Electrochemical Corrosion and Impedance Studies of Porous Ti–xNb–Ag Alloy in Physiological Solution

Porous titanium (Ti) and its alloys are promising materials for orthopedic applications due to their low elastic modulus, high strength, excellent corrosion resistance, and biocompatibility. In this study, the porous Ti–xNb–5Ag (x = 25, 30 and 35 wt%) alloys were synthesized using the powder metallurgy approach. The effects of Nb content on the porosity, mechanical properties, and electrochemical corrosion behavior of the alloys were investigated. XRD analysis revealed that the porous alloys mainly consist of α-Ti, β-Ti, intermetallic compound (Ti₄Nb), and oxides of TiO₂ and NbO phases. Porous alloys possess the porosity ranging from 57 to 65%, due to the addition of NH₄HCO₃ (45 wt%). Increase in Nb content lead to a reduction in the elastic modulus and compression strengths of the sintered porous Ti–xNb–5Ag alloys. All three developed porous Ti–xNb–5Ag alloys show the optimum combination of elastic modulus and compression strength, which is suitable for orthopedic applications. These porous alloys exhibit excellent electrochemical corrosion resistance in the simulated body fluids, and the samples having low porosity exhibit higher corrosion resistance than high-porosity samples.

     

Defect centres and thermoluminescence in CaSO4:Dy,Ag phosphor

The defect centres formed in the TL phosphor CaSO4:Dy,Ag are studied using the technique of Electron Spin Resonance. The Ag co-doped phosphor exhibits three glow peaks around 130, 220 and 375 degrees C in contrast with the two glow peaks observed in the CaSO4:Dy phosphor at 130 and 220 degrees C at a gamma ray dose of 1Gy. ESR studies show that the additional peak at 375 degrees C correlates with a Ag2+ centre formed due to gamma irradiation and observable only below -170 degrees C. The Ag2+ centre is characterised by an axial g-tensor with principal values g(parallel) = 2.38 and g(perpendicular) = 2.41. ESR studies further indicate that the precursor to a centre observable at low temperature (-170 degrees C) appears to act as the recombination centre for the TL peak at 375 degrees C; this radical is characterised by the g-values g(parallel) = 2.0023 and g(perpendicular) = 2.0038 and is assigned to SO3- radical. It is observed that there is more incorporation of Ag in the CaSO4:Dy system as compared with that in pure CaSO4 system.     

Solid state chemistry of Ruddlesden-Popper type complex oxides

Various criteria of formation of perovskites and K₂NiF₄-type compounds, which are the end members of homologous Ruddlesden-Popper series of phases, have been discussed. RP-phases show some general trends in their physical properties. Literature survey of the formation of these phases, their properties, and effect of oxygen stoichiometry and doping is presented. Some conditions for their synthesis are also described.     

Liquid chromatographic separation of some PTH-amino acids

Liquid chromatographic studies on the separation of ten PTH-amino acids were carried out using normal phase untreated silica gel plates, C-18 RP precoated plates and RP-HPLC. Resolution of a complex mixture of PTH-amino acids was achieved using all the three types. Certain new successful solvent systems have been worked out in each case. HPLC was carried out with Lichrosphere 100 RP-18 (5 microns) column. Acetonitrile and sodium acetate buffer of pH 4.0 was used for reversed phase chromatography while for normal phase TLC combinations of chloroform-acetonitrile and chloroform-tetrahydrofuran were applied.     

Mechanical property and dimensional stability of substrates for magnetic tapes

We have performed a comparative study on mechanical property and dimensional stability of substrates for magnetic tapes. The substrates include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and aromatic polyamide (ARAMID), which could be used for linear-type magnetic tapes for computer data storage. We have demonstrated that ARAMID is the most attractive substrate and that PET has the advantage of considerably smaller irreversible creep deformation and lateral contraction caused by tension as compared to PEN film. In this paper, we also introduce recently developed PET (Advanced PET) with higher glass transition temperature compared to conventional PET; moreover, we discuss the relationship between film properties and polymeric structures of these substrates.     

Photoconductivity of chemically deposited rare-earth-doped CdS films

Highly photosensitive films with photocurrent to dark current ratios of the order of 10⁵ have been prepared by doping CdS with Nd and Pr. The conditions for preparing such films with different fluxes are described and results of excitation spectra, transmission spectra and rise-decay curves are presented. Values of trap depths are also calculated.     

Improved Endurance Limit of Zirconia Ceramics by Overloading

The influence of initial overloads upon the subsequent fatigue crack growth in transformation-toughened ceramics (TTCs) is investigated. It is revealed that initial overloading can be beneficial to these ceramics. In particular, it is shown that an overload will facilitate crack arrest in a low transformation strength material which would otherwise be prone to cyclic fatigue degradation and eventual failure. Based on the results of this investigation, a proof test may be designed to screen out TTC components which do not attain a prescribed endurance limit.