Development and study of the compositions of unshaped fireclay-based heat-insulating refractories and a technology for making them

Abstract

Results are presented from a study of the compositions of foams for making heat-insulating refractory products with the use of a slag-alkali binder. It is shown that use of the given binder can yield materials with an ultimate compressive strength of up to 20 -22 MPa. These materials can be used as heat-insulating materials and as structural materials.With the rapid progress being made in the development of technologies that intensify thermal processes while saving energy resources, recent years have seen an increasing focus on the creation of new high-efficiency heat-insulating materials for equipment used in power generation, oil refining, and metallurgy. These materials must satisfy diverse and sometimes conflicting requirements: on the one hand, they should reduce conductive heat flow in the structures that they are being used to protect; on the other hand, they should also have structural properties which will ensure a long service life for the thermal equipment as a whole. Only by satisfying both of these needs can the optimum effect be obtained from using materials of the given type.Different bonding agents are currently being used as binders in the production of heat-insulating materials. In the view of the authors, one of the most promising trends is the use of inorganic chemical binders. This class of materials includes slag-alkali binders. The slag-alkali component increases the plastic strength of the product and allows rapid removal of the forms used to make products by foam technology. Slags with the necessary activity must be used to ensure a short turnaround time for the forms, reduce shrinkage, and ensure that the resulting thermal insulation is of high quality [1].Clay of grade LT-1from the Latnensk deposit, vibro-milled fireclay (35 -40% Al 2 O 3 ), sodium silicate, and slag from the Oskol'sk Electrometallurgical Combine (OEMK) that has undergone dry cooling in air are presently used as the raw materials. The OEMK slag is mechanically activated by crushing it in a "Sand-1" planetary ball mill equipped with 10-mm-diam. balls and rotating at a speed of roughly 200 min -1 . Fractions of slag finer than 0.315 mm are used in the production process. Data obtained from x-ray phase analysis shows that the main phase in the slag is dicalcium silicate g-2CaO·SiO 2 . The slag also contains hematite, ferrous oxide, and periclase. The clay in the Latnensk deposit is a kaolin clay and contains a negligible amount of quartz. The vibro-milled fireclay is a finely dispersed powder which consists of particles smaller than 0.315 mm and also contains mullite and crystoballite.The frothing agent that was used was "Piner-152," which is a homogeneous transparent liquid ranging in color from light yellow to brown. The agent has a density of 1000 -1200 kg/m 3 at 20 -25°C and has the pH 7.0 -10.0. The expansion ratio of the foam formed from a working solution containing 3 vol.% of the frothing agent is less than 7.0. The stability of the foam is at least 360 sec. The compositions of the foams used in the studies being d...