Preparation of powders based on bauxite HCBS (Highly Concentrated Ceramic Binding Suspensions) containing high-disperse quartz glass and plasticized with refractory clay is described. The powders, molded at moderate pressure (50 -100 MPa), give a high-density material with an initial porosity of 20 -25%. Mixes containing 10 to 43% commercial alumina are tested. The materials can be used as matrices for press-molded high-alumina ceramic castables which, when sintered, show a high mechanical strength and volume constancy.Among high-alumina ceramic castables commercially available from the Pervouralsk Dinas Plant JSC [1, 2], there has recently been an increased output of press-molded refractories based on mixed HCBS in the system bauxite (90%) -quartz glass (10%). Formerly, the traditional product was mixed brick (mostly shaped by friction pressing technology) with a long service life (capable of sustaining as many as two thousand pouring cycles); currently, the production of pressed refractories of mullite-corundum composition (MKTP-85 grade) for the lining of steel ladles has been launched [2]. The HCBS-based refractories, when compared to their compositional analogs of grades MK, MKS, MKT or MKB, show a substantially lower porosity, higher mechanical strength and thermal stability (by a factor of 2 -3), and smaller production costs [2]. Economy has been achieved owing to the fact that the HCBS-based refractories require lower sintering temperatures in comparison to the products prepared by the conventional technology.An advantage of the HCBS-based refractories is their enhanced operational stability [2]. Furthermore, these refractories may be a convenient alternative to conventional refractories of similar composition currently used in many sectors of industry. One would attempt a suggestion, not without reason, that the new technology for production of aluminosilicate components (with 50 -95% Al 2 O 3 ) will play, in the near future, a leading role in the field. Viewed in this light, further development of the technology of press-molded ceramic castables based on Al 2 O 3 -containing composites and study of their structure and properties are at present a challenging task. The properties of press-molded ceramic castables, like those of monolithic and vibrocast castables [1], are mainly controlled by the composition and properties of their matrix composed of HCBS and plasticizing, thinning, or strengthening additives. In our study, the compositions of both matrix and refractory fillers were varied over a wide concentration range.In step 1 of our work, the matrix systems were studied for compaction and the properties of the finely dispersed component of press-molded ceramic castables were examined.Starting materials. Compaction and properties of matrix systems based on a wet-ground mixture of bauxite HCBS and 10% quartz glass were studied [1]. The HCBS-based matrices are exceptionally efficient owing to the involvement of a low-temperature mullitization mechanism which imparts enhanced thermomechanical properties t...
The effect of lignosulfonate (LST) and surface-active substances (SAS) on compaction and properties of bauxite-quartz glass matrix systems is studied. LST added at an optimum concentration to bauxite-based highly concentrated ceramic binding suspensions (HCBS) causes a 2 -3% decrease in preform porosity. In materials sintered at high temperature the effect of decreased porosity is more pronounced. In preforms molded at 500 -700 MPa no defect due to overpress is observed. The SAS, judged from their efficiency for decreasing porosity, are arranged in ascending order: sodium silicate water glass, sodium tripolyphosphate, complex organomineral thinner, and FS-20 castament.Previously [1,2], the pressure-induced compaction of materials composed of bauxite-based highly concentrated ceramic binding suspensions (HCBSs) with the addition of 10% highly dispersed quartz glass and 3% plasticizing refractory clay has been studied in some detail. Our goal in this work was: (i) to find ways to reduce the porosity of pressure-molded preforms by introducing, apart from the refractory clay, processing additives; (ii) to study the compaction process over a pressure range wider than that used in [1, 2]; (iii) to examine the effect of additives on the mechanical strength of green and dried preforms, and (iv) to study the effect of sintering temperature on properties of a material containing various additives.The processing additives were selected with regard for their plasticizing or deflocculating (thinning) effect on the bauxite HCBS. In greater detail, the