Cast refractories of the Al2O3-Cr2O3-CaO system

Kolomeitseva, E. F.; Попов, О. Н.

doi:10.1007/bf01326654

Cited by 6 publications

(2 citation statements)

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“…Similar specimens were cut out of the hard zone of an A-Cr-Ca casting containing 45% wt.% Cr 2 O 3 [27,28]. High-density, fine-grained Al 2 O 3 specimens containing~10 vol.%.…”

Section: Experimental and Theoretical Study Into The Thermal Stabilitmentioning

confidence: 99%

Thermal stability of high-temperature materials. Part 2

et al. 2004

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Experimental methods for determining thermal stability of high-temperature materials under dynamic and static thermal loading conditions are considered. Experimentally, thermal stability is characterized by the destructive temperature difference or critical (destructive) rate of change of the temperature field in the bulk or at the surface of the material. It is shown that, with the observance of special conditions, the thermal-shock method, based on sharp cooling of heated specimens in water, provides an acceptable destructive temperature difference for a particular material, in agreement with theory. At present, however, no unique method for experimental determination of the thermal stability of high-temperature materials has been developed. A route towards standardizing static methods for determining the destructive temperature difference is proposed. THERMAL STABILITY OF HIGH-TEMPERATURE MATERIALS. GENERALITIESHigh-temperature materials 2 determine technological, economic, and environmental conditions and the dynamics of development of the leading research and industrial complexes of the world community [1]. While differing in chemical and phase composition, structure and properties, manufacturing technology, and application, these materials share general characteristics of which the thermal stability is of prime importance.The high-temperature materials [2] are divided into the following groups:1. Whisker-type single crystals. 2. Bulky single crystals.3. High-density (with a density close to theoretical) fine-grained polycrystalline materials.4. Porous fine-grained polycrystalline materials. 5. Porous coarse-grained polycrystalline materials. 6. High-porosity polycrystalline materials. 7. Fibrous (filamentary) polycrystalline materials. Except for materials of the 1st and 2nd groups (which are single-phase), the rest of materials may be single-or multiphase, quasi-homogeneous of heterogeneous.Knowledge of the relations between fundamental properties of materials, principles of design of engineering structures intended for service under thermal shock conditions is of importance both for theory and practice. A theory of thermal stability that has been developed within the framework of the maximum stress theory and. quantum field theory of thermal states provides an adequate description of the behavior of materials in a nonstationary temperature field [3,4]. Thermal stability was substantiated as a physical property of materials related to the fundamental properties of matter. However, numerical analysis of the thermally stressed state of high-temperature materials in a high-intensity nonstationary temperature field and associated therewith technological implications is an arduous task; for this reason, experimental determination of thermal stability is frequently a preferable alternative.As an example of an approximate numerical analysis one may refer to the determination of the critical heating rate of a refractory lining by solving the nonstationary heat conduction equation using destructive temperature grad...

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“…Similar specimens were cut out of the hard zone of an A-Cr-Ca casting containing 45% wt.% Cr 2 O 3 [27,28]. High-density, fine-grained Al 2 O 3 specimens containing~10 vol.%.…”

Section: Experimental and Theoretical Study Into The Thermal Stabilitmentioning

confidence: 99%

Thermal stability of high-temperature materials. Part 2

et al. 2004

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“…Kaiser et al investigated the phase relations in the CaO–CaCr 2 O 4 –CaAl 2 O 4 system and reported that Ca 4 Al 6 CrO 16 coexisted with CaCrO 4 and calcium aluminates in air while a Cr(III)‐containing phase Ca 6 Al 4 Cr 2 O 15 formed in the moderately reducing atmosphere of a 1:1 H 2 /CO 2 gas mixture. Cast refractories of the Al 2 O 3 –CaO–Cr 2 O 3 system were studied by Kolomeitseva and Popov where they found an unknown phase, but its details were never reported. Cr(VI) can be inhibited or eliminated through favoring the formation of some stable Cr(III)‐containing phases.…”

Section: Introductionmentioning

confidence: 99%

A new ternary phase in the system CaO–Al₂O₃–Cr₂O₃: Crystal structure and thermal expansion of CaAl₂Cr₂O₇

et al. 2019

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Polycrystalline material of a novel phase in the system CaO–Al2O3–Cr2O3 has been obtained by solid‐state reactions. Chemical analysis indicated the composition CaAl2Cr2O7. Single‐crystal growth of the new compound using borax as a mineralizer was successful. Diffraction experiments at ambient conditions on a crystal with composition CaAl2.13Cr1.87O7 yielded the following basic crystallographic data: space group P 3, a = 7.7690(5) Å, c = 7.6463(5) Å, V = 399.68(6) Å3, Z = 3. Structure determination and subsequent least‐squares refinements resulted in a residual of R(|F|) = 2.3% for 1440 independent observed reflections and 113 parameters. To the best of our knowledge, the structure of CaAl2.13Cr1.87O7 or CaAl2Cr2O7 represents a new structure type. It belongs to the group of double layer structures where individual double layers contain octahedrally and tetrahedrally coordinated cation positions. Linkage between neighboring sheet packages is provided by additional calcium cations. Furthermore, thermal expansion has been studied in the interval between 29 and 790°C using in situ high‐temperature single‐crystal diffraction. No indications for a structural phase transition were observed. From the evolution of the lattice parameters the thermal expansion tensor has been obtained. A pronounced anisotropy is evident. The response of structural building units to variable temperature has been discussed.

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