Highly concentrated ceramic binder suspensions. Dispersion medium, stabilization, and binding properties

Abstract

In the previous series of papers on the highly concentrated ceramic binder suspensions (HCBS), it was shown that a number of technological principles must be followed directly during the process of wet milling for producing HCBS: it is necessary to maintain high concentration and high temperature [i] and optimum degree of dispersion, granulometric distribution, dilution of HCBS, and dissolution of the solid phase [2]. The properties of HCBS obtained by following the aforementioned principles can be significantly improved by their additional stabilization.The principle of additional stabilization forms a concluding and highly effective principle in the technology of HCBS of acidic and acidic-amphoteric systems. As was shown in our previous studies [3,4], the rheological method of stabilization (involving mechanical gravitational mixing at a specific peripheral speed for certain duration) is particularly used for HCBS of these systems. In the technology of HCBS, the rheological method of stabilization is treated as a special technological operation that makes it possible to obtain qualitative changes in their properties: to achieve an additional reduction of viscosity (as compared to the viscosity obtained during grinding) and to increase the resistance of the suspensions to aggregation and sedimentation along with a corresponding increase in the density and the strength of the castings (binder) based on them [4]. In the case of HCBS of acidic and acidic-amphoteric systems, the maximum effect is achieved by a combination of electrolyte additions (or wet milling in the optimum pH range) and subsequent mechanical stabilization [4][5][6]. This paper* presents the results of a detailed study on the effect of the stabilization processes of a number of materials beloning to the acidic and acidic-amphoteric classes of HCBS [i] on their binding (strength) properties. In this case, the effect of the characteristics of the dispersion (dispersing) medium (the content of the colloidal component in it) on the properties of HCBS received particular attention. In order to evaluate the effect of stabilization, we used the previously suggested [4] stabilization coefficient Kst that indicates the relative increase of the content of the kinetically free dispersion medium CWk in the system during the process of stabilization.The following raw materials were used for obtaining HCBS: fused quartz (99.5% SiOa), Vol'sk quartz sand (98.8% SiOa), and the scrap of the ShB-5 grade refractories (28.1% Al2Oa, 66.3% SiO 2) and the MKS-83 (76.0% Al2Oa, 19.5% SiO a) refractories of the Semiluksk refractories plant.Highly concentrated binder suspensions were produced by wet milling the raw materials in a ceramic-lined ball mill according to the previously developed technology [4,7]. The obtained suspensions were characterized by close granulometric compositions: the content of the particles up to 5 ~wn 25-35% and coarser than 50 Bm 5-10%.Dispersion Medium of HCBS and the Content of the Colloidal Component in It. It was previously shown [2] that th...

Nanodisperse silica and some aspects of nanotechnologies in the field of silicate materials science. Part 1

“…In order to obtain additional and important data on the characteristics of the dispersion composition of HCBS it was suggested in [31] to single out two conventional levels (ranges) of dispersity, i.e., (I) that of particles of solid phase with a size ranging from 0.2 -0.5 mm to a maximum value of 30 -100 mm and (II) particles with a size below 0.2 mm. The latter range can be conventionally treated as that of nanoparticles.…”

“…In [31] we used an ultracentrifuge with rotor speed of 18,000 rpm rotated for 15 min for separating the colloidal component. We studied samples of a dispersion medium obtained by long-term settling of repeatedly diluted suspensions.…”

“…System studies of the content and characteristics of nanoparticles in fused quartz and quarts sand HCBS are presented in [12,31,32]. As an example, we characterize the fineness and the grain distribution of fused quartz suspension with different contents of nanoparticles in Fig.…”

Refractory concretes of new generation. General characteristics of the binder systems

“…According to us, as was shown earlier [5], the main distinguishing feature of the cementfree refractory binders is the methodological separation of the solid phase of the binder system into two levels of dispersion, viz., i) the particles having a size ranging from 0.2-0.5 up to i00 pm that form a mineralogical microfilier having an active surface; and 2) the particles having a size below 0.2-0.5 pm that are classified as the colloidal component. These two levels of dispersion play different roles in the process of structure evolution during dehydration and determine the other characteristic properties of the new group of binders.…”

“…Chemical binders include molecular-or colloidal-dispersed solutions and inorganic sols that are characterized by their polymerization nature of hardening (liquid glass, phosphate binders, oxychloride solutions silica-and aluminasols etc.). The refractory concretes obtained using the aforementioned binders are characterized by a high degree of heterogeneity with respect to chemical and mineralogical composition because of which the service characteristics of these materials are most adversely affected.As was indicated in our previous papers on this subject [3,4], the main methods of solving the aforementioned problem include changing the material composition of the binder by replacing a large portion of the cement with an ultrafine (highly dispersed) mineralogical component and obtaining homogeneous systems (highly concentrated binder systems HCBS) whose dispersing medium consists of a sol or a gel synthesized during the preparation of HCBS and dispersed phase consists of an activated microfiller of the same refractory composition (system).Our previous studies [5,6] demonstrated for the first time that the content Ccc of the colloidal component, i.e., the content of the ultrafine (30-40 run) particles "generated' during wet milling and stabilization of HCBS forms the main parameter determining their rheoiogical, technological, and binding properties. Figure 1 shows a typical example of the effect of the relative (with respect to the total mass of the solid phase of HCBS) content of the colloidal component Ccc (in the given case, its quantity was controlled by the duration of stabilization by mechanical agitation) on the characteristics of HCBS of the muilite-corundum system.…”