Strength of corundum concretes

Abstract

Accelerating production processes with the use of heating equipment that operates under the action of various corrosive agents requires the development of refractory materials that will provide effective and reliable operation. Increased demands are placed on the refractory linings under such conditions. In particular, the refractories should possess a high strength, which is one of the decisive criteria of the working capacity of the heating plant during prolonged operation.The Ukrainian Institute has developed highly refractory, volume-constant corundum concretes [i] which can be recommended for unfired, monolithic linings in various high-temperature units working in reducing, neutral, and oxidizing gaseous atmospheres at service temperatures of 1800-1900~Studies carried out at IPP AN UkSSR showed [2-6] that ceramics and refractories are classified with the nonlinear-elastic systems.This agrees with data in [7][8][9]. In particular, from the results given in [8,9] it follows that ignoring the nonlinearity of the diagrams during their treatment leads to considerable errors in determining the strength.Experimental investigations of the strength properties of corundum concretes were carried out on equipment at IPP AN UkSSR using the methods stated in [2][3][4][5].The specimens were tested according to the four-point bending scheme on equipment designed on the basis of the RM-101M rupture machine.The arrangement of the equipment is shown in Fig. 1. It has special supports with distances of 50 and 30 mm between the internal points of application of the loads, and i00 and 60 mm between the loads. These supports are different from those described in [2,5] in that the rollers i transmitting the force onto the specimen 2 are arranged on the plates (in Fig. I not shown) which can be rotated around cylindrical rods coaxial with the specimen.Electromagnets are used to fix the initial position of the rollers. A rigid plate dynamometer 3 is built into the support~ and the deformations of this are measured with strain gauges, and the bending meter 4, designed on the basis of the small inductive displacement sensor which was designed in IPP AN UkSSR, is built into the support.As a result of improvements made to the metering circuit it is possible to register, on two-coordinate potentiometers, the deformation diagrams not only with the use of the strain gauges (P--a, see Fig. I) glued to the specimen in the compression zone 5 and in the tension zone 6, but also with the aid of the bending meter 4 (P--~, see Fig. 1).In order to study the acoustic emission (AE), diagnosing the development in the specimens of cracks during deformation, use is made of a special instrument [6]; and we developed a metering-information system which ensures the measurement in a stated range of frequencies of the parameters of acoustic emission (total number of impulses, their intensity, amplitude, and the number of elementary events --acts of acoustic emission); in addition, a synchronized signal is transmitted to one of the channels about the change i...

Critierional evaluation of thermal destruction of corundum concretes

“…where a and b are the length and the width of the specimen, m; P is the maximum load, N; h is the notch depth, m; H is the specimen height, m; and y is a geometric parameter that is calculated according to the following equation [15]:…”

“…The structure of the specimens determines the observed differences in the properties of the concretes [15,16]. Table I gives the physical and mechanical properties required for the criterional evaluation of the thermal crack resistance of the concretes , and their heat treatment temperature t (c); the numbers of the curves correspond to the system numbers given in Table i.…”

Influence of plasticizers on the properties of corundum concretes

“…Moreover, the use of the phosphate bond is desirable for refractories used in oxidizing conditions [6]. Moreover, the use of the phosphate bond is desirable for refractories used in oxidizing conditions [6].…”