Corundum refractories

Kainarskii, I. S.; Degtyareva, �. V.; Kabakova, I. I.

doi:10.1007/bf01290100

Cited by 14 publications

(14 citation statements)

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“…Various types of corundum refractories of multiphase compositions can be produced from commercial alumina by varying the technology [10]. These refractories are characterized by high strength (notably in abrasion), resistance to creep over a wide range of temperatures, chemical stability in strongly reducing gaseous media and to the actionof solid carbon, high thermal conductivity, a low coefficient of thermal expansion, and volumetric stability.…”

Section: 500mentioning

confidence: 99%

More efficient utilization of alumina in refractories production

Kainarskii¹

1978

Refractories

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Commercial alumina is used for the production of refractories either alone or in combination, i.e., mainly with silica and magnesia. Most of the alumina is used for the production of high-alumina refractories containing a minimum of 62 and 72% A1203 in conformity with TU 14-8-207-76. These refractories can be produced more efficiently from a natural high-alumina raw material, a fact which is demonstrated by the experience of foreign countries [1] and the use of low-iron bauxite by the Soviet refractories industry.High-alumina chamotte is produced by sintering a mix of commercial alumina and clean refractory clay or kaolin in various types of kilns. To produce mullite chamotte a mix of commercial alumina and Novoselitsy kaolin must be fired at 1700~ and a mix with Prosyanovsk clay at a temperature not below 1750~ [2, 3], i.e., at a temperature which gives a thoroughly sintered corundum chamotte. Up to a temperature of 1500"C the alumina and clay mixes give mullite of the composition 3A1203 9 2SiO~ but higher temperatures (up to 1750~ and an excess of alumina will produce mullites of varied composition right up to 2A120 ~ "SiO~ [4], The properties of refractories produced from mixes of commercial alumina ~nd clay are not stable enough. It is known [5] that the protracted afterfiring of the commercial refractories VG-62 and VG-78 containing 62 and 78% Al203, respectively, at 1350~ (25-300 h) and 1500~ (25-100 h) results in an increase in the open porosity of the VG-78 type products and in a decrease in their strength when fired for 300 h at 1350~ but in its increase when they are fired for 10O h at 1500~ while the refractoriness under a load of 2 kgf/cm ~ increases by 80 and 70~ respectively, and the rate of deformation in creep tests also increases. The properties of VG-62 refractories are more stable than those of the VG-78 type; the refractoriness under a load of 2 kgf/cm 2 and the rate of deformation in creep tests of these refractories are similar to those of the VG-78 type. This behavior in protracted heating is explained by the fact that the viscosity of the liquid phase decreases and the proportion of solid phase increases with an increase in the A1203 content [6] with the result that the deformation properties of the refractories undergo a change.

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Section: 500mentioning

confidence: 99%

More efficient utilization of alumina in refractories production

Kainarskii¹

1978

Refractories

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“…Despite the high water concentration the suspensions of alumina with the ball diameters of <i mm have the highest constant factors for rheological flow, which is apparently connected with the denser packing of the polystyrene balls of this diameter. The calculated effective viscosity for the yield point of the structure ~min with increase in the ball diameter from <0.5 to <I mm is increased from 1.6 to 2.1 Pa'sec, and the shear stress at the commencement of flow is increased from 76 to 125 Pa. With the incorporation of polystyrene balls of diameter <i mm we note a maximum for the lowest shear stress (Pk, = I00 Pa); and for the highest (when Pk2 = 125 Pa); the least plastic viscosity n m under these conditions has the highest value --0.82 Pa'sec (Table 2).It is known [2,3] that alumina slips are unstable in regard to their sedimentation and aggregative properties. It is possible to give a system stability, i.e., increase the interaction of the disperse phase with the dispersion phase, by incorporating electrolytes or surface-active agents.…”

