K. Salama

University of Houston, Houston, TX, United States

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Publications (226)357.15 Total impact

  • S. Ghalsasi, G. Majkic, K. Salama
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    ABSTRACT: We present results of a study aimed at understanding the formation of BaZrO<sub>3</sub> (BZO) precipitates in YBCO using the TFA-MOD process, as well as optimizing the BZO concentration with respect to the flux pinning performance. A reference YBCO sample containing no BZO, as well as three samples containing 4, 5 and 6% BZO were made and characterized with respect to in-field critical current ( IC ) performance and angular field IC dependence. Furthermore, the samples were analysed using transmission electron microscopy to identify the morphology of pinning precipitates and correlate it to the flux pinning behavior. The introduction of BZO does not result in formation of c-axis peaks in the angular field IC behavior, but rather in considerable widening of the ab-plane peaks in the field angular IC behavior with increasing BZO content, as well as in decreased field-angular anisotropy of IC . This behavior is analysed and correlated to the underlying microstructure of pinning precipitates.
    IEEE Transactions on Applied Superconductivity 07/2011; · 1.20 Impact Factor
  • V. Selvamanickam, K. Salama
    MRS Online Proceeding Library 01/2011; 169.
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    ABSTRACT: We present a method for spark plasma sintering (SPS) with reduced thermal and electrical losses compared to all-graphite SPS. Relative to the all-graphite configuration, the present design significantly reduces both the required power input and total current for the same synthesis temperature (e.g., 7.5 vs 0.6 kW and 1530 vs 350 A at 900 oC). These reductions allow for significantly smaller power source and process chamber, drastic reduction in energy consumption, easier thermal management, and enhanced synthesis/homogenization by eliminating die “leakage” currents, allowing for maximization of current density and its intrinsic effect on homogenization by diffusion. A finite element (FE) model solution for temperature and current distributions, as well as thermal losses for both the present and the all-graphite SPS setups, is presented and compared to experimental results.
    Metallurgical and Materials Transactions A 10/2009; 40(10):2401-2409. · 1.73 Impact Factor
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    ABSTRACT: This paper describes a promising route to introduce columnar defects into YBCO films by chemical doping process. A series of Y<sub>2</sub>O<sub>3</sub> and BaZrO<sub>3</sub> doped YBCO films were fabricated by a TFA_MOD process. The J<sub>c</sub> of Y<sub>2</sub>O<sub>3</sub> doped YBCO film was found to be larger than that of pure YBCO film at all fields though no columnar defects were observed. On the other hand, high density nanoscale Zr enriched columnar defects were successfully achieved in Zr-doped YBCO. The size of these defects was as small as 10 nm. Effects of heat treatment temperatures (760<sup>deg</sup>C ~ 820<sup>deg</sup>C), dwell times (0.5 h ~ 3 h) and partial pressures of oxygen (0 ~ 1%) on defects formation in BaZrO<sub>3</sub> doped YBCO were investigated. It was found that the formation of columnar defects depends on process conditions. Films with such nanoscale columnar defects exhibited a significant enhancement of J<sub>c</sub> at all fields. Maximum pinning force density exceeding 8 GN m<sup>-3</sup> was obtained in 5% BZO-doped YBCO films.
    IEEE Transactions on Applied Superconductivity 07/2009; · 1.20 Impact Factor
  • Source
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    ABSTRACT: Ti-sheathed MgB<sub>2</sub> wires doped with different amount of TiC nanoparticles were investigated. X-ray diffraction pattern suggested the existence of TiC<sub>0.59</sub> phase and carbon incorporation into MgB<sub>2</sub> lattice to form Mg(B<sub>1-x</sub>C<sub>x</sub>)<sub>2</sub>. Strong enhancement of in-field current carrying capability was observed on 2.5% TiC doped sample. The temperature effect was also studied. It was found that 850<sup>deg</sup>C was the optimized annealing temperature.
    IEEE Transactions on Applied Superconductivity 07/2009; · 1.20 Impact Factor
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    ABSTRACT: In order for superconducting coil applications to operate safely at high current densities, thermal stability of the wire must be addressed in terms of quench development and protection. In this study, we investigate quench propagation in stacks of commercially available MgB<sub>2</sub> superconducting wire taking into account both longitudinal heat transfer along the wire and transverse heat transfer across the insulation to adjacent wire segments. We present a two-dimensional Finite Element Method model, to simulate quench propagation. Wires and insulation layers are explicitly modeled as separate subdomains, where the wire domain takes into account the composite nature of these tapes. We report results for Minimum Quench Energy and Quench Propagation Velocity as a function of operating temperature and applied magnetic field. We also present a comparison of the behavior of the present model to alternative formulations where layers of tape and insulation are treated as a homogeneous single domain with lumped properties.
    IEEE Transactions on Applied Superconductivity 07/2009; · 1.20 Impact Factor
