• J James

      Articles written in Bulletin of Materials Science

    • Interface-durability correlations in concrete

      J James

      More Details Abstract Fulltext PDF

      The performance of concrete is dictated mostly by the characteristics of the transition zone. Internal bleeding leads to a higher effective water/cement ratio and hence a more open, porous structure at the cement/aggregate interface. Besides, more of AFt, AFm and CH phases and halides, sulphate, alkalis and other admixture components and less of C-S-H are found in this zone. These cause the deterioration of the reinforcing materials like steel, silicious aggregates, glass and natural fibres. The orientation of the crystalline phases parallel to the interface also weakens the mortar. The porosity and related effects are considerably modified by the use of plasticizers, fine pozzolanic additives and reduced water cement ratio. The mechanism of interfacial structure formation and their resulting effects on the reinforcement are discussed together with the possible precautionary measures.

    • Novel ceramic substrates for high Tc superconductors

      J Koshy J Kurian R Jose Asha M John P K Sajith J James S P Pai R Pinto

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      A group of complex perovskite oxides REBa2NbO6 (RE=La and Dy) have been synthesized and developed for their use as substrates for both YBa2Cu3O7-δ and Bi(2223) superconductors. These materials have a complex cubic perovskite (A2BB′O6) structure with lattice constants,a=8·48−8·60 Å. REBa2NbO6 did not show any phase transition in the temperature range 30–1300°C. The thermal expansion coefficient, thermal diffusivity and thermal conductivity values of REBa2NbO6 are favourable for their use as substrates for highTc superconductors. The dielectric constant and loss factor of REBa2NbO6 are in a range suitable for their use as substrates for microwave applications. Both YBa2Cu3O7-δ and Bi(2223) superconductors did not show any detectable chemical reaction with REBa2NbO6 even under extreme processing conditions. Dip coated YBa2Cu3O7-δ thick films on polycrystalline REBa2NbO6 substrate gave aTc(0) of 92 K and a current density of ∼1·1×104 A/cm2 and Bi(2223) thick film on polycrystalline REBa2NbO6 substrate gave aTc(0) of 110 K and a current density of ∼ 4×103 A/cm2 at 77 K and zero magnetic field. A laser ablated YBa2Cu3O7-δ thin film deposited on polycrystalline REBa2NbO6 substrate gave aTc(0) of 90 K and a current density of ∼5×105 A/cm2.

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