Al2O3 SiO2 System Research Articles

Novel ceramic materials based on industrial wastes within the CaO–MgO–Al2O3–SiO2 system

The use of solid waste and raw materials such as ceramic sludge, klin rollers, magnesite, and limestone to produce low cost refractory ceramics after sintering at 1300 °C for 2 h was studied. Sample D30 with a composition of, 30 % diopside and 70 % mullite, was selected to be treated at 1200 °C for 2 h to investigate the effect of temperature on phase evolution. Microstructure, morphology and physical properties were also studied. Several techniques including XRF, XRD, SEM, EDX, flexural strength, and dielectric properties were used for samples characterisation. Densification parameters, morphology and microstructure were studied in order to evaluate the influence of the formed phases on the properties of produced ceramic materials. The study showed that the bulk density increased with the formation of corundum and mullite phases and decreased with the formation of anorthite and spinel phases. Bulk density also increased at higher firing temperatures. In contrast, porosity and water absorption showed the opposite trend to density. The main phases developed after firing at 1300 °C for 2 h were corundum, spinel, mullite, and anorthite. Flexural strength values were increased by increasing the precipitation pecent of corundum and mullite phases, as well as with bulk density. But it decreased with increasing porosity and both anorthite and spinel contents; ranging between 8.00 and 11.00 MPa. Bulk density increased with increasing of mullite content and temperature, ranging from 1.72 to 2.00 g/cm3, while porosity and water absorption ratio decreased from 32.59 to 22.10 and from 19.66 to 10.98, respectively. The microstructure morphology was converted from coarse-grained to fine-grained with increasing anorthite and spinel phases by increasing the temperature. To investigate the effect of the phases precipitated from the diopside-mullite system on their dielectric properties, parameters such as permeability (ε’), dielectric loss (ε′′), alternating current conductivity (σac) and Modulus'' were measured at the frequency range from 10−1 Hz–106 Hz. There is no noticeable effect on any of the dielectric parameters by increasing the concentration of diopside (CaMgSi₂O₆). In addition, the conductivity indicated that all the samples are insulators (σdc ≈ 10 pS/cm at f = 0.1 Hz) without any noticeable effect of composition.

Radio-transparent celsian ceramics modified with glass in a pseudoternary system BaO–Al2O3–SiO2: synthesis, microstructure, thermal and physical properties

The article presents the results of the study of radio-transparent celsian ceramics, in which part of the components were introduced using eutectic glass of the pseudoternary BaO–Al2O3–SiO2 system. The bonding of the components of the experimental glass into the celsian phase was realized according to the principle of reactive structure formation by adding the missing components (crystalline fillers). In this case, the obtained dense sintered water-resistant ceramic, the only crystalline phase in the composition of which is the monoclinic form of celsian, which forms a microhomogeneous structural matrix of the material. Celsian is represented by distinct prismatic crystals of tetragonal and hexagonal shape. The size of celsian crystals increases from 3–5 m to 7–10 m with increasing the content of eutectic glass. The developed celsian ceramic has a set of enhanced physical and thermal properties: zero water absorption and open porosity, mechanical compressive strength (up to 157 MPa), refractory index is 1540–15800C. Celsian ceramic is characterized by a coefficient of linear thermal expansion of 3410–7 0C–1, which provides a sufficiently high thermal shock resistance of 7000C. In terms of the level of relative dielectric permittivity (5.5) and dielectric losses (0.0005) at a frequency of 1010 Hz, the developed ceramic meets the requirements for ultra-high-frequency radio-transparent materials for aviation and rocket technology, which operate under conditions of high-speed high-temperature heating.

Crystallization Behavior and Structure of CaO–SiO2–Al2O3 Melts Representing the Oxide Inclusions in Si‐Mn Deoxidized Steel

For further optimization of the inclusion plasticization control process of Si‐Mn deoxidized steel, the crystallization behavior and structure of CaO–SiO2–Al2O3 system inclusions are investigated. The crystallization behavior of four typical low melting point CaO–SiO2–Al2O3 inclusions at 1000 to 1250 °C is studied by steel crucible isothermal heating experiment. The obtained results reveal that the glassy stability of the inclusions is high when the composition of low melting point inclusion is located in the eutectic region of tridymite, pseudowollastonite, and anorthite in the ternary phase diagram. However, when the composition of the inclusion is located in the eutectic region of melilite, pseudowollastonite, and anorthite, it is easy to undergo glass‐crystallization transformation and precipitate wollastonite and anorthite crystalline phases when isothermal heating at 1100 to 1200 °C. In addition, the crystallization mode of these inclusions is mainly surface crystallization, and the crystallization degree of inclusions increases with the increase of heat treatment temperature and time. The activation energy of crystallization and the content of nonbridging oxygen in the silicate structure NBO/T can be used to predict the crystallization ability of inclusions. The greater the activation energy of crystallization and the smaller the NBO/T value, the higher the glassy stability of the inclusions.

