The development of new technological p r o c e s s e s in the power, metallurgical, engineering, p e t r ochemical, and other industries r e q u i r e s the creation of lightweight m a t e r i a l s capable of withstanding the action of carbon-containing reducing media and possessing good heat-insulating properties. Outside the Soviet Union, anorthite lightweight artifacts obtained by casting from kaolin--gypsumlike m a s s e s are used for service at 1100-1260~ [1, 2]. The low iron oxide content of these artifacts (0.28-0.62%)* is due to the use of pore initial m a t e r i a l for their manufacture. The relatively simple technology, which lends itself to mechanization, the use of cheap raw m a t e r i a l , and the high heat-insulating p r o p e r t i e s of anorthite lightweight r e f r a c t o r i e s were the basis for development of their production.It is known [3] that artifacts with an apparent density of 0.60-0.65 g / c m 3 and a c o m p r e s s i v e strength of up to 1.5 MPa are obtainable on the basis of secondary kaolins and builder's gypsum with added sawdust which s e r v e s a burning additive. The service t e m p e r a t u r e of the artifacts is 1150-1200~ This article gives the r e s u l t s of preparation in the laboratory of anorthite lightweight r e f r a c t o r i e s with an apparent density of less than 0.5 g / c m 3, a high strength, low t h e r m a l conductivity, and a m a x i m u m service t e m p e r a t u r e of 1300~Recently, various h i g h -m o l e c u l a r synthetic compounds --polyethylene, polystyrene, polyvinyl, e t c . -have been used extensively as r o c k -f o r m i n g additives [4][5][6]. To obtain r e f r a c t o r i e s with a low apparent density, PSV foaming polystyrene suspension was used. Its incorporation into the paste p e r m i t s the preparation of artifacts with an open porosity of 85% [7]. Thanks to the spherical shape of the polystyrene grains the p o r e s in the m a t e r i a l are spherical with smooth walls; as in the case of cellular c e r a m i c , this * H e r e and below we give the percentages by weight.

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The aim of the studies was to determine the technological parameters for obtaining products having an apparent density not exceeding I.i g/cm 3 and meeting the specifications concerning the strength and the thermal conductivity of cast light-weight ShL-0.9 grade products .We obtained the chamotte concrete heat-insulating products according to the method of semidry compaction.This made it possible to mechanize the technological process.The minus 15 mm fraction of the ShGR-3, ShGR-4, and ShGR-5 grade chamottes, the scrap of the ShL-I.3 grade chamotte products having an apparent density exceeding 2.0 and 1.3 g/cm 3, and the waste products of the light-weight MKRL-0.8 and ShL-0.4 refractories were used as fillers.The high-alumina cements obtained at the Pilot plant of the UkrNIIO and the Klyuchevsk plant and the alumina cement supplied by the Pashiisk plant were used as binders. Table 1 shows the properties of the cements. Perlite and polystyrene were used as pore-forming additives.Specimens were compacted at a pressure of 3 and 5 N/mm 2. The specimens were subjected to setting by steam-curing and, also, under wet conditions or in air for a period of 3 and 7 days with or without subsequent drying.We studied the dependence of the properties of the chamotte concrete heat-insulating specimens after setting for 3 and 7 days on the content of the high-alumina cement in the charge (Fig. i). The moisture content of the specimens amounted to 25%. On increasing the cement content from 15 up to 40% and the duration of setting from 3 up to 7 days, Papt and Ocm of the specimens were found to increase. When the cement content of the charge does not exceed 25%, the apparent density of the specimens differs (varies) insignificantly; this difference increases more significantly as the cement content increases. We note that when setting is carried out in wet saw dust, Papt and Ocm of the specimens are higher than those obtained in air (at a given duration of setting).The specimens compacted at a pressure of 5 N/mm 2 have a higher apparent density than those compacted at 3 N/mm 2.However, the specimens cured under wet saw dust without subsequent drying are not suitable for determining the properties since they have a high Papt and a low Ocm.These regularities are retained when varying the technological parameters and, therefore, it is necessary to carry out drying at II0~ (until a constant weight is obtained) before determining the properties of the specimens.Replacing the scrap of the dense chamotte products (having an apparent density exceeding 2.0 g/cm 3) with the ShGR type chamotte does not lead to a change in the properties of the specimens.In order to reduce the duration of setting, some specimens were subjected to steam'curing for a period of 5 h and were subsequently dried at II0~ until a constant weight was attained. The properties of the steam-cured specimens were similar to those of the specimens subjected to setting in wet saw dust for a period of 3 days.We studied the dependence of the properties of the heat-insulating co...

At the present time, technological progress in the construction and maintenance (repairs) of thermal units requires mass-scale application of heat-resistant concretes whose specifications are becoming more stringent due to the developments taking place in the technology and the techniques and the intensification of the processes occurring in the thermal units. In view of the fact that high-alumina cement (HAC) is the most promising binding (bonding) agent for the refractory concretes working at a temperature exceeding 1773~ (under controlled atmospheres also), numerous studies have been carried out [1][2][3][4] for identifying the possible methods of improving its properties and for understanding the mechanisms and the kinetics of the reactions occurring during its synthesis.We carried out extensive (complex) studies aimed at identifying the optimum technological parameters for producing clinker of HAC by sintering in order to improve the service properties of the concretes based on the cement obtained from this clinker. This paper presents the results of the studies conducted on the kinetics of the solid Dhase reactions occurring during the sintering process of the clinker.In order to study the stability of the individual phases and compounds and to establish the most general regularities in the occurrence of the solid-phase reactions, thermodynamic analysis is carried out using the principle of calculating the change in the isobaric potential (AG) with respect to the compositions (constitutuents); the application of this principle involves investigation of each possible reaction under the assumption that the quantity of the initial substances is identical [5].The change AG was calculated by integrating the Gibbs-Helmholtz equation.The following equations depicting the temperature dependence of AG were obtained on the basis of the cal~ culation carried out taking into account the polymorphic transformation of 7-A1203 into ~o AI203 :A G O = --6584,470 --7,102 TIn T q-2,400 X 10-3T~--2,710 9 105T-'~-39,994T (for the aluminate having the composition ClzAT) ;A G~ = --7529,960 --6,830 T In T q-1,690,10-aT2--2,675 9 105T-'q-38,288T(for the aluminate having the composition CA) ; and 218T (for the aluminate having the composition CAz)Based on the obtained equations, the values of AG~ were calculated at different temperatures in the I073-1873"K range for the compounds CA, CAz, and C12A 7. The results of our calculations (Fig. I) showed the thermodynamic feasibility (possibility) for the formation of the aluminates CA and C12A 7 in the mixture of the experimental (system) (besides calcium dialuminate having a more negative value of AG o in the entire temperature range under consideration). The conclusion regarding the thermodynamic probability of formation of the aluminates CA, CA2, and CI2A 7 in the experimental system agree with the data of Fedorov et al. [4].It is known that the occurrence of a reaction depends not only on the magnitude of AG, but also on the kinetic factors among which the rate and the activation en...