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  • Author: A. Gokhale, x
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Abstract

Pure niobium metal, produced by alumino-thermic reduction of niobium oxide, contains various impurities which need to be reduced to acceptable levels to obtain aerospace grade purity. In the present work, an attempt has been made to refine niobium metals by electron beam drip melting technique to achieve purity confirming to the ASTM standard. Input power to the electron gun and melt rate were varied to observe their combined effect on extend of refining and loss of niobium. Electron beam (EB) melting is shown to reduce alkali metals, trace elements and interstitial impurities well below the specified limits. The reduction in the impurities during EB melting is attributed to evaporation and degassing due to the combined effect of high vacuum and high melt surface temperature. The % removal of interstitial impurities is essentially a function of melt rate and input power. As the melt rate decreases or input power increases, the impurity levels in the solidified niobium ingot decrease. The EB refining process is also accompanied by considerable amount of niobium loss, which is attributed to evaporation of pure niobium and niobium sub-oxide. Like other impurities, Nb loss increases with decreasing melt rate or increase in input power.

Abstract

The individual and combined effects of W and Zr additions on macrostructure, microstructure and mechanical properties of Nb have been investigated. Nb, Nb-10 wt% W, Nb-2.5 wt% Zr and Nb-10 wt% W-2.5 wt% Zr alloy ingots were prepared by electron beam drip melting using high purity Nb, W and Zr rods. Additions of W and Zr resulted in significant improvement in hardness and room temperature tensile strength. It is seen that the effect of 10 wt% W addition is more than that of 2.5 wt% Zr addition in improving room temperature strength of Nb, although on ‘per wt% addition’ basis, Zr is a more effective strengthener than W. It is also observed that the cumulative effects of 10 wt% W and 2.5 wt% Zr on grain refinement and strengthening are more than their respective individual effects.

Abstract

Passion fruit (Passiflora edulis flavicarpa) is a seasonal, tropical, pulpy fruit, known for a rich source of Vitamin C, antioxidants, and delicate flavor. Presently, freezing technique has been used to preserve the pulp. This article reports alternate method of preservation by foam mat convective air drying of fruit pulp under moderate temperatures. The optimization of process parameters, particularly air temperature, was done with subsequent mathematical modeling of the process and assessment of quality parameters by retention of physicochemical properties and antioxidant capacity of the fruit powder. Sixty degree Celsius was found to be the optimum temperature, and Henderson and Pabis model showed best fit to the drying characteristics data (R2 = 0.99). Diffusivity characteristics of moisture during drying were also studied. As drying temperature was increased, total color difference and rehydration ratio decreased, whereas non-enzymatic browning index, total phenolic content, and total antioxidant activity showed increase that was attributed to inhibition of oxidative enzymes and biochemical changes. Dried passion fruit powder showed overall acceptability in terms of organoleptic properties and total antioxidant activity.