Phase equilibria in the low-TiO2 part of the CaO–MgO–SiO2–Al2O3–TiO2 system at a fixed MgO/CaO mass ratio of 0.2 and Al2O3/SiO2 mass ratio of 0.4

Adding titanium oxide has become a common practice in modern blast furnace operating procedures. The blast furnace slag is based on the CaO–MgO–Al2O3–SiO2–TiO2 low titanium slag system rather than CaO–MgO–Al2O3–SiO2 system. Phase equilibria in the CaO–SiO2–Al2O3–MgO–TiO2 system in the low-TiO2 part have been experimentally determined by means of high temperature equilibration and quenching technique followed by electron probe X-ray microanalysis. Introducing a small quantity of titanium-bearing materials can lower the liquidus temperature. The TiO2 content in the slag should be controlled below 4.6 wt%, otherwise it will enter the perovskite phase region where the liquidus temperatures increases rapidly. The compositions of the solid solutions corresponding to the liquidus have been precisely measured and should be utilized for developing the thermodynamic database.

Melting Behavior of a CaO–SiO2–Al2O3 Flux with Varying MnO Concentration for Use in Fusion Welding of Low‐Carbon Steel

CaF2 has been a very common constituent in the fluxes used for welding of low‐carbon steel plates, owing to its strong ability to lower the liquidus temperature as well as viscosity of the molten flux. But the adverse impact of fluoride evaporation from molten slag on the health of operating personnel and the environment has prompted a worldwide effort to replace CaF2 with more benign constituents. Three compositions with varying MnO concentration in the CaO–MnO–SiO2–Al2O3 system, identified in the current work, have shown promise in terms of ability to control oxygen transfer and modify inclusion generation in the molten metal during the welding of low carbon low alloy steels. However, the melting behavior of a flux needs to be established before recommending its use for welding. Three compositions, with varying MnO concentration, are chosen in the current work. Aided by experimental measurements using high‐temperature microscopy, DTA and simulations using the commercially available thermodynamic package FactSage (version 8.3), this work aims to understand the melting characteristics of the developed fluxes. These characteristics seem to be comparable with a commercial CaF2‐containing welding flux, used as a reference for comparison. In addition, simulations using FactSage suggest that transfer of dissolved O, Si and Mn to the weld metal, while using these fluxes, would be benefitial to performance of the welded joint.

Thermodynamic descriptions of the CaO–Al2O3 and CaO–Al2O3–SiO2 systems over the whole composition and temperature ranges

AbstractThe CaO–Al2O3–SiO2 system is a fundamental system in aluminosilicate materials, and its thermodynamic description provides key information for ceramic design, cement production, slag tapping, and geological prediction. However, the existing thermodynamic calculations for the CaO–Al2O3 system show inaccurate heats of formation for the compounds and consequently a decomposition of the CA2 (CaO⋅2Al2O3) phase at a low temperature. Besides, the solid solutions in anorthite and cristobalite have never been considered in the previous thermodynamic assessments for the CaO–Al2O3–SiO2 system. Therefore, thermodynamic reassessments of the CaO–Al2O3 and CaO–Al2O3–SiO2 systems are carried out in the present work using the CALculation of PHAse Diagram method, considering the solid solution in anorthite and cristobalite for the first time. The anorthite and cristobalite phases are modeled based on the individual mechanism of solid solution, with the anorthite described by (Ca+2, Va)1(Al+3, Si+4)2(Si+4)2(O−2)8 and the cristobalite described by (Va, Ca+2)1(Si+4, Al+3)2(O−2)4. The present assessment solves the above issues and provides consistent thermodynamic descriptions for the liquid and solid phases. Based on the established thermodynamic database, a Scheil solidification simulation is carried out for a cement clinker and the variations of mass fractions of the phases as well as the composition of liquid during Scheil cooling are calculated. The present work guides the design of relevant materials and lays an essential foundation for the establishment of the thermodynamic database of multicomponent aluminosilicate materials.

