Corundum refractories technology

Kainarskii, I. S.; Gaodu, A. N.; Karyakin, L. I.; Usatikov, I. F.

doi:10.1007/bf01284598

Cited by 4 publications

(5 citation statements)

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“…Their average aftershrinkage after exposure for 24 h at 1750~ is 1.17% and their thermal-shock resistance (1300~ -air) over 15 reversals [21]. These refractories can be used in conditions of unilateral heating at 1750-1800~ in masonry under a load, e.g., in the thrust roof of periodic kilns.…”

Section: 500mentioning

confidence: 98%

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: 98%

More efficient utilization of alumina in refractories production

Kainarskii¹

1978

Refractories

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“…8) or the region of the optimum distribution (see Fig. In this case a major role compared with the other methods of forming [5,8] is played by the type of solid phase and the stabilitY of the molding system. Thus, the compositions Nos.…”

Section: Curves Inmentioning

confidence: 99%

“…The feature being examined for the dispersed component of VKVS is very important in the development of the bonding (cementing) properties, and answers the question as to why on the basis of powders after dry milling or powders washed free of tramp iron [8,9] (i.e., systems where the indicated colloidal fractions are absent, or present in the mimimum amounts) it is impossible to obtain VKVS with bonding properties. Besides the general factors of dPav and S the overall characteristics can include spec the median diameter of the particles d m, corresponding on the integral curves (see Fig.…”

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confidence: 99%

Highly concentrated ceramic bonding suspensions: Dispersion composition and porosity of casting

Pivinskii

1989

Refractories

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In the production of materials based on highly concentrated ceramic bonding suspensions (VKVS), as a rule, one of the main problems is to obtain castings with a high density (low porosity). The porosity of the castings is a complicated function of the technical and rheological properties of the VKVS, the characteristics of the dispersion, and the molding or shaping conditions. The porosity of the casting to a large degree is governed both by the original and the "secondary" structure of the material formed in the sintering process or the heating procedure (for example, during the service of unfired materials).One of the main factors in reducing the porosity of the greenware formed by different methods is the choice of the optimum grain-size composition.In the present article* on the basis of generalized results of previous work [i, 2] and also new experimental data we were faced with the problem of determing the influence of the dispersion composition of the various types of VKVS on the density of the castings made from them.Characteristics and Features of the Dispersion Composition. Considering that the principle of the optimum dispersion and grain-size distribution [3] in the technology of VKVS is considered to be decisive, we need an all-round analysis of the main factors of their dispersion composition. The solid phase of VKVS should be characterized by a complete integral curve for the grain-size distribution, taking into account the particles of both the overscreen (more than 50 ~m) and the colloidal (less than 0.1-0.2 ~m) sizes. These curves for VKVS based on fused quartz are shown in Fig. i. In this case the content of particles plus 50 ~m was determined by the screen method, particles from 50 to 0.01 pm by the sedimentation method (on an automatic x-ray sedimentograph), and the colloidal component (less than 0.03 ~m) bv the ultracentrifuge method [4]. The section of the curves in the region d = 0.I-0.03 J ~m were extrapolated. As follows from the curves, the composition of the solid phases of VKVS is characterized by the polydispersion nature -extreme valuesof the particle sizes are distinguished by five orders (from 0.i mm to several nanometers).On the basis of the complete integral curve for the grain-size distribution of the particles it becomes possible to calculate the average dispersion parameters: average surface diameter of the particles d~v , pm [5]; and the specific surface of the solid phase Sspec , m2/g, as a function of dPav: 1 O0 6000 dPv = ~r S " = ,, spee dP ,Qs' av av

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“…In order to further increase the porosity of the chromic oxide articles, we used the method, traditional in the refractory industry, of adding burning additives [Ii,12]. With the addition to the batch of Cryptol of 2-0.2 mm fractions in amounts of 20%, the porosity of the specimens increases one-to twofold while the ultimate compressive strength *Here and elsewhere mass fractions are given.…”

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confidence: 99%