System Ho-Rh-O: Phase Equilibria, Chemical Potentials and Gibbs Energy of Formation of HoRhO3

The thermodynamic properties of the HoRhO₃ were determined in the temperature range from 900 to 1300?K by using a solid-state electrochemical cell incorporating calcia-stabilized zirconia as the electrolyte. The standard Gibbs free energy of formation of orthorhombic perovskite HoRhO₃, from Ho₂O₃ with C-rare earth structure and Rh₂O₃ with orthorhombic structure, can be expressed by the equation; $$ \Updelta G_{{{\text{f}}({\text{ox}})}}^{ \circ } \left( { \pm 78} \right)/({\text{J}}/{\text{mol}}) = - 50535 + 3.85\left( {T/{\text{K}}} \right) $$ Using the thermodynamic data of HoRhO₃ and auxiliary data for binary oxides from the literature, the phase relations in the Ho-Rh-O system were computed at 1273?K. Thermodynamic data for intermetallic phases in the binary Ho-Rh were estimated from experimental enthalpy of formation for three compositions from the literature and Miedema??s model, consistent with the phase diagram. The oxygen potential-composition diagram and three-dimensional chemical potential diagram at 1273?K, and temperature-composition diagrams at constant oxygen partial pressures were computed for the system Ho-Rh-O. The decomposition temperature of HoRhO₃ is 1717(±2)?K in pure O₂ and 1610(±2)?K in air at a total pressure p ^o?=?0.1?MPa.     

Thermodynamic Properties of YbRhO<Subscript>3</Subscript> and Phase Relations in the System Yb-Rh-O

Thermodynamic properties of the ternary oxide YbRhO₃ were determined by using a solid-state electrochemical cell incorporating calcia-stabilized zirconia as the solid electrolyte in the temperature range from 900 to 1300 K. The standard Gibbs energy of formation of YbRhO₃ from component binary oxides Yb₂O₃ with C-rare earth type structure and Rh₂O₃ with orthorhombic structure can be represented by the equation,

$$\Delta_{\text{f(ox)}} G^{\text{o}} ( \pm 130)/{\text{J/mol}} = - 43164 + 3.436\,({\text{T/K}}).$$

Standard enthalpy of formation of YbRhO₃ from elements in their normal standard states is ?1153.18(±3) kJ/mol and its standard entropy is 100.93(±0.6) J/K/mol at 298.15 K. The decomposition temperature of YbRhO₃ is 1671(±3) K in pure oxygen, 1566(±3) K in air and 1047(±3) K at an oxygen partial pressure of \(\left( {P_{{{\text{O}}_{2} }} /{\text{P}}^{\text{o}} } \right) = 10^{ - 6}\), where P^o = 0.1 MPa is the standard pressure. Decomposition temperature was confirmed by DTA/TGA. Phase diagrams for the system Yb-Rh-O are computed using the thermodynamic data.

     

Timing Traceability and the Link Between ISRO-NPLI

We present an algorithm for timescale prediction of IRNSS Network Time (IRNWT) using a GNSS link for daily exchange of data between Indian Space Research Organization and CSIR-NPL. A link between CSIR-NPL and IRNWT through Two Way Satellite Time and Frequency Transfer is also being established.     

Synthesis of cube-shaped gold nanostructures by electron irradiation

The needle-like gold nanostructures were synthesized by using chloroauric acid (HAuCl₄) as a metal precursor and sodium borohydride (NaBH₄) as the reducing agent. These needle-like nanostructures of gold were irradiated with high energy electrons (E ~ 6 MeV, ? ~ 10¹² e cm⁻² s⁻¹). The pre- and post-irradiated gold nanostructures were characterized by Scanning Electron Microscopy (SEM), UV-vis spectroscopy, X-ray Diffraction (XRD) and contact angle measurement (GBX-Model Digidrop) techniques. The results of the SEM revealed that after electron irradiation, the needle-like gold structures got fragmented into identical cube-shaped gold nanostructures, though of different sizes. The XRD analysis indicated that the average crystallite size of the gold nanostructures remained unchanged even after irradiation with high energy electrons. A glass surface showed hydrophilic behavior when coated with needle-like nanostructures and became ultra hydrophilic when coated with cube-shaped gold nanostructures.