Refractory clays and articles based on them are widely used in the national economy [1][2][3].They are mainly used as heat-resistant coatings in the ferrous-metals industries [i], in the production of building products [2], and for electrovacuum and radioengineering ceramics [3]. Usually, refractory goods are made from various sorts of clays with the use of lime or other bonds [3, 4].In the development of new formulas for refractory bodies, an important role is played by improving the methods of checking the quality of the refractories. A large part of them in terms of electrophysical properties relate to the group of dielectrics or semiconductors. The measurements of the specific electric conductivity of refractories during research is used as a sensitive parameter of the solid-phase reactions, processes of sintering, crystallization, etc. [4].This article presents data, absent from the literature, on time-related changes in the specific electric conductivity of refractories on the basis of aqueous solutions of potassium aluminate with natural clays. We present the results of conductivity measurements on hardened specimens from the above systems during heating at 20-800~The compositions studied are used as refractory coatings for metals, and also as high-temperature adhesives.The study used Prosyanovsk kaolin, Idzhevansk bentonite, chamotte produced by the Novomoskovsk refractories factory, and a water solution of potassium aluminate with a density of 1.54 g/cm s, prepared by the method described in [5]. The mixtures were prepared by slaking from i0 to 50%* of clay with a water solution of potassium aluminate.The specific electrical conducitivity of the suspension was measured with an AC bridge (P5010) and a cell with plane-parallel electrodes (GOST 6581--75), In this case the electrical conductivity of the suspension was studied during storage for 1-30 days.The electroconductivity of hardened mixtures during heating was measured with the method described in [4]. The specimens were prepared as follows:37% clay was slaked in 63% water solution of potassium aluminate, after which the mixture was hardened at 300~ in i h in a drying chamber.Then the mixture was ground in an agate mortar to a particle size of 80-i00 ~m. The resulting mixture was manually pressed into tablets 16 mm in diameter and 1.5-2.0 mm thick. The tablets were placed between the two steel, platinized electrodes of a metering cell which was placed in the resistance furnace.The furnace was heated to the prescribed temperature and then switched off, and the volume resistance of the specimen was measured.The value of the specific electric conductivity of these systems was calculated from the well-known formula [4].The data obtained show (Fig. i) that the addition of even small amounts of clay (up to 10%) to the water solutions potassium aluminate reduces by a factor of 2-4 their specific electric conductivity; the maximum reduction in the values of u is noted in the supensions containing bentonite (by a factor of four).Further increase in the concent...
Clays and clay minerals are widely used in various industries [1][2][3][4]. The investigation of the texture and chemical changes occurring during the heating of clays and of mixtures based on them has been the subject of many articles and monographs [2][3][4][5][6][7]. Studies have been made of the processes taking place during the reaction of clays and orthophosphoric acid [4], sodium silicate glasses [5], and alkalis [6].This article provides data, absent from the literature, on the change in the porosity and morphology of compositions based on potassium aluminate and natural clays occurring during heating in the range from 20 to 1200~ Prosyanovsk kaolins were taken as the objects of the study, together with Idzhevansk bentonite and aqueous solutions of potassium aluminate with a density of 1.54 g/cm 3, prepared by the method described in [8]. The mixtures were prepared by slaking 37% clay and 63~ (mass proportions) solution of potassium aluminate, followed by setting at 550 and 1100~The study of various components of these mixtures and also mixtures of a water solution of potassium aluminate with kaolin and bentonite was carried out by the methods of electron microscopy and solution microscopy on the ]~VM-100LM and REM-200 apparatus. The texture of the specimens was studied on the Sarptomat instrument.In the electron microscopic investigations the clay and potassium aluminate specimens were predried at 105~ in a drying cupboard for 1 h, and ground in an agate mortar to a particle size of 80-100 #m. Before applying the specimens onto the subject lattice, they were dispersed by ultrasonics with a frequency of 22 kHz in isopropyl alcohol for 2 rain so as to break up the aggregates. The specimens of clay and potassium aluminate and mixtures of them were heated with a focused electron beam from the microscope [9] in order to identify the possible textures and chemical changes. The temperature in the specimen zone was determined from calibration graphs, constructed according to reference points of the phase inversions taking place mainly in copper carbonate (320~ and aluminum powder (660~ and als0 according to the reference point for the modification change y-A1203~ ~-A1203 (1200~ The morphology of kaolin consists of particles of irregular shape and of different dimensions. We can clearly see the particles of needle shape, whose lengths range from I to 10 #m (Fig. la). However, for bentonite (Fig. lb) there is a typically more clearly expressed laminated structure and a greater homogeneity in the grain-size composition. The potassium aluminate (Fig. lc) consists of particles of two forms. These are particles measuring about 10 pro, not having visible pores with the stated magnification, and particles having a needlelike structure with needle lengths of about 5 ~m and diameter 0.3 pro. The needles cover the surface of the particles from which their V-form growth takes place.For specimens of potassium aluminate and kaolin there is typically a greater dispersion of particles than for the bentonite. Thus, the average d...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.