Anorthite lightweight refractories for service in carbon-containing media

Abstract

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.

Production of anorthite refractory insulating firebrick from mixtures of clay and recycled paper waste with sawdust addition

“…In other words, thermal conductivities of the samples were reduced with decreasing bulk densities. The lowest bulk density and thermal conductivity values of 0.87 g/ cm 3 and 0.20 W/mK, respectively, were achieved in samples with 30wt% sawdust that were fired at 1200 8C. The samples linearly shrunk up to 4.5% during firing.…”

“…Bulk density values of the firebricks ranged from 1.12 to 0.64 g/cm 3 depending on the mass ratio of sawdust addition (Table 2). Their bulk densities decreased with increasing sawdust addition.…”

“…During firing, the combustible material burns out, and leaves a large fraction of pores within the fired body. Different types of pore-formers such as sawdust, foam polystyrene, fine coke, binders and organic foams, or granular materials such as hollow microspheres and bubble alumina are commonly used to obtain decreased density or to produce porous bodies in the insulating material [2][3][4][5][6][7][8]. Insulating firebricks that have a highly porous structure (between 45% and 90% porosity) exhibit low thermal conductivity values.…”

“…For example, the groups 20 and 23 with high CaO content represent the anorthite (CaOÁAl 2 O 3 Á2SiO 2 ) based insulating firebricks with maximum temperature limits of 1093 and 1260 8C, respectively. Anorthite insulating firebricks are mainly manufactured from mixtures of clay, gypsum (CaSO 4 Á2H 2 O) binder and sawdust [3]. The mixture hardens after forming and is fired.…”

“…However, an important problem of this method is environmentally the release of sulfur compounds from gypsum, which is highly undesirable. In the early works, some researchers developed the low density anorthite refractories using kaolin and gypsum slurry mixtures [3,7]. In these products, several different pore making agents like perlite foam, sawdust and polystyrene have been used [3,7].…”