Studying the features of complex beryllium-containing silicate phases co-crystallization in zonal samples using the x-ray electron probe microanalysis method

Research subject. Silicate ingots containing four species-forming components Be, Mg, Al, and Si and belonging to the crystallization region of beryllium indialite (with the formula of Mg2BeAl2Si6O18 and a beryl-type structure). Aim. To investigate the fundamental problem of identifying the patterns of matter differentiation and the stable and metastable phase formation in silicate matrices. Methods. The evolution of the phase composition of silicate melts was registered using a temperature gradient method. Results. New data on the features of phase transformations in silicate melts belonging to the region of beryllium indialite were obtained by electron probe microanalysis (EPMA). Co-existing metastable and stable mineral phases were identified, and the similarity of their compositions with different structures was shown. The nature of impurity phases at each stage of crystallization was established. Conclusions. The evolutionary sequence of phase associations ensuring the crystallization of beryllium indialite and metastable phases of a similar composition, the nature of which is determined by the initial ratio of components, was experimentally recorded. The range of possible phase associations that co-crystallize or replace a stable phase with a beryl structure in melts from the region of existence of beryllium indialite in the BeO–MgO–Al2O3–SiO2 system was extended. The selectivity of the coloring element chromium entry into various phases of the studied system is shown depending on the capabilities of their structure. The addition of a chromophore is a reliable criterion for visualizing successive layers, zones, and areas of changing phase associations in the final ingot.

Thermodynamics of cordierite formation during firing of water-permeable ceramics

The analysis of the influence of an increase in firing temperature on the thermodynamic possibilities of solid-phase chemical reactions in the MgO–Al2O3–SiO2 system in the direction of cordierite formation has been conducted. The thermodynamic direction of solid-phase reactions in the MgO–Al2O3–SiO2 system allows determining rational firing temperatures of materials containing cordierite for the manufacture of products for various purposes. During low-temperature firing (up to 1200 K) of finely dispersed masses based on talc-clay-alumina compositions, materials with high open porosity but low strength characteristics can be obtained. This is because the reactive sintering mainly occurs due to reactions forming intermediates for cordierite synthesis and incomplete processes of destruction in natural mineral raw materials. In the firing temperature range of 1200–1500 K, the thermodynamic probability of reactions immediately via several cordierite formation mechanisms increases, which should limit the growth of individual crystals while increasing their quantity. This should positively affect the strength and heat resistance of materials due to low values of the thermal coefficient of linear expansion. Firing temperatures of 1500–1659 K correspond to the limits for cordierite formation and contribute to the consolidation of the material with a change in the nature of porosity from open to closed. Exceeding firing temperatures above 1659 K results in the thermodynamic instability of the cordierite-corundum phase combination and can lead to the formation of defects due to the appearance of a significant amount of melt in the phase composition of the material.

Influence of zinc-containing compounds on the properties of ceramic materials based on the Li<sub>2</sub>O–MgO–Al<sub>2</sub>O<sub>3</sub>–SiO<sub>2</sub> system

The results of a study the influence of magnesium oxide substitution with zinc oxide in the Li2O–MgO– Al2O3–SiO2 system, as well as the introduction of pre-synthesized ganite ZnAl2O4, on sintering, phase formation and thermal expansion of synthesized materials are presented. It was found that after substitution of 4 % magnesium oxide MgO with zinc oxide ZnO, the ceramic material synthesized at a temperature of 1 150 °C was characterized by higher values of apparent density (not less than 1 835 kg/m3), mechanical compressive strength (300 MPa), and heat resistance (more than 80 thermal cycles), as well as low values of LTEC (–0,25 ∙ 10–6 K–1), which is due to the formation of crystalline phases of spodumene, spinel, forsterite, corundum, ganite and quartz.

Preparation of innovative glass-ceramic materials based on mica schist within the CaO–MgO–Al2O3–SiO2 system

The preparation of affordable glass-ceramic materials by induced crystallization of glass-based mica schists and other natural raw materials (dolomite & limestone), as well as magnesite as a mine waste, was investigated for the first time. Five glass batches were designed based on the eutectic composition of the diopside-anorthite ratio with increasing the enstatite content from 0–40 wt.% within the quaternary CaO–MgO–Al2O3–SiO2 system. After melting at 1400 to 1500 °C, casting into discs & rod shapes, and annealing process, the prepared glasses were subjected to careful heat treatment schedules. Several techniques were used to characterize the applied raw materials, glass, and glass-ceramic materials such as X-ray Fluorescence (XRF), Differential Thermal Analysis (DTA), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Polarizing-light Microscopy. The produced glass-ceramic from the glass batch with 30 wt% enstatite that was nucleated at 750 °C /2h followed by crystallization at 950 °C /h, displayed the well-developed product on the level of volume crystallization and pore formation.

