V. Z. Abdrahimov, Formation of Mullite at Roasting of Acid- Resistants, Material Science, 2003, N 4, pp V. F. Pavlov, Physical and Chemical Bases of Roasting of Products of Building Ceramics (Moscow, 1972) [in Russian]. 8. V. Z. Abdrahimov, I. V. Kovkov, Ye. S. Abdrahimova, Technology and Phase Structure of Ceramic Building Materials of More Than Hundred Years of Age (Samara, 2010) [in Russian]. 9. V. Z. Abdrahimov, V. A. Kukikov, I. V. Kovkov, Physical and Chemical Research of the Ceramic Brick of the Ipatievsky Monastery of More Than Six Hundred Years of Age, Bashkir Chemical Journal, 2009, vol. 16, N 4, pp Abdrahimova, Ye. S., Abdrahimov, V. Z., Transformation of Oxide Iron at Roasting of Beidellite Clay, Journal of Inorganic Chemistry, 2009, vol. 54, N 1, pp Ye. S. Abdrahimova, V. Z. Abdrahimov, Structural Transformations of Connections of Iron into Clay Materials on the Data Based on Mossbauer Spectroscopy, Journal of Physical Chemistry, 2006, vol. 80, N 7, pp Ye. S. Abdrahimova, A. V. Abdrahimov, V. Z. Abdrahimov, Features of Structural Transformations of Connections of Iron in Clay Materials of Various Chemical and Mineralogical Structure, Material Science, 2002, N 12, pp V. Z. Abdrahimov, The Study of Ferriferous Traditional Natural and Technical Raw Material Effect on Sintering of Ceramic Materials. The Effect of Fe 2+ and Fe 3+ Ions on Formation of Low Temperature Mullite (Samara, 2009) [in Russian]. 14. G. I. Litvinova, V. P. Pirohgkova, Petrography of Nonmetallic Inclusions (Moscow, 1972) [in Russian]. 15. Ye. S. Abdrahimova, V. Z. Abdrahimov, On the Issue of Isomorphism Occurring at Roasting of a Clay Material, Journal of Refractory Materials and Technical Ceramics, 2005, N 9, pp