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    ABSTRACT: We analyze the effect of Mn addition to Gd-substituted YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-delta</sub>(YBCO) on transport current and behavior under applied magnetic field. The high-temperature superconducting tapes were manufactured by ion-beam assisted deposition and metal organic chemical vapor deposition on hastelloy substrates. The field dependence measurements as a function of Mn concentration were performed in applied magnetic fields up to 1.5 T at 77 K. The dependence of critical current on the field angle was measured in the plane perpendicular to the sample longitudinal axis (current axis). The effect of Mn concentration on critical temperature is also reported. The results are characterized and discussed.
    IEEE Transactions on Applied Superconductivity 07/2009; · 1.20 Impact Factor
  • Source
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    ABSTRACT: The effects of thermal neutron irradiation and excess oxygen on the properties of Ti-sheathed MgB<sub>2</sub> wires were investigated separately in this paper. No significant influence was observed when thermal neutron irradiation with fluence levels of 1.23 times 10<sup>14</sup> and 5.75 times 10<sup>14</sup> cm<sup>-2</sup> were applied on the sample, while fluence level of 3.16 times 10<sup>15</sup> cm<sup>-2</sup> provided a strong suppression of in-field critical current density. Excess oxygen in sample preparation process had negative effect on the properties of the MgB<sub>2</sub> wires. The samples prepared in air possessed lower critical temperature and in-field current carrying capability in comparison with the sample prepared in glove box.
    IEEE Transactions on Applied Superconductivity 07/2009; · 1.20 Impact Factor
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    ABSTRACT: Fabrication of thick YBa<sub>2</sub>Cu<sub>3</sub>O<sub>y</sub> (YBCO) films with high critical current densities(J<sub>c</sub>) has remained one of the major challenges in the coated conductor development process. In this work, we report successful fabrication of several multi-layer YBCO films with thicknesses ranging from 0.1 micrometers to 1.2 micrometers. The films were deposited on a single crystal substrate by using a multi-layer TFA-MOD technique. The effect of variation in the thickness of an individual layer in a multi-layer film on the overall properties of the film was studied by processing multi-layer films with individual layers of 0.1 micrometers, 0.2 micrometers and 0.5 micrometers. The J<sub>c</sub> value for the 0.1 micrometers thick single-layer film was as high as 7 MA/cm<sup>2</sup>, and the J<sub>c</sub> for 6-layer1.2 micrometers thick film was 1 MA/cm<sup>2</sup> at 77 K and self field. XRD, SEM and TEM were used to study the dependence of J<sub>c</sub> on the orientation, texture and microstructure of the film. It was found that the texture, connections between the two successive layers, porosity, and the crack formation affect the J<sub>c</sub> of the film. In addition, we report a multi layer fabrication route with a shorter duration of the pyrolysis reaction according to the number of coats.
    IEEE Transactions on Applied Superconductivity 07/2009; · 1.20 Impact Factor
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    ABSTRACT: Combined twist and tensile loading states are expected in many applications of YBCO coated conductors. Wire twist is introduced due to winding on complex shapes or for AC loss reduction, while tensile loading originates from sources such as differential thermal expansion and inertial forces. In this study, we analyse the electromechanical behavior of an IBAD/MOCVD YBCO coated conductor configuration with the superconducting layer deposited on hastelloy substrate and encapsulated by copper. The effect of pre-applied twist on degradation of current carrying capability as a function of tensile stress was studied via experimental measurements on tapes with 1 micron thick YBCO layer and 50 micron thick hastelloy substrate at 77 K. In addition, the stress states under pure torsion are modeled using continuum mechanics. Both numerical and approximate analytical solutions are presented, and the stress and strain distributions as a function of applied twist angle are analysed.
    IEEE Transactions on Applied Superconductivity 07/2009; · 1.20 Impact Factor
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    ABSTRACT: The thermal stability of superconducting wires is one of the important issues for wire applications. We present a numerical study on the effect of the wire design parameters on the quench behavior of superconducting MgB2 wire employed in coils. The model considers a stack of MgB2 wires of rectangular cross section separated by insulation layers and subjected to a thermal disturbance. The problem is solved on a two-dimensional domain and employs the current sharing concept in the transition between superconducting and normal states. The effects of three design parameters in wire manufacturing are investigated. Quench behavior is compared for wires having different filling factor of superconducting filaments, different volume of copper stabilizer, and different residual resistivity ratio (RRR) values for copper. The results indicate that the quench propagation velocity (QPV) at 1.5 T is weakly affected by changes in the volume and electrical properties of copper, whereas the minimum quench energy (MQE) is strongly dependent on the RRR value of copper and can increase by a factor of nearly 2 with the RRR varying from 30 to 150. Both the MQE and QPV change remarkably by varying the MgB2 filling factor. The MQE drops by a factor of 6 and the QPV increases by a factor of 2 with the filling factor varying from 10.5% to 25%.