MAGNESIUM AND IRON OXIDES INFLUENCE ON SINTERING PROCESSES AND PHASE FORMATION OF ANORTHITE CERAMICS BASED ON NATURAL RAW MATERIALS

Ceramic proppants based on silicates and aluminosilicates with various structures are used in the hydrocarbons mining with hydraulic fracturing method. The disadvantage of these known proppants is their high apparent density. Anorthite CaO∙Al2O3∙2SiO2 is a prospective material for proppants production. However, its wide application in this field is restricted due to insufficient knowledge of the MgO-CaO-Fe2O3(FeO)-Al2O3-SiO2 system. Consequently, the physical and chemical processes in the mixes of kaolin and chalk with magnesium oxide and iron(III) oxide additives during firing for anorthite ceramics were studied. It was found that adding of 5 – 10% magnesium oxide in batch for anorthite synthesis leads to obtain ceramics with near-zero water absorption at 1250 °C. Increasing the firing temperature to 1300 °C leads to overfiring of the ceramic and a decrease in its strength. Magnesium oxide reacts with the kaolin to form spinel and forsterite. The highest compressive strength (350 – 390 MPa) is achieved for ceramics with 5% MgO in the batch. The ceramics has fine-grained structure with the grain sizes less than 5 μm. Iron(III) oxide is a weak mineralizer for anorthite synthesis, and its mineralizing effect occurs during the formation of gehlenite-based solid solutions. The sintering process of anorthite ceramics is intensified at 1350 °C due to the melting of the anorthite – iron(III) oxide eutectic. This leads to decrease the water absorption of ceramics with 5 – 10% Fe2O3 in batch to about 2 – 3%. The compressive strength of this ceramics is about 230 – 250 MPa.

Reactive Condensation of Cr Vapor on Aluminosilicates Containing Alkaline Oxides

The research presented herein is part of a larger project delving into the mechanisms and pathways for reactive condensation of Chromium (Cr) vapors in high-temperature (>500o C) environments. The overall goal of this research project is to improve fundamental understanding of reactive condensation pathways for chromium (Cr) vapors generated in high-temperature systems such as exhaust manifolds, steam turbines, boilers, or solid oxide fuel cells (SOFCs). Reactive evaporation of Cr from stainless steels commonly used in these systems is well-documented; however, the interactions between volatilized Cr species and surrounding interfaces during complex and dynamic system exposures is poorly understood. Understanding the interactions between volatilized Cr species and downstream components during operation is critical for improving system performance, environmental health, and safety as some condensed Cr forms toxic hexavalent Cr(VI) species. The focus of this study is on the effects of alkaline oxides present within the substrate material on reactive condensation mechanisms of Cr vapors. Studying the reaction mechanisms between Cr vapors and ceramic surfaces has direct application to SOFCs as these materials are widely used in the field. For example, alumina-silica glass-ceramics are used as sealants in SOFCs. These materials belong to the SiO2–Al2O3 system and contain different compositions of oxides including CaO, Na2O, MgO, K2O, B2O3, Y2O3, and BaO. Another sealing material used in SOFCs is mica, a class of silicate minerals that forms into distinct layers. Two types of mica commonly used in SOFC applications are muscovite (potassium aluminum silicate hydroxide fluoride, KAl2(AlSi3O10)(F,OH)2), and phlogopite (potassium magnesium aluminum silicate hydroxide, KMg3(AlSi3O10)(OH)2). The specific research objective is to explore the effects of alkaline oxide additives in aluminosilicates on Cr collection and speciation. To accomplish this objective, an experimental platform was designed to assess interactions between samples of high-temperature steel alloys or Cr oxide (Cr2O3) powder with ceramic insulating materials. The chemical composition of the insulating materials used in this study range from pure silica (SiO2) and alumina (Al2O3) to combinations thereof with and without inclusions of alkaline earth metals (e.g., Ca, Mg). Preliminary results show three- to four-fold increases in Cr(VI) formation on silica fibers with weight percentages of ~30 and ~40 percent alkaline oxides (CaO and MgO), respectively, after exposure to volatile Cr species, relative to low-alkaline silica. Figure 1 presents an overview of the experimental concept, Cr(VI) test kit, and preliminary results for dependency on alkaline oxide content. Figure 1

