The oxidation resistance of Ti-Al intermetallics is superior to many of their counterparts at high temperatures. High-temperature stability of these intermetallics appears to improve with a ternary alloying addition such as Mo, Nb, etc. A detailed analysis of oxidation of the Ti 3 Al intermetallics, Ti 3 Al-2.9 at. pct Mo and Ti 3 Al-1.1 at. pct Nb, in pure oxygen using crystallographic and microscopic techniques is presented here. The alloy containing 1.1 at. pct Nb did not show an improvement in oxidation resistance over the base alloy but that containing 2.9 at. pct Mo showed marked resistance to oxidation. Activation energies of oxidation for both the alloys were comparable with those reported in the literature for similar compositions. TiO 2 and Al 2 O 3 were the major phases present in the oxide scales of the oxidized alloys. The crystal orientations from the X-ray diffraction (XRD) patterns and the morphologies from scanning electron microscopy (SEM) were in good agreement and were helpful in further analysis of the oxidation process. The effective diffusion of oxygen in the oxide layers was calculated using the mole fraction of individual oxide and the diffusivity of oxygen in pure oxide. The activation energy for the effective diffusion of oxygen through the oxide layers was determined to bẽ 24 kJ/mol. The activation energy for the oxidation process was higher than that of the diffusion of oxygen. Hence, it can be concluded that the oxidation process in both the alloys studied is not diffusion controlled.
Synthesis of titanium diboride has been carried out using thermal plasma processing technique. Thermodynamic simulations have been carried out to determine the molar ratio of the reducing gas to be used in TiO 2 -B 2 O 3 -CH 4 system. The reducing gas used was methane and the molar ratio of reducing gas to that of the solid feed was varied between 4 and 7. The maximum yield of TiB 2 of about 40 mol% was obtained with a feed molar ratio of TiO 2 W B 2 O 3 W CH 4 D 1 W 1 W 5 and a power of 23.4 kW. Relatively higher solid feed rates (5:367 10 5 kg=s instead of 3:583 10 5 kg=s) increased the yield of TiB 2 . The TiB 2 spherical particles formed are in the range of 20-100 10 9 m. A change in crystal structure was observed in TiO 2 from anatase to rutile. The formation and amounts of product powders are discussed and compared with theoretical calculations.
Overview energy conservationHow would you… …describe the overall signifi cance of this paper? The properties of nanomaterials change with the change in their particle size. The extent of this change will determine its function as a potential choice of material in various applications including renewable energy applications. …describe this work to a materials science and engineering professional with no experience in your technical specialty? Structure determines properties. For a particular structure with excellent properties, size could be a deteriorating factor. The properties in macro and micro scales are different from the properties measured in the nano scale. The nanomaterials have high surface energy and low melting point, just to name a few. …describe this work to a layperson? Ice dissolves in water. Under same conditions, ice with smaller size will dissolve faster in the same in the quantity of water. Sugar melting to form a syrup is a similar case. Smaller particles melt faster. The same analogy can be used to explain the melting temperatures of elements. In very small dimensions the surface energy increases, while the melting point decreases.
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