Alumino Silicatos Refractarios

Refractories and Industrial Ceramics

Vol. 51, No. 5, January, 2011

ALUMINOSILICATE REFRACTORIES BASED ON HIGH-ALUMINA HCBS. PART 1. REFRACTORIES BASED ON MIXED HCBS IN THE SYSTEM BAUXITE — SILICA
Yu. E. Pivinskii1 and Pavel V. Dyakin2
Translated from Novye Ogneupory, No. 10, pp. 21 – 29, October 2010.

Original article submitted August 2, 2010. Comparative studies are provided for theproperties of compacted and cast specimens of fine-grained ceramic concrete prepared on the basis of a mixed HCBS and two varieties of refractory filler with different Al2O3 content from bauxite and chamotte based on Arkalyk clay. For specimens containing a chamotte filler, after firing at above 1250°C there is typically significant linear growth (up to 2.5%), connected with secondary mulliteformation and caused by interphase reaction of SiO2 from filler grains and very fine Al2O3 of the matrix system. The correlation of matrix system properties and materials with a refractory filler is analyzed. Keywords: SiO2–Al2O3 system, highly concentrated ceramic binder suspension (HCBS), matrix system, chamotte, bauxite, mullite, secondary mullite formation, strength, porosity, temperature for thestart of deformation under load Tg.

In spite of a marked reduction in the last ten years of the production and demand for dinas and chamotte refractories, high-temperature materials of the SiO2–Al2O3 system are as important as in the past. This is due not only to an increase in the production of high-alumina objects, but the fact that about 70% of the world production of unmolded refractories,and primarily concretes and torcrete mixes, is related to high-alumina or corundum refractories [1, 2]. In the overwhelming majority these materials contain a quite considerable (3 – 5%) addition of microsilica [1 – 3], and in a number of cases also colloidal silica, i.e. silica sol [3]. In accordance with known classical compositions diagrams for the binary SiO2–Al2O3 system in [2] an additionaldiagram is presented for the system (Fig. 1), which may be conditionally called production or operational. On the diagram in accordance with the liquidus curve 1, there are also such important characteristics as the area of values of refractoriness 2, maximum application temperature in operation with one-sided heating (curves 3 ), temperature for the start of deformation under load (curves 4 ), andalso the area of application temperatures during operation with all-round heating 5, and the compositions of different refractories in this system are shown.
1 2

From analysis of the areas bounded by curves 3 and 4 in Fig. 1 it follows that for aluminosilicate refractories there is a broad range of values of temperature for the start of deformation under load Tg, and correspondingly alsoindices for the maximum application temperature. Here it is typical that the difference increases with an increase in Al2O3 content in a refractory. Whereas with content of 85% Al2O3 the range of Tg reaches 280°C, with a reduction in Al2O3 content to 40% it reaches 140 – 150°C. This marked difference in the values of Tg is due not only to the type of material and content within of a melt, but a numberof other production factors, including the condition and dispersion of the matrix system of refractories and their preparation technology. Here the significance of these factors increases as there is an increase in Al2O3 content in the material. The problem of improving and developing new aluminosilicate refractories consists of improving their property indices on the basis on the same rawmaterial. This work is devoted to this subject. COMPARATIVE EVALUATION OF TRADITIONAL HIGH-ALUMINA REFRACTORIES AND WITH THE USE OF HCBS TECHNOLOGY Traditional technology for preparing high-alumina refractories consists of preparing densely sintered high-alu358
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