Effect of Tm2O3 on the properties of corundum‐mullite composite ceramics for solar heat transmission pipelines

AbstractCorundum‐mullite composite ceramics appropriate for application in solar heat transmission pipelines were fabricated by the addition of Tm2O3 and sintered at atmospheric pressure. The results demonstrated that with the introduction of Tm2O3 (1–7 wt.%), the physical and mechanical properties, corrosion resistance, and thermal shock resistance of the composite ceramics were significantly enhanced. The sintered sample AT5 (with 5 wt.% of Tm2O3 added) showed the best overall performance at 1550°C. The residual bending strength remained higher than 186 MPa after corrosion with 20 wt.% H2SO4 solution and 10 wt.% sodium hydroxide solution. The reaction of Tm2O3 with the Al2O3–SiO2 system produced the Tm2O3–Al2O3–SiO2 liquid phase. This liquid phase eliminated the pores through viscous flow, resulting in a dense microstructure. Furthermore, more mullite and dithulium disilicate were generated after thermal shock cycles, and their inhibition of crack deflection and extension allowed the composite ceramics to achieve excellent thermal shock resistance (residual bending strength as high as 199 MPa). The prepared corundum‐mullite composite ceramics have a good potential for application in solar heat transmission pipelines.

Thermodynamic analysis of the reactions of strontium anorthite formation during the firing of thermal shock resistance ceramics based on the eutectic glasses of the SrO–Al2O3–SiO2 systems

Thermal shock resistance ceramic materials must have a high degree of sintering to ensure the required mechanical strength, erosion resistance, and resistance to high-temperature oxidation. However, the search for effective ways to achieve a high degree of sintering of ceramic materials based on the SrO–Al2O3–SiO2 system at low temperatures requires a large amount of experimental research. The aim of this work is to analyze thermodynamically the reactions of strontium-anorthite phase formation at the points of triple eutectics of the SrO–Al2O3–SiO2 system under low-temperature firing conditions. The eutectic points were selected in the region of strontium anorthite crystallization and had a temperature not exceeding 14000C. It has been established that in the case of compliance with the stoichiometric ratio, the final product of the interaction of the components of eutectic glasses S-1 and S-2 with the charging components is the strontium anorthite phase. The most probable is the formation of strontium anorthite in the interaction of eutectic glass components with Al2O32SiO2, which is a product of kaolinite dehydration (Al2O32SiO22H2O). It has been found that the compounds SrOSiO2 and 2SrOAl2O3SiO2 are most active in the interaction with the charging components in the direction of formation of the strontium anorthite phase than SiO2 tridymite. As a result, the sintering of strontium-anorthite compositions at a temperature of 9000C causes a significant increase in the content of the crystalline phase of strontium anorthite. The determined patterns allow making a reasonable choice of glass in the SrO–Al2O3–SiO2 system for the further manufacture of low-temperature strontium-anorthite ceramics.

TRANSPARENT GLASS-CERAMICS BASED ON LITHIUM ALUMINOSILICATE SYSTEM

Methods of laser micro- and nanomodification structure of transparent dielectrics open promising prospects for the creation of a new type glass-crystalline materials and new applications. In this work, after a brief excursion into the history of glass-ceramics, transparent aluminosilicate glass-ceramics are discussed, mainly using the example of the Li2O–Al2O3–SiO2 system, and the areas of their new applications. The recently discovered possibilities of laser micromodification of structures and direct laser writing of elements photonics and integrated optics in their volume are considered. In this case, special attention is paid to transparent glass-ceramics with coefficient of thermal expansion close to zero.

Multi‐ion diffusion model and application to solid dissolution in CaO–Al2O3–SiO2 melts

AbstractA general multi‐ion diffusion model for liquid slag is developed for silicate melts by combining the tracer diffusivities of ions and chemical potentials from the CALculation of PHAse Diagrams thermodynamic database. For the demonstration of the model, the tracer diffusivities of Ca, Al, Si, and O ions in CaO–Al2O3–SiO2 melts were optimized as functions of temperature and composition using available isotope experimental data. The present model successfully simulates liquid‐junction diffusion in the CaO–Al2O3–SiO2 system and the dissolution of solid SiO2 and Al2O3 particles in CaO–Al2O3–SiO2 melts. Furthermore, the model can be readily expanded to multicomponent systems, making it potentially applicable to refractory dissolution in liquid slag and various other diffusion‐controlled high temperature processes involving liquid oxide melts.

