Thermal damage to corundum refractory

Gogotsi, G. A.; Negovskii, A. N.; Zhukovskaya, A. E.

doi:10.1007/bf01398348

Refractories

1984

DOI: 10.1007/bf01398348

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Thermal damage to corundum refractory

G. A. Gogotsi

A. N. Negovskii

A. E. Zhukovskaya

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1986

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Cited by 6 publications

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“…As was shown in the previously published papers, the method of AE can also be used for evaluating the characteristics of crack resistance [12,14,15] and thermal shock resistance [I0, 15,16] of ceramics. However, in this case, it is necessary to consider the specific features of deformation of ceramic materials (just as in the case of strength evaluation) and for for this purpose, the magnitude of their brittleness index can be used successfully.…”

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Effectiveness of the acoustic-emission method for evaluating the strength properties of ceramics and refractories depending on the specific features of their deformation

Gogotsi

Negovskii

1988

Refractories

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Active acoustic methods are being successfully used for evaluating the strength characteristics of ceramics and refractories [i]. These methods are based on recording the parameters of propagation of ultrasonic waves in the materials. The effectivenees of their application is not the same in all materials and depends on the structural features. There are situations where the largest (coarsest) structural inhomogeneities alone are revealed by ultrasonic control whereas the strength is determined by the considerably smaller cracklike defects that cannot be recorded during such a control. This leads to a decreased reliability of the data of ultrasonic control and to an increased probability of obtaining inadmissibly large errors when evaluating the strength characteristics of the materials.In view of this, Sadowska-Boczar et al. [2] and the authors attempted to use a passive acoustic method, i.e., an acoustic emission (AE) method that makes it possible to reveal only those defects that are developed during the loading process and are, consequently, the most danterous ones (for the given type of the stress'-strain state of the body). In view of the fact that AE is caused by the deformation and fracture processes of materials under the action of an applied stress, its nature is closely related to the specific features of these processes. In order to take these features into account, we used the structure-sensitive brittleness index X [i, 3] which was determined on the basis of the deformation diagrams of the materials and was found to be a fairly effective parameter for predicting the behavior of the ceramics subjucted to mechanical and thermal loads [4]. The conducted experiments showed the differences in the degrees of effectiveness of the AE method when testing brittle (X = I) and relatively brittle (X < i) materials [3].In order to evaluate the strength levels of ceramics and refractories, AE was recorded during bend tests of the specimens of these materials (according to the four-point bending scheme) using an AF-II apparatus fitted with a wide-band receiving transducer having a band frequency ranging from 0.02 up to 2.0 MHz. In contrast to the previously followed procedure [5], numerous measures were taken in the present study to improve the accuracy of the AE measurements.Incorporating a SA-100 multichannel analyzer of the spectrum of the AE signals in the measuring circuit made it possible to determine the frequenzy ranges in Which AE is observed in different types of ceramics and to establish the corresponding ranges of measurements of the AF-II apparatus.In this case, the obtained data indicate that in the majority of brittle ceramics (such as boron and silicon carbides, silicon nitride, and aluminum oxide), fairly wide-band AE signals emerge (within the measuring range 0.02-2.0 MHz of the SA-100 device). The spectrum of the AE signals of relatively brittle materials and most of-,the coarse-grained materials (such as luminoboron nitride, aluminosilicates, and magnesites) is narrower and, as a rule, its limit...

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confidence: 98%

Effectiveness of the acoustic-emission method for evaluating the strength properties of ceramics and refractories depending on the specific features of their deformation

Gogotsi

Negovskii

1988

Refractories

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“…3). In this case the polymorphic inversion of the zirconia may be slowed down prior to the action of the peak of the destructive crack causing a phase inversion and energy absorption [15,16].…”

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confidence: 99%

“…With the incorporation of ZrO 2 into the ceramic bond of the articles there is a reduction in the brittleness measure from 0.96 to 0.29 for compositions MKh and SZ respectively [7,15].…”

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confidence: 99%

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Influence of complex oxide additives on the structure and technical properties of corundum refractories

et al. 1988

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perfect faces and dimensional accuracy.The products made from Austrian magnesite powder were severely welded in the bottom two rows; welds were absent in the top five rows and the products had a satisfactory appearance. CONCLUSIONSLaboratory-scale technological studies were carried out for developing the technology of periclase products based on different magnesite powders.Our studies showed the possibility of producing periclase refractories meeting the property specifications of GOST 4689-74 from certain imported powders. INFLUENCE OF COMPLEX OXIDE ADDITIVES ON THE STRUCTURE AND TECHNICAL PROPERTIES OF CORUNDUM REFRACTORIESA. E. Zhukovskaya, Fo S. Kaplan, A. A. Kortel', and E. A. Sherman UDC 666.762.11.001.4 In recent years there has been a substantial increase in the proportion of high-quality oxide refractories, including corundum [I, 2], in the overall volume of refractories production in technically developed countries.This tendency is typical of the development of the refractories industry of our country. We have developed and introduced a number of new industrial processes for making refractories based on sintered or fused corundum with a granular composition, which in contrast to processes based on the use of finely dispersed corundum enables us to carry out the production of large items, for example, slabs for the gate valves of ladles [I, 3, 4].The structure and also the technical properties of corundum refractories can be regulated by introducing various oxides and compositions based on them [5].In order to create such refractories with a grained structure, possessing a range of defined technical characteristics, studies are being carried out aimed at discovering the influence of additions of Mg, Ti and Cr oxides, and also mixtures of them, on the sintering and structure of corundum refractories [6]. Determinations have been made of the parameters of the structure, ensuring the maximum densification and strengthening of the material, and the main elements of the technology have been ascertained related to the the formation of such a structure, in particular the substance and quantitative compositions of the complex oxide additives [6].The investigations were carried out on the newly developed materials in conditions of various thermomechanical loading which showed their high "rigidity" and as a consequence low spalling resistance [7]. This considerably limited the possible regions of use of the mate ~ rials and required further improvements in their structure aimed at increasing the spalling resistance.The improvement in the structure of corundum refractories in order to increase the resistance to thermal loading is based, as a rule, on the initiation of the formation of microcracks by introducing into the structure of the materials inclusions of another phase [i, 8]. The microcracks develop on the grain boundaries, the pores, or inclusions, and contribute to the dissemination of the energy of the destructive cracks.Of great promise is the introduction to the corundum matrix of small additions o...

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“…To reveal the features of deformation and microdamages of ceramic materials attempts have been made to use the acoustic emission method [2,4], which is based on the detection and recording of the elastic waves occurring in local rearrangements of the structure of the material [5]. This work is devoted to an investigation of the features of deformation and the acoustic emission process in bending of CZ and MZ corundum refractories [6] to the charge of which was added monoclinic unstabilized zirconium dioxide for formation of microcracks in them.…”

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confidence: 99%

Acoustic emission in the deformation and failure of corundum refractories

Gogotsi¹,

Drozdov²

1986

Refractories

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Thermal damage to corundum refractory

Cited by 6 publications

References 3 publications

Effectiveness of the acoustic-emission method for evaluating the strength properties of ceramics and refractories depending on the specific features of their deformation

Effectiveness of the acoustic-emission method for evaluating the strength properties of ceramics and refractories depending on the specific features of their deformation

Influence of complex oxide additives on the structure and technical properties of corundum refractories

Acoustic emission in the deformation and failure of corundum refractories

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