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Tuxtamushova Anisaxon Ubayevna,
senior teacher,
Tashkent Chemical-Technological Institute Yunusov Mirjalil Yusupovich, professor,
Tashkent Chemical-Technological Institute, Ikramova Zulfiya Adilovna, PhD., Tashkent Pediatrics Medical Institute Alimxodjayeva Nazira Tillaxodjayevna, PhD., Tashkent Pediatrics Medical Institute Sulaymonova Gulchexra Gaybullayevna, PhD., Tashkent Pediatrics Medical Institute E-mail: [email protected]
INFLUENCE CRYSTALISTION ABILITIES OF GLASSES ON FORMATION PYROXENES STRUCTURES
Abstact: The general formula of obtained glasses of pyroxene composition is XYZ2O6. By virtue of optimal composition of the glass (Na02Ca08Mg08Al02Si2O6), glass crystalline material was obtained, which was underwent to physical and chemical exploring. It is revealed that upon 2 hours heat treatment with temperature of 850 °C, crystalline phases are energetically precipitated in all the studied objects, which coincide with solid solutions of pyroxene structure.
Keywords: glass, diopside, glass-ceramic materials, pyroxsen, Isomorphic replacement.
Introduction. Currently, the creation of materi- In pyroxene sitalls, even with the participation
als based on low-cost raw materials for energy and of components introduced in small concentrations,
resource-saving technologies with a set of valuable solid solutions with somewhat different properties
properties dictated by the conditions of their opera- are formed compared to the phase not containing
tion does not lose relevance. Such materials are si- isomorphous impurities.
talls - glass-ceramic materials (hereinafter referred Objects of study. The objects of study were
to as SCM), obtained on the basis of glasses by di- taken glass pyroxene composition and glass-ceramic
rectional crystallization. On the example of a sys- materials based on them.
tematic integrated study [1, 124-134] in the field of Research methods. Complex studies, such as
obtaining pyroxene sitalls with desired properties, it electron microscopic analysis (EMA), differen-
is necessary to take into account that, in designing the tial thermal analysis (DTA), X-ray phase analysis
required crystalline phase in a sitall, there are other (XRD), IR spectroscopic (X-ray analysis), as well as
factors besides common factors [2], feature of the physicochemical methods of pyroxene glass samples
structure and structure of the original melt and glass. and SCM, obtained on the basis of the optimal com-
The widespread use of the known phenomenon of position according to the standard technique.
zomorphism makes it possible to promptly manage Results and its discussion. The purpose of this
the properties of the cellars in the desired direction. study is to: obtain crystalline sitalls based on pyrox-
ene glass, by isomorphous substitution; elucidation of the dependence of the technological, physicom-echanical, chemical properties and crystallization ability of the melt on the phase composition, as well as the identification of areas of coexistence of these phases in optimal ratios for obtaining SCM with desired properties. The design and selection of glass compositions for the further production of SCM from them predetermines what properties the resulting product of their crystallization should have.
The glass composition under appropriate synthesis conditions and heat treatment modes of the glasses under study determines the type, quantitative and qualitative composition ofthe formed mineral phases, their ratio, composition, residual glass properties, structure and properties ofthe resulting glass by directional crystallization, carried out with the aim of partial or complete crystallization ofthe melt. A characteristic feature of crystallized pyroxene glasses is homogeneous mi-crocrystallinity, the presence of which is a necessary condition for the strength of the material.
In sitalls fine crystals are evenly distributed in the vitreous matrix.
Sitalls containing pyroxene solid solutions based on hedenbergite, diopside, aegirine, augite as the dominant phase have high physicochemical properties. For structural studies and the determination of physicochemical and physicomechanical properties, appropriate samples were made. To study the material composition, phase and structural transformations in the process of melting the raw material mixture and crystallization of the resulting melt, a set of research methods was used, including X-ray phase analysis, diffractometry, microscopy and other analyzes. In terms of their chemical composition, all SCM are silicate materials, which are based on, in addition to silicon oxide SiO2, a number of other oxides - aluminum Al2O3, calcium CaO, magnesium MgO, sodium Na2O, etc., which provide the specified technological and operational properties.