Mechanism of Al Coordination Change in Alkaline-earth Aluminosilicate Glasses: An Application of Bond Valence Model

Aluminum cations are generally present in four-fold ([4]Al3+) or five-fold coordination ([5]Al3+) in aluminosilicate slags, where the concentration of [5]Al3+ varies depending on the type of charge compensator, for example, Mg2+ and Ca2+. Although it has been reported that the amount of [5]Al3+ species increases with the replacement of CaO with MgO in the CaO–MgO–SiO2–Al2O3 system, the detailed mechanism underlying the change in the local structure near the aluminum cations remains unclear. Because the residual negative charge on the bridging oxygen between [4]Si4+ and [5]Al3+ ([4]Si4+–OBO–[5]Al3+) is larger than that of [4]Si4+–OBO–[4]Al3+, it is essential to understand the positive charge contributions of alkaline-earth cations to compensate for these negative charges on the bridging oxygens. In the present study, the valence of a single chemical bond near Mg2+ and Ca2+ cations in the chosen aluminosilicate glasses was determined using a simple empirical model, which enabled calculation of the bond valence from the observed interatomic distance of near alkaline-earth cations by synchrotron X-ray total scattering. Magnesium cations had a larger average bond valence (+0.39) than calcium cations (+0.31). The difference in the positive charge contribution from Mg2+ and Ca2+ should explain the variation in the coordination number of aluminum cations.

STATE DIAGRAM OF THE ZrO<sub>2</sub>–SiO<sub>2</sub>–Al<sub>2</sub>O<sub>3</sub> SYSTEM WITH VISUALIZATION BY COMPUTER 3D-MODEL AND CALCULATION USING THE NUCLEA DATABASE

The three-dimensional (3D) computer model of the isobaric phase diagram of the ZrO2–SiO2–Al2O3 system with formation of the ZrSiO4 and Al6Si2O13 compounds is presented. The development of its geometric structure was carried out through the sequential construction of the phase reaction scheme, including all polymorphic transitions in the sub-solidus and the rearrangement of the interaction of binary compounds as well as zirconium and aluminum oxides, its transformation into the scheme of uni- and invariant states in the tabular and graphical (3D) forms, the construction of the prototype, and its transformation into a spatial model of the phase diagram of the real ZrO2–SiO2–Al2O3 system. Features of the isothermal sections and isopleths of the phase diagram of the considered system calculated using the thermodynamic NUCLEA database are discussed in the comparison with the 3D model sections.

State Diagram of the ZrO2–SiO2–Al2O3 System with Visualization by Computer 3D-Model and Calculation Using the NUCLEA Database

State Diagram of the ZrO2–SiO2–Al2O3 System with Visualization by Computer 3D-Model and Calculation Using the NUCLEA Database

Описание химического взаимодействия в системе CaO-Al 2O3-SiO2

In this study the construction of a phase tree and the description of the chemical interaction for the ternary oxide system CaO-Al 2O3-SiO2 are given. Particular interest to a system consisting of oxides of calcium, aluminum and silicon is associated with the production of highly demanded functional materials with desired properties. Melts of the CaO-Al2O3-SiO2 system are of great theoretical and applied importance. This is due to the significant role of melts of these oxides and their mixtures in metallurgy, ceramics production, and other industries. Phase relationships in the system with the complete disappearance of liquid in the CaO-Al2O3-SiO2 system has made it possible to construct a phase tree of the system, which includes a linear part and two cycles. The construction of the phase tree is given taking into account the formation of four double compounds in the CaO-SiO2 system, five double compounds in the CaO-Al2O3 system, one double compound in the Al2O3-SiO2 system, and two ternary compounds. The stable complex includes fifteen secondary phase triangles, interconnected by sixteen stable secants. For mixtures corresponding to equivalence points (points of intersection of unstable and stable secants), the chemical interaction is described in accordance with the law of equivalents. It is concluded that for all mixtures corresponding to equivalence points, interactions are thermodynamically possible under standard conditions. The prediction of crystallizing phases is made.