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Structure formation of water suspensions of alumina containing polystyrene additions

et al. 1987

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Increasing the working temperature and using protective and controlled atmospheres in furnaces require a Boost in the production and an expansion of the range of corundum, heatinsulating products of high purity with more than 99% concentration of ~-A1203.Corundum insulating articles produced by our industry in grades KL-I.3, with a reduced concentration of A1203 (95%) and a high porosity (62-65%) possess moderate working temperatures (1550~ and a low corrosion resistance (they contain 3.5% CaO and 0.5% Si02).Previous studies were made of the effect of powdered AI=03 fineness [i], the pH of the dispersion medium [2], and surface-active agents [3] on the casting properties of slips and the properties of the corundum articles.The present article gives the results of a study of the rheological and structuralmechanical properties of alumina suspensions with additions of polystyrene used for preparing, by casting, corundum heat-insulating articles containing not less than 98% AI=O3, of a stated structure and with an application temperature of up to 1800~ (after-contraction not more than 1%).The starting components consisted of alumina grades GK and G-O0, and powdered formed polystyrene as the additive [4].The rheological properties of the alumina suspension were determined on a rotation viscometer RV-8, and the fluidity of the slips on the "Konus AzNII" apparatus~ The electrolytes used to alter the pH consisted of HCI and NH~OH.The experiments were done with the use of polystyrene balls diameter <0.5,

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“…This is connected with the different phase compositions of the aluminas. In G-00, not subjected to calcination, the content of ~-AI203 does not exceed 30%, while the remainder consists of transition forms, from hydrates to oxides of aluminum 7-A1203, and 8-A1203, which, changing into corundum, cause increased shrinkage in firing [4]. The use of 40% GK alumina in which there is 99% corundum leads to a reduction in the shrinkage of the specimens in firing (from 42.7% for the corresponding amount of raw unmilled alumina as filler to 34.5%), and in this case there is a simultaneous increase in the apparent density (from 0.82 to 1.17 g/cm3), and to an even greater increase in strength (from 2 to 20.4 N/mm2).…”

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confidence: 97%

“…Well known is the relationship between the properties of dense corundum ceramics and the type of alumina used, and the various oxide additives [4]. The present paper gives the results of a study of the influence of the type of alumina and certain additives on the properties of corundum heat-insulating refractories.…”

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Influence of the type of alumina and additives on the properties of corundum heat-insulating refractory

1987

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The production of corundum refractories for high-temperature applications is based on the use of various pore-forming additives [i, 2], corundum granules, and porous corundum briquet [3]. Well known is the relationship between the properties of dense corundum ceramics and the type of alumina used, and the various oxide additives [4]. The present paper gives the results of a study of the influence of the type of alumina and certain additives on the properties of corundum heat-insulating refractories.The articles were prepared by slip casting in metal molds and the pore-forming agent consisted of ashless combustible -foamed polystyrene [2] with grain sizes of less than 3 mm in amounts of 60% (by volume) in relation to the alumina. The bond constituent consisted of alumina G-00 ground in a vibromill to a grain size of 6-12 ~m, to which we added three types of filler in order to reduce the shrinkage: unground alumina grade GK and G-00, and also alumina calcined at 1550~ and vibromilled to a grain size of less than 4 #m using the G-00 type.An increase in the amount of bond from 20 to 60-70% regardless of the type of filler leads to an increase in the shrinkage in firing (Fig. i), but an even greater effect on the shrinkage results from the prehistory of the alumina serving as the filler. Thus, the addition of 30% unfired and unmilled alumina G-00 as a filler with the same shrinkage in firing (46%) ensures the production of articles with a much lower apparent density (0.92 g/cm 3) than for specimens to which we added 40% calcined (1550~ and vibromilled alumina G-00, (1.42 g/cm3). This is connected with the different phase compositions of the aluminas. In G-00, not subjected to calcination, the content of ~-AI203 does not exceed 30%, while the remainder consists of transition forms, from hydrates to oxides of aluminum 7-A1203, and 8-A1203, which, changing into corundum, cause increased shrinkage in firing [4]. The use of 40% GK alumina in which there is 99% corundum leads to a reduction in the shrinkage of the specimens in firing (from 42.7% for the corresponding amount of raw unmilled alumina as filler to 34.5%), and in this case there is a simultaneous increase in the apparent density (from 0.82 to 1.17 g/cm3), and to an even greater increase in strength (from 2 to 20.4 N/mm2). The addition of milled G-00 alumina also containing 99% corundum causes an increase in the shrinkage (with the addition of 60% from 34.5 to 46%), in the density (from 1.17 to 1.42 g/cm3), and in the strength (from 20.2 to 33 N/mm2).

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Corundum refractories

Cited by 14 publications

References 1 publication

More efficient utilization of alumina in refractories production

More efficient utilization of alumina in refractories production

Structure formation of water suspensions of alumina containing polystyrene additions

Influence of the type of alumina and additives on the properties of corundum heat-insulating refractory

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