• Ashok Sharma

      Articles written in Bulletin of Materials Science

    • Supramolecular structure of S-(+)-marmesin-a linear dihydrofuranocoumarin

      Sanjeev Goswami Vivek K Gupta Ashok Sharma B D Gupta

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      The title compound, C14H14O4, a linear dihydrofuranocoumarin, was isolated from the bark of Aegle marmelos, a plant widely used in Ayurvedic system of medicine for the treatment of various ailments. The crystal structure was determined from X-ray diffraction data using direct methods. The compound crystallizes into monoclinic space group 𝑃21 with unit cell parameters: 𝑎 = 5.721(1) Å, 𝑏 = 13.810(1) Å, 𝑐 = 7.864(2) Å, 𝛽 = 100.39(1)°, 𝑍 = 2. The structure was refined by full-matrix least-squares to a final 𝑅 value of 0.0523 for 1184 observed reflections. The benzopyran moiety is perfectly planar. The dihedral angle between the pyrone and benzene rings is 0.3(1)°. The furan ring has a 2𝛼-envelope conformation. The molecules are linked by O–H…O hydrogen bonds into chains and these chains are linked into sheets by C–H…O hydrogen bonds. Further, the 𝜋−𝜋 stacking and C–H$\ldots\pi$(arene) interactions link all of the sheets into a supramolecular structure.

    • Effect of carbides on erosion resistance of 23-8-N steel

      Aniruddha A Gadhikar Ashok Sharma D B Goel C P Sharma

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      Microstructure is one of the most important parameters influencing erosion behaviour of materials. The role of carbides in the matrix is very complicated in controlling the erosion rate of the materials. Conflicting results have been reported in the literature about the effect of carbides on erosion resistance. Carbides are of great importance especially as obstacles against the penetration of erosive particles into the material surface. However, they are susceptible to cracking and causing matrix decohesion which may increase the overall erosion rate. In 23-8-N nitronic steel, carbides present in the form of bands are observed to accelerate the erosion rate. Coarse carbides cause depletion of carbon in the austenite matrix which adversely affects the strain hardening tendency thus causing deterioration in erosion resistance of the bulk material. The dissolution of carbides in the austenitic matrix after solution annealing is observed to improve the erosion resistance of 23-8-N nitronic steel.

    • Synthesis of functionalized pyrazolopyran derivatives: comparison of two-step vs. one-step vs. microwave-assisted protocol and X-ray crystallographic analysis of 6-amino-1,4-dihydro-3-methyl-4-phenylpyrano[2,3-c]pyrazole-5-carbonitrile

      Paritosh Shukla Ashok Sharma Sumati Anthal Rajni Kant

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      A library of pyrazolopyran heterocycles was synthesized first by the traditional heating techniques using two-step and one-step procedures and then by microwave-assisted (MWA) multicomponent condensation of ethyl acetoacetate, hydrazine, malonodinitrile and a variety of substituted aldehydes. A comparison of the foregoing methods was first done based on the yields and then based on the time taken for the completion of the reactions. It was found that although the traditional methods gave slightly better yields, the MWA syntheses lead to substantial reduction in reaction timings. The title compound crystallizes in the triclinic crystal system with space group P–1. The crystal structure as elucidated by X-ray diffraction methods shows the presence of different intermolecular interactions, and the nature and energetics associated with these interactions have been characterized using PIXEL software.

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