    Superconductor Science and Technology 02/2009; 22(3):034021. · 2.76 Impact Factor
  • P.T. Putman, K. Salama
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    ABSTRACT: In a coaxial magnetic brake, the changing field produced by movement of a solenoidal magnet induces a current in the wall of a conductive tube. The interaction of the field and current leads to a repulsive force that slows the motion of the magnet. We have tested the performance of this type of brake by firing a projectile carrying a permanent magnet into an aluminum tube. The results were compared to a model based on published theoretical results. The model was then used to predict braking distance for speeds and masses of interest in hypervelocity research, and it was found that brakes incorporating presently available superconducting materials are capable of stopping projectiles in practical distances. In addition, a new means of centering the projectile in the catch tube is presented, accompanied by a calculation of the centering force on the projectile, and high-speed photographs showing the alignment of a projectile with the brake tube.
    IEEE Transactions on Magnetics 02/2009; · 1.42 Impact Factor
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    ABSTRACT: The authors regret that text in sections 1 (Introduction) and 2 (Processing of CSD film) (pp R1-R7) in the above review article was reproduced from references 11 and 12 (Schwartz R W 1997 Chem. Mater. 9 2325 and Schwartz R W, Schneller T and Waser R 2004 C. R. Chim. 7 433) without the permission of the authors or the publishers. The primary author, a postdoctoral research associate, mistakenly thought that referencing the reproduced text and figures was sufficient; however, all authors take responsibility for failing to catch this error and obtain copyright permission from the publishers. We regret this unfortunate incident and we sincerely apologize to the authors, Dr Schneller, Dr Schwartz and Dr Waser; the publishers and readers for any inconvenience arising from this error.
    Superconductor Science and Technology 01/2009; 22(4):9801-049801. · 2.76 Impact Factor
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    ABSTRACT: A study was performed to examine the Jc behavior as a function of thickness in MgB2 films fabricated by ex situ annealing at 840 °C of boron films, grown by chemical vapor deposition, in Mg vapor. The film thicknesses range between 300 nm and 10 µm. The values of Jc range from 1.2 × 107 A cm−2 for 300 nm to 1.9 × 105 A cm−2 for 10 µm film thicknesses at 20 K and self-field. The study shows that the critical current density (Jc) in MgB2 films decreases with increasing film thickness, similar to that observed in YBCO-coated conductors. Moreover, our study shows that critical current (Ic) reaches its maximum value of 728 A cm−1 width at ~1 µm thick MgB2 films at 20 K and self-field, which is, interestingly, the same thickness of pulsed-laser-deposited YBCO-coated conductors at which Ic reaches its maximum value. The high Jc values carried by our films show that the ex situ fabrication method can produce high quality MgB2 films at low processing temperatures, which is promising for RF cavity applications and coated-conductor wires and tapes.
    Superconductor Science and Technology 12/2008; 22(1):015024. · 2.76 Impact Factor
  • P.T. Putman, K. Salama
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    ABSTRACT: In a coaxial magnetic brake, the changing field produced by movement of a solenoidal magnet induces a current in the wall of a conductive tube. The interaction of the field and current leads to a repulsive force that slows the motion of the magnet. We have tested the performance of this type of brake by firing a projectile carrying a permanent magnet into an aluminum tube. The results were compared to a model based on published theoretical results. The model was then used to predict braking distance for speeds and masses of interest in hypervelocity research, and it was found that brakes incorporating presently available superconducting materials are capable of stopping projectiles in practical distances. In addition, a new means of centering the projectile in the catch tube is presented, accompanied by a calculation of the centering force on the projectile, and high-speed photographs showing the alignment of a projectile with the brake tube.
    Electromagnetic Launch Technology, 2008 14th Symposium on; 07/2008
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    ABSTRACT: Magnesium diboride has a great potential for magnet applications in many areas such as high energy physics, MRI, and space-related projects. The main goal of our ongoing research effort is to study magnet design, winding process, and magnet testing. Last year, in a 14 cm bore solenoid we reached a central magnetic flux density of 1 tesla at 16 K with almost 500 m of commercial multifilament tape. In order to design appropriate quench detection and protection systems, it is important to define the quench propagation characteristics in solenoids made with this superconductor. In this work we show our experimental activity, from winding to testing, with a 14 cm bore solenoid made with commercial multifilament MgB<sub>2</sub> tape. In particular we address a quench propagation study on a coil made with 2 m of the same tape.
