Flux-Assisted Preparation of Powdered Bismuth Superconductors

1989 ◽  
Vol 169 ◽  
Author(s):  
R. H. Arendt ◽  
M. F. Garbauskas ◽  
L. L. Schilling
Keyword(s):  
Transition Temperature ◽  
Reaction Temperature ◽  
Solvent Content ◽  
Phase Pure ◽  
Post Synthesis ◽  
Powdered Form

AbstractResults are presented on efforts to prepare both the 80K, Bi2CaSr2Cu2Oz (2122), and 11 OK, (Bi,Pb)2Ca2Sr2Cu3Oz (2223), transition temperature bismuth superconducting species in either phase pure or nearly phase pure, powdered form using either equimolar NaCI-KCI or NaBiOz as molten fluxes. Data are presented on the effects of variation of the reaction temperature and duration, solvent content, relative CaO and CuO contents, and of post-synthesis anneals of the product materials.

Preparation of YBa2Cu3O7−x using barium hydroxide flux

1990 ◽  
Vol 5 (12) ◽  
pp. 2755-2758 ◽  
Author(s):  
N. Coppa ◽  
A. Kebede ◽  
J. W. Schwegler ◽  
I. Perez ◽  
R. E. Salomon ◽  
...  
Keyword(s):  
Transition Temperature ◽  
Liquid Phase ◽  
Barium Hydroxide ◽  
Bunsen Burner ◽  
High Quality ◽  
Heat Treated ◽  
Phase Pure ◽  
Hydroxide Flux ◽  
Conventional Methods ◽  
Response Field

High quality bulk YBa2Cu3O7−x was synthesized by fusing stoichiometric amounts of yttrium and copper nitrates and barium hydroxide in air, using an ordinary Bunsen burner. The starting materials go through a short-lived liquid phase yielding a solid black product which was subsequently heat treated (900 °C, 18–24 h in air, followed by 500 °C, 5 h in O2). These materials were greater than 99% phase pure with CuO as the only other phase and they exhibited a transition temperature of 92 K, a 15.5% perfect diamagnet response (field cooled). This synthesis represents an improvement over the much more labor and time intensive conventional methods in that it allows high quality materials of various compositions to be prepared quickly.

A modified citrate gel route for the synthesis of phase pure Bi2Sr2CaCu2O8 superconductor

1994 ◽  
Vol 9 (6) ◽  
pp. 1357-1362 ◽  
Author(s):  
Sujatha P. Devi ◽  
H.S. Maiti
Keyword(s):  
Thermal Decomposition ◽  
Transition Temperature ◽  
Combustion Process ◽  
Superconducting Phase ◽  
Mechanism Of Formation ◽  
Sharp Transition ◽  
Simple Method ◽  
Phase Pure ◽  
Plausible Mechanism

A simple method for the bulk synthesis of 80 K bismuth-based superconducting phase (2212) is described. It employs a modified citrate gel route giving rise to an auto-ignited combustion process. The precursor ash obtained after combustion is further calcined at 800 °C to produce the desired superconducting powder with excellent homogeneity and fineness, leading to good sinterability and fairly sharp transition temperature. For a particular citrate-nitrate ratio, the nature of combustion of the gels containing two different bases has been compared. The thermal decomposition characteristics of the gels and the plausible mechanism of formation of the superconducting phase are also described.

scholarly journals Polymorphic Forms of Lamivudine: Characterization, Estimation of Transition Temperature, and Stability Studies by Thermodynamic and Spectroscopic Studies

2012 ◽  
Vol 2012 ◽  
pp. 1-8 ◽  
Author(s):  
Renu Chadha ◽  
Poonam Arora ◽  
Swati Bhandari
Keyword(s):  
Transition Temperature ◽  
Enthalpy Of Solution ◽  
Pharmaceutical Preparations ◽  
Spectroscopic Studies ◽  
Stability Studies ◽  
Order Form ◽  
Phase Pure ◽  
Melting Endotherm ◽  
Polymorphic Forms ◽  
Stable Forms

The present study is focused on estimation of transition temperature and stability of various forms of lamivudine. The forms were recrystallized from variety of solvents and preliminarily identification on the basis of SEM revealed existence of three forms (Forms I, II, III). DSC scans of Forms I and III show that these are metastable and undergo heat mediated transformation to Form IH and Form IIIH, respectively. Form II is phase pure with single sharp melting endotherm at 178.6°C. The thermal events are visually observed by hot stage microscopy. Enthalpy of solution of the forms is endothermic and magnitude varies in the order Form II > Form IL > Form IIIL suggesting Form IIIL to be least crystalline which is well correlated with XRPD data. The transition temperature of the polymorphic pairs IL/IH and IIIL/IIIH derived from enthalpy of solution and solubility data revealed monotropy whereas enantiotropy exists in IIIH/II. The slurry experiments showed Form II to be thermodynamically most stable. Forms IL and IIIL though stable in water are converted to Form II in ethanol, acetonitrile, and propanol after 1 day. Form IIIL is converted to Form IL in water after 7 days and the observation is of importance as this instability can effect the pharmaceutical preparations whereas Form IL shows a balance between stability and solubility.