A feature of these materials is that the vitreous and crystalline phases coexist in their structure, the
volume ratio of which can vary within wide limits [3]. Depending on the ratio of these phases, it is possible to obtain SCM ofvarious structures, which are used in the future as intended.The structure of the material, the predominant glass phase, results in glass marble, glass crystal or glass silicon, where the individual crystalline formations are dispersed throughout the volume of the vitreous matrix.
If the amount of the crystalline phase in the structure of the material is more than 50-60%, then the glass phase will act as a cementing layer that holds individual crystals of silicates - pyroxenes, etc. Depending on the chemical composition used by us, you can determine the type of the dominant crystalline phase. The chemical composition of glass includes glass-forming oxides such as SiO2, A12O3, CaO, MgO, FeO + Fe2O3, Na2O + K2O, which under a thermal effect in a certain combination can enter into the pyroxene structure.
In order to obtain SCM based on the classical pyroxene composition, we designed and synthesized 18 glass compositions that meet the general formula: (Me +, Me2 +, Me3+) 2Si2O6, where Me + = Na +, K +;
Me2 + = Ca2 +, Mg2 +, Sr2 +; Me3 + = Al3 +; Fe3 +.
We have chosen glass compositions obtained from chemical reagents of the "chd" brand. In the investigated samples of glasses from chemical reagents, the effects of crystallization initiators were studied. For this purpose, we selected 4 glass compositions:
Na Ca Mg Al Si 2O6, where the values of a and d range from 0.05 to 0.2; the values of b and c are in the range 1.0 ^ 0.6.
Glass melting and sample preparation for the study were carried out in the laboratory using the accepted classical glass melting technology.
Selection of an effective crystallization stimulator, to which the requirements of non-volatility, durability and effective stimulating action are presented, as crystallization nucleators, we tested the additives Fe2O3-2%, Cr2O3-1%, which were introduced into the glass in excess of 100%. The effect of combined stimulants was also studied, in particular, the total effect of Fe2O3
+ Cr2O3, which provides the bulk crystallization of pyroxene glass compositions, was studied. The choice of the type and concentration of the above additives is due to the fact that the compositions of a number of raw materials and industrial waste such as loess, kaolin, slags and others contain the indicated oxides. Combined combined use of various types of natural materials and metallurgical slags for the synthesis of pyroxene sitalls can be without the introduction of special stimulating components and base materials, which provides significant economic efficiency, since these materials are composed of those elements that act as initiators of crystallization, forming embryos. Glasses of compositions A11 - A18 without stimulants crystallize volumetrically, but their structure is crystalline and porous.
To determine the stimulating role of Fe2O3, Cr2O3 oxides, as well as the total effect of Fe2O3 + + Cr2O3 oxides, glasses with the specified additives were welded at temperatures of 1350-145 °C, with an exposure of 1 hour, in oxidizing conditions. According to the results of the research it was established that the introduction of additives in the specified amounts does not have a significant impact on the technological properties of glasses of pyroxene composition. All investigated glasses are boiled, brightened and formed satisfactorily. The results of the gradient crystallization in the temperature range of600-12000 °C showed that the best catalytic effect of all the crystallization stimulants studied is the combined additive of the total effect ofiron and chromium oxides (Fe2O3 + + Cr2O3), provided that the coadministration of 2 and 1% is observed respectively. A12, A14 glasses (380and 410 °C, respectively) have the widest range ofcrystal-lization. At the same time, the greatest decrease in the temperature of the lower limit of bulk crystallization (at 60-800 °C) and the formation of a dense crystalline structure were noted.Since the most effective stimulant has a combined additive (Fe2 O3 + Cr2O3), in order to clarify the optimal concentration of Cr2O3, it was introduced in amounts of 0.5-1.5% through 0.1% at a constant concentration of iron
oxide (2%). It is established that an increase in the addition of Cr2O3 from 0.5 to 0.9% significantly expands the temperature range of bulk crystallization (from 150 to 3500 °C) and causes the formation of a dense homogeneous crystalline structure. With a further increase in the concentration of Cr2O3 from 0.9% to 1.5%, the catalytic efficiency of the crystallization process almost does not change. Thus, the optimal amount of introduced initiator of crystallization of Cr2O3 should be considered to be 0.9% - 1%, when the content of Fe2O3 is 2%.
