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Chikhradze N.,Mining Institute of Georgia | Politis C.,University of Patras | Henein H.,University of Alberta | Bokuchava G.,I. Vekua Sukhumi Institute Physics and Technology | And 2 more authors.
Proceedings of the World Powder Metallurgy Congress and Exhibition, World PM 2010 | Year: 2010

Pure nano sized (50nm) Si and ultra-disperse Si0.68Ge0.32 powders were consolidated to full or near-full density by shock-compaction technology. To form ultra-fine grained bulk Si and Si0.68Ge0.32 compacts, the nano-Si, coarse-Si and ultra-disperse Si0.68Ge0.32 particles were placed in a sealed container and explosively compacted using a standard cylindrical detonation set-up. Ammonium nitride based industrial explosives were used for the generation of shock waves. Explosive compaction experiments were performed over a range of pressure impulses of 5-20 GPA at elevated temperatures. This process occurs in a combination of two stages. The first is the preliminary application of a static pressure to a container with pure elemental Si and Si0.68Ge0.32 powder, and is followed by the second stage, shock-wave compaction (SC). X-ray diffraction (XRD), microstructural investigations and micro-hardness measurements were used to characterize the composition and mechanical properties of the consolidated compacts. The relationships between the compacting conditions, the precursor particle sizes, and the consolidation and properties of this new ultra high performance alloy are discussed. Source


Metskhvarishvili I.R.,I. Vekua Sukhumi Institute Physics and Technology | Dgebuadze G.N.,I. Vekua Sukhumi Institute Physics and Technology | Bendeliani B.G.,I. Vekua Sukhumi Institute Physics and Technology | Lobzhanidze T.E.,Tbilisi State University | And 2 more authors.
Journal of Physics: Conference Series | Year: 2014

We report the effects of the addition of Sb2O3 on the superconducting properties of Bi-2223 system. Samples with composition Bi 1.7Pb0.3Ca2Sr2Cu3Sb xOy (x=0,0-0.8 wt.%) are prepared by the solid-state reaction method. Ac susceptibility and high harmonic response of polycrystalline superconductors are measured in weak ac and dc magnetic fields. Critical state models are used to explain the nonlinear magnetic response and it is found that the low field odd harmonic response is qualitatively explained reasonably well within the Kim-Anderson regime. We observed that, the low level Antimony doping enhances the transport critical current densities Jc. © Published under licence by IOP Publishing Ltd. Source


Bokuchava G.V.,I. Vekua Sukhumi Institute Physics and Technology | Sanaia E.E.,I. Vekua Sukhumi Institute Physics and Technology | Barbaqadze K.G.,I. Vekua Sukhumi Institute Physics and Technology | Chedia R.V.,I. Vekua Sukhumi Institute Physics and Technology
Euro PM 2014 Congress and Exhibition, Proceedings | Year: 2014

Magnesium diboride bulk superconductor samples (targets) with a >50 mm diameter have been obtained in an induction furnace using hot pressing and spark-plasma synthesis methods. These methods enable to obtain small-diameter (up to <10 mm) samples without any difficulties by gradual temperature increase 20-1050°C. The samples with an increased diameter (>50 mm) reveal a number of problems. Despite the fact that big-diameter samples' phase content is like that of small ones, their porosity is increased and 45-50 % of the obtained samples produce macro cracks, and in some cases the samples may be completely destroyed. Bulk samples were obtained in optimal condition at 600-1050°C in induction furnace. The samples' Tc = 38.5-39K. Source


Metskhvarishvili I.R.,I. Vekua Sukhumi Institute Physics and Technology | Dgebuadze G.N.,I. Vekua Sukhumi Institute Physics and Technology | Bendeliani B.G.,I. Vekua Sukhumi Institute Physics and Technology | Metskhvarishvili M.R.,Georgian Technical University | And 2 more authors.
Journal of Superconductivity and Novel Magnetism | Year: 2015

We have studied harmonic generation in the ultra-weak magnetic fields of bulk sample of the HgBa2Ca 2Cu 3O8+δpolycrystalline superconductor. Dependence of the odd and even harmonics on the dc magnetic field, amplitude of the ac magnetic field, and the temperature was investigated. We observe very high-order odd harmonics generation when H=0. When dc field H≠0 is applied, even harmonics also appear and shape of the odd harmonics does not change. Our experiments show that the amplitudes of the odd harmonics squarely depend on the magnitude of the dc field. Numerical results of our experiments have demonstrated that the Jc=Jc(0)HO2/H+HO2/(H+H20)$ critical-state theoretical model is preferable for investigating the sample. © 2014, Springer Science+Business Media New York. Source


Margiani N.G.,Georgian Technical University | Metskhvarishvili I.R.,I. Vekua Sukhumi Institute Physics and Technology | Adamia Z.A.,Tbilisi State University | Medoidze T.D.,Georgian Technical University | And 3 more authors.
Journal of Superconductivity and Novel Magnetism | Year: 2013

The influence of addition of lead borate Pb(BO2)2 and boron oxide B2O3 on the phase evolution and superconducting properties of (Bi, Pb)-2223 HTSs synthesized by the solid-state reaction method in alumina crucibles has been studied. X-ray diffraction, resistivity, critical current density, and AC susceptibility measurements were performed on the prepared compounds. Obtained results have shown that boron-containing dopants lead to the drastic enhancement of the (Bi, Pb)-2223 phase formation. Boron-doped samples reveal a significant increase in both the zero resistivity temperature and transport critical current density compared to the undoped specimen. On the other hand, a high content of boron-containing dopants causes the appearance of a very low-Tc 2201 phase and leads to a deterioration of coupling between superconducting grain boundaries. Obtained results could enable us to develop a cheap and energy efficient fabrication technology for nearly single (Bi, Pb)-2223 phase superconducting materials via heat treatment of boron-incorporated precursors in an alumina crucibles. © 2012 Springer Science+Business Media New York. Source

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