Graphite-containing refractories have become widely used in recent years [1][2].The technical solution in the field of production of these refractories envisages special conditions for the slowing down of the carbon-oxidation process in the products: firing in a neutral or reducing medium; glazing of the articles [3]; the addition of ferrosilicon or silicon to the batch to bind the carbon as silicon carbide; additives to produce a liquid phase [4]; and so on.One of the ways of controlling the resistance of the materials to oxidation is to chemically modify the surface of the SiC powder by molecular modification of the surface [5,6].The extent of the combustion of carbon in graphite-containing refractories depends largely on the structure of the refractory and the operational temperature.The kinetics of the carbon combustion in unfired graphite-containing high-alumina articles heated from 800 to 1600~ was studied and also the character of the carbon combustion in various directions and at various distances from the surface of the articles was investigated.Specimens in the form of cylinders 25 mmindiameter and height were molded from low-and high-carbon masses* [7] using a semidry pressing method at a pressure of 40 MPa. The batch of the low-carbon articles included 15% of Polozhsk kaolin, 20% of laminar graphite, 45% of highalumina chamotte (-82% AI~03), and 20% of SI-65 ferrosilicon; the batch for the high-carbon articles contained the same components but in the following amounts, respectively: 15, 50, 15, and 20%, To i00 parts of the batch we added 8 parts each of AKPS and 4 parts of distillery waste. The specimens were dried at II0~ and heat treated at 600~ with a dwell of 4 h. One specimen each in a corundum beaker was placed in the isothermal zone of a Kryptol furnace heated to a specified temperature and in a weakly oxidizing medium.We used a mathematical method to plan the experiment: the central composite orthogonal planning (CCOP) 22 [8]. We took the following as the factors: heating temperature X~, ~ and duration of heating X2, min. The optimization parameter was the degree of combustion of the carbon, % (relative).It is well known [9, i0] that the most intense oxidation of graphite starting at 750-800~ occurs in three stages: penetration of oxygen from the air into the particles of graphite; interaction between graphite and the atmospheric oxygen in accordance with the reactions:the removal of the interaction products.In service, complex physicochemical processes of the formation of a liquid phase as well as a change in the chemical and phase compositions and in the structure of the refractory occur in unfired and fired graphite-containing refractories. These processes have a significant effect on the extent of combustion of the graphite.*The designation of the masses was arbitrary.L. I. Brezhnev Dnepropetrovsk Metallurgical Institute.
At the present time the bottoms of soaking pits are made of magnesia spinel refractories, and the walls of large concrete blocks or panels of siliceous composition. In order to speed up repairs to the bottom it is possible to line it with large panels of special design [1].The present authors (with the assistance of A. V. Ivankina) used magnesia spinel concretes [2] for lining the bottoms. The binder for the concretes consisted of aluminous cement, and the filler consisted of waste formed at the factory for beneficiating scrap magnesite alumina spinel articles from the Nikitovsk dolomite factory. The scrap consisted of crushed material impregnated with metal and slag (mainly the working zone of spent articles). It contains (average): 51.04%* MgO, 9.91170 Cr203, 3.02%A1203, 6.26% Fe203, 14.02% FeO, 2.74% CaO, 5.32% SiO 2, 6.13% Fe; calcination loss 1.15%. The grain-size composition (average) is: 0.5% 45-35 mm, 0.6% 35-30 mm, 0.3% 30-25 mm, 3.6% 25-20 mm, 33.6% 20-5 ram, 27.7% 5-1 mm, 33.7% 1-0 ram.The mechanical metal inclusions in the form of plates, rods, etc. measuring not more than 200 mm are present mainly in the scrap fractions coarser than 20 mm (2.9-8.4~); the amount of inclusions in the scrap fraction 20-5 mm equals 0.6-1.4%, and in the <5 mm fraction less than 0.1%.Petrographic studies$ established that the structure of the scrap is irregular, not uniformly fine-grained, and cracked in places (Fig. 1). The pores vary in character and in shape in different sections -closed and communicating, isometric or less regular and measuring 0.04-0.08 mm. The phase composition consists of grains of chromite, perielase, chrome spinels, and silicates. The perielase part of the specimen contains buttons of metal from 0.08 to 0.02 mm in size. The main phase is periclase in the form of large aggregate accumulations and separate grains. Close to the chromite grains the periclase is saturated with separation of magnesioferrite. The optimum water-cement ratio for the concrete based on magnesia-spine[ filler and aluminous cement equals 0.42 (Fig. 2).In order to determine the setting periods we studied the hardening kinetics of magnesia spinel concrete. For comparison, Fig. 3 shows the setting kinetics of concrete with a chamotte filler prepared by the Khristoforovsk factory. The concrete composition was: 80% scrap firebrick and 20% aluminous cement.
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.
hi@scite.ai
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.