Treatment of Graphite for Oxidation Resistant Mag-Carbon Refractories

Abstract

Graphite has extraordinary properties, viz. high corrosion resistance against liquid metals and slag s, good spalling resistance and impact on reduction of porosity and finer pore size distribution in oxides -carbon composite refractories. However, it has poor oxidation resistance which restricts its use i n pyrometallurgical operation and gives poor campaign life. Different antioxidants such as Al, Si, Al/M g, B 4 C, SiC, etc have been used in commercial production of carbon bearing composite refractories for improvement of their oxidation resistance. Coating of graphite with oxides such as Al 2 O 3 , SiO 2 , TiO 2 , ZrO 2 , etc has been the recent trend of R & D work to improve the oxidation resistance of graphite in composite refractories. In the present investigation, graphite powders have been coated with MagnesioAluminate Hydrate (M AH). The coated powders were characterized by TGA/DTGA, DTA and calcinations at 1000°C to study their oxidation loss. Liquid resin was also specially treated with M AH. Both MAH treated graphite and resin were used to make M gO-C composites. Present work reveals remarkable improvement of oxidation resistance of both graphite and M gO-C composites when graphite powders were coated with M AH. IntroductionGraphite has excellent refractory properties that include its non-wetting behaviour and high chemical inertness against liquid metal and slag, extreme low value of coefficient of linear expansion and high mechanical strength at elevated temperatures. Combined refractory properties of oxide and graphite make oxide-graphite composite refractories more corrosion resistant and spalling resistant in pyrometallurgical applications. Among oxide-graphite refractories, MgO-C refractories are the most suitable in steel melting processes, particularly in converter lining.The wear mechanism of MgO-C refractories is caused due to the following reasons : a) Oxidation of carbon that is also classified as oxidation of O 2 and CO 2 in ambient gas (gas phase oxidation) and oxidation by iron oxides in slag (liquid phase oxidation). b) Dissolution of MgO aggregates by slag. It is dependent on the crystal size and purity of the aggregates, nature of impurities and their distribution as mineral phases in the aggregates. c) Oxidation-reduction reaction between the brick components (i.e. MgO and carbon at high temperatures near hot face of the bricks), which causes structural degradation. d) Physical properties of composite bricks, such as brick porosity during use (i.e. coked porosity), its pore size distribution, hot strength, etc. e) Mechanical stress during use.

Electrochemical aspects of coinage metal nanoparticles for catalysis and spectroscopy

“… 27 The simple photochemical method is another reproducible technique. 28 Eventually, metal colloids, i.e. , MNPs, often behave as a microelectrode without a connection to the battery.…”

“…The evolved Au nanoparticles have application for the determination of cyanide ions, avoiding the aggregation of the Au particles in solution. 28 …”

“…48 Similar manipulation has been elaborated from the galvanic replacement reaction to obtain a ‘hollow core–shell’ structure over time. 28,55 In catalysis, when larger gold particles are needed, a gold-coated base metal can be used. The chemical and physical properties of the nanoparticles can be tuned by using the core–shell structure.…”

“…27 The simple photochemical method is another reproducible technique. 28 Eventually, metal colloids, i.e., MNPs, oen behave as a microelectrode without a connection to the battery. These MNPs can then transfer electrons for a chemical reaction with or without illumination.…”