The effect of organosilicon and aluminophosphate binders on the physicomechanical properties of corundum-carbon refractories is studied. The environmental safety of the binders is discussed. Binders for use in sintered and nonfired components are developed.The range of refractories commercially available in Russia and around the world is exceptionally wide; oxide-carbon components constitute the major part of them. As a rule, the physical and engineering properties of oxide-carbon refractories are to a significant extent dependent on the binder. To manufacture oxide-carbon refractories, various organic resins are commonly employed, for example, phenol-formaldehyde resins of the resol-novolac type. The role of an organic-resin binder is that, during the heat treatment, the resin undergoes degradation to convert to a reinforcing carbon framework over the entire volume of the component. The active carbon thus formed takes part in the phase formation of secondary compounds (carbides or oxycarbides); this process can occur during sintering in a nonoxidazing medium, or during the service of the component.Viewed from an ecological standpoint, the use of such a binder may raise objections for the reason that it releases substances hazardous to human health and environment: phenols, cresols, xylylenes, formaldehyde, etc. [1]. To remedy the situation, the production technology should be provided with additional facilities for filtering by suction or afterburn of the species released, which increases the cost of the final product.The development of an environment-friendly binder capable of providing the useful properties of oxide-carbon refractories has been and continues to be a major challenge to technologists; still, the results so far obtained remain inconclusive. It was thought of interest to consider the potential application of a widely used aluminophosphate bond and well-known organosilicon binders in the production of oxide-carbon refractories [2, 3]. Our attention was focused on a previously studied organosilicon binder of the ÉSK series [2] and an aluminophosphate bond (APB) taken in different combinations.The ÉSK-type binder was obtained by dispersing solid polymethylphenylsiloxane resins (113-101) in a medium of ethyl silicate-40 (ÉTS-40) using, for example, a ball mill. The colloidal solution thus prepared was stable over time and, when stored in a tightly sealed container, had a shelf life of several years. To enhance the mechanical strength of the raw material (the compressive strength should not be less than 1.2 MPa [4,5]), an adhesive agent, for example, lignosulfonates, polyvinyl acetate (PVA), etc., is added to the ÉSK binder. As compared to refractory materials prepared using lignosulfonates, the use of ÉSK makes it possible to improve the mechanical strength, thermal stability and density of the components, to decrease sintering shrinkage and open porosity, to lower the sintering temperature, and to improve the resistance to attack by molten metal and slag. Expertise has been gained in using an ÉSK bin...
Silicon carbide and boron carbide are used in various fields of industry owing to their high levels of physicochemical properties and hardness.In the absence of special additives, these materials are usually sintered at elevated (2000~ and above) temperatures.The materials based on silicon carbide in which binding agents form at relatively low temperatures (1500~ with the participation of a gaseous medium (atmosphere) are finding wide application.In view of this, it was of interest to explore the possibility of using a similar technological route for boron carbide also. For this purpose, we studied the behavior of boron carbide during heat treatment in a carbonaceous particulate charge consisting of a mixture of coke and quartz sand.It is known that the gaseous phase in the C--Si02 system consists of CO, C02, and SiO [i]; besides this, the gaseous phase of the aforementioned charge contains nitrogen and traces of oxygen.The information available on the behavior of boron carbide in various gaseous media is quite limited.In the atmosphere of pure oxygen [2], oxidation of boron carbide starts at 600~ and the oxidation rate increases at 800-i000~ thereafter, it decreases and at 1200-1300~ it abruptly increases once again due to the formation of liquid B20s and its vaporization. Besides this, the formation of volatile lower oxides of boron is also possible.
REACTION-SINTERED CARBIDE-NITRIDE SYSTEMST. P. Markholiya, I. I. Kozelkova, T. M. Bragina, and L. M 9 Aksel'rod UDC 666.762.85.046.4 In order to develop high-temperature technology and to intensify metallurgical and chemical processes, it is necessary to create materials possessing high strength and wear resistance in combination with thermal shock resistance and corrosion resistance in aggressive media. In this context, composite materials containing carbides and nitrides [1-3] are important. However, it is known that obtaining the products from the high-temperature (refractory) materials according to the hot-pressing technique is costly and that pressureless sintering does not ensure the required strength levels in most cases [4, 5]. The technology of producing high-temperature materials according to the method of reaction sintering is quite promising.We studied composite materials (systems) based on boron carbide containing boron nitride and silicon carbide that were obtained in a dried and decontaminated nitrogen atmosphere (the content of the impurities was less than 3 vol.%). Table 1 shows the composition of the Nos. i-3. The base of the charge consists of amorphous boron or boron carbide. Besides these constituents, silicon and quartz glass additives were introduced into the Nos. 1 and 2 bodies. Specimens were compacted using bakelite as a temporary binder and were fired at 1450~ in a nitrogen atmosphere using a furnace available at the Semiluksk Refractories Plant 9The phase composition was controlled according to x-ray structural analysis; the analysis was carried out on a DRON-2,0 diffractometer using Cu Ks-radiation and a nickel filter. ,,,= zooo Fig. i.7590
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