To assess the effect of heat treatment on the structural changes of the samples under study, as well as on their properties, a comprehensive study was conducted, including X-ray phase, differential thermal, electron-microscopic, IR - spectroscopic methods of analysis and some properties (density, chemical stability, TCLE and other).
The IR spectra of the original glass are characterized by the presence of two wide absorption bands in the regions of900-1,200 and 400-600 cm - 1. The position of the main absorption band in the region of 1060-1100 cm-1 indicates the frame structure of the main silica-oxygen groups.The absorption bands in the region of400-600 cm - 1 can be caused by both the deformation vibrations of the Si - O - Si bridging bonds and the Me - O bond vibrations characteristic of spinel formations. The infrared absorption spectra of the products of crystallization of glasses at 650-8000 °C are caused by the appearance of absorption bands of 520, 650, 960 cm -1. The absorption bands at 960 cm - 1 are associated with the formation of groups close to metasilicates, which are characterized by a chained arrangement of silicon-oxygen tetrahedra.
The alignment of tetrahedra in chains, relative to each other, is also confirmed by the appearance of an absorption band in the region of 770-790 cm -1, which, in the absence of diffraction maxima in the diffractograms of the samples, is obviously explained by the processes of structural ordering and chemical differentiation of glasses preceding its crystallization.
Heat treatment affects the properties of the studied samples in the temperature range of 600 --6500 °C, there is a slight change in the indicators of the properties of the samples. Chemical resistance to INHCl is minimal. Heat treatment of glass at 8000 °C leads to a certain decrease in the density values and temperature coefficient of linear expansion of samples. Obviously, such an ability of the character of changing the values of properties can be explained by the intensification of the processes of chemical differentiation of glass by a pronounced segregation.
Since the complex introduction of iron oxides and chromium has a significant effect on the crystallization of the glass A11-A18 synthesized by us. We studied the change of some properties (chemical stability, density, softening temperature) of chromium and iron containing glasses depending on the ratio of Na2O and CaO.
It was established that the type of catalytic additive does not play a significant role in the change of properties, only acid resistance. Properties vary mainly depending on the ratio of CaO: MgO and Na2O: Al2O3. An analysis of the experimental data showed that the ratio of Na2O/CaO has a significant effect in the process of forming the glass-ceramic structure. When the ratio of Na2O/CaO is 1: 4 and 2: 3 mol, there is a slight bend in the change in properties, which is probably explained by the active formation of pyroxene structural groups in the glasses under study at the indicated ratios of Na2O/CaO, which affect the physicochemical properties.
In the products of crystallization of glasses having the ratio of Na2O : CaO = 0.1 : 0.9, the pyroxene phase is formed. This is because the indicated ratios of Na2O/CaO determine the possibility of formation of structural groups close to pyroxene in glasses, which subsequently apparently facilitates the crystallization of the pyroxene phase in the presence of appropriate stimulants.
Based on a comprehensive study of the effects of additives in glasses A11 - A18, in combination with a change in some properties and phase composition of crystallization products, it was found that the most dense homogeneous structure is formed in the process of crystallization of glasses having a stoichiometric composition 0.1Na2O • 0.8 CaO 0.8MgO 0.1Al2O3 2SiO2 and 0.15Na2O • • 0.7CaO • 0.7MgO 0.15Al3O32SiO2with the introduction of a combined additive (2% Fe2O3 + 1% Cr2O3), the monomineral pyroxene phase is released in the crystallization products.
Conclusion. It should be noted that the data on the determination of optimal compositions, conditions and modes of heat treatment, as well as phase formation for crystallization of glasses synthesized from chemical reagents is somewhat different from the data and conclusions made by us for similar compositions of glasses from natural materials. Apparently this is due to the impurities contained in the natural raw materials. From the crystal chemical point of view, this phenomenon can be considered an isomorphous substitution, both in the cationic and anionic sublattices of natural pyroxenes.
References:
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Саркисов П. Д. Направленная кристаллизация стекла основа получения многофункциональных стеклокристаллических материалов.- М.: РХТУ им. Д. И. Менделеева, 1997 г. Тыкачинский И. Д. Исследования процессов катализированной кристаллизации стекол. Разработка и применение ситаллов // Сборник докладов симпозиума «Катализированная кристаллизация». - М.: ГНИИС, 1982 г. 3. URL: http://www.eatu.ru/book-pub/byt/index.pl 05.04.2012 г.
