The work of our company on new binders for refractory materials has been carried out with the aim of reducing their production costs, primarily reducing energy costs, shortening the time for preparing mold materials for operating conditions, and increasing the application temperature of these materials.
We have mainly worked on binders for monolithic refractory materials, especially for cement-free refractory materials, in order to shorten the time of heat treatment of concrete before commissioning. This is a natural desire of both refractory manufacturers and their consumers.
It is known that the monolithic lining of thermal units, especially those where the lining works directly in contact with liquid metal, requires a very mild and long heating regime to prevent the destruction of the lining during the dehydration of cement and to reduce the effect of polymorphic transformations during heating. For this reason, the time of heat treatment of monolithic linings on a cement binder is more than 70 hours, and the thicker the lining, the longer this process takes. In addition, the energy consumption for the production of cement itself is quite high, and its production requires a large amount of natural gas and accordingly additional carbon dioxide emissions into the atmosphere. These factors prompted us to search for alternative binder types for the production of refractory materials and technical ceramics.
During the work, various types of binders were tested, but none of them fully met our tasks – some of them reduced the operating temperature of refractory materials, while others were excluded by us as harmful components for health and the environment.
The 2D-S binder developed by our company proved to be the material that can withstand not only high temperature loads, but also has two properties for which this work was started, namely, that with its use we obtained a product from which the temperature rise rate during heating of a monolithic lining can reach over 300 degrees per hour and the second quality – the work of the aggregate with such a binder increases by at least 150 degrees compared to the cement binder and practically reaches the softening temperature of the original aggregate. This binder allows operating the lining for 15-20 hours at maximum temperatures without fear of its destruction.
In other words, we have obtained a binder that provides maximum thermal loads for all refractory aggregates, except for aggregates containing free oxides of alkaline earth oxides.
That is, this is a fairly wide range of aggregates, containing corundum and aluminum silicate, as well as silicon carbide and zirconium oxide.
As for clay-containing aggregates, our binder for this type of materials has proven to be one of the few types of binders that allow the production of cement-free concretes or, as they are also called, two-component concretes. There are a number of advantages of our binder over analogues, but in this article we do not want to focus on them.
I would like to address the more problematic refractory materials of the AZS system: Refractory products from oxides of zirconium, aluminum, and silicon represent a special family of refractory materials used in glass furnaces, and these refractory materials are unique today. The refractory materials of this system are mainly produced by melting the listed oxides, which accordingly requires a significant power consumption, and additionally, the melted casting products are subjected to a heat treatment process to relieve internal stresses in these products.
Attempts to produce a monolithic lining or concretes based on these three oxides in the AZS system were unsuccessful. The main reason is the presence of calcium oxide in cement, which, when interacting with silicon oxide in the presence of aluminum oxide or, worse still, in the presence of potassium and sodium oxides, quickly destroys the lining of a glass melting furnace.
The same effect of lining destruction, but according to a different scenario, occurs with the refractory materials of this system in furnaces producing cement clinker.
Our company conducted research with the aim of using 2D-S binder as a binder for the production of cement-free concrete from aggregates of the AZS system.
Concrete samples were made and tested not only from purely melted materials of this system but also from materials that passed service and recycling modes.
Without going into details of these studies, in which, in addition to our binder, binders of other compositions, including those of well-known manufacturers, were tested, results were obtained that not only showed similar properties compared to melt-cast refractory materials but also surpassed conventional products of the AZS system in a number of indicators. This applies to properties such as heat resistance and mechanical strength. Thermal resistance, expressed in thermal air cycles, exceeded 50 thermal cycles, and compressive strength after heat treatment at 1200°C is more than 110 MPa. The open porosity does not exceed 10%, and what is very important, the size of open pores is on average 3-5 micrometers. This prevents the glass from penetrating into the pores and thereby destroying the working layer of the lining.
In interaction with melts of window and bottle glass, the results of the chemical resistance of refractory concrete on our binder and melt-cast refractory masses are practically the same. Also, the temperature of the onset of deformation under load remained the same.
Thus, the advantage of using 2D-S binder over AZS melt-cast refractory materials is particularly noticeable when it comes not only to the quality of the material but also to the cost of its production. Essentially, in addition to our binder, we use two to three types of aggregates, mostly recycled.
A significant reduction in energy consumption for the production of such products without reducing quality can be the decisive factor for the use of this technology in the production of cement-free concrete or products based on our proposed technology using 2D-S binder.
With this binder, it is also possible to produce cement-free concretes based on a system of two oxides – aluminum oxide and zirconium oxide.
It is characteristic that products with Bacor composition (Al2O3 and ZrO2), produced using traditional slip technology, require long-term firing at temperatures above 1500°C, which also affects excessive consumption of natural gas. Finally, I would like to mention some peculiarities of the 2D-S binder, as it requires certain measures for its application.
As mentioned above, the aggregate should not contain free oxides of alkaline earth metals such as CaO and MgO. The content of bound oxides of this group should not exceed 17 wt.%. This binder gains strength when moisture is removed or when it is heated to a temperature above 1100°C. After removing the water contained in the binder, the lining can be heated at the maximum possible speed or at the speed required for the thermal unit.