Ten Minute Preparation Of Yba2Cu3O7−x Using Barium Hydroxide

1990 ◽  
Vol 180 ◽  
Author(s):  
N. Coppa ◽  
A. Kebede ◽  
J. W. Schwegler ◽  
I. Perez ◽  
R. E. Salomon ◽  
...  
Keyword(s):  
Transition Temperature ◽  
Liquid Phase ◽  
Barium Hydroxide ◽  
Zero Field ◽  
Bunsen Burner ◽  
High Quality ◽  
Diamagnetic Response ◽  
Heat Treated ◽  
Phase Pure ◽  
Response Field

ABSTRACTHigh quality bulk YBa2CuOx−7 was synthesized by fusing stoichiometric amounts of yttrium and copper nitrates and barium hydroxide, in air, using an ordinary Bunsen burner. The starting materials go through a short-lived liquid phase yielding a solid black product which was subsequently heat treated, (900 C, 18–24 h, in air, followed by 500 C, 5 h., in O2). These materials were greater than 99% phase pure with CuO as the only other phase and they exhibited a transition temperature of 92 K, a 15.5% perfect diamagnetic response (field cooled), 76% (zero field cooled). This synthesis represents an improvement over the much more labor and time intensive conventional methods in that it allows high quality materials of various compositions to be prepared quickly

scholarly journals Effect of pressure on the order–disorder phase transitions of B cations in AB′1/2 B′′1/2O3 perovskites

2019 ◽  
Vol 75 (6) ◽  
pp. 1034-1041
Author(s):  
Nikita V. Ter-Oganessian ◽  
Vladimir P. Sakhnenko
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Transition Temperature ◽  
Statistical Model ◽  
Atomic Order ◽  
Atomic Ordering ◽  
Synthesis Conditions ◽  
Disorder Phase Transition ◽  
Effect Of Pressure ◽  
Post Synthesis

Perovskite-like oxides AB′1/2 B′′1/2O3 may experience different degrees of ordering of the B cations that can be varied by suitable synthesis conditions or post-synthesis treatment. In this work the earlier proposed statistical model of order–disorder phase transitions of B cations is extended to account for the effect of pressure. Depending on the composition, pressure is found to either increase or decrease the order–disorder phase transition temperature. The change in transition temperature due to pressure in many cases reaches several hundred kelvin at pressures accessible in the laboratory, which may significantly change the degree of atomic ordering. The work is intended to help in determining how pressure influences the degree of atomic ordering and to stimulate research into the effect of pressure on atomic order–disorder phase transitions in perovskites.

Preparation of Ultrafine SiC Powders by Carbothermal Reduction

2008 ◽  
Vol 368-372 ◽  
pp. 821-823
Author(s):  
Fu Wang ◽  
Wen Bin Cao ◽  
Jia Lin Sun ◽  
Rong Liang He
Keyword(s):  
Silicon Carbide ◽  
Phase Composition ◽  
Reaction Temperature ◽  
Carbothermal Reduction ◽  
Reduction Method ◽  
Silica Sol ◽  
Holding Time ◽  
Pure Silicon ◽  
Sic Particles ◽  
Phase Pure

SiC powder was synthesized by carbothermal reduction method using silica sol and amylum as reactants in closed and open graphite crucibles, respectively. The phase composition and morphology of the powders were characterized. Formation of phase-pure silicon carbide can be achieved at 1700°C for 1h. Increasing reaction temperature and extending holding time can greatly promote the production of SiC. The products synthesized in open graphite crucibles are mainly composed of equiaxial β-SiC particles while those synthesized in closed graphite crucibles are β-SiC particles and nanorods.

Synthesis of high phase pure cuprate superconductors via xerogel precursors

1992 ◽  
Vol 7 (5) ◽  
pp. 1046-1051 ◽  
Author(s):  
J. Macho ◽  
R.W. Schaeffer ◽  
G.H. Myer ◽  
R.E. Salomon ◽  
J.E. Crow
Keyword(s):  
Transition Temperature ◽  
Cuprate Superconductors ◽  
Barium Carbonate ◽  
Amorphous Structure ◽  
Metal Salts ◽  
Gelling Agent ◽  
Atmospheric Conditions ◽  
Copper Salts ◽  
Gelling Agents ◽  
Phase Pure