effect due to lignosulfonate (LST) additives was considered. It is well known [3] that lignosulfonates are produced from lignin by sulfate cooking of wood in the production of cellulose [3]. They are lyophilic water-soluble colloids capable of carrying an electric charge on the colloidal particles; furthermore, they belong to a class of surface-active substance and are capable of adsorbing in an orderly arrangement on solid material particles. Currently, LSTs are understood to be high-molecularweight compounds of natural occurrence with molecular mass varying over a wide range (2000 -100,000). The elementary composition of LST, %, is: carbon, 53 -57; hydrogen, 5 -6; sulfur, 4 -7; nitrogen, £ 5; oxygen, 27 -34; sodium, £ 8; calcium, £ 6 [3]. In the refractory molding technology [4], LST is widely used as a plasticizing and hardening additive (bond).The LST additive was introduced into bauxite HCBS in the form of a powder of concentration varying from 0.05 to 2.5%. Other inorganic and organic additives, sodium silicate water glass, sodium tripolyphosphate (SPP), FS-20-grade castament [5], and complex organomineral thinner (COMT) [6] were used at the same concentration of 0.1% (based on dry residue).The object of our study was a suspension prepared under industrial conditions from a Rota HD sintered bauxite (89% Al 2 O 3 ) from China and fused quartz (10%) [6]. The precursor HCBS had median particle diameter d m = 6 mm; 12% of the total of particles were less than 2 mm across. The m...
Experimental data are provided and summarized for the efficiency of adding very fine quartz glass (VFQG) in high-alumina and corundum ceramic concrete technology. Similar suspensions are prepared for very fine quartz sand (VFQS) and a mixed suspension in the bauxite -VFQS system. The properties of both mixed suspensions and some materials based on them are studied.Keywords: ceramic concretes, highly concentrated binding suspension (HCBS), low-cement refractory concrete (LCRC), microsilica, micro-silicon dioxide, very fine quartz glass (VFQG), very fine quartz sand (VFQS), mixed suspensions, mullite, integral and differential curves.A basic tendency in development of the refractory industry is expansion of production and application of multifunctional molded and unmolded refractory objects with improved operating characteristics [1]. In this respect a significant role may be played by improved (with respect to technology and properties) high-alumina and corundum refractories.There is a common tendency of increasing the proportion of out put and use of unmolded refractories whose production in Japan reached 67% [1]. Here refractory concretes, torcrete mixes within the balance of unmolded refractories is about 70%. It is supposed that 60 -70% of the latter relate in composition to high-alumina or corundum refractories whose production is spread universally. Taking this factor into account and the known volume of production in Japan of molded objects of this chemical and mineral composition, it may be assumed that in the overall balance of refractories they are in first place. According to data [2], production of high-alumina and corundum objects in Russia is insignificant (116 thousand tons/year) and is less by about a factor of seven than chamotte refractories, i.e. within the country as before chamotte molded refractories predominate. In addition the development of the production noted in recent years in the field of unmolded refractories in Russia mainly concerns high-alumina and corundum materials.In order to improve the quality of low-cement refractory concretes (LCRC) of high-alumina and corundum compositions there is extensive use of addition of very fine amorphous silica, given the name micro-silica or micro-silicon oxide (MS) [3,4]. The main form of high-alumina refractories may be considered as ceramic concrete, i.e. molded or unmolded refractories (vibration poured and rammed concretes, torcrete mixes), prepared on the basis of HCBS and refractory fillers [5,6]. EFFECT OF VERY FINE QUARTZ GLASS (VFQG) ON CERAMIC CONCRETE PROPERTIESApplied to LCRC technology addition micro-silica has a polyfunctional effect consisting of improving both the rheotechnological properties of the original molding systems and also the properties of refractory concretes prepared with this addition. It is well known that the size of the finest particles in LCRC matrix systems (reactive alumina, high-alumina cement (HAC)) is 0.5 -0.1 mm. In this case the MS particles introduced are a unique microfiller. On mixing (suspension) they ...
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