    IEEE Transactions on Applied Superconductivity 07/2008; · 1.20 Impact Factor
  • P.T. Putman, K. Salama
    [Show abstract] [Hide abstract]
    ABSTRACT: In coaxial magnetic brakes, the changing field produced by movement of a solenoidal magnet induces a current in the wall of a conductive tube. The interaction of the field and current leads to a repulsive force that slows the motion of the magnet. For brake applications that require high force density, melt-textured YBCO is a clear choice of material for the magnet because it can carry high currents at a given field and temperature, and is inherently capable of operating in persistent current mode. We present calculations of the performance of this type of brake as a function of magnet current density for catch tubes composed of aluminum and titanium. These results are validated with low speed (20 m/s) tests. Calculations indicate that melt-textured magnets can decelerate projectiles with a mass of 1 kg from 2000 m/s to rest in distances on the order of 10 m. This suggests that this type of brake is suitable for use in hypervelocity experiments, which sometimes requires nondestructive deceleration of projectiles for diagnostic purposes.
    Materials Science and Engineering B 06/2008; · 1.85 Impact Factor
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    ABSTRACT: Several practical applications require relatively thick Y1Ba2Cu3O7 (YBCO) coated conductors (1–2 µm) to carry a high critical current (Ic). However, as the thickness of the YBCO film increases, its critical current density (Jc) decreases. In this work, we report the successful fabrication of thick YBCO films using a multiple coatings technique while maintaining a high Jc. In particular, several YBCO films with different numbers of layers were fabricated on a LaAlO3 substrate by a multiple coatings process using a trifluoroacetate metal organic deposition method (TFA-MOD). No cracks or pores were observed in cross-sectional transmission electron microscope (TEM) images of these films; further, the layers were well connected with the smooth interface. The majority of the grains in the films were c-axis oriented. Full-width at half-maximum (FWHM) values for in-plane and out-of-plane alignments for a five-layer film were 2.45° and 1.2° respectively. Jc exceeding 1.6 MA cm−2 and critical current (Ic) of 160 A cm−1 have been obtained for a 1 µm thick film with five layers at 77 K.
    Superconductor Science and Technology 03/2008; 21(4):045015. · 2.76 Impact Factor
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    ABSTRACT: Low residual resistivity in superconducting thin films is required for their applications in radio frequency (RF) cavities. Here we report on clean epitaxial MgB2 films fabricated by the ex situ annealing of B films, grown by chemical vapour deposition, in Mg vapour. The films show sharp superconducting transitions at about 40 K and a high residual resistivity ratio of about 10. The result indicates that a clean precursor B film and a contamination-free annealing procedure are important for a viable MgB2 film fabrication process for RF cavity applications.
    Superconductor Science and Technology 02/2008; 21(4):045005. · 2.76 Impact Factor
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    ABSTRACT: This study investigated the effect of hydrogen partial pressure (pH2) on the creep behavior of (3 mol% Y-TZP)/50 vol.% Pd cermet (YSZ/Pd), a hydrogen permeable material under development for separating hydrogen from mixed gases. Samples were subjected to uniaxial compression creep under both an inert (pure argon) atmosphere and pH2=10−2 to 0.5 atm (balance Ar), in the temperature and stress ranges of 1150–1250 °C and 10–30 MPa, respectively. The creep measurements in Ar atmosphere yielded stress exponent and activation energy of n ≈ 2 and E = 582 kJ/mol, respectively, which is in good agreement with superplastic deformation of pure YSZ. The composite exhibits a tendency of decreasing n values with increase in pH2, reaching n ≈ 1.5 at pH2=0.5 atm. The effect of hydrogen partial pressure on creep can be described by an exponent of r ≈ 1/6, resulting in an increase in creep rate by a factor of 2.5 upon switching from Ar to pH2=0.5   atm.
    Materials Science and Engineering: B. 01/2008;

Publication Stats

2k Citations
357.15 Total Impact Points

Institutions

  • 1988–2011
    • University of Houston
      • • Department of Mechanical Engineering
      • • Texas Center for Superconductivity
      Houston, TX, United States
  • 2006–2009
    • Sam Houston State University
      • Department of Physics
      Huntsville, Texas, United States
  • 1998–2003
    • Oak Ridge National Laboratory
      • Chemical Sciences Division
      Oak Ridge, Florida, United States
    • Argonne National Laboratory
      Lemont, Illinois, United States
  • 1989–1998
    • University of Texas Health Science Center at Houston
      Houston, Texas, United States
    • Karlsruhe Institute of Technology
      • Institute of Technical Physics
      Karlsruhe, Baden-Wuerttemberg, Germany
  • 1995
    • University of Wisconsin, Madison
      • Department of Materials Science and Engineering
      Mississippi, United States
  • 1991
    • Fraunhofer Institute for Nondestructive Testing IZFP
      Saarbrücken, Saarland, Germany
    • National Institute of Standards and Technology
      Maryland, United States