Phase pure YBa2Cu3O7 high transition temperature superconductor powders were synthesized by a new precursor route. This new synthesis procedure is easy, leads to an atomic mixture of the relevant constituents, and is readily adaptable to many other systems or to the doping of existing systems. A gel of yttrium, barium, and copper salts was prepared using organic gelling agents. The gel was then dried and ground, leaving the xerogel precursor. These xerogels are perfectly stable even under high humidity atmospheric conditions and show an amorphous structure when characterized by x-ray diffraction, which is consistent with the existence of an atomic mixture of the three relevant metal salts. The organic gelling agent was selected after optimization studies focused on such issues as ash residue after calcination, solubility, and chemical interference with the metal salts. From a great variety of these gelling agents (agar, xanthan gum, gelatin, alginates, and others), gelatin was chosen as the ideal gelling agent for this specific application. The final product characterization shows very unexpected results. The crystalline phase purity of the YBa2Cu3O7 superconducting phase was about 99%, with no traces of barium carbonate, as expected from pseudo-organic precursors (xerogels). The product shows superconducting properties even before oxygen anneal (Tc ≍ 70 K), and after oxygen annealing of the powders the transition temperature was found to be 91 K, showing a linear behavior of the resistivity versus temperature before the drop at Tc, extrapolating to zero at 0 K. The particle size of these powders is smaller than 1 μm, as shown by SEM.

Effect of Temperature and Catalyst Concentrations on the Thermal Properties of Polyamide Adhesives at Low Operating Pressure

2010 ◽  
Vol 5 (1) ◽  
Author(s):  
Nayef M. Ghasem
Keyword(s):  
Weight Loss ◽  
Glass Transition ◽  
Thermal Properties ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Melting Point ◽  
Reaction Temperature ◽  
Catalyst Concentration ◽  
Sample Weight ◽  
Sample Weight Loss

The polyamides used for hot-melt adhesives were synthesized from C36 dimer fatty acids and ethylenediamine under 200 mmHg and atmospheric pressures. The kinetics of the reaction rate at low pressure and the effect on the thermal properties of the produced polyamide adhesive were experimentally investigated. The effects of reaction temperature and catalyst concentration on polyamide melting point, glass transition temperature, sample weight loss and foaming height were studied. The kinetic rate constants were obtained for polymerization reaction carried out at three different reaction temperatures, 115, 120, and 135 °C, fixed mixing rate of 100 rpm and low operation pressure of 200 mmHg. Polymers produced at atmospheric pressure and reaction temperatures 140, 170, 180, and 190 °C where used to investigate the polyamide thermal properties using thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). Thermal properties such as melting point, glass transition temperature and the temperature at which 5% and 10% weight loss were recorded by TGA at a heating rate of 10 C/min in N2 atmosphere. The effect of foaming height as a function of reaction temperature and catalyst concentration was measured. The analysis makes known that the reaction temperature and catalyst concentration has a noteworthy impact on the glass transition temperature, foam height and melting point and insignificant effect on the sample weight loss.

In situ Tensile Experiments at Low Temperatures on Niobium Single Crystals by H.V.E.M.

1975 ◽  
Vol 33 ◽  
pp. 58-59
Author(s):  
F. H. Louchet ◽  
L. P. Kubin
Keyword(s):  
Electron Microscope ◽  
Transition Temperature ◽  
Low Temperature ◽  
Slip System ◽  
Low Temperatures ◽  
Tensile Axis ◽  
Image Intensifier ◽  
Screw Dislocations ◽  
Source Operation

Experiments have been carried out on the 3 MeV electron microscope in Toulouse. The low temperature straining holder has been previously described Images given by an image intensifier are recorded on magnetic tape.The microtensile niobium samples are cut in a plane with the two operative slip directions [111] and lying in the foil plane. The tensile axis is near [011].Our results concern:- The transition temperature of niobium near 220 K: at this temperature and below an increasing difference appears between the mobilities of the screw and edge portions of dislocations loops. Source operation and interactions between screw dislocations of different slip system have been recorded.

The structure of membranes and membrane proteins embedded in amorphous ice

1992 ◽  
Vol 50 (1) ◽  
pp. 432-433
Author(s):  
Uwe Lücken ◽  
Joachim Jäger
Keyword(s):  
Phase Transition ◽  
Transition Temperature ◽  
Membrane Proteins ◽  
Phase Transition Temperature ◽  
Lipid Vesicles ◽  
Freezing Stress ◽  
Amorphous Ice ◽  
Different Temperatures ◽  
Band Pass ◽  
Lipid Polymorphism

TEM imaging of frozen-hydrated lipid vesicles has been done by several groups Thermotrophic and lyotrophic polymorphism has been reported. By using image processing, computer simulation and tilt experiments, we tried to learn about the influence of freezing-stress and defocus artifacts on the lipid polymorphism and fine structure of the bilayer profile. We show integrated membrane proteins do modulate the bilayer structure and the morphology of the vesicles.Phase transitions of DMPC vesicles were visualized after freezing under equilibrium conditions at different temperatures in a controlled-environment vitrification system. Below the main phase transition temperature of 24°C (Fig. 1), vesicles show a facetted appearance due to the quasicrystalline areas. A gradual increase in temperature leads to melting processes with different morphology in the bilayer profile. Far above the phase transition temperature the bilayer profile is still present. In the band-pass-filtered images (Fig. 2) no significant change in the width of the bilayer profile is visible.

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