Obtaining Silicon-Carbide-Based Ceramics from Ash and Slag Wastes
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ing Silicon-Carbide-Based Ceramics from Ash and Slag Wastes A. Ya. Paka*, V. E. Gubina, and G. Ya. Mamontova a
Tomsk Polytechnic University, Tomsk, 634050 Russia *e-mail: [email protected]
Received March 23, 2020; revised April 13, 2020; accepted April 13, 2020
Abstract—The possibility of obtaining solid silicon-carbide-based ceramics from ash and slag wastes (ASWs) is demonstrated. The technological process contains three stages: (i) nonvacuum processing of the initial ASWs in dc arc discharge carbon plasma under normal atmospheric condition, (ii) cleaning of the obtained powdered material from unbound carbon by annealing in atmospheric furnace, and (iii) final spark plasma sintering of the powder. Analytical data indicate that the obtained product is a silicon-carbide-based ceramics with a density of 3.05 g/cm3 and a hardness of up to 19.9 GPa. Keywords: silicon carbide, electric-arc synthesis, nonvacuum method, spark plasma sintering. DOI: 10.1134/S1063785020070226
Disposal of ash and slag wastes (ASWs) resulting from the combustion of natural coals is among the main ecological problems related to power engineering [1], which has been the subject of much research across the world [1, 2]. In view of the broad range of accessible temperatures, plasma methods of waste processing are highly promising, although the R&D basis is as of yet insufficient for their wide implementation [3]. The main tasks in the development of plasma processing technology for hardly disposable wastes include the need to simplify plasma reactors, increasing their energy efficiency, and the search for methods of obtaining appropriate materials as a result of plasma processing [4, 5]. Possible solutions can be based on using methods of waste processing at atmospheric pressure [6] and obtaining products in the form of solid (mostly oxide) ceramics based on silicon and aluminum [7, 8]. This Letter presents results of experimental investigations devoted to the synthesis of silicon-carbidebased ceramics from ASWs of natural coal combustion processed in dc arc discharge carbon plasma under normal atmospheric conditions. To the best of our knowledge, the possible implementation of this approach to ASW disposal has not been reported in the literature before. In preparing this series of experiments, ASWs of natural coal combustion were first ground in a ball mill for 30 min. The obtained powder (0.5 g) was charged into a hollow graphite cathode and processed by nonvacuum method in dc arc discharge plasma [9]. This process is based on the phenomenon of reaction volume screening from atmospheric oxygen during
intense generation of carbon oxides and dioxides in dc arc discharge under normal atmospheric conditions [9–11]. This approach significantly reduces the amount of consumed energy, simplifies the reactor design, and increases the product yield [9–11]. Experiments were carried out at a discharge circuit current within 190–200 A for 30 s, which corresponded to a deposited energy of ~158 kJ at an average discharge power of ~5.1 